Insights into the Structure of Dot@Rod and Dot@Octapod CdSe@CdS HeterostructuresClick to copy article linkArticle link copied!
- Anna Corrias
- Erika Conca
- Giannantonio Cibin
- Gavin Mountjoy
- Diego Gianolio
- Francesco De Donato
- Liberato Manna
- Maria Francesca Casula
Abstract
CdSe@CdS dot@rods with diameter around 6 nm and length of either 20, 27, or 30 nm and dot@octapods with pod diameters of ∼15 nm and lengths of ∼50 nm were investigated by X-ray absorption spectroscopy. These heterostructures are prepared by seed-mediated routes, where the structure, composition, and morphology of the CdSe nanocrystals used as a seed play key roles in directing the growth of the second semiconducting domain. The local structural environment of all the elements in the CdSe@CdS heterostructures was investigated at the Cd, S, and Se K-edges by taking advantage of the selectivity of X-ray absorption spectroscopy, and was compared to pure reference compounds. We found that the structural features of dot@rods are independent of the size of the rods. These structures can be described as made of a CdSe dot and a CdS rod, both in the wurtzite phase with a high crystallinity of both the core and the rod. This result supports the effectiveness of high temperature colloidal synthesis in promoting the formation of core@shell nanocrystals with very low defectivity. On the other hand, data on the CdSe@CdS with octapod morphology suggest the occurrence of a core composed of a CdSe cubic sphalerite phase with eight pods made of CdS wurtzite phase. Our findings are compared to current models proposed for the design of functional heterostructures with controlled nanoarchitecture.
1 Introduction
Figure 1
Figure 1. Schematic representation of the model proposed for the seeded growth of anisotropic chalcogenide heterostructures: CdSe@CdS rods (a) and octapods (b).
2 Experimental Section
Reference Materials
Synthesis of the CdSe@CdS Anisotropic Nanocrystals
Sample Characterization
X-ray Absorption Spectroscopy Measurements and Data Analysis
sample | EXAFS sample | investigated edges | features |
---|---|---|---|
Rod 1 | toluene suspension | Cd K-edge (T) S K-edge (TEY) Se K-edge (F) | dot size 4.9 nm rod length 21.5 ± 2.6 nm rod diameter 6.0 ± 0.6 nm |
Rod 2 | toluene suspension | Cd K-edge (T) S K-edge (TEY) Se K-edge (F) | dot size 4.9 nm rod length 27.7 ± 8.7 nm rod diameter 5.6 ± 0.6 nm |
Rod 3 | toluene suspension | Cd K-edge (T) S K-edge (TEY) Se K-edge (F) | dot size 4.9 nm rod length 30.1 ± 3.9 nm rod diameter 6.0 ± 0.6 nm |
Octa | toluene suspension | Cd K-edge (T) S K-edge (TEY) Se K-edge (F) Cu K-edge (F,T) | dot size 15 nm arm length 50.0 ± 2.2 nm arm width 14.9 ± 1.8 nm |
CdS | commercial powder | Cd K-edge (T) S K-edge (F) | wurtzite polymorph |
CdSe | commercial powder | Cd K-edge (T) Se K-edge (T) | wurtzite polymorph |
CuCl | commercial powder | Cu K-edge (T) | sphalerite polymorph |
The EXAFS edges investigated in the detection mode (T = transmission; TEY = total electron yield; F = fluorescence) are also given.
3 Results and Discussion
3.1 X-ray Diffraction and Transmission Electron Microscopy
Figure 2
Figure 2. Transmission electron microscopy images (A) and X-ray diffraction patterns (B) of CdSe@CdS (d) Rod 1, (c) Rod 2, (b) Rod 3, and (a) Octa samples. Scale bar for all TEM images is 20 nm.
3.2 X-ray Absorption Spectroscopy
Cd K-Edge
Cd K-edge | ||
---|---|---|
R (Å) | N (Atoms) | |
Bulk Wurtzite CdS | ||
S | 2.526 | 3 |
S | 2.532 | 1 |
Cd | 4.119 | 6 |
Cd | 4.136 | 6 |
Bulk Wurtzite CdSe | ||
Se | 2.628 | 3 |
Se | 2.640 | 1 |
Cd | 4.295 | 6 |
Cd | 4.299 | 6 |
Bulk Sphalerite CdSe | ||
Se | 2.631 | 4 |
Cd | 4.297 | 12 |
Figure 3
Figure 3. Experimental Cd K-edge k2χ(k) (A) and corresponding FTs (B) for the CdSe (a) and CdS (b) reference compounds, and for the Rod 1 (c) and Octa (d) samples.
Cd K-edge | ||||||
---|---|---|---|---|---|---|
Rod 1 | Octa | |||||
R (Å) | N (Atoms) | 2σ2 (Å2) | R (Å) | N (Atoms) | 2σ2 (Å2) | |
S | 2.504 ± 0.007 | 3 | 0.0060 ± 0.0006 | 2.517 ± 0.006 | 3 | 0.0043 ± 0.0005 |
S | 2.509 ± 0.007 | 1 | 0.0060 ± 0.0006 | 2.522 ± 0.006 | 1 | 0.0043 ± 0.0005 |
Cd | 4.08 ± 0.06 | 6 | 0.05 ± 0.01 | 4.14 ± 0.04 | 6 | 0.032 ± 0.008 |
Cd | 4.09 ± 0.06 | 6 | 0.05 ± 0.01 | 4.16 ± 0.04 | 6 | 0.032 ± 0.008 |
E0 = 0.8 ± 0.5 | E0 = 2.4 ± 0.5 | |||||
S0 = 0.831 | S0 = 0.831 | |||||
R-factor = 0.04054 | R-factor = 0.0242 |
Se K-edge | ||||||
---|---|---|---|---|---|---|
sphalerite structure | ||||||
Octa | ||||||
R (Å) | N (Atoms) | 2σ2 (Å2) | ||||
Cd | 2.601 ± 0.005 | 4 | 0.0041 ± 0.0004 | |||
Se | 4.33 ± 0.05 | 12 | 0.023 ± 0.009 | |||
E0 = 0.8 ± 0.4 | ||||||
S0 = 0.76 | ||||||
R-factor = 0.04201 |
wurtzite structure | ||||||
---|---|---|---|---|---|---|
Rod 1 | Octa | |||||
R (Å) | N (Atoms) | 2σ2 (Å2) | R (Å) | N (Atoms) | 2σ2 (Å2) | |
Cd | 2. 600 ± 0.005 | 3 | 0.0046 ± 0.0004 | 2.597 ± 0.004 | 3 | 0.0042 ± 0.0004 |
Cd | 2.612 ± 0.005 | 1 | 0.0046 ± 0.0004 | 2.610 ± 0.004 | 1 | 0.0042 ± 0.0004 |
Se | 4.32 ± 0.07 | 6 | 0.03 ± 0.01 | 4.32 ± 0.05 | 6 | 0.023 ± 0.009 |
Se | 4.32 ± 0.07 | 6 | 0.03 ± 0.01 | 4.33 ± 0.05 | 6 | 0.023 ± 0.009 |
E0 = 0.8 ± 0.4 | E0 = 0.7 ± 0.4 | |||||
S0 = 0.76 | S0 = 0.76 | |||||
R-factor =0.03761 | R-factor =0.04507 |
S K-edge | ||||||
---|---|---|---|---|---|---|
Rod 1 | Octa | |||||
R (Å) | N (Atoms) | 2σ2 (Å2) | R (Å) | N (Atoms) | 2σ2 (Å2) | |
Cd | 2.516 ± 0.009 | 3 | 0.0056 ± 0.0009 | 2.516 ± 0.007 | 3 | 0.0053 ± 0.0007 |
Cd | 2.522 ± 0.009 | 1 | 0.0056 ± 0.0009 | 2.522 ± 0.007 | 1 | 0.0053 ± 0.0007 |
S | 4.06 ± 0.03 | 6 | 0.022 ± 0.005 | 4.06 ± 0.02 | 6 | 0.018 ± 0.003 |
S | 4.08 ± 0.03 | 6 | 0.022 ± 0.005 | 4.07 ± 0.02 | 6 | 0.018 ± 0.003 |
E0 = 3.3 ± 0.6 | E0 = 2.6 ± 0.5 | |||||
S0 = 0.821 | S0 = 0.821 | |||||
R-factor =0.06633 | R-factor =0.04146 |
Se K-Edge
Figure 4
Figure 4. Experimental Se K-edge k2χ(k) (A) and corresponding FTs (B) for the CdSe (a) reference compound, and for the Rod 1 (b) and Octa (c) samples.
