Improvement of the conducting parameters of YBa2Cu3Ox films grown on sapphire through the use of a strontium titanate buffer layer

High-T _c superconducting films of YBa₂Cu₃O_x on sapphire with an additional buffer layer of strontium titanate (actually, on heterostructures (100)SrTiO₃/(001)YBa₂Cu₃O_x/(100)CeO₂/(1102)Al₂O₃) are obtained by laser deposition, and their superconducting characteristics are investigated. It is shown that that buffering the sapphire by a strontium titanate film can raise the critical temperature of the YBa₂Cu₃O_x films by two degrees and give a severalfold increase in the critical current density. Pis’ma Zh. Tekh. Fiz. 24, 30–35 (September 12, 1998)     

Possible formation of BaCeO3 during deposition of YBa2Cu3O7−x films on the surface of cerium oxide

Results are presented from an experimental study of the crystallographic parameters of (1102)Al₂O₃/(001)CeO₂/(001)YBa₂Cu₃O_7−x film heterostructures fabricated by cathode sputtering at high substrate temperatures T=600–800°C. It is shown that the main limitation on the temperature for deposition of a YBa₂Cu₃O_7−x film on a CeO₂ surface is due to the chemical interaction between YBa₂Cu₃O_7−x and CeO₂ to form a polycrystalline BaCeO₃ layer. Pis’ma Zh. Tekh. Fiz. 23, 8–13 (October 12, 1997)     

Study of the growth of YBa2Cu3O7−x films on a Al2O3 single crystal with a CeO2 buffer sublayer

Superconducting YBa₂Cu₃O_7−x films were prepared by magnetron sputtering on Al₂O₃ single crystals with a CeO₂ sublayer. Scattering of moderate-energy ions and x-ray diffraction were used to show that the films exhibit good single-crystal properties over the entire thickness up to 2.6 μm. The hypothesis is advanced that the indentations formed by the growth of films above “extraneous” phase grains may act as defect sinks. Pis’ma Zh. Tekh. Fiz. 24, 91–95 (January 12, 1998)     

Preparation of thick YBa2Cu3O7−δ films by dc magnetron sputtering

High-temperature superconducting films up to 3.6 μm thick were obtained and their properties requisite for the development of microwave devices were investigated. It is shown that YBa₂Cu₃O_7−δ films of thickness exceeding 3–5λ _L may be obtained for use in the microwave range. Pis’ma Zh. Tekh. Fiz. 24, 89–94 (October 12, 1998)     

Deposition of thick YBa2Cu3O7−x films on sapphire with a sublayer of cerium oxide

A report is made on the results of experiments to prepare YBa₂Cu₃O_7−x films up to 2.6 μm thick on Al₂O₃/CeO₂ with good structural perfection and electrophysical parameters. Pis’ma Zh. Tekh. Fiz. 23, 39–43 (March 12, 1997)     

Dependence of the empirical model parameters of the surface resistance of a high-temperature superconducting film on the parameters of the technological process

The dependence of the surface resistance on the substrate heater temperature has been investigated for the purpose of optimizing the conditions for preparing YBa₂Cu₃O_7−δ films. It is shown that the resistance R _sur is highly sensitive to the accuracy of maintaining the substrate holder temperature to minimize the surface resistance of the films and maximize the parameter γ, which determines the temperature-dependent curves σ(t) and λ_L(t). Pis’ma Zh. Tekh. Fiz. 23, 79–84 (August 12, 1997)     

Influence of low-temperature annealing on the properties of Y1Ba2Cu3O7−δ thin films

The influence of annealing at 180 °C on the structure, critical temperature, and electrical resistivity of Y₁Ba₂Cu₃O_7−δ thin films has been investigated. It is shown that films grown at reduced temperatures are sensitive to this annealing, which can substantially alter these film parameters. Pis’ma Zh. Tekh. Fiz. 24, 55–58 (January 12, 1998)     

Preparation and investigation of films of (Zn1−x Cdx)3(P1−y Asy)2 solid solutions

Pulsed laser evaporation was used to prepare thin films of (Zn_1−x Cd_x)₃(P_1−y As_y)₂ solid solutions. It was shown that varying the flux density of the laser radiation and the substrate temperature allows films to be obtained whose composition, structure, and electrical properties are similar to those of the bulk samples. Pis’ma Zh. Tekh. Fiz. 24, 85–88 (October 12, 1998)     

Protection of YBa2Cu3O7−δ films from atmospheric degradation

Thin (40–80 nm) layers of YSZ deposited on the surface of YBa₂Cu₃O_7−δ films reliably protect the superconductor from atmospheric degradation. The high rate of oxygen diffusion in the protective layer allows further oxidation of the YBa₂Cu₃O_7−δ . Processes accompanied by release of oxygen from the YBa₂Cu₃O_7−δ cause the protective properties of the coating to be lost. Pis’ma Zh. Tekh. Fiz. 24, 45–49 (December 26, 1998)     

