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Synthesis and Thermal Study of Hexacoordinated Aluminum(III) Triazenides for Use in Atomic Layer Deposition
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  • Rouzbeh Samii
    Rouzbeh Samii
    Department of Physics, Chemistry and Biology, Linköping University, SE-581 83 Linköping, Sweden
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    Orcidhttp://orcid.org/0000-0001-9380-4072
  • David Zanders
    David Zanders
    Faculty of Chemistry and Biochemistry, Ruhr University Bochum, Universitätsstraße 150, 44801 Bochum, Germany
    Department of Chemistry, Carleton University, 1125 Colonel By Drive, Ottawa, Ontario K1S5B6, Canada
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  • Sydney C. Buttera
    Sydney C. Buttera
    Department of Chemistry, Carleton University, 1125 Colonel By Drive, Ottawa, Ontario K1S5B6, Canada
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  • Vadim Kessler
    Vadim Kessler
    Department of Molecular Sciences, Swedish University of Agricultural Sciences, P.O. Box 7015, 75007 Uppsala, Sweden
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  • Lars Ojamäe
    Lars Ojamäe
    Department of Physics, Chemistry and Biology, Linköping University, SE-581 83 Linköping, Sweden
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    Orcidhttp://orcid.org/0000-0002-5341-2637
  • Henrik Pedersen
    Henrik Pedersen
    Department of Physics, Chemistry and Biology, Linköping University, SE-581 83 Linköping, Sweden
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    Orcidhttp://orcid.org/0000-0002-7171-5383
  • Nathan J. O’Brien*
    Nathan J. O’Brien
    Department of Physics, Chemistry and Biology, Linköping University, SE-581 83 Linköping, Sweden
    *E-mail: [email protected]
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    Orcidhttp://orcid.org/0000-0003-3633-9674
Open PDFSupporting Information (3)

Inorganic Chemistry

Cite this: Inorg. Chem. 2021, 60, 7, 4578–4587
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https://doi.org/10.1021/acs.inorgchem.0c03496
Published March 12, 2021

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Abstract

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Amidinate and guanidinate ligands have been used extensively to produce volatile and thermally stable precursors for atomic layer deposition. The triazenide ligand is relatively unexplored as an alternative ligand system. Herein, we present six new Al(III) complexes bearing three sets of a 1,3-dialkyltriazenide ligand. These complexes volatilize quantitatively in a single step with onset volatilization temperatures of ∼150 °C and 1 Torr vapor pressures of ∼134 °C. Differential scanning calorimetry revealed that these Al(III) complexes exhibited exothermic events that overlapped with the temperatures of their mass loss events in thermogravimetric analysis. Using quantum chemical density functional theory computations, we found a decomposition pathway that transforms the relatively large hexacoordinated Al(III) precursor into a smaller dicoordinated complex. The pathway relies on previously unexplored interligand proton migrations. These new Al(III) triazenides provide a series of alternative precursors with unique thermal properties that could be highly advantageous for vapor deposition processes of Al containing materials.

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Synopsis

Six aluminum(III) 1,3-dialkyltriazenides were synthesized and their thermal properties explored. The compounds were purified by recrystallization and could be easily sublimed. Thermogravimetric analysis of compounds showed that all, except one, gave a single step evaporation with onset volatilization temperatures of ∼150 °C. DFT calculations revealed a unique decomposition pathway that leads to a small and more reactive Al species that would be highly advantageous for the surface reactions of atomic layer deposition.

1. Introduction

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Aluminum nitride (AlN) is a semiconductor material widely used in current day electronic devices. (1) This is due to its desirable chemical, optical, and electronic properties, such as high thermal stability, a wide direct band gap, and piezoelectricity. (2) As electronic devices rapidly miniaturize with increasingly complex surface structures, atomic layer deposition (ALD) becomes a vital technique for depositing uniform thin films of high-performance materials for future microelectronics. (3) In ALD, the metal and nonmetal precursors are introduced into the reaction chamber separately, which allows the film mechanism to be governed by two independent and self-limiting half reactions. These are complex surface reactions that can incorporate impurities into the film if the metal precursor does not possess suitable physical and chemical properties. A desirable ALD metal precursor must be thermally stable until reaching the film surface. (4) Here, it should undergo a clean and fast reaction to form a single stable monolayer without trapping unwanted byproducts. (3) This monolayer should then react with the second precursor (e.g., NH3 or H2O) in the same way. To maximize the growth rate of a thin film, a precursor must be sufficiently volatile and have ligands of low steric bulk for fast surface saturation and maximum density of the deposited precursor. Due to its high volatility and reactivity, trimethylaluminum (AlMe3) has been used to deposit AlN by ALD. (5−13) These films contain high levels of carbon impurities due to the strong Al–C bonds, making it difficult to remove all of the methyl ligands of the deposited precursor at low temperatures. (5,6) Replacing the Al–C of AlMe3 with more reactive Al–N bonds has led to homoleptic tricoordinated amide precursors (Al(NMe2)3) (14) and (Al(NEt2)3), (15) which have been used to deposit AlN by ALD. (16−19) Although these precursors are highly volatile and reactive, the low thermal stability of the deposited surface species renders films with carbon impurities. (20)
Amidinate and guanidinate bidentate ligands have been employed to improve thermal stability of group 13 metal precursors. Although these ligands improve thermal stability in comparison to monodentate ligated precursors, their drawback is compounds that lack volatility or surface reactivity, or both, the latter due to crowding of the metal center. (21−27) In particular, homoleptic hexacoordinated M–N bonded Al(III) amidinate (Al(amd)3) and guanidinate (Al(guan)3) compounds possess increased thermal stability compared to tricoordinated Al(III) amides, (26,27) but have not been used in an ALD process due to insufficient volatility. A ligand closely related to the amidinate and guanidinate is the triazenide, differing by the nitrogen atom in the endocyclic position of the ligand backbone. Homoleptic hexacoordinated Al(III) triazenide complexes have previously been reported; (28,29) however, they are not volatile due to their 1,3-diphenyltriazenide ligands. Recently, we reported the first examples of highly volatile homoleptic 1,3-dialkyltriazenide complexes, tris(1,3-diisopropyltriazenide)In(III) (In(triaz)3) (30) and Ga(III) (Ga(triaz)3), (31) and their use as ALD precursors. These new triazenide precursors underwent gas-phase decomposition at higher temperatures inside the ALD reactor, giving a smaller and more reactive M(III) species. This in situ thermolysis was highly advantageous for film growth, giving higher growth rates and films with near stoichiometric M/N ratios without unwanted carbon impurities. To further explore the unique properties of the 1,3-dialkyltriazenide ligand, we envisaged its ability to stabilize the Al(III) center to develop a new series of precursors that can be used for future ALD processes. Herein, we describe the synthesis, structure, and thermal properties of six homoleptic Al(III) 1,3-dialkyltriazenide complexes. These compounds were easily synthesized in good yields and are the first example of volatile hexacoordinated M–N bonded aluminum compounds. Furthermore, the compounds exhibit unique thermal properties, similar to Ga(triaz)3 and In(triaz)3. Using quantum-chemical density functional theory (DFT) calculations, we mapped out a previously unexplored decomposition pathway utilizing interligand interactions. The pathway is supported by electron impact mass spectrometry (EI-MS) data. The unique thermal properties of these compounds make them potentially advantageous as precursors for vapor deposition processes.

2. Results and Discussion

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2.1. Synthesis and Characterization of Aluminum Complexes

Tris(1,3-dialkyltriazenide)aluminum(III) compounds 1–6 were prepared in good yields by reacting the (1,3-dialkyltriazenide)lithium(I) intermediate, generated from an alkylazide (32,33) and alkyllithium, with AlCl3 (Scheme 1). All compounds were purified by recrystallization and were fully characterized by nuclear magnetic resonance (NMR) spectroscopy, elemental analysis (EA), sublimation temperature, and melting point. No decomposition was observed when stored under an inert atmosphere at room temperature for long periods of time. However, the compounds decomposed, without clear visual signs, when exposed to air and were no longer soluble in dry hexane. Presumably, the compounds formed nonsoluble mixed aluminum hydroxides and oxides.

Scheme 1

Scheme 1. Synthesis of Tris(1,3-dialkyltriazenide)aluminum(III) Compounds 1–6
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Purification of the crudes of 1–6 by vacuum sublimation was unsuccessful due to impurities that cosublimed. We suspect that these impurities decomposed during sublimation to form white solids, which were insoluble in n-hexane, Et2O, THF, and toluene. Interestingly, the 1H NMR spectra of 1–6 showed no impurities after sublimation. However, satisfactory EA was not obtained from the sublimed and filtered solid. To obtain satisfactory EA, the compounds were therefore purified by recrystallization from Et2O/MeCN.
The crystal structure of 6 showed the aluminum in an octahedral coordination geometry bearing three sets of the 1,3-di-tert-butyltriazenide ligand (Figure 1). A large degree of disorder was observed in the diffraction data. The ligands are distorted over a multitude of positions (at least 8 individual sets of possible arrangements). The Al–N bond length for 6 (av 1.96(5) Å) are similar to that for tris(1,3-diphenyltriazenide)aluminum(III) (av 1.972(5) Å) (28) but slightly shorter than those of Al(guan)3 (av 2.024 Å) (26) and Al(amd)3 (av 2.0195 and 2.0261 Å). (34) Thus, the triazenide ligand only has a small effect on the Al–N bond length in comparison to Al(guan)3 and Al(amd)3. Compound 1 has an analogous structure to that of 6, but suffers from even more severe disorder and therefore no successful refinement could be completed (see the Supporting Information).

Figure 1

Figure 1. ORTEP drawing for one of two independent molecules in the unit cell of 6. Thermal ellipsoids are displayed at the 50% probability level, and hydrogen atoms are omitted for clarity.

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The DFT calculated geometry of 6 is consistent with its crystal structure. The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) are both localized on the ligands (Figure 2). While the HOMO is spread over all three ligands, the LUMO only covers the N3 backbone of two ligands. For the HOMO, one node is centered on the endocyclic nitrogen, while the LUMO has nodes between the endocyclic and exocyclic nitrogens. The natural charges of the exocyclic nitrogens (−0.48) and Al metal center (+1.66) indicate a highly polarized Al–N bond character. The primary carbons (−0.60) show negative charges, while the endocyclic nitrogens (+0.044) and tertiary carbons (+0.11) have slightly positive charges. Comparing the natural bond orbital charge of the Al center of 1 (1.61) and its formamidinate analogue (1.86) shows the greater electron donating ability of the triazenide ligand over the formamidinate (see the Supporting Information).

Figure 2

Figure 2. (a) HOMO (−5.74 eV) and (b) LUMO (−0.78 eV) for 6 from DFT calculations.

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The 27Al NMR spectra of compounds 1–6 each gave a broad peak at δAl = 25.1–27.5 ppm (see the Supporting Information). These chemical shifts are consistent with previously reported hexacoordinated Al(III) triazenide complexes (δAl = 25–28 ppm). (28,29) Dynamic effects were observed by 1H NMR for the unsymmetrical ligated compounds 2, 3, and 5 at 25 °C (see the Supporting Information). These effects are most likely caused by isomerization hindered by the bulky ligands surrounding the small Al(III) center. (35,36) Therefore, the complexes isomerize slowly, resulting in significant lifetimes for the signals in relation to the difference in resonance frequencies. (37) Heating resolves the lifetime broadening by increasing the rate of isomerization. Mild line broadening was observed for compound 2 at 25 °C and was resolved at 35 °C. Line splitting was observed for all but the CH signals for compounds 3 and 5. These more severe effects are caused by the presence of the bulky tert-butyl groups, which further inhibit isomerization. The line splitting was resolved at 45 °C with only line broadening remaining. Heating to 50 °C resolved the line broadening for compound 3. However, mild line broadening was still observed for 5.

2.2. Thermal Analysis of Aluminum Complexes

Compounds 1, 3, 5, and 6 volatilize quantitatively with exponential mass loss in thermogravimetric analysis (TGA) (Figure 3). Compound 2 has 4% residual mass by TGA, undergoing slight decomposition, as observed by an inflection in the derivative at approximately 200 °C (see the Supporting Information). TGA of 4 showed two distinct events of mass loss, giving 5–7% residual mass. We speculate that 4 decomposes into volatile fragments during the mass loss events. However, we were unable to obtain a satisfactory elemental analysis for 4; therefore, the residual mass may be due to impurities. Overall, TGA shows that compounds 1–6 are sufficiently volatile for use in ALD. In fact, compounds 1–6 are far more volatile than Al(amd)3 and Al(guan)3, (26,27) which can be explained by more electron density residing on the triazenide ligand. This leads to weaker intermolecular interactions in the crystal structure of the compound, which is conditional for faster volatilization (see the Supporting Information for a comparison of charges between 1 and its amidinate analogue).

Figure 3

Figure 3. Thermogravimetric analysis of 1–6.

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Differential scanning calorimetry (DSC) was employed to study exothermic events of 1–6. All compounds have exothermic events, most likely due to decomposition, overlapping with their onset of volatilization displayed in TGA (see the Supporting Information). The TGA and DSC results for 1–6 are summarized in Table 1. Compounds 1 and 5 have exothermic events starting at 150 and 160 °C, respectively. Both compounds give peaks with irregular shape, indicating overlapping exothermic events occurring. Two distinct exotherms are observed for 2, 3, and 6: the first event initiates at 130, 160, and 230 °C, respectively, and the second between 234 and 300 °C. Compound 4 has a small exotherm starting at ∼100 °C, followed by a larger event at ∼200 °C. The unsymmetrical compounds 2, 3, and 5 undergo exothermic events at similar temperatures to 1. That is, greater ligand bulk does not increase thermal stability of these compounds. However, the exothermic event of 6 is at significantly higher temperatures compared to 1. Interestingly, 1 and 6 have similar calculated 1 Torr vapor pressure temperatures (Table 1).
Table 1. Summarized TGA and DSC Results for 1–6
 1st DSC exotherm (°C)onset of volatilization (°C)1 Torr vapor pressure (°C)residual mass (%)sublimation tempa (°C)
1150–230155134290
2130–190153138490
3160–3001611372105
4105–160N/AN/A790
5160–2401751720120
6230–2801511340125
a

Vacuum sublimation was undertaken at 0.5 mbar.

To study the long-term thermal stability of compounds 1–6, their solids were each flamed sealed in an NMR tube and heated to 5 °C above their 1 Torr vapor pressure temperature (Table 1) for 7 days. After heat exposure, compounds 1, 2, and 5 fully dissolved in C6D6 while 3 and 6 had a small amount of insoluble solid. None of the compounds showed signs of decomposition by 1H NMR.
A solution of 1 in C6D6 was heated in a flame-sealed NMR tube to various temperatures for 1 h, followed by acquiring 1H NMR spectra (Figure 4). After flame sealing but before heating the sample, the 1H NMR spectrum showed newly formed, low-intensity impurity signals (red asterisk, Figure 4). Only small changes to 1 occurred when heating up to 180 °C, and the solution remained colorless. Above 210 °C, the solution turned yellow, and 1H NMR signals of the doublet and septet, at 1.25 and 3.88 ppm, respectively, decreased in intensity. A white precipitate formed at 225 °C, and the overall 1H NMR signal of 1 had decreased significantly. Traces of various decomposition products appear in the ranges 3.0–2.7, 2.4–2.5, and 2.0–0.7 ppm (see the Supporting Information).

Figure 4

Figure 4. The 1H NMR (500 MHz, C6D6) spectra from a decomposition study of 1 between 0.8–1.3 and 3.7–4.0 ppm separated by an axis break. For visibility, the y-axis is scaled up ∼18 times on the left of the axis break compared to the right side. Prior to flame sealing, the compound showed no traces of impurities by 1H NMR analysis. The peaks marked with an asterisk appeared after flame sealing the tube. Compound 1 was heated in C6D6, and all spectra were acquired at 50 °C to suppress line broadening. The decomposition of 1 accelerates after 210 °C, which is shown by the diminished quartet and doublet peaks.