S K-edge
Figure 5
Figure 5. Experimental S K-edge k2χ(k) (A) and corresponding FTs (B) for the CdS (a) reference compound, and for the Rod 1 (b) and Octa (c) samples.
Cu K-Edge
Figure 6
Figure 6. Experimental k2χ(k) (A) and corresponding FTs (B) at the at the Cu K-edge for the CuCl (a) reference compound and for the Octa (b) sample.
4 Conclusions
Supporting Information
Comparison of the data at the Cd, Se and S K-edge for the Rod 1 and Rod 2 samples; XANES spectra at the at the Cd, Se, and S K-edge; differences at the Cd K-edge between the EXAFS of Rod 1, Octa, and CdSe with respect to CdS; Fit results at the Cd, Se and S K-edge for the Rod 1 and Octa samples; EXAFS spectrum at the Cu K edge for the Octa sample. The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.jpcc.5b04593.
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.
Acknowledgment
This work has been supported by the Regione Autonoma della Sardegna under Project CRP18013-2009 L.R. 7/2007. We also thank Diamond Light Source for access to beamline B18 (Proposal SP9759) that contributed to the results presented here. Dr. Andrea Falqui and Mee-Rahn Kim are gratefully acknowledged for their support at early stages of this project.
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This article references 32 other publications.
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- 19Carta, D.; Casula, M. F.; Mountjoy, G.; Corrias, A. Formation and Cation Distribution in Supported Manganese Ferrite Nanoparticles: an X-Ray Absorption Study Phys. Chem. Chem. Phys. 2008, 10, 3108– 3117 DOI: 10.1039/b800359aGoogle Scholar19Formation and cation distribution in supported manganese ferrite nanoparticles: an X-ray absorption studyCarta, Daniela; Casula, Maria Francesca; Mountjoy, Gavin; Corrias, AnnaPhysical Chemistry Chemical Physics (2008), 10 (21), 3108-3117CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)Extended X-ray absorption fine structure (EXAFS) and X-ray absorption near-edge structure (XANES) techniques at both Fe and Mn K-edges were used to investigate the formation of MnFe2O4 nanoparticles embedded in a silica aerogel matrix as a function of calcination temp. (at 450, 750 and 900 °C). Up to 450 °C, two sepd. highly-disordered phases of iron and manganese are present. With increasing the temp. (to 750 and 900 °C), the structure of aerogel nanoparticles becomes progressively similar to that of the spinel structure MnFe2O4 (jacobsite). Quant. detn. of cations distribution in the spinel structure shows that aerogels calcined at 750 and 900 °C have a degree of inversion i = 0.20. A pure jacobsite sample synthesized by co-pptn. and used as a ref. compd. shows a much higher degree of inversion (i = 0.70). The different distribution of iron and manganese cations in the octahedral and tetrahedral sites in pure jacobsite and in the aerogels can be ascribed to partial oxidn. of Mn2+ to Mn3+ in pure jacobsite, confirmed by XANES anal., probably due to the synthesis conditions.
- 20Carta, D.; Loche, D.; Mountjoy, G.; Navarra, G.; Corrias, A. NiFe2O4 Nanoparticles Dispersed in an Aerogel Silica Matrix: An X-Ray Absorption Study J. Phys. Chem. C 2008, 112, 15623– 15630 DOI: 10.1021/jp803982kGoogle ScholarThere is no corresponding record for this reference.
- 21Carta, D.; Casula, M. F.; Falqui, A.; Loche, D.; Mountjoy, G.; Sangregorio, C.; Corrias, A. A Structural and Magnetic Investigation of the Inversion Degree in Ferrite Nanocrystals MFe2O4 (M = Mn, Co, Ni) J. Phys. Chem. C 2009, 113, 8606– 8615 DOI: 10.1021/jp901077cGoogle Scholar21A Structural and Magnetic Investigation of the Inversion Degree in Ferrite Nanocrystals MFe2O4 (M = Mn, Co, Ni)Carta, D.; Casula, M. F.; Falqui, A.; Loche, D.; Mountjoy, G.; Sangregorio, C.; Corrias, A.Journal of Physical Chemistry C (2009), 113 (20), 8606-8615CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)The structural and magnetic properties of nanocryst. manganese, cobalt, and nickel spinel ferrites dispersed in a highly porous SiO2 aerogel matrix were studied. X-ray diffraction and high-resoln. TEM indicate that single cryst. ferrite nanoparticles are well dispersed in the amorphous matrix. The cation distribution between the octahedral and tetrahedral sites of the spinel structure was studied by x-ray absorption spectroscopy. The anal. of both the x-ray absorption near edge structure and the extended X-ray absorption fine structure indicates that the degree of inversion of the spinel structure increases in the series Mn, Co, and Ni spinel, in accordance with the values commonly found in the corresponding bulk spinels. In particular, fitting of the EXAFS data indicates that the degree of inversion in nanosized ferrites is 0.20 for MnFe2O4, 0.68 for CoFe2O4, and 1.00 for NiFe2O4. Magnetic characterization further supports these findings.
