Quantification of the Interaction Forces between Metals and Graphene by Quantum Chemical Calculations and Dynamic Force Measurements under Ambient Conditions
- Petr Lazar ,
- Shuai Zhang ,
- Klára Šafářová ,
- Qiang Li ,
- Jens Peter Froning ,
- Jaroslav Granatier ,
- Pavel Hobza ,
- Radek Zbořil ,
- Flemming Besenbacher ,
- Mingdong Dong , and
- Michal Otyepka
Abstract

The two-dimensional material graphene has numerous potential applications in nano(opto)electronics, which inevitably involve metal graphene interfaces.Theoretical approaches have been employed to examine metal graphene interfaces, but experimental evidence is currently lacking. Here, we combine atomic force microscopy (AFM) based dynamic force measurements and density functional theory calculations to quantify the interaction between metal-coated AFM tips and graphene under ambient conditions. The results show that copper has the strongest affinity to graphene among the studied metals (Cu, Ag, Au, Pt, Si), which has important implications for the construction of a new generation of electronic devices. Observed differences in the nature of the metal–graphene bonding are well reproduced by the calculations, which included nonlocal Hartree–Fock exchange and van der Waals effects.
Results and Discussion
Figure 1

Figure 1. (A) Schematic of AFM operation in dynamic range force spectroscopy showing a metal-coated probe scanning a graphene sheet on a SiO2 support; (B) atomic level model of metal-coated tip on graphene used in the DFT calculations; (C) SEM image of AFM tip coated by gold (see Supplementary Figure 3 for EDS spectrum); (D) optical image of the graphene substrate on SiO2 used during the experiment. The dashed square indicates the location of the inset of Figure 2A.
Figure 2

Figure 2. Graphene morphology and interaction force curves between metal-coated AFM probe and graphene: (A) AFM morphology images of graphene; (B) typical force vs time curve of Cu-coated probe and graphene; red B and green C dots indicate the adhesion force during approach and withdrawal, respectively; (C) typical force vs separation curves derived from the approach process (Fapp); (D) typical force vs separation curves derived from the withdrawal process (Fw).
Figure 3

Figure 3. Calculated interaction energy curves (upper panel) and derived interaction forces (lower panel) between Au tip and graphene. The crosses denote the total energies calculated with various functionals (PBE, PBE+vdW, EE+vdW, and EE+vdW with spin–orbit coupling).
Figure 4

Figure 4. The experimentally derived interaction forces from the approach processes (in blue) are compared with the interaction forces calculated by the EE-vdW method (in red).
| metal | Eint(kcal/mol) | Fint (nN) | Fapp (nN) | Fw (nN) |
|---|---|---|---|---|
| Cu | 24.6 | 1.6 | 1.6 ± 0.3 | 7.4 ± 1.4 |
| Ag | 15.8 | 1.3 | 1.2 ± 0.1 | 5.2 ± 0.2 |
| Au | 16.3 | 0.8 | 0.8 ± 0.2 | 2.0 ± 0.1 |
| Pt | 16.5 | 1.2 ± 0.6 | 6.2 ± 0.3 | |
| Si | 4.9 | 0.3 | 0.7 ± 0.2 | 1.4 ± 0.1 |
The experimental interaction forces were recorded during both the approach (Fapp) and withdrawal (Fw) processes.
| metal | PBE | PBE+vdW | EE+vdW |
|---|---|---|---|
| Cu | 1.2 | 0.9 | 1.6 |
| Ag | 0.6 | 0.5 | 1.3 |
| Au | 0.7 | 0.5 | 0.8 |
| Au* | 0.6 | 0.7 | 1.8 |
| Si | 0.02 | 0.2 | 0.3 |
In the case of the Au4 cluster, we also include the results calculated within a scalar relativistic approximation (denoted by an asterisk (∗)).
Conclusion
Methods
Preparation of Graphene Samples
SEM Analysis
AFM Method
Theoretical Calculations
Supporting Information
TheSupporting Information contains SEM images and EDS spectra of AFM tips (Supplementary Figures 1–6), interaction energies calculated for various positions on graphene (Supplementary Table 1) and singlet states (Supplementary Table 2) and scalar relativistic Au4 (Supplementary Table 3), typical curves from dynamic AFM measurements (Supplementary Figure 7), and distributions of forces from AFM experiments (Supplementary Figures 8 and 9). This material is available free of charge via the Internet at http://pubs.acs.org.
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 was supported by the Grant Agency of the Czech Republic [P208/12/G016]. This work was also supported by the Operational Program Research and Development for Innovations—European Regional Development Fund (CZ.1.05/2.1.00/03.0058) and European Social Fund (CZ.1.07/2.3.00/20.0017), the Danish National Research Foundation and the Villum Foundation (M.D.) and a student project of Palacký University Olomouc (PrF_2012_028). The support of Praemium Academiae of the Academy of Sciences of the Czech Republic awarded to P.H. in 2007 is also gratefully acknowledged.
References
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- 17Giovannetti, G.; Khomyakov, P. A.; Brocks, G.; Karpan, V. M.; van den Brink, J.; Kelly, P. J. Doping Graphene with Metal Contacts Phys. Rev. Lett. 2008, 101, 026803[Crossref], [PubMed], [CAS], Google Scholar17https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1cXosVynt7w%253D&md5=ecd4c2578fa5cf738e716843224ecf10Doping graphene with metal contactsGiovannetti, G.; Khomyakov, P. A.; Brocks, G.; Karpan, V. M.; van den Brink, J.; Kelly, P. J.Physical Review Letters (2008), 101 (2), 026803/1-026803/4CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)Making devices with graphene necessarily involves making contacts with metals. We use d. functional theory to study how graphene is doped by adsorption on metal substrates and find that weak bonding on Al, Ag, Cu, Au, and Pt, while preserving its unique electronic structure, can still shift the Fermi level with respect to the conical point by ∼0.5 eV. At equil. sepns., the crossover from p-type to n-type doping occurs for a metal work function of ∼5.4 eV, a value much larger than the graphene work function of 4.5 eV. The numerical results for the Fermi level shift in graphene are described very well by a simple anal. model which characterizes the metal solely in terms of its work function, greatly extending their applicability.
- 18Johll, H.; Kang, H. C.; Tok, E. S. Density Functional Theory Study of Fe, Co, and Ni Adatoms and Dimers Adsorbed on Graphene Phys. Rev. B 2009, 79, 245416Google ScholarThere is no corresponding record for this reference.
- 19Khomyakov, P. A.; Giovannetti, G.; Rusu, P. C.; Brocks, G.; van den Brink, J.; Kelly, P. J. First-Principles Study of the Interaction and Charge Transfer between Graphene and Metals Phys. Rev. B 2009, 79, 195425[Crossref], [CAS], Google Scholar19https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1MXmvF2rtbk%253D&md5=30520d6c0154305b51afd483e991ad25First-principles study of the interaction and charge transfer between graphene and metalsKhomyakov, P. A.; Giovannetti, G.; Rusu, P. C.; Brocks, G.; van den Brink, J.; Kelly, P. J.Physical Review B: Condensed Matter and Materials Physics (2009), 79 (19), 195425/1-195425/12CODEN: PRBMDO; ISSN:1098-0121. (American Physical Society)Measuring the transport of electrons through a graphene sheet necessarily involves contacting it with metal electrodes. The authors study the adsorption of graphene on metal substrates using 1st-principles calcns. at the level of d.-functional theory. The bonding of graphene to Al, Ag, Cu, Au, and Pt (111) surfaces is so weak that its unique ultrarelativistic electronic structure is preserved. The interaction does, however, lead to a charge transfer that shifts the Fermi level by up to 0.5 eV with respect to the conical points. The crossover from p-type to n-type doping occurs for a metal with a work function ∼5.4 eV, a value much larger than the work function of free-standing graphene, 4.5 eV. The authors develop a simple anal. model that describes the Fermi-level shift in graphene in terms of the metal substrate work function. Graphene interacts with and binds more strongly to Co, Ni, Pd, and Ti. This chemisorption involves hybridization between graphene pz states and metal d states that opens a band gap in graphene, and reduces its work function considerably. The supported graphene is effectively n-type doped because in a current-in-plane device geometry the work-function lowering will lead to electrons being transferred to the unsupported part of the graphene sheet.