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2.3. Gas-Phase Decomposition by DFT Computations

In previous work, we demonstrated high-quality thin films of indium nitride and gallium nitride by ALD, using the Ga(triaz)3 and In(triaz)3 as precursors, respectively. (31,30) From the thermal properties of the compounds, we speculated that the depositions are activated by gas-phase decomposition of the precursor in the ALD reactor. Compounds 1–6 have similar thermal properties as Ga(triaz)3 and In(triaz)3 and are therefore expected to undergo a similar decomposition. DFT was used to study gas-phase thermal decomposition pathways of 1. We found a decomposition pathway relying on Brönsted–Lowry acid–base reactions between neighboring ligands. Overall, the first ligand leaves as triazene while the second decomposes into an imido ligand. Figure 5 shows the free energy profile for the release and decomposition of the first and second ligand, respectively, at 250 °C and 10 hPa. The third ligand decomposes in the same manner as the second, only with minor differences (Figure 6). The largest free energy barriers are 211 and 214 kJ mol–1, for TS-3 (Figure 5) and TS-8 (Figure 6), respectively. These barriers are slightly smaller for 6 (192 and 197 kJ mol–1). The Supporting Information contains pictures and Cartesian coordinates of all optimized geometries and their respective enthalpies and free energies.

Figure 5

Figure 5. Free energy profile (at 250 °C and 10 hPa) for the first half of the decomposition pathway. Here, 1 loses a triazene ligand (after TS-2), and one ligand decomposes into an imido ligand (TS-5). TS-3 has the largest free energy (211 kJmol–1) for the displayed part of the decomposition pathway. The overall largest free energy barrier is found at TS-8 (214 kJmol–1): the analogous step to TS-3 but for the last ligand. At 250 °C and 10 hPa, the adduct structures I-2A separate spontaneously (i.e., the process is barrierless and has a negative free energy difference) and is therefore not included.

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Figure 6

Figure 6. Free energy profile continuing from I-5. The steps that transform I-5 into I-10 are analogous to the steps that transform 1 into I-5. The reverse step through TS-7 has a significantly larger free energy barrier compared to the analogous TS-2 (290 vs 85 kJ mol–1, respectively).

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Starting from 1, a ligand dechelates from the metal center by a 180° rotation of a N–N bond (TS-1), resulting in I-1. This ligand dechelation enables the isopropyl moiety on the coordinated nitrogen to move closer to neighboring ligands and the metal center. Next, a methyl proton of the isopropyl group migrates to an exocyclic nitrogen on a neighboring ligand (TS-2). Simultaneously, a bond is formed between the deprotonated isopropyl group and the metal center. In I-2A, the deprotonated ligand regains a bidentate binding mode, now with a C,N-coordination to the metal center. Meanwhile, the protonated ligand dechelates and only has a coordination bond to the metal center. Due to the proton transfer in TS-2, the deprotonated and protonated ligand become dianionic and neutral, respectively. I-2A is an adduct structure consisting of a triazene (LH) coordinated to the I-2 structure.
The two steps that transform 1 into I-2A are reversible. In contrast, separating I-2A into LH and I-2 may be reversible or irreversible depending on the reaction conditions (Scheme 2). I-2A separates spontaneously under reduced pressure and elevated temperature, conditions commonly employed in ALD. Therefore, we assume that when the adduct structure separates, LH becomes inaccessible to I-2 and cannot facilitate the backward reaction, i.e., making the forward reaction irreversible.

Scheme 2

Scheme 2. Separation of the Adduct Structure I-2A into a Triazene and I-2a
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aThe I-2 intermediate has one monoanionic N,N-coordinated and one dianionic C,N-coordinated triazenide ligand.

I-2 has two triazenide ligands: the dianionic C,N-coordinated ligand and an unaltered N,N-coordinated ligand. The dianionic ligand decomposes in three irreversible steps, transforming the C,N-coordinated triazenide into an imido ligand (Scheme S2). First, a methyl proton migrates from the isopropyl group on the β-nitrogen to the α-nitrogen, with respect to the coordinated nitrogen (TS-3). This proton transfer results in a molecule of propene leaving the structure, giving I-3. Second, the proton on the α-nitrogen migrates to the coordinated nitrogen (TS-4), releasing dinitrogen to give I-4. Third, passing through TS-5, the former isopropyl group, which coordinated to the metal center in TS-2, leaves as propene to give I-5.
Other than the newly formed imido ligand, I-5 has one intact triazenide ligand that decomposes in a similar fashion as the first (Figure 6). Moving from I-5 toward TS-6, the intact triazenide dechelates by rotating 180° along a N–N bond, breaking the four-membered ring with the metal center. This step is analogous to the dechelation that transform 1, via TS-1, into I-1. In contrast to I-1, however, where the ligand remained monodentate, I-6 is a less crowded structure and allows the triazenide ligand to regain a bidentate binding mode. In I-6, two adjacent nitrogen atoms of the triazenide ligand bind to the metal center, forming a three-membered ring. For the interligand proton migration (TS-7) to occur, the ligand must adopt a monodentate binding mode. When approaching TS-7 from I-6, the three-membered ring open and the ligand becomes monodentate without passing a transition state. Next, the second interligand proton transfer of the decomposition pathway occurs (TS-7). This step is similar to the first (TS-2) except that, now, the neighboring imido ligand acts as the Brønsted–Lowry base instead of a neighboring triazenide ligand. Furthermore, this step has a significantly lower free energy barrier compared to TS-2 due to the imido being a much stronger base compared to the triazenide ligand. For the same reason, the free energy barrier for the reverse reaction via TS-7 is very large (290 kJ mol–1), essentially blocking the backward reaction. After passing TS-7, the deprotonated and protonated ligands transform into a dianionic C,N-coordinated triazenide and an amido ligand, respectively, to give I-7.
The second dianionic triazenide decompose into an imido ligand via TS-8 to TS-10, which are analogous to TS-3 to TS-5, giving the adduct structure I-10A. The adduct separates spontaneously into the final structure, I-10, and propene. A lack of viable options for I-10 to further decompose makes it thermally stable in the gas phase. However, based on the structure, I-10 is expected to be highly reactive toward surfaces. EI-MS data for 1 show four signals consistent with fragments for intermediates of the presented decomposition pathway (see the Supporting Information). Three potential fragments are identified for 6 and these fragments are structurally analogous to fragments found for 1. Furthermore, both compounds give a low intensity signal (∼1%) at m/z 58, matching I-10. The calculated and found m/z for all fragments are given in Table 2.
Table 2. Summarized EI-MS Signals (Given in m/z) And Their Matching Intermediate Fragments from the Presented Decomposition Pathway for Compounds 1 and 6

3. Conclusion

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In conclusion, six tris(1,3-dialkyltriazenide)aluminum(III) compounds have been made in good yields. The crystal structure of 6 revealed a homoleptic complex with three sets of the 1,3-di-tert-butyltriazenide ligand chelating to the Al(III) center. The complexes are highly volatile and, with the exception of 4, volatilize in a single step with exponential mass loss. Exponential mass loss indicated that the compounds volatilize without decomposing. However, DSC revealed exothermic events, most likely due to decomposition, overlapping with the temperature range for the mass loss event in TGA. Therefore, the compounds may undergo decomposition upon or after volatilization. Using DFT, a gas-phase decomposition pathway was found that relies on protons migrating between ligands. One ligand leaves the complex as a molecule of triazene, and the two remaining ligands transform into C,N-coordinated dianionic triazenide ligands that decompose into imido ligands. The largest free energy barrier for the pathway is 214 kJ mol–1 (at 10 hPa and 250 °C) during decomposition of the second dianionic ligand (Figure 6, TS-8). A slightly lower free energy barrier of 211 kJ mol–1 (at 10 hPa and 250 °C) is found for TS-3 (decomposition of the first ligand, analogous to TS-8). The final intermediate of the pathway is predicted to be highly reactive. Further studies are required to form a better understanding of how the compounds behave during the mass loss events observed in TGA. To our knowledge, compounds 1–6 are the first hexacoordinated Al–N bonded compounds that are sufficiently volatile for use as Al precursors in vapor deposition. Based on thermal analysis and DFT calculations, we postulate that the compounds decompose into smaller and more reactive species in the gas phase, which would be highly beneficial for ALD.

4. Experimental Section

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4.1. General Experimental Procedures

Caution! As catenated nitrogen compounds are known to be associated with explosive hazards, alkylazides and compounds1–6are possible explosive energetic materials. Although we have not experienced any problems in the synthesis, characterization, sublimation, heating, and handling of compounds1–6, their energetic properties have not been fully investigated and are therefore unknown. We therefore highly recommend that all appropriate standard safety precautions for handling explosive materials (safety glasses, face shield, blast shield, leather gloves, polymer apron, and ear protection) be used at all times when working with isopropyl-, sec-butyl-, and tert-butylazide and compounds1–6.
All reactions and manipulations were carried out under a N2 atmosphere on a Schlenk line using Schlenk air-free techniques, or in a N2-filled drybox from Glovebox-Systemtechnik. All anhydrous solvents were purchased from Sigma-Aldrich and further dried with molecular sieves 4 Å. Isopropyllithium (0.7 M in pentane), sec-butyllithium (1.4 M in cyclohexane), and tert-butyllithium (1.7 M in pentane) were purchased from Sigma-Aldrich, and AlCl3 (99.985%) was purchased from Alfa Aesar; all were used without further purification. Tert-butyl-, sec-butyl-, and isopropylazide were synthesized according to previously reported literature procedures. (32,33) All NMR spectra were measured with Oxford Varian 300 and AS500 spectrometers at room temperature unless otherwise stated. Solvents’ peaks were used as an internal standard for the 1H NMR (300 and 500 MHz) and 13C NMR (75 and 125 MHz) spectra. For temperature stability measurements using NMR, a 40 g L–1 solution of 1 in C6D6 was added to a heavy-walled NMR tube, and the tube was flame-sealed. EI-MS data for 1 and 6 were acquired using a Varian MAT spectrometer operated at 70 eV in the electron ionization mode. Samples were filled into steel cartridges, sealed with lids, and individually fed to the spectrometer via a load-lock chamber which was pumped to ultrahigh vacuum prior to sample transfer to the main chamber. Melting points were determined for samples under N2 atmosphere, flame-sealed in capillaries, using a Stuart SMP10 melting point apparatus and are uncorrected. Elemental analysis was performed by Mikroanalytisches Laboratorium Kolbe, Germany. Purification of compounds 1–6 by sublimation gave unsatisfactory EA results. Satisfactory EA results were obtained by recrystallizing the sublimed compounds.

4.2. General Synthesis Procedure for Al(III) Triazenide Complexes

Alkyllithium (3 equiv) was added to a solution of alkyl azide (3 equiv) in Et2O at −78 °C, and the reaction mixture was stirred at this temperature for 30 min and then at room temperature for 1 h. This solution was then added to a −78 °C solution of AlCl3 (1 equiv) in Et2O via cannula. The reaction mixture was stirred at this temperature for 30 min and then slowly warmed to room temperature and stirred for 16 h. The reaction mixture was then concentrated under reduced pressure, and the resulting residue was suspended in n-hexane. Solids were filtered off through a pad of Celite and concentrated under reduced pressure to give the crude product. Purifying the crude product by sublimation resulted in unsatisfactory purity by EA. The crude product was therefore purified by recrystallization from Et2O/MeCN at −35 °C to give the desired tris(1,3-dialkyltriazenide)aluminum(III) complexes, 1–6.

Tris(1,3-diisopropyltriazenide)aluminum(III) (1)

Compound 1 was synthesized according to the general procedure using isopropyl azide (0.42 g, 4.93 mmol) in Et2O (25 mL), isopropyllithium (7.05 mL, 4.93 mmol), and AlCl3 (0.22 g, 1.65 mmol) in Et2O (25 mL). The solid was purified by recrystallization to give 1 as a solid (0.39 g, 58%).
1: Colorless solid, mp 255–257 °C. Sublimation: 90 °C (at 0.5 mbar). 1H NMR (300 MHz, C6D6): δ 1.25 (d, J = 6.7 Hz, 36H, CH3), 3.88 (sept, J = 6.7 Hz, 6H, CH). 13C{1H} NMR (75 MHz, C6D6): δ 23.4 (s, CH3), 52.6 (s, CH). 27Al NMR (78 MHz, C6D6): δ 25.1 (br s). EI-MS (LR): 43.1 (60%), 84.1 (4.3%), 156.2 (15%), 170.3 (1.4%), 197.2 (9.3%), 211.2 (19%), 283.3 (30%). Anal. Calcd for C18H42AlN9: C, 52.53%; H, 10.29%; N, 30.63%. Found: C, 51.70%; H, 10.31%; N, 30.04%.

Tris(1-isopropyl-3-sec-butyltriazenide)aluminum(III) (2)

Compound 2 was synthesized according to the general procedure using sec-butyl azide (0.59 g, 5.95 mmol) in Et2O (30 mL), isopropyllithium (8.50 mL, 5.95 mmol), and AlCl3 (0.26 g, 1.98 mmol) in Et2O (30 mL). The solid was purified by recrystallization to give 2 as a solid (0.55 g, 61%).
2: Colorless solid, mp 187–192 °C. Sublimation: 90 °C (at 0.5 mbar). 1H NMR (300 MHz, C6D6): δ 0.92 (t, J = 7.5 Hz, 9H, CH3), 1.26 (d, J = 6.6 Hz, 18H, CH3), 1.26 (d, J = 6.6 Hz, 9H, CH3), 1.42–1.60 (m, 3H, CH2), 1.71–1.88 (m, 3H, CH2), 3.63 (sext, J = 6.6 Hz, 3H, CH), 3.87 (sept, J = 6.6 Hz, 3H, CH). 13C{1H} NMR (75 MHz, C6D6): δ 11.3 (s, CH3), 20.2 (br s, CH3), 23.4 (s, CH3), 30.7 (s, CH2), 52.4 (s, CH), 58.7 (s, CH). 27Al NMR (78 MHz, C6D6): δ 26.0 (br s). Anal. Calcd for C21H48AlN9: C, 55.60%; H, 10.67%; N, 27.79%. Found: C, 53.92%; H, 10.46%; N, 26.42%.

Tris(1-isopropyl-3-tert-butyltriazenide)aluminum(III) (3)

Compound 3 was synthesized according to the general procedure using tert-butyl azide (0.38 g, 3.83 mmol) in Et2O (20 mL), isopropyllithium (5.48 mL, 3.83 mmol), and AlCl3 (0.17 g, 1.28 mmol) in Et2O (20 mL). The solid was purified by recrystallization to give 3 as a solid (0.42 g, 72%).
3: Colorless crystals, mp >300 °C. Sublimation: 105 °C (at 0.5 mbar). 1H NMR (300 MHz, C6D6, 50 °C): δ 1.26 (d, J = 6.5 Hz, 18H, CH3), 1.34 (s, 27H, CH3), 3.82 (sept, J = 6.6 Hz, 3H, CH). 13C{1H} NMR (75 MHz, C6D6, 50 °C): δ 23.4 (br s, CH3), 30.7 (s, CH3), 52.1 (s, CH), 56.4 (s, Cq). 27Al NMR (78 MHz, C6D6): δ 25.5 (br s). Anal. Calcd for C21H48AlN9: C, 55.60%; H, 10.67%; N, 27.79%. Found: C, 55.07%; H, 10.71%; N, 27.54%.

Tris(1,3-di-sec-butyltriazenide)aluminum(III) (4)

Compound 4 was synthesized according to the general procedure using sec-butyl azide (0.29 g, 2.93 mmol) in Et2O (20 mL), sec-butyllithium (2.09 mL, 2.93 mmol), and AlCl3 (0.13 g, 0.98 mmol) in Et2O (20 mL). The solid was purified by sublimation at 90 °C to give 4 as a semisolid (0.21 g, 43%).
4: Colorless semi-solid. Sublimation: 90 °C (at 0.5 mbar). 1H NMR (300 MHz, C6D6, 50 °C): δ 0.93 (t, J = 7.5 Hz, 18H, CH3), 1.28 (d, J = 6.0 Hz, 18H, CH3), 1.42–1.63 (m, 6H, CH2), 1.75–1.88 (m, 6H, CH2), 3.62 (sext, J = 6.6 Hz, 6H, CH). 13C{1H} NMR (75 MHz, C6D6, 50 °C): δ 11.3 (s, CH3), 20.2 (s, CH3), 30.7 (s, CH2), 58.6 (s, CH). 27Al NMR (78 MHz, C6D6, 50 °C): δ 27.5 (br s). A satisfactory elemental analysis could not be obtained for compound 4.

