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P Kratzer

Publications and source records attributed to P Kratzer.

9 recordsLinked to original sources
PubMed2004

Atomic structure of the GaAs(001)-c(4x4) surface: first-principles evidence for diversity of heterodimer motifs.

The GaAs(001)-c(4x4) surface was studied using ab initio atomistic thermodynamics based on density-functional theory calculations. We demonstrate that in a range of stoichiometries, between those of the conventional three As-dimer and the new three Ga-As-dimer models, there exists a diversity of atomic structures featuring Ga-As heterodimers. These results fully explain the experimental scanning tunneling microscopy images and are likely to be relevant also to the c(4x4)-reconstructed (001) surfaces of other III-V semiconductors.

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PubMed2002

Quantum Monte Carlo calculations of H2 dissociation on Si(001).

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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PubMed2002

Reaction-limited island nucleation in molecular beam epitaxy of compound semiconductors.

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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PubMed2001

Probing interface electronic structure with overlayer quantum-well resonances: Al/Si(111).

The dispersion of quantum-well resonances in ultrathin epitaxial Al films on Si(111) reveals energy- and wave vector-dependent reflection properties at the Al/Si interface. The substrate electronic structure strongly influences the phase shift of the electron waves upon reflection at the interface. Thus the details of the substrate electronic structure need to be taken into account for a complete analysis of metallic quantum-well resonances. Furthermore, the assumption of loss of parallel wave vector information upon reflection or transmission through a lattice-mismatched interface is challenged. The changes induced in the electronic structure of the overlayer can be used to probe the ground-state substrate band edges.

Journal Article↗
PubMed2001

Role of electronic correlation in the Si(100) reconstruction: a quantum Monte Carlo study.

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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PubMed2001

GaAs(2 5 11): a new stable surface within the stereographic triangle.

The atomic structure of GaAs(2 5 11), a hitherto unknown stable surface, has been determined by in situ scanning tunneling microscopy and first-principles electronic structure calculations. This orientation is located within the stereographic triangle, i.e., far away from all low-index surfaces. A low-energy ( 1x1) reconstruction containing arsenic dimers forms on the surface. The analysis of the surface structure shows that, for semiconductor surfaces, the gain in stability due to minimization of the number of dangling bonds is more important than the gain from rendering a semiconducting ground state.

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PubMed2001

Atomic Structure of the Stoichiometric GaAs(114) Surface.

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.

Journal Article↗
PubMed1985

Patients' expectations from renal grafting and transplantation outcome.

Prevailing reports on psychological prediction of renal graft integration are rare, mostly based on case studies. Focusing on patients' expectations from the transplantation process before grafting, we investigate the influence of psychological data and statements on the final transplantation results. In the whole group (n = 83) the attitude toward transplantation was very optimistic. Comparing the features of patients with successful graft outcome (n = 23) and graft failure or patient's death (n = 10) the latter group shows: lower scale values of optimistic attitude toward transplantation outcome, higher level of fear concerning surgical treatment, less willingness to agree preoperatively to second transplantation in case of first graft failure. Psychological data indicate a greater tendency toward more submissive, rigid, and depressive behavior. It is assumed that the patient's attitude and expectation on grafting is a part of the conditions influencing the final transplantation result. Further studies should prove this concept.

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