- 22Carta, D.; Corrias, A.; Falqui, A.; Brescia, R.; Fantechi, E.; Pineider, F.; Sangregorio, C. EDS, HRTEM/STEM, and X-Ray Absorption Spectroscopy Studies of Co-Substituted Maghemite Nanoparticles J. Phys. Chem. C 2013, 117, 9496– 9506 DOI: 10.1021/jp401706cGoogle ScholarThere is no corresponding record for this reference.
- 23Carta, D.; Marras, C.; Loche, D.; Mountjoy, G.; Ahmed, S. I.; Corrias, A. An X-Ray Absorption Spectroscopy Study of the Inversion Degree in Zinc Ferrite Nanocrystals Dispersed on a Highly Porous Silica Aerogel Matrix J. Chem. Phys. 2013, 138, 054702 DOI: 10.1063/1.4789479Google Scholar23An x-ray absorption spectroscopy study of the inversion degree in zinc ferrite nanocrystals dispersed on a highly porous silica aerogel matrixCarta, D.; Marras, C.; Loche, D.; Mountjoy, G.; Ahmed, S. I.; Corrias, A.Journal of Chemical Physics (2013), 138 (5), 054702/1-054702/9CODEN: JCPSA6; ISSN:0021-9606. (American Institute of Physics)The structural properties of ZnFe2O4 nanoparticles with spinel structure dispersed in a highly porous SiO2 aerogel matrix were compared with a bulk Zn ferrite sample. The details of the cation distribution between the octahedral (B) and tetrahedral (A) sites of the spinel structure were detd. using x-ray absorption spectroscopy. The anal. of both the x-ray absorption near edge structure and the extended x-ray absorption fine structure indicates that the degree of inversion of the Zn ferrite spinel structures varies with particle size. In particular, in the bulk microcryst. sample, Zn2+ ions are at the tetrahedral sites and trivalent Fe3+ ions occupy octahedral sites (normal spinel). When particle size decreases, Zn2+ ions are transferred to octahedral sites and the degree of inversion increases as the nanoparticle size decreases. This is the 1st time that a variation of the degree of inversion with particle size is obsd. in ferrite nanoparticles grown within an aerogel matrix. (c) 2013 American Institute of Physics.
- 24Rockenberger, J.; Troger, L.; Rogach, A. L.; Tischer, M.; Grundmann, M.; Eychmuller, A.; Weller, H. J. Chem. Phys. 1998, 108, 7807– 7815 DOI: 10.1063/1.476216Google ScholarThere is no corresponding record for this reference.
- 25Marcus, M. A.; Flood, W.; Stiegerwald, M.; Brus, L.; Bawendi, M. Structure of Capped Cadmium Selenide Clusters by EXAFS J. Phys. Chem. 1991, 95, 1572– 1576 DOI: 10.1021/j100157a012Google ScholarThere is no corresponding record for this reference.
- 26Kim, M. R.; Miszta, K.; Povia, M.; Brescia, R.; Christodoulou, S.; Prato, M.; Marras, S.; Manna, L. The Influence of Chloride Ions on the Synthesis of Colloidal Branched CdSe/CdS Nanocrystal by Seeded Growth ACS Nano 2012, 6, 11088– 11096 DOI: 10.1021/nn3048846Google ScholarThere is no corresponding record for this reference.
- 27Conca, E.; Aresti, M.; Saba, M.; Casula, M. F.; Quochi, F.; Mula, G.; Loche, D.; Kim, M. R.; Manna, L.; Corrias, A. Pt Decoration of CdSe@CdS Octapods: Effects on Charge Separation Nanoscale 2014, 6, 2238– 2243 DOI: 10.1039/c3nr05567aGoogle ScholarThere is no corresponding record for this reference.
- 28Klug, H. P.; Alexander, L. E. X-Ray Diffraction Procedures; Wiley: New York, 1974.Google ScholarThere is no corresponding record for this reference.
- 29Dent, A. J.; Cibin, G.; Ramos, S.; Smith, A. D.; Scott, S. M.; Varandas, L.; Pearson, M. R.; Krumpa, N. A.; Jones, C. P.; Robbins, P. E. J. Phys. Conf. Ser. 2009, 190, 012039 DOI: 10.1088/1742-6596/190/1/012039Google ScholarThere is no corresponding record for this reference.
- 30Ravel, B.; Newville, M. ATHENA, ARTEMIS, HEPHAESTUS: Data Analysis for X-Ray Absorption Spectroscopy Using IFEFFIT J. Synchrotron Radiat. 2005, 12, 537– 541 DOI: 10.1107/S0909049505012719Google Scholar30ATHENA, ARTEMIS, HEPHAESTUS: data analysis for x-ray absorption spectroscopy using IFEFFITRavel, B.; Newville, M.Journal of Synchrotron Radiation (2005), 12 (4), 537-541CODEN: JSYRES; ISSN:0909-0495. (Blackwell Publishing Ltd.)A software package for the anal. of x-ray absorption spectroscopy (XAS) data is presented. This package is based on the IFEFFIT library of numerical and XAS algorithms and is written in the Perl programming language using the Perl/Tk graphics toolkit. The programs described here are: (i) ATHENA, a program for XAS data processing, (ii) ARTEMIS, a program for EXAFS data anal. using theor. stds. from FEFF and (iii) HEPHAESTUS, a collection of beamline utilities based on tables of at. absorption data. These programs enable high-quality data anal. that is accessible to novices while still powerful enough to meet the demands of an expert practitioner. The programs run on all major computer platforms and are freely available under the terms of a free software license.
- 31Deka, S.; Miszta, K.; Dorfs, D.; Genovese, A.; Bertoni, G.; Manna, L. Octapod-Shaped Colloidal Nanocrystals of Cadmium Chalcogenides via ″One-Pot″ Cation Exchange and Seeded Growth Nano Lett. 2010, 10, 3770– 3776 DOI: 10.1021/nl102539aGoogle Scholar31Octapod-Shaped Colloidal Nanocrystals of Cadmium Chalcogenides via "One-Pot" Cation Exchange and Seeded GrowthDeka, Sasanka; Miszta, Karol; Dorfs, Dirk; Genovese, Alessandro; Bertoni, Giovanni; Manna, LiberatoNano Letters (2010), 10 (9), 3770-3776CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)The growth behavior of cadmium chalcogenides (CdE = CdS, CdSe, and CdTe) on sphalerite Cu2-xSe nanocrystals (size range 10-15 nm) is studied. Due to the capability of Cu2-xSe to undergo a fast and quant. cation exchange reaction in the presence of excessive Cd2+ ions, no Cu2-xSe/CdE heterostructures are obtained and instead branched CdSe/CdE nanocrystals are built which consist of a sphalerite CdSe core and wurtzite CdE arms. While CdTe growth yields multiarmed structures with overall tetrahedral symmetry, CdS and CdSe arm growth leads to octapod-shaped nanocrystals. These results differ significantly from literature findings about the growth of CdE on sphalerite CdSe particles, which until now had always yielded tetrapod-shaped nanocrystals.
