D. A. Valdaitsev

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.

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.

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.

Device for visualizing the atomic structure of surface layers based on an electron focusing effect

A description is given of a simple device for visualizing the atomic structure of surface layers by recording the focusing maxima in the spatial distribution of 1–3 keV electrons reflected from a sample with energy losses up to ≈300 eV. This is based on a wide-angle retarding-field energy analyzer with a microchannel electron flux analyzer and video system for data acquisition and processing, which can obtain data at a rate of up to 50 distributions per second, allowing the dynamics of structural rearrangements to be studied in a surface region approximately 15 Å thick. The low primary electron beam current (0.1 µA) minimizes the electronstimulated effects on the object being studied.

Initial stages in the intercalation of 1T-TiS2(0001) single crystals by potassium

A study is reported of spontaneous intercalation of 1T-TiS2(0001) by potassium, which takes place when an alkali metal is deposited on the surface of this layered material. The experiments were carried out in ultrahigh vacuum at room temperature within the 0–10 adsorbate monolayer range. An analysis of electron diffraction patterns visualizing the crystalline structure of the nanometer-scale surface layer of the studied samples showed that penetration of the intercalant into TiS2 stimulates a 1T → 3R(I) structural phase transition and brings about a substantial (by 2.2 Å) increase in the interlayer separation in this compound. It was found that the process passes through stages of gradual filling of the interlayer gaps and that this is accompanied by a lateral displacement of the titanium and sulfur layer sandwiches in the original crystal.

Focusing of electrons reflected from layered crystal

The mechanism of the formation of the diffraction patterns upon inelastic reflection of mean-energy electrons from the VSe2(0001) layered crystal has been investigated. It is found that the strong scattering of electrons by short atomic chains of the Se-V-Se layer triads leads to the weakening of electron focusing and the enhancement of diffraction scattering in deeper layers, which gives rise to the Kikuchi lines. It is demonstrated that, at an energy of 2 keV, the diffraction pattern is adequately described by the cluster model of single scattering. The atomic structure of thin near-the-surface layer of VSe2 has been investigated by the computer simulation of experimental data.

Visualization of the atomic structure of the subsurface region of a solid

A new variant is proposed for a method of visualizing the atomic structure of the subsurface region of a solid, based on the focusing of medium-energy reflected electrons and suitable for studying atomic processes at the surface in real time. An original device developed for this purpose is briefly described. The possibilities of the method are illustrated by examples of studying the atomic structure of epitaxial silver films grown on the surface of an Si(100) single crystal and also in the subsurface region of a layered VSe2(0001) crystal.