L. E. Bykova

Solid-phase reactions, self-propagating high-temperature synthesis, and order-disorder phase transition in thin films

The results of experimental studies of self-propagating high-temperature synthesis in double-layer Cu/Au thin-film systems are presented. It is shown that the synthesis initiation temperature for a Cu/Au film is determined by the order-disorder phase-transition temperature in the Cu-Au system. The order-disorder transition temperature for thin films is found to be lower than for the bulky samples. It is assumed that the temperatures of initiation of solid-phase reactions in thin films can be associated with the structural phase-transition temperatures.

Self-propagating high-temperature synthesis and solid-phase reactions in bilayer thin films

Self-propagating high-temperature synthesis (SHS) in Al/Ni, Al/Fe, and Al/Co bilayer thin films is investigated. It is established that SHS is achieved in thin films at initiation temperatures 300–350° lower than in powders. The mechanism of SHS in thin films is similar to the process of explosive crystallization. It is shown that at the initial stage solid-phase reactions arising on the contact surface of condensate films can be self-propagating high-temperature synthesis. SHS could find application in different technologies for obtaining film components for microelectronics.

Solid-phase synthesis of L10-FePd(001) epitaxial thin films: Structural transformations and magnetic anisotropy

The solid-phase synthesis of the L10-FePd magnetically hard phase in Fe(001)/Pd(001) epitaxial films has been experimentally investigated. The formation of three types of L10-FePd ordered crystallites whose c axes coincide with the 〈100〉 directions of the MgO(001) substrate begins at the Fe/Pd interface at a temperature of 450°C. After an increase in the annealing temperature to 500°C, structural rearrangement occurs and gives rise to the predominant growth of L10-FePd crystallites with the c axis perpendicular to the film plane. After 10-h annealing, the fraction of such crystallites becomes dominant, leading to large perpendicular anisotropy. The first magnetocrystalline-anisotropy constant of the L10-FePd phase has been determined and the second constant has been estimated. It has been shown that magnetic anisotropy in the L10-FePd(001) basal plane cannot be described by the biaxial anisotropy of the tetragonal crystal. The annealing above 500°C results in the evolution of L10-FePd to a disordered cubic phase.

Reversible UV induced metal–semiconductor transition in In2O3 thin films prepared by autowave oxidation

We have prepared thin indium oxide films by the autowave oxidation reaction. Measurements of temperature dependence of resistivity, Hall carrier concentration and Hall mobility have been conducted in the temperature range 5–272 K. Before ultraviolet (UV) irradiation, the indium oxide film had a semiconductor-like temperature dependence of resistivity ρ and the ratio of ρ (5 K)/ρ(272 K) was very limited (∼1.2). It was found that after UV irradiation of the In2O3 film, the metal–semiconductor transition (MST) was observed at ∼100 K. To show that this MST is reversible and repeatable, two full cycles of ‘absence of MST–presence of MST’ have been done using UV irradiation (photoreduction) as the induced mechanism and exposure to an oxygen environment as the reversible mechanism, respectively. MST in transparent conducting oxide (TCO) is possibly associated with the undoped structure of metal oxide, which has some disorder of oxygen vacancies. It was suggested that reversible UV induced metal–semiconductor transition would occur in other TCOs.

Formation of NiAl Shape Memory Alloy Thin Films by a Solid-State Reaction

NiAl shape memory alloy thin films have been fabricated by a solid-state reaction in Al/Ni bilayer films. Two kinds of synthesis have been used. The first one consists in heating an Al/Ni bilayer film system to temperatures above 480 K. The second one implies the successive deposition of nickel and aluminum films onto a substrate with a temperature above 480 K. Regardless of a kind of the solid-state synthesis, the films obtained reveal a two-way shape memory effect. It is supposed that the solid-state reaction in Al/Ni bilayers starts at a temperature AS of the reverse of the martensitic transition in NiAl alloy. This indicates that the NiAl shape memory alloy thin films can be formed directly during the synthesis without need for lengthy heat treatment.