- 32Greegor, R. B.; Lytle, F. W. Morphology of Supported Metal Clusters: Determination by EXAFS and Chemisorption J. Catal. 1980, 63, 476– 486 DOI: 10.1016/0021-9517(80)90102-5Google Scholar32Morphology of supported metal clusters: determination by EXAFS and chemisorptionGreegor, R. B.; Lytle, F. W.Journal of Catalysis (1980), 63 (2), 476-86CODEN: JCTLA5; ISSN:0021-9517.When small metal clusters are examd. by the extended x-ray absorption fi ne structure (EXAFS) technique the apparent av. coordination no. is smaller than that obsd. in the bulk metal because of the high proportion of surface atoms. This effect id dependent on the size and shape of the metal cluster. Geometrical shape models were derived for spheres, cubes, and disks, which give the EXAFS av. coordination no. for 1st, 2nd, and 3rd coordination spheres as a function of cluster size. Dispersion models (via chemisorption measurements) are also presented for different cluster shapes and sizes. Electron microscopy is used to support the analyses where possible.
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Abstract
Figure 1
Figure 1. Schematic representation of the model proposed for the seeded growth of anisotropic chalcogenide heterostructures: CdSe@CdS rods (a) and octapods (b).
Figure 2
Figure 2. Transmission electron microscopy images (A) and X-ray diffraction patterns (B) of CdSe@CdS (d) Rod 1, (c) Rod 2, (b) Rod 3, and (a) Octa samples. Scale bar for all TEM images is 20 nm.
Figure 3
Figure 3. Experimental Cd K-edge k2χ(k) (A) and corresponding FTs (B) for the CdSe (a) and CdS (b) reference compounds, and for the Rod 1 (c) and Octa (d) samples.
Figure 4
Figure 4. Experimental Se K-edge k2χ(k) (A) and corresponding FTs (B) for the CdSe (a) reference compound, and for the Rod 1 (b) and Octa (c) samples.
Figure 5
Figure 5. Experimental S K-edge k2χ(k) (A) and corresponding FTs (B) for the CdS (a) reference compound, and for the Rod 1 (b) and Octa (c) samples.
Figure 6
Figure 6. Experimental k2χ(k) (A) and corresponding FTs (B) at the at the Cu K-edge for the CuCl (a) reference compound and for the Octa (b) sample.
References
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- 2Li, H.; Kanaras, A. G.; Manna, L. Colloidal Branched Semiconductor Nanocrystals: State of the Art and Perspectives Acc. Chem. Res. 2013, 46, 1387– 1396 DOI: 10.1021/ar30024092Colloidal Branched Semiconductor Nanocrystals: State of the Art and PerspectivesLi, Hongbo; Kanaras, Antonios G.; Manna, LiberatoAccounts of Chemical Research (2013), 46 (7), 1387-1396CODEN: ACHRE4; ISSN:0001-4842. (American Chemical Society)A review. Colloidal inorg. nanocrystals are versatile nanoscale building blocks. Advances in their synthesis have yielded nanocrystals with various morphologies including spheres, polyhedra, rods, disks, sheets, wires, and a wide range of branched shapes. Recent developments in chem. methods gave colloidal nanocrystals made of sections of different inorg. materials connected together. Many research groups are studying these nanocrystals' structural and photophys. properties exptl. and theor., and many have examd. their prospects for com. applications. Branched nanocrystals, in particular, are gaining attention, in part for their potential applications in solar cells or electronic devices. In this Account, the authors review recent developments in synthesis and controlled assembly of colloidal branched nanocrystals. Synthesis of branched nanocrystals builds on previous work with spherical nanocrystals and nanorods, but a unique factor is the need to control the branching event. Multiple arms can branch from a nucleus, or secondary branches can form from a growing arm. Branching can be governed by mechanisms including twinning, crystal splitting, polymorphism, oriented attachment, and others. One of the most relevant parameters is the choice of appropriate surfactant mols., which can bind selectively to certain crystal facets or can even promote specific crystallog. phases during nucleation and growth. Also, seeded growth approaches recently have allowed great progress in the synthesis of nanocrystals with elaborate shapes. In this approach, nanocrystals with a specified chem. compn., size, shape, cryst. habit, and phase act as seeds on which multiple branches of a 2nd material nucleate and grow. These approaches yield nanostructures with improved homogeneity in distribution of branch length and cross section. Ion exchange reactions allow further manipulation of branched nanocrystals by transforming crystals of one material into crystals with the same size, shape, and anion sublattice but with a new cation. Combining seeded growth with ion exchange provides a method for greatly expanding the library of branched nanocrystals. Assembly of morphol. complex nanocrystals is evolving in parallel to developments in chem. synthesis. While researchers have made many advances in the past decade in controlled assembly of nanocrystals with simple polyhedral shapes, modeling and exptl. realization of ordered superstructures of branched nanocrystals are still in their infancy. In the only case of ordered superstructure reported so far, the assembly proceeds by steps in a hierarchical fashion, in analogy to several examples of assembly found in nature. Meanwhile, disordered assemblies of branched nanocrystals are also interesting and may find applications in various fields.
- 3Kovalenko, M. V.; Manna, L.; Cabot, A.; Hens, Z.; Talapin, D. V.; Kagan, C. R.; Klimov, V. I.; Rogach, A. L.; Reiss, P.; Milliron, D. J. Prospects of Nanoscience with Nanocrystals ACS Nano 2015, 9, 1012– 1057 DOI: 10.1021/nn506223h3Prospects of Nanoscience with NanocrystalsKovalenko, Maksym V.; Manna, Liberato; Cabot, Andreu; Hens, Zeger; Talapin, Dmitri V.; Kagan, Cherie R.; Klimov, Victor I.; Rogach, Andrey L.; Reiss, Peter; Milliron, Delia J.; Guyot-Sionnnest, Philippe; Konstantatos, Gerasimos; Parak, Wolfgang J.; Hyeon, Taeghwan; Korgel, Brian A.; Murray, Christopher B.; Heiss, WolfgangACS Nano (2015), 9 (2), 1012-1057CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)A review. Colloidal nanocrystals (NCs, i.e., cryst. nanoparticles) have become an important class of materials with great potential for applications ranging from medicine to electronic and optoelectronic devices. Today's strong research focus on NCs was prompted by the tremendous progress in their synthesis. Impressively narrow size distributions of just a few percent, rational shape-engineering, compositional modulation, electronic doping, and tailored surface chemistries are now feasible for a broad range of inorg. compds. The performance of inorg. NC-based photovoltaic and light-emitting devices has become competitive to other state-of-the-art materials. Semiconductor NCs hold unique promise for near- and mid-IR technologies, where very few semiconductor materials are available. On a purely fundamental side, new insights into NC growth, chem. transformations, and self-organization can be gained from rapidly progressing in situ characterization and direct imaging techniques. New phenomena are constantly being discovered in the photophysics of NCs and in the electronic properties of NC solids. In this Nano Focus, the authors review the state of the art in research on colloidal NCs focusing on the most recent works published in the last 2 years.
