Carrier transport in In-doped CuO thin films

Temperature-dependent conductivity and thermopower measurements are carried out for undoped and In-doped CuO thin films. We investigate the effects of In-doping on carrier transport properties of CuO thin films in the temperature range of 300?<?T?<?400?K. Carrier transport is dominated by simple thermally activated conduction in the undoped film. On the other hand, small polarons play an essential role in the carrier transport properties in the In-doped films. By increasing the In content, the conduction behaviour transits from adiabatic limit to the non-adiabatic limit, and the conductivity decreases.     

The electrical transport properties of thin metal films containing neutral impurities

Summary In this paper we have calculated the expressions for the electrical conductivity and the thermoelectric power of thin metal films containing unionized or neutral impurities and having equal surface specularity parameters. The calculation is based on the solutions of the Boltzmann transport equation in the presence of a weak electric field and a small temperature gradient. The results indicate that the electrical conductivity decreases whereas the thermoelectric power increases.     

Electron transport in thin metal films having ionized impurities and unequal surface specularity parameters

Summary In this paper analytical expressions for the electrical conductivity and thermoelectric power of thin metal films have been calculated for films containing ionized impuritiesand having unequal surface specularity parameters. The effects of alteration in the energy dependence of the electron relaxation time as well as unequal probabilities of scattering from the two surfaces are thus completely taken into account.     

On the mechanism of electronic transport in polycrystalline CdO thin films

Cadmium Oxide (CdO) thin films (d = 0.16−0.62 μm) were deposited onto glass substrates by thermal evaporation under vacuum (quasi closed volume technique) of high purity (99.99%) CdO polycrystalline powders. The substrate temperature was 300 and 473 K, respectively. After a post-deposition heat treatment, the temperature dependence of the electrical conductivity becomes reversible. The electronic transport mechanism in studied samples is explained in terms of Seto’s model for polycrystalline semiconducting films. The values of optical bandgap have been determined from absorption spectra.     

Microstructure and transport properties of various 90° grain boundaries in YBa2Cu3O7 thin films

The microstructure and transport properties of various 90° grain boundaries in (103) oriented YBa₂Cu₃O₇(YBCO) thin films grown epitaxially in situ by 90° off-axis sputtering are compared. The (103) films grown on (101) LaAlO₃ and (101) SrTiO₃ substrates have specific sets of 90° grain boundaries in both principal in-plane directions: 90° [010] twist boundaries along the [101] direction, and 90° [010] symmetrical tilt boundaries and 90° [010] basal-plane-faced tilt boundaries along the (301) direction. No weak-link behavior is observed across some of these boundaries by transport critical current density and normalized magnetic field dependence of J _c measurements along both those in-plane directions. High-resolution transmission electron microscopy reveals variations in the structure and microfaceting of the 90° boundaries, which may contribute to the absence of weak-link behavior. These results have important implications for understanding the behavior of step-edge Josephson junctions.     

Structural study of TiO2 thin films by micro-Raman spectroscopy

The Raman spectroscopy method was used for structural characterization of TiO₂ thin films prepared by atomic layer deposition (ALD) and pulsed laser deposition (PLD) on fused silica and single-crystal silicon and sapphire substrates. Using ALD, anatase thin films were grown on silica and silicon substrates at temperatures 125–425 °C. At higher deposition temperatures, mixed anatase and rutile phases grew on these substrates. Post-growth annealing resulted in anatase-to-rutile phase transitions at 750 °C in the case of pure anatase films. The films that contained chlorine residues and were amorphous in their as-grown stage transformed into anatase phase at 400 °C and retained this phase even after annealing at 900 °C. On single crystal sapphire substrates, phase-pure rutile films were obtained by ALD at 425 °C and higher temperatures without additional annealing. Thin films that predominantly contained brookite phase were grown by PLD on silica substrates using rutile as a starting material.     

Composition dependence of photoconductivity in amorphous thin films of Se70Te30−xSbx

Summary The present paper reports the composition dependence of steady-state and transient photoconductivity in amorphous thin films of Se₇₀Te_30-xSb_x, wherex is varied from 0 to 10. The results indicate that photoconductivity is highly composition dependent in this system and a discontinuity in various electrical parameters is observed at 4 at. % of Sb. This is explained in terms of increased disorder up to 4 at. % of Sb. However, at higher concentration of Sb, an ordered structure may be established due to the formation of microcrystalline phases as observed in X-ray diffraction patterns.     