- 20Hohenberg, P.; Kohn, W. Inhomogeneous Electron Gas Phys. Rev. B 1964, 136, B864
- 21Kohn, W.; Sham, L. J. Self-Consistent Equations Including Exchange and Correlation Effects Phys. Rev. 1965, 140, 1133
- 22Granatier, J.; Lazar, P.; Otyepka, M.; Hobza, P. The Nature of the Binding of Au, Ag, and Pd to Benzene, Coronene, and Graphene: From Benchmark CCSD(T) Calculations to Plane-Wave DFT Calculations J. Chem. Theory Comput. 2011, 7, 3743– 3755[ACS Full Text
], [CAS], Google Scholar22https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3MXhtlaqtr3I&md5=8509d55dff8de47d9912a0a48fe20833The Nature of the Binding of Au, Ag, and Pd to Benzene, Coronene, and Graphene: From Benchmark CCSD(T) Calculations to Plane-Wave DFT CalculationsGranatier, Jaroslav; Lazar, Petr; Otyepka, Michal; Hobza, PavelJournal of Chemical Theory and Computation (2011), 7 (11), 3743-3755CODEN: JCTCCE; ISSN:1549-9618. (American Chemical Society)The adsorption of Ag, Au, and Pd atoms on benzene, coronene, and graphene has been studied using post Hartree-Fock wave function theory (CCSD(T), MP2) and d. functional theory (M06-2X, DFT-D3, PBE, vdW-DF) methods. The CCSD(T) benchmark binding energies for benzene-M (M = Pd, Au, Ag) complexes are 19.7, 4.2, and 2.3 kcal/mol, resp. We found that the nature of binding of the three metals is different: while silver binds predominantly through dispersion interactions, the binding of palladium has a covalent character, and the binding of gold involves a subtle combination of charge transfer and dispersion interactions as well as relativistic effects. We demonstrate that the CCSD(T) benchmark binding energies for benzene-M complexes can be reproduced in plane-wave d. functional theory calcns. by including a fraction of the exact exchange and a nonempirical van der Waals correction (EE+vdW). Applying the EE+vdW method, we obtained binding energies for the graphene-M (M = Pd, Au, Ag) complexes of 17.4, 5.6, and 4.3 kcal/mol, resp. The trends in binding energies found for the benzene-M complexes correspond to those in coronene and graphene complexes. DFT methods that use empirical corrections to account for the effects of vdW interactions significantly overestimate binding energies in some of the studied systems. - 23Vanin, M.; Mortensen, J. J.; Kelkkanen, A. K.; Garcia-Lastra, J. M.; Thygesen, K. S.; Jacobsen, K. W. Graphene on Metals: A van der Waals Density Functional Study Phys. Rev. B 2010, 81, 081408Google ScholarThere is no corresponding record for this reference.
- 24Olsen, T.; Yan, J.; Mortensen, J. J.; Thygesen, K. S. Dispersive and Covalent Interactions between Graphene and Metal Surfaces from the Random Phase Approximation Phys. Rev. Lett. 2011, 107, 156401[Crossref], [PubMed], [CAS], Google Scholar24https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3MXhsVansbfN&md5=9f45b6c3509ae089bb4b8c07c6e1d844Dispersive and covalent interactions between graphene and metal surfaces from the random phase approximationOlsen, Thomas; Yan, Jun; Mortensen, Jens J.; Thygesen, Kristian S.Physical Review Letters (2011), 107 (15), 156401/1-156401/5CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)We calc. the potential energy surfaces for graphene adsorbed on Cu(111), Ni(111), and Co(0001) using d. functional theory and the RPA (RPA). For these adsorption systems covalent and dispersive interactions are equally important and while commonly used approxns. for exchange-correlation functionals give inadequate descriptions of either van der Waals or chem. bonds, RPA accounts accurately for both. It is found that the adsorption is a delicate competition between a weak chemisorption min. close to the surface and a physisorption min. further from the surface.
- 25Venugopal, A.; Colombo, L.; Vogel, E. M. Contact Resistance in Few and Multilayer Graphene Devices Appl. Phys. Lett. 2010, 96, 013512Google ScholarThere is no corresponding record for this reference.
- 26Pi, K.; McCreary, K. M.; Bao, W.; Han, W.; Chiang, Y. F.; Li, Y.; Tsai, S. W.; Lau, C. N.; Kawakami, R. K. Electronic Doping and Scattering by Transition Metals on Graphene Phys. Rev. B 2009, 80, 075406Google ScholarThere is no corresponding record for this reference.
- 27Schimka, L.; Harl, J.; Stroppa, A.; Gruneis, A.; Marsman, M.; Mittendorfer, F.; Kresse, G. Accurate Surface and Adsorption Energies from Many-Body Perturbation Theory Nat. Mater. 2010, 9, 741– 744[Crossref], [PubMed], [CAS], Google Scholar27https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXhtVGlsr%252FK&md5=cc1717ff227c13a08e77b89f66a1b19dAccurate surface and adsorption energies from many-body perturbation theorySchimka, L.; Harl, J.; Stroppa, A.; Grueneis, A.; Marsman, M.; Mittendorfer, F.; Kresse, G.Nature Materials (2010), 9 (9), 741-744CODEN: NMAACR; ISSN:1476-1122. (Nature Publishing Group)Kohn-Sham d. functional theory is the workhorse computational method in materials and surface science. Unfortunately, most semilocal d. functionals predict surfaces to be more stable than they are exptl. Naively, we would expect that consequently adsorption energies on surfaces are too small as well, but the contrary is often found: chemisorption energies are usually overestimated. Modifying the functional improves either the adsorption energy or the surface energy but always worsens the other aspect. This suggests that semilocal d. functionals possess a fundamental flaw that is difficult to cure, and alternative methods are urgently needed. Here we show that a computationally fairly efficient many-electron approach, the RPA to the correlation energy, resolves this dilemma and yields at the same time excellent lattice consts., surface energies and adsorption energies for and on transition-metal surfaces.
- 28Grimme, S. Density Functional Theory with London Dispersion Corrections WIREs Comput. Mol. Sci. 2011, 1, 211– 228[Crossref], [CAS], Google Scholar28https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3MXksVGlu70%253D&md5=f24d3bf3624d506052109c1e9093ef6bDensity functional theory with london dispersion correctionsGrimme, StefanWiley Interdisciplinary Reviews: Computational Molecular Science (2011), 1 (2), 211-228CODEN: WIRCAH; ISSN:1759-0884. (Wiley-Blackwell)A review. Dispersion corrections to std. Kohn-Sham d. functional theory (DFT) are reviewed. The focus is on computationally efficient methods for large systems that do not depend on virtual orbitals or rely on sepd. fragments. The recommended approaches (van der Waals d. functional and DFT-D) are asymptotically correct and can be used in combination with std. or slightly modified (short-range) exchange-correlation functionals. The importance of the dispersion energy in intramol. cases (conformational problems and thermochem.) is highlighted.
- 29Cramer, C. J.; Truhlar, D. G. Density Functional Theory for Transition Metals and Transition Metal Chemistry Phys. Chem. Chem. Phys. 2009, 11, 10757– 10816[Crossref], [PubMed], [CAS], Google Scholar29https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1MXhsVentrfK&md5=3bb9a3202e5d1493390a1ad863f60c4cDensity functional theory for transition metals and transition metal chemistryCramer, Christopher J.; Truhlar, Donald G.Physical Chemistry Chemical Physics (2009), 11 (46), 10757-10816CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)A review. We introduce d. functional theory and review recent progress in its application to transition metal chem. Topics covered include local, meta, hybrid, hybrid meta, and range-sepd. functionals, band theory, software, validation tests, and applications to spin states, magnetic exchange coupling, spectra, structure, reactivity, and catalysis, including mols., clusters, nanoparticles, surfaces, and solids.
- 30Dong, M.; Sahin, O. A Nanomechanical Interface to Rapid Single-Molecule Interactions Nat. Commun. 2011, 2, 247[Crossref], [PubMed], [CAS], Google Scholar30https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BC3M3ovV2lsQ%253D%253D&md5=0f55dfc9dc55ef373897caf805720237A nanomechanical interface to rapid single-molecule interactionsDong Mingdong; Sahin OzgurNature communications (2011), 2 (), 247 ISSN:.Single-molecule techniques provide opportunities for molecularly precise imaging, manipulation, assembly and biophysical studies. Owing to the kinetics of bond rupture processes, rapid single-molecule measurements can reveal novel bond rupture mechanisms, probe single-molecule events with short lifetimes and enhance the interaction forces supplied by single molecules. Rapid measurements will also increase throughput necessary for technological use of single-molecule techniques. Here we report a nanomechanical sensor that allows single-molecule force spectroscopy on the previously unexplored microsecond timescale. We probed bond lifetimes around 5 μs and observed significant enhancements in molecular interaction forces. Our loading-rate-dependent measurements provide experimental evidence for an additional energy barrier in the biotin-streptavidin complex. We also demonstrate quantitative mapping of rapid single-molecule interactions with high spatial resolution. This nanomechanical interface may allow studies of molecular processes with short lifetimes and development of novel biological imaging, single-molecule manipulation and assembly technologies.
- 31Dong, M. D.; Husale, S.; Sahin, O. Determination of Protein Structural Flexibility by Microsecond Force Spectroscopy Nat. Nanotechnol. 2009, 4, 514– 517[Crossref], [PubMed], [CAS], Google Scholar31https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1MXpsFSisbY%253D&md5=10070f6f4aaf3a9a87ad7c36650d3d6fDetermination of protein structural flexibility by microsecond force spectroscopyDong, Mingdong; Husale, Sudhir; Sahin, OzgurNature Nanotechnology (2009), 4 (8), 514-517CODEN: NNAABX; ISSN:1748-3387. (Nature Publishing Group)Proteins are dynamic mol. machines having structural flexibility that allows conformational changes. Current methods for the detn. of protein flexibility rely mainly on the measurement of thermal fluctuations and disorder in protein conformations and tend to be exptl. challenging. Moreover, they reflect at. fluctuations on picosecond timescales, whereas the large conformational changes in proteins typically happen on micro- to millisecond timescales. Here, the authors directly det. the flexibility of bacteriorhodopsin - a protein that uses the energy in light to move protons across cell membranes - at the microsecond timescale by monitoring force-induced deformations across the protein structure with a technique based on at. force microscopy. In contrast to existing methods, the deformations the authors measure involve a collective response of protein residues and operate under physiol. relevant conditions with native proteins.