- 4Saruyama, M.; So, Y.-G.; Kimoto, K.; Taguchi, S.; Kanemitsu, Y.; Teranishi, T. Spontaneous Formation of Wurzite-CdS/Zinc Blende-CdTe Heterodimers through a Partial Anion Exchange Reaction J. Am. Chem. Soc. 2011, 133, 17598– 17601 DOI: 10.1021/ja20782244Spontaneous Formation of Wurzite-CdS/Zinc Blende-CdTe Heterodimers through a Partial Anion Exchange ReactionSaruyama, Masaki; So, Yeong-Gi; Kimoto, Koji; Taguchi, Seiji; Kanemitsu, Yoshihiko; Teranishi, ToshiharuJournal of the American Chemical Society (2011), 133 (44), 17598-17601CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)Ion exchange of ionic semiconductor nanoparticles (NPs) is a facile method for the synthesis of type-II semiconductor heterostructured NPs with staggered alignment of band edges for photoelec. applications. Through consideration of the crystallog. orientation and strain at the heterointerface, well-designed heterostructures can be constructed through ion exchange reactions. Here the authors report the selective synthesis of anisotropically phase-segregated cadmium sulfide (CdS)/ cadmium telluride (CdTe) heterodimers via a novel anion exchange reaction of CdS NPs with an org. telluride precursor. The wurtzite-CdS/zinc blende-CdTe heterodimers resulted from spontaneous phase segregation induced by the differences in the crystal structures of the two phases, accompanying a centrosymmetry breaking of the spherical CdS NPs. The CdS/CdTe heterodimers exhibited photoinduced spatial charge sepn. because of their staggered band-edge alignment.
- 5Zhang, D.; Wong, A. B.; Yu, Y.; Brittman, S.; Sun, J.; Fu, A.; Beberwyck, B.; Alivisatos, A. P.; Yang, P. Phase Selective Cation-Exchange Chemistry in Sulfide Nanowire Systems J. Am. Chem. Soc. 2014, 136, 17430– 17433 DOI: 10.1021/ja511010qThere is no corresponding record for this reference.
- 6Carbone, L.; Nobile, C.; DeGiorgi, M.; DellaSala, F.; Morello, G.; Pompa, P.; Hytch, M.; Snoeck, E.; Fiore, A.; Franchini, I. R. Synthesis and Micrometer-Scale Assembly of Colloidal CdSe/CdS Nanorods Prepared by a Seeded Growth Approach Nano Lett. 2007, 7 (10) 2942– 2950 DOI: 10.1021/nl07176616Synthesis and Micrometer-Scale Assembly of Colloidal CdSe/CdS Nanorods Prepared by a Seeded Growth ApproachCarbone, Luigi; Nobile, Concetta; De Giorgi, Milena; Della Sala, Fabio; Morello, Giovanni; Pompa, Pierpaolo; Hytch, Martin; Snoeck, Etienne; Fiore, Angela; Franchini, Isabella R.; Nadasan, Monica; Silvestre, Albert F.; Chiodo, Letizia; Kudera, Stefan; Cingolani, Roberto; Krahne, Roman; Manna, LiberatoNano Letters (2007), 7 (10), 2942-2950CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)Key limitations of the colloidal semiconductor nanorods that have been reported so far are a significant distribution of lengths and diams. as well as the presence of irregular shapes produced by the current synthetic routes and, finally, the poor ability to fabricate large areas of oriented nanorod arrays. Here, we report a seeded-growth approach to the synthesis of asym. core-shell CdSe/CdS nanorods with regular shapes and narrow distributions of rod diams. and lengths, the latter being easily tunable up to 150 nm. These rods are highly fluorescent and show linearly polarized emission, whereby the emission energy depends mainly on the core diam. We demonstrate their lateral alignment as well as their vertical self-alignment on substrates up to areas of several square micrometers.
- 7Talapin, D. V.; Nelson, J. H.; Shevchenko, E. V.; Aloni, S.; Sadtler, B.; Alivisatos, A. P. Seeded Growth of Highly Luminescent CdSe/CdS Nanoheterostructures with Rod and Tetrapod Morphologies Nano Lett. 2007, 7, 2951– 2959 DOI: 10.1021/nl072003g7Seeded Growth of Highly Luminescent CdSe/CdS Nanoheterostructures with Rod and Tetrapod MorphologiesTalapin, Dmitri V.; Nelson, James H.; Shevchenko, Elena V.; Aloni, Shaul; Sadtler, Bryce; Alivisatos, A. PaulNano Letters (2007), 7 (10), 2951-2959CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)Seeded growth of nanocrystals offers a convenient way to design nanoheterostructures with complex shapes and morphologies by changing the cryst. structure of the seed. By using CdSe nanocrystals with wurtzite and Zn blende structure as seeds for growth of CdS nanorods, the authors synthesized CdSe/CdS heterostructure nanorods and nanotetrapods, resp. Both of these structures showed excellent luminescent properties, combining high photoluminescence efficiency (∼80 and ∼50% for nanorods and nanotetrapods, correspondingly), giant extinction coeffs. (∼2 × 107 and ∼1.5 × 108 M-1 cm-1 at 350 nm for nanorods and nanotetrapods, correspondingly), and efficient energy transfer from the CdS arms into the emitting CdSe core.
- 8Luo, Y.; Wang, L. W. Electronic Structures of CdSe/CdS Core Shell Nanorods ACS Nano 2010, 4, 91– 98 DOI: 10.1021/nn9010279There is no corresponding record for this reference.