Switching phenomena in CdIn2S4 thin films

Summary Two kinds of switching phenomena in CdIn₂S₄ polycrystalline and amorphous thin films which were prepared by the vacuum evaporation method and the d.c. sputtering method, respectively, were studied. One is the so-called memory switching phenomenon arising from the low resistive filament path. Another is a characteristic switching phenomenon in which the resistivity abruptly changes whenever the ambient temperature reaches a critical value. The switching time is fast and about 100 ns. This switching phenomenon is related to the native defects in the CdIn₂S₄ lattice, because they can be observed in the polycrystalline as well as in the amorphous thin films. Paper presented at the ?V International Conference on Ternary and Multinary Compounds?, held in Cagliari, September 14–16, 1982.     

Extraordinary Hall effect on Fe-rich amorphous thin films and Fe-rich/Cu multilayers

In this study we investigated the magnetic and transport properties of thin Fe-rich amorphous films and Fe-rich/Cu multilayers. We compared the extraordinary Hall effect in these two types of samples and discussed it in terms of thickness and sample structure. The thicker films exhibited a strong in-plane magnetic anisotropy, and by decreasing film thickness both saturated Hall resistivity and Hall sensitivity increase. A Hall resistivity value of 20 μΩ cm is observed in 100 nm thick Fe-rich films at 12 K and a sensitivity of 1.3 Ω/T is obtained at room temperature. Electrical conductance increases and Hall resistivity decreases when the films are sandwiched with Cu.     

纳米晶氧化锡薄膜的接触特性

在 Ar和 O2 气体中 ,基片温度在 15 0～ 40 0℃的条件下 ,用直流磁控溅射的方法可以制备纳米晶透明导电薄膜。实验利用 TL M模型测试了纳米晶 Sn O2 透明导电薄膜的方块电阻、单位面积薄膜的接触电阻和电极与薄膜的结合力随热处理温度的变化情况     

BaNb_xTi_(1-x)O_3薄膜的电学性质及结构相变(英文)

我们利用激光分子束外延设备(L MBE)在MgO上外延生长了一系列BaNbxTi1-xO3(0 相似文献   

Doped thin metal oxide films for catalytic gas sensors

TiO₂ and Pt doped TiO₂ thin films were grown by pulsed laser deposition on 〈0 0 1〉 SiO₂ substrates. The doped films were compared with undoped ones deposited in similar experimental conditions. An UV KrF* (λ = 248 nm, τ_FWHM ≅ 20 ns, ν = 2 Hz) excimer laser was used for the irradiation of the TiO₂ or Pt doped TiO₂ targets. The substrate temperatures were fixed during the growth of the thin films at values within the 300-500 °C range. The films’ surface morphology was investigated by atomic force microscopy and their crystalline quality by X-ray diffractometry. The corresponding transmission spectra were recorded with the aid of a double beam spectrophotometer in the spectral range of 400-1100 nm. No contaminants or Pt segregation were detected in the synthesized anatase phase TiO₂ thin films composition. Titania crystallites growth inhibition was observed with the increase of the dopant concentration. The average optical transmittance in the visible-infrared spectral range of the films is higher than 85%, which makes them suitable for sensor applications.     

Sensing of LPG with nanostructured zinc oxide thin films grown by spray pyrolysis technique

Nanostructured zinc oxide thin films were prepared by spray pyrolysis technique using Zn(NO₃)₂·6H₂O as the precursor solution. The resulting films were investigated by X-ray diffraction and scanning electron microscopy to know crystal structure, size of crystallites and surface morphology. The films have been found to be polycrystalline zinc oxide, possessing hexagonal wurtzite crystal structure and nanocrystallite with grain size of approximately 30-35 nm. The LPG sensing performance of the films has been investigated at various concentrations of LPG in air at operating temperatures varying from 225 to 400 °C. At 325 °C the maximum responses of 46.3% and 48.9% have been observed, respectively, for concentrations of 0.8 and 1 vol% of LPG in air (1 vol% of LPG in air corresponds to 50% LEL of LPG in air). The recovery time has been found to be less than the response time for all concentrations of LPG. A possible reaction mechanism of LPG sensing has been proposed.     

