AbstractDependence of the texture tilt and excitation efficiency of shear waves on the working gas pressure in an interval of 0.14–0.74 mTorr that corresponds to the transition from collisionless to almost diffusion deposition is studied for the ZnO films with a thickness of about 0.45–1.2 μm that are synthesized in a planar dc magnetron system. It is shown that an increase in the pressure from about 0.14–0.24 to 0.74 mTorr causes a decrease in the tilt angle of the column texture from ~25°–27° to ~7° and a decrease in the efficiency of acoustic excitation. Films that are synthesized at pressures of ~0.14–0.24 mTorr close to the transition from the Townsend to glow discharge exhibit the highest excitation efficiency of shear waves. For such films, the insertion loss reaches a minimum level at thicknesses of 0.45–0.75 μm and the number of echo pulses amounts to 20–40, so that the reflected sound can be observed with a delay of up to 80 μs at a length of an acoustic guiding crystal of 10 mm.

Dependence of the texture tilt and excitation efficiency of shear waves on the working gas pressure in an interval of 0.14–0.74 mTorr that corresponds to the transition from collisionless to almost diffusion deposition is studied for the ZnO films with a thickness of about 0.45–1.2 μm that are synthesized in a planar dc magnetron system. It is shown that an increase in the pressure from about 0.14–0.24 to 0.74 mTorr causes a decrease in the tilt angle of the column texture from ~25°–27° to ~7° and a decrease in the efficiency of acoustic excitation. Films that are synthesized at pressures of ~0.14–0.24 mTorr close to the transition from the Townsend to glow discharge exhibit the highest excitation efficiency of shear waves. For such films, the insertion loss reaches a minimum level at thicknesses of 0.45–0.75 μm and the number of echo pulses amounts to 20–40, so that the reflected sound can be observed with a delay of up to 80 μs at a length of an acoustic guiding crystal of 10 mm.

Влияние материала металлического подслоя и геометрии осаждения на формирование текстуры в пьезоактивных пленках ZnO© А.Г.Веселов, 1 В

Spin injection and accumulation have been studied for NiFe–InSb–NiFe and NiFe–Cu–NiFe planar spin valves with direct injection current I in nonlocal (NLSV) and local (LSV) measurement configurations at temperature 8–300 K. The value of the generated voltage U and the character of the dependence U(I) drastically changed for currents I greater some critical value Ic due to thermoelectric effects. For NLSV configuration and currents I<Ic the value of U is of 2–3 order of magnitude higher for NiFe–InSb–NiFe (U ≈ 1–3 mV at 300 K) structures in comparison with NiFe–Cu–NiFe (U ≈ 4–20 µV at 8 K). For LSV geometry electrical detection of spin current was observed only for NiFe–Cu–NiFe structure, where for I<Ic the magnetoresistance (MR) effect of the order 0.5% was detected. For currents I of 1.5–2% higher than Ic the MR of the order of 10–30% was observed for both NLSV and LSV configurations for studied structures.

Effect of material of metal sublayer (aluminum, vanadium, chromium, iron, cobalt, nickel, and copper) and deposition configuration on the formation of the oblique and straight texture in the ZnO films is studied. The films that are synthesized in a dc magnetron sputtering system. It is shown that the piezoactive ZnO films with oblique texture that can generate shear waves are formed on the Cr and V metal sublayers in the shifted deposition configuration when the substrate is shifted relative to the magnetron axis toward the region of the target erosion. The piezoactive ZnO films with the straight structure that can generate longitudinal waves are formed on a chemically pure Al sublayer in the symmetric deposition configuration when the substrate is centered with respect to the target. Changes of the sublayer material in both deposition configurations or preliminary oxidation of the sublayer lead to the formation of the piezoactive ZnO films with mixed texture that excite shear and longitudinal waves. Chemical etching is used to show that the ZnO films with the oblique and straight textures exhibit piezoactive properties and can generate hypersound at thicknesses of no less than about 0.3 and about 0.9 μm, respectively.

Затухание продольных и сдвиговых акустических волн в структуре с пленками ZnO с прямой и наклонной текстурами© А.Г.Веселов

We have reported on the results of an investigation of the damping of longitudinal and shear hyperacoustic waves in Al/ZnO/Al/ZnO/YAG structures (lutetium-doped yttrium–aluminum garnet) based on ZnO piezo-active films with straight and inclined textures, which are synthesized at substrate temperatures T ≈ 25–400°C in an unbalanced planar magnetron sputtering system. It has been shown that anomalously high values of damping up to 45 dB is observed for the passage of acoustic waves through ZnO films with straight textures, which are grown at a substrate temperature T ≈ 200–300°C; an increase in the deposition temperature to T ≈ 400°C leads to a decrease in the introduced acoustic losses by 30–40 dB.

