Investigation of the temperature dependences of the electrical resistance of SmS single crystals at different pressures

The pressure-induced shift of impurity levels under hydrostatic pressure at T = 300 K (−9.6 meV/MPa) has been obtained from measurements of the temperature dependences of the electrical resistance of SmS single crystals at different pressures. The obtained value confirms the validity of the existing model of the semiconductor-metal phase transition in samarium monosulfide.     

The electrical properties of thin permalloy films

The magnetic properties of thin Permalloy films have been the subject of many investigations, but the work on their electrical properties is very limited [1]. By observing the change in electrical resistance with temperature the structural transformations taking place during the annealing of the condensates can be inferred.The authors of [1] did not undertake a detailed study of the electrical properties of Permalloy. They used Permalloy 79NMA in their investigation, and the dependence of the change in electrical resistance on the temperature of annealing in a magnetic field enabled them to reach conclusions about the nature of the uniaxial anisotropy of thin films.In the present work a detailed study has been made of the electrical resistance of Permalloy films in relation to the temperature of the substrate during evaporation and annealing; the temperature coefficient of resistance (TCR) has also been studied.     

Influence of boron carbide on properties of CVD-diamond thin films at various deposition pressures

Microcrystalline boron-doped diamond (BDD) films are synthesized on the silicon substrate by the hot-filament chemical vapor deposition method under the gas mixture of hydrogen and methane in the presence of boron carbide (B₄C) placed in front of filaments. The observed results of scanning electron microscopy, Raman spectroscopy and X-ray diffraction show the morphologies. Microstructures for various deposition pressures of as-grown diamond films are found to be dependent on the change of deposition pressure. These results reveal that with the increase of deposition pressure, resistivity decreases and increase in the grain size is noted in the presence of B₄C. Resistivity shows a sudden fall of about three orders of magnitude by the addition of boron in the diamond films. This is due to the crystal integrity induced by B-atoms in the structure of diamond in the presence of B₄C. These results are also significant for the conventional applications of BDD materials. The effects of deposition pressure on the overall films morphology and the doping level dependence of the diamond films have also been discussed.     

Investigation of impurity levels in thin polycrystalline SmS films

Data obtained in the study of the behavior with temperature of the electrical resistance of thin polycrystalline SmS films (thickness ～0.5–0.8 μm) performed in the temperature region 4.2–440 K have been used to correct the band structure model of this material. It has been shown that the main impurity levels in thin polycrystalline SmS films are levels corresponding to localized states close to the conduction band bottom, as well as the impurity donor levels E _i which belong to Sm ions filling vacancies in the S sublattice. The tail of localized states has been found to extend up to the energy of impurity donor levels.     

Microstructure — Electrical properties relationship of YSZ thin films reactively sputter-deposited at different pressures

In order to decrease the operating temperature of Solid Oxide Fuel Cells (SOFC) from about 1000 °C to around 700 °C, the thickness of commonly used electrolytes such as Yttria Stabilised Zirconia (YSZ) must be decreased for about one order of magnitude in the range 1–10 μm. In this paper, we investigate the suitability of reactive magnetron sputtering for deposition of about 1 μm-thick YSZ films dedicated to SOFC. The coatings are synthesised by sputtering a metallic Zr-16 at.%Y target in the presence of a reactive argon-oxygen discharge. The deposition stage is controlled by Optical Transmission Interferometry (OTI) in order to guarantee the film transparency and its thickness. The influence of the deposition pressure on the chemical, structural and morphological properties of the coatings is studied in order to establish relationships with their ionic conductivity, determined by impedance spectroscopy. Paper presented at the Patras Conference on Solid State Ionics — Transport Properties, Patras, Greece, Sept. 14 – 18, 2004.     

Optical and electrical properties of InGaZnON thin films

The substrate temperature(T_s)and N_2 partial pressure(P_(N2))dependent optical and electrical properties of sputtered InGaZnON thin films are studied.With the increased T_s and P_(N2),the thin film becomes more crystallized and nitrified.The Hall mobility,free carrier concentration(Ne),and electrical conductivity increase with the lowered interfacial potential barrier during crystal growing.The photoluminescence(PL)intensity decreases with the increased Ne.The band gap(Eg)narrows and the linear refractive index(n1)increases with the increasing concentration of N in the thin films.The Stokes shift between the PL peak and absorption edge decreases with Eg.The n1,dispersion energy,average oscillator wavelength,and oscillator length strength all increase with n1.The single oscillator energy decreases with n1.The nonlinear refractive index and third order optical susceptibility increase with n1.The Seebeck coefficient,electron effective mass,mean free path,scattering time,and plasma energy are all Ne dependent.     