Tris(1-sec-butyl-3-tert-butyltriazenide)aluminum(III) (5)

Compound 5 was synthesized according to the general procedure using tert-butyl azide (0.34 g, 3.43 mmol) in Et2O (20 mL), sec-butyllithium (2.45 mL, 3.43 mmol), and AlCl3 (0.15 g, 1.14 mmol) in Et2O (20 mL). The solid was purified by recrystallization to give 5 as a solid (0.43 g, 75%).
5: Colorless crystals, mp >300 °C. Sublimation: 120 °C (at 0.5 mbar). 1H NMR (300 MHz, C6D6, 50 °C): δ 0.92 (t, J = 7.4 Hz, 9H, CH3), 1.27 (d, J = 6.6 Hz, 9H, CH3), 1.35 (s, 27H, CH3), 1.40–1.62 (m, 3H, CH2), 1.75–1.94 (m, 3H, CH2), 3.51–3.66 (m, 3H, CH). 13C{1H} NMR (755 MHz, C6D6, 50 °C): δ 10.4–12.1 (m, CH3), 17.9–19.7 (m, CH3), 30.5–30.9 (m, CH3), 31.0 (s, CH2), 56.4 (Cq), 57.5–58.6 (m, CH). 27Al NMR (78 MHz, C6D6): δ 26.0 (br s). Anal. Calcd for C24H54AlN9: C, 58.15%; H, 10.98%; N, 25.43%. Found: C, 55.92%; H, 10.66%; N, 24.42%.

Tris(1,3-di-tert-butyltriazenide)aluminum(III) (6)

Compound 6 was synthesized according to the general procedure using tert-butyl azide (0.45 g, 4.54 mmol) in Et2O (25 mL), tert-butyllithium (2.67 mL, 4.54 mmol), and AlCl3 (0.20 g, 1.51 mmol) in Et2O (25 mL). The solid was purified by recrystallization to give 6 as a solid (0.59 g, 78%).
6: Colorless crystals, mp >300 °C. Sublimation: 125 °C (at 0.5 mbar). 1H NMR (300 MHz, C6D6): δ 1.38 (s, 54H, CH3). 13C{1H} NMR (75 MHz, C6D6): δ 31.3 (s, CH3), 57.3 (s, Cq). 27Al NMR (78 MHz, C6D6): δ 23.7 (br s). EI-MS (LR): 41.1 (3.7%), 57.1 (19%), 98.1 (1.1%), 198.2 (9.9%), 239.3 (2.2%), 339.4 (100%), 495.5 (0.51%). Anal. Calcd for C24H54AlN9: C, 58.15%; H, 10.98%; N, 25.43%. Found: C, 58.21%; H, 10.96%; N, 25.41%.

4.3. X-ray Crystallographic Analysis

Colorless single crystals for 6 were obtained by recrystallization from n-hexanes at −35 °C. The single crystals were used for X-ray diffraction data collection on a Bruker D8 SMART Apex-II diffractometer, using graphite-monochromated Mo Kα radiation (λ = 0.710 73 Å) at 153 K. All data were collected in hemisphere with over 95% completeness to 2θ < 50.05°. The structure is monoclinic, centrosymmetric, space group C2/m, a = 28.940(5), b = 16.958(3), c = 9.8864(17) Å, β = 94.118(2)°. In spite of data collection at low temperature, the data produce an electron density map that is rather “flat”, which is a result of very heavy disorder, rendering an almost amorphous structure. The structure was solved by direct methods. Coordinates of metal atoms were determined from the initial solutions, and from the N and C methods, located in subsequent differential Fourier syntheses. The solution does not contain much residual electron density, but it stays for a multitude of additional possible positions of light atoms. All nonhydrogen atoms were refined, first in isotropic and then in anisotropic approximation, using Bruker SHELXTL software. Additional crystal data treatment details are available from the Cambridge Crystallographic Data Centre, deposition no. CCDC 2046808.
The data collection on crystals of 1 was carried out under same conditions as for 6. An even less featured electron density map was obtained from the reflections provided by an analogous structure, monoclinic centrosymmetric, space group C2/m, a = 26.639(25), b = 15.817(15), c = 9.184(9) Å, β = 95.069(14)°. A model analogous to that for 6 was obtained but could not be refined successfully because of poor data quality. The details for the model obtained for the structure of 1 are available in the Supporting Information.

4.4. Thermogravimetric Analysis

Volatilization and vapor pressure curves were collected using a TA Instruments thermogravimetric analysis Q500 tool operating inside a N2-filled glovebox. The ramp experiment of compounds 1–6 was undertaken in tared platinum pans loaded with ∼5–10 mg for low mass volatilization experiments. The furnace was heated at a rate of 10 °C min–1 to 500 °C with a maintained N2 flow rate of 60 sccm. The Langmuir vapor pressure equations for compounds 1–4 and 6 were derived from TGA mass-loss derivative data of the ramp experiments according to a previously reported method (38) employing bis(2,2,6,6-tetramethyl-3,5-heptanedionato)copper(II) as a calibrant. (39)

4.5. Differential Scanning Calorimetry Analysis

DSC measurements were performed using a TA Instruments DSC Q10 tool. For each compound, 1–6, 0.2–0.5 mg of the compound was sealed in a platinum pan in a N2-filled glovebox. All experiments were performed at a heating rate of 10 °C min–1 between 25 and 400 °C. Exothermic and endothermic events are indicated by positive and negative heat flow, respectively.

4.6. Quantum-Chemical Computations

All quantum-chemical computations were performed using Gaussian 16 software. (40) Structural optimization and harmonic normal mode vibrational calculations were performed using the hybrid DFT method B3LYP (41,42) together with Grimme’s version 3 dispersion correction (43) and def2TZVP (44,45) basis set. The decomposition pathway was investigated by searching for possible stable structures as well as finding transition states connecting these structures. Minima were confirmed to have no imaginary frequencies, while transition states were verified to have one imaginary frequency, lying along the reaction path.

Supporting Information

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The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acs.inorgchem.0c03496.

  • Characterization of the compounds and computational calculation details (PDF)

  • Compound 1 (CIF)

  • Compound 6 (CIF)

Accession Codes

CCDC 2046808 contains the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing [email protected], or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

Terms & Conditions

Most electronic Supporting Information files are available without a subscription to ACS Web Editions. Such files may be downloaded by article for research use (if there is a public use license linked to the relevant article, that license may permit other uses). Permission may be obtained from ACS for other uses through requests via the RightsLink permission system: http://pubs.acs.org/page/copyright/permissions.html.

Author Information

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  • Corresponding Author
  • Authors
    • Rouzbeh Samii - Department of Physics, Chemistry and Biology, Linköping University, SE-581 83 Linköping, Sweden;  Orcidhttp://orcid.org/0000-0001-9380-4072
    • David Zanders - Faculty of Chemistry and Biochemistry, Ruhr University Bochum, Universitätsstraße 150, 44801 Bochum, Germany;  Department of Chemistry, Carleton University, 1125 Colonel By Drive, Ottawa, Ontario K1S5B6, Canada
    • Sydney C. Buttera - Department of Chemistry, Carleton University, 1125 Colonel By Drive, Ottawa, Ontario K1S5B6, Canada
    • Vadim Kessler - Department of Molecular Sciences, Swedish University of Agricultural Sciences, P.O. Box 7015, 75007 Uppsala, Sweden
    • Lars Ojamäe - Department of Physics, Chemistry and Biology, Linköping University, SE-581 83 Linköping, Sweden;  Orcidhttp://orcid.org/0000-0002-5341-2637
    • Henrik Pedersen - Department of Physics, Chemistry and Biology, Linköping University, SE-581 83 Linköping, Sweden;  Orcidhttp://orcid.org/0000-0002-7171-5383
  • Notes
    The authors declare no competing financial interest.

Acknowledgments

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The authors acknowledge Seán Barry for access to TGA and DSC instruments. This project was funded by the Swedish foundation for Strategic Research through the project “Time-resolved low temperature CVD for III-nitrides” (SSF-RMA 15-0018) and by the Knut and Alice Wallenberg foundation through the project “Bridging the THz gap” (KAW 2013.0049). L.O. acknowledges financial support from the Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linköping University (Faculty Grant SFO Mat LiU 2009 00971). Supercomputing resources were provided by the Swedish National Infrastructure for Computing (SNIC) and the Swedish National Supercomputer Centre (NSC).

