Transport properties of InSe x flash evaporated thin films

Thin films of InSe _x were obtained by vacuum evaporation of polycrystalline materials onto substrates at moderate temperatures,T _s. Electrical properties of films grown from different stoichiometries of flash source materials are reported in this work. The temperature dependence of the conductivities shows two conduction regimes. The low temperature regime exhibits aT ^–1/4 conductivity dependence which fits well, using the Mott model, with an average localized states density value ofN(E _F ) 8×10¹⁸cm^–3eV^–1. Hall measurements as a function of temperature show that the predominant conduction mechanism is scattering by grain boundaries in polycystalline films.     

Eliashberg analysis of the specific heat of Nb0.75Zr0.25

The specific heat of Nb_0.75Zr_0.25 is measured from 1.2 to 50 K in zero magnetic field. A phonon density of statesF() and a spectral electron-phonon coupling function ²()F() are fitted to the data in the normal state and in the superconducting state. The results are compared with a previous similar analysis of the specific heat of pure Nb and with published tunneling data. It is found that in Nb_0.75Zr_0.25, –*=1.13, _log=109 K, and N(0)=0.85 eV^–1 at^–1 spin^–1, compared with the figures 0.84, 146 K, and 0.85 eV^–1 at^–1 spin^–1, respectively, in pure Nb. These data confirm that the increase ofT _c upon the alloying of Nb with Zr is due to phonon softening. They further show that the electronic density of states at the Fermi level is identical in Nb and Nb_0.75Zr_0.25. Dimensionless thermodynamic ratios predicted from tunneling data are entirely confirmed, thus confirming the internal consistency of the Eliashberg theory for superconductivity.     

Plasma-enhanced chemical vapour deposited silicon-nitride films for interface studies

Silicon nitride (SiN _x ) films of varying stoichiometry (x=1.04, 1.39 and 1.63) were deposited on silicon substrates at 250 C by plasma-enhanced chemical vapour deposition (PECVD). The N/Si ratios were determined by electron spectroscopy for chemical analysis (ESCA) and Rutherford backscattering (RBS) measurements. Optical, electrical and interface characterization were carried out for the films. It was observed that nitrogen-rich films (x=1.63) gave the best electrical properties and the lowest interface state density, which was 1.1 × 10¹¹ eV^–1 cm^–2. The resistivity and breakdown field of these films were 5.1 × 10¹³ cm and 1.5 × 10⁶ V cm^–1, respectively.     

Determination of the Thermal Diffusivity of Edible Films

One of the most important factors in the preparation of edible films regards the choice of ingredients. Edible films are commonly prepared with single or mixed high-molecular-weight compounds like proteins and gums. In the present work, protein and gum-based edible films were prepared and their thermal diffusivity determined by photoacoustics. The films were prepared with different concentrations of four basic ingredients: whey protein concentrate, mesquite gum, sodium alginate, and -carrageenan. In single-component films, the highest thermal diffusivity was found in mesquite gum (1.97×10^–7m²s^–1), followed by sodium alginate, whey protein concentrate, and -carrageenan samples. In composed films, the highest thermal diffusivity was obtained in a ternary film made of mesquite gum, whey protein concentrate, and sodium alginate in identical parts (5.20×10^–7m²s^–1).     

Proton conducting polymer electrolyte: II poly ethylene oxide + NH4l system

A new proton conducting polymer electrolyte PEO + NH₄l system has been investigated. The solution-cast films of different stochiometric ratios have been prepared and characterized. Proton transport has been established using various experimental studies, namely optical microscopy, X-ray diffraction, differential thermal analysis, infrared, coulometry transient ionic current and electrical conductivity measurements at different temperatures and humidity. The maximum conductivity of the complexed material has been found to be 10^–5 S cm^–1. Both H⁺ ion and I^– anion movements are involved with respective transference numbers and mobilities ast _H+=0.74, ,t _l–=0.09, _H+=4.97 × 10^–6 cm² V^–1 s^–1 and _l–=7.65.     

X-ray studies on the thermal expansion of tellurium dioxide

Using a Unicam 19 cm high temperature powder camera, the precision lattice parameters of tellurium dioxide have been determined at different temperatures in the range 30 to 461 °C. Using this data, the coefficients of thermal expansion, and parallel and perpendicular to the principal axis respectively, have been evaluated. The temperature dependence of the coefficients of thermal expansion is represented by the following equations: =29.673×10^–6+1.552sx10^–8 T+1.069sx10^–10 T ² =9.875sx10^–6–5.440sx10^–9 T+4.572sx 10^–12 T² HereT is the temperature in °C. The thermal expansion of tellurium dioxide has been explained in terms of the interionic distances.     

