I.F. Koval

Adsorption of bismuth on Si(001) studied by AES, REELS and mass spectrometry

The morphology of bismuth layers on Si(001) has been investigated by electron spectroscopy methods (AES, EELS) and thermodesorption mass-spectrometry. Island formation on the first Bi continuous monolayer occurs during bismuth deposition at room temperature. The thermodesorption of this system at a temperature of ∼ 500°C leads to the formation of at least one stable adsorbed Bi phase with a coverage of ∼ 0.6-0.7 ML. Bi O 4,5 -line REELS of the Bi/Si(001) system has demonstrated the covalent character of the Bi-Si bond

Extended fine structure in elastically scattered electron spectra : nature and application to structure analysis

Abstract Extended fine structure (EFS) has been observed in elastically scattered electron (ESE) spectra. EFS has been observed in the energy range up to 2000 eV, its effect being not related to the thresholds of excitation of inner atomic levels. It has been shown that the EFS at electron energies above 100–200 eV can be discribed in the terms of a kinematic model of diffraction. Evidence of this is the dependence of the Fourier-spectra maxima on scattering angle. The interatomic distances determined from analysis of the EFS in terms of the kinematic model are in good agreement with literature data for all materials studied. The EFS in the low-energy region of the EFS-spectra is due, in our opinion, to multiple electron scattering effects. These multiple scattering effects reveal themselves as additional maxima in the Fourier-spectra of the ESE EFS.

Diffusion of Si and Ge dimers on Ge (001) surfaces

We have studied the various diffusion pathways of Si and Ge dimers on the Ge (001) surface using scanning tunneling microscopy. The adsorbed dimers can be classified into two categories: Dimers adsorbed on top of the substrate rows and dimers adsorbed in the troughs between the substrate rows. There are three different diffusion pathways for the dimers: Along the substrate rows, across the substrate rows, and in the troughs between the substrate rows. The activation barriers for diffusion of these three pathways have been determined for both Ge and Si dimers on Ge (001). The barriers for dimer diffusion of the system Ge/Ge (001) are slightly lower than for the Si/Ge (001) system. As compared to Si on Si (001) the activation barriers for dimer diffusion on Ge (001) are significantly lower

Interaction of O2 with the BiSi(001) system: from passivation to promoted oxidation

Abstract Bismuth-covered Si(001) surface has been investigated by means of electron energy loss and Auger electron spectroscopy. The submonolayer coverage of Bi on Si(001) was found to reduce an initial sticking coefficient of molecular oxygen by two orders of magnitude in comparison with the clean Si(001) surface, whereas Bi-promoted formation of SiO 2 -like species was found at oxygen exposures > 10 5 L.

STM investigation of the initial adsorption stage of Bi on Si(1 0 0)-(2×1) and Ge(1 0 0)-(2×1) surfaces

Scanning tunneling microscopy has been used to investigate the initial adsorption stage of Bi on Si(1 0 0) and Ge(1 0 0) surfaces at room temperature. The most favorable position for a Bi ad-dimer on both surfaces is the B-configuration (Bi ad-dimer positioned on-top of the substrate rows with its dimer bond aligned along the substrate dimer row direction). For Si(1 0 0) the A-type dimers (dimer bond aligned perpendicular to the substrate dimer row direction) occasionally rotate back and forth to a B-configuration. The diffusion rates of B-type and A-type dimers along the substrate row and the B–A, A–B rotations on Si(1 0 0) are extracted from an analysis of many sequences of STM images. Finally, it is shown that the presence of an attractive interaction between Bi ad-dimers (irrespective of their orientation) positioned on neighboring substrate dimer rows leads to the formation of local regions with a 2×2 reconstruction.

Simulation of radiation effects on reflectors using heavy ion beams

Abstract The results on modelling the behaviour of metal mirrors under neutron irradiation in a fusion reactor are presented. Mirror-like specimens were irradiated with beams of ions: Cr + (stainless steel), Cu + (copper) and Ne + and/or He + (beryllium). The energy of ions was in the range of a few keV (He + ) to 3 MeV (Cr + and Cu + ). The reflectivity as a function of irradiation dose was measured in the interval of spectrum 0.2–1.0 μm. There was no strong degradation of the mirror reflectivity up to doses ∼ 10 dpa in a near surface layer. In contrast, all used methods showed definite change of surface characteristics.

The concerted movements of weakly bonded Bi dimers on the Si(1 0 0)2×1 surface

Abstract It is found that Bi dimers in B positions (with axis perpendicular to Si dimer row) can make concerted movements in the same row. The estimated probability of such concerted movements of B dimers is at least by three orders of magnitude higher than unconcerted one. The evidence of weak interaction between dimers in the same row was found under detailed analysis of STM-images of neighboring Bi dimers. The interaction becomes visible in high-resolution STM-images as breaking of symmetry of neighboring Bi dimers with respect to symmetric free Bi dimer.

Rotation of Ge ad-dimers on Ge(0 0 1)

Structural calculations of the Ge ad-dimer rotation on Ge(0 0 1)-2×1 and Ge(0 0 1)-c(4×2) surfaces were performed by ab initio and semiempirical methods. Besides the two (already known) stable adsorption sites on top of the substrate dimer rows (angles between substrate dimer bond and ad-dimer bond are 0° and 90°, respectively) a new local minimum was found. The angle between the substrate dimer bond and the ad-dimer of this local minimum is about 45°. This theoretical result might explain the observation of the so-called A/B Ge ad-dimers on Ge(0 0 1).