Effects of Mn‐doping on surface acoustic wave properties of ZnO films

Surface acoustic wave (SAW) filters based on Mn‐doped ZnO films have been fabricated and effects of Mn‐doping on SAW properties are investigated. It is found that the electromechanical coupling coefficient (K²) of Zn_0.913Mn_0.087O films is 0.73 ± 0.02%, which is 73.8% larger than that of undoped ZnO films (0.42 ± 0.02%). Zn_0.913Mn_0.087O film filters also exhibit a lower absolute value of insertion loss (|IL|) of 16.1 dB and larger bandwidth (BW) of 5.9 MHz compared with that of undoped ZnO film filter. However, Zn_0.952Mn_0.048O film filters exhibit a smaller K² of 0.34 ± 0.02%, larger |IL| of 26.9 dB and smaller BW of 3.5 MHz. It is suggested that the SAW properties can be improved by appropriate Mn‐doping and Mn–ZnO/Si multilayer structure with large d₃₃ is promising for wide‐band and low‐loss SAW applications. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

SAW spectral characteristics of the YZ-LiNbO3-thin-lead-film layered structure

An acousto-optical study of the effect of a lead film on propagation of high-power surface acoustic waves (SAW) along the Z direction on the Y cut of LiNbO₃ is reported. The presence of the metal film has been found to stimulate spatial oscillations of SAW components and suppress the onset of nonlinearity. If the film is more narrow than the SAW aperture, one observes considerable inflow of acoustic energy from the free surface to the film region. A study of the film-induced sound-velocity dispersion revealed it to have a linear pattern. An analysis of the results within the present theoretical models of soliton development showed that a soliton-like monopulse can form only if a very thin (～150 Å) lead film is present.     

Propagation of surface acoustic waves in structures incorporating high-temperature superconductors

Analysis of the propagation of surface acoustic waves (SAW) was carried out in piezoelectric-high-temperature superconductor (HTSC) film-dielectric structure near the superconducting transition of the HTSC film. By considering a change in the resistive state of the film, its inhomogeneity in a direction perpendicular to the substrate, and the mechanical load of the piezoelectric, equations describing the temperature dependence of the velocity and attenuation of the SAW were obtained. Our calculations agree with experimental results for LiNbO₃-YBa₂Cu₃O₇ structures if possible inhomogeneities in the film are taken into account.Institute for Automated Control Systems and Radio Electronics, Tomsk. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 38–45, July, 1992.     

One-and two-front states of equilibrium in a thin superconducting film

Two-phase states of equilibrium of a thin superconducting film carrying a current under conditions of convective heat exchange at the free surface of the film are studied. It is shown that for a classical superconductor the two-phase state of the film remains a single-front state over a wide range of parameters of the system. For high-T _c superconductors there exists a maximum value of the Steckl number above which weakly nonequilibrium stationary states can only be multifront states. The solutions of the boundary-value problem modeling a two-front state of equilibrium are investigated, and the conditions under which they obtain are examined. Zh. Tekh. Fiz. 68, 84–87 (March 1998)     

Propagation of magnetostatic waves in a ferrite plus high-T c superconductor structure in the presence of transport current in the superconductor

A thin-film structure consisting of a ferrite and a high-T _c superconductor was used to investigate the effct of the transport current in the superconductor on the amplitude-frequency characteristic and dispersion of surface magnetostatic waves (MSWs) in a ferrite film. It was found that the nature of energy transfer between the MSWs and the superconducting film undergoes a significant change as the transport current is varied. In particular, in one of the current ranges, energy can be transferred both from the MSWs to the superconductor and back again, whereas in another range it can only be efficently transferred to the superconductor. Fiz. Tverd. Tela (St. Petersburg) 39, 2195–2202 (December 1997)     

Shear surface acoustic waves in the stratified structure piezoelectric—High-temperature granular superconductor

The interaction of a Gulyaev-Bluestain surface wave with a granular high-temperature superconducting (HTSC) medium has been investigated. For piezoelectrics of symmetry 4mm and 6mm, dispersion equations have been derived that describe the characteristics of surface acoustic waves (SAWs). The temperature dependences of the SAW attenuation and phase have been calculated forZnO andBa ₂Si₂TiO₃ crystals. It is shown that at temperatures higher than the critical temperature an attenuation jump and a phase shift are observed. The effect intensifies with increase in the electromechanical coupling coefficient and with decrease in the thickness of the HTSC film. For theBa ₂Si₂TiO₃ crystal the attenuation jump and phase shift are11 dB/cm and38 deg/cm, respectively, at a frequency of820 MHz. The results obtained can also be generalized for periodic HTSC structures and can be used to design frequency-selective devices and fast-response bolometric photodetectors. Tomsk State University of Control Systems and Radioelectronics. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 49–52, April, 1999.     

