Ab initio pseudopotentials for electronic structure calculations of poly-atomic systems using density-functional theory

Recent development in 2D materials beyond graphene

The package fhi98PP allows one to generate norm-conserving pseudopotentials adapted to density-functional theory total-energy calculations for a multitude of elements throughout the periodic table, including first-row and transition metal elements. The package also facilitates a first assessment of the pseudopotentials' transferability, either in semilocal or fully separable form, by means of simple tests carried out for the free atom. Various parameterizations of the local-density approximation and the generalized gradient approximation for exchange and correlation are implemented.

Size dependence of nanostructures: Impact of bond order deficiency

Instabilities in semiconductor heterostructure growth can be exploited for the self-organized formation of nanostructures, allowing for carrier confinement in all three spatial dimensions. Beside the description of various growth modes, the experimental characterization of structural properties, such as size and shape, chemical composition, and strain distribution is presented. The authors discuss the calculation of strain fields, which play an important role in the formation of such nanostructures and also influence their structural and optoelectronic properties. Several specific materials systems are surveyed together with important applications.

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Structural properties of self-organized semiconductor nanostructures

Extremely well-resolved Si 2p core-level spectra have been obtained from the clean Si(001) surface. Spectra from the cold c(4×2) and the RT 2×1 surfaces are very similar, implying that the local structure of the two reconstructions is the same. Shifted components originating from both up and down atoms of asymmetric dimers, as well as second-layer atoms, are identified. The split of ∼0.55 eV between the two dimer-atom components points to a substantial charge transfer within the dimers. We find no support for the recently proposed crystal-field splitting of the surface components

Core-level spectroscopy of the clean Si(001) surface: Charge transfer within asymmetric dimers of the 2 x 1 and c(4 x 2) reconstructions.

Scanning tunneling microscopy and synchrotron x-ray diffraction have been used to investigate nanoscale Ge hut clusters on Sis001d. We have been able to identify the contributions to the scattered x-ray intensity which arise solely from the hut clusters and have shown that x-ray diffraction can be very sensitive to the strain field in the hut clusters. At the Ge ySi interface the Ge clusters are almost fully strained with a misfit of only 0.5% but towards the apex of the clusters the strain is relaxed and the atomic spacing is close to the natural Ge lattice spacing with a 4.2% misfit. [S0031-9007(96)01009-5]

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Strain in nanoscale germanium hut clusters on Si(001) studied by X-Ray diffraction

We present the atomic structure of the c(8 x 2) reconstructions of InSb-, InAs-, and GaAs-(001) surfaces as determined by surface x-ray diffraction using direct methods. Contrary to common belief, group III dimers are not prominent on the surface, instead subsurface dimerization of group III atoms takes place in the second bilayer, accompanied by a major rearrangement of the surface atoms above the dimers to form linear arrays. By varying the occupancies of four surface sites the (001)-c(8 x 2) reconstructions of III-V semiconductors can be described in a unified model.

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Subsurface dimerization in III-V semiconductor (001) surfaces.

The surface-state band structure and symmetry properties of the Si(111)-(\ensuremath{\surd}3 \ifmmode\times\else\texttimes\fi{} \ensuremath{\surd}3) R30\ifmmode^\circ\else\textdegree\fi{}-Ag surface have been studied with polarization-dependent, angle-resolved photoemission. In contradiction to the prevailing picture of this surface, we find an intrinsic, dispersive surface-state band in the bulk band gap. The minimum of this band is located 0.1 eV above the valence-band maximum (${E}_{V}$), and the observed partial occupation of the band determines the Fermi-level position (0.2 eV above ${E}_{V}$) on this surface.

E. Landemark

Papers

Core-level spectroscopy of the clean Si(001) surface: Charge transfer within asymmetric dimers of the 2 x 1 and c(4 x 2) reconstructions.

Strain in nanoscale germanium hut clusters on Si(001) studied by X-Ray diffraction

Subsurface dimerization in III-V semiconductor (001) surfaces.

Fermi-level pinning and surface-state band structure of the Si(111)-(√3×√3) R 30°-Ag surface

Atomic origins of the surface components in the Si 2p core-level spectra of the Si(111)7 x 7 surface.