I. I. Pronin

Magnetic ordering of the Fe/Si interface and its initial formation

High-resolution photoelectron spectroscopy with synchrotron radiation and magnetic linear dichroism in Fe 3p core-level photoemission has been used to study both the initial stages of Fe/Si(111)7×7 and Fe/Si(100)2×1 interface formation and their ferromagnetic ordering. The correlation between the phase composition, electronic structure, and magnetic behavior of the interfaces has been established. It is shown that in-plane ferromagnetic ordering of the interfaces has a threshold nature and arises after the deposition of ∼7 A Fe in both systems. However, the remanent magnetization of Fe/Si(111) is greater than that of Fe/Si(100) due to the difference in the chemistry of the phases being formed. In the former case, it was found that at room temperature an ultrathin metastable FeSi film with the CsCl structure grows at the first stage of Fe deposition on Si. At higher Fe coverages, a Si solid solution in iron, and later an Fe film, is found to develop on FeSi. The magnetic properties of the solid solution an...

Photoelectron Spectroscopy of Atomic Core Levels on the Silicon Surface: A Review

Recent studies of the atomic structure of the single-crystal silicon surface (both clean and covered by adsorbates) that are performed by high-resolution core-level photoelectron spectroscopy using synchrotron radiation are reviewed. The physical principles of the method, experimental techniques, the spectrum processing procedure, and the procedure of determining the energy shifts of the core levels in the subsurface layer are outlined. Emphasis is placed on the surface modes of silicon 2p spectra, which are observed for the main types of silicon surface reconstruction (Si(111)-7×7 and Si(100)-2×1), and on a correlation between these modes and the atomic structure of the (111) and (100) surfaces. Also, particular attention is given to the studies of the Ge/Si system, which is viewed as a promising material of nanoelectronics, as well as to those concerned with metal and gas adsorption on basic (low-index) silicon faces. These studies clearly demonstrate that core-level photoelectron spectroscopy provides extremely detailed information on the structure of adsorbed layers and on the adsorption-stimulated reconstruction of the substrate surface.

The Co/Si(111) interface formation: a temperature dependent reaction

We have investigated the reaction of Co with the Si(1 1 1) surface both at room temperature (RT) and at high temperature (500–650 C). The temperature evolution of the RT deposited 10 ML film has also been studied. The films, prepared by the different methods, have been structurally characterized by means of primary-beam diffraction modulated electron emission. Auger electron spectroscopy has been used to follow their stoichiometric evolution. For RT deposition the films have been found to have a B-type (180 rotated with respect to the underlying Si(1 1 1) surface) cubic structure with a Co content and an interlayer spacing increasing with thickness. After 650 C annealing, the films are completely reacted and have an unstrained B-type CoSi2 structure. High temperature (500 C) deposition of Co leads to the formation of stoichiometric CoSi2 films. Both annealed and high temperature grown films are found to be Si terminated. 2002 Elsevier Science B.V. All rights reserved.

Reactive epitaxy of cobalt disilicide on Si(111)

A study of the mechanism governing the initial stages in silicide formation under deposition of 1–10 monolayers of cobalt on a heated Si(111) 7×7 crystal is reported. The structural data were obtained by an original method of diffraction of inelastically scattered medium-energy electrons, which maps the atomic structure of surface layers in real space. The elemental composition of the near-surface region to be analyzed was investigated by Auger electron spectroscopy. Reactive epitaxy is shown to stimulate epitaxial growth of a B-oriented CoSi2(111) film on Si(111). In the initial stages of cobalt deposition (1–3 monolayers), the growth proceeds through island formation. The near-surface layer of a CoSi2(111) film about 30 Å thick does not differ in elemental composition from the bulk cobalt disilicide, and the film terminates in a Si-Co-Si monolayer triad.