- 9Brescia, R.; Miszta, K.; Dorfs, D.; Manna, L.; Bertoni, G. Birth and Growth of Octapod-Shaped Colloidal Nanocrystals Studied by Electron Tomography J. Phys. Chem. C 2011, 115, 20128– 20133 DOI: 10.1021/jp206253w9Birth and Growth of Octapod-Shaped Colloidal Nanocrystals Studied by Electron TomographyBrescia, Rosaria; Miszta, Karol; Dorfs, Dirk; Manna, Liberato; Bertoni, GiovanniJournal of Physical Chemistry C (2011), 115 (41), 20128-20133CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)The growth of octapod-shaped colloidal nanocrystals is analyzed in detail by electron tomog. The 3-dimensional shape of the starting cubic berzelianite Cu2-xSe seeds is studied, and their evolution into the final structure composed of a sphalerite CdSe core and eight wurtzite CdS pods is followed. The 3-dimensional reconstruction shows markedly different shapes of the pods, four of them having sharp tips and four flat ends. Also, the combination of the tomog. results with high-resoln. and energy-filtered TEM analyses leads to a precise identification of the structure and compn. of the final particles. An interpretation of the different shapes of the pod ends is given based on the intrinsic anisotropy of both the sphalerite CdSe and the wurtzite CdS crystal structures and the different reactivity of their facets in the growth environment.
- 10Corrado, C.; Jiang, Y.; Oba, F.; Kozina, M.; Bridges, F.; Zhang, J. Z. Synthesis, Optical and Structural Properties of Cu-doped ZnS Nanomaterials J. Phys. Chem. A 2009, 113, 3830– 3839 DOI: 10.1021/jp809666tThere is no corresponding record for this reference.
- 11Sakamoto, M.; Inoue, K.; Saruyama, M.; So, Y.-G.; Kimoto, K.; Okano, M.; Kanemitsu, Y.; Teranishi, T. Investigation on Photo-induced Charge Separation in CdS/CdTe Nanopencils Chem. Sci. 2014, 5, 3831– 3835 DOI: 10.1039/C4SC00635F11Investigation on photo-induced charge separation in CdS/CdTe nanopencilsSakamoto, Masanori; Inoue, Koki; Saruyama, Masaki; So, Yeong-Gi; Kimoto, Koji; Okano, Makoto; Kanemitsu, Yoshihiko; Teranishi, ToshiharuChemical Science (2014), 5 (10), 3831-3835CODEN: CSHCCN; ISSN:2041-6520. (Royal Society of Chemistry)CdS/CdTe nanopencils were synthesized via anion exchange. The effect of the geometry on the carrier dynamics was investigated. Transient absorption measurements indicated that these factors did not affect the charge sepn. rate in CdS/CdTe nanopencils. The results provide important insight for designing heterostructured nanocrystals with efficient charge sepn. and integrated structures.
- 12Koninbsberger, D. C.; Prins, R. X-Ray Absorption: Principles, Applications, Techniques of EXAFS, SEXAFS and XANES Eds; Wiley: New York, 1987.There is no corresponding record for this reference.
- 13Bordiga, S.; Groppo, E.; Agostini, G.; Van Bokhoven, J. A.; Lamberti, C. Reactivity of Surface Species in Heterogeneous Catalysts Probed by In Situ X-Ray Absorption Techniques Chem. Rev. 2013, 113, 1736– 1850 DOI: 10.1021/cr200089813Reactivity of Surface Species in Heterogeneous Catalysts Probed by In Situ X-ray Absorption TechniquesBordiga, Silvia; Groppo, Elena; Agostini, Giovanni; van Bokhoven, Jeroen A.; Lamberti, CarloChemical Reviews (Washington, DC, United States) (2013), 113 (3), 1736-1850CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)A review; reactivity of surface species in heterogeneous catalysts probed by in situ x-ray absorption techniques is discussed.
- 14Mostafa, S.; Behafarid, F.; Croy, J. R.; Ono, L. K.; Li, L.; Yang, J. C.; Frenkel, A. I.; Cuenya, B. R. Shape-Dependent Catalytic Properties of Pt Nanoparticles J. Am. Chem. Soc. 2010, 132, 15714– 15719 DOI: 10.1021/ja106679z14Shape-Dependent Catalytic Properties of Pt NanoparticlesMostafa, Simon; Behafarid, Farzad; Croy, Jason R.; Ono, Luis K.; Li, Long; Yang, Judith C.; Frenkel, Anatoly I.; Cuenya, Beatriz RoldanJournal of the American Chemical Society (2010), 132 (44), 15714-15719CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)Tailoring the chem. reactivity of nanomaterials at the at. level is one of the most important challenges in catalysis research. In order to achieve this elusive goal, fundamental understanding of the geometric and electronic structure of these complex systems at the at. level must be obtained. This article reports the influence of the nanoparticle shape on the reactivity of Pt nanocatalysts supported on γ-Al2O3. Nanoparticles with analogous av. size distributions (∼ 0.8-1 nm), but with different shapes, synthesized by inverse micelle encapsulation, were found to display distinct reactivities for the oxidn. of 2-propanol. A correlation between the no. of undercoordinated atoms at the nanoparticle surface and the onset temp. for 2-propanol oxidn. was obsd., demonstrating that catalytic properties can be controlled through shape-selective synthesis.
- 15Mandal, S.; Mandale, A. B.; Sastry, M. Keggin Ion-Mediated Synthesis of Aqueous Phase-pure Au@Pd and Au@Pt Core-Shell Nanoparticles J. Mater. Chem. 2004, 14, 2868– 2871 DOI: 10.1039/b409033kThere is no corresponding record for this reference.
- 16Carta, D.; Mountjoy, G.; Gass, M.; Navarra, G.; Casula, M. F.; Corrias, A. Structural Characterisation Study of FeCo Alloy Nanoparticles in a Highly Porous Aerogel Silica Matrix J. Chem. Phys. 2007, 127, 204705 DOI: 10.1063/1.2799995There is no corresponding record for this reference.
- 17Padovani, S.; Sada, C.; Mazzoldi, P.; Brunetti, B.; Borgia, I.; Sgamellotti, A.; Giulivi, A.; D’Acapito, F.; Battaglin, G. Copper in Glazes of Renaissance Luster Pottery: Nanoparticles, Ions, and Local Environment J. Appl. Phys. 2003, 93, 10058– 10063 DOI: 10.1063/1.157196517Copper in glazes of Renaissance luster pottery: nanoparticles, ions, and local environmentPadovani, S.; Sada, C.; Mazzoldi, P.; Brunetti, B.; Borgia, I.; Sgamellotti, A.; Giulivi, A.; D'Acapito, F.; Battaglin, G.Journal of Applied Physics (2003), 93 (12), 10058-10063CODEN: JAPIAU; ISSN:0021-8979. (American Institute of Physics)Following the recent finding that luster decorations in glazes of historical pottery consist of copper and silver nanoparticles dispersed in a glassy medium, the glaze in-depth compn. and distribution of copper nanoparticles, copper ions, and their local environment have been studied in original samples of gold and red luster. The study has been fully carried out by nondestructive techniques such as Rutherford backscattering spectrometry, UV and visible spectroscopy, x-ray fluorescence, and extended x-ray absorption fine structure (EXAFS). Elemental analyses indicate that gold decorations are characterized by silver and copper, while red decorations by copper only. The color is detd. mainly by metal nanoparticles. Specifically, silver nanoparticles det. the gold color, while the red color is detd. by nanoparticles of copper. EXAFS measurements, carried out at the Cu K edge, indicate that in both gold and red luster copper is mostly the oxidized form (Cu+ and Cu2+) with a large prevalence of Cu+. States and local environment of copper ions are similar to those found in copper-alkali ion-exchanged silicate glass samples. This strongly supports the view that luster formation is mediated by a copper- and silver-alkali ion exchange as a first step, followed by nucleation and growth of metal nanoparticles.