Microstructure and electrical properties of SnS thin films

Thin SnS films are of interest for optoelectronics. The influence of the preparation modes on the microstructure and electrical properties of thin SnS films obtained by the hot-wall method on substrates made of pure glass and glass with a molybdenum sublayer has been investigated. It has been established that the formation of SnS films with two texture types (111) and (010) is possible on the substrates made of pure glass, depending on the mode. The resistivity and the temperature coefficient of thermoelectric power of the SnS films on glass vary in the range from 12 to 817 Ω cm and from 37 to 597 μV/K, respectively, depending on the preparation modes. The activation energy is 0.11–0.12 eV.     

Enhanced electrical properties in bilayered ferroelectric thin films

Sr2Bi4Ti5O18(SBTi) single layered and Sr2Bi4Ti5O18 /Pb(Zr0.53Ti0.47)O3(SBTi/PZT) bilayered thin films have been prepared on Pt/TiO2/SiO2/Si substrates by pulsed-laser deposition(PLD).The related structural characterizations and electrical properties have been comparatively investigated.X-ray diffraction reveals that both films have crystallized into perovskite phases and scanning electron microscopy shows the sharp interfaces.Both films show well-saturated ferroelectric hysteresis loops,however,compared with the single layered SBTi films,the SBTi/PZT bilayered films have significantly increased remnant polarization(Pr) and decreased coercive field(Ec),with the applied field of 260 kV/cm.The measured Pr and Ec of SBTi and SBTi/PZT films were 7.9 C/cm 2,88.1 kV/cm and 13.0 C/cm 2,51.2 kV/cm,respectively.In addition,both films showed good fatigue-free characteristics,the switchable polarization decreased by 9% and 11% of the initial values after 2.2 10 9 switching cycles for the SBTi single layered films and the SBTi/PZT bilayered films,respectively.Our results may provide some guidelines for further optimization of multilayered ferroelectric thin films.     

Structural and electrical properties of evaporated Fe thin films

Series of Fe thin films have been prepared by thermal evaporation onto glass and Si(1 0 0) substrates. The Rutherford backscattering (RBS), X-ray diffraction (XRD), Scanning electron microscopy (SEM) and the four point probe techniques have been used to investigate the structural and electrical properties of these Fe thin films as a function of the substrate, the Fe thickness t in the 76-431 nm range and the deposition rate. The Fe/Si samples have a 〈1 1 0〉 for all thicknesses, whereas the Fe/glass grows with a strong 〈1 0 0〉 texture; as t increases (>100 nm), the preferred orientation changes to 〈1 1 0〉. The compressive stress in Fe/Si remains constant over the whole thickness range and is greater than the one in Fe/glass which is relieved when t > 100 nm. The grain size D values are between 9.2 and 30 nm. The Fe/glass films are more electrically resistive than the Fe/Si(1 0 0) ones. Diffusion at the grain boundary seems to be the predominant factor in the electrical resistivity ρ values with the reflection coefficient R greater in Fe/glass than in Fe/Si. For the same thickness (100 nm), the decrease of the deposition rate from 4.3 to 0.3 Å/s did not affect the texture and the reflection coefficient R but led to an increase in D and a decrease in the strain and in ρ for both Fe/glass and Fe/Si systems. On the other hand, keeping the same deposition rate (0.3 Å/s) and increasing the thickness t from 76 to 100 nm induced different changes in the two systems.     

SmS phase transition in thin films prepared by reactive evaporation

Preparation and analysis of thin films containing samarium sulfide (SmS) is presented along with a review of relevant SmS properties. Films were deposited onto unheated substrates by the reactive evaporation of samarium in a backpressure of hydrogen sulfide. This technique yields films that contain significant quantities of impurities; however high-quality SmS crystals are also formed. A phase transition in the SmS crystals was observed both by spectrophotometry and x-ray diffraction. The film optical properties can be modeled with an effective medium calculation. The predicted spectra successfully reproduce the observed qualitative features over a wide range of wavelengths.     

Optical properties of methanol at high pressures

The pressure dependence of the refractive index of methanol has been measured in a diamond-anvil cell up to 5·6 GPa at room temperature. These experiments cover the liquid phase of methanol (below 3·6 GPa) as well as the ‘superpressed fluid’ phase above 3·6 GPa. We have extracted the polarizability of methanol from our experimental data and the equation of state by using the Lorentz-Lorenz equation.     

Investigation on properties of TiO2 thin films deposited at different oxygen pressures

TiO₂ thin films were prepared by electron beam evaporation at different oxygen partial pressures. The influences of oxygen partial pressure on optical, mechanical and structural properties of TiO₂ thin films were studied. The results showed that with the increase of oxygen partial pressure, the optical transmittance gradually increased, the transmittance edge gradually shifted to short wavelength, and the corresponding refractive index decreased. The residual stresses of all samples were tensile, and the value increased as oxygen partial pressure increasing, which corresponded to the evolutions of the packing densities. The structures of TiO₂ thin films all were amorphous because deposition particles did not possess enough energy to crystallize.     

Structure and electrical properties of thin films of copper selenide

Electron-diffraction and electron-microscope methods were used to investigate the structure of Cu₂Se films of close to stoichiometric composition. It is shown that in polycrystalline and single-crystal films of thickness >400Å at room temperature, the tetragonal modification is stable, which at temperatures above 400°K is transformed into the cubical modification. In thinner films d<400 Å the cubical modification of copper selenide is stable at room temperature. A sharp peak is observed at 400°K on the temperature dependence of the resistance; this is connected with the phase transition. At room temperature, copper selenide is a degenerate p-type semiconductor with carrier concentration 5 · 10²²–8 · 10²⁰ cm^–3, depending on the thickness of the film.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 90–94, August, 1973.     

Optical and electrical properties of thermally oxidized bismuth thin films

Bismuth trioxide (Bi₂O₃) thin films were prepared by dry thermal oxidation of metallic bismuth films deposited by vacuum evaporation. The oxidation process of Bi films consists of a heating from the room temperature to an oxidation temperature (T_o = 673 K), with a temperature rate of 8 K/min; an annealing for 1 h at oxidation temperature and, finally, a cooling to room temperature. The optical transmission and reflection spectra of the films were studied in spectral domains ranged between 300 nm and 1700 nm, for the transmission coefficient, and between 380 nm and 1050 nm for the reflection coefficient, respectively. The thin-film surface structures of the metal/oxide/metal type were used for the study of the static current-voltage (I-U) characteristics. The temperature of the substrate during bismuth deposition strongly influences both the optical and the electrical properties of the oxidized films. For lower values of intensity of electric field (ξ < 5 × 10⁴V/cm), I-U characteristics are ohmic.     

The electrical properties of sulfur-implanted cubic boron nitride thin films

Cubic boron nitride (c-BN) thin films are deposited on p-type Si wafers using radio frequency (RF) sputtering and then doped by implanting S ions. The implantation energy of the ions is 19 keV, and the implantation dose is between 10 15 ions/cm 2 and 10 16 ions/cm 2 . The doped c-BN thin films are then annealed at a temperature between 400°C and 800 C. The results show that the surface resistivity of doped and annealed c-BN thin films is lowered by two to three orders, and the activation energy of c-BN thin films is 0.18 eV.     

Insulated-ceystal method for measuring electrical properties of thin semiconducting films

Procedure and apparatus are described for measuring the resistivity, free-charge density, and free-charge mobility in thin semiconducting films. The method is based on the dependence of the power transmitted to a microwave transmission line on the density and mobility of free charge in a semiconductor in the line insulated from electrodes on both sides by dielectric layers. Experimental results are reported.Translated from Izvestiya VUZ. Fizika, No. 5, pp. 105–109, May, 1971.     

General electrical transport properties of polycrystalline multi-layered metallic thin films

We have derived, following the recent theoretical calculation of the electrical conductivity of multi-layered metallic thin films, a general solution of the electrical conductivity for those films with grain structures, since those structures give important contributions to the electrical transport properties of polycrystalline thin film. The temperature coefficients of resistivity have also been obtained.     

The representation of thermodynamic properties at high pressures

It is sometimes advantageous to have an expression for the Gibbs energy, G_m(T,P), from which one can analytically derive an expression for the Heimholtz energy, F_m(T, V_m). Such an expression is suggested for solid substances and it is shown how expressions for other physical properties can be derived from it.     

The electrical and magnetic properties of epitaxial orthorhombic YMnO3 thin films grown under various oxygen pressures

Orthorhombic YMnO₃ thin films were epitaxially grown on bare and LaNiO₃ buffered (0 0 1)-SrTiO₃ substrates by pulsed laser deposition under various oxygen pressures from 5 to 30 Pa. The crystal structure and microstructure of these films have been characterized by both X-ray diffractions and transmission electron microscopy. The leakage current, modeled as the space charge limited current (SCLC) mechanism, decreased significantly with the increase of oxygen content. It is further found that the magnetic property of films is greatly enhanced in YMnO₃ films grown under high oxygen pressure, which can be explained decreased oxygen vacancies. In addition, bipolar switching behavior was obtained only in the films grown under 30 Pa oxygen pressure, which is attributed to the decrease of voltage-driven oxygen vacancy migration.