Electron structure and electron dynamics at InSb(111)2×2 semiconductor surface

The conduction band electronic structure and the electron dynamics of the clean InSb(111)2×2 surface have been studied by laser based pump-and-probe photoemission. The results are compared to earlier studies of the InSb(110) surface. It is found that both the energy location and the time dependence of the photoexcited structures are very similar for the two surfaces. This indicates that the dominant part of the photoemission signal in the conduction band region is due to excitations of electrons in the bulk region and that the surface electronic states play a minor role. The fast decay of the excited state, τ∼12 ps, indicates that diffusion of hot electrons into the bulk is an important mechanism. Received: 9 May 2001 / Accepted: 9 July 2002 / Published online: 25 October 2002 RID="*" ID="*"Corresponding author. Fax: +46-0824/913-1, E-mail: gm@matphys.kth.se     

Ab initio electronic structure of the Ge(111)-(2 × 1) surface in the presence of surface vacancy. Application to STM data analysis

We present the results of ab initio modeling of Ge(111)-(2 × 1) surface in the presence of atomic vacancy in surface bilayer. We showed that simple crystal structure defect affects surface electronic structure to the extent comparable with the influence of doping atom. We demonstrated the strong difference of surface LDOS structure above surface defects of different kind. We have proved that spatial oscillations of LDOS exist around individual surface vacancy in the same tunneling bias range as in case of donor doping atom on Ge(111)-(2 × 1) surface.     

Bond length inequalities and relaxations at the Rh(110)-c(2 × 2)-S surface structure studied by LEED crystallography

A tensor LEED analysis has been made for the Rh(110)-c(2 × 2)-S surface structure using intensity-versus-energy curves measured for twelve independent beams at normal incidence. Each S atom chemisorbs on a centre site of the Rh(110) surface. It bonds to the second layer Rh atom directly below, with a bond distance equal to about 2.27 Å, and to four neighbouring first layer Rh atoms at close to 2.47 Å. A significant feature of this structure is that the second metal layer is buckled; those Rh atoms directly below the S atoms relax down by about 0.11 Å compared with the other second layer Rh atoms. This buckling is apparently driven by the need to reduce the difference that would otherwise occur between these two types of S-Rh bond lengths. A component in the observed difference between the S-Rh distances appears to be dependent on the metallic coordination number for the Rh atoms; in this regard, a comparison is made with the structural details for O chemisorbed on reconstructed Ni(110).     

Lattice dynamics of the si(111) surface: folding effects in the 2×1 structure

We report a bond-charge-model calculation for Si(111):H(1×1). This configuration may be assumed to represent the “ideal” (1×1) surface, as long as the saturation of the dangling bonds by H atoms produces a slight perturbation of the dynamical matrix. We display also the geometric folding of these dispersion curves into the (2×1) configuration and compare our results to recent He scattering data and “ab initio” calculations. Thus we are in the position to discuss which dynamical features of the 2×1 pattern arise from the mere folding of the (1×1) pattern and which are due to the physical changes produced by the specific reconstruction.     

Simulation of a vacancy defect at the C(111)–2 × 1 surface

The configurations of a vacancy defect on the C(111)–2 × 1 surface, containing atoms with one or two dangling bonds, possessing a high adsorption activity, are calculated. We study the configurations of the vacancy defect at the surface of diamond C(111)–2 × 1 using the semiempirical MNDO method (MOPAC) and the ab initio Hartree–Fock method (PC GAMESS). We calculate the energies of clusters, the orders of atomic bonds, the populations of atomic orbitals, and the localized molecular orbitals.     

Correlated development of a (2 × 2) reconstruction and a charge accumulation layer on the InAs(111)–Bi surface

We have studied the formation of a Bi-induced (2 × 2) reconstruction on the InAs(111)B surface. In connection to the development of the (2 × 2) reconstruction, a two dimensional charge accumulation layer located at the bottom of the InAs conduction band appears as seen through a photoemission structure at the Fermi level. Not well ordered Bi layers do not induce a charge accumulation. The Bi-induced reconstruction reduces the polarization of the pristine surface and changes the initial charge distribution. InAsBi alloying occurs below the surface where Bi acts as charge donor leading to the charge accumulation layer.     

