Electron focusing in backscattering from single-crystal Si(100)

Diffraction patterns produced by quasi-elastically backscattered electrons focused in a thin single-crystal Si(100)2×1 near-surface layer have been studied. The measurements performed in the 0.6–2-keV range are compared with calculations made in the single-scattering cluster approximation. This model is shown to describe adequately the experiment. An analysis is made of the relation among the diffraction patterns observed for different silicon faces, and of the effect of the primary-electron beam orientation. The relations governing the focusing of quasi-elastically backscattered electrons escaping from the crystal along the main crystallographic directions have been established. The various aspects of the effect for backscattered electrons undergoing inelastic interaction with the electron subsystem of the crystal have been investigated. Fiz. Tverd. Tela (St. Petersburg) 40, 1364–1369 (July 1998)     

Photoelectron Si 2<Emphasis Type="Italic">p</Emphasis> spectra of ultrathin CoSi<Subscript>2</Subscript> 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.     

Effect of focusing of primary electrons on their reflection from a crystal and on the associated Auger emission

The orientational dependence for different groups of secondary electrons — quasi-elastically scattered, inelastically reflected with excitation of a plasmon and with ionization of the core level M _4.5, and the Auger electrons M _4.5 VV — are measured in the primary electron energy range 0.6–1.5 keV. The data are obtained for a Nb (100) single crystal by varying the azimuthal angle of incidence of the primary beam, with complete collection of secondaries. A relationship is established between the processes of focusing and defocusing of the electrons that have penetrated into the crystal in the 〈110〉 and 〈133〉 directions, which differ substantially in the atomic packing density. Specific details of the Auger orientation effect, due to the focusinginduced variation of the flux density of the reflected electrons, are identified and explained. The contributions, both of anisotropy of ionization of the core level and of variation of the backscattering intensity, to the angular dependence of Auger emission and reflection with ionization loss are estimated. The possibilities of using such orientational dependences for an element-sensitive analysis of the local atomic structure of surfaces are assessed. Zh. Tekh. Fiz. 67, 117–123 (August 1997)     

Ferromagnetic alignment of iron nanostructures on the silicon surface

The phase composition, electronic structure, and magnetic properties of nanostructures formed upon deposition of iron on the surface of the Si(556) vicinal face coated by a submonolayer silver film with a √3×√3-Ag structure have been studied using high-energy-resolution photoelectron spectroscopy and analysis of magnetic linear dichroism in photoemission of Fe 3p electrons. The effective thickness of the deposited iron layer is varied from 1 to 25 ?. It has been shown that a 1- to 2-? Fe coverage leads to the formation of a metastable iron silicide thin layer with a CsCl-type structure on the surface of the sample. A further deposition of Fe (up to ≈7 ?) brings about the formation of chains consisting of nonmagnetic islands of the Fe—Si solid solution on this layer, which are oriented along the steps of the substrate. A ferromagnetic alignment of the system along the surface of the sample appears only at coverages of approximately 10 ?, when larger (≈100 nm) iron islands start to grow on the solid solution layer.     

Focusing of electrons reflected from a crystal with loss of energy

A study is made of the features arising in the spatial distributions of reflected electrons as a result of a focusing effect. Experiments are conducted on single-crystal Mo (100) with primary electron energies of 0.5–2 keV and detection of electrons which lose fixed amounts of energy up to 300 eV. An analysis of the data establishes the dependence of the electron focusing efficiency on the amount of energy loss. It is shown that when electrons are reflected with single losses through plasmon excitation, the magnitude of the effect is determined mainly by the average number of scattering atoms encountered by an electron along its path to the surface. When the energy losses are high, defocusing owing to multiple elastic and inelastic scattering of the electrons is found to predominate. Zh. Tekh. Fiz. 68, 128–133 (June 1998)     

Binding energy of silicon 2p electrons in iron silicides

Experimental data for the binding energies of Si 2p electrons in a number of stable and metastable iron silicides are analyzed and generalized. The silicides are applied on the Si(100)2 × 1 and Si(111)7 × 7 reconstructed single-crystal faces with solid-phase epitaxy. Core electron spectra are taken by means of high-energy-resolution photoelectron spectroscopy using synchrotron radiation. It is shown that the binding energies of Si 2p electrons in stable silicides, as well as in the silicon-iron solid solution, increase with increasing silicon content in them, since the role of interatomic relaxation in photoelectron excitation events grows feeble.     

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.     

Reactive epitaxy of cobalt disilicide on Si(100)

The growth of cobalt disilicide on the Si(100) surface by reactive epitaxy at T=350°C was studied within the 10–40 ML cobalt coverage range. A new method of mapping the atomic structure of the surface layer by inelastically scattered medium-energy electrons was employed. The films thus formed were shown to consist of CoSi₂(221) grains of four azimuthal orientations turned by 90° with respect to one another. This domain structure originates from substrate surface faceting by (111) planes, a process occurring during silicide formation. B-oriented CoSi₂(111) layers grow epitaxially on (111) facets.     

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.     

Formation of ultrathin iron magnetic films on the silicon vicinal surface

Physics of the Solid State - The phase composition, electronic structure, and magnetic properties of ultrathin layers of iron and iron silicides formed upon deposition of 1- to 25-Å-thick Fe...