- 32Rico, F.; Su, C.; Scheuring, S. Mechanical Mapping of Single Membrane Proteins at Submolecular Resolution Nano Lett. 2011, 11, 3983– 3986[ACS Full Text
], [CAS], Google Scholar32https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3MXpslajsbY%253D&md5=77c1ae451b8b9508dc1d82fe551e675fMechanical Mapping of Single Membrane Proteins at Submolecular ResolutionRico, Felix; Su, Chan-Min; Scheuring, SimonNano Letters (2011), 11 (9), 3983-3986CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)The capacity of proteins to carry out different functions is related to their ability to undergo conformation changes, which depends on the flexibility of protein structures. In this work, the authors applied a novel imaging mode based on indentation force spectroscopy to map quant. the flexibility of individual membrane proteins in their native, folded state at unprecedented submol. resoln. The authors' results enabled them to correlate protein flexibility with crystal structure and showed that α-helixes are stiff structures that may contribute importantly to the mech. stability of membrane proteins, while interhelical loops appeared more flexible, allowing conformational changes related to function. - 33Medalsy, I.; Hensen, U.; Muller, D. J. Imaging and Quantifying Chemical and Physical Properties of Native Proteins at Molecular Resolution by Force-Volume AFM Angew. Chem., Int. Ed. 2011, 50, 12103– 12108[Crossref], [CAS], Google Scholar33https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3MXhtlahsbvP&md5=746eae8ed4f0a83ddf0202d602194df9Imaging and Quantifying Chemical and Physical Properties of Native Proteins at Molecular Resolution by Force-Volume AFMMedalsy, Izhar; Hensen, Ulf; Muller, Daniel J.Angewandte Chemie, International Edition (2011), 50 (50), 12103-12108, S12103/1-S12103/9CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)The authors introduce high-resoln. force-vol. AFM imaging of the native purple membrane (PM) from Halobacterium salinarum. PM consists of the light-driven proton-pump bacteriorhodopsin (BR) and lipids. During the photocycle BR goes through conformational changes and creates a proton gradient across the cellular membrane that is used to power cellular processes. Measurements show that proton transfer along the PM surface is much faster than proton exchange to the bulk water. This unique property that kinetically traps protons is facilitated by the asym. phys. and chem. properties of PM surfaces. High-resoln. (∼0.5 nm) contact-mode AFM of BR revealed extracellular polypeptide loops changing their conformation with the membrane protein assembly and cytoplasmic loops undergoing force-induced conformational changes. Using force-vol. AFM the authors imaged PM adsorbed onto freshly cleaved mica in buffer soln. For every pixel of the AFM topog. the authors recorded a F-D curve approaching and retracting AFM tip and PM. The maximal force (trigger force) applied in these approach-retract cycles was limited to 100 pN. When reaching the trigger force the distance travelled by tip and sample was taken to reconstruct the topog.
- 34Lantz, M. A.; Hug, H. J.; Hoffmann, R.; van Schendel, P. J. A.; Kappenberger, P.; Martin, S.; Baratoff, A.; Guntherodt, H. J. Quantitative Measurement of Short-Range Chemical Bonding Forces Science 2001, 291, 2580– 2583[Crossref], [PubMed], [CAS], Google Scholar34https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3MXisFekt7Y%253D&md5=55f89d9168d05324b22ccd7d8087896aQuantitative measurement of short-range chemical bonding forcesLantz, M. A.; Hug, H. J.; Hoffmann, R.; van Schendel, P. J. A.; Kappenberger, P.; Martin, S.; Baratoff, A.; Guntherodt, H.-J.Science (Washington, DC, United States) (2001), 291 (5513), 2580-2583CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)We report direct force measurements of the formation of a chem. bond. The expts. were performed using a low-temp. at. force microscope, a silicon tip, and a silicon (111) 7x7 surface. The measured site-dependent attractive short-range force, which attains a max. value of 2.1 nanonewtons, is in good agreement with first-principles calcns. of an incipient covalent bond in an analogous model system. The resoln. was sufficient to distinguish differences in the interaction potential between inequivalent adatoms, demonstrating the ability of at. force microscopy to provide quant., at.-scale information on surface chem. reactivity.
- 35Hoffmann, R.; Kantorovich, L. N.; Baratoff, A.; Hug, H. J.; Guntherodt, H. J. Sublattice Identification in Scanning Force Microscopy on Alkali Halide Surfaces Phys. Rev. Lett. 2004, 92, 146103Google ScholarThere is no corresponding record for this reference.
- 36Sugimoto, Y.; Pou, P.; Abe, M.; Jelinek, P.; Perez, R.; Morita, S.; Custance, O. Chemical Identification of Individual Surface Atoms by Atomic Force Microscopy Nature 2007, 446, 64– 67[Crossref], [PubMed], [CAS], Google Scholar36https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2sXit1arsL0%253D&md5=5f7d3086b09adac56614ef10214340b3Chemical identification of individual surface atoms by atomic force microscopySugimoto, Yoshiaki; Pou, Pablo; Abe, Masayuki; Jelinek, Pavel; Perez, Ruben; Morita, Seizo; Custance, OscarNature (London, United Kingdom) (2007), 446 (7131), 64-67CODEN: NATUAS; ISSN:0028-0836. (Nature Publishing Group)Scanning probe microscopy is a versatile and powerful method that uses sharp tips to image, measure and manipulate matter at surfaces with at. resoln. At cryogenic temps., scanning probe microscopy can even provide electron tunnelling spectra that serve as fingerprints of the vibrational properties of adsorbed mols. and of the electronic properties of magnetic impurity atoms, thereby allowing chem. identification. But in many instances, and particularly for insulating systems, detg. the exact chem. compn. of surfaces or nanostructures remains a considerable challenge. In principle, dynamic force microscopy should make it possible to overcome this problem: it can image insulator, semiconductor and metal surfaces with true at. resoln., by detecting and precisely measuring the short-range forces that arise with the onset of chem. bonding between the tip and surface atoms and that depend sensitively on the chem. identity of the atoms involved. Here the authors report precise measurements of such short-range chem. forces, and show that their dependence on the force microscope tip used can be overcome through a normalization procedure. This allows one to use the chem. force measurements as the basis for at. recognition, even at room temp. The authors illustrate the performance of this approach by imaging the surface of a particularly challenging alloy system and successfully identifying the 3 constituent at. species Si, Sn and lead, even though these exhibit very similar chem. properties and identical surface position preferences that render any discrimination attempt based on topog. measurements impossible.
- 37Yi, H.-B.; Diefenbach, M.; Choi, Y. C.; Lee, E. C.; Lee, H. M.; Hong, B. H.; Kim, K. S. Interactions of Neutral and Cationic Transition Metals with the Redox System of Hydroquinone and Quinone: Theoretical Characterization of the Binding Topologies, and Implications for the Formation of Nanomaterials Chem.—Eur. J. 2006, 12, 4885– 4892[Crossref], [PubMed], [CAS], Google Scholar37https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD28Xmtlyjt7o%253D&md5=f232b2c7a9ce88c5fd4999222da54ec6Interactions of neutral and cationic transition metals with the redox system of hydroquinone and quinone: theoretical characterization of the binding topologies, and implications for the formation of nanomaterialsYi, Hai-Bo; Diefenbach, Martin; Choi, Young Cheol; Lee, Eun Cheol; Lee, Han Myoung; Hong, Byung Hee; Kim, Kwang S.Chemistry--A European Journal (2006), 12 (18), 4885-4892CODEN: CEUJED; ISSN:0947-6539. (Wiley-VCH Verlag GmbH & Co. KGaA)To understand the self-assembly process of the transition metal (TM) nanoclusters and nanowires self-synthesized by hydroquinone (HQ) and calix[4]hydroquinone (CHQ) by electrochem. redox processes, we have investigated the binding sites of HQ for the transition-metal cations TMn+ = Ag+, Au+, Pd2+, Pt2+, and Hg2+ and those of quinone (Q) for the reduced neutral metals TM0, using ab initio calcns. For comparison, TM0-HQ and TMn+-Q interactions, as well as the cases for Na+ and Cu+ (which do not take part in self-synthesis by CHQ) are also included. In general, TM-ligand coordination is controlled by symmetry constraints imposed on the resp. orbital interactions. Calcns. predict that, due to synergetic interactions, silver and gold are very efficient metals for one-dimensional (1D) nanowire formation in the self-assembly process, platinum and mercury favor both nanowire/nanorod and thin film formation, while palladium favors two-dimensional (2D) thin film formation.
- 38Granatier, J.; Lazar, P.; Prucek, R.; Safarova, K.; Zboril, R.; Otyepka, M.; Hobza, P. Interaction of Graphene and Arenes with Noble Metals J. Phys. Chem. C 2012, 116, 14151– 14162
- 39Blonski, P.; Dennler, S.; Hafner, J. Strong Spin-orbit Effects in Small Pt Clusters: Geometric Structure, Magnetic Isomers and Anisotropy J. Chem. Phys. 2011, 134, 034107Google ScholarThere is no corresponding record for this reference.
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Abstract

Figure 1

Figure 1. (A) Schematic of AFM operation in dynamic range force spectroscopy showing a metal-coated probe scanning a graphene sheet on a SiO2 support; (B) atomic level model of metal-coated tip on graphene used in the DFT calculations; (C) SEM image of AFM tip coated by gold (see Supplementary Figure 3 for EDS spectrum); (D) optical image of the graphene substrate on SiO2 used during the experiment. The dashed square indicates the location of the inset of Figure 2A.
Figure 2

Figure 2. Graphene morphology and interaction force curves between metal-coated AFM probe and graphene: (A) AFM morphology images of graphene; (B) typical force vs time curve of Cu-coated probe and graphene; red B and green C dots indicate the adhesion force during approach and withdrawal, respectively; (C) typical force vs separation curves derived from the approach process (Fapp); (D) typical force vs separation curves derived from the withdrawal process (Fw).