Switching time of planar ferroelectric capacitors using strontium titanate and barium strontium titanate films

A microstripe cavity was used to make microwave (f∼10 GHz) measurements of the time of variation of the permittivity of SrTiO₃ and (Ba,Sr)TiO₃ films exposed to unipolar video-frequency voltage pulses. It was shown that the permittivity of SrTiO₃ films varies over times less than 30 ns. For (Ba,Sr)TiO₃ films two characteristic times of variation of the permittivity were identified: a fast variation over times less than 30 ns and a slower variation, on the order of 20 μs. Pis’ma Zh. Tekh. Fiz. 24, 19–25 (October 12, 1998)     

New Insights on the Intrinsic Anisotropy of YBCO Films

Careful investigation of the angular dependence of resistivity ρ(θ) (θ is the angle between the magnetic field and the ab-planes) and the temperature dependence of resistivity ρ(T) within the superconducting transition in an applied magnetic field B up to 1 T for a series of YBa₂Cu₃O_7−δ (YBCO) thin films revealed a large variation of intrinsic anisotropy factor γ. The series of films studied included both optimally doped and underdoped samples of different T _c , critical current density J _c , film thickness, and preparation techniques. The variation in the shape and depth of the minimum measured for ρ(θ) near θ=0° could be directly correlated to the intrinsic anisotropy of the YBCO films. The results of fitting of ρ(θ) using Bardeen–Stephen theory allowed a quantitative determination of the value of γ which varies between 7 and 230, and is independent of T _c , film thickness, or J _c . The sharper the minimum in ρ(θ) around θ=0° the larger is the anisotropy. For highly anisotropic film, ρ(θ) showed an identical behavior for B ∥ J and B ⊥ J (i.e., ρ(θ) is independent of the angle θ between B and J for this film). The large variation in γ could be attributed to the “buckling” of the CuO₂ planes.     

Structure and polytypic faults in Ba4NdMn3O12 compound

We have studied the structure and polytypic defect formation in the 12R perovskite-type Ba₄NdMn₃O₁₂ compound. Its structure was characterized using transmission electron microscopy (TEM). Like in the 12R ordered oxides of Ba₄CeMn₃O₁₂ and Ba₄PrMn₃O₁₂ (Fuentes et al., J. Solid State Chem. 177 (2004) 714), a cationic ordering between Nd and Mn is also expected to be established in Ba₄NdMn₃O₁₂ with the Nd ions located in the corner-sharing octahedra and the Mn ions located in the face-sharing octahedra. We also observed in the Ba₄NdMn₃O₁₂ phase two types of polytypic faults, i.e., the extrinsic hexagonal-type fault with the stacking sequence …cch h hcc… and the extrinsic cubic-type fault with the stacking sequence …hhc c chh….     

Structural and electrical properties of Ta<Subscript><Emphasis Type="Bold">2</Emphasis></Subscript>O<Subscript><Emphasis Type="Bold">5</Emphasis></Subscript> thin films prepared by photo-induced CVD

Tantalum oxide (Ta ₂ O ₅ ) films and Al/Ta ₂ O ₅ /Si MOS capacitors were prepared at various powers by ultraviolet photo-inducing hot filament chemical vapour deposition (HFCVD). Effects of ultraviolet light powers on the structure and electrical properties of Ta ₂ O ₅ thin films were studied using X-ray diffraction (XRD) and atomic force microscopy (AFM). The dielectric constant, leakage current density and breakdown electric field of the samples were studied by the capacitance–voltage (C–V) and current–voltage (I–V) measurements of the Al/Ta ₂ O ₅ /Si MOS capacitors. Results show that the Ta ₂ O ₅ thin films grown without inducement of UV light belong to amorphous phase, whereas the samples grown with inducement of UV-light belong to δ-Ta ₂ O ₅ phase. The dielectric constant and leakage current density of the Ta ₂ O ₅ thin films increase with increasing powers of the UV- lamps. Effects of UV- lamp powers on the structural and electrical properties were discussed.     

Processing and magneto-electric properties of sol–gel-derived Pb(Zr0.52Ti0.48)O3–Ni0.8Zn0.2Fe2O4 2-2 type multilayered films

Pb(Zr_0.52Ti_0.48)O₃–Ni_0.8Zn_0.2Fe₂O₄ (PZT–NZFO) multilayered thin films with various volume fractions of the PZT phase (100, 74, 58, 48, 33, and 0%) were prepared on Pt/Ti/SiO₂/Si substrates using sol–gel spin-coating method. X-ray diffraction shows polycrystalline structure and scanning electron microscopy reveals good multilayer morphology of the composite thin film as annealed at 700 °C in air. The thickness of the composite films was estimated in the range of ~400 to ~600 nm. The ferroelectric and magnetic properties were measured as function of the volume fractions of the PZT phase. The magnetoelectric (ME) effect was investigated under various bias magnetic fields. The maximum ME voltage coefficient (α _E  = dE/dH) is 278 mV/cmOe for the composite film with the volume fractions of the PZT phase of ~48%.     