References

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    The influence of growth parameters on the properties of AlN films fabricated by plasma-enhanced at. layer deposition using AlEt3 and NH3 precursors was investigated. The at. concns., refractive index, mass d., crystallinity, and surface roughness were studied from the films grown in the temp. range of 100-300° with plasma discharge times between 2.5-30 s. The AlN films were shown to be H-rich having H concns. in the range of 13-27 at.% with inverse dependence on the growth temp. The C and O concns. in the films were <2.6% and 0.2%, resp. The refractive index and mass d. of the films correlated with the H concn. so that higher concns. (lower growth temps.) resulted in smaller refractive index and mass d. The film grown at 300° was found to be cryst. whereas lower growth temp. produced amorphous films.
  13. 13
    Nepal, N.; Qadri, S. B.; Hite, J. K.; Mahadik, N. A.; Mastro, M. A.; Eddy, C. R. Epitaxial Growth of {AlN} Films via Plasma-Assisted Atomic Layer Epitaxy. Appl. Phys. Lett. 2013, 103, 82110,  DOI: 10.1063/1.4818792
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    Epitaxial growth of AlN films via plasma-assisted atomic layer epitaxy
    Nepal, N.; Qadri, S. B.; Hite, J. K.; Mahadik, N. A.; Mastro, M. A.; Eddy, C. R., Jr.
    Applied Physics Letters (2013), 103 (8), 082110/1-082110/5CODEN: APPLAB; ISSN:0003-6951. (American Institute of Physics)
    Thin AlN layers were grown at 200-650 °C by plasma assisted at. layer epitaxy (PA-ALE) simultaneously on Si(111), sapphire (11-20), and GaN/sapphire substrates. The AlN growth on Si(111) is self-limited for trimethyaluminum (TMA) pulse of length > 0.04 s, using a 10 s purge. However, the AlN nucleation on GaN/sapphire is non-uniform and has a bimodal island size distribution for TMA pulse of ≤0.03 s. The growth rate (GR) remains almost const. for Tg between 300 and 400 °C indicating ALE mode at those temps. The GR is increased by 20% at Tg = 500 °C. Spectroscopic ellipsometry (SE) measurement shows that the ALE AlN layers grown at Tg ≤ 400 °C have no clear band edge related features, however, the theor. estd. band gap of 6.2 eV was measured for AlN grown at Tg ≥ 500 °C. X-ray diffraction measurements on 37 nm thick AlN films grown at optimized growth conditions (Tg = 500 °C, 10 s purge, 0.06 s TMA pulse) reveal that the ALE AlN on GaN/sapphire is (0002) oriented with rocking curve full width at the half max. (FWHM) of 670 arc sec. Epitaxial growth of cryst. AlN layers by PA-ALE at low temps. broadens application of the material in the technologies that require large area conformal growth at low temps. with thickness control at the at. scale. (c) 2013 American Institute of Physics.
  14. 14
    Waggoner, K. M.; Olmstead, M. M.; Power, P. P. Structural and Spectroscopic Characterization of the Compounds [Al(NMe2)3]2, [Ga(NMe2)3]2, [(Me2N)2Al{μ-N(H)1-Ad}]2 (1-Ad = 1-Adamantanyl) and [{Me(μ-NPh2)Al}2NPh(μ-C6H4)]. Polyhedron 1990, 9, 257– 263,  DOI: 10.1016/S0277-5387(00)80578-1
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    14
    Structural and spectroscopic characterization of the compounds [Al(NMe2)3]2, [Ga(NMe2)3]2, [(Me2N)2Al{μ-N(H)1-Ad}]2 (1-Ad = 1-adamantanyl) and [{Me(μ-NPh2)Al}2NPh(μ-C6H4)]
    Waggoner, K. M.; Olmstead, M. M.; Power, P. P.
    Polyhedron (1990), 9 (2-3), 257-63CODEN: PLYHDE; ISSN:0277-5387.
    [Al(NMe2)3]2 (I), [Ga(NMe2)3]2 (II), [(Me2N)2Al{μ-1-AdNH}]2 (III; 1-AdNH2 = adamantanylamine) and [{Me(μ-NPh2)Al}2NPh(μ-C6H4)].0.5PhMe (IV) were prepd. and structurally and spectroscopically characterized by x-ray crystallog., 1H, 13C, 27Al, 69Ga and 71Ga NMR. A new synthesis is also provided for the previously known compd. I. The structures of I and II are the 1st reported structures of tris-dialkylamides of Al or Ga. Both possess dimeric structures in the solid with dimethylamide bridges and distorted tetrahedral geometry at the metal. The terminal NMe2 groups display significant deviation from planarity in both compds. The transamination reaction between I and 1 equiv of 1-AdNH2 affords III in high yield. IV was prepd. by treatment of AlMe3 with 2 equiv of HNPh2 in refluxing toluene and is somewhat surprising in view of the prior synthesis of Al(NPh2)3 via a similar reaction. I and II are triclinic, space group P‾1, R = 0.041 and 0.035, resp.; III and IV are monoclinic, space group P21/c, R = 0.047 and 0.066, resp.
  15. 15
    Wade, C. R.; Silvernail, C.; Banerjee, C.; Soulet, A.; McAndrew, J.; Belot, J. A. Tris(Dialkylamino)Aluminums: Syntheses, Characterization, Volatility Comparison and Atomic Layer Deposition of Alumina Thin Films. Mater. Lett. 2007, 61, 5079– 5082,  DOI: 10.1016/j.matlet.2007.04.009
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    Tris(dialkylamino)aluminums: Syntheses, characterization, volatility comparison and atomic layer deposition of alumina thin films
    Wade, Casey R.; Silvernail, Carter; Banerjee, Chiranjib; Soulet, Axel; McAndrew, James; Belot, John A.
    Materials Letters (2007), 61 (29), 5079-5082CODEN: MLETDJ; ISSN:0167-577X. (Elsevier B.V.)
    The syntheses and characterization of both tris(diethylamino)aluminum and tris(diisopropylamino)aluminum are presented. Characterization includes vapor pressure measurements and comparison of the 2 non-pyrophoric precursors showing them to be viable alternatives to trimethylaluminum. Tris(diisopropyl)aluminum was successful in the at. layer deposition of alumina thin films.
  16. 16
    Liu, G.; Deguns, E.; Lecordier, L.; Sundaram, G.; Becker, J. Atomic Layer Deposition of AlN with Tris(Dimethylamido)Aluminum and NH. ECS Trans. 2011, 41, 219– 225,  DOI: 10.1149/1.3633671
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    Atomic layer deposition of AlN with tris(dimethylamido)aluminum and NH3
    Liu, G.; Deguns, E. W.; Lecordier, L.; Sundaram, G.; Becker, J. S.
    ECS Transactions (2011), 41 (2, Atomic Layer Deposition Applications 7), 219-225CODEN: ECSTF8; ISSN:1938-5862. (Electrochemical Society)
    Atomic layer deposition of aluminum nitride on Si wafers using tris(dimethylamido)aluminum and ammonia has been investigated in the temp. range from 180 to 400°C. Satd. growth behavior not obsd. with NH3 pulsed in continuous mode has been achieved in NH3 exposure mode. Thin AlN films have been analyzed by spectroscopic ellipsometry and SIMS for optical and chem. properties, X-ray diffraction for crystallinity, and mercury probe for elec. properties. Polycryst. and high purity AlN films have been obtained at 300°C or higher. A high dielec. const. in the range of 7.4-7.7 and high breakdown field of 5.3-5.6 MV/cm with relatively low leakage current in the 10-7 to 10-8 A/cm2 range at 2MV/cm have been obtained for AlN films deposited between 300 and 400°C in NH3 exposure mode.
  17. 17
    Kim, K. H.; Gordon, R. G.; Ritenour, A.; Antoniadis, D. A. Atomic Layer Deposition of Insulating Nitride Interfacial Layers for Germanium Metal Oxide Semiconductor Field Effect Transistors with High-κ Oxide/Tungsten Nitride Gate Stacks. Appl. Phys. Lett. 2007, 90, 212104,  DOI: 10.1063/1.2741609
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    Atomic layer deposition of insulating nitride interfacial layers for germanium metal oxide semiconductor field effect transistors with high-κ oxide/tungsten nitride gate stacks
    Kim, Kyoung H.; Gordon, Roy G.; Ritenour, Andrew; Antoniadis, Dimitri A.
    Applied Physics Letters (2007), 90 (21), 212104/1-212104/3CODEN: APPLAB; ISSN:0003-6951. (American Institute of Physics)
    At. layer deposition (ALD) was used to deposit passivating interfacial nitride layers between Ge and high-κ oxides. High-κ oxides on Ge surfaces passivated by ultrathin (1-2 nm) ALD Hf3N4 or AlN layers exhibited well-behaved C-V characteristics with an equiv. oxide thickness as low as 0.8 nm, no significant flatband voltage shifts, and midgap d. of interface states values of 2 × 1012 cm-1 eV-1. AlN. Functional n-channel and p-channel Ge field effect transistors with nitride interlayer/high-κ oxide/metal gate stacks are demonstrated.
  18. 18
    Abdulagatov, A. I.; Ramazanov, S. M.; Dallaev, R. S.; Murliev, E. K.; Palchaev, D. K.; Rabadanov, M. K.; Abdulagatov, I. M. Atomic Layer Deposition of Aluminium Nitride Using Tris(Diethylamido)Aluminum and Hydrazine or Ammonia. Russ. Microelectron. 2018, 47, 118– 130,  DOI: 10.1134/S1063739718020026
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    18
    Atomic Layer Deposition of Aluminum Nitride Using Tris(diethylamido)aluminum and Hydrazine or Ammonia
    Abdulagatov, A. I.; Ramazanov, Sh. M.; Dallaev, R. S.; Murliev, E. K.; Palchaev, D. K.; Rabadanov, M. Kh.; Abdulagatov, I. M.
    Russian Microelectronics (2018), 47 (2), 118-130CODEN: RUICE5; ISSN:1063-7397. (Pleiades Publishing, Ltd.)
    Aluminum nitride (AlNx) films were obtained by at. layer deposition (ALD) using tris(diethylamido) aluminum(III) (TDEAA) and hydrazine (N2H4) or ammonia (NH3). The quartz crystal microbalance (QCM) data showed that the surface reactions of TDEAA and N2H4 (or NH3) at temps. from 150 to 225°C were self-limiting. The rates of deposition of the nitride film at 200°C for systems with N2H4 and NH3 coincided: ∼1.1 Å/cycle. The ALD AlN films obtained at 200°C using hydrazine had higher d. (2.36 g/cm3, 72.4% of bulk d.) than those obtained with ammonia (2.22 g/cm3, 68%). The elemental anal. of the film deposited using TDEAA/N2H4 at 200°C showed the presence of carbon (∼1.4 at %), oxygen (∼3.2 at %), and hydrogen (22.6 at %) impurities. The N/Al at. concn. ratio was ∼1.3. The residual impurity content in the case of N2H4 was lower than for NH3. In general, it was confirmed that hydrazine has a more preferable surface thermochem. than ammonia.
  19. 19
    Abdulagatov, A. I.; Amashaev, R. R.; Ashurbekova, K. N.; Ashurbekova, K. N.; Rabadanov, M. K.; Abdulagatov, I. M. Atomic Layer Deposition of Aluminum Nitride and Oxynitride on Silicon Using Tris(Dimethylamido)Aluminum, Ammonia, and Water. Russ. J. Gen. Chem. 2018, 88, 1699– 1706,  DOI: 10.1134/S1070363218080236
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    19
    Atomic Layer Deposition of Aluminum Nitride and Oxynitride on Silicon Using Tris(dimethylamido)aluminum, Ammonia, and Water
    Abdulagatov, A. I.; Amashaev, R. R.; Ashurbekova, Kr. N.; Ashurbekova, K. N.; Rabadanov, M. Kh.; Abdulagatov, I. M.
    Russian Journal of General Chemistry (2018), 88 (8), 1699-1706CODEN: RJGCEK; ISSN:1070-3632. (Pleiades Publishing, Ltd.)
    Thin films of aluminum nitride and oxynitride were deposited by at. layer deposition (ALD) in the temp. range from 170 to 290°C (optimal deposition temp. 200-230°C). Tris(dimethylamido) aluminum and ammonia were used as precursors for the at. layer deposition of aluminum nitride (AlN). The av. AlN film thickness per ALD cycle (deposition rate) at 200°C was ∼0.8 Å. Films were deposited on a silicon <100> substrate with a native oxide layer. The N/Al at. concn. ratio in the obtained films was ∼1.3. Aluminum oxynitride films obtained by periodical dose of water vapor in the course of at. layer deposition of AlN at 200°C. The compn. of the deposited oxynitride films was Al0.5O0.43N0.07.
  20. 20
    Gordon, R. G. Atomic Layer Deposition for Semiconductors. In Atomic Layer Deposition for Semiconductors; Hwang, C. S., Yoo, C. Y., Eds.; Springer US: New York, 2014; pp 15– 46.
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    Kim, S. B.; Jayaraman, A.; Chua, D.; Davis, L. M.; Zheng, S. L.; Zhao, X.; Lee, S.; Gordon, R. G. Obtaining a Low and Wide Atomic Layer Deposition Window (150–275 °C) for In2O3 Films Using an InIII Amidinate and H2O. Chem. - Eur. J. 2018, 24, 9525– 9529,  DOI: 10.1002/chem.201802317
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    Obtaining a low and wide atomic layer deposition window (150-275 °C) for In2O3 films using an InIII amidinate and H2O
    Kim, Sang Bok; Jayaraman, Ashwin; Chua, Danny; Davis, Luke M.; Zheng, Shao-Liang; Zhao, Xizhu; Lee, Sunghwan; Gordon, Roy G.
    Chemistry - A European Journal (2018), 24 (38), 9525-9529CODEN: CEUJED; ISSN:0947-6539. (Wiley-VCH Verlag GmbH & Co. KGaA)
    Indium oxide is a major component of many technol. important thin films, most notably the transparent conductor indium tin oxide (ITO). Despite being pyrophoric, homoleptic indium(III) alkyls do not allow at. layer deposition (ALD) of In2O3 using water as a co-precursor at substrate temps. below 200 °C. Several alternative indium sources have been developed, but none allows ALD at lower temps. except in the presence of oxidants such as O2 or O3, which are not compatible with some substrates or alloying processes. We have synthesized a new indium precursor, tris(N,N'-diisopropylformamidinato)indium(III), compd. 1, which allows ALD of pure, carbon-free In2O3 films using H2O as the only co-reactant, on substrates in the temp. range 150-275 °C. In contrast, replacing just the H of the anionic iPrNC(H)NiPr ligand with a Me group (affording the known tris(N,N'-diisopropylacetamidinato)indium(III), compd. 2) results in a considerably higher and narrower ALD window in the analogous reaction with H2O (225-300 °C). Kinetic studies demonstrate that a higher rate of surface reactions in both parts of the ALD cycle gives rise to this difference in the ALD windows.
  22. 22
    Rouf, P.; O’Brien, N. J.; Rönnby, K.; Samii, R.; Ivanov, I. G.; Ojamaë, L.; Pedersen, H. The Endocyclic Carbon Substituent of Guanidinate and Amidinate Precursors Controlling Atomic Layer Deposition of InN Films. J. Phys. Chem. C 2019, 123, 25691– 25700,  DOI: 10.1021/acs.jpcc.9b07005
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    The Endocyclic Carbon Substituent of Guanidinate and Amidinate Precursors Controlling Atomic Layer Deposition of InN Films
    Rouf, Polla; O'Brien, Nathan J.; Roennby, Karl; Samii, Rouzbeh; Ivanov, Ivan G.; Ojamaee, Lars; Pedersen, Henrik
    Journal of Physical Chemistry C (2019), 123 (42), 25691-25700CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
    Indium nitride (InN) is an interesting material for future high-frequency electronics due to its high electron mobility. The problematic deposition of InN films currently prevents full exploration of InN-based electronics. We present studies of at. layer deposition (ALD) of InN using In precursors with bidentate ligands forming In-N bonds: tris(N,N-dimethyl-N',N''-diisopropylguanidinato)indium(III), tris(N,N'-diisopropylamidinato)indium(III), and tris(N,N'-diisopropylformamidinato)indium(III). These compds. form a series were the size of the substituent on the endocyclic position decreases from -NMe2 to -Me and to -H, resp. We show that when the size of the substituent decreases, the InN films deposited have a better cryst. quality, of better optical quality, lower roughness, and an In/N ratio closer to unity. From quantum chem. calcns., we show that the smaller substituents lead to less steric repulsion and weaker bonds between the ligand and In center. We propose that these effects render a more favored surface chem. for the nitridation step in the ALD cycle, which explains the improved film properties.
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    Gebhard, M.; Hellwig, M.; Parala, H.; Xu, K.; Winter, M.; Devi, A. Indium-Tris-Guanidinates: A Promising Class of Precursors for Water Assisted Atomic Layer Deposition of In2O3 Thin Films. Dalt. Trans. 2014, 43, 937– 940,  DOI: 10.1039/C3DT52746H
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    Indium-tris-guanidinates: a promising class of precursors for water assisted atomic layer deposition of In2O3 thin films
    Gebhard, M.; Hellwig, M.; Parala, H.; Xu, K.; Winter, M.; Devi, A.
    Dalton Transactions (2014), 43 (3), 937-940CODEN: DTARAF; ISSN:1477-9226. (Royal Society of Chemistry)
    Two closely related mononuclear homoleptic In-tris-guanidinate complexes were synthesized and characterized as precursors for at. layer deposition (ALD) of In2O3. In a water-assisted ALD process, high quality In2O3 thin films were fabricated for the first time using the new class of precursors as revealed by the promising ALD growth characteristics and film properties.
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    Barry, S. T.; Gordon, P. G.; Ward, M. J.; Heikkila, M. J.; Monillas, W. H.; Yap, G. P. A.; Ritala, M.; Leskelä, M. Chemical Vapour Deposition of In2O3 Thin Films from a Tris-Guanidinate Indium Precursor. Dalt. Trans. 2011, 40, 9425– 9430,  DOI: 10.1039/c1dt10877h
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    Chemical vapour deposition of In2O3 thin films from a tris-guanidinate indium precursor
    Barry, Sean T.; Gordon, Peter G.; Ward, Matthew J.; Heikkila, Mikko J.; Monillas, Wesley H.; Yap, Glenn P. A.; Ritala, Mikko; Leskelae, Markku
    Dalton Transactions (2011), 40 (37), 9425-9430CODEN: DTARAF; ISSN:1477-9226. (Royal Society of Chemistry)
    A new homoleptic sublimable indium(III) guanidinate, (In[(NiPr)2CNMe2]3) (I), was synthesized from a facile high-yield procedure. Compd. I crystd. is a P‾1 space group; a = 10.5989(14) Å, b = 11.0030(15) Å, c = 16.273(2) Å, α = 91.190(2)°, β = 96.561(2)°, γ = 115.555(2)°; R = 3.50%. Thermogravimetric anal. showed I to produce elemental indium as a residual mass. Thermolysis in a sealed NMR tube showed carbodiimide and protonated dimethylamine by 1H NMR. Chem. vapor deposition expts. at > 275°C with air as the reactant gas showed I to readily deposit cubic indium oxide with good transparency.
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    Brazeau, A. L.; DiLabio, G. A.; Kreisel, K. A.; Monillas, W.; Yap, G. P. A.; Barry, S. T. Theoretical and Experimental Investigations of Ligand Exchange in Guanidinate Ligand Systems for Group 13 Metals. J. Chem. Soc. Dalt. Trans. 2007, (30), 3297– 3304,  DOI: 10.1039/b706044k
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    Kenney, A. P.; Yap, G. P. A.; Richeson, D. S.; Barry, S. T. The Insertion of Carbodiimides into Al and Ga Amido Linkages. Guanidinates and Mixed Amido Guanidinates of Aluminum and Gallium. Inorg. Chem. 2005, 44, 2926– 2933,  DOI: 10.1021/ic048433g
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    The Insertion of Carbodiimides into Al and Ga Amido Linkages. Guanidinates and Mixed Amido Guanidinates of Aluminum and Gallium
    Kenney, Amanda P.; Yap, Glenn P. A.; Richeson, Darrin S.; Barry, Sean T.
    Inorganic Chemistry (2005), 44 (8), 2926-2933CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)
    The insertion of carbodiimides into existing metal-heteroatom bonds is an important preparative route for the synthesis of useful ligand systems such as amidinates and guanidinates. The authors' interest lies in multiple insertions at one metal center and the mechanisms of insertion and rearrangement. The authors synthesized and characterized [Me2NC(NiPr)2]nM(NMe2)3-n (n = 1, 2, 3; M = Al, Ga). The authors have studied the mechanism of synthesis and discovered a ligand transfer step that is important for the formation of the final products.
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    Brazeau, A. L.; Wang, Z.; Rowley, C. N.; Barry, S. T. Synthesis and Thermolysis of Aluminum Amidinates: A Ligand-Exchange Route for New Mixed-Ligand Systems. Inorg. Chem. 2006, 45, 2276– 2281,  DOI: 10.1021/ic051856d
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    Synthesis and Thermolysis of Aluminum Amidinates: A Ligand-Exchange Route for New Mixed-Ligand Systems
    Brazeau, Allison L.; Wang, Zhaohui; Rowley, Chris N.; Barry, Sean T.
    Inorganic Chemistry (2006), 45 (5), 2276-2281CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)
    A novel ligand-exchange route for the synthesis of amidinate-contg. compds. of aluminum is explored. Aluminum amidinates RC(NiPr)2AlR12 (4, 5; R = Me, R1 = Et; R = Et, R1 = Me) were prepd. starting from the corresponding carbodiimides, RLi and R12AlCl; guanidinate [Me2NC(NiPr)2]2AlH (6) was prepd. by redistribution reaction of the tris-guanidinate with AlH3·NMe2Et. The thermal reactivities of these compds. and their parent homoleptic compds. [MeC(NiPr)2]3Al (1), [Me2NC(NiPr)2]3Al (2), and [EtC(NiPr)2]3Al (3) were explored and analyzed with respect to their utility as potential at.-layer-deposition precursors for aluminum-contg. films. The major mechanism of thermal decompn. is found to be carbodiimide deinsertion to form aluminum alkyls or amides. Because of their thermal characteristics, both compds. 3 and 5 hold promise for use as precursors.
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    Leman, J. T.; Barron, A. R. Synthesis of 1,3-Diphenyltriazenide Complexes of Aluminium, Gallium and Indium: Crystal Structure of Tris(1,3-Diphenyltriazenido)Aluminium(III). Polyhedron 1989, 8, 1909– 1912,  DOI: 10.1016/S0277-5387(00)86413-X
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    Synthesis of 1,3-diphenyltriazenide complexes of aluminum, gallium and indium: crystal structure of tris(1,3-diphenyltriazenido)aluminum(III)
    Leman, John T.; Barron, Andrew R.; Ziller, Joseph W.; Kren, Robert M.
    Polyhedron (1989), 8 (15), 1909-12CODEN: PLYHDE; ISSN:0277-5387.
    The reaction of AlMe3 with 1,3-diphenyltriazene [Hdpt] in toluene gave Al(dpt)3, even when AlMe3 was in large excess. Monomeric Al(dpt)3 crystd. in space group C2/c with a 20.587(3), b 16.005(3), c 13.236(3) Å and β 119.172(12)°, Z 4, R 0.067 and Rw 0.083. The Al(III) is coordinated by 3 chelating triazenido ligands to give a trigonally distorted octahedral geometry. The Ga and In analogs are also reported.
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    Leman, J. T.; Braddock-Wilking, J.; Coolong, A. J.; Barron, A. R. 1,3-Diaryltriazenido Compounds of Aluminum. Inorg. Chem. 1993, 32, 4324– 4336,  DOI: 10.1021/ic00072a028
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    1,3-Diaryltriazenido compounds of aluminum
    Leman, John T.; Braddock-Wilking, Janet; Coolong, Alanna J.; Barron, Andrew R.
    Inorganic Chemistry (1993), 32 (20), 4324-36CODEN: INOCAJ; ISSN:0020-1669.
    Reaction of AlH(iBu)2 with 1 and 2 equiv of 1,3-diphenyltriazene, PhN:NNHPh, yields [cyclic] Al(iBu)2[N(Ph)NN(Ph)] (1) and [cyclic] Al(iBu)[N(Ph)NN(Ph)]2 (2), resp. Compd. 2 undergoes ligand exchange in soln. to give an equimolar mixt. of 1 and [cyclic] Al[N(Ph)NN(Ph)]3. The reaction of Al(tBu)3 with PhN:NNHPh gives [cyclic] Al(tBu)2[N(Ph)NN(Ph)] (3) as the only product. Addn. of 1 equiv of PhN:NNHPh to AlMe2(BHT)(OEt2) (BHT-H = 2,6-di-tert-butyl-4-methylphenol) allows for the isolation of [cyclic] AlMe(BHT)[N(Ph)NN(Ph)] (4); however, a higher equiv of PhN:NNHPh yields only [cyclic] Al[N(Ph)NN(Ph)]3. The bis(triazenide) complex [cyclic] Al(BHT)[N(Ph)NN(Ph)]2 (5) is isolated from the reaction of PhN:NNHPh with AlH2(BHT)(NMe3), while [cyclic] Al(BHT)2[N(Ph)NN(Ph)] (6) is formed from the reaction of PhN:NNHPh with AlMe(BHT)2. Although the reaction of 1 with H2salen [N,N'-ethylenebis(salicylideneamine)] does not yield [cyclic] Al[N(Ph)NN(Ph)](salen) (8) but rather yields Al(iBu)(salen) (7), compd. 8 may be isolated from interaction of PhN:NNHPh with AlMe(salen). The reaction between AlMe3 and 3 equiv of substituted 1,3-diaryltriazenes, ArN:NNHAr, yields the 6-coordinate aluminum tris(1,3-diaryltriazenido) compds., [cyclic] Al[N(Ar)NN(Ar)]3 [Ar = 2-MeC6H4 (9), 4-MeC6H4 (10), 4-MeOC6H4 (11), 4-FC6H4 (12), 4-ClC6H4 (13), 4-BrC6H4 (14), C6F5 (15)]. The unsym. diaryltriazene complex [cyclic] Al[N(Ph)NN(4-MeOC6H4)]3 (16) adopts a trans-meridional conformation. The spectroscopic characterization of the tris(triazenido) complexes is discussed with respect to the nature of the aryl substituents. The X-ray structures of 1, 6, AlMe(salen), 9, 11, 13, (C6F5)N:NN(H)(C6F5), and (2-MeC6H4)N:NN(H)(2-MeC6H4).(2-MeC6H4)NH2 have been detd.
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    O’Brien, N. J.; Rouf, P.; Samii, R.; Rönnby, K.; Buttera, S. C.; Hsu, C.-W.; Ivanov, I. G.; Kessler, V.; Ojamäe, L.; Pedersen, H. In-Situ Activation of an Indium(III) Triazenide Precursor for Epitaxial Indium Nitride by Atomic Layer Deposition. Chem. Mater. 2020, 32, 4481– 4489,  DOI: 10.1021/acs.chemmater.9b05171
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    In Situ Activation of an Indium(III) Triazenide Precursor for Epitaxial Growth of Indium Nitride by Atomic Layer Deposition
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    Chemistry of Materials (2020), 32 (11), 4481-4489CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
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  • Abstract

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    Scheme 1

    Scheme 1. Synthesis of Tris(1,3-dialkyltriazenide)aluminum(III) Compounds 1–6
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    Figure 1

    Figure 1. ORTEP drawing for one of two independent molecules in the unit cell of 6. Thermal ellipsoids are displayed at the 50% probability level, and hydrogen atoms are omitted for clarity.