The influence of the gas pressure in a magnetron sputtering system on the efficiency of volume hypersound generation in the synthesized ZnO films has been experimentally studied at pressures close to the transition from glow discharge to Townsend regime, whereby the ion and electron mean free path length increases and a drift component appears in the flux of deposited particles. It is established that the efficiency of hypersound generation (at a frequency above 1 GHz) in ZnO films deposited under these conditions increases. Based on a comparison to the properties of films deposited in a classical diffuse glow discharge, this result is explained by a lower nucleation texture and higher density of the films grown in a critical regime.

A simple version of a flow-forming plasma sputtering system is proposed. The causes that determine the properties of the deposited films are revealed when the composition, energy, and particle density of the flow are controlled. The electron component of the plasma flow and an increase in its ion component are found to degrade the magnetic properties of the films. The ferromagnetic resonance (FMR) line half-width of 10- to 150-nm-thick films is shown to mainly depend on the energy of the neutral flow component, which is specified by the sputtering conditions at an anode voltage of 400–700 V. In this rather narrow energy range, the FMR line half-width is 25 Oe for cold substrates.

Film formation in low-temperature plasma in the pulsed mode was studied. The voltage’s pulse sequence in the sputtering system contained trains of short and long pulses; the short pulse time was chosen shorter than the stabilization time of the glow discharge mode. The formation of the nanoscale composition periodicity in grown films was confirmed by secondary-ion mass spectrometry. Photoluminescence of the films synthesized in the pulsed mode was studied, as well as the possibility of controlling the luminescence behavior and intensity.

The crystallographic and optical properties of ZnO films obtained in the recombination burning zone of a low-temperature plasma are investigated. The refractive index is determined, and its correlation with the lattice constant along the c axis is found. A planar homogeneous structure consisting of two ZnO films with different refractive indices is fabricated to demonstrate areas of application of the technique suggested.

The magnetic properties of Permalloy films are studied as a function of substrate bombardment rate in the process of film synthesis in the recombination burning region of a glow discharge. An unambiguous relationship is found between the film properties and recombination burning intensity. By reconfiguring the recombination region, optimal conditions were found for the synthesis of 30-to 60-nm-thick films with a spread in magnetic properties of about 1% on cold substrates comparable to erosion zones on the target in surface area.

Optical and structural properties of thin films of zinc oxide synthesized under the conditions of bombardment with components of a low-temperature plasma are studied. The films were synthesized on a cold substrate located at a distance from the target comparable to the free-path length of particles knocked from the target. The refractive index, optical band gap, and interlayer spacing for the films under study are determined. It is found that these parameters depend on the free-path length of the particles, controlled by pressure in the sputtering chamber. Consistent correlation is found between the films' parameters and the bombardment intensity. A qualitative explanation of the phenomena observed is suggested; this explanation is based on an analysis of the energy conditions of the film's synthesis.

The structure and refractive index of thin zinc oxide films grown in reactive gas-discharge plasma have been studied. Reactions on the substrate and film growth occur under conditions of complete or partial reagent ionization. The ion recombination and kinetic energies activate film growth. Thermal heating of the films is absent. Under certain concentration of recombining ions, the films are found to acquire new structural and electrooptic properties rather than being destructed. To a thickness of 1500 Å, the films are optically dense and have high mechanical and chemical resistance and changed interplanar spacing and refractive index as compared to the analogous properties of the ZnO films synthesized during thermal activation.

The photodissociation of RbI molecules via the second excited state under the action of circularly polarized radiation with a wavelength of 266 nm is studied. By using sub-Doppler Faraday spectroscopy, the angular distributions of the orientation of spins of Rb(52S1/2) atoms formed are studied and the anisotropy parameters describing these angular distributions are determined. Based on the anisotropy parameters, the ratio between the amplitudes of the inelastic scattering matrix elements corresponding to the two possible photodissociation channels is determined to be rΩ=1/rΩ=0=0.71±0.15, while the phase difference for these matrix elements is found to amount to Δφ = 173° ± 29°.

In the microwave-length band, acoustic losses make a substantial contribution into the processes of acoustoelectronic interaction in piezosemiconductor devices. The paper deals with discussing of the influence of the after-growth treatment of a polycryatalline InSb film in the InSb-LiNb03 structure on the acoustic and electronic loss At frequencies of about 300-500 M H i , the acoustic losses in a film produced by melting are 0,012-0,015 &/A, i.e., they are comparable to the electronic losses. For amplifiers, convolvers and SAW detectors, lower acoustic losses will provide their hlgher operation efficiency. Along with this, it is quite obvious that the acoustic SAW attenuation in the film is to a considerable extent defined by its structure and thus by the after-growth treatment techniques. In the previous papers, the findings of producing the structure by various methods have been presented. It was noted that the after-growth treatment of such films can be performed by low-energy oxygen plasma, which is one of the surface modification methods.

We demonstrate the possibility of melting thin (0.1–0.5 µm) InSb films directly in atmosphere under the protective layer of native oxides to obtain high mobility of majority carriers (up to 25 000 cm2/V s). The features of the film synthesis process based on thermal pulsed evaporation of InSb powder in vacuum are studied experimentally. Such a technique makes it possible to provide necessary compositional inhomogeneity of the deposited film for subsequent melting in air.