Showing papers on "Atmospheric temperature range published in 1984"

Precise determination of lattice parameter and thermal expansion coefficient of silicon between 300 and 1500 K

Abstract: The lattice parameter of high‐purity silicon is measured as a function of temperature between 300 and 1500 K, and the linear thermal expansion coefficient is accurately determined. Precise measurements are made by the high‐temperature attachment for Bond’s x‐ray method to a few parts per million. It is found that the temperature dependence of the linear thermal expansion coefficient α(t) is empirically given by α(t)=(3.725{1−exp[−5.88×10−3{(t−124)} +5.548×10−4t)×10−6 (K−1), where t is the absolute temperature ranging from 120 to 1500 K. It is shown that the lattice parameter in the above temperature range can be calculated using α(t) and the lattice parameter at 273.2 K (0.5430741 nm). Measured values of the lattice parameter and the thermal expansion coefficient for high‐purity float‐zoned (100 kΩ cm) and Czochralski‐grown (30 Ω cm) single crystals are uniformly distributed within ±1×10−5 nm and ±2×10−7 K−1 with respect to the values obtained from the above empirical formula.

A Universal Scale of Apparent Temperature

Abstract: Based on the total thermal resistance required by a human model to effect equilibrium, a scale is prepared showing apparent temperature for any combination of dry-bulb temperature, vapor pressure, wind speed and extra radiation likely to be encountered meteorologically. Application to normal midday climates of the United States shows that dry-bulb temperature is modified by the three other variables by from −5 to +7 K. However, multiple linear regression indicates that dry-bulb temperature correlates most strongly with apparent temperature, and provides simple computing formulas.

Selective Low Pressure Chemical Vapor Deposition of Tungsten

Abstract: We have examined the kinetics of low pressure chemical vapor deposition of tungsten by the hydrogen and silicon reduction of within a pressure range of 0.1–5 torr and a temperature range of 250°–500°C. The rate‐limiting mechanism for the hydrogen reduction system was determined to be the dissociation of adsorbed on the surface, with an activation energy of 0.71 eV. A self‐limiting deposit results from the reaction, the thickness and structure of which are dependent upon the initial native oxide characteristics. Deposition occurs selectively on materials that react directly with or yield monatomic hydrogen. In the presence of hydrogen, the degree of selectivity is a function of temperature, substrate material, and surface cleanliness.

Attachment coefficients for the reactions of electrons with CCl4, CCl3F, CCl2F2, CHCl3, Cl2 and SF6 determined between 200 and 600 K using the FALP technique

Abstract: The rate coefficients, beta , for the attachment reactions of electrons with CCl4, CCl3F, CCl2F2, CHCl3, Cl2 and SF6 have been measured under truly thermal conditions over the approximate temperature range 200-600K using a flowing-afterglow/Langmuir probe apparatus. The beta values obtained at 300K are 3.9*10-7, 2.6*10-7, 3.2*10-9, 4.4*10-9, 2.0*10-9 and 3.1*10-7 cm3 s-1 respectively. From the variation with temperature of beta for the CCl2F2, CHCl3 and Cl2 dissociative attachment reactions, activation energies, Ea, of 0.15, 0.12 and 0.05 eV respectively were derived. The beta for CCl4, CCl3F and SF6 are close to their theoretical limiting values within the temperature range investigated. While Cl- was the only product ion observed for the reactions involving chlorine-containing molecules, both SF6- and SF5- were observed for the SF6 reaction. The data obtained are compared with previous data and the separate influences of electron temperature and gas temperature are noted.

The exponential optical absorption band tail of Hg1−xCdxTe

Abstract: The optical absorption edges of Hg0.71Cd0.29Te and CdTe were measured over the temperature range 80≤T≤300 K. The refractive indices of these materials are determined over a large energy range at T=300 K and their dispersion relation is given. The absorption band tail of Hg1−xCdxTe has an exponential shape. Its slope increases with decreasing temperature. It is suggested that this tail is not caused by permanent lattice disorder but is a material property. An empirical expression for the absorption coefficient as a function of temperature and composition is derived. Using this expression, the zero‐intercept cut‐on energy of the infrared transmission spectrum at room temperature is used to define the composition for any desired thickness of Hg1−xCdxTe sample.

Defects introduced in silicon wafers during rapid isothermal annealing: Thermoelastic and thermoplastic effects

Abstract: The temperature and stress distribution induced in silicon wafers during ‘‘rapid isothermal’’ annealing have been calculated for two commonly used heating methods: (a) by a strip heater and (b) by uniform irradiation with an energy flux. Analytical expressions have been obtained for the temperature and stress profiles which show that thermoelastic effects, originated by the temperature drop at the sample edge, are much higher in case (b). The conditions of plastic deformation and consequent damage introduction have been established by comparing the yield stress with the value of stress resolved on the {111} planes in the 〈110〉 slip directions. As a result, the topographic distribution of the slip lines, the extension of the peripheral damaged region, and the temperature threshold for damage introduction have been evaluated for 2‐ and 4‐in. wafers. Rapid isothermal annealing experiments have been performed to check the results of the calculations. Two‐inch silicon wafers were irradiated uniformly for 15 sec in the temperature range from 930 to 1400 °C by using a shuttered electron gun. The threshold temperature for damage onset was found to lie in the interval 1030–1090 °C; the observed geometrical distribution of the slip lines and their extension were consistent with theoretical estimates.

An infrared and neutron scattering analysis of the precipitation of oxygen in dislocation-free silicon

Abstract: The precipitation of oxygen in silicon has been studied in the temperature range 650 to 1050 degrees C using the techniques of chemical etching, IR absorption applied to the 9 mu m band (4.2K), and small-angle neutron scattering (SANS). The IR data and etch pit counts, relating to the number densities of precipitate particles, have been fitted to Ham's theoretical model for the diffusion limited growth of randomly distributed particles. Full allowance is made for the increase in size of the precipitates with increasing time and good agreement is found over the complete period starting from zero time. Values of the diffusion coefficient of oxygen so determined are in excellent agreement with other data obtained by different methods, including SANS measurements at 750 degrees C described in the present work. The combined data give D=0.11 exp(-2.51 eV/kT) cm2s-1. The SANS data also indicate that the precipitates are not spherical in shape after a short initial period, and they show that the initial concentration of particles nucleated decreases with annealing time. The solid solubility cs(T) is determined at each temperature and compared with previous measurements. The authors conclude that the best combination of results leads to cs(T)=2.6*1022 exp(-1.4 eV/kT) down to 850 degrees C. At lower temperatures cs decreases more slowly with decreasing temperature, indicating a possible change in the structure or the form of the precipitated SiO2 phase.

High‐temperature electrical properties of 3C‐SiC epitaxial layers grown by chemical vapor deposition

Abstract: Electrical properties of 3C‐SiC layers, epitaxially grown on silicon by chemical vapor deposition, have been investigated at the temperatures between room temperature and 850 °C. In this temperature range, the electron mobility changes with temperature as μH∼T−1.2∼−1.4. The weaker temperature dependence of mobility and the larger mobilities compared with other polytypes of SiC suggest that 3C‐SiC is a promising material for devices operated at high temperatures.

Electrical transport properties of CoSi2 and NiSi2 thin films

Abstract: Transport studies have been performed on thin films of CoSi2 and NiSi2 in the temperature range 1–300 K. The conductivities are metallic with essentially the same temperature dependence; however, the residual resistivities are markedly different even though the two silicides are structurally similar (the room‐temperature resistivity of NiSi2 being at least twice that of CoSi2 of 15 μΩ cm). The difference is attributed to intrinsic defects in NiSi2. This defect has been simulated by ion bombardment of the film where it is also shown that Matthiessen’s rule is obeyed over a remarkable range of bombardment doses.

Kinetic limitations to surface segregation during MBE growth of III–V compounds: Sn in GaAs

Abstract: The incorporation of Sn as a dopant in GaAs has been studied in the temperature range of 500°–650° C, over a wide range of Ga and As fluxes, the latter being incident as either As4 or As2 molecules. The results are explained in terms of a surface segregation model in which the behaviour at high growth temperatures (above ∼600 °C) approaches thermal equilibrium, but growth at lower temperatures involves a kinetic limitation to the segregation process.

Temperature dependence of the electron mobility in GaAs‐GaAlAs heterostructures

Abstract: We have studied the temperature dependence of the mobility of two‐dimensional electron gases formed at the interface of high‐quality GaAs‐GaAlAs heterostructures, focusing on the temperature range 4–40 K. The inverse mobility is shown to increase linearly with temperature, with a slope which increases with the electron density and is independent of the zero‐temperature mobility. The results are consistent with a theoretical model for the acoustic‐phonon mobility that includes screening, indicating that the temperature dependence in high mobility GaAs‐GaAlAs structures is dominated by phonons rather than ionized impurities. A good agreement between theory and experiment is found using a value of 13.5 eV for the deformation potential of GaAs.

Kinetics of formation of the midgap donor EL2 in neutron irradiated GaAs materials

Abstract: Fast neutron irradiation of n‐GaAs mainly induces two deep electron traps in the band gap. The first of these is referred to as EL6 and has an energy level at Ec −0.35 eV, where Ec is the conduction band minimum; the second one has a wide energy distribution around Ec −0.5 V and is referred to as the U band. The annealing kinetics of these two levels is studied, and it is found that EL6 vanishes by a pair‐defect (short‐range) type recombination while the U band anneals by a long range migration process. Both annealing processes can be observed between 400 and 500 °C. In this annealing temperature range, the concentration of deep donor level EL2 (Ec −0.75 eV) increases with temperature. It is suggested that the defect giving rise to the EL2 level is created during irradiation but that medium range (tens to hundreds of A) interactions with other neighboring defects strongly influence the electric properties of the overall defect, which is then detected as the U band. Due to long range migration, annealing r...