Figure 3

Figure 3. Calculated interaction energy curves (upper panel) and derived interaction forces (lower panel) between Au tip and graphene. The crosses denote the total energies calculated with various functionals (PBE, PBE+vdW, EE+vdW, and EE+vdW with spin–orbit coupling).
Figure 4

Figure 4. The experimentally derived interaction forces from the approach processes (in blue) are compared with the interaction forces calculated by the EE-vdW method (in red).
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ARTICLE SECTIONSThis article references 46 other publications.
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- 2Novoselov, K. S.; Geim, A. K.; Morozov, S. V.; Jiang, D.; Katsnelson, M. I.; Grigorieva, I. V.; Dubonos, S. V.; Firsov, A. A. Two-Dimensional Gas of Massless Dirac Fermions in Graphene Nature 2005, 438, 197– 200[Crossref], [PubMed], [CAS], Google Scholar2https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2MXhtF2nsrnI&md5=56138229370ff26ece1857a049f00f53Two-dimensional gas of massless Dirac fermions in grapheneNovoselov, K. S.; Geim, A. K.; Morozov, S. V.; Jiang, D.; Katsnelson, M. I.; Grigorieva, I. V.; Dubonos, S. V.; Firsov, A. A.Nature (London, United Kingdom) (2005), 438 (7065), 197-200CODEN: NATUAS; ISSN:0028-0836. (Nature Publishing Group)Quantum electrodynamics (resulting from the merger of quantum mechanics and relativity theory) has provided a clear understanding of phenomena ranging from particle physics to cosmol. and from astrophysics to quantum chem. The ideas underlying quantum electrodynamics also influence the theory of condensed matter, but quantum relativistic effects are usually minute in the known exptl. systems that can be described accurately by the non-relativistic Schroedinger equation. Here we report an exptl. study of a condensed-matter system (graphene, a single at. layer of carbon) in which electron transport is essentially governed by Dirac's (relativistic) equation. The charge carriers in graphene mimic relativistic particles with zero rest mass and have an effective 'speed of light' c* ≈ 106 m s-1. Our study reveals a variety of unusual phenomena that are characteristic of two-dimensional Dirac fermions. In particular we have obsd. the following: first, graphene's cond. never falls below a min. value corresponding to the quantum unit of conductance, even when concns. of charge carriers tend to zero; second, the integer quantum Hall effect in graphene is anomalous in that it occurs at half-integer filling factors; and third, the cyclotron mass mc of massless carriers in graphene is described by E = mcc*2. This two-dimensional system is not only interesting in itself but also allows access to the subtle and rich physics of quantum electrodynamics in a bench-top expt.
- 3Geim, A. K.; Novoselov, K. S. The Rise of Graphene Nat. Mater. 2007, 6, 183– 191[Crossref], [PubMed], [CAS], Google Scholar3https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2sXit1Khtrg%253D&md5=c2c02ce70a1725e6c559c173156568c5The rise of grapheneGeim, A. K.; Novoselov, K. S.Nature Materials (2007), 6 (3), 183-191CODEN: NMAACR; ISSN:1476-1122. (Nature Publishing Group)A review. Graphene is a rapidly rising star on the horizon of materials science and condensed-matter physics. This strictly two-dimensional material exhibits exceptionally high crystal and electronic quality, and, despite its short history, has already revealed a cornucopia of new physics and potential applications, which are briefly discussed here. Whereas one can be certain of the realness of applications only when com. products appear, graphene no longer requires any further proof of its importance in terms of fundamental physics. Owing to its unusual electronic spectrum, graphene has led to the emergence of a new paradigm of 'relativistic' condensed-matter physics, where quantum relativistic phenomena, some of which are unobservable in high-energy physics, can now be mimicked and tested in table-top expts. More generally, graphene represents a conceptually new class of materials that are only one atom thick, and, on this basis, offers new inroads into low-dimensional physics that has never ceased to surprise and continues to provide a fertile ground for applications.
- 4Gomes, K. K.; Mar, W.; Ko, W.; Guinea, F.; Manoharan, H. C. Designer Dirac Fermions and Topological Phases in Molecular Graphene Nature 2012, 483, 306– 310[Crossref], [PubMed], [CAS], Google Scholar4https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38XktVaksLY%253D&md5=d5e8815f3b199c5503c70d5e5b92e71dDesigner Dirac fermions and topological phases in molecular grapheneGomes, Kenjiro K.; Mar, Warren; Ko, Wonhee; Guinea, Francisco; Manoharan, Hari C.Nature (London, United Kingdom) (2012), 483 (7389), 306-310CODEN: NATUAS; ISSN:0028-0836. (Nature Publishing Group)The observation of massless Dirac fermions in monolayer graphene has generated a new area of science and technol. seeking to harness charge carriers that behave relativistically within solid-state materials. Both massless and massive Dirac fermions have been studied and proposed in a growing class of Dirac materials that includes bilayer graphene, surface states of topol. insulators and iron-based high-temp. superconductors. Because the accessibility of this physics is predicated on the synthesis of new materials, the quest for Dirac quasi-particles has expanded to artificial systems such as lattices comprising ultracold atoms. Here we report the emergence of Dirac fermions in a fully tunable condensed-matter system-mol. graphene-assembled by at. manipulation of carbon monoxide mols. over a conventional two-dimensional electron system at a copper surface. Using low-temp. scanning tunneling microscopy and spectroscopy, we embed the symmetries underlying the two-dimensional Dirac equation into electron lattices, and then visualize and shape the resulting ground states. These expts. show the existence within the system of linearly dispersing, massless quasi-particles accompanied by a d. of states characteristic of graphene. We then tune the quantum tunneling between lattice sites locally to adjust the phase accrual of propagating electrons. Spatial texturing of lattice distortions produces atomically sharp p-n and p-n-p junction devices with two-dimensional control of Dirac fermion d. and the power to endow Dirac particles with mass. Moreover, we apply scalar and vector potentials locally and globally to engender topol. distinct ground states and, ultimately, embedded gauge fields, wherein Dirac electrons react to pseudo' elec. and magnetic fields present in their ref. frame but absent from the lab. frame. We demonstrate that Landau levels created by these gauge fields can be taken to the relativistic magnetic quantum limit, which has so far been inaccessible in natural graphene. Mol. graphene provides a versatile means of synthesizing exotic topol. electronic phases in condensed matter using tailored nanostructures.
- 5Britnell, L.; Gorbachev, R. V.; Jalil, R.; Belle, B. D.; Schedin, F.; Mishchenko, A.; Georgiou, T.; Katsnelson, M. I.; Eaves, L.; Morozov, S. V.et al. Field-Effect Tunneling Transistor Based on Vertical Graphene Heterostructures Science 2012, 335, 947– 950[Crossref], [PubMed], [CAS], Google Scholar5https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38XisFarsLw%253D&md5=4805f4ceb53a5d06cbc14bdca01600bcField-Effect Tunneling Transistor Based on Vertical Graphene HeterostructuresBritnell, L.; Gorbachev, R. V.; Jalil, R.; Belle, B. D.; Schedin, F.; Mishchenko, A.; Georgiou, T.; Katsnelson, M. I.; Eaves, L.; Morozov, S. V.; Peres, N. M. R.; Leist, J.; Geim, A. K.; Novoselov, K. S.; Ponomarenko, L. A.Science (Washington, DC, United States) (2012), 335 (6071), 947-950CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)An obstacle to the use of graphene as an alternative to silicon electronics has been the absence of an energy gap between its conduction and valence bands, which makes it difficult to achieve low power dissipation in the OFF state. We report a bipolar field-effect transistor that exploits the low d. of states in graphene and its one-at.-layer thickness. Our prototype devices are graphene heterostructures with atomically thin boron nitride or molybdenum disulfide acting as a vertical transport barrier. They exhibit room-temp. switching ratios of ≈50 and ≈10,000, resp. Such devices have potential for high-frequency operation and large-scale integration.
- 6Tassin, P.; Koschny, T.; Kafesaki, M.; Soukoulis, C. M. A Comparison of Graphene, Superconductors and Metals as Conductors for Metamaterials and Plasmonics Nat. Photon. 2012, 6, 259– 264[Crossref], [CAS], Google Scholar6https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38Xjt1eltro%253D&md5=029bac02c11bca27b30be1d02c586cacA comparison of graphene, superconductors and metals as conductors for metamaterials and plasmonicsTassin, Philippe; Koschny, Thomas; Kafesaki, Maria; Soukoulis, Costas M.Nature Photonics (2012), 6 (4), 259-264CODEN: NPAHBY; ISSN:1749-4885. (Nature Publishing Group)Recent advancements in metamaterials and plasmonics have promised a no. of exciting applications, in particular at terahertz and optical frequencies. Unfortunately, the noble metals used in these photonic structures are not particularly good conductors at high frequencies, resulting in significant dissipative loss. Here, we address the question of what is a good conductor for metamaterials and plasmonics. For resonant metamaterials, we develop a figure-of-merit for conductors that allows for a straightforward classification of conducting materials according to the resulting dissipative loss in the metamaterial. Application of our method predicts that graphene and high-Tc superconductors are not viable alternatives for metals in metamaterials. We also provide an overview of a no. of transition metals, alkali metals and transparent conducting oxides. For plasmonic systems, we predict that graphene and high-Tc superconductors cannot outperform gold as a platform for surface plasmon polaritons, because graphene has a smaller propagation length-to-wavelength ratio.