存储器用铁电薄膜及电极材料的研究

铁电体独特的自发电极化双稳性质和非线性光学性质使其在光电子器件中得到广泛应用．为了实现器件的小型化和与微电子、光电子工艺兼容，铁电薄膜已成为一个研究热点．自发电极化的大小和取向以及外电场、缺陷和铁电薄膜／电极界面与自发电极化的交互作用决定了铁电薄膜的性质和服役行为．文章以铁电存储器和光电子器件应用为背景，选择了具有重大应用前景的Bi4-xLaxTi3O12（BLT）、SrBi2Ta2O9（SBT）、PbZrxTi1-xO3（PET）和LiNbO3（LN）铁电薄膜以及相关的La（Sr，Co）O3（LSCO）和LaNiO3（LNO）等电极材料为研究对象，研究了缺陷电荷和电畴的交互作用和它们在交变外电场中的动力学行为，探明了铁电薄膜疲劳现象的物理本质；从晶格结构与缺陷的观察研究入手，探索了材料铁电性质的起源和优化材料铁电性质的途径；从铁电薄膜／电极界面结构与性质的研究入手，寻找更有效、更稳定的电极材料与结构，从而为器件应用打下了基础；在研究外电场对铁电薄膜生长机制影响的基础上，找到了利用外电场调控铁电薄膜结构的新途径，发展了新的、与半导体器件和光电子器件工艺兼容的制膜方法．     

Pulsed laser deposition of tungsten and tungsten oxide thin films with tailored structure at the nano- and mesoscale

Nanostructured thin films synthesized by assembling atoms or clusters present a structure characterized by a modulation at the nanoscale and by a large effective area, which can be exploited for the tailoring of specific structural or electronic properties. These systems are appealing for functional applications, e.g. in sensing and catalysis. We have investigated the deposition of tungsten and tungsten oxide thin films with a wide range of morphologies by exploiting nanosecond pulsed laser deposition (PLD) in an inert background atmosphere (He, Ar and Kr). We show that the non-dimensional ratio of the target-to-substrate distance to the time integrated visible plume length, which depends on the gas mass and pressure and on the substrate position, permits to select morphologies ranging from a compact structure with a density similar to bulk, to a film with an open, low density foam-like mesostructure and a high fraction of voids.     

Luminescence centers in thin films of yttrium oxide and yttrium-aluminum garnet activated with bismuth

Luminescence spectra and photoluminescence excitation spectra of Y₂O₃:Bi and Y₃Al₅O₁₂:Bi thin films were investigated. Luminescence was stimulated by the emission from two types of centers that were associated with the substitution of Bi³⁺ for Y³⁺ in sites of the crystal lattice of Y₂O₃ (Y₃Al₅O₁₂) with point symmetries C₂ and C_3i (D₂ and C_3i). The emission of Bi³⁺ in the site with point symmetry C_3i causes blue luminescence in both Y₂O₃:Bi and Y₃Al₅O₁₂:Bi films with maxima at 3.03 eV and 3.15 eV, respectively, that is related to the ³P₁-¹S₀ transition. The emission of Bi³⁺ in the site with point symmetry C₂ gives green luminescence in Y₂O₃:Bi with the maximum at 2.40 eV that is also related to the ³P₁-¹S₀ transition. The emission of Bi³⁺ in the site with point symmetry D₂ leads to ultraviolet luminescence in Y₃Al₅O₁₂:Bi with the maximum at 3.75 eV that corresponds to the ³P₁-¹S₀ transition. The red luminescence band with the maximum at 1.85 eV in Y₂O₃:Bi is due to the presence of structural defects. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 2, pp. 202–207, March–April, 2008.     