Structural and electrical properties of cadmium-sulpho-selenide solid solutions

Complete solid solutions of CdS _x Se_1–x (0x1) were synthesized by vacuum fusion of stoichiometric proportions of CdS and CdSe. X-ray diffraction data revealed that they possess the hexagonal wurtzite structure. The unit cell lattice constants vary linearly with the composition parameter,x, following Vegard's law.Thin films of CdS _x Se_1–x (0x1) solid solutions could be deposited onto glass substrates by thermal evaporation of the bulk material in 10^–4 Pa vacuum. Structural investigation showed that the films are polycrystalline with predominant appearance of the (002) reflecting plane. On annealing at 250°C in 10^–2 Pa vacuum atmosphere, aggregation and rearrangement of the as-deposited tiny crystallite occurred, preserving the same crystal structure.The dark electrical resistivity of the films is independent on the film thickness, but it varies appreciably with the composition parameter,x, showing a minimum resistivity of 0.02 cm atx=0.55. The temperature dependence of the resistivity follows the semiconducting behaviour with an extrinsic and an intrinsic conduction below and above 70°C, respectively. The determined activation energies 0.2 eV and 0.8 eV, respectively, correspond to shallow and deep trap levels, respectively.     

Transport properties of CdGa2Se4 thin films

The d.c. conductivity was determined for CdGa₂Se₄ thin films in the temperature range 300–625 K for as-deposited and heat-treated films. The conductivity at room temperature of films of thickness 326 nm prepared at a temperature of 573 K was found to be 10^–12 ( cm)^–1. The dependence of the electrical conductivity on the annealing temperature in a vacuum of 1 Pa for a thin film of thickness 140 nm, shows that the electrical conductivity increases with increasing annealing temperature. However, the activation energies E and E decrease with increasing annealing temperature. The data of these annealed films are in agreement with the Meyer–Neldel rule. The thermoelectric power measurements indicate p-type conduction in the as-deposited films as well as for the heat-treated films. The p-type conduction is due to the cadmium deficiency as indicated by EDX. The difference between the value of the activation energy calculated from the thermoelectric power E _S and that obtained from the conductivity E indicates the presence of long-range potential fluctuations.     

Dependence of the flux flow viscosity coefficient on the Ginzburg-Landau parameter κ in superconducting indium films

The flux flow viscosity coefficient b ^–1 (in units of ₀ H _{c n} ^–1 c ^–2) of vacuum-deposited indium thin films with low values (1.0–2.8) is measured at temperatures between 0.5T _cand 0.98T _cin the weak magnetic field region. At each temperature, b ^–1 decreases as increases for larger than 1.7. The decrease of b ^–1 with increasing is more rapid as the temperature increases. From an analysis of the present results as well as the existing data on intermediate- and high- superconducting alloys, the relation between b ^–1 and is established over a wide range of . The dependence of b ^–1 on is qualitatively explained by taking into account the contribution of the normal electron dissipation to the viscosity coefficient in the Bardeen-Stephen model.Financial support provided by the Fonds National Suisse de la Recherche Scientifique.On leave from the Department of Electronic Engineering, Faculty of Engineering, Kyushu Industrial University, Fukuoka, Japan.     

Some electrical characteristics of lithium and yttrium sialons

Some electrical properties of hot-pressed lithium sialons, Li _x/8Si_6–3x/4Al_5x/8O _x N_8–x havingx<5 and an yttrium sialon were measured between 291 and 775 K; the former consisted essentially of a single crystalline phase whereas the latter contained 98% glassy phase. For lithium sialons, the charging and discharging current followed al(t) t ^–nlaw withn=0.8 at room temperature. The d.c. conductivities were about 10^–13 ohm^–1 cm^–1 at 291 K and rose to 5×10^–7 ohm^–1 cm^–1 at 775 K. At high temperatures electrode polarization effects were observed in d.c. measurements. The variation of the conductivity over the frequency range 200 Hz to 9.3 GHz followed the () ⁿ law. The data also fitted the Universal dielectric law,() ^n–1 well, and approximately fitted the Kramers-Kronig relation()/()– =cot (n/2) withn decreasing from 0.95 at 291 K to 0.4 at 775 K. The temperature variations of conductivities did not fit linearly in Arrhenius plots. Very similar behaviour was observed for yttrium sialon except that no electrode polarization was observed. The results have been compared with those obtained previously for pure sialon; the most striking feature revealed being that _d.c. for lithium sialon can be at least 10³ times higher than that of pure sialon. Interpretation of the data in terms of hopping conduction suggests that very similar processes are involved in all three classes of sialon.     

Microstructural study of Au-Pd-Zn ohmic contacts to p-type InGaAsP-InP

A detailed microstructural study has been done on Au-Pd-Zn ohmic contacts to p-type InGaAsP epitaxially grown on InP. The doping level in the InGaAsP was 1.0 × 10¹⁹ to 1.5 × 10¹⁹ cm^–3 near the surface with the Zn concentration graded to a value of 7 × 10¹⁸ cm^–3 at the InGaAsP-InP interface. Metal layers (10 nm Pd,3 nmZn, 25 nm Pd and 50 nm Au) were deposited sequentially by electron beam evaporation. Contact resistances less than 10^–4 cm² were achieved for all annealing temperatures studied (380–440 C) and a minimum contact resistance of 2 × 10^–6 cm² was obtained for an anneal at 400 C for 20 s. Comparisons were made to similar metallizations on p-type InP. Lower contact resistances were achieved for the quaternary material compared with the binary material, however, contact stability and uniformity were worse.     

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

Ta_100-x B _x alloy films were prepared by r.f.-sputtering in the chemical composition range 45 x 77. Ta_100-x B _x (45 x 58) films consist of the amorphous phase, while the TaB₂ crystal phase was observed in Ta_100-x B _x (66 x 77) films. A remarkable preferred orientation with the (001) plane of TaB₂ parallel to the film surface was observed in Ta₃₄B₆₆. The d.c. electrical conductivity of Ta_100-x B _x (45 x 77) films decreases with increasing boron content in the range 6.7 × 10³ to 1.3 × 10^3–1 cm^–1. The micro-Vickers hardness of Ta_100-x B _x (45 x 77) films was in the range 2200 to 2600 kg mm^–2.     

Metrological Characteristics of MN-3 Solid-Body DC Voltage Measures

Results of theoretical and experimental investigations into the statistical characteristics of the voltage instability of type MN-3 measures are presented. The capabilities of linear mathematical models of the voltage instability of solid-body measures are considered and evaluated. It is shown that MN-3 type measures maintain a relative measurement (comparison) error in the range 1·10^–8–3·10^–8 only for a measurement period t 1 h and that with t 1 day, the error increases to values in the range 5·10^–8–8·10^–8, while when t 1–3 months it increases to 5·10^–7.     

Coarsening of precipitates and dispersoids in aluminium alloy matrices: a consolidation of the available experimental data

Experimental data on the coarsening of precipitates and dispersoids in aluminium-based matrices are reviewed. Available data are tabulated as K=(r ³–r ₀ ³ )/t where r ₀ is the initial particle radius and r is its value after time t at temperature T, and then plotted as log (KT) against 1/T for consolidation and assessment. The considerable body of data for -A₃Li in Li-containing alloys is well represented by K=(K ₀/T) exp (–Q/RT) with K ₀=(1.3 _–0.5 ^+3.0 ) × 10^–13m³Ks^–1 and Q=115±4kJ mol^–1. The relatively limited data for and in Cucontaining alloys are representable by the same relationship with K ₀4 × 10^–8 and — 4 × 10^–10 m³ Ks^–1, respectively, and Q — 140 kJ mol^–1. Available data for coarsening of L1₂ ^– Al₃(Zr, V) and related phases in Zr-containing alloys and of Al₁₂Fe₃Si and related phases in Al-Fe based alloys indicate (i) rates of coarsening at 375 to 475 °C (0.7 to 0.8T_m) five to eight orders of magnitude less than would be expected for , and in this temperature range, and (ii) high activation energies of 300 and 180 kJ mol^–1, respectively.     

Thermophysical Property Measurements of Supercooled and Liquid Rhodium

The density, the isobaric heat capacity, the surface tension, and the viscosity of liquid rhodium were measured over wide temperature ranges, including the supercooled phase, using an electrostatic levitation furnace. Over the 1820 to 2250 K temperature span, the density can be expressed as (T)=10.82×10³–0.76(T–T _m ) (kgm^–3) with T _m =2236 K, yielding a volume expansion coefficient (T)=7.0×10^–5 (K^–1). The isobaric heat capacity can be estimated as C _P (T)=32.2+1.4×10^–3(T–T _m ) (Jmol^–1K^–1) if the hemispherical total emissivity of the liquid remains constant at 0.18 over the 1820 to 2250 K interval. The enthalpy and entropy of fusion have also been measured, respectively, as 23.0 kJmol^–1 and 10.3 Jmol^–1K^–1. In addition, the surface tension can be expressed as (T)=1.94×10³–0.30(T–T _m ) (mNm^–1) and the viscosity as (T)=0.09 exp[6.4×10⁴(RT)] (mPas) over the 1860 to 2380 K temperature range.     

