Yu. N. Makogon

Low-temperature formation of the FePt phase in the presence of an intermediate Au layer in Pt /Au /Fe thin films

Pt /Fe and Pt /Au /Fe layered films were deposited at room temperature by dc magnetron sputtering on Al2O3(0 0 0 1) single crystalline substrates and heat treated in vacuum at 330 °C with different durations (up to 62 h). It is shown by secondary neutral mass spectrometry depth profiling and x-ray diffraction that the introduction of an additional Au layer between Pt /Fe layers leads to enhanced intermixing and formation of the partially chemically ordered L10 FePt phase. The underlying diffusion processes can be explained by the grain boundary diffusion induced reaction layer formation mechanism. During the solid state reaction between Pt and Fe, the Au layer moves towards the substrate interface replacing the Fe layer. This was explained by the much faster diffusion of Fe, as compared to Pt, along the grain boundaries in Au. Enhancement of the process and formation of the ordered FePt phase in the presence of the Au intermediate layer were interpreted by the effect of stress accumulation during the grain boundary reactions: the disordered FePt phase formed initially at different Au and Pt grain boundaries can experience appropriate compressive stress along the {1 0 0} directions, which can initiate the formation of the chemically ordered L10 FePt phase.

Formation of nanocrystalline structure of TaSi2 films on silicon

The nanocrystalline structure and mechanical properties of TaSi2 films deposited by sputtering of TaSi2 target have been investigated by x-ray diffraction, cross-sectional transmission electron microscopy (TEM), four-point electrical resistance measurement, and cyclic depth-sensitive nanoindentation. The purpose of this work is to study the formation of nanocrystalline structure in TaSi2 films on a silicon substrate. As revealed, a decrease in the deposition rate leads to an increase in the O and C impurity content in the films. Contamination of the film by O and C atoms during a low-rate deposition causes the formation of an amorphous phase in the deposited films. Upon annealing, the amorphous structures crystallize into mixtures of disilicide and a small amount of polysilicide, i.e. TaSi2 and Ta5Si3, respectively. After annealing at 970 K, the formation of a nanocrystalline structure with a grain size about 10 nm takes place in the film produced at a deposition rate of 0.2 nm/sec. The formation of a nanocrystalline structure changes drastically the mechanical properties of the film. The nanohardness and elastic modulus increase significantly, and the film becomes brittle and overstressed. After deposition in the film produced at the 1 nm/sec deposition rate mainly Ta disilicide and the amorphous phase are observed. After annealing, the amorphous phase near the Si substrate coexists with column-shape grains of Ta disilicide of size 150 × 500 nm. The annealed thin film becomes nonuniform in thickness. The nanohardness and elastic modulus increase.

Influence of Annealing Environment and Film Thickness on the Phase Formation in the Ti/Si(100) and (Ti +Si)/Si(100) Thin Film Systems

Influence of an annealing environment and film thickness on the phase formation in the Ti(30 nm)/Si(100), [(Ti+Si) 200 nm]/Si(100) thin film systems produced by magnetron sputtering and the Ti(200 nm)/Si(100) thin film system produced by electron-beam sputtering were investigated by X-ray and electron diffraction, Auger electron spectroscopy (AES), secondary ion mass-spectrometry (SIMS) and resistivity measurements. Solid-state reactions in the thin film systems under investigation were caused by diffusion processes during annealing in the different gas environments: under vacuum of 10-4 - 10-7 Pa, flow of nitrogen and hydrogen. It is shown that the decrease of Ti layer thickness from 200 to 30 nm in the Ti/Si(100) film system causes the increase of the transition temperature of the metastable C49 TiSi2 phase to the stable C54 TiSi2 phase up to 1070 K at vacuum annealing. During annealing in the nitrogen flow of the Ti(30 nm)/Si(100) thin film system the C49 TiSi2 is the first crystal phase which is formed at 870 K. For annealings of the [(Ti+Si) 200 nm]/Si(100) thin film system by impulse heating method or for furnace annealings in inert gas atmosphere of N2, Ar, H or higher vacuum (10-5 Pa) the crystallization process has two stages: the first metastable C49 TiSi2 phase is formed at 870 K and then at higher temperatures it is transformed to the stable C54 TiSi2 phase.