Kosterlitz-Thouless transition and radiation defects in a superconducting thin film

The thermodynamics of a system of Pearl vortices in a superconducting thin film containing radiation defects is studied. It is shown that three phase transition scenarios are possible, depending on the defect density. At low densities there is one stable state of the system. When the first critical density n _d 1 is reached, there appears a temperature interval in which the system can be in two stable states. If the density exceeds n _d 2, then the lower limit of stability of the metastable states shifts abruptly to zero. Pis’ma Zh. éksp. Teor. Fiz. 69, No. 9, 643–648 (10 May 1999)     

Role of anisotropy of the coupling constant in a superconductor model with singularities near the Fermi surface

The role of anisotropy of the coupling constant in the influence of nonmagnetic impurities on the behavior of the superconducting transition temperature T _c is investigated in the high-temperature superconductor (HTSC) model, where high values of T _c result from an increase in the density of states near the Fermi surface. It is shown that this model is more sensitive to impurities than the BCS model; Anderson compensation does not occur in the HTSC model, even for identical distributions of the densities of states in the superconducting and impurity channels, and the impurity contributions are no longer linear with respect to the impurity concentration in the vicinity of T _c. Anisotropy of the superconducting gap Δ and the possibility of its disappearance at certain points on the Fermi surface due to various types of pairing are manifested in the stability of the superconducting phase against the influence of impurities. Fiz. Tverd. Tela (St. Petersburg) 39, 1940–1942 (November 1997)     

The characteristics of surface acoustic waves on AlN/LiNbO3 substrates

The characteristics of surface-acoustic-wave (SAW) devices on various substrates were measured by a network analyzer in the temperature range from 0 to 80 °C. Based on the structure of IDT/AlN/LiNbO₃, it was revealed that the magnitude of the temperature coefficient of frequency (TCF) of a SAW on a LiNbO₃ substrate was significantly decreased due to the thickness increase of AlN thin film deposited on the LiNbO₃ substrate. The TCF of a SAW on an AlN/LiNbO₃ device was measured to be about -51 ppm/°C at h/λ=0.1, where h is the thickness of the AlN film and λ is the wavelength of the SAW. This indicates that the deposition of an AlN film on a LiNbO₃ substrate could improve the temperature stability, as compared with that of a SAW on a LiNbO₃ substrate (-73 ppm/°C). The SAW device on the ST-X quartz is shown to have a positive TCF as the AlN thin film is deposited on the surface of the ST-X quartz. In addition, the phase velocity (V_p) of the SAW on an AlN/LiNbO₃ substrate was significantly increased by the increase of AlN thickness (h/λ). Received: 14 October 2002 / Accepted: 15 October 2002 / Published online: 29 January 2003 RID="*" ID="*"Corresponding author. Fax: +886-7/525-4199, E-mail: ycc@ee.nsysu.edu.tw     

Surface acoustic wave device properties of (B, Al)N films on 128° Y-X LiNbO3 substrate

A c-axis orientated aluminium nitride (AlN) film on a 128° Y-X lithium niobate (LiNbO₃) surface acoustic wave (SAW) device which exhibit a large electromechanical coupling coefficient (k²) and a high SAW velocity property, is needed for future communication applications. In this study, a c-axis orientated (B, Al)N film (with 2.6 at.% boron) was deposited on a 128° Y-X LiNbO₃ substrate by a co-sputtering system to further boost SAW device properties. The XRD and TEM results show that the (B, Al)N films show highly aligned columns with the c-axis perpendicular to the substrate. The hardness and Young's modulus of (B, Al)N film on 128° Y-X LiNbO₃ substrates are at least 17% and 7% larger than AlN films, respectively. From the SAW device measurement, the operation frequency characteristic of (B, Al)N film on 128° Y-X LiNbO₃ is higher than pure AlN on it. The SAW velocity also increases as (B, Al)N film thickness increases (at fixed IDT wavelength). Furthermore, the k² of (B, Al)N on the IDT/128° Y-X LiNbO₃ SAW device shows a higher value than AlN on it.     

Superconductivity in the Ti-D system under pressure

The pressure dependence of the superconducting transition temperature in TiD_0.74 has been measured up to 30 GPa in a diamond high-pressure chamber. It is found that the deuteride TiD_0.74 becomes a superconductor at pressures corresponding to the transition to the high-pressure ζ phase, with a transition temperature that increases from 4.17 to 4.43 K in the interval P=14–30 GPa. The value extrapolated to atmospheric pressure T _c (0)=4.0 K is significantly lower than the superconducting transition temperature (T _c =5.0 K) measured earlier in the metastable state obtained by quenching TiD_0.74 under pressure. It is assumed that the significant difference of the extrapolated value from the superconducting transition temperature in the metastable state after quenching under pressure is caused by a phase transition on the path from the stability region of the ζ phase under pressure to the region of the metastable state at atmospheric pressure. Fiz. Tverd. Tela (St. Petersburg) 40, 2153–2155 (December 1998)     

Laser acceleration of electrons in a thin metal film

A mechanism acceleration of electrons to relativistic velocities in a thin metal film irradiated with ultrashort (τ _L ≤1 ps) high-power (I>¹⁶ W/cm²) laser pulses is proposed. The acceleration is due to a resonance action of the nonuniform field on a portion of the electrons, viz., those which oscillate in the direction transverse to the film with a frequency close to the frequency of the field. Pis’ma Zh. éksp. Teor. Fiz. 66, No. 1, 8–12 (10 July 1997)     