- 7Ju, L.; Geng, B. S.; Horng, J.; Girit, C.; Martin, M.; Hao, Z.; Bechtel, H. A.; Liang, X. G.; Zettl, A.; Shen, Y. R.et al. Graphene Plasmonics for Tunable Terahertz Metamaterials Nat. Nanotechnol. 2011, 6, 630– 634[Crossref], [PubMed], [CAS], Google Scholar7https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3MXhtFWrsr7L&md5=cc654d40a2f7c87e12af7fae0caab2abGraphene plasmonics for tunable terahertz metamaterialsJu, Long; Geng, Bai-Song; Horng, Jason; Girit, Caglar; Martin, Michael; Hao, Zhao; Bechtel, Hans A.; Liang, Xiao-Gan; Zettl, Alex; Shen, Y. Ron; Wang, FengNature Nanotechnology (2011), 6 (10), 630-634CODEN: NNAABX; ISSN:1748-3387. (Nature Publishing Group)Plasmons describe collective oscillations of electrons. They have a fundamental role in the dynamic responses of electron systems and form the basis of research into optical metamaterials. Plasmons of 2-dimensional massless electrons, as present in graphene, show unusual behavior that enables new tunable plasmonic metamaterials and, potentially, optoelectronic applications in the terahertz frequency range. Here the authors explore plasmon excitations in engineered graphene micro-ribbon arrays. Graphene plasmon resonances can be tuned over a broad terahertz frequency range by changing micro-ribbon width and in situ electrostatic doping. The ribbon width and carrier doping dependences of graphene plasmon frequency demonstrate power-law behavior characteristic of 2-dimensional massless Dirac electrons. The plasmon resonances have remarkably large oscillator strengths, resulting in prominent room-temp. optical absorption peaks. In comparison, plasmon absorption in a conventional 2-dimensional electron gas was previously obsd. only at 4.2 K. The results represent a 1st look at light-plasmon coupling in graphene and point to potential graphene-based terahertz metamaterials.
- 8Kim, K.; Choi, J. Y.; Kim, T.; Cho, S. H.; Chung, H. J. A Role for Graphene in Silicon-Based Semiconductor Devices Nature 2011, 479, 338– 344[Crossref], [PubMed], [CAS], Google Scholar8https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3MXhsVyktbzL&md5=c3eb28d6fab1a2c3d7b37a1b7c2ea5dbA role for graphene in silicon-based semiconductor devicesKim, Kinam; Choi, Jae-Young; Kim, Taek; Cho, Seong-Ho; Chung, Hyun-JongNature (London, United Kingdom) (2011), 479 (7373), 338-344CODEN: NATUAS; ISSN:0028-0836. (Nature Publishing Group)A review. As silicon-based electronics approach the limit of improvements to performance and capacity through dimensional scaling, attention in the semiconductor field has turned to graphene, a single layer of carbon atoms arranged in a honeycomb lattice. Its high mobility of charge carriers (electrons and holes) could lead to its use in the next generation of high-performance devices. Graphene is unlikely to replace silicon completely, however, because of the poor on/off current ratio resulting from its zero bandgap. But it could be used to improve silicon-based devices, in particular in high-speed electronics and optical modulators.
- 9Bunch, J. S.; van der Zande, A. M.; Verbridge, S. S.; Frank, I. W.; Tanenbaum, D. M.; Parpia, J. M.; Craighead, H. G.; McEuen, P. L. Electromechanical Resonators from Graphene Sheets Science 2007, 315, 490– 493[Crossref], [PubMed], [CAS], Google Scholar9https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2sXotFCjtw%253D%253D&md5=f859c3843b1c4165e3dce8c5ffe64eafElectromechanical Resonators from Graphene SheetsBunch, J. Scott; van der Zande, Arend M.; Verbridge, Scott S.; Frank, Ian W.; Tanenbaum, David M.; Parpia, Jeevak M.; Craighead, Harold G.; McEuen, Paul L.Science (Washington, DC, United States) (2007), 315 (5811), 490-493CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)Nanoelectromech. systems were fabricated from single- and multilayer graphene sheets by mech. exfoliating thin sheets from graphite over trenches in silicon oxide. Vibrations with fundamental resonant frequencies in the megahertz range are actuated either optically or elec. and detected optically by interferometry. The authors demonstrate room-temp. charge sensitivities down to 8 × 10-4 electrons per root hertz. The thinnest resonator consists of a single suspended layer of atoms and represents the ultimate limit of two-dimensional nanoelectromech. systems.
- 10Kim, K. S.; Zhao, Y.; Jang, H.; Lee, S. Y.; Kim, J. M.; Kim, K. S.; Ahn, J.-H.; Kim, P.; Choi, J.-Y.; Hong, B. H. Large-Scale Pattern Growth of Graphene Films for Stretchable Transparent Electrodes Nature 2009, 457, 706– 710[Crossref], [PubMed], [CAS], Google Scholar10https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1MXht1ehtL4%253D&md5=0eef5b83d20b2e74add31eb1aa19337eLarge-scale pattern growth of graphene films for stretchable transparent electrodesKim, Keun Soo; Zhao, Yue; Jang, Houk; Lee, Sang Yoon; Kim, Jong Min; Kim, Kwang S.; Ahn, Jong-Hyun; Kim, Philip; Choi, Jae-Young; Hong, Byung HeeNature (London, United Kingdom) (2009), 457 (7230), 706-710CODEN: NATUAS; ISSN:0028-0836. (Nature Publishing Group)Problems assocd. with large-scale pattern growth of graphene constitute one of the main obstacles to using this material in device applications. Recently, macroscopic-scale graphene films were prepd. by two-dimensional assembly of graphene sheets chem. derived from graphite crystals and graphene oxides. However, the sheet resistance of these films was found to be much larger than theor. expected values. Here we report the direct synthesis of large-scale graphene films using chem. vapor deposition on thin nickel layers, and present two different methods of patterning the films and transferring them to arbitrary substrates. The transferred graphene films show very low sheet resistance of ∼280 Ω per square, with ∼80% optical transparency. At low temps., the monolayers transferred to silicon dioxide substrates show electron mobility greater than 3,700 cm2 V-1 s-1 and exhibit the half-integer quantum Hall effect, implying that the quality of graphene grown by chem. vapor deposition is as high as mech. cleaved graphene. Employing the outstanding mech. properties of graphene, we also demonstrate the macroscopic use of these highly conducting and transparent electrodes in flexible, stretchable, foldable electronics.
- 11Leonard, F.; Talin, A. A. Electrical Contacts to One- and Two-Dimensional Nanomaterials Nat. Nanotechnol. 2011, 6, 773– 783[Crossref], [PubMed], [CAS], Google Scholar11https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3MXhsFeitLvM&md5=8e101a55da714164674e8b7893bb980fElectrical contacts to one- and two-dimensional nanomaterialsLeonard, Francois; Talin, A. AlecNature Nanotechnology (2011), 6 (12), 773-783CODEN: NNAABX; ISSN:1748-3387. (Nature Publishing Group)A review. Existing models of elec. contacts are often inapplicable at the nanoscale because there are significant differences between nanostructures and bulk materials arising from unique geometries and electrostatics. In this Review, we discuss the physics and materials science of elec. contacts to carbon nanotubes, semiconductor nanowires and graphene, and outline the main research and development challenges in the field. We also include a case study of gold contacts to germanium nanowires to illustrate these concepts.
- 12Lee, H.; Heo, K.; Park, J.; Park, Y.; Noh, S.; Kim, K. S.; Lee, C.; Hong, B. H.; Jian, J.; Hong, S. Graphene-nanowire Hybrid Structures for High-Performance Photoconductive Devices J.Mater. Chem. 2012, 22, 8372– 8376Google ScholarThere is no corresponding record for this reference.
- 13Zan, R.; Bangert, U.; Ramasse, Q.; Novoselov, K. S. Interaction of Metals with Suspended Graphene Observed by Transmission Electron Microscopy J. Phys. Chem. Lett. 2012, 3, 953– 958[ACS Full Text
], [CAS], Google Scholar13https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38XjsVSrtrk%253D&md5=099c8807063ba5740c240573933d42f9Interaction of Metals with Suspended Graphene Observed by Transmission Electron MicroscopyZan, Recep; Bangert, Ursel; Ramasse, Quentin; Novoselov, Konstantin S.Journal of Physical Chemistry Letters (2012), 3 (7), 953-958CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)A review. In this Perspective, the authors present an overview of how different metals interface with suspended graphene, providing a closer look into the metal-graphene interaction by employing high-resoln. TEM, esp. using high-angle dark field imaging. All studied metals favor sites on the omnipresent hydrocarbon surface contamination rather than on the clean graphene surface and present nonuniform distributions, which never result in continuous films but instead in clusters or nanocrystals, indicating a weak interaction between the metal and graphene. This behavior can be altered to some degree by surface pretreatment (hydrogenation) and high-temp. vacuum annealing. Graphene etching is obsd. in a scanning transmission electron microscope (STEM) under high vacuum and 60 kV electron beam acceleration voltage conditions for all metals, except for Au. This unusual metal-mediated etching sheds new light on the metal-graphene interaction; it might explain the obsd. higher frequency of cluster nucleation for certain transition metals and might have implications regarding controlled nanomanipulation, i.e., for self-assembly and sculpturing of future graphene-based devices. - 14Georgakilas, V.; Otyepka, M.; Bourlinos, A. B.; Chandra, V.; Kim, N.; Kemp, K. C.; Hobza, P.; Zboril, R.; Kim, K. S. Functionalization of Graphene: Covalent and Non-covalent Approaches, Derivatives and Applications Chem. Rev. 2012, 112, 6156– 6214[ACS Full Text
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- 16Chan, K. T.; Neaton, J. B.; Cohen, M. L. First-Principles Study of Metal Adatom Adsorption on Graphene Phys. Rev. B 2008, 77, 235430[Crossref], [CAS], Google Scholar16https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1cXot1yks7w%253D&md5=547ab53a0673aa18484a382ccedc6ba9First-principles study of metal adatom adsorption on grapheneChan, Kevin T.; Neaton, J. B.; Cohen, Marvin L.Physical Review B: Condensed Matter and Materials Physics (2008), 77 (23), 235430/1-235430/12CODEN: PRBMDO; ISSN:1098-0121. (American Physical Society)The adsorption of 12 different metal adatoms on graphene is studied using first-principles d.-functional theory with the generalized gradient approxn. The adsorption energy, geometry, d. of states (DOS), dipole moment, and work function of each adatom-graphene system are calcd. For the adatoms studied from groups I-III of the Periodic Table, the results are consistent with ionic bonding, and the adsorption is characterized by minimal change in the graphene electronic states and large charge transfer. For transition, noble, and group IV metals, the calcns. are consistent with covalent bonding, and the adsorption is characterized by strong hybridization between adatom and graphene electronic states. For ionically bonded adatoms, the charge transfer is calcd. quant. using 2 methods, one based on the DOS and the other based on the real-space-charge d. A variation in dipole moments and work-function shifts across the different adatoms is obsd. In particular, the work-function shift shows a general correlation with the induced interfacial dipole of the adatom-graphene system and the ionization potential of the isolated atom.
