Characterization of nanocrystals in laser condensates deposited through vanadium evaporation in an oxygen atmosphere

The influence of the substrate temperature T _sub (20–360°C) and the oxygen pressure P(O₂) (5 × 10⁻³−0.13 Pa) in an evaporation chamber on the structure and phase composition of films prepared through laser sputtering of a vanadium target is investigated by electron diffraction and in situ transmission electron microscopy (with the use of the bend extinction contour technique for determining the bending of the crystal lattice). It is demonstrated that the oxygen content in the films increases with an increase in the oxygen pressure P(O₂) at a fixed substrate temperature T _sub and decreases with an increase in the substrate temperature T _sub at a fixed oxygen pressure P(O₂). The conditions responsible for the formation and composition of the crystalline (VO_0.9) and amorphous (V₂O₃) phases in the films are determined. It is established that the phase composition of the film depends on the angle of condensation of the vapor-plasma flow. The crystallization of the V₂O₃ amorphous phase is accompanied by an increase in the density by 9.2%. It is revealed that the V₂O₃ spherulites growing in the amorphous film have a bent crystal lattice. The bending of the crystal lattice can be as large as ∼42 deg/μm.

     

Effect of annealing on ESR characteristics of zirconia nanopowders with different impurity compositions

Physics of the Solid State - An ESR study is performed for four groups of zirconia nanopowder samples: nominally pure ZrO2 powders (first group), zirconia samples with Y2O3 and Sc2O3 impurities...     

Microwave-frequency spin-dependent tunneling in nanocomposites

The transmission coefficient of films of Co_51.5Al_19.5O₂₉, Co_50.2Ti_9.1O_40.7, Co_52.3Si_12.2O_35.5, and (Co_0.4Fe_0.6)₄₈(MgF)₅₂ ferromagnetic metal-insulator magnetic nanocomposites exhibiting tunneling magnetoresistance and the magnetorefractive effect for electromagnetic waves was studied in the frequency range 30–50 GHz. The transmission coefficient of the first two compositions varies strongly under an applied magnetic field, and its variation exhibits a linear correlation with the field dependence of magnetoresistance. For the other two compositions, the transmission coefficient does not depend on magnetic field. The data obtained are interpreted in terms of the concept of microwave spin-dependent tunneling.     

Electron microscopic investigations of the layer, Island, and dendrite polymorphic crystallizations of amorphous films

The structural and morphological features of the crystallization of thin amorphous films, which proceeds without changes in the composition, are investigated via the transmission electron microscopy and electronography methods. It is demonstrated that classification based on several structural and morphological features is reasonable and three (layer, island, and dendrite) types of polymorphic crystallizations can be distinguished. It is shown, that layer polymorphic crystallization enables us to interpret crystallization-line motion to the amorphous phase by analogy with the propagation of a light-wave front according to the Huygens principle.     

Phase transformations in films deposited by laser ablation of Hf in an oxygen Atmosphere

The structure of the hafnium dioxide films grown during pulsed laser sputtering of an Hf target in an oxygen atmosphere is examined, and the phase transformations that occur in them at annealing are studied by transmission electron microscopy and electron diffraction. Amorphous, tetragonal, orthorhombic, and monoclinic HfO₂ phases are detected in the films. The tetragonal modification of HfO₂ exhibits an epitaxy effect on a KCl(001) substrate. When the amorphous film is annealed in vacuum or air, it crystallizes to form the monoclinic modification of HfO₂. The action of an electron beam on the amorphous film in vacuum leads to the formation of the orthorhombic and monoclinic modifications of HfO₂. The transformation from the orthorhombic to the monoclinic modification of HfO₂ is accompanied by a phase size effect. At the final stage of crystallization, the monoclinic modification represented by HfO₂ dendrite crystals is the predominant structural constituent.     

Electron Spin Resonance Properties of Magnetic Granular GMI—Nanostructures in Millimeter Waveband

The millimeter waveband giant magnetoimpedance (GMI) and magnetoresonance (FMR) properties of thin-layered magnetic nanostructures are analyzed experimentally for wide temperature range. The correlation between FMR and GMI features are under discussion. The manifestation of the anisotropy established by the millimeter waveband FMR experiments and possible reasons of anisotropy appearance are given.     

Electron microscopic investigation of the kinetics of the layer and island crystallization of amorphous V<Subscript>2</Subscript>O<Subscript>3</Subscript> films deposited by pulsed laser evaporation

An electron microscopic investigation was performed on the kinetics of the layer and island crystallization of amorphous V₂O₃ films deposited by pulsed laser evaporation of vanadium in an oxygen atmosphere. The crystallization was initiated by the action of an electron beam on an amorphous film in the column of a transmission electron microscope. The kinetic curves were plotted on the basis of a frame-by-frame analysis of the video recorded during the crystallization of the film. It was found that the layer crystallization of amorphous films is characterized by a quadratic dependence of the fraction of the crystalline phase x on the time t, whereas the island crystallization is described by an exponential dependence of x on t. The kinetic curves of island crystallization of amorphous films were analyzed on the basis of the α-version of the Kolmogorov model. For each type of crystallization, there are specific values of the dimensionless relative length unit δ₀, which is equal to the ratio of the characteristic length unit to the parameter characterizing the unit cell of the crystal. It was established that, for the layer crystallization, the relative length unit lies in the range δ₀ ~ 4300–4700, whereas for the fine-grained island crystallization, it amounts to δ₀ ~ 110.     

Formation of ZrO<Subscript>2</Subscript> cubic phase microcrystals during crystallization of amorphous films deposited by laser ablation of Zr in an oxygen atmosphere

The structure and phase transformations during annealing of zirconium dioxide films grown by pulsed laser sputtering of a Zr target in an oxygen atmosphere have been studied by transmission electron microscopy and electron diffraction methods. The conditions of the formation of both amorphous and cubic ZrO₂ phases have been determined. The electron beam impact on the amorphous film in vacuum is accompanied by the formation of zirconium dioxide microcrystals with fcc lattice. The average grain size in the crystallized film is ～0.5 μm. The phase transformation is accompanied by film material densification. The relative change in the density during ZrO₂ crystallization is 10.27 ± 2.14%.     

Formation,structure, and magnetic changes at annealing of films deposited by laser sputtering of Ni and Pd

The electron microscopy investigations of Pd, Ni, and Ni-Pd alloy films are carried out. The films were produced by laser sputtering of one- and two-element targets. It is shown that, in the case of alternate deposition of nickel and palladium, polycrystalline films with a metastable hcp lattice are formed. The hcp lattice parameters increase monotonically with increasing palladium content in the film. As a result of the annealing, Ni and Ni-Pd alloy films acquire an equilibrium fcc structure. A positive deviation from Vegard’s law occurs for the dependence of the lattice parameter of the solid solution on the Pd concentration. The as-prepared Ni and Ni-Pd alloy films with the hcp structure are characterized by the absence of a magnetic moment. The transition into the ferromagnetic state occurs after annealing, and hysteresis is observed upon magnetization reversal.