- 18Carta, D.; Mountjoy, G.; Navarra, G.; Casula, M. F.; Loche, D.; Marras, S.; Corrias, A. X-Ray Absorption Investigation of the Formation of Cobalt Ferrite Nanoparticles in an Aerogel Silica Matrix J. Phys. Chem. C 2007, 111, 6308– 6317 DOI: 10.1021/jp0708805There is no corresponding record for this reference.
- 19Carta, D.; Casula, M. F.; Mountjoy, G.; Corrias, A. Formation and Cation Distribution in Supported Manganese Ferrite Nanoparticles: an X-Ray Absorption Study Phys. Chem. Chem. Phys. 2008, 10, 3108– 3117 DOI: 10.1039/b800359a19Formation and cation distribution in supported manganese ferrite nanoparticles: an X-ray absorption studyCarta, Daniela; Casula, Maria Francesca; Mountjoy, Gavin; Corrias, AnnaPhysical Chemistry Chemical Physics (2008), 10 (21), 3108-3117CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)Extended X-ray absorption fine structure (EXAFS) and X-ray absorption near-edge structure (XANES) techniques at both Fe and Mn K-edges were used to investigate the formation of MnFe2O4 nanoparticles embedded in a silica aerogel matrix as a function of calcination temp. (at 450, 750 and 900 °C). Up to 450 °C, two sepd. highly-disordered phases of iron and manganese are present. With increasing the temp. (to 750 and 900 °C), the structure of aerogel nanoparticles becomes progressively similar to that of the spinel structure MnFe2O4 (jacobsite). Quant. detn. of cations distribution in the spinel structure shows that aerogels calcined at 750 and 900 °C have a degree of inversion i = 0.20. A pure jacobsite sample synthesized by co-pptn. and used as a ref. compd. shows a much higher degree of inversion (i = 0.70). The different distribution of iron and manganese cations in the octahedral and tetrahedral sites in pure jacobsite and in the aerogels can be ascribed to partial oxidn. of Mn2+ to Mn3+ in pure jacobsite, confirmed by XANES anal., probably due to the synthesis conditions.
- 20Carta, D.; Loche, D.; Mountjoy, G.; Navarra, G.; Corrias, A. NiFe2O4 Nanoparticles Dispersed in an Aerogel Silica Matrix: An X-Ray Absorption Study J. Phys. Chem. C 2008, 112, 15623– 15630 DOI: 10.1021/jp803982kThere is no corresponding record for this reference.
- 21Carta, D.; Casula, M. F.; Falqui, A.; Loche, D.; Mountjoy, G.; Sangregorio, C.; Corrias, A. A Structural and Magnetic Investigation of the Inversion Degree in Ferrite Nanocrystals MFe2O4 (M = Mn, Co, Ni) J. Phys. Chem. C 2009, 113, 8606– 8615 DOI: 10.1021/jp901077c21A Structural and Magnetic Investigation of the Inversion Degree in Ferrite Nanocrystals MFe2O4 (M = Mn, Co, Ni)Carta, D.; Casula, M. F.; Falqui, A.; Loche, D.; Mountjoy, G.; Sangregorio, C.; Corrias, A.Journal of Physical Chemistry C (2009), 113 (20), 8606-8615CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)The structural and magnetic properties of nanocryst. manganese, cobalt, and nickel spinel ferrites dispersed in a highly porous SiO2 aerogel matrix were studied. X-ray diffraction and high-resoln. TEM indicate that single cryst. ferrite nanoparticles are well dispersed in the amorphous matrix. The cation distribution between the octahedral and tetrahedral sites of the spinel structure was studied by x-ray absorption spectroscopy. The anal. of both the x-ray absorption near edge structure and the extended X-ray absorption fine structure indicates that the degree of inversion of the spinel structure increases in the series Mn, Co, and Ni spinel, in accordance with the values commonly found in the corresponding bulk spinels. In particular, fitting of the EXAFS data indicates that the degree of inversion in nanosized ferrites is 0.20 for MnFe2O4, 0.68 for CoFe2O4, and 1.00 for NiFe2O4. Magnetic characterization further supports these findings.
- 22Carta, D.; Corrias, A.; Falqui, A.; Brescia, R.; Fantechi, E.; Pineider, F.; Sangregorio, C. EDS, HRTEM/STEM, and X-Ray Absorption Spectroscopy Studies of Co-Substituted Maghemite Nanoparticles J. Phys. Chem. C 2013, 117, 9496– 9506 DOI: 10.1021/jp401706cThere is no corresponding record for this reference.
- 23Carta, D.; Marras, C.; Loche, D.; Mountjoy, G.; Ahmed, S. I.; Corrias, A. An X-Ray Absorption Spectroscopy Study of the Inversion Degree in Zinc Ferrite Nanocrystals Dispersed on a Highly Porous Silica Aerogel Matrix J. Chem. Phys. 2013, 138, 054702 DOI: 10.1063/1.478947923An x-ray absorption spectroscopy study of the inversion degree in zinc ferrite nanocrystals dispersed on a highly porous silica aerogel matrixCarta, D.; Marras, C.; Loche, D.; Mountjoy, G.; Ahmed, S. I.; Corrias, A.Journal of Chemical Physics (2013), 138 (5), 054702/1-054702/9CODEN: JCPSA6; ISSN:0021-9606. (American Institute of Physics)The structural properties of ZnFe2O4 nanoparticles with spinel structure dispersed in a highly porous SiO2 aerogel matrix were compared with a bulk Zn ferrite sample. The details of the cation distribution between the octahedral (B) and tetrahedral (A) sites of the spinel structure were detd. using x-ray absorption spectroscopy. The anal. of both the x-ray absorption near edge structure and the extended x-ray absorption fine structure indicates that the degree of inversion of the Zn ferrite spinel structures varies with particle size. In particular, in the bulk microcryst. sample, Zn2+ ions are at the tetrahedral sites and trivalent Fe3+ ions occupy octahedral sites (normal spinel). When particle size decreases, Zn2+ ions are transferred to octahedral sites and the degree of inversion increases as the nanoparticle size decreases. This is the 1st time that a variation of the degree of inversion with particle size is obsd. in ferrite nanoparticles grown within an aerogel matrix. (c) 2013 American Institute of Physics.