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    Figure 2

    Figure 2. (a) HOMO (−5.74 eV) and (b) LUMO (−0.78 eV) for 6 from DFT calculations.

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    Figure 3

    Figure 3. Thermogravimetric analysis of 1–6.

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    Figure 4

    Figure 4. The 1H NMR (500 MHz, C6D6) spectra from a decomposition study of 1 between 0.8–1.3 and 3.7–4.0 ppm separated by an axis break. For visibility, the y-axis is scaled up ∼18 times on the left of the axis break compared to the right side. Prior to flame sealing, the compound showed no traces of impurities by 1H NMR analysis. The peaks marked with an asterisk appeared after flame sealing the tube. Compound 1 was heated in C6D6, and all spectra were acquired at 50 °C to suppress line broadening. The decomposition of 1 accelerates after 210 °C, which is shown by the diminished quartet and doublet peaks.

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    Figure 5

    Figure 5. Free energy profile (at 250 °C and 10 hPa) for the first half of the decomposition pathway. Here, 1 loses a triazene ligand (after TS-2), and one ligand decomposes into an imido ligand (TS-5). TS-3 has the largest free energy (211 kJmol–1) for the displayed part of the decomposition pathway. The overall largest free energy barrier is found at TS-8 (214 kJmol–1): the analogous step to TS-3 but for the last ligand. At 250 °C and 10 hPa, the adduct structures I-2A separate spontaneously (i.e., the process is barrierless and has a negative free energy difference) and is therefore not included.

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    Figure 6

    Figure 6. Free energy profile continuing from I-5. The steps that transform I-5 into I-10 are analogous to the steps that transform 1 into I-5. The reverse step through TS-7 has a significantly larger free energy barrier compared to the analogous TS-2 (290 vs 85 kJ mol–1, respectively).

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    Scheme 2

    Scheme 2. Separation of the Adduct Structure I-2A into a Triazene and I-2a
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    aThe I-2 intermediate has one monoanionic N,N-coordinated and one dianionic C,N-coordinated triazenide ligand.

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      Taniyasu, Yoshitaka; Kasu, Makoto; Makimoto, Toshiki
      Nature (London, United Kingdom) (2006), 441 (7091), 325-328CODEN: NATUAS; ISSN:0028-0836. (Nature Publishing Group)
      Compact high-efficiency UV solid-state light sources-such as light-emitting diodes (LEDs) and laser diodes-are of considerable technol. interest as alternatives to large, toxic, low-efficiency gas lasers and Hg lamps. Microelectronic fabrication technologies and the environmental sciences both require light sources with shorter emission wavelengths: the former for improved resoln. in photolithog. and the latter for sensors that can detect minute hazardous particles. UV solid-state light sources are also attracting attention for potential applications in high-d. optical data storage, biomedical research, H2O and air purifn., and sterilization. Wide-bandgap materials, such as diamond and III-V nitride semiconductors (GaN, AlGaN and AlN; refs. 3-10), are potential materials for UV LEDs and laser diodes, but suffer from difficulties in controlling elec. conduction. Here the authors report the successful control of both n-type and p-type doping in Al nitride (AlN), which has a very wide direct bandgap of 6 eV. This doping strategy allows one to develop an AlN PIN (p-type/intrinsic/n-type) homojunction LED with an emission wavelength of 210 nm, which is the shortest reported to date for any kind of LED. The emission is attributed to an exciton transition, and represents an important step towards achieving exciton-related light-emitting devices as well as replacing gas light sources with solid-state light sources.
    2. 2
      Li, J.; Nam, K. B.; Nakarmi, M. L.; Lin, J. Y.; Jiang, H. X.; Carrier, P.; Wei, S.-H. Band Structure and Fundamental Optical Transitions in Wurtzite AlN. Appl. Phys. Lett. 2003, 83, 5163– 5165,  DOI: 10.1063/1.1633965
      2
      Band structure and fundamental optical transitions in wurtzite AlN
      Li, J.; Nam, K. B.; Nakarmi, M. L.; Lin, J. Y.; Jiang, H. X.; Carrier, Pierre; Wei, Su-Huai
      Applied Physics Letters (2003), 83 (25), 5163-5165CODEN: APPLAB; ISSN:0003-6951. (American Institute of Physics)
      With a recently developed unique deep UV picoseconds time-resolved photoluminescence (PL) spectroscopy system and improved growth technique, the authors are able to det. the detailed band structure near the Γ point of wurtzite (WZ) AlN with a direct band gap of 6.12 eV. Combined with 1st-principles band structure calcns. the fundamental optical properties of AlN differ drastically from that of GaN and other WZ semiconductors. The discrepancy in energy band gap values of AlN obtained previously by different methods is explained in terms of the optical selection rules in AlN and is confirmed by measurement of the polarization dependence of the excitonic PL spectra.
    3. 3
      George, S. M. Atomic Layer Deposition: An Overview. Chem. Rev. 2010, 110, 111– 131,  DOI: 10.1021/cr900056b
      3
      Atomic Layer Deposition: An Overview
      George, Steven M.
      Chemical Reviews (Washington, DC, United States) (2010), 110 (1), 111-131CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)
      A review. A review on the at. layer deposition and its application to the fabrication of semiconductor device and nanodevices. The nucleation and growth mechanism during at. layer deposition are discussed.
    4. 4
      Koponen, S. E.; Gordon, P. G.; Barry, S. T. Principles of Precursor Design for Vapour Deposition Methods. Polyhedron 2016, 108, 59– 66,  DOI: 10.1016/j.poly.2015.08.024
      4
      Principles of precursor design for vapour deposition methods
      Koponen, Sara E.; Gordon, Peter G.; Barry, Sean T.
      Polyhedron (2016), 108 (), 59-66CODEN: PLYHDE; ISSN:0277-5387. (Elsevier Ltd.)
      A review. CVD and at. layer deposition (ALD) are attractive techniques for depositing a wide spectrum of thin solid film materials, for a broad spectrum of industrial applications. These techniques rely on volatile, reactive, and thermally stable mol. precursors to transport and deposit growth materials in a kinetically controlled manner, resulting in uniform, conformal, high purity films. Developments in these fields depend on careful precursor design. The qualities that make successful CVD or ALD precursors (low m.p., high volatility, stability and specific reactivity) and the widely applicable design principles used to achieve them, through examples of Group 11 and 13 precursors including amidinates, guanidinates and iminopyrrolidinates are discussed. The authors highlight the most valuable techniques that the authors use to asses potential precursors from the discussed qualities, and to elucidate relevant mechanisms of decompn. and surface reactivity. There is a strong focus on TGA, and solid state (SS) and soln. NMR studies.
    5. 5
      Van Bui, H.; Nguyen, M. D.; Wiggers, F. B.; Aarnink, A. A. I.; De Jong, M. P.; Kovalgin, A. Y. Self-Limiting Growth and Thickness- And Temperature- Dependence of Optical Constants of ALD AlN Thin Films. ECS J. Solid State Sci. Technol. 2014, 3, P101– P106,  DOI: 10.1149/2.020404jss
      5
      Self-limiting growth and thickness- and temperature-dependence of optical constants of ALD AlN thin films
      Van Bui, H.; Nguyen, M. D.; Wiggers, F. B.; Aarnink, A. A. I.; de Jong, M. P.; Kovalgin, A. Y.
      ECS Journal of Solid State Science and Technology (2014), 3 (4), P101-P106CODEN: EJSSBG; ISSN:2162-8769. (Electrochemical Society)
      We have investigated the growth characteristics and optical consts. of thin AlN films made by thermal at. layer deposition (ALD) from AlMe3 and NH3. We obsd. the nucleation, closure and growth after closure of the films using AFM and in-situ spectroscopic ellipsometry. A fully covered surface was obtained for films with a thickness of about 2 nm. The self-limiting ALD growth was obsd. at temps. of 330 and 350° with deposition rates of 1.5 and 2.1 Å/cycle, resp. At 370°, thermal decompn. of TMA dominated the growth mechanism, resulting in a fast and non-self-limiting deposition. Low concns. of O (0.8-2.5%) and C (5-7.5%) incorporated into the films were measured. We found that the refractive index increased remarkably with increasing film thickness and growth temp.
    6. 6
      Riihelä, D.; Ritala, M.; Matero, R.; Leskelä, M.; Jokinen, J.; Haussalo, P. Low Temperature Deposition of AlN Films by an Alternate Supply of Trimethyl Aluminum and Ammonia. Chem. Vap. Deposition 1996, 2, 277– 283,  DOI: 10.1002/cvde.19960020612
      There is no corresponding record for this reference.
    7. 7
      Liu, X.; Ramanathan, S.; Lee, E.; Seidel, T. E. Atomic Layer Deposition of Aluminum Nitride Thin Films from Trimethyl Aluminum (TMA) and Ammonia. MRS Online Proceedings Library 2003, 811, 158– 153,  DOI: 10.1557/PROC-811-D1.9
      There is no corresponding record for this reference.
    8. 8
      Jung, Y. C.; Hwang, S. M.; Le, D. N.; Kondusamy, A. L. N.; Mohan, J.; Kim, S. W.; Kim, J. H.; Lucero, A. T.; Ravichandran, A.; Kim, H. S.; Kim, S. J.; Choi, R.; Ahn, J.; Alvarez, D.; Spiegelman, J.; Kim, J. Low Temperature Thermal Atomic Layer Deposition of Aluminum Nitride Using Hydrazine as the Nitrogen Source. Materials 2020, 13, 3387,  DOI: 10.3390/ma13153387
      8
      Low temperature thermal atomic layer deposition of aluminum nitride using hydrazine as the nitrogen source
      Jung, Yong Chan; Hwang, Su Min; Le, Dan N.; Kondusamy, Aswin L. N.; Mohan, Jaidah; Kim, Sang Woo; Kim, Jin Hyun; Lucero, Antonio T.; Ravichandran, Arul; Kim, Harrison Sejoon; Kim, Si Joon; Choi, Rino; Ahn, Jinho; Alvarez, Daniel; Spiegelman, Jeff; Kim, Jiyoung
      Materials (2020), 13 (15), 3387CODEN: MATEG9; ISSN:1996-1944. (MDPI AG)
      Aluminum nitride (AlN) thin films were grown using thermal at. layer deposition in the temp. range of 175-350 °C. The thin films were deposited using tri-Me aluminum (TMA) and hydrazine (N2H4) as a metal precursor and nitrogen source, resp. Highly reactive N2H4, compared to its conventionally used counterpart, ammonia (NH3), provides a higher growth per cycle (GPC), which is approx. 2.3 times higher at a deposition temp. of 300 °C and, also exhibits a low impurity concn. in as-deposited films. Low temp. AlN films deposited at 225 °C with a capping layer had an Al to N compn. ratio of 1:1.1, a close to ideal compn. ratio, with a low oxygen content (7.5%) while exhibiting a GPC of 0.16 nm/cycle. We suggest that N2H4 as a replacement for NH3 is a good alternative due to its stringent thermal budget.
    9. 9
      Dendooven, J.; Deduytsche, D.; Musschoot, J.; Vanmeirhaeghe, R. L.; Detavernier, C. Conformality of Al2O3 and AlN Deposited by Plasma-Enhanced Atomic Layer Deposition. J. Electrochem. Soc. 2010, 157, G111,  DOI: 10.1149/1.3301664
      9
      Conformality of Al2O3 and AlN Deposited by Plasma-Enhanced Atomic Layer Deposition
      Dendooven, J.; Deduytsche, D.; Musschoot, J.; Vanmeirhaeghe, R. L.; Detavernier, C.
      Journal of the Electrochemical Society (2010), 157 (4), G111-G116CODEN: JESOAN; ISSN:0013-4651. (Electrochemical Society)
      This paper focuses on the conformality of the plasma-enhanced at. layer deposition (PE-ALD) of Al2O3 using trimethylaluminum [AlMe3; (TMA)] as a precursor and O2 plasma as an oxidant source. The conformality was quantified by measuring the deposited film thickness as a function of depth into macroscopic test structures with aspect ratios of ∼5, 10, and 22. A comparison with the thermal TMA/H2O process indicates that the conformality of the plasma based process is more limited due to the surface recombination of radicals during the plasma step. The conformality can slightly be improved by raising the gas pressure or the radiofrequency power. Prolonging the plasma exposure time results in further improvement of the conformality. Also, there are indications that the H2O produced during the plasma step in the PE-ALD process for Al2O3 contributes to the obsd. conformality through a secondary thermal ALD reaction. The conformality of Al2O3 is also compared to the conformality of AlN deposited by PE-ALD from TMA and NH3 plasma. For the same exposure, O2 plasma results in better conformality compared to NH3 plasma, suggesting a faster recombination of the radicals in the NH3 plasma.
    10. 10
      Ozgit, C.; Donmez, I.; Alevli, M.; Biyikli, N. Self-Limiting Low-Temperature Growth of Crystalline AlN Thin Films by Plasma-Enhanced Atomic Layer Deposition. Thin Solid Films 2012, 520, 2750– 2755,  DOI: 10.1016/j.tsf.2011.11.081
      10
      Self-limiting low-temperature growth of crystalline AlN thin films by plasma-enhanced atomic layer deposition
      Ozgit, Cagla; Donmez, Inci; Alevli, Mustafa; Biyikli, Necmi
      Thin Solid Films (2012), 520 (7), 2750-2755CODEN: THSFAP; ISSN:0040-6090. (Elsevier B.V.)
      We report on the self-limiting growth and characterization of AlN thin films. AlN films were deposited by plasma-enhanced at. layer deposition on various substrates using AlMe3 and NH3. At 185°, deposition rate satd. for AlMe3 and NH3 doses starting from 0.05 and 40 s, resp. Saturative surface reactions between AlMe3 and NH3 resulted in a const. growth rate of ≈0.86 Å/cycle from 100-200°. Within this temp. range, film thickness increased linearly with the no. of deposition cycles. At higher temps. (≥225°) deposition rate increased with temp. Chem. compn. and bonding states of the films deposited at 185° were investigated by XPS. High resoln. Al 2p and N 1s spectra confirmed the presence of AlN with peaks located at 73.02 and 396.07 eV, resp. Films deposited at 185° were polycryst. with a hexagonal wurtzite structure regardless of the substrate selection as detd. by grazing incidence x-ray diffraction. High-resoln. TEM images of the AlN thin films deposited on Si (100) and glass substrates revealed a microstructure consisting of nanometer sized crystallites. Films exhibited an optical band edge at ≈ 5.8 eV and an optical transmittance of >95% in the visible region of the spectrum.
    11. 11
      Ozgit-Akgun, C.; Goldenberg, E.; Okyay, A. K.; Biyikil, N. Hollow Cathode Plasma-Assisted Atomic Layer Deposition of Crystalline AlN, GaN and AlxGa1-XN Thin Films at Low Temperatures. J. Mater. Chem. C 2014, 2, 2123– 2136,  DOI: 10.1039/C3TC32418D
      11
      Hollow cathode plasma-assisted atomic layer deposition of crystalline AlN, GaN and AlxGa1-xN thin films at low temperatures
      Ozgit-Akgun, Cagla; Goldenberg, Eda; Okyay, Ali Kemal; Biyikli, Necmi
      Journal of Materials Chemistry C: Materials for Optical and Electronic Devices (2014), 2 (12), 2123-2136CODEN: JMCCCX; ISSN:2050-7534. (Royal Society of Chemistry)
      The authors report on the use of hollow cathode plasma for low-temp. plasma-assisted at. layer deposition (PA-ALD) of cryst. AlN, GaN and AlxGa1-xN thin films with low impurity concns. Depositions were carried out at 200° using trimethylmetal precursors and NH3 or N2/H2 plasma. XPS showed 2.5-3 at. % O in AlN and 1.5-1.7 at. % O in GaN films deposited using NH3 and N2/H2 plasma, resp. No C impurities were detected within the films. Secondary ion mass spectroscopy analyses performed on the films deposited using NH3 plasma revealed O, C (both <1 at.%), and H impurities. GIXRD patterns indicated polycryst. thin films with wurtzite crystal structure. Hollow cathode PA-ALD parameters were optimized for AlN and GaN thin films using N2/H2 plasma. Trimethylmetal and N2/H2 satn. curves evidenced the self-limiting growth of AlN and GaN at 200°. AlN exhibited linear growth with a growth per cycle (GPC) of ∼1.0 Å. For GaN, the GPC decreased with the increasing no. of deposition cycles, indicating substrate-enhanced growth. The GPC calcd. from a 900-cycle GaN deposition was 0.22 Å. Ellipsometric spectra of the samples were modeled using the Cauchy dispersion function, from which the refractive indexes of 59.2 nm thick AlN and 20.1 nm thick GaN thin films are 1.94 and 2.17 at 632 nm, resp. Spectral transmission measurements of AlN, GaN and AlxGa1-xN thin films grown on double side polished sapphire substrates revealed near-ideal visible transparency with minimal absorption. Optical band edge values of the AlxGa1-xN films shifted to lower wavelengths with the increasing Al content, indicating the tunability of band edge values with the alloy compn.
    12. 12
      Bosund, M.; Sajavaara, T.; Laitinen, M.; Huhtio, T.; Putkonen, M.; Airaksinen, V. M.; Lipsanen, H. Properties of AlN Grown by Plasma Enhanced Atomic Layer Deposition. Appl. Surf. Sci. 2011, 257, 7827– 7830,  DOI: 10.1016/j.apsusc.2011.04.037
      12
      Properties of AlN grown by plasma enhanced atomic layer deposition
      Bosund, Markus; Sajavaara, Timo; Laitinen, Mikko; Huhtio, Teppo; Putkonen, Matti; Airaksinen, Veli-Matti; Lipsanen, Harri
      Applied Surface Science (2011), 257 (17), 7827-7830CODEN: ASUSEE; ISSN:0169-4332. (Elsevier B.V.)
      The influence of growth parameters on the properties of AlN films fabricated by plasma-enhanced at. layer deposition using AlEt3 and NH3 precursors was investigated. The at. concns., refractive index, mass d., crystallinity, and surface roughness were studied from the films grown in the temp. range of 100-300° with plasma discharge times between 2.5-30 s. The AlN films were shown to be H-rich having H concns. in the range of 13-27 at.% with inverse dependence on the growth temp. The C and O concns. in the films were <2.6% and 0.2%, resp. The refractive index and mass d. of the films correlated with the H concn. so that higher concns. (lower growth temps.) resulted in smaller refractive index and mass d. The film grown at 300° was found to be cryst. whereas lower growth temp. produced amorphous films.
    13. 13
      Nepal, N.; Qadri, S. B.; Hite, J. K.; Mahadik, N. A.; Mastro, M. A.; Eddy, C. R. Epitaxial Growth of {AlN} Films via Plasma-Assisted Atomic Layer Epitaxy. Appl. Phys. Lett. 2013, 103, 82110,  DOI: 10.1063/1.4818792
      13
      Epitaxial growth of AlN films via plasma-assisted atomic layer epitaxy
      Nepal, N.; Qadri, S. B.; Hite, J. K.; Mahadik, N. A.; Mastro, M. A.; Eddy, C. R., Jr.
      Applied Physics Letters (2013), 103 (8), 082110/1-082110/5CODEN: APPLAB; ISSN:0003-6951. (American Institute of Physics)
      Thin AlN layers were grown at 200-650 °C by plasma assisted at. layer epitaxy (PA-ALE) simultaneously on Si(111), sapphire (11-20), and GaN/sapphire substrates. The AlN growth on Si(111) is self-limited for trimethyaluminum (TMA) pulse of length > 0.04 s, using a 10 s purge. However, the AlN nucleation on GaN/sapphire is non-uniform and has a bimodal island size distribution for TMA pulse of ≤0.03 s. The growth rate (GR) remains almost const. for Tg between 300 and 400 °C indicating ALE mode at those temps. The GR is increased by 20% at Tg = 500 °C. Spectroscopic ellipsometry (SE) measurement shows that the ALE AlN layers grown at Tg ≤ 400 °C have no clear band edge related features, however, the theor. estd. band gap of 6.2 eV was measured for AlN grown at Tg ≥ 500 °C. X-ray diffraction measurements on 37 nm thick AlN films grown at optimized growth conditions (Tg = 500 °C, 10 s purge, 0.06 s TMA pulse) reveal that the ALE AlN on GaN/sapphire is (0002) oriented with rocking curve full width at the half max. (FWHM) of 670 arc sec. Epitaxial growth of cryst. AlN layers by PA-ALE at low temps. broadens application of the material in the technologies that require large area conformal growth at low temps. with thickness control at the at. scale. (c) 2013 American Institute of Physics.
    14. 14
      Waggoner, K. M.; Olmstead, M. M.; Power, P. P. Structural and Spectroscopic Characterization of the Compounds [Al(NMe2)3]2, [Ga(NMe2)3]2, [(Me2N)2Al{μ-N(H)1-Ad}]2 (1-Ad = 1-Adamantanyl) and [{Me(μ-NPh2)Al}2NPh(μ-C6H4)]. Polyhedron 1990, 9, 257– 263,  DOI: 10.1016/S0277-5387(00)80578-1
      14
      Structural and spectroscopic characterization of the compounds [Al(NMe2)3]2, [Ga(NMe2)3]2, [(Me2N)2Al{μ-N(H)1-Ad}]2 (1-Ad = 1-adamantanyl) and [{Me(μ-NPh2)Al}2NPh(μ-C6H4)]
      Waggoner, K. M.; Olmstead, M. M.; Power, P. P.
      Polyhedron (1990), 9 (2-3), 257-63CODEN: PLYHDE; ISSN:0277-5387.
      [Al(NMe2)3]2 (I), [Ga(NMe2)3]2 (II), [(Me2N)2Al{μ-1-AdNH}]2 (III; 1-AdNH2 = adamantanylamine) and [{Me(μ-NPh2)Al}2NPh(μ-C6H4)].0.5PhMe (IV) were prepd. and structurally and spectroscopically characterized by x-ray crystallog., 1H, 13C, 27Al, 69Ga and 71Ga NMR. A new synthesis is also provided for the previously known compd. I. The structures of I and II are the 1st reported structures of tris-dialkylamides of Al or Ga. Both possess dimeric structures in the solid with dimethylamide bridges and distorted tetrahedral geometry at the metal. The terminal NMe2 groups display significant deviation from planarity in both compds. The transamination reaction between I and 1 equiv of 1-AdNH2 affords III in high yield. IV was prepd. by treatment of AlMe3 with 2 equiv of HNPh2 in refluxing toluene and is somewhat surprising in view of the prior synthesis of Al(NPh2)3 via a similar reaction. I and II are triclinic, space group P‾1, R = 0.041 and 0.035, resp.; III and IV are monoclinic, space group P21/c, R = 0.047 and 0.066, resp.