Thermal analysis and NMR study of a poly(ethylene oxide) complex electrolyte: PEO(LiCF3SO3)x

Abstract: We have determined the equilibrium diagram between the different phases which coexist in the complexes between the poly(ethylene oxide) PEO and the salt LiCF3SO3, by using DSC and NMR techniques. We have also measured the variation of the glass transition temperature as a function of the salt concentration dTg/dx = 280 K/(mole of salt per mole of monomer unit). We show that in the temperature range 340-420 K the ionic conduction 03C3 only takes place in the amorphous phase. The thermal dependence of 03C3, previously interpreted in term of Arrhenius law, indeed results from that of three terms : the salt concentration in the amorphous phase (number of carriers), the local dynamics of the polymer chains (diffusion coefficient) and the respective amounts of crystalline and amorphous phases. The temperature dependence of each of these parameters has been estimated from experiments in the sample x-1 = 8 and they combine to give a fair description of 03C3(T). A striking result is the small temperature dependence of the diffusion coefficient (D03C3 ~ 6 x 10-8 cm2 s-1 at 375 K).

Simplified models for the temperature dependence of linewidths at elevated temperatures and applications to CO broadened by Ar and N2

Abstract: The broadening coefficients for i.r. lines of CO perturbed by Ar are calculated in the temperature range 300–3500 K using the formalism previously developed by two of us (D.R. and J.B.). The results are compared with high-resolution spectroscopic measurements of shock-heated CO-Ar gas mixtures. A simplified model is proposed to describe the temperature dependence of the linewidths. The resulting model is applied to CO broadened by N 2 and the results are critically discussed.

Application of wide‐gap semiconductors to surface ionization: Work functions of AlN and SiC single crystals

Abstract: For surface ionization purposes, a study of the work functions of SiC and AlN, both refractory wide‐gap semiconductors, has been undertaken. Work function measurements have been performed in the 300–1600‐K range using the Shelton retarding field method. Surface cleaning was carried out by heating in uhv to a high temperature using of a cw CO2 laser. Both n‐ and p‐type 6H SiC single crystals with extreme bulk doping levels were investigated. For each doping type, the work functions have been found to be temperature independent. They exhibit only a slight variation from the n to the p type (4.75 and 4.85 eV, respectively) giving evidence, as in the case of Ge and Si, of Fermi level pinning at the surface by the intrinsic surface states. For an n‐type AlN single crystal, the work function, measured in the high temperature range, remains constant as the temperature varies. The value of 5.35 eV obtained for AlN makes it a most attractive material for positive surface ionization applications.

Viscosity of aqueous NaCl solutions in the temperature range 25–200 °C and in the pressure range 0.1–30 MPa

Abstract: New precise viscosity data are presented for aqueous solutions of NaCl; these data cover the temperature range 25–200 °C, the pressure range 0.1–30 MPa, and the concentration range 0–6 mol · kg−1. The experimental precision is ±0.5%; a comparison of the present results with data available in the literature indicates that the accuracy of the present data is also of the order of ±0.5%. Two empirical correlations that reproduce the data within the precision are also given.

A molecular beam surface scattering study of ammonia oxidation on the platinum(111) crystal face

Abstract: The catalyzed reaction of ammonia and molecular oxygen on a Pt(111) single-crystal surface was studied over the crystal temperature range of 550-1100 K. A molecular beam-surface scattering technique was utilized and two-photon ionization was used to probe the NO product. Two different NO production kinetics were observed. These could be characterized by activation energies of 29 +/- 4 and 14 +/- 3 kcal/mol for the faster and slower processes, respectively. The internal energy distribution of the scattered NO product, e.g., rotational and vibrational energies, were found to have a lower temperature than the crystal temperature. Possible reaction mechanisms are discussed.

Electron tunneling in heavily In‐doped polycrystalline CdS films

Abstract: The electrical properties of heavily In‐doped polycrystalline CdS films have been studied as a function of the doping level. The films were prepared by vacuum coevaporation of CdS and In. Conductivity and Hall measurements were performed over the temperature range 77–400 K. The conductivity decreases weakly with the temperature and shows a tendency towards saturation at low temperatures. A simple relationship σ=σ0(1+βT2) is found in the low‐temperature range. The temperature dependence of the mobility is similar to that of the conductivity since the Hall coefficient is found to be a constant in the whole temperature range. We interpret the experimental results in terms of a modified version of grain‐boundary trapping Seto’s model, taking into account thermionic emission and tunneling of carriers through the potential barriers. The barriers are found to be high and narrow, and tunneling becomes the predominating transport mechanism.