Photoelectric properties ofp-CuInSe2 thin films obtained by pulsed laser vaporization

Using the method of phase-sensitive detection, we investigated the photoconductivity spectra of polycrystalline p-CuInSe₂ films obtained in vacuum by the method of pulsed laser vaporization of initial single crystals. We show that, in contrast to single crystals, films are characterized by monopolar photoconductivity in the extrinsic and intrinsic regions of optical absorption and by a linear mechanism of recombination of nonequilibrium charge carriers at the intensities of illumination 0–100 mW/cm² in the temperature range 80–300 K. Institute of the Solid-State and Semiconductor Physics, National Academy of Sciences of Belarus, 17, P. Brovka St., Minsk 220072, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii. Vol. 66, No. 1, pp. 138–141, January–February, 1999.     

Cobalt and tantalum additions for enhanced electrochromic performances of nickel-based oxide thin films grown by pulsed laser deposition

Aiming at improving the durability of anodic electrochromic nickel oxide thin films, Ni-M-O (M = Co, Ta) thin films were grown by pulsed laser deposition (PLD), using optimized conditions, namely room temperature and 10⁻¹ mbar oxygen pressure. For low Co and Ta contents (<5%), both additions lead to a loss of the [1 1 1] preferred orientation of the NiO rock-salt structure followed by a film amorphization with increasing Ta amount. Among the two series of metal additions (M ≤ 20%), the Ni-Co-O (5% Co) and Ni-Ta-O (10% Ta) thin films show the highest electrochemical performances especially in respect of improved durability. If the enhanced properties are associated with a limited dissolution of the oxidized phase for the Ni-Ta-O system, the opposite trend is observed for the Ni-Co-O system as compared to pure NiO.     

Martensitic transformation in as-grown and annealed near-stoichiometric epitaxial Ni2MnGa thin films

Magnetic shape memory nanostructures have a great potential in the field of the nanoactuators. The relationship between dimensionality, microstructure and magnetism characterizes the materials performance. Here, we study the martensitic transformation in supported and free-standing epitaxial Ni₄₇Mn₂₄Ga₂₉ films grown by sputtering on (0?0?1) MgO using a stoichiometric Ni₂MnGa target. The films have a Curie temperature of ~390 K and a martensitic transition temperature of ~120 K. Similar transition temperatures have been observed in films with thicknesses of 1, 3 and 4 μm. Thicker films (with longer deposition time) present a wider martensitic transformation range that can be associated with small gradients in their chemical concentration due to the high vapour pressure of Mn and Ga. The magnetic anisotropy of the films shows a strong change below the martensitic transformation temperature. No features associated with variant reorientation induced by magnetic field have been observed. Annealed films in the presence of a Ni₂MnGa bulk reference change their chemical composition to Ni₄₉Mn₂₆Ga₂₅. The change in the chemical composition increases the martensitic transformation temperature, being closer to the stoichiometric compound, and reduces the transformation hysteresis. In addition, sharper transformations are obtained, which indicate that chemical inhomogeneities and defects are removed. Our results indicate that the properties of Ni–Mn–Ga thin films grown by sputtering can be optimized (fixing the chemical concentration and removing crystalline defects) by the annealing process, which is promising for the development of micromagnetic shape memory devices.     

Electronic transport mechanisms in tetraphenyleprophyrin thin films

Thermally-evaporated thin films of tetraphenylporphyrin, TPP, with thickness range from (175 to 735) nm had been prepared. Annealing temperatures ranging from (273–473) K do not influence the amorphous structure of these films. The influence of environmental conditions: film thickness, temperature and frequency on the electrical properties of TPP thin films had been reported. It was found that dc conductivity increases with increasing temperature and film thickness. The extrinsic conduction mechanism is operating in temperature range of (293–380) K with activation energy of 0.13 eV. The intrinsic one is in temperatures >380 K via phonon assisted hopping of small polaron with activation energy of 0.855 eV. The ac electrical conductivity and dielectric relaxation in the temperature range (293–473) K and in frequency range (0.1–100) kHz had been also studied. It had been shown that theoretical curves generated from correlated barrier hopping (CBH) model gives the best fitting with experimental results. Analysis of these results proved that conduction occurs at low temperatures (300–370) K by phonon assisted hopping between localized states and it is performed by single polaron hopping process at higher temperatures. The temperature and frequency dependence of both the real and imaginary parts of dielectric constant had been reported.