    15. 15
      Wade, C. R.; Silvernail, C.; Banerjee, C.; Soulet, A.; McAndrew, J.; Belot, J. A. Tris(Dialkylamino)Aluminums: Syntheses, Characterization, Volatility Comparison and Atomic Layer Deposition of Alumina Thin Films. Mater. Lett. 2007, 61, 5079– 5082,  DOI: 10.1016/j.matlet.2007.04.009
      15
      Tris(dialkylamino)aluminums: Syntheses, characterization, volatility comparison and atomic layer deposition of alumina thin films
      Wade, Casey R.; Silvernail, Carter; Banerjee, Chiranjib; Soulet, Axel; McAndrew, James; Belot, John A.
      Materials Letters (2007), 61 (29), 5079-5082CODEN: MLETDJ; ISSN:0167-577X. (Elsevier B.V.)
      The syntheses and characterization of both tris(diethylamino)aluminum and tris(diisopropylamino)aluminum are presented. Characterization includes vapor pressure measurements and comparison of the 2 non-pyrophoric precursors showing them to be viable alternatives to trimethylaluminum. Tris(diisopropyl)aluminum was successful in the at. layer deposition of alumina thin films.
    16. 16
      Liu, G.; Deguns, E.; Lecordier, L.; Sundaram, G.; Becker, J. Atomic Layer Deposition of AlN with Tris(Dimethylamido)Aluminum and NH. ECS Trans. 2011, 41, 219– 225,  DOI: 10.1149/1.3633671
      16
      Atomic layer deposition of AlN with tris(dimethylamido)aluminum and NH3
      Liu, G.; Deguns, E. W.; Lecordier, L.; Sundaram, G.; Becker, J. S.
      ECS Transactions (2011), 41 (2, Atomic Layer Deposition Applications 7), 219-225CODEN: ECSTF8; ISSN:1938-5862. (Electrochemical Society)
      Atomic layer deposition of aluminum nitride on Si wafers using tris(dimethylamido)aluminum and ammonia has been investigated in the temp. range from 180 to 400°C. Satd. growth behavior not obsd. with NH3 pulsed in continuous mode has been achieved in NH3 exposure mode. Thin AlN films have been analyzed by spectroscopic ellipsometry and SIMS for optical and chem. properties, X-ray diffraction for crystallinity, and mercury probe for elec. properties. Polycryst. and high purity AlN films have been obtained at 300°C or higher. A high dielec. const. in the range of 7.4-7.7 and high breakdown field of 5.3-5.6 MV/cm with relatively low leakage current in the 10-7 to 10-8 A/cm2 range at 2MV/cm have been obtained for AlN films deposited between 300 and 400°C in NH3 exposure mode.
    17. 17
      Kim, K. H.; Gordon, R. G.; Ritenour, A.; Antoniadis, D. A. Atomic Layer Deposition of Insulating Nitride Interfacial Layers for Germanium Metal Oxide Semiconductor Field Effect Transistors with High-κ Oxide/Tungsten Nitride Gate Stacks. Appl. Phys. Lett. 2007, 90, 212104,  DOI: 10.1063/1.2741609
      17
      Atomic layer deposition of insulating nitride interfacial layers for germanium metal oxide semiconductor field effect transistors with high-κ oxide/tungsten nitride gate stacks
      Kim, Kyoung H.; Gordon, Roy G.; Ritenour, Andrew; Antoniadis, Dimitri A.
      Applied Physics Letters (2007), 90 (21), 212104/1-212104/3CODEN: APPLAB; ISSN:0003-6951. (American Institute of Physics)
      At. layer deposition (ALD) was used to deposit passivating interfacial nitride layers between Ge and high-κ oxides. High-κ oxides on Ge surfaces passivated by ultrathin (1-2 nm) ALD Hf3N4 or AlN layers exhibited well-behaved C-V characteristics with an equiv. oxide thickness as low as 0.8 nm, no significant flatband voltage shifts, and midgap d. of interface states values of 2 × 1012 cm-1 eV-1. AlN. Functional n-channel and p-channel Ge field effect transistors with nitride interlayer/high-κ oxide/metal gate stacks are demonstrated.
    18. 18
      Abdulagatov, A. I.; Ramazanov, S. M.; Dallaev, R. S.; Murliev, E. K.; Palchaev, D. K.; Rabadanov, M. K.; Abdulagatov, I. M. Atomic Layer Deposition of Aluminium Nitride Using Tris(Diethylamido)Aluminum and Hydrazine or Ammonia. Russ. Microelectron. 2018, 47, 118– 130,  DOI: 10.1134/S1063739718020026
      18
      Atomic Layer Deposition of Aluminum Nitride Using Tris(diethylamido)aluminum and Hydrazine or Ammonia
      Abdulagatov, A. I.; Ramazanov, Sh. M.; Dallaev, R. S.; Murliev, E. K.; Palchaev, D. K.; Rabadanov, M. Kh.; Abdulagatov, I. M.
      Russian Microelectronics (2018), 47 (2), 118-130CODEN: RUICE5; ISSN:1063-7397. (Pleiades Publishing, Ltd.)
      Aluminum nitride (AlNx) films were obtained by at. layer deposition (ALD) using tris(diethylamido) aluminum(III) (TDEAA) and hydrazine (N2H4) or ammonia (NH3). The quartz crystal microbalance (QCM) data showed that the surface reactions of TDEAA and N2H4 (or NH3) at temps. from 150 to 225°C were self-limiting. The rates of deposition of the nitride film at 200°C for systems with N2H4 and NH3 coincided: ∼1.1 Å/cycle. The ALD AlN films obtained at 200°C using hydrazine had higher d. (2.36 g/cm3, 72.4% of bulk d.) than those obtained with ammonia (2.22 g/cm3, 68%). The elemental anal. of the film deposited using TDEAA/N2H4 at 200°C showed the presence of carbon (∼1.4 at %), oxygen (∼3.2 at %), and hydrogen (22.6 at %) impurities. The N/Al at. concn. ratio was ∼1.3. The residual impurity content in the case of N2H4 was lower than for NH3. In general, it was confirmed that hydrazine has a more preferable surface thermochem. than ammonia.
    19. 19
      Abdulagatov, A. I.; Amashaev, R. R.; Ashurbekova, K. N.; Ashurbekova, K. N.; Rabadanov, M. K.; Abdulagatov, I. M. Atomic Layer Deposition of Aluminum Nitride and Oxynitride on Silicon Using Tris(Dimethylamido)Aluminum, Ammonia, and Water. Russ. J. Gen. Chem. 2018, 88, 1699– 1706,  DOI: 10.1134/S1070363218080236
      19
      Atomic Layer Deposition of Aluminum Nitride and Oxynitride on Silicon Using Tris(dimethylamido)aluminum, Ammonia, and Water
      Abdulagatov, A. I.; Amashaev, R. R.; Ashurbekova, Kr. N.; Ashurbekova, K. N.; Rabadanov, M. Kh.; Abdulagatov, I. M.
      Russian Journal of General Chemistry (2018), 88 (8), 1699-1706CODEN: RJGCEK; ISSN:1070-3632. (Pleiades Publishing, Ltd.)
      Thin films of aluminum nitride and oxynitride were deposited by at. layer deposition (ALD) in the temp. range from 170 to 290°C (optimal deposition temp. 200-230°C). Tris(dimethylamido) aluminum and ammonia were used as precursors for the at. layer deposition of aluminum nitride (AlN). The av. AlN film thickness per ALD cycle (deposition rate) at 200°C was ∼0.8 Å. Films were deposited on a silicon <100> substrate with a native oxide layer. The N/Al at. concn. ratio in the obtained films was ∼1.3. Aluminum oxynitride films obtained by periodical dose of water vapor in the course of at. layer deposition of AlN at 200°C. The compn. of the deposited oxynitride films was Al0.5O0.43N0.07.
    20. 20
      Gordon, R. G. Atomic Layer Deposition for Semiconductors. In Atomic Layer Deposition for Semiconductors; Hwang, C. S., Yoo, C. Y., Eds.; Springer US: New York, 2014; pp 15– 46.
      There is no corresponding record for this reference.
    21. 21
      Kim, S. B.; Jayaraman, A.; Chua, D.; Davis, L. M.; Zheng, S. L.; Zhao, X.; Lee, S.; Gordon, R. G. Obtaining a Low and Wide Atomic Layer Deposition Window (150–275 °C) for In2O3 Films Using an InIII Amidinate and H2O. Chem. - Eur. J. 2018, 24, 9525– 9529,  DOI: 10.1002/chem.201802317
      21
      Obtaining a low and wide atomic layer deposition window (150-275 °C) for In2O3 films using an InIII amidinate and H2O
      Kim, Sang Bok; Jayaraman, Ashwin; Chua, Danny; Davis, Luke M.; Zheng, Shao-Liang; Zhao, Xizhu; Lee, Sunghwan; Gordon, Roy G.
      Chemistry - A European Journal (2018), 24 (38), 9525-9529CODEN: CEUJED; ISSN:0947-6539. (Wiley-VCH Verlag GmbH & Co. KGaA)
      Indium oxide is a major component of many technol. important thin films, most notably the transparent conductor indium tin oxide (ITO). Despite being pyrophoric, homoleptic indium(III) alkyls do not allow at. layer deposition (ALD) of In2O3 using water as a co-precursor at substrate temps. below 200 °C. Several alternative indium sources have been developed, but none allows ALD at lower temps. except in the presence of oxidants such as O2 or O3, which are not compatible with some substrates or alloying processes. We have synthesized a new indium precursor, tris(N,N'-diisopropylformamidinato)indium(III), compd. 1, which allows ALD of pure, carbon-free In2O3 films using H2O as the only co-reactant, on substrates in the temp. range 150-275 °C. In contrast, replacing just the H of the anionic iPrNC(H)NiPr ligand with a Me group (affording the known tris(N,N'-diisopropylacetamidinato)indium(III), compd. 2) results in a considerably higher and narrower ALD window in the analogous reaction with H2O (225-300 °C). Kinetic studies demonstrate that a higher rate of surface reactions in both parts of the ALD cycle gives rise to this difference in the ALD windows.
    22. 22
      Rouf, P.; O’Brien, N. J.; Rönnby, K.; Samii, R.; Ivanov, I. G.; Ojamaë, L.; Pedersen, H. The Endocyclic Carbon Substituent of Guanidinate and Amidinate Precursors Controlling Atomic Layer Deposition of InN Films. J. Phys. Chem. C 2019, 123, 25691– 25700,  DOI: 10.1021/acs.jpcc.9b07005
      22
      The Endocyclic Carbon Substituent of Guanidinate and Amidinate Precursors Controlling Atomic Layer Deposition of InN Films
      Rouf, Polla; O'Brien, Nathan J.; Roennby, Karl; Samii, Rouzbeh; Ivanov, Ivan G.; Ojamaee, Lars; Pedersen, Henrik
      Journal of Physical Chemistry C (2019), 123 (42), 25691-25700CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
      Indium nitride (InN) is an interesting material for future high-frequency electronics due to its high electron mobility. The problematic deposition of InN films currently prevents full exploration of InN-based electronics. We present studies of at. layer deposition (ALD) of InN using In precursors with bidentate ligands forming In-N bonds: tris(N,N-dimethyl-N',N''-diisopropylguanidinato)indium(III), tris(N,N'-diisopropylamidinato)indium(III), and tris(N,N'-diisopropylformamidinato)indium(III). These compds. form a series were the size of the substituent on the endocyclic position decreases from -NMe2 to -Me and to -H, resp. We show that when the size of the substituent decreases, the InN films deposited have a better cryst. quality, of better optical quality, lower roughness, and an In/N ratio closer to unity. From quantum chem. calcns., we show that the smaller substituents lead to less steric repulsion and weaker bonds between the ligand and In center. We propose that these effects render a more favored surface chem. for the nitridation step in the ALD cycle, which explains the improved film properties.
    23. 23
      Gebhard, M.; Hellwig, M.; Parala, H.; Xu, K.; Winter, M.; Devi, A. Indium-Tris-Guanidinates: A Promising Class of Precursors for Water Assisted Atomic Layer Deposition of In2O3 Thin Films. Dalt. Trans. 2014, 43, 937– 940,  DOI: 10.1039/C3DT52746H
      23
      Indium-tris-guanidinates: a promising class of precursors for water assisted atomic layer deposition of In2O3 thin films
      Gebhard, M.; Hellwig, M.; Parala, H.; Xu, K.; Winter, M.; Devi, A.
      Dalton Transactions (2014), 43 (3), 937-940CODEN: DTARAF; ISSN:1477-9226. (Royal Society of Chemistry)
      Two closely related mononuclear homoleptic In-tris-guanidinate complexes were synthesized and characterized as precursors for at. layer deposition (ALD) of In2O3. In a water-assisted ALD process, high quality In2O3 thin films were fabricated for the first time using the new class of precursors as revealed by the promising ALD growth characteristics and film properties.
    24. 24
      Barry, S. T.; Gordon, P. G.; Ward, M. J.; Heikkila, M. J.; Monillas, W. H.; Yap, G. P. A.; Ritala, M.; Leskelä, M. Chemical Vapour Deposition of In2O3 Thin Films from a Tris-Guanidinate Indium Precursor. Dalt. Trans. 2011, 40, 9425– 9430,  DOI: 10.1039/c1dt10877h
      24
      Chemical vapour deposition of In2O3 thin films from a tris-guanidinate indium precursor
      Barry, Sean T.; Gordon, Peter G.; Ward, Matthew J.; Heikkila, Mikko J.; Monillas, Wesley H.; Yap, Glenn P. A.; Ritala, Mikko; Leskelae, Markku
      Dalton Transactions (2011), 40 (37), 9425-9430CODEN: DTARAF; ISSN:1477-9226. (Royal Society of Chemistry)
      A new homoleptic sublimable indium(III) guanidinate, (In[(NiPr)2CNMe2]3) (I), was synthesized from a facile high-yield procedure. Compd. I crystd. is a P‾1 space group; a = 10.5989(14) Å, b = 11.0030(15) Å, c = 16.273(2) Å, α = 91.190(2)°, β = 96.561(2)°, γ = 115.555(2)°; R = 3.50%. Thermogravimetric anal. showed I to produce elemental indium as a residual mass. Thermolysis in a sealed NMR tube showed carbodiimide and protonated dimethylamine by 1H NMR. Chem. vapor deposition expts. at > 275°C with air as the reactant gas showed I to readily deposit cubic indium oxide with good transparency.
    25. 25
      Brazeau, A. L.; DiLabio, G. A.; Kreisel, K. A.; Monillas, W.; Yap, G. P. A.; Barry, S. T. Theoretical and Experimental Investigations of Ligand Exchange in Guanidinate Ligand Systems for Group 13 Metals. J. Chem. Soc. Dalt. Trans. 2007, (30), 3297– 3304,  DOI: 10.1039/b706044k
      There is no corresponding record for this reference.
    26. 26
      Kenney, A. P.; Yap, G. P. A.; Richeson, D. S.; Barry, S. T. The Insertion of Carbodiimides into Al and Ga Amido Linkages. Guanidinates and Mixed Amido Guanidinates of Aluminum and Gallium. Inorg. Chem. 2005, 44, 2926– 2933,  DOI: 10.1021/ic048433g
      26
      The Insertion of Carbodiimides into Al and Ga Amido Linkages. Guanidinates and Mixed Amido Guanidinates of Aluminum and Gallium
      Kenney, Amanda P.; Yap, Glenn P. A.; Richeson, Darrin S.; Barry, Sean T.
      Inorganic Chemistry (2005), 44 (8), 2926-2933CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)
      The insertion of carbodiimides into existing metal-heteroatom bonds is an important preparative route for the synthesis of useful ligand systems such as amidinates and guanidinates. The authors' interest lies in multiple insertions at one metal center and the mechanisms of insertion and rearrangement. The authors synthesized and characterized [Me2NC(NiPr)2]nM(NMe2)3-n (n = 1, 2, 3; M = Al, Ga). The authors have studied the mechanism of synthesis and discovered a ligand transfer step that is important for the formation of the final products.
    27. 27
      Brazeau, A. L.; Wang, Z.; Rowley, C. N.; Barry, S. T. Synthesis and Thermolysis of Aluminum Amidinates: A Ligand-Exchange Route for New Mixed-Ligand Systems. Inorg. Chem. 2006, 45, 2276– 2281,  DOI: 10.1021/ic051856d
      27
      Synthesis and Thermolysis of Aluminum Amidinates: A Ligand-Exchange Route for New Mixed-Ligand Systems
      Brazeau, Allison L.; Wang, Zhaohui; Rowley, Chris N.; Barry, Sean T.
      Inorganic Chemistry (2006), 45 (5), 2276-2281CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)
      A novel ligand-exchange route for the synthesis of amidinate-contg. compds. of aluminum is explored. Aluminum amidinates RC(NiPr)2AlR12 (4, 5; R = Me, R1 = Et; R = Et, R1 = Me) were prepd. starting from the corresponding carbodiimides, RLi and R12AlCl; guanidinate [Me2NC(NiPr)2]2AlH (6) was prepd. by redistribution reaction of the tris-guanidinate with AlH3·NMe2Et. The thermal reactivities of these compds. and their parent homoleptic compds. [MeC(NiPr)2]3Al (1), [Me2NC(NiPr)2]3Al (2), and [EtC(NiPr)2]3Al (3) were explored and analyzed with respect to their utility as potential at.-layer-deposition precursors for aluminum-contg. films. The major mechanism of thermal decompn. is found to be carbodiimide deinsertion to form aluminum alkyls or amides. Because of their thermal characteristics, both compds. 3 and 5 hold promise for use as precursors.
    28. 28
      Leman, J. T.; Barron, A. R. Synthesis of 1,3-Diphenyltriazenide Complexes of Aluminium, Gallium and Indium: Crystal Structure of Tris(1,3-Diphenyltriazenido)Aluminium(III). Polyhedron 1989, 8, 1909– 1912,  DOI: 10.1016/S0277-5387(00)86413-X
      29
      Synthesis of 1,3-diphenyltriazenide complexes of aluminum, gallium and indium: crystal structure of tris(1,3-diphenyltriazenido)aluminum(III)
      Leman, John T.; Barron, Andrew R.; Ziller, Joseph W.; Kren, Robert M.
      Polyhedron (1989), 8 (15), 1909-12CODEN: PLYHDE; ISSN:0277-5387.
      The reaction of AlMe3 with 1,3-diphenyltriazene [Hdpt] in toluene gave Al(dpt)3, even when AlMe3 was in large excess. Monomeric Al(dpt)3 crystd. in space group C2/c with a 20.587(3), b 16.005(3), c 13.236(3) Å and β 119.172(12)°, Z 4, R 0.067 and Rw 0.083. The Al(III) is coordinated by 3 chelating triazenido ligands to give a trigonally distorted octahedral geometry. The Ga and In analogs are also reported.
    29. 29
      Leman, J. T.; Braddock-Wilking, J.; Coolong, A. J.; Barron, A. R. 1,3-Diaryltriazenido Compounds of Aluminum. Inorg. Chem. 1993, 32, 4324– 4336,  DOI: 10.1021/ic00072a028
      30
      1,3-Diaryltriazenido compounds of aluminum
      Leman, John T.; Braddock-Wilking, Janet; Coolong, Alanna J.; Barron, Andrew R.
      Inorganic Chemistry (1993), 32 (20), 4324-36CODEN: INOCAJ; ISSN:0020-1669.
      Reaction of AlH(iBu)2 with 1 and 2 equiv of 1,3-diphenyltriazene, PhN:NNHPh, yields [cyclic] Al(iBu)2[N(Ph)NN(Ph)] (1) and [cyclic] Al(iBu)[N(Ph)NN(Ph)]2 (2), resp. Compd. 2 undergoes ligand exchange in soln. to give an equimolar mixt. of 1 and [cyclic] Al[N(Ph)NN(Ph)]3. The reaction of Al(tBu)3 with PhN:NNHPh gives [cyclic] Al(tBu)2[N(Ph)NN(Ph)] (3) as the only product. Addn. of 1 equiv of PhN:NNHPh to AlMe2(BHT)(OEt2) (BHT-H = 2,6-di-tert-butyl-4-methylphenol) allows for the isolation of [cyclic] AlMe(BHT)[N(Ph)NN(Ph)] (4); however, a higher equiv of PhN:NNHPh yields only [cyclic] Al[N(Ph)NN(Ph)]3. The bis(triazenide) complex [cyclic] Al(BHT)[N(Ph)NN(Ph)]2 (5) is isolated from the reaction of PhN:NNHPh with AlH2(BHT)(NMe3), while [cyclic] Al(BHT)2[N(Ph)NN(Ph)] (6) is formed from the reaction of PhN:NNHPh with AlMe(BHT)2. Although the reaction of 1 with H2salen [N,N'-ethylenebis(salicylideneamine)] does not yield [cyclic] Al[N(Ph)NN(Ph)](salen) (8) but rather yields Al(iBu)(salen) (7), compd. 8 may be isolated from interaction of PhN:NNHPh with AlMe(salen). The reaction between AlMe3 and 3 equiv of substituted 1,3-diaryltriazenes, ArN:NNHAr, yields the 6-coordinate aluminum tris(1,3-diaryltriazenido) compds., [cyclic] Al[N(Ar)NN(Ar)]3 [Ar = 2-MeC6H4 (9), 4-MeC6H4 (10), 4-MeOC6H4 (11), 4-FC6H4 (12), 4-ClC6H4 (13), 4-BrC6H4 (14), C6F5 (15)]. The unsym. diaryltriazene complex [cyclic] Al[N(Ph)NN(4-MeOC6H4)]3 (16) adopts a trans-meridional conformation. The spectroscopic characterization of the tris(triazenido) complexes is discussed with respect to the nature of the aryl substituents. The X-ray structures of 1, 6, AlMe(salen), 9, 11, 13, (C6F5)N:NN(H)(C6F5), and (2-MeC6H4)N:NN(H)(2-MeC6H4).(2-MeC6H4)NH2 have been detd.