- 24Rockenberger, J.; Troger, L.; Rogach, A. L.; Tischer, M.; Grundmann, M.; Eychmuller, A.; Weller, H. J. Chem. Phys. 1998, 108, 7807– 7815 DOI: 10.1063/1.476216There is no corresponding record for this reference.
- 25Marcus, M. A.; Flood, W.; Stiegerwald, M.; Brus, L.; Bawendi, M. Structure of Capped Cadmium Selenide Clusters by EXAFS J. Phys. Chem. 1991, 95, 1572– 1576 DOI: 10.1021/j100157a012There is no corresponding record for this reference.
- 26Kim, M. R.; Miszta, K.; Povia, M.; Brescia, R.; Christodoulou, S.; Prato, M.; Marras, S.; Manna, L. The Influence of Chloride Ions on the Synthesis of Colloidal Branched CdSe/CdS Nanocrystal by Seeded Growth ACS Nano 2012, 6, 11088– 11096 DOI: 10.1021/nn3048846There is no corresponding record for this reference.
- 27Conca, E.; Aresti, M.; Saba, M.; Casula, M. F.; Quochi, F.; Mula, G.; Loche, D.; Kim, M. R.; Manna, L.; Corrias, A. Pt Decoration of CdSe@CdS Octapods: Effects on Charge Separation Nanoscale 2014, 6, 2238– 2243 DOI: 10.1039/c3nr05567aThere is no corresponding record for this reference.
- 28Klug, H. P.; Alexander, L. E. X-Ray Diffraction Procedures; Wiley: New York, 1974.There is no corresponding record for this reference.
- 29Dent, A. J.; Cibin, G.; Ramos, S.; Smith, A. D.; Scott, S. M.; Varandas, L.; Pearson, M. R.; Krumpa, N. A.; Jones, C. P.; Robbins, P. E. J. Phys. Conf. Ser. 2009, 190, 012039 DOI: 10.1088/1742-6596/190/1/012039There is no corresponding record for this reference.
- 30Ravel, B.; Newville, M. ATHENA, ARTEMIS, HEPHAESTUS: Data Analysis for X-Ray Absorption Spectroscopy Using IFEFFIT J. Synchrotron Radiat. 2005, 12, 537– 541 DOI: 10.1107/S090904950501271930ATHENA, ARTEMIS, HEPHAESTUS: data analysis for x-ray absorption spectroscopy using IFEFFITRavel, B.; Newville, M.Journal of Synchrotron Radiation (2005), 12 (4), 537-541CODEN: JSYRES; ISSN:0909-0495. (Blackwell Publishing Ltd.)A software package for the anal. of x-ray absorption spectroscopy (XAS) data is presented. This package is based on the IFEFFIT library of numerical and XAS algorithms and is written in the Perl programming language using the Perl/Tk graphics toolkit. The programs described here are: (i) ATHENA, a program for XAS data processing, (ii) ARTEMIS, a program for EXAFS data anal. using theor. stds. from FEFF and (iii) HEPHAESTUS, a collection of beamline utilities based on tables of at. absorption data. These programs enable high-quality data anal. that is accessible to novices while still powerful enough to meet the demands of an expert practitioner. The programs run on all major computer platforms and are freely available under the terms of a free software license.
- 31Deka, S.; Miszta, K.; Dorfs, D.; Genovese, A.; Bertoni, G.; Manna, L. Octapod-Shaped Colloidal Nanocrystals of Cadmium Chalcogenides via ″One-Pot″ Cation Exchange and Seeded Growth Nano Lett. 2010, 10, 3770– 3776 DOI: 10.1021/nl102539a31Octapod-Shaped Colloidal Nanocrystals of Cadmium Chalcogenides via "One-Pot" Cation Exchange and Seeded GrowthDeka, Sasanka; Miszta, Karol; Dorfs, Dirk; Genovese, Alessandro; Bertoni, Giovanni; Manna, LiberatoNano Letters (2010), 10 (9), 3770-3776CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)The growth behavior of cadmium chalcogenides (CdE = CdS, CdSe, and CdTe) on sphalerite Cu2-xSe nanocrystals (size range 10-15 nm) is studied. Due to the capability of Cu2-xSe to undergo a fast and quant. cation exchange reaction in the presence of excessive Cd2+ ions, no Cu2-xSe/CdE heterostructures are obtained and instead branched CdSe/CdE nanocrystals are built which consist of a sphalerite CdSe core and wurtzite CdE arms. While CdTe growth yields multiarmed structures with overall tetrahedral symmetry, CdS and CdSe arm growth leads to octapod-shaped nanocrystals. These results differ significantly from literature findings about the growth of CdE on sphalerite CdSe particles, which until now had always yielded tetrapod-shaped nanocrystals.
- 32Greegor, R. B.; Lytle, F. W. Morphology of Supported Metal Clusters: Determination by EXAFS and Chemisorption J. Catal. 1980, 63, 476– 486 DOI: 10.1016/0021-9517(80)90102-532Morphology of supported metal clusters: determination by EXAFS and chemisorptionGreegor, R. B.; Lytle, F. W.Journal of Catalysis (1980), 63 (2), 476-86CODEN: JCTLA5; ISSN:0021-9517.When small metal clusters are examd. by the extended x-ray absorption fi ne structure (EXAFS) technique the apparent av. coordination no. is smaller than that obsd. in the bulk metal because of the high proportion of surface atoms. This effect id dependent on the size and shape of the metal cluster. Geometrical shape models were derived for spheres, cubes, and disks, which give the EXAFS av. coordination no. for 1st, 2nd, and 3rd coordination spheres as a function of cluster size. Dispersion models (via chemisorption measurements) are also presented for different cluster shapes and sizes. Electron microscopy is used to support the analyses where possible.
Supporting Information
Supporting Information
Comparison of the data at the Cd, Se and S K-edge for the Rod 1 and Rod 2 samples; XANES spectra at the at the Cd, Se, and S K-edge; differences at the Cd K-edge between the EXAFS of Rod 1, Octa, and CdSe with respect to CdS; Fit results at the Cd, Se and S K-edge for the Rod 1 and Octa samples; EXAFS spectrum at the Cu K edge for the Octa sample. The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.jpcc.5b04593.
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