Temperature Dependence of Intermodulation Power in Y1Ba2Cu3O7−δ Films on LaAlO3 Substrates

Measurements of resonators from two groups on the temperature dependence of the third-order intermodulation power of Y₁Ba₂Cu₃O_7−δ films on LaAlO₃ substrates are analyzed, evaluated, and plotted according to very similar definitions. At a fixed circulating power in the resonator both groups found a distinct minimum of the normalized intermodulation power below half the critical temperature in agreement with the theoretical prediction of Dahm and Scalapino [Appl. Phys. Lett. 69, 4248 (1996)] for d-wave superconductors. Also in agreement with theory, for Niobium as a s-wave superconductor, no intermodulation power minimum could be found down to T/T _C≈ 0.2.     

Preparation of thin films of new ZnGa2S4 wide-gap semiconductors

An investigation was made of a possible method of obtaining thin films of new ZnGa₂S₄ semiconductors by pulsed laser deposition and quasi-equilibrium deposition from a Knudsen cell. It was established that these films are transparent in the range 0.3–26 μm, their band gap is 3.79 eV, and the refractive index in the region of transparency is 2.19. Pis’ma Zh. Tekh. Fiz. 24, 85–87 (March 26, 1998)     

Properties of Va metal-B films prepared by r.f.-sputtering

Nb_100−x B _x alloy films were prepared by the r.f.-sputtering method in the chemical composition range of 30 ≦x ≦ 76. Nb_100−x B _x (30 ≦x ≦ 54) films consisted of the amorphous state, and NbB₂ crystal phase was observed on Nb_100−xB_x (67 ≦x ≦ 76) films. A remarkable preferred orientation with the (001) plane of NbB₂ in parallel to the film surface was observed on Nb₃₃B₆₇ film. d.c. electrical conductivity of Nb_100−xB_x (30 ≦x ≦ 76) films decreased with increasing content of boron in the range from 7.3×10³ to 7.6 ×10²Ω⁻¹cm⁻¹. Micro-Vickers hardness of Nb_100−x B _x (30 ≦x ≦ 76) films exhibited the values of 1070 to 2060 kg mm².     

Electric resistance and magnetoresistance of 30-nm-Thick La<Subscript>0.67</Subscript>Ca<Subscript>0.33</Subscript>MnO<Subscript>3</Subscript> films elastically compressed in the (110) plane

We have studied the structure, electric resistance, and magnetoresistance of 30-nm-thick (110)La_0.67Ca_0.33MnO₃ (LCMO) films grown by laser deposition on (001)-oriented LaAlO₃ substrates. The unit cell parameters a and b (along the [100] and [010]LCMO axes, respectively) of these manganite films are significantly (by ∼1.2%) increased as compared to the corresponding values in the pseudocubic unit cell of bulk stoichiometric LCMO crystals. At T < 150 K, the temperature dependence of the resistivity of LCMO films is well described by the relation ρ = ρ₁ + ρ₂ (H) T ^4.5. The value of ρ 2 decreases with increasing magnetic field and is close to the analogous coefficient for manganite films grown on substrates with small lattice misfit.     

Photoelectrochemical properties of brush plated Cd x Zn1−x Se films

Cd _x Zn_1−x Se films(0 ≤ x ≤ 1) were deposited for the first time by the brushplating technique at room temperature from an aqueous bath containing zincsulphate, cadmium sulphate and selenium oxide. The deposition current densitywas varied in the range of 50–250 mA cm⁻². The as deposited films exhibitedcubic structure. Composition of the films was estimated by EDAX studies. XPSstudies indicated the binding energies corresponding to Zn(2p_3/2), Cd(3d_5/2 and 3d_3/2) and Se(3d_5/2 and 3d_3/2). Optical band gap of the films varied from 1.72 to 2.70 eV as the composition varied from CdSe to ZnSe side. Atomic forcestudies indicated grain size in the range of 20–150 nm. Photoelectrochemical cells were made with polysulphide as the redox electrolyte. The output was maximum for the photoelectrodes of composition Cd_0.9Zn_0.1Se.     

Langmuir-Blodgett films made from C60 fullerene with grafted macromolecules

Langmuir-Blodgett films made from C₆₀ fullerene with grafted polymer chains —polystyrene and polyethylene oxide — are obtained for the first time. The Langmuir-Blodgett films are obtained by the transfer of Langmuir films onto substrates of single-crystal silicon. The Langmuir films and the single-layer Langmuir-Blodgett films of C₆₀ with grafted polystyrene are nonuniform over their thickness and form a network consisting of aggregates with a size of ≤6 μm. The Langmuir films of C₆₀ with grafted polyethylene oxide are much more uniform. They can easily be used to obtain Langmuir-Blodgett films containing up to 20 layers and having a surface that appears smooth under an optical microscope. Pis’ma Zh. Tekh. Fiz. 24, 88–94 (June 26, 1998)