Solid-State Synthesis and Martensitic Transformations in Thin Films

This paper presents experimental data on solid-phase synthesis in double-layer thin-film systems. The rule of the first phase formed at the interface of film reagents at elevated temperatures of annealing is formulated for solid-phase reactions determined by martensite transformations. The temperature at which synthesis is initiated in NinTi, CdnAu, and AlnNi films coincides with the temperature of the back martensite transition in NiTi, AuCd, and AlNi alloys so that martensite phases are formed in the reaction products. The first phase rule was also verified for solid-phase synthesis in CdnAg, NinMn, FeMn, and AunMn systems. In thin films, low-energy processes initiate solid-phase reactions associated with martensite transformations, mass transfer of reagents being up to 200 nm. The martensite model of atomic transfer through the reaction product during solid-phase synthesis in thin films is considered. Martensite shifts can play the dominant role in mass transfer of reagents through the reaction product. It is assumed that the first phase initially formed at the interface of film reagents is formed irrespective of the mode of solidphase synthesis initiation.

Phase transformations in Mn/Fe(001) films: Structural and magnetic investigations

The solid-phase synthesis in epitaxial Mn/Fe(001) bilayer film systems with 24 at % of Mn has been shown to start at a temperature of 220°C with the formation of a γ-austenite lattice and the Mn and Fe films react completely under annealing to 600°C. In the sample cooling process after annealing below 220°C, the γ austenite undergoes a martensitic transformation to an oriented ∈(100) martensite. When the annealing temperature is increased above 600°C, Mn atoms migrate from the γ-lattice, which becomes unstable, and the film is partially again transformed to the epitaxial Fe(001) layer. The solid-phase synthesis in Mn/Fe(001) bilayer nanofilms and multilayers is assumingly determined by the inverse ε → γ martensitic transformation in the Mn-Fe system. The existence of a new low-temperature (∼220°C) structure transition in the Mn-Fe system with a high iron content is assumed.

Solid-phase synthesis of solid solutions in Cu/Ni(001) epitaxial nanofilms

Solid-phase synthesis of solid solutions in the epitaxial Cu/Ni(001) bilayer film systems of compositions 3Cu: 1Ni, 1Cu: 1Ni, and 1Cu: 3Ni has been studied using the X-ray diffraction methods. The saturation magnetization and the magnetic crystallographic anisotropy constant on nickel vary in accordance with the solid solution formation. The initiation temperature of the solid solutions is about 350 °C and is independent of the Ni: Cu layer thickness ratio. The solid-phase synthesis of the solid solutions is presumably attributed to the transport of the Cu atoms to the epitaxial Ni(001) layer. It is found that the solid-phase synthesis in the Cu/Ni bilayer nanofilms and multilayers is determined by the spinodal decomposition in the Cu-Ni system.

Multiple self-propagating high-temperature synthesis and solid-phase reactions in thin films

A variety of self-propagating high-temperature synthesis in thin films has been found and investigated. This modification, called multiple self-propagating high-temperature synthesis, occurs in the solid phase and is a reversible phase transition. Multiple self-propagating high-temperature synthesis is similar in many respects to a metal—insulator phase transition. It is shown that for eutectic systems it is equivalent to a repeated transition through the eutectic temperature of bulk samples. It is inferred that multiple self-propagating high-temperature synthesis in bilayer films is governed by phase separation mechanisms that take place during eutectic solidification and eutectoid decomposition.

Structural and optical properties of thin In2O3 films produced by autowave oxidation

Cubic-phase In2O3 films are produced by the autowave oxidation reaction. Electron microscopy and photoelectron spectroscopy of the atomic profiles show that the samples are homogeneous over the entire area and throughout the thickness, with the typical grain size being 20–40 nm. The optical and electrical properties are studied for In2O3 films fabricated at different pressures in the vacuum chamber. In the wave-length range from 400 to 1100 nm, the transparency of the films was higher than 85%; the resistivity of the films was 1.8 × 10−2 Ω cm.