INSTITUTE OF METAL PHYSICS OF NASU.

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HISTORY AND RESEARCH ACTIVITY

The pioneer studies in the field of metal surface physics started at the Institute of Metal Physics of the Academy of Sciences of Ukrainian SSR as far back as 1965 by Valentin T. Cherepin, then senior researcher, who took the lead of constructing an ion mass-spectral microscope. The microscope was put into operation in 1969, for the first time in the USSR. An initially small research group turned into the laboratory and then grew into the department of metal surface physics officially registered in 1969. Until 2004 Professor V.T. Cherepin, corresponding member of the National Academy of Sciences, was in charge of this department. Yu.P. Maifet, Yu.N. Ivashchenko, M.A. Vasylyev, and S.P. Chenakin were the first scientific workers of the department. Yu.N. Ivashchenko was the first to defend a Ph.D. thesis on the new subject in 1971. Since then 25 scientific workers of the department have upheld their Ph.D. theses and were conferred a degree of Candidate of Science, and 5 persons (V.T. Cherepin, M.A. Vasylyev, S.P. Chenakin, A.A. Kosyachkov, S.D. Gorodetsky) obtained a degree of Doctor of Science. In 1985 the department of atomic structure and surface dynamics under the direction of Dr. M.A. Vasylyev separated from the department of metal surface physics as an independent subdivision. In 2004 these two departments re-merged. The joint unit preserved the name “department of atomic structure and surface dynamics”, and Professor Vasylyev M.A. became its head.

Basic scientific interests of the department are the following: static and dynamic defects of the surface and subsurface layers in the nanometer range; interaction of atomic particles with the solid surfaces and employment of accompanying phenomena for study and modification of the composition, structure and physical properties of the surface of materials.

A set of modern original ultrahigh vacuum devices was developed in the department which enable up-to-date investigation of the surface using the methods of secondary ion mass spectrometry, ion scattering spectroscopy, Auger electron spectroscopy, electron stimulated ion desorption with high energy, angular and mass resolution and also simultaneous analysis of two emission processes.

Physics of secondary emission phenomena and development of techniques of the local and layer-by-layer analysis of solid surfaces are the leading subjects of research activities at the department. The regularities of secondary ion emission from various metals and alloys under bombardment by Ar⁺, He⁺, O⁺, and H⁺ primary ions have been systematically investigated. As a result, the role of physical, chemical and structural factors in the processes of ionization of sputtered atoms was determined (V.T. Cherepin, M.A. Vasylyev, S.P. Chenakin, A.A. Kosyachkov, I.N. Makeyeva).

In past years, new features of the structural sensitivity of secondary ion emission were revealed which enlarge the capabilities of surface diagnostics:

For iron-based amorphous alloys, an enhancement of ion emission and an increase in the most probable energy of secondary ions of the components are observed as compared to crystallized alloys; an enhancement of secondary ion emission is also found for defect areas of metals preliminarily damaged by the implantation of inert gas ions and self ions (V.T. Cherepin, S.P. Chenakin, A.L. Pivovarov);
The characteristics of secondary ion emission and ion scattering for high-temperature superconductive compounds and amorphous metallic alloys are established to provide an information on the short-range chemical and topological atomic order, on the variations in the local electronic structure, inter-atomic distances, atomic binding energy and correlate with the physical properties of the materials (V.T. Cherepin, S.P. Chenakin, I.Yu. Panichkin);
The differential distributions of secondary ion emission measured with high energy and angular resolutions are characterized by a fine structure which depends on the crystalline-structure properties of a target, on differences in binding energies and orientation of bonds of the surface atoms, on the presence of an adsorbate and also on the charge-exchange conditions and electrostatic interaction of secondary ions with the surface and with ions of bombarding beam (V.T. Cherepin, A.A. Kosyachkov);
The dissipation of energy of impinging ions in the atom collision cascades at the surface of amorphous, polycrystalline and single crystal materials is characterized by self-anisotropy, which predetermines the interrelation between the emission direction and energy of sputtered neutral atoms and secondary ions (V.T. Cherepin, A.A. Kosyachkov, S.M. Chichkan’).