Low-energy electron-diffraction analysis of the Rh(110)-(2 × 1)-O phase

A quantitative low-energy electron-diffraction (LEED) analysis of the Rh(110)-(2 × 1)pg-O structure revealed a model which consists of O zigzag chains with oxygen located in threefold-coordinated sites on an otherwise undistorted Rh(110) surface. Due to the strong interaction of oxygen with Rh the contraction of the first Rh interlayer spacing (observed for the clean surface) is globally removed. LEED investigations on the (2 × 2)pg-O structure prove the presence of a missing-row reconstruction of the Rh substrate.     

LEED crystallographic investigations of two surface structures designated Zr(0001)-(1 × 1)-C

Multiple scattering analyses of LEED intensities have been made for two Zr(0001)-(1 × 1)-C surfaces corresponding to a low and a high coverage of C. For the first, a moderate level of correspondence between experimental and calculated I(E) curves is reached when the C atoms occupy octahedral holes between the first and second metal layers to give a ZrC bond distance of 2.29 Å. In this case the absorbed C causes only a 3.5% increase in the neighbouring ZrZr interlayer spacing. However, the normal incidence study for the high-coverage surface suggests that this spacing is then increased by about 25% over the bulk value; such an expansion is consistent with C incorporation into tetrahedral hole underlayer sites.     

Ab initio study of surface electronic structure of phosphorus donor impurity on Ge(111)-(2×1) surface

We present the results of numerical modeling of the electronic properties of the Ge(111)-(2 × 1) surface in the vicinity of a P donor impurity atom near the surface. We have shown that, in spite of well-established bulk donor impurity energy level position at the very bottom of the conduction band, the surface donor impurity might produce an energy level below the Fermi energy, depending on impurity atom local environment. It has been demonstrated that the impurity located in subsurface atomic layers is visible in scanning tunneling microscopy experiment. The quasi-one-dimensional character of the impurity image observed in scanning tunneling microscopy experiments is confirmed by our computer simulations.     

The adsorption of nitric oxide on a silicon (100) 2 × 1 surface studied with Auger electron spectroscopy

We present an Auger electron spectroscopy (AES) study of the adsorption of nitric oxide (NO) on a clean Si(100)2 × 1 surface at 300 and 550 K. Accurate measurement reeveal well resolved fine structure at Auger SiL_2.3VV transitions at 62 and 83 eV. These peaks can be attributed to SiO and SiN bonds. Furthermore, it is argued that the broadening in the SiLi_2.3VV Auger transition at 83 eV at 300 K may be composed of two nearby peaks, which could be attributed to two different kinds of chemical bonding, SiN and SiO. The absence of a peak at 69 eV at room temperature strongly suggests the NO adsorption on a Si(100)2 × 1 surface to be molecular. Dissociation of NO on the Si(100)2 × 1 surface is observed at 550 K.     

Electronic structure study of ultrathin Ag(111) films modified by a Si(111) substrate and √3 × √3-Ag2Bi surface

Angle-resolved photoemission spectroscopy experiments show that the electronic structure of a Ag(111) film grown on Si(111) is markedly perturbed by the formation of a √3 × √3-Ag(2)Bi Rashba-type surface alloy. Four spin-split surface states, with different band dispersions and energy contours, intercept and hybridize selectively with the sp-derived quantum well states of the Ag layer. Detailed two-dimensional band mapping of the system was carried out and constant energy contours at different energies result in hexagonal-, star- and flower-like distortions of the quantum well states as a result of various interactions. Further wavy-like modulations of the electronic structure of the film are found to originate from umklapp reflections of the Ag film states according to the surface periodicity.     

LEED surface crystallography,R-factors and the structure of the (110) surfaces of III–V semiconductors

Investigation of InSb(110) is presented which is used as the basis for a study of the way in which R-factors are used in LEED methods. These are general comments on the nature of R-factors and the methodology of LEED appropriate to many of the complex surfaces such as the zincblende (110) surface now being studied.