Supercooling of In2Bi and InBi Melts

The effect of melt overheating T ⁺ on the critical supercooling T ^– of liquid In₂Bi and InBi is studied by cyclic thermal analysis. It is shown that, the T ^– for In₂Bi is 2.0 K, independent of the melt preheating temperature. In contrast, the T ^– for InBi varies jumpwise with T ⁺: T ^– 1.0–1.6 K at T ⁺ < 5 K, and T ^– 16 K at T ⁺ = 5–300 K, independent of the cooling rate (varied from 0.002 to 8.0 K/s). The solidification behaviors of In₂Bi and InBi are shown to correlate with the structures of their liquid and solid phases.     

Isochoric p–ρ–T Measurements for Binary Refrigerant Mixtures Containing Difluoromethane (R32), Pentafluoroethane (R125), 1,1,1,2-Tetrafluoroethane (R134a), and 1,1,1-Trifluoroethane (R143a) from 200 to 400 K at Pressures to 35 MPa

The p––T relationships were measured for binary refrigerant mixtures by an isochoric method with gravimetric determinations of the amount of substance. Temperatures ranged from 200 to 400 K, while pressures extended up to 35 MPa. Measurements were conducted on compressed gas and liquid samples with the following mole fraction compositions: 0.4997 R32+0.5003 R134a, 0.3288 R32+0.6712 R134a, 0.4996 R32+0.5004 R125, 0.5001 R125+0.4999 R134a, and 0.5000 R125+0.5000 R143a. Most published p––T data are in good agreement with this study. The uncertainty is 0.03 K for temperature and is 0.01% for pressure at p>3 MPa and 0.05% at p<3 MPa. The principal source of uncertainty is the cell volume (28.5 cm³), with a standard uncertainty of 0.003 cm³. When all components of experimental uncertainty are considered, the expanded relative uncertainty (with a coverage factor k=2 and, thus, a two-standard deviation estimate) of the density measurements is estimated to be 0.05%.     

Electrical and optical properties of vacuum-evaporated CdS films

1 m CdS films for the window layer of CdS/CulnSe₂ solar cells have been prepared by vacuum evaporation at various deposition conditions. Deposition rates were 0.73 and 3.3 nms^–1, and substrate temperature ranged from 50 to 225 C. The effect of the deposition conditions on the properties of CdS films was investigated by measuring electrical resistivity, optical transmittance and reflectance.The resistivity of the evaporated CdS films strongly decreased as substrate temperature decreased and the films with high deposition rate showed lower resistivity compared to the films with low deposition rate. Interestingly, the combination of high deposition rate and very low substrate temperature resulted in an increase of resistivity. The optical transmittance of CdS films increased as substrate temperature decreased and then decreased with further decrease in substrate temperature. The transmittance strongly depended on deposition rate at low substrate temperature (<100C), while it was independent of deposition rate at high substrate temperature (>100C). In particular, high transmittance can be extended to lower substrate temperature by reducing deposition rate. Low optical reflectance can be obtained by lowering substrate temperature. The results indicate that CdS films of low resistivity and high transmittance can be produced by vacuum evaporation at low substrate temperature and low deposition rate.     

Epitaxial growth of CdS on ionic substrates

Transmission electron microscopy has been used to study the structure of films of CdS evaporatedin vacua in the 10^–5 torr range on to (100) cleavage faces and cut and polished (110) and (111) faces of NaCl, and also on to (111) cleavage faces of BaF₂, (111) substrate faces were found to produce wurtzite structure (hexagonal) films with great structural perfection over wider ranges of epitaxial growth temperature than (100) substrate faces. The (100) and (110) substrates produced sphalerite structure (cubic) films. Electron beam evaporation and generally clean growth conditions were found to produce good quality films at low substrate temperatures. The films were in general free of any included grains and the diffraction patterns free of satellite spots. 111 or 10¯10 streaking was present in the diffraction patterns, however, except in the case of films grown on BaF₂ above 170° C, and on NaCl (111) above 250° C. These films were also free of planar defects and only contained of the order of 10¹⁰ dislocations per cm².     

Critical current density and dynamical relaxation rate below the matching field in thin films of YBa2Cu3O7−δ

We studied the superconducting current density j _s (B, T) and dynamical relaxation rate Q(B, T) of laser ablated thin films of YBa ₂ Cu ₃ O _7– with various dislocation densities (n _disl 7-70 m ^–2 ). In these films dislocations act as strong pinning centers like columnar defects in heavy ion-irradiated crystals. The matching field clearly manifests itself in a constant j _s (B) 5·10 ¹¹ - 1·10 ¹² Am ^–2 at T = 4.2 K and ₀ H 0.7 B and a constant Q(B). In contrast to irradiated crystals, in films we do not observe a peak in the relaxation rate Q versus T below the matching field B n _disl · ₀ . Instead, in thin films Q(T) increases monotonously with increasing temperature. We conclude that the influence of vortex-vortex interactions in thin films is greatly reduced due to the non-random distribution of pinning sites and the low matching field.