Showing papers on "Atmospheric temperature range published in 1983"

Diffusion of metals in silicon dioxide

Abstract: The diffusion coefficient and solubilities of several metals (Ag, Cu, Au, Pd, and Ti) have been investigated by bias temperature stress (BTS) of (MOS) structures using the candidate metal as the electrode. Temperatures ranged from 250° to 600°C, and the electric fields ranged from +106 to −106 V/cm in ambients of vacuum (10−6 torr), nitrogen, and forming gas . In dry , the activation energy for silver diffusion is found to be 1.24 eV in the temperature range of 275°–365°C. The diffusion coefficient for silver at 300°C in silicon dioxide is . Copper diffusion has an activation energy of 1.82 eV in the temperature range of 350°–450°C in a forming gas environment and a diffusion coefficient in at 450°C of . A thermodynamic model to predict the activation energy of the solid solubility of these metals in and an interstitial diffusion model, that includes both strain and electrostatic energies, which predicts the diffusion activation energy, have been developed. Diffusion coefficients are estimated from a closed form solution of the diffusion equation and the observed behavior of the metal in .

Carbon monoxide oxidation on the Pt(111) surface: Temperature programmed reaction of coadsorbed atomic oxygen and carbon monoxide

Abstract: Carbon dioxide formation from coadsorbed atomic oxygen and molecular carbon monoxide has been characterized using temperature programmed reaction spectroscopy over a wide range of initial oxygen and carbon monoxide coverages. The experiments were performed in an apparatus containing Auger electron spectroscopy, low energy electron diffraction, and a multiplexed mass spