76
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Lundgren E, Gustafson J, Mikkelsen A, Andersen JN, Stierle A, Dosch H, Todorova M, Rogal J, Reuter K, Scheffler M. Kinetic hindrance during the initial oxidation of Pd(100) at ambient pressures. PHYSICAL REVIEW LETTERS 2004; 92:046101. [PMID: 14995387 DOI: 10.1103/physrevlett.92.046101] [Citation(s) in RCA: 86] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/22/2003] [Indexed: 05/24/2023]
Abstract
The oxidation of the Pd(100) surface at oxygen pressures in the 10(-6) to 10(3) mbar range and temperatures up to 1000 K has been studied in situ by surface x-ray diffraction (SXRD). The results provide direct structural information on the phases present in the surface region and on the kinetics of the oxide formation. Depending on the (T,p) environmental conditions, we observe either a thin (sqrt[5]xsqrt[5])R27 degrees surface oxide or the growth of a rough, poorly ordered bulk oxide film of PdO predominantly with (001) orientation. By either comparison to the surface phase diagram from first-principles atomistic thermodynamics or by explicit time-resolved measurements we identify a strong kinetic hindrance to the bulk oxide formation even at temperatures as high as 675 K.
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77
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Güimil R, Beier M, Scheffler M, Rebscher H, Funk J, Wixmerten A, Baum M, Hermann C, Tahedl H, Moschel E, Obermeier F, Sommer I, Büchner D, Viehweger R, Burgmaier J, Stähler CF, Müller M, Stähler PF. Geniom technology--the benchtop array facility. NUCLEOSIDES NUCLEOTIDES & NUCLEIC ACIDS 2003; 22:1721-3. [PMID: 14565504 DOI: 10.1081/ncn-120023122] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
Febit AG develops an integrated benchtop instrument for in situ microarrays preparation, hybridization, readout and data analysis.
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78
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Pentcheva R, Fichthorn KA, Scheffler M, Bernhard T, Pfandzelter R, Winter H. Non-arrhenius behavior of the island density in metal heteroepitaxy: Co on Cu(001). PHYSICAL REVIEW LETTERS 2003; 90:076101. [PMID: 12633249 DOI: 10.1103/physrevlett.90.076101] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/12/2002] [Indexed: 05/24/2023]
Abstract
We present a combined theoretical and experimental study of island nucleation and growth in the deposition of Co on Cu(001)-a prototype for understanding heteroepitaxial growth involving intermixing. Experimentally, ion scattering is employed. Using density-functional theory, we obtain energy barriers for the various elementary processes and incorporate these into a kinetic Monte Carlo program to simulate the heteroepitaxial growth. Both the simulations and the experiments show a unique N-shape dependence of the island density on temperature that stems from the interplay and competition of the different processes involved.
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79
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Teo S, Scheffler M, Stirling D, Thomas S, Khetani V. A single-Dose, 2-Way Crossover, Bioequivalence Study of Dexmethylphenidate With and Without Food in Healthy Subjects. Clin Pharmacol Ther 2003. [DOI: 10.1016/s0009-9236(03)90489-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
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80
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Filippi C, Healy SB, Kratzer P, Pehlke E, Scheffler M. Quantum Monte Carlo calculations of H2 dissociation on Si(001). PHYSICAL REVIEW LETTERS 2002; 89:166102. [PMID: 12398737 DOI: 10.1103/physrevlett.89.166102] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/19/2002] [Indexed: 05/24/2023]
Abstract
The dissociative adsorption of H2 on the Si(001) surface is theoretically investigated for several reaction pathways using quantum Monte Carlo methods. Our reaction energies and barriers are at large variance with those obtained with commonly used approximate exchange-correlation density functionals. Our results for adsorption support recent experimental findings, while, for desorption, the calculations give barriers in excess of the presently accepted experimental value, pinpointing the role of coverage effects and desorption from steps.
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81
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Todorova M, Li WX, Ganduglia-Pirovano MV, Stampfl C, Reuter K, Scheffler M. Role of subsurface oxygen in oxide formation at transition metal surfaces. PHYSICAL REVIEW LETTERS 2002; 89:096103. [PMID: 12190418 DOI: 10.1103/physrevlett.89.096103] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/03/2001] [Indexed: 05/23/2023]
Abstract
We present a density-functional theory trend study addressing the incorporation of oxygen into the basal plane of the late 4d transition metals (TMs) from Ru to Ag. Occupation of subsurface sites is always connected with a significant distortion of the host lattice, rendering it initially less favorable than on-surface chemisorption. Penetration starts only after a critical coverage theta(c), which is lower for the softer metals towards the right of the TM series. The computed theta(c) are found to be very similar to those above which the bulk oxide phase becomes thermodynamically more stable, thus suggesting that the initial incorporation of O actuates the formation of a surface oxide on TM surfaces.
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82
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Kratzer P, Scheffler M. Reaction-limited island nucleation in molecular beam epitaxy of compound semiconductors. PHYSICAL REVIEW LETTERS 2002; 88:036102. [PMID: 11801074 DOI: 10.1103/physrevlett.88.036102] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/18/2001] [Indexed: 05/23/2023]
Abstract
Kinetic Monte Carlo simulations on the basis of rates derived from density-functional calculations are used to investigate the atomic processes in molecular beam epitaxy of GaAs. This approach puts us in a position to describe island nucleation and growth in all relevant atomistic detail by bridging the gap in length and time scales between the mesoscopic scale of growth morphology and the atomic scale. We observe a nonmonotonic dependence of the island density on growth temperature related to a reversible surface reaction of As2 with Ga adatoms.
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83
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Healy SB, Filippi C, Kratzer P, Penev E, Scheffler M. Role of electronic correlation in the Si(100) reconstruction: a quantum Monte Carlo study. PHYSICAL REVIEW LETTERS 2001; 87:016105. [PMID: 11461481 DOI: 10.1103/physrevlett.87.016105] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/21/2001] [Indexed: 05/23/2023]
Abstract
Recent low-temperature scanning tunneling experiments have questioned the generally accepted picture of buckled silicon dimers as the ground state reconstruction of the Si(100) surface, undermining the ability of density functional theory to accurately describe electronic correlations at surfaces. We present quantum Monte Carlo calculations on large cluster models of the surface, and conclude that buckling remains energetically favorable even when the present-day best treatment of electronic correlation is employed. The implications for experimental interpretation are discussed.
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84
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Dohmen R, Pichlmeier J, Petersen M, Wagner F, Scheffler M. Parallel FP-LAPW for distributed-memory machines. Comput Sci Eng 2001. [DOI: 10.1109/5992.931900] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
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85
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86
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Márquez J, Kratzer P, Geelhaar L, Jacobi K, Scheffler M. Atomic Structure of the Stoichiometric GaAs(114) Surface. PHYSICAL REVIEW LETTERS 2001; 86:115-118. [PMID: 11136107 DOI: 10.1103/physrevlett.86.115] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/06/2000] [Indexed: 05/23/2023]
Abstract
The stoichiometric GaAs(114) surface has been prepared using molecular beam epitaxy followed by annealing in ultrahigh vacuum. Based on in situ scanning tunneling microscopy measurements and first-principles electronic-structure calculations, we determine the surface reconstruction which we call alpha2(2x1). Contrary to what is expected for a high-index surface, it is surprisingly elementary. The (2x1) unit cell contains two As dimers and two rebonded Ga atoms. The surface energy is calculated as 53 meV/Å(2), which falls well within the range of low-index GaAs surface energies.
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87
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Schirmer OF, Scheffler M. Determination of deep donor binding energies from their g values. ACTA ACUST UNITED AC 2000. [DOI: 10.1088/0022-3719/15/21/001] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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88
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Feibelman PJ, Hammer B, Nørskov JK, Wagner F, Scheffler M, Stumpf R, Watwe R, Dumesic J. The CO/Pt(111) Puzzle. J Phys Chem B 2000. [DOI: 10.1021/jp002302t] [Citation(s) in RCA: 597] [Impact Index Per Article: 24.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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89
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Lee SH, Moritz W, Scheffler M. GaAs(001) surface under conditions of low As pressure: evidence for a novel surface geometry. PHYSICAL REVIEW LETTERS 2000; 85:3890-3893. [PMID: 11041953 DOI: 10.1103/physrevlett.85.3890] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/19/2000] [Indexed: 05/23/2023]
Abstract
Using density-functional theory we identify a new low-energy structure for GaAs(001) in an As-poor environment. The discovered geometry is qualitatively different from the usual surface-dimer based reconstructions of III-V semiconductor (001) surfaces. The stability of the new structure, which has a c(8x2) periodicity, is explained in terms of bond saturation and favorable electrostatic interactions between surface atoms. Simulated scanning tunneling microscopy images are in good agreement with experimental data, and a low-energy electron diffraction analysis supports the theoretical prediction.
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90
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Ebert P, Urban K, Aballe L, Chen CH, Horn K, Schwarz G, Neugebauer J, Scheffler M. Symmetric versus nonsymmetric structure of the phosphorus vacancy on InP(110). PHYSICAL REVIEW LETTERS 2000; 84:5816-5819. [PMID: 10991062 DOI: 10.1103/physrevlett.84.5816] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/30/1999] [Indexed: 05/23/2023]
Abstract
The atomic and electronic structure of positively charged P vacancies on InP(110) surfaces is determined by combining scanning tunneling microscopy, photoelectron spectroscopy, and density-functional theory calculations. The vacancy exhibits a nonsymmetric rebonded atomic configuration with a charge transfer level 0.75+/-0.1 eV above the valence band maximum. The scanning tunneling microscopy (STM) images show only a time average of two degenerate geometries, due to a thermal flip motion between the mirror configurations. This leads to an apparently symmetric STM image, although the ground state atomic structure is nonsymmetric.