- 17Giovannetti, G.; Khomyakov, P. A.; Brocks, G.; Karpan, V. M.; van den Brink, J.; Kelly, P. J. Doping Graphene with Metal Contacts Phys. Rev. Lett. 2008, 101, 026803[Crossref], [PubMed], [CAS], Google Scholar17https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1cXosVynt7w%253D&md5=ecd4c2578fa5cf738e716843224ecf10Doping graphene with metal contactsGiovannetti, G.; Khomyakov, P. A.; Brocks, G.; Karpan, V. M.; van den Brink, J.; Kelly, P. J.Physical Review Letters (2008), 101 (2), 026803/1-026803/4CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)Making devices with graphene necessarily involves making contacts with metals. We use d. functional theory to study how graphene is doped by adsorption on metal substrates and find that weak bonding on Al, Ag, Cu, Au, and Pt, while preserving its unique electronic structure, can still shift the Fermi level with respect to the conical point by ∼0.5 eV. At equil. sepns., the crossover from p-type to n-type doping occurs for a metal work function of ∼5.4 eV, a value much larger than the graphene work function of 4.5 eV. The numerical results for the Fermi level shift in graphene are described very well by a simple anal. model which characterizes the metal solely in terms of its work function, greatly extending their applicability.
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- 19Khomyakov, P. A.; Giovannetti, G.; Rusu, P. C.; Brocks, G.; van den Brink, J.; Kelly, P. J. First-Principles Study of the Interaction and Charge Transfer between Graphene and Metals Phys. Rev. B 2009, 79, 195425[Crossref], [CAS], Google Scholar19https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1MXmvF2rtbk%253D&md5=30520d6c0154305b51afd483e991ad25First-principles study of the interaction and charge transfer between graphene and metalsKhomyakov, P. A.; Giovannetti, G.; Rusu, P. C.; Brocks, G.; van den Brink, J.; Kelly, P. J.Physical Review B: Condensed Matter and Materials Physics (2009), 79 (19), 195425/1-195425/12CODEN: PRBMDO; ISSN:1098-0121. (American Physical Society)Measuring the transport of electrons through a graphene sheet necessarily involves contacting it with metal electrodes. The authors study the adsorption of graphene on metal substrates using 1st-principles calcns. at the level of d.-functional theory. The bonding of graphene to Al, Ag, Cu, Au, and Pt (111) surfaces is so weak that its unique ultrarelativistic electronic structure is preserved. The interaction does, however, lead to a charge transfer that shifts the Fermi level by up to 0.5 eV with respect to the conical points. The crossover from p-type to n-type doping occurs for a metal with a work function ∼5.4 eV, a value much larger than the work function of free-standing graphene, 4.5 eV. The authors develop a simple anal. model that describes the Fermi-level shift in graphene in terms of the metal substrate work function. Graphene interacts with and binds more strongly to Co, Ni, Pd, and Ti. This chemisorption involves hybridization between graphene pz states and metal d states that opens a band gap in graphene, and reduces its work function considerably. The supported graphene is effectively n-type doped because in a current-in-plane device geometry the work-function lowering will lead to electrons being transferred to the unsupported part of the graphene sheet.
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- 22Granatier, J.; Lazar, P.; Otyepka, M.; Hobza, P. The Nature of the Binding of Au, Ag, and Pd to Benzene, Coronene, and Graphene: From Benchmark CCSD(T) Calculations to Plane-Wave DFT Calculations J. Chem. Theory Comput. 2011, 7, 3743– 3755[ACS Full Text
], [CAS], Google Scholar22https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3MXhtlaqtr3I&md5=8509d55dff8de47d9912a0a48fe20833The Nature of the Binding of Au, Ag, and Pd to Benzene, Coronene, and Graphene: From Benchmark CCSD(T) Calculations to Plane-Wave DFT CalculationsGranatier, Jaroslav; Lazar, Petr; Otyepka, Michal; Hobza, PavelJournal of Chemical Theory and Computation (2011), 7 (11), 3743-3755CODEN: JCTCCE; ISSN:1549-9618. (American Chemical Society)The adsorption of Ag, Au, and Pd atoms on benzene, coronene, and graphene has been studied using post Hartree-Fock wave function theory (CCSD(T), MP2) and d. functional theory (M06-2X, DFT-D3, PBE, vdW-DF) methods. The CCSD(T) benchmark binding energies for benzene-M (M = Pd, Au, Ag) complexes are 19.7, 4.2, and 2.3 kcal/mol, resp. We found that the nature of binding of the three metals is different: while silver binds predominantly through dispersion interactions, the binding of palladium has a covalent character, and the binding of gold involves a subtle combination of charge transfer and dispersion interactions as well as relativistic effects. We demonstrate that the CCSD(T) benchmark binding energies for benzene-M complexes can be reproduced in plane-wave d. functional theory calcns. by including a fraction of the exact exchange and a nonempirical van der Waals correction (EE+vdW). Applying the EE+vdW method, we obtained binding energies for the graphene-M (M = Pd, Au, Ag) complexes of 17.4, 5.6, and 4.3 kcal/mol, resp. The trends in binding energies found for the benzene-M complexes correspond to those in coronene and graphene complexes. DFT methods that use empirical corrections to account for the effects of vdW interactions significantly overestimate binding energies in some of the studied systems. - 23Vanin, M.; Mortensen, J. J.; Kelkkanen, A. K.; Garcia-Lastra, J. M.; Thygesen, K. S.; Jacobsen, K. W. Graphene on Metals: A van der Waals Density Functional Study Phys. Rev. B 2010, 81, 081408Google ScholarThere is no corresponding record for this reference.
- 24Olsen, T.; Yan, J.; Mortensen, J. J.; Thygesen, K. S. Dispersive and Covalent Interactions between Graphene and Metal Surfaces from the Random Phase Approximation Phys. Rev. Lett. 2011, 107, 156401[Crossref], [PubMed], [CAS], Google Scholar24https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3MXhsVansbfN&md5=9f45b6c3509ae089bb4b8c07c6e1d844Dispersive and covalent interactions between graphene and metal surfaces from the random phase approximationOlsen, Thomas; Yan, Jun; Mortensen, Jens J.; Thygesen, Kristian S.Physical Review Letters (2011), 107 (15), 156401/1-156401/5CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)We calc. the potential energy surfaces for graphene adsorbed on Cu(111), Ni(111), and Co(0001) using d. functional theory and the RPA (RPA). For these adsorption systems covalent and dispersive interactions are equally important and while commonly used approxns. for exchange-correlation functionals give inadequate descriptions of either van der Waals or chem. bonds, RPA accounts accurately for both. It is found that the adsorption is a delicate competition between a weak chemisorption min. close to the surface and a physisorption min. further from the surface.
- 25Venugopal, A.; Colombo, L.; Vogel, E. M. Contact Resistance in Few and Multilayer Graphene Devices Appl. Phys. Lett. 2010, 96, 013512Google ScholarThere is no corresponding record for this reference.
- 26Pi, K.; McCreary, K. M.; Bao, W.; Han, W.; Chiang, Y. F.; Li, Y.; Tsai, S. W.; Lau, C. N.; Kawakami, R. K. Electronic Doping and Scattering by Transition Metals on Graphene Phys. Rev. B 2009, 80, 075406Google ScholarThere is no corresponding record for this reference.
- 27Schimka, L.; Harl, J.; Stroppa, A.; Gruneis, A.; Marsman, M.; Mittendorfer, F.; Kresse, G. Accurate Surface and Adsorption Energies from Many-Body Perturbation Theory Nat. Mater. 2010, 9, 741– 744[Crossref], [PubMed], [CAS], Google Scholar27https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXhtVGlsr%252FK&md5=cc1717ff227c13a08e77b89f66a1b19dAccurate surface and adsorption energies from many-body perturbation theorySchimka, L.; Harl, J.; Stroppa, A.; Grueneis, A.; Marsman, M.; Mittendorfer, F.; Kresse, G.Nature Materials (2010), 9 (9), 741-744CODEN: NMAACR; ISSN:1476-1122. (Nature Publishing Group)Kohn-Sham d. functional theory is the workhorse computational method in materials and surface science. Unfortunately, most semilocal d. functionals predict surfaces to be more stable than they are exptl. Naively, we would expect that consequently adsorption energies on surfaces are too small as well, but the contrary is often found: chemisorption energies are usually overestimated. Modifying the functional improves either the adsorption energy or the surface energy but always worsens the other aspect. This suggests that semilocal d. functionals possess a fundamental flaw that is difficult to cure, and alternative methods are urgently needed. Here we show that a computationally fairly efficient many-electron approach, the RPA to the correlation energy, resolves this dilemma and yields at the same time excellent lattice consts., surface energies and adsorption energies for and on transition-metal surfaces.