A new model analysis of the third harmonic voltage in inductive measurement for critical current density of superconducting films

The critical current density J c is one of the most important parameters of high temperature superconducting films in superconducting applications,such as superconducting filter and superconducting Josephson devices.This paper presents a new model to describe inhomogeneous current distribution throughout the thickness of superconducting films applying magnetic field by solving the differential equation derived from Maxwell equation and the second London equation.Using this model,it accurately calculates the inductive third-harmonic voltage when the film applying magnetic field with the inductive measurement for J c.The theoretic curve is consistent with the experimental results about measuring superconducting film,especially when the third-harmonic voltage just exceeds zero.The J c value of superconducting films determined by the inductive method is also compared with results measured by four-probe transport method.The agreements between inductive method and transport method are very good.     

Parallel upper critical field of niobium/graphite bilayers

The influence of the superconducting proximity effect to the upper critical field (H_C) in niobium/graphite bilayers was studied and related to the ratio : and are the transition temperature of Nb/KG film and that of Nb film respectively. The thickness of niobium (Nb) film was controlled about 40 nm, and that of graphite (kish graphite: KG) film ranged from 120 nm to 140 nm. For making a specimen, Nb was deposited on a KG film and a quartz glass substrate simultaneously, and magnetic field was applied parallel to the Nb/KG interface. H_C of Nb/KG film () lowered from that of Nb film () at all temperatures within this work, and the value of ΔH_C defined as showed different temperature dependence among samples, depending on whether < or 1.00. This behavior of H_C suggests the additional existence of the interference of electrons in the clean KG film.     

Anharmonicity and superconductivity in Ba0.6K0.4BiO3

The temperature dependence of the x-ray absorption spectra above the L ₃ absorption edge of bismuth in the superconducting oxide Ba_0.6K_0.4BiO₃ are investigated. It is found that the local structure is different from the simple cubic structure indicated by x-ray and neutron-diffraction data. It is shown that the oxygen atoms move in an anharmonic double-well potential arising as a result of the existence of two nonequivalent types of octahedral environments of bismuth. Vibrations in such potential modulate the Bi-O bond lengths at the low frequency of the rotational (“tilting” type) mode of the oxygen octahedra and thus give rise to a strong electron-phonon interaction, which explains the quite high superconducting transition temperatures T _c ∼30 K. Pis’ma Zh. éksp. Teor. Fiz. 67, No. 12, 977–982 (25 June 1998)     

Modification of several physicochemical properties of a high-temperature superconducting yttrium ceramic upon doping with gold

The influence of additions of gold (5 and 10 at. %) on the lattice parameters, the superconducting transition temperature, and the diamagnetic susceptibility of the high-temperature superconducting ceramic YBa₂Cu₃O_7−δ is investigated. The influence of gold on the kinetics of the release of weakly bound oxygen during heating of the ceramic in a vacuum is also studied. It is shown that doping the ceramic with gold causes uniaxial expansion of the lattice of the material, a significant decrease in the diamagnetic susceptibility, and nonmonotonic variation of the kinetic parameters of the oxygen release, while the superconducting transition temperature remains nearly unchanged. Zh. Tekh. Fiz. 67, 31–34 (February 1997)     

Excitation of intrinsic defects in ionic crystals by high-power optical and electron beams

The efficiency of excitation and recharging of intrinsic defects by hot charge carriers has been investigated in ionic crystals acted on by high-power optical and electron beams. The interaction cross sections of hot electrons and holes with intrinsic lattice sites and F _n -type defects (n=1,2) are shown to be commensurate. It is also shown that the potential of the intracrystalline field in the vicinity of F and F ₂ centers is nearly regular. Fiz. Tverd. Tela (St. Petersburg) 40, 1030–1035 (June 1998)     

Superconductivity of tin selenide at pressures up to 70 GPa

We report the discovery of superconductivity in SnSe with T _c around 4.5 K at pressures exceeding 58 GPa. It is conjectured that the high-pressure superconducting modification has the CsCl structure. Fiz. Tverd. Tela (St. Petersburg) 39, 236 (February 1997)     

Far IR transmission spectra of an YBa2Cu3O7−δ thin film

Abstract

The FIR transmission of an YBa₂Cu₃O_7-δ film 1000 Å thick deposited on an MgO plate has been studied from 20 cm^?1 to 4000 cm^?1 at T = 300 K, and at 120 K, 80 K and 7 K. i) The spectra for the normal state are well fitted if a mid-IR oscillator of high strength and high damping is added to the simplest Drude model. ii) The spectra for the superconductive state do not show significant variations of transmission vs. temperature for ω > 120 cm^?1, which should be in agreement with a weak BCS coupling 2Δ = 3.5 kT_c . iii) The FIR transmission at 7 K for ω = 20 cm^?1 is not zero (around 1%) and seems to confirm that the low-temperature perovskite is made of two phases: a superconducting, and a normal one, the proportion of the first one increasing when the film temperature is decreased.