A. Kostyuchenko

Dielectric losses and ac conductivity of Si–LiNbO3 heterostructures grown by the RF magnetron sputtering method

Single-axis <0001> textured polycrystalline LiNbO3 films were grown on (001) Si substrates by the RF magnetron sputtering method. Dielectric losses that occur in the Si–LiNbO3 heterostructures are caused by the conductivity of the LiNbO3 films. Analysis of temperature and frequency dependence of ac conductivity in the frequency range fxa0=xa025/105 Hz has demonstrated that it is expressed by the power law σ(ω)xa0=xa0Aωs and is described in the framework of the correlated barrier-hopping model. Thermal annealing (TA) of the Si–LiNbO3 heterostructures causes an increase in the density of the localized states in the band gap of LiNbO3 from Dxa0=xa07xa0×xa01024 m−3 to Dxa0=xa02xa0×xa01025 m−3. The conduction mechanism is changed radically after TA and phonon-assisted tunneling influences ac conductivity at the frequency of up to 800xa0Hz. At high frequency (fxa0>xa0800xa0Hz), dielectric relaxation predominates affecting frequency dependence σ(ω) on relaxation time τxa0=xa06.6xa0×xa010−5 s.

Current–voltage characteristics and impedance spectroscopy of LiNbO3 films grown by RF magnetron sputtering

Polycrystalline LiNbO3 films with random orientation of grains on (001)Si substrates have been grown by RF magnetron sputtering method. Electrical conductance of the formed (001)Si–LiNbO3 heterostructures is defined through hopping mechanism by charge localization centers (CLC) in the band gap of LiNbO3 with concentration Ntxa0=xa02.3xa0×xa01024 m−3. Analysis of the impedance frequency spectrum has disclosed two relaxation processes of Maxwell–Wagner type with relaxation times τ1xa0=xa00.1xa0s and τ2xa0=xa01xa0×xa010−4 s. Thermal annealing at Txa0=xa0650xa0°C leads to an increase in the average grain size from 50 to 95xa0nm; it also leads to a decrease in the CLC concentration down to Ntxa0=xa02.8xa0×xa01020xa0m−3. Electrical conductance of (001)Si–LiNbO3 heterostructures after thermal annealing is determined by space charge limited conduction mechanism. There have been defined parameters of dielectric hysteresis loops. It has been demonstrated that thermal annealing leads to a decrease in values of remanent polarization and coercive field.

Effect of Thermal Annealing on Electrical Properties of Si-LiNbO3

The substructure and electrical properties of the films with the thickness up to 2.0 µm deposited on Si by the methods of the radio frequency magnetron and ion-beam sputtering of a LiNbO3 target have been investigated. It has been established that in thermally annealed samples an activated conduction mechanism with variable jump distance takes place. As a result of thermal annealing a decrease in the charge localization centers (CLC) in the LiNbO3 films from Nt=3·1018cm-3 to Nt=3·1016cm-3 occurs.

Hardness and microplasticity of nanocrystalline and amorphous calcium phosphate coatings

The hardness of thin (1.0–4.0 μm) hydroxyapatite coatings with different structures (nanocrystalline, amorphous-crystalline, and amorphous) grown by rf magnetron sputtering on Ti and Si plates has been studied using the nanoindentation method. All the grown structures are characterized by the strain which has reversible and irreversible components. The hardness of nanocrystalline coatings (about 10 GPa) corresponds to the average hardness of hydroxyapatite single crystals. The structure of nanocrystalline coatings in the indentation zone and outside it has been investigated and changes in the structure under the indenter have been revealed using high-resolution transmission electron microscopy. From a comparison of the hardnesses of coatings with different structures and based on an analysis of the intragranular structure, it has been assumed that the plastic deformation occurs according to a dislocation-free mechanism. The plastic deformation is interpreted in terms of the cluster representation of the hydroxyapatite structure and amorphous calcium phosphates of the same elemental composition and cluster-boundary sliding during the deformation.

Influence of thermal annealing on structural properties and oxide charge of LiNbO3 films

C-oriented polycrystalline lithium niobate (LiNbO3) films have been deposited on Si substrate by the radio-frequency magnetron sputtering method in an Ar atmosphere and Arxa0+xa0O2 gas mixture. All as-grown LiNbO3 films manifested positive fixed oxide charge regardless of the sputtering conditions. Donor centers are formed in Si substrate because of diffusion of O2 molecules during sputtering process. Thermal annealing (TA) of the deposited films leads to increase in the surface roughness and grain size as well as formation of LiNb3O8 phase in the studied films. Also, TA resulting in the decline of positive oxide charge due to the diffusion of oxygen molecules into LiNbO3 films from air and out-diffusion from Si substrate.

On the substructure of compact ceramics based on hydroxyapatite

Hydroxyapatite Ca10(PO4)6(OH)2 (HA), space group of symmetry Р63/m, is a key calcium phosphate employed for the manufacture of biologically active ceramic materials for medical purposes used to recon� struct bone tissue defects [1]. Therefore, the views on the intragrain substructure, the structure of internal

Structure and hardness of ceramics produced through high-temperature nitridation of zirconium foil

We have studied the structure and microstructure of ZrN prepared by high-temperature nitridation of zirconium foil and estimated its hardness. The results demonstrate the feasibility of producing a composite heterostructure with the composition ZrN-(α-solid solution of nitrogen in zirconium/ZrN)-ZrN in the conditions of the process under consideration by heating to a temperature above the peritectic reaction temperature.

Hardness and the nature of microplasticity of hydroxyapatite

The hardness of thin (1.0–4.0 μm) hydroxyapatite (HA) coatings with different structures (nanocrystalline, amorphous-crystalline, and amorphous) grown on Ti and Si by rf magnetron sputtering has been studied using nanoindentation. In all of the coatings, deformation was observed to have an elastoplastic nature. The hardness of the nanocrystalline coatings corresponds to medium hardness values of HA microcrystals. The structure of the nanocrystalline coatings has been studied by high-resolution transmission electron microscopy in the indent zone and away from it. Comparison of the hardness values of coatings with different structures and analysis of the intragranular structure leads us to assume a nondislocation mechanism of plastic deformation. Its nature is interpreted in terms of a cluster representation of the structure of HA and amorphous calcium phosphates and cluster-boundary sliding in the course of deformation.

Fabrication, substructure and properties of LiNbO 3 films

By the method of magnetron sputtering the nanocrystalline films LiNbO3 on the surfaces of (001)Si, (111)Si and of Si- SiO2 heterostructure have been synthesized. The elemental and phase composition, structure and surface morphology, the electrical-physical parameters of the heterostructures (001)Si-LiNbO3 and (111)Si-SiO2-LiNbO3 have been studied.

Electrical properties and local domain structure of LiNbO3 thin film grown by ion beam sputtering method

The nanocrystalline ferroelectric LiNbO3 films on (001) Si substrates with the random orientation of polycrystalline grains and the predominance of the grains with lateral orientation of the polar axis were grown using the ion beam sputtering method. The remanent polarization and the coercive field are 12 µC/cm2 and 29 kV/cm, respectively. The thermal annealing leads to the coarsening of the grains. The appearance of the “local texture,” which gives rise to the unipolarity of the heterostructures caused by the predominance of the one direction in the vertical component of the spontaneous polarization, is investigated.