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91
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Fichthorn KA, Scheffler M. Island nucleation in thin-film epitaxy: A first-principles investigation. PHYSICAL REVIEW LETTERS 2000; 84:5371-5374. [PMID: 10990946 DOI: 10.1103/physrevlett.84.5371] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/17/1999] [Indexed: 05/23/2023]
Abstract
We describe a theoretical study of the role of adsorbate interactions in island nucleation and growth, using Ag/Pt(111) heteroepitaxy as an example. From density-functional theory, we obtain the substrate-mediated Ag adatom pair interaction and we find that, past the short range, a repulsive ring is formed about the adatoms. The magnitude of the repulsion is comparable to the diffusion barrier. In kinetic Monte Carlo simulations, we find that the repulsive interactions lead to island densities over an order of magnitude larger than those predicted by nucleation theory and thus identify a severe limitation of its applicability.
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92
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Wang XG, Chaka A, Scheffler M. Effect of the environment on alpha-Al2O3 (0001) surface structures. PHYSICAL REVIEW LETTERS 2000; 84:3650-3653. [PMID: 11019168 DOI: 10.1103/physrevlett.84.3650] [Citation(s) in RCA: 113] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/30/1999] [Indexed: 05/23/2023]
Abstract
We report that calculating the Gibbs free energy of the alpha-Al2O3 (0001) surfaces in equilibrium with a realistic environment containing both oxygen and hydrogen species is essential for obtaining theoretical predictions consistent with experimental observations. Using density-functional theory we find that even under conditions of high oxygen partial pressure the metal-terminated surface is surprisingly stable. An oxygen-terminated alpha-Al2O3 (0001) surface becomes stable only if hydrogen is present on the surface. In addition, including hydrogen on the surface resolves discrepancies between previous theoretical work and experimental results with respect to the magnitude and direction of surface relaxations.
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93
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Bonn M, Funk S, Hess C, Denzler DN, Stampfl C, Scheffler M, Wolf M, Ertl G. Phonon- versus electron-mediated desorption and oxidation of CO on Ru(0001). Science 1999; 285:1042-5. [PMID: 10446045 DOI: 10.1126/science.285.5430.1042] [Citation(s) in RCA: 235] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
Heating of a ruthenium surface on which carbon monoxide and atomic oxygen are coadsorbed leads exclusively to desorption of carbon monoxide. In contrast, excitation with femtosecond infrared laser pulses enables also the formation of carbon dioxide. The desorption is caused by coupling of the adsorbate to the phonon bath of the ruthenium substrate, whereas the oxidation reaction is initiated by hot substrate electrons, as evidenced by the observed subpicosecond reaction dynamics and density functional calculations. The presence of this laser-induced reaction pathway allows elucidation of the microscopic mechanism and the dynamics of the carbon monoxide oxidation reaction.
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94
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Penev E, Kratzer P, Scheffler M. Effect of the cluster size in modeling the H2 desorption and dissociative adsorption on Si(001). J Chem Phys 1999. [DOI: 10.1063/1.478279] [Citation(s) in RCA: 143] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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95
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Harrison NM, Wang XG, Muscat J, Scheffler M. The influence of soft vibrational modes on our understanding of oxide surface structure. Faraday Discuss 1999. [DOI: 10.1039/a906386b] [Citation(s) in RCA: 99] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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96
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Stampfl C, Schwegmann S, Over H, Scheffler M, Ertl G. Structure and Stability of a High-Coverage (1 x 1) Oxygen Phase on Ru(0001). PHYSICAL REVIEW LETTERS 1996; 77:3371-3374. [PMID: 10062203 DOI: 10.1103/physrevlett.77.3371] [Citation(s) in RCA: 80] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
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97
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Moll N, Kley A, Pehlke E, Scheffler M. GaAs equilibrium crystal shape from first principles. PHYSICAL REVIEW. B, CONDENSED MATTER 1996; 54:8844-8855. [PMID: 9984566 DOI: 10.1103/physrevb.54.8844] [Citation(s) in RCA: 126] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/12/2023]
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98
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Wilke S, Cohen MH, Scheffler M. Local Isoelectronic Reactivity of Solid Surfaces. PHYSICAL REVIEW LETTERS 1996; 77:1560-1563. [PMID: 10063109 DOI: 10.1103/physrevlett.77.1560] [Citation(s) in RCA: 26] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
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99
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Yu BD, Scheffler M. Anisotropy of Growth of the Close-Packed Surfaces of Silver. PHYSICAL REVIEW LETTERS 1996; 77:1095-1098. [PMID: 10062989 DOI: 10.1103/physrevlett.77.1095] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
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100
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Stampfl C, Scheffler M. Theoretical study of O adlayers on Ru(0001). PHYSICAL REVIEW. B, CONDENSED MATTER 1996; 54:2868-2872. [PMID: 9986142 DOI: 10.1103/physrevb.54.2868] [Citation(s) in RCA: 102] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/12/2023]
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