A significant research project of the department deals with modification of the surface physical and chemical properties of materials by energetic ion beams and plasma fluxes. The kinetics of oxygen chemisorptions on the original and Ar⁺-ion irradiated surface of pure metals, poly- and single-crystalline Fe–Ni alloys, amorphous metallic alloys has been thoroughly studied as a function of composition and structure of the material, dosage and energy of bombarding ions, target temperature.

It was found that Ar⁺-ion implantation into a material resulted, as a rule, in the retardation of oxidation of the irradiated surface, with the magnitude of the retardation effect depending not only on the sample characteristics and irradiation parameters but on the oxygen exposure as well. A model of this phenomenon has been developed (S.P. Chenakin, A.B. Goncharenko, T.I. Bratus’). In iron-based amorphous alloys irradiated with Ar⁺ ions a more disordered and loose amorphous structure and also precipitates of new metastable boride phases with face-centered cubic (f.c.c.) and hexagonal close-packed (h.c.p.) structure that are not formed during thermal crystallization of the alloys were revealed (V.T. Cherepin, S.P. Chenakin, A.L. Pivovarov). The interaction of radio-frequency discharge plasma in atmospheres of N and H with the surface of metals, intermetallic compounds and multilayer thin films has been investigated. An anomalously deep penetration of atoms of the working gas into the bulk of material and an enhanced atomic intermixing with formation of nitride and hydride phases were revealed. A model of accelerated mass transfer of atoms from plasma into the bulk of a solid was developed (V.T. Cherepin, S.P. Chenakin, A.L. Pivovarov, V.Yu. Nosenko). Theoretical works on the electronic structure of a surface are carried out in the department. A new method was developed which enabled the self-consistent computation of the surface electronic structure of low-index faces for different metals. As a result, local and partial electronic densities of states, spectra of surface states and resonances, work functions, and core-level electron binding energy shifts at the surface were obtained; two-dimensional Fermi surfaces for the low-index faces of transition metals and a generalized susceptibility of individual surface layers were calculated (V.T. Cherepin, A.A. Ostroukhov, V.N. Tomilenko, S.V. Man’kovsky). Development of novel up-to-date scientific instruments and setups is in progress. A system with sub-micron ion probe based on the liquid metal ion source has been constructed for nanostructuring of materials. It also allows three-dimensional secondary-ion mass-spectral analysis of the modified surface layers of a solid with high lateral and layer-by-layer resolution (V.T. Cherepin, S.P. Chenakin, I.A. Zotov). A scanning tunneling microscope, a surface profilometer to resolve nanorelief and a table equipped with a piezodrive and capacitance-type sensor of micro-displacements were designed (V.T. Cherepin, A.P. Shulyarenko). A concept of the fundamentally new mass-analyzer “Spherotron” was worked out and computer simulations of its operation were performed; the prototype of the analyzer was manufactured and tested (V.T. Cherepin, A.V. Churpita, V.M. Floka).

A new qualitative jump in the development of notions on the structure of both outermost surface layer and immediate near-surface region down to the bulk lattice is associated with setting up in the department a new experimental complex, which corresponds to the world standards. This complex includes the following ultra-high vacuum techniques: low-energy electron diffraction, reflection high-energy electron diffraction, low energy ion spectroscopy, Auger electron spectroscopy, electron energy loss spectroscopy, appearance potential spectroscopy, secondary ion mass spectrometry. By using this complex and original computer-controlled techniques the following characteristics of the metal surface can be analyzed: geometrical parameters and symmetry of the surface lattice including its reconstruction and relaxation, Debye characteristic temperatures, mean-square thermal atom displacements, thermal expansion coefficients, chemical composition and other physical, chemical and electronic properties. Layer-by-layer characteristics are registered with a sub-nanometer resolution in the temperature range from room temperature up to 1500 K. Experimental and theoretical works of the department are aimed first of all on obtaining new fundamental data on the effect of heating in vacuum and low-energy ion bombardment on the composition, crystalline structure and dynamic characteristics involving several atomic layers in the surface region of ferromagnetic metals and alloys, in the bulk of which order-disorder transitions and magnetic transformations take place; another trend of research work is the determination of the physical nature of the surface segregation phenomena in alloys based on transition metals. Applied works involve the in-depth physical-chemical analysis of the surface layers of materials and thin films with sub-nanometer resolution, the development of techniques of low-temperature ion-plasma modification of surface characteristics, protective coating application.

Recently, in studying surface properties of single crystals of ferromagnetic metals and Fe–Ni, Co–Ni and Co–Pt alloys, the following important results have been obtained obtained:

In single crystals of Ni and FeNi₃, low-energy electron scattering and thermal expansion of the surface lattice exhibit ferromagnetic anomalies. A theoretical analysis shows that in the region of magnetic phase transition scattering on magnetic subsystem predominates over scattering on the lattice thermal fluctuations (M.A. Vasylyev, S.D. Gorodetsky);
Layer-by-layer values of Debye temperature, mean-square atomic displacements, thermal expansion coefficients, relaxation of harmonic and anharmonic components of interatomic interaction strength are determined for atomically-clean surfaces of single crystals Ni, Fe, Fe₃Ni, FeNi₃, CoNi₃, CoNi, Co₂₀Pt₈₀ (M.A. Vasylyev, S.D. Gorodetsky, A.G. Blashchuk, I.N. Makeyeva, V.A. Tinkov);
In alloy Fe–Ni, the temperature dependence of the surface composition and in-depth distribution of the components demonstrate a non-monotonic behaviour which is caused, according to a theoretical analysis, by magnetic transformation and order-disorder phase transition occurring in the crystal bulk and in the surface layers of the ferromagnetic material (M.A. Vasylyev, L.N. Babanskaya, S.D. Gorodetsky, A.M. Moseychuk, A.G. Blashchuk);
The segregation processes occurring in CoNi (100) and Co₂₀Pt₈₀ (111) are revealed to cause a f.c.c.-h.c.p. thermo- and radiation-enhanced phase transition in the surface layer of the single crystals (M.A. Vasylyev, I.N. Makeyeva, A.G. Blashchuk, V.A. Tinkov).

Important results were obtained which demonstrate correlation of the electronic structure parameters and surface physical properties with radiation-enhanced processes occurring in the bulk of metallic alloys subjected to γ-irradiation (A.M. Shalayev, I.N. Makeyeva). The process of low-energy He⁺-ion sputtering of monolayers of hexadecanethiol (HDT) molecules, CH₃(CH₂)₁₅SH, self-assembled on Au (111) and Ag (111) substrates has been extensively studied as a function of ion dose, ion energy and angle of incidence. A distinct two-stage process associated with scission of long hydrocarbon chains was revealed in sputtering kinetics for HDT/Ag and was not distinguished for the HDT/Au system, which manifested a significantly higher rate of destruction of the molecular film. A model mechanism of sputtering of such self-assembled molecular structures is suggested (S.P. Chenakin). Lately, systematic studies of the influence of external impacts on the surface physico-chemical properties of metallic alloys to be employed in dentistry have been launched (M.A. Vasylyev, V.S. Filatova, L.F. Yatsenko). The research efforts in the department are also focused on the surface characterization of novel catalysts being developed for wide utilization in industry. In particular, the study of the surface composition and the chemical state of atomic components of aluminovanadate oxide as a function of preparation conditions of the catalyst has revealed a clear dependence of surface characteristics of the oxide on precipitation pH and its correlation with the pH-dependence of catalytic properties (S.P. Chenakin).