    30. 30
      O’Brien, N. J.; Rouf, P.; Samii, R.; Rönnby, K.; Buttera, S. C.; Hsu, C.-W.; Ivanov, I. G.; Kessler, V.; Ojamäe, L.; Pedersen, H. In-Situ Activation of an Indium(III) Triazenide Precursor for Epitaxial Indium Nitride by Atomic Layer Deposition. Chem. Mater. 2020, 32, 4481– 4489,  DOI: 10.1021/acs.chemmater.9b05171
      31
      In Situ Activation of an Indium(III) Triazenide Precursor for Epitaxial Growth of Indium Nitride by Atomic Layer Deposition
      O'Brien, Nathan J.; Rouf, Polla; Samii, Rouzbeh; Roennby, Karl; Buttera, Sydney C.; Hsu, Chih-Wei; Ivanov, Ivan G.; Kessler, Vadim; Ojamaee, Lars; Pedersen, Henrik
      Chemistry of Materials (2020), 32 (11), 4481-4489CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
      Indium nitride (InN) is characterized by its high electron mobility, making it a ground-breaking material for high frequency electronics. The difficulty of depositing high-quality cryst. InN currently impedes its broad implementation in electronic devices. A new highly volatile In(III) triazenide precursor is reported, and its ability to deposit high-quality epitaxial hexagonal InN by at. layer deposition (ALD) is demonstrated. The new In(III) precursor, the 1st example of a homoleptic triazenide used in a vapor deposition process, was easily synthesized and purified by sublimation. TGA showed single step volatilization with an onset temp. of 145° and negligible residual mass. Two temp. intervals with self-limiting growth were obsd. when depositing InN films. In the high-temp. interval, the precursor underwent a gas-phase thermal decompn. inside the ALD reaction chamber to produce a more reactive In(III) compd. while retaining self-limiting growth behavior. D. functional theory calcns. revealed a unique 2-step decompn. process, which liberates 3 mols. of each propene and N2 to give a smaller tricoordinated In(III) species. Stoichiometric InN films with low levels of impurities were grown epitaxially on 4H-SiC. The InN films deposited at 325° had a sheet resistivity of 920 Ω/sq. This new triazenide precursor enables ALD of InN for semiconductor applications and provides a new family of M-N bonded precursors for future deposition processes. Crystallog. data are given.
    31. 31
      Rouf, P.; Samii, R.; Rönnby, K.; Bakhit, B.; Buttera, S. C.; Martinovic, I.; Ojamäe, L.; Hsu, C.-W.; Palisaitis, J.; Kessler, V.; Pedersen, H.; O’Brien, N. J. Hexacoordinated Gallium(III) Triazenide Precursor for Epitaxial Gallium Nitride by Atomic Layer Deposition. ChemRxiv 2020,  DOI: 10.26434/chemrxiv.13190636.v1 .
      There is no corresponding record for this reference.
    32. 32
      Bottaro, J. C.; Penwell, P. E.; Schmitt, R. J. Expedient Synthesis of T-Butyl Azide. Synth. Commun. 1997, 27, 1465– 1467,  DOI: 10.1080/00397919708006078
      33
      Expedient synthesis of tert-butyl azide
      Bottaro, Jeffrey C.; Penwell, Paul E.; Schmitt, Robert J.
      Synthetic Communications (1997), 27 (8), 1465-1467CODEN: SYNCAV; ISSN:0039-7911. (Dekker)
      A simple, economical synthesis of bulk (1-10,000 mol) amts. of Me3CN3 is described, using only Me3COH, H2O, NaN3 and H2SO4.
    33. 33
      Swetha, M.; Ramana, P. V.; Shirodkar, S. G. Simple and Efficient Method for the Synthesis of Azides in Water-THF Solvent System. Org. Prep. Proced. Int. 2011, 43, 348– 353,  DOI: 10.1080/00304948.2011.594002
      34
      Simple and efficient method for the synthesis of azides in water-THF solvent system
      Swetha, M.; Ramana, P. Venkata; Shirodkar, S. G.
      Organic Preparations and Procedures International (2011), 43 (4), 348-353CODEN: OPPIAK; ISSN:0030-4948. (Taylor & Francis Ltd.)
      The synthesis of azides under mild reaction conditions using a simple work-up was reported. Treatment of alkyl halides, mesylates, triflates, acetates, and tosylates with NaN3 in water-THF (95:5) at reflux yielded the corresponding alkyl azides. Addnl., arom. and aliph. acid chlorides were converted into acyl azides.
    34. 34
      Mayo, D. H.; Peng, Y.; Zavalij, P.; Bowen, K. H.; Eichhorn, B. W. Aluminium(III) Amidinates Formed from Reactions of “AlCl” with Lithium Amidinates. Acta Crystallogr., Sect. C: Cryst. Struct. Commun. 2013, 69, 1120– 1123,  DOI: 10.1107/S0108270113023135
      35
      Aluminium(III) amidinates formed from reactions of AlCl with lithium amidinates
      Mayo, Dennis H.; Peng, Yang; Zavalij, Peter; Bowen, Kit H.; Eichhorn, Bryan W.
      Acta Crystallographica, Section C: Crystal Structure Communications (2013), 69 (10), 1120-1123CODEN: ACSCEE; ISSN:0108-2701. (International Union of Crystallography)
      The disproportionation of AlCl(THF)n (THF is tetrahydrofuran) in the presence of lithium amidinate species gives aluminum(III) amidinate complexes with partial or full chloride substitution. Three aluminum amidinate complexes formed during the reaction between aluminum monochloride and lithium amidinates are presented. The homoleptic complex tris(N,N'-diisopropylbenzimidamido)aluminum(III), [Al(C13H19N2)3] or Al{PhC[N(i-Pr)]2}3, (I), crystallizes from the same soln. as the heteroleptic complex chloridobis(N,N'-diisopropylbenzimidamido)aluminum(III), [Al(C13H19N2)2Cl] or Al{PhC[N(i-Pr)]2}2Cl, (II). Both have two crystallog. independent mols. per asym. unit (Z' = 2) and (I) shows disorder in four of its N(i-Pr) groups. Changing the ligand substituent to the bulkier cyclohexyl allows the isolation of the partial THF solvate chloridobis(N,N'-dicyclohexylbenzimidamido)aluminum(III) THF 0.675-solvate, [Al(C19H27N2)2Cl]·0.675C4H8O or Al[PhC(NCy)2]2Cl·0.675THF, (III). Despite having a twofold rotation axis running through its Al and Cl atoms, (III) has a similar mol. structure to that of (II).
    35. 35
      Springer Jr, C. S.; Sievers, R. E. Intramolecular Isomerization of Octahedral Complexes by Mechanisms Not Involving Bond Rupture. Inorg. Chem. 1967, 6, 852– 854,  DOI: 10.1021/ic50050a049
      There is no corresponding record for this reference.
    36. 36
      Rodger, A.; Johnson, B. F. Which Is More Likely: The Ray-Dutt Twist or the Bailar Twist?. Inorg. Chem. 1988, 27, 3061– 3062,  DOI: 10.1021/ic00291a001
      37
      Which is more likely: the Ray-Dutt twist or the Bailar twist?
      Rodger, Alison; Johnson, Brian F. G.
      Inorganic Chemistry (1988), 27 (18), 3061-2CODEN: INOCAJ; ISSN:0020-1669.
      A recently developed model for detg. the relative stabilities of MLn systems is applied to the transition states of the non-bond breaking rearrangement mechanisms of tris chelate metal complexes. It is concluded that a complex with chelate bite much smaller than the distance between ligating atoms in the reactant proceeds via a Bailar twist mechanism, and that the Ray Dutt twist is favored under the opposite circumstances.
    37. 37
      Bryant, R. G. The NMR Time Scale. J. Chem. Educ. 1983, 60, 933– 935,  DOI: 10.1021/ed060p933
      38
      The NMR time scale
      Bryant, Robert G.
      Journal of Chemical Education (1983), 60 (11), 933-5CODEN: JCEDA8; ISSN:0021-9584.
      Ambiguity in the NMR time-scale is discussed which can be extd. from different aspects of the spectrum. These include the relaxation rates assocd. with the lines, scalar coupling patterns, and resonance frequencies or chem. shifts.
    38. 38
      Kunte, G. V.; Shivashankar, S. A.; Umarji, A. M. Thermogravimetric Evaluation of the Suitability of Precursors for MOCVD. Meas. Sci. Technol. 2008, 19, 025704,  DOI: 10.1088/0957-0233/19/2/025704
      39
      Thermogravimetric evaluation of the suitability of precursors for MOCVD
      Kunte, G. V.; Shivashankar, S. A.; Umarji, A. M.
      Measurement Science and Technology (2008), 19 (2), 025704/1-025704/7CODEN: MSTCEP; ISSN:0957-0233. (Institute of Physics Publishing)
      A method based on the Langmuir equation for the estn. of vapor pressure and enthalpy of sublimation of subliming compds. is described. The variable temp. thermogravimetric/differential thermogravimetric (TG/DTG) curve of benzoic acid is used to arrive at the instrument parameters. Employing these parameters, the vapor pressure-temp. curves are derived for salicylic acid and camphor from their TG/DTG curves. The values match well with vapor pressure data in the literature, obtained by effusion methods. By employing the Clausius-Clapeyron equation, the enthalpy of sublimation could be calcd. Extending the method further, two precursors for metal-org. chem. vapor deposition (MOCVD) of titanium oxide, bis-iso-Pr bis tert-Bu 2-oxobutanoato titanium, Ti(OiPr)2(tbob)2, and bis-oxo-bis-tert-Bu 2-oxobutanoato titanium, [TiO(tbob)2]2, have been evaluated. The complex Ti(OiPr)2(tbob)2 is found to be a more suitable precursor. This approach can be helpful in quickly screening for the suitability of a compd. as a CVD precursor.
    39. 39
      Colominas, C.; Lau, K. H.; Hildenbrand, D. L.; Crouch-Baker, S.; Sanjurjo, A. Vapor Pressures of the Copper and Yttrium β-Diketonate MOCVD Precursors. J. Chem. Eng. Data 2001, 46, 446– 450,  DOI: 10.1021/je0003445
      40
      Vapor Pressures of the Copper and Yttrium β-Diketonate MOCVD Precursors
      Colominas, Carles; Lau, Kai H.; Hildenbrand, Donald L.; Crouch-Baker, Steven; Sanjurjo, Angel
      Journal of Chemical and Engineering Data (2001), 46 (2), 446-450CODEN: JCEAAX; ISSN:0021-9568. (American Chemical Society)
      The vapor pressures and vapor mol. wts. of the copper and yttrium β-diketonate MOCVD precursors Cu(C11H19O2)2(c) and Y(C11H19O2)3(c) were measured by a torsion-effusion/mass-loss method in the ranges (346 to 375) K and (361 to 387) K, resp. The mol. wt. data indicate that the satd. vapors of both precursors are highly monomeric. Vapor pressures, estd. to be accurate within 5%, are presented in equation form for reliable extrapolation to higher temps. The results are compared with other detns. in the literature.
    40. 40
      Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Petersson, G. A.; Nakatsuji, H.; Li, X.; Caricato, M.; Marenich, A. V.; Bloino, J.; Janesko, B. G.; Gomperts, R.; Mennucci, B.; Hratchian, H. P.; Ortiz, J. V.; Izmaylov, A. F.; Sonnenberg, J. L.; Williams-Young, D.; Ding, F.; Lipparini, F.; Egidi, F.; Goings, J.; Peng, B.; Petrone, A.; Henderson, T.; Ranasinghe, D.; Zakrzewski, V. G.; Gao, J.; Rega, N.; Zheng, G.; Liang, W.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Vreven, T.; Throssell, K.; Montgomery, J. A., Jr.; Peralta, J. E.; Ogliaro, F.; Bearpark, M.; Heyd, J. J.; Brothers, E. N.; Kudin, K. N.; Staroverov, V. N.; Kobayashi, R.; Normand, J.; Raghavachari, K.; Rendell, A.; Burant, J. C.; Iyengar, S. S.; Tomasi, J.; Cossi, M.; Millam, J. M.; Klene, M.; Adamo, C.; Cammi, R.; Ochterski, J. W.; Martin, R. L.; Morokuma, K.; Farkas, O.; Foresman, J. B.; Fox, D. J. Gaussian 16, revision B.01; Gaussian, Inc.: Wallingford CT, 2016.
      There is no corresponding record for this reference.
    41. 41
      Hanson-Heine, M. W. D.; George, M. W.; Besley, N. A. Calculating Excited State Properties Using Kohn-Sham Density Functional Theory. J. Chem. Phys. 2013, 138, 064101,  DOI: 10.1063/1.4789813
      42
      Calculating excited state properties using Kohn-Sham density functional theory
      Hanson-Heine, Magnus W. D.; George, Michael W.; Besley, Nicholas A.
      Journal of Chemical Physics (2013), 138 (6), 064101/1-064101/8CODEN: JCPSA6; ISSN:0021-9606. (American Institute of Physics)
      The accuracy of excited states calcd. with Kohn-Sham d. functional theory using the max. overlap method has been assessed for the calcn. of adiabatic excitation energies, excited state structures, and excited state harmonic and anharmonic vibrational frequencies for open-shell singlet excited states. The computed Kohn-Sham adiabatic excitation energies are improved significantly by post SCF spin-purifn., but remain too low compared with expt. with a larger error than time-dependent d. functional theory. Excited state structures and vibrational frequencies are also improved by spin-purifn. The structures show a comparable accuracy to time-dependent d. functional theory, while the harmonic vibrational frequencies are found to be more accurate for the majority of vibrational modes. The computed harmonic vibrational frequencies are also further improved by perturbative anharmonic corrections, suggesting a good description of the potential energy surface. Overall, excited state Kohn-Sham d. functional theory is shown to provide an efficient method for the calcn. of excited state structures and vibrational frequencies in open-shell singlet systems and provides a promising technique that can be applied to study large systems. (c) 2013 American Institute of Physics.
    42. 42
      Lecklider, T. Evaluation Engineering: Maintaining a Healthy Rhythm , 2011. https://www.evaluationengineering.com/home/article/13005576/maintaining-a-healthy-rhythm.
      There is no corresponding record for this reference.
    43. 43
      Grimme, S.; Antony, J.; Ehrlich, S.; Krieg, H. A Consistent and Accurate Ab Initio Parametrization of Density Functional Dispersion Correction (DFT-D) for the 94 Elements H-Pu. J. Chem. Phys. 2010, 132, 154104,  DOI: 10.1063/1.3382344
      44
      A consistent and accurate ab initio parametrization of density functional dispersion correction (DFT-D) for the 94 elements H-Pu
      Grimme, Stefan; Antony, Jens; Ehrlich, Stephan; Krieg, Helge
      Journal of Chemical Physics (2010), 132 (15), 154104/1-154104/19CODEN: JCPSA6; ISSN:0021-9606. (American Institute of Physics)
      The method of dispersion correction as an add-on to std. Kohn-Sham d. functional theory (DFT-D) has been refined regarding higher accuracy, broader range of applicability, and less empiricism. The main new ingredients are atom-pairwise specific dispersion coeffs. and cutoff radii that are both computed from first principles. The coeffs. for new eighth-order dispersion terms are computed using established recursion relations. System (geometry) dependent information is used for the first time in a DFT-D type approach by employing the new concept of fractional coordination nos. (CN). They are used to interpolate between dispersion coeffs. of atoms in different chem. environments. The method only requires adjustment of two global parameters for each d. functional, is asymptotically exact for a gas of weakly interacting neutral atoms, and easily allows the computation of at. forces. Three-body nonadditivity terms are considered. The method has been assessed on std. benchmark sets for inter- and intramol. noncovalent interactions with a particular emphasis on a consistent description of light and heavy element systems. The mean abs. deviations for the S22 benchmark set of noncovalent interactions for 11 std. d. functionals decrease by 15%-40% compared to the previous (already accurate) DFT-D version. Spectacular improvements are found for a tripeptide-folding model and all tested metallic systems. The rectification of the long-range behavior and the use of more accurate C6 coeffs. also lead to a much better description of large (infinite) systems as shown for graphene sheets and the adsorption of benzene on an Ag(111) surface. For graphene it is found that the inclusion of three-body terms substantially (by about 10%) weakens the interlayer binding. We propose the revised DFT-D method as a general tool for the computation of the dispersion energy in mols. and solids of any kind with DFT and related (low-cost) electronic structure methods for large systems. (c) 2010 American Institute of Physics.
    44. 44
      Weigend, F.; Ahlrichs, R. Balanced Basis Sets of Split Valence, Triple Zeta Valence and Quadruple Zeta Valence Quality for H to Rn: Design and Assessment of Accuracy. Phys. Chem. Chem. Phys. 2005, 7, 3297– 3305,  DOI: 10.1039/b508541a
      45
      Balanced basis sets of split valence, triple zeta valence and quadruple zeta valence quality for H to Rn: Design and assessment of accuracy
      Weigend, Florian; Ahlrichs, Reinhart
      Physical Chemistry Chemical Physics (2005), 7 (18), 3297-3305CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)
      Gaussian basis sets of quadruple zeta valence quality for Rb-Rn are presented, as well as bases of split valence and triple zeta valence quality for H-Rn. The latter were obtained by (partly) modifying bases developed previously. A large set of more than 300 mols. representing (nearly) all elements-except lanthanides-in their common oxidn. states was used to assess the quality of the bases all across the periodic table. Quantities investigated were atomization energies, dipole moments and structure parameters for Hartree-Fock, d. functional theory and correlated methods, for which we had chosen Moller-Plesset perturbation theory as an example. Finally recommendations are given which type of basis set is used best for a certain level of theory and a desired quality of results.
    45. 45
      Metz, B.; Stoll, H.; Dolg, M. Small-Core Multiconfiguration-Dirac-Hartree-Fock-Adjusted Pseudopotentials for Post-d Main Group Elements: Application to PhB and PbO. J. Chem. Phys. 2000, 113, 2563– 2569,  DOI: 10.1063/1.1305880
      46
      Small-core multiconfiguration-Dirac-Hartree-Fock-adjusted pseudopotentials for post-d main group elements: Application to PbH and PbO
      Metz, Bernhard; Stoll, Hermann; Dolg, Michael
      Journal of Chemical Physics (2000), 113 (7), 2563-2569CODEN: JCPSA6; ISSN:0021-9606. (American Institute of Physics)
      Relativistic pseudopotentials (PPs) of the energy-consistent variety have been generated for the post-d group 13-15 elements, by adjustment to multiconfiguration Dirac-Hartree-Fock data based on the Dirac-Coulomb-Breit Hamiltonian. The outer-core (n-1)spd shells are explicitly treated together with the nsp valence shell, with these PPs, and the implications of the small-core choice are discussed by comparison to a corresponding large-core PP, in the case of Pb. Results from valence ab initio one- and two-component calcns. using both PPs are presented for the fine-structure splitting of the ns2np2 ground-state configuration of the Pb atom, and for spectroscopic consts. of PbH (X 2Π1/2, 2Π3/2) and PbO (X 1Σ+). In addn., a combination of small-core and large-core PPs has been explored in spin-free-state shifted calcns. for the above mols.

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