Effect of Copper on the Formation of Ordered L10(FePt) Phase in Nanosized Fe50Pt50/Cu/Fe50Pt50 Films on SiO2/Si (001) Substrates

The effect from thickness of an intermediate copper layer in nanosized Fe50Pt50 (15 nm)/Cu (x)/Fe50Pt50 (15 nm) (x = 7.5, 15, and 30 nm) composite films on SiO2 (100 nm)/Si(001) substrates on the diffusion-controlled phase formation processes—transformation of the disordered magnetically soft A1(FePt) phase into the ordered magnetically hard L10(FePt) phase during annealing in vacuum—is studied by physical materials science methods: X-ray diffraction and measurement of magnetic properties. The A1(FePt) phase forms in all films during deposition. Annealing in vacuum in the temperature range 300–900°C is accompanied by thermally activated diffusion processes between the Cu and FePt layers. When thickness of the intermediate Cu layer increases from 7.5 nm up to 15 nm, the onset temperature of A1(FePt) → L10(FePt) phase transformation raises by 100°C, i.e., to 800°C. Simultaneously, the coercivity in films decreases since Cu dissolves in the FePt lattice.

Thermally Activated Processes of the Phase Composition and Structure Formation of the Nanoscaled Co–Sb Films

It is investigated the formation of the phase composition and structure in the nanoscaled CoSbx (30 nm) (1.82 ≤ x ≤ 4.16) films deposited by the method of molecular-beam epitaxy on the substrates of the oxidated monocrystalline silicon at 200°C and following thermal treatment in vacuum in temperature range of 300–700°C. It is established that the films after the deposition are polycrystalline without texture. With increase in Sb content the formation of the phase composition in the films takes place in such sequence as this is provided by phase diagram for the bulky state of the Co–Sb system. At annealing in vacuum at temperature above 450–500°C a sublimation not only of the crystalline Sb phase but from the antimonides occurs. This is reflected on the phase composition change by following chemical reactions: CoSb2→600°CSb↑=CoSb,CoSb3→600°CSb↑=CoSb2,CoSb3+Sb↑→600°CCoSb3

Formation of phase composition and structure in nanodimensional films on base of CoSb 3 skutterudite — Functional elements of thermoelectricity

{\mathrm{CoSb}}_2\overset{600{}^{\circ}\mathrm{C}}{\to}\mathrm{S}\mathrm{b}\uparrow =\mathrm{CoSb},{\mathrm{CoSb}}_3\overset{600{}^{\circ}\mathrm{C}}{\to}\mathrm{S}\mathrm{b}\uparrow ={\mathrm{CoSb}}_2,{\mathrm{CoSb}}_3+\mathrm{S}\mathrm{b}\uparrow \overset{600{}^{\circ}\mathrm{C}}{\to }{\mathrm{CoSb}}_3

Nanotechnology of CoSi 2 epitaxial film formation on monocryctalline silicon

and leads to increase in amount of the CoSb and CoSb2 phases and decrease in amount of the CoSb3. CoSbx (30 nm) (1.8 < x < 4.16) films under investigation are thermostable up to ~350°C.

Diffusion Formation of Silicide Phases in Ni/Si(001) Nanodimensional Film System

We have studied the phase composition and crystal structure of CoSbx (1.82 ≤ x ≤ 4.16) nanofilms (30 nm) grown by molecular beam epitaxy on oxidized single-crystal silicon substrates at a temperature of 200°C, followed by heat treatment in vacuum at temperatures from 300 to 700°C. The as-grown films were found to be polycrystalline, with no preferential orientation. The effect of Sb content on the phase composition of the films was consistent with equilibrium phase diagram data for bulk Co-Sb materials. Vacuum annealing at temperatures above 450–500°C led to Sb sublimation not only from the crystalline phase but also from the antimonides, thereby increasing the percentages of the CoSb and CoSb2 phases and reducing the amount of CoSb3. The 30-nm-thick CoSbx (1.8 ≤ x ≤ 4.16) films were thermally stable at temperatures of up to 350°C.