We have studied diffusion of Ge into subsurface layers of Si(100). Auger electron diffraction measurements show Ge in the fourth layer after submonolayer growth at temperatures as low as 500 degrees C. Density functional theory predictions of equilibrium Ge subsurface distributions are consistent with the measurements. We identify a surprisingly low energy pathway resulting from low interstitial formation energy in the third and fourth layers. Doping significantly affects the formation energy, suggesting that n-type doping may lead to sharper Si/Ge interfaces.

Reproducibility and reusability of research results is an important concern in scientific communication and science policy. A foundational element of reproducibility and reusability is the open and persistently available presentation of research data. However, many common approaches for primary data publication in use today do not achieve sufficient long-term robustness, openness, accessibility or uniformity. Nor do they permit comprehensive exploitation by modern Web technologies. This has led to several authoritative studies recommending uniform direct citation of data archived in persistent repositories. Data are to be considered as first-class scholarly objects, and treated similarly in many ways to cited and archived scientific and scholarly literature. Here we briefly review the most current and widely agreed set of principle-based recommendations for scholarly data citation, the Joint Declaration of Data Citation Principles (JDDCP). We then present a framework for operationalizing the JDDCP; and a set of initial recommendations on identifier schemes, identifier resolution behavior, required metadata elements, and best practices for realizing programmatic machine actionability of cited data. The main target audience for the common implementation guidelines in this article consists of publishers, scholarly organizations, and persistent data repositories, including technical staff members in these organizations. But ordinary researchers can also benefit from these recommendations. The guidance provided here is intended to help achieve widespread, uniform human and machine accessibility of deposited data, in support of significantly improved verification, validation, reproducibility and re-use of scholarly/scientific data.

In order to test the reliability of plane-wave and Gaussian-orbital based DFT methods for calculating reaction energies and activation barriers, detailed calculations are performed for several reactions involving gas phase silanes and a simple model of H 2 desorption from the Si͑100͒2ϫ1 surface. This study is motivated in particular by apparent discrepancies between the results of cluster-model and slab-model calculations of the activation energy for H 2 desorption from the Si͑100͒2ϫ1 surface. The DFT results obtained with several different exchange-correlation functionals are compared with the results of calculations with the generally reliable QCISD͑T͒ method and, where possible, with experiment. It is found that the functionals usually employed in plane-wave DFT calculations significantly underestimate the activation energies. The Becke3LYP functional, on the other hand, is found to give reaction and activation energies close to experiment and to those from QCISD͑T͒ calculations.

By pseudopotential methods the electronic properties of a quasicrystalline metal are examined from the nearly-free-electron viewpoint. The procedure results in the appearance of band gaps associated with each quasicrystal reciprocal-lattice vector, and these lead to singularities in both the density of states and the joint optical density of states. If observable by reflectivity, soft-x-ray emission, or tunneling measurements, these quantities will give information on several properties of the quasicrystalline state.PACS numbers: 71.20. Cf, 72.15.Eb, 78.20.Ci Since the discovery of the icosahedral phase of some Al-Mn alloys^ theoretical interest in the problem of determining the correct structure of this and other observed quasicrystalline phases continues undiminished. In addition, an understanding of what the properties of electrons and ions in such structures are, and why such a phase might be stable in the first place, is important. Thus far, the electronic problem has been attacked largely through tight-binding models on finite lattices,'^"'^ but in this Letter we begin from the opposite viewpoint, regarding the electrons as nearly free. The point here is to examine the implications of this model for the properties of a quasicrystal. It allows a much easier discussion not only of band gaps, the main subject of this Letter, but also of a possible Hume-Rothery explanation for the stability, a point that has already been raised by Bancel and Heiney.^ Since the principal component of the observed quasicrystals is often a simple metal, with no occupied delectron states, most of the electrons can be well described by a nearly-free-electron picture (particularly for the Al-Zn-Mg class^). The other components (in the binary or ternary alloys) can have a clear rf-electron character which may certainly be of importance, but is not central to the point being made in the Letter. We treat as a model system a hypothetical icosahedral phase for a pure nearly-free-electron metal, with aluminum as paradigm. It is also possible to reinterpret this system as a virtual (quasi)crystal in the sense implied by alloy theory,^ and through this picture we can then comment on the possible effect of introducing other constituents.In the approach adopted here, we use a simple deterministic model for the structure, and with a local empty-core pseudopotential proceed to calculate the band gaps, the form of interband optical transitions, and the density of states. The band gaps produce sharp van Hove singularities in the density of states, and the increased number of interband transitions directly associated with the icosahedral structure leads to a corresponding increase in the magnitude of the optical conductivity, to an increased plasmon linewidth, and to additional features in the optical reflectivity.

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