- 28Grimme, S. Density Functional Theory with London Dispersion Corrections WIREs Comput. Mol. Sci. 2011, 1, 211– 228[Crossref], [CAS], Google Scholar28https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3MXksVGlu70%253D&md5=f24d3bf3624d506052109c1e9093ef6bDensity functional theory with london dispersion correctionsGrimme, StefanWiley Interdisciplinary Reviews: Computational Molecular Science (2011), 1 (2), 211-228CODEN: WIRCAH; ISSN:1759-0884. (Wiley-Blackwell)A review. Dispersion corrections to std. Kohn-Sham d. functional theory (DFT) are reviewed. The focus is on computationally efficient methods for large systems that do not depend on virtual orbitals or rely on sepd. fragments. The recommended approaches (van der Waals d. functional and DFT-D) are asymptotically correct and can be used in combination with std. or slightly modified (short-range) exchange-correlation functionals. The importance of the dispersion energy in intramol. cases (conformational problems and thermochem.) is highlighted.
- 29Cramer, C. J.; Truhlar, D. G. Density Functional Theory for Transition Metals and Transition Metal Chemistry Phys. Chem. Chem. Phys. 2009, 11, 10757– 10816[Crossref], [PubMed], [CAS], Google Scholar29https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1MXhsVentrfK&md5=3bb9a3202e5d1493390a1ad863f60c4cDensity functional theory for transition metals and transition metal chemistryCramer, Christopher J.; Truhlar, Donald G.Physical Chemistry Chemical Physics (2009), 11 (46), 10757-10816CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)A review. We introduce d. functional theory and review recent progress in its application to transition metal chem. Topics covered include local, meta, hybrid, hybrid meta, and range-sepd. functionals, band theory, software, validation tests, and applications to spin states, magnetic exchange coupling, spectra, structure, reactivity, and catalysis, including mols., clusters, nanoparticles, surfaces, and solids.
- 30Dong, M.; Sahin, O. A Nanomechanical Interface to Rapid Single-Molecule Interactions Nat. Commun. 2011, 2, 247[Crossref], [PubMed], [CAS], Google Scholar30https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BC3M3ovV2lsQ%253D%253D&md5=0f55dfc9dc55ef373897caf805720237A nanomechanical interface to rapid single-molecule interactionsDong Mingdong; Sahin OzgurNature communications (2011), 2 (), 247 ISSN:.Single-molecule techniques provide opportunities for molecularly precise imaging, manipulation, assembly and biophysical studies. Owing to the kinetics of bond rupture processes, rapid single-molecule measurements can reveal novel bond rupture mechanisms, probe single-molecule events with short lifetimes and enhance the interaction forces supplied by single molecules. Rapid measurements will also increase throughput necessary for technological use of single-molecule techniques. Here we report a nanomechanical sensor that allows single-molecule force spectroscopy on the previously unexplored microsecond timescale. We probed bond lifetimes around 5 μs and observed significant enhancements in molecular interaction forces. Our loading-rate-dependent measurements provide experimental evidence for an additional energy barrier in the biotin-streptavidin complex. We also demonstrate quantitative mapping of rapid single-molecule interactions with high spatial resolution. This nanomechanical interface may allow studies of molecular processes with short lifetimes and development of novel biological imaging, single-molecule manipulation and assembly technologies.
- 31Dong, M. D.; Husale, S.; Sahin, O. Determination of Protein Structural Flexibility by Microsecond Force Spectroscopy Nat. Nanotechnol. 2009, 4, 514– 517[Crossref], [PubMed], [CAS], Google Scholar31https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1MXpsFSisbY%253D&md5=10070f6f4aaf3a9a87ad7c36650d3d6fDetermination of protein structural flexibility by microsecond force spectroscopyDong, Mingdong; Husale, Sudhir; Sahin, OzgurNature Nanotechnology (2009), 4 (8), 514-517CODEN: NNAABX; ISSN:1748-3387. (Nature Publishing Group)Proteins are dynamic mol. machines having structural flexibility that allows conformational changes. Current methods for the detn. of protein flexibility rely mainly on the measurement of thermal fluctuations and disorder in protein conformations and tend to be exptl. challenging. Moreover, they reflect at. fluctuations on picosecond timescales, whereas the large conformational changes in proteins typically happen on micro- to millisecond timescales. Here, the authors directly det. the flexibility of bacteriorhodopsin - a protein that uses the energy in light to move protons across cell membranes - at the microsecond timescale by monitoring force-induced deformations across the protein structure with a technique based on at. force microscopy. In contrast to existing methods, the deformations the authors measure involve a collective response of protein residues and operate under physiol. relevant conditions with native proteins.
- 32Rico, F.; Su, C.; Scheuring, S. Mechanical Mapping of Single Membrane Proteins at Submolecular Resolution Nano Lett. 2011, 11, 3983– 3986[ACS Full Text
], [CAS], Google Scholar32https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3MXpslajsbY%253D&md5=77c1ae451b8b9508dc1d82fe551e675fMechanical Mapping of Single Membrane Proteins at Submolecular ResolutionRico, Felix; Su, Chan-Min; Scheuring, SimonNano Letters (2011), 11 (9), 3983-3986CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)The capacity of proteins to carry out different functions is related to their ability to undergo conformation changes, which depends on the flexibility of protein structures. In this work, the authors applied a novel imaging mode based on indentation force spectroscopy to map quant. the flexibility of individual membrane proteins in their native, folded state at unprecedented submol. resoln. The authors' results enabled them to correlate protein flexibility with crystal structure and showed that α-helixes are stiff structures that may contribute importantly to the mech. stability of membrane proteins, while interhelical loops appeared more flexible, allowing conformational changes related to function. - 33Medalsy, I.; Hensen, U.; Muller, D. J. Imaging and Quantifying Chemical and Physical Properties of Native Proteins at Molecular Resolution by Force-Volume AFM Angew. Chem., Int. Ed. 2011, 50, 12103– 12108[Crossref], [CAS], Google Scholar33https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3MXhtlahsbvP&md5=746eae8ed4f0a83ddf0202d602194df9Imaging and Quantifying Chemical and Physical Properties of Native Proteins at Molecular Resolution by Force-Volume AFMMedalsy, Izhar; Hensen, Ulf; Muller, Daniel J.Angewandte Chemie, International Edition (2011), 50 (50), 12103-12108, S12103/1-S12103/9CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)The authors introduce high-resoln. force-vol. AFM imaging of the native purple membrane (PM) from Halobacterium salinarum. PM consists of the light-driven proton-pump bacteriorhodopsin (BR) and lipids. During the photocycle BR goes through conformational changes and creates a proton gradient across the cellular membrane that is used to power cellular processes. Measurements show that proton transfer along the PM surface is much faster than proton exchange to the bulk water. This unique property that kinetically traps protons is facilitated by the asym. phys. and chem. properties of PM surfaces. High-resoln. (∼0.5 nm) contact-mode AFM of BR revealed extracellular polypeptide loops changing their conformation with the membrane protein assembly and cytoplasmic loops undergoing force-induced conformational changes. Using force-vol. AFM the authors imaged PM adsorbed onto freshly cleaved mica in buffer soln. For every pixel of the AFM topog. the authors recorded a F-D curve approaching and retracting AFM tip and PM. The maximal force (trigger force) applied in these approach-retract cycles was limited to 100 pN. When reaching the trigger force the distance travelled by tip and sample was taken to reconstruct the topog.
- 34Lantz, M. A.; Hug, H. J.; Hoffmann, R.; van Schendel, P. J. A.; Kappenberger, P.; Martin, S.; Baratoff, A.; Guntherodt, H. J. Quantitative Measurement of Short-Range Chemical Bonding Forces Science 2001, 291, 2580– 2583[Crossref], [PubMed], [CAS], Google Scholar34https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3MXisFekt7Y%253D&md5=55f89d9168d05324b22ccd7d8087896aQuantitative measurement of short-range chemical bonding forcesLantz, M. A.; Hug, H. J.; Hoffmann, R.; van Schendel, P. J. A.; Kappenberger, P.; Martin, S.; Baratoff, A.; Guntherodt, H.-J.Science (Washington, DC, United States) (2001), 291 (5513), 2580-2583CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)We report direct force measurements of the formation of a chem. bond. The expts. were performed using a low-temp. at. force microscope, a silicon tip, and a silicon (111) 7x7 surface. The measured site-dependent attractive short-range force, which attains a max. value of 2.1 nanonewtons, is in good agreement with first-principles calcns. of an incipient covalent bond in an analogous model system. The resoln. was sufficient to distinguish differences in the interaction potential between inequivalent adatoms, demonstrating the ability of at. force microscopy to provide quant., at.-scale information on surface chem. reactivity.
- 35Hoffmann, R.; Kantorovich, L. N.; Baratoff, A.; Hug, H. J.; Guntherodt, H. J. Sublattice Identification in Scanning Force Microscopy on Alkali Halide Surfaces Phys. Rev. Lett. 2004, 92, 146103Google ScholarThere is no corresponding record for this reference.
- 36Sugimoto, Y.; Pou, P.; Abe, M.; Jelinek, P.; Perez, R.; Morita, S.; Custance, O. Chemical Identification of Individual Surface Atoms by Atomic Force Microscopy Nature 2007, 446, 64– 67[Crossref], [PubMed], [CAS], Google Scholar36https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2sXit1arsL0%253D&md5=5f7d3086b09adac56614ef10214340b3Chemical identification of individual surface atoms by atomic force microscopySugimoto, Yoshiaki; Pou, Pablo; Abe, Masayuki; Jelinek, Pavel; Perez, Ruben; Morita, Seizo; Custance, OscarNature (London, United Kingdom) (2007), 446 (7131), 64-67CODEN: NATUAS; ISSN:0028-0836. (Nature Publishing Group)Scanning probe microscopy is a versatile and powerful method that uses sharp tips to image, measure and manipulate matter at surfaces with at. resoln. At cryogenic temps., scanning probe microscopy can even provide electron tunnelling spectra that serve as fingerprints of the vibrational properties of adsorbed mols. and of the electronic properties of magnetic impurity atoms, thereby allowing chem. identification. But in many instances, and particularly for insulating systems, detg. the exact chem. compn. of surfaces or nanostructures remains a considerable challenge. In principle, dynamic force microscopy should make it possible to overcome this problem: it can image insulator, semiconductor and metal surfaces with true at. resoln., by detecting and precisely measuring the short-range forces that arise with the onset of chem. bonding between the tip and surface atoms and that depend sensitively on the chem. identity of the atoms involved. Here the authors report precise measurements of such short-range chem. forces, and show that their dependence on the force microscope tip used can be overcome through a normalization procedure. This allows one to use the chem. force measurements as the basis for at. recognition, even at room temp. The authors illustrate the performance of this approach by imaging the surface of a particularly challenging alloy system and successfully identifying the 3 constituent at. species Si, Sn and lead, even though these exhibit very similar chem. properties and identical surface position preferences that render any discrimination attempt based on topog. measurements impossible.
- 37Yi, H.-B.; Diefenbach, M.; Choi, Y. C.; Lee, E. C.; Lee, H. M.; Hong, B. H.; Kim, K. S. Interactions of Neutral and Cationic Transition Metals with the Redox System of Hydroquinone and Quinone: Theoretical Characterization of the Binding Topologies, and Implications for the Formation of Nanomaterials Chem.—Eur. J. 2006, 12, 4885– 4892[Crossref], [PubMed], [CAS], Google Scholar37https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD28Xmtlyjt7o%253D&md5=f232b2c7a9ce88c5fd4999222da54ec6Interactions of neutral and cationic transition metals with the redox system of hydroquinone and quinone: theoretical characterization of the binding topologies, and implications for the formation of nanomaterialsYi, Hai-Bo; Diefenbach, Martin; Choi, Young Cheol; Lee, Eun Cheol; Lee, Han Myoung; Hong, Byung Hee; Kim, Kwang S.Chemistry--A European Journal (2006), 12 (18), 4885-4892CODEN: CEUJED; ISSN:0947-6539. (Wiley-VCH Verlag GmbH & Co. KGaA)To understand the self-assembly process of the transition metal (TM) nanoclusters and nanowires self-synthesized by hydroquinone (HQ) and calix[4]hydroquinone (CHQ) by electrochem. redox processes, we have investigated the binding sites of HQ for the transition-metal cations TMn+ = Ag+, Au+, Pd2+, Pt2+, and Hg2+ and those of quinone (Q) for the reduced neutral metals TM0, using ab initio calcns. For comparison, TM0-HQ and TMn+-Q interactions, as well as the cases for Na+ and Cu+ (which do not take part in self-synthesis by CHQ) are also included. In general, TM-ligand coordination is controlled by symmetry constraints imposed on the resp. orbital interactions. Calcns. predict that, due to synergetic interactions, silver and gold are very efficient metals for one-dimensional (1D) nanowire formation in the self-assembly process, platinum and mercury favor both nanowire/nanorod and thin film formation, while palladium favors two-dimensional (2D) thin film formation.
- 38Granatier, J.; Lazar, P.; Prucek, R.; Safarova, K.; Zboril, R.; Otyepka, M.; Hobza, P. Interaction of Graphene and Arenes with Noble Metals J. Phys. Chem. C 2012, 116, 14151– 14162
- 39Blonski, P.; Dennler, S.; Hafner, J. Strong Spin-orbit Effects in Small Pt Clusters: Geometric Structure, Magnetic Isomers and Anisotropy J. Chem. Phys. 2011, 134, 034107Google ScholarThere is no corresponding record for this reference.
- 40Cleveland, J. P.; Manne, S.; Bocek, D.; Hansma, P. K. A Nondestructive Method for Determining the Spring Constant of Cantilevers for Scanning Force Microscopy Rew. Sci. Instrum. 1993, 64, 403– 405[Crossref], [CAS], Google Scholar40https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK3sXhvFyqtbc%253D&md5=bd8bb6ecf4280918129bf1e0ef76cf79A nondestructive method for determining the spring constant of cantilevers for scanning force microscopyCleveland, J. P.; Manne, S.; Bocek, D.; Hansma, P. K.Review of Scientific Instruments (1993), 64 (2), 403-5CODEN: RSINAK; ISSN:0034-6748.The spring const. of microfabricated cantilevers used in scanning force microscopy (SFM) can be detd. by measuring their resonant frequencies before and after adding small end masses. These masses adhere naturally and can be removed easily before using the cantilever for SFM, making the method nondestructive. The obsd. variability in spring const. (almost an order of magnitude for a single type of cantilever) necessitates calibration of individual cantilevers in work where precise knowledge of forces is required. The measurements also revealed that the spring const. scales with the cube of the unloaded resonant frequency, providing a simple way to est. the spring const. for less precise work.
- 41Pou, P.; Ghasemi, S. A.; Jelinek, P.; Lenosky, T.; Goedecker, S.; Perez, R. Structure and Stability of Semiconductor Tip Apexes for Atomic Force Microscopy Nanotechnology 2009, 20, 264015Google ScholarThere is no corresponding record for this reference.
- 42Blochl, P. E. Projector Augmented-Wave Method Phys. Rev. B 1994, 50, 17953– 17979[Crossref], [PubMed], [CAS], Google Scholar42https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BC2sfjslSntA%253D%253D&md5=1853d67af808af2edab58beaab5d3051Projector augmented-wave methodBlochlPhysical review. B, Condensed matter (1994), 50 (24), 17953-17979 ISSN:0163-1829.There is no expanded citation for this reference.
- 43Kresse, G.; Joubert, D. From Ultrasoft Pseudopotentials to the Projector Augmented-Wave Method Phys. Rev. B 1999, 59, 1758– 1775[Crossref], [CAS], Google Scholar43https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK1MXkt12nug%253D%253D&md5=78a73e92a93f995982fc481715729b14From ultrasoft pseudopotentials to the projector augmented-wave methodKresse, G.; Joubert, D.Physical Review B: Condensed Matter and Materials Physics (1999), 59 (3), 1758-1775CODEN: PRBMDO; ISSN:0163-1829. (American Physical Society)The formal relationship between ultrasoft (US) Vanderbilt-type pseudopotentials and Blochl's projector augmented wave (PAW) method is derived. The total energy functional for US pseudopotentials can be obtained by linearization of two terms in a slightly modified PAW total energy functional. The Hamilton operator, the forces, and the stress tensor are derived for this modified PAW functional. A simple way to implement the PAW method in existing plane-wave codes supporting US pseudopotentials is pointed out. In addn., crit. tests are presented to compare the accuracy and efficiency of the PAW and the US pseudopotential method with relaxed-core all-electron methods. These tests include small mols. (H2, H2O, Li2, N2, F2, BF3, SiF4) and several bulk systems (diamond, Si, V, Li, Ca, CaF2, Fe, Co, Ni). Particular attention is paid to the bulk properties and magnetic energies of Fe, Co, and Ni.
- 44Dion, M.; Rydberg, H.; Schroder, E.; Langreth, D. C.; Lundqvist, B. I. Van der Waals Density Functional for General Geometries Phys. Rev. Lett. 2004, 92, 246401[Crossref], [PubMed], [CAS], Google Scholar44https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2cXltVerur4%253D&md5=abbf50b023000f126ba66af15c786583Van der Waals Density Functional for General GeometriesDion, M.; Rydberg, H.; Schroeder, E.; Langreth, D. C.; Lundqvist, B. I.Physical Review Letters (2004), 92 (24), 246401/1-246401/4CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)A scheme within d. functional theory is proposed that provides a practical way to generalize to unrestricted geometries the method applied with some success to layered geometries [H. Rydberg et al., Phys. Rev. Lett. 91, 126402 (2003)]. It includes van der Waals forces in a seamless fashion. By expansion to second order in a carefully chosen quantity contained in the long-range part of the correlation functional, the nonlocal correlations are expressed in terms of a d.-d. interaction formula. It contains a relatively simple parametrized kernel, with parameters detd. by the local d. and its gradient. The proposed functional is applied to rare gas and benzene dimers, where it is shown to give a realistic description.
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Supporting Information
Supporting Information
ARTICLE SECTIONSTheSupporting Information contains SEM images and EDS spectra of AFM tips (Supplementary Figures 1–6), interaction energies calculated for various positions on graphene (Supplementary Table 1) and singlet states (Supplementary Table 2) and scalar relativistic Au4 (Supplementary Table 3), typical curves from dynamic AFM measurements (Supplementary Figure 7), and distributions of forces from AFM experiments (Supplementary Figures 8 and 9). This material is available free of charge via the Internet at http://pubs.acs.org.
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