Interaction of iron atoms with the Si(100)-2 × 1 surface

Interaction of iron atoms with the Si(100)-2 × 1 surface at room temperature is studied by core-level photoelectron spectroscopy using synchrotron radiation for Fe coverages ranging from a fraction of a monolayer to six monolayers. It is shown that the Fe/Si(100)-2 × 1 interface is chemically active: the Fe-Si solid solution forms early in deposition of iron on silicon. When the Fe coverage reaches four to five monolayers, the state of the system is changed and Fe3Si silicide arises.

In-situ intercalation of VSe2(0001) with K: direct observation of near-surface structure transformation by incoherent medium-energy electron diffraction

Abstract The intercalation of VSe 2 with K is investigated in situ by a new technique for imaging the near-surface atomic structure, which is based on forward focusing of backscattered electrons. It is shown that room-temperature deposition of a few K monolayers on to the VSe 2 (0001) surface results in drastic changes of the crystal structure. Both a considerable expansion of the crystal lattice (the interlayer SeSe distance is increased by 75%) and a transition from 1T to 3R(I) structure are revealed.

Silicon surface reconstruction lost upon cobalt adsorption

We have studied the room-temperature adsorption of cobalt in the range of submonolayer coverages on a reconstructed Si(100)2×1 surface. The measurements were performed by methods of high-resolution (∼140 meV) photoelectron spectroscopy using synchrotron radiation (hν=130 eV). An analysis of changes in the Si 2p line shape in the course of cobalt deposition showed that the metal adsorption leads to the loss of the initial substrate surface reconstruction. The results are interpreted using a model whereby adatoms arriving at the silicon surface are incorporated into the uppermost atomic monolayer, occupying positions between four Si atoms and forming rows parallel to the 〈110〉 directions in the substrate.

Photoelectron Si 2p spectra of ultrathin CoSi2 layers formed on Si(100)2×1

Solid-phase formation of ultrathin CoSi2 layers on Si(100)2×1 was studied using high-resolution (∼140 meV) photoelectron spectroscopy with synchrotron radiation (hν=130 eV). The evolution of Si 2p spectra was recorded both under deposition of cobalt on the surface of samples maintained at room temperature and in the course of their subsequent annealing. It was shown that Co adsorption on Si(100)2×1 is accompanied by a loss of reconstruction of the original silicon surface while not bringing about the formation of a stable CoSi2-like phase. As the amount of deposited cobalt continues to increase (up to six monolayers), a discontinuous film of the Co-Si solid solution begins to grow on the silicon surface coated by chemisorbed cobalt. The solid-phase reaction of CoSi2 formation starts at a temperature close to 250°C and ends after the samples have been annealed to ∼350°C.

Initial Stages of Cobalt Film Growth on MgO(001) Surface

The initial stages of cobalt film growth on a MgO(001) surface was studied by methods of sample surface structure imaging by reflected electrons, low-energy electron diffraction, and Auger electron spectroscopy. The measurements were performed at room temperature for cobalt layer thicknesses up to 40 Å. It is established that cobalt film growth proceeds according to the island mechanism. In the interval of cobalt film thicknesses below ∼ 10 Å, the dominating surface phase has the form of cobalt islands with an fcc structure; at greater layer thicknesses, the surface film consists predominantly of cobalt grains with an hcp structure.

Kikuchi-band formation in medium-energy electron-diffraction patterns

To reveal the mechanism of Kikuchi-band formation, the total Si(100) diffraction pattern produced by 2-keV quasi-elastically backscattered electrons is compared to model calculations made in the single-scattering approximation for clusters constructed with different numbers of close-packed (110) planes. The formation of the Kikuchi bands is shown to be governed by two types of electron scattering in a crystal. The dominant contribution to enhanced electron-scattering intensity within a band comes from the forward-focusing effect as the electrons move along the numerous interatomic directions in the (110) planes. The other mechanism responsible for the sharp edge regions in the Kikuchi bands involves electron scattering from the nearest planes. It is proposed to use the specific profile of the Kikuchi bands in estimating the shape and size of light-element crystallites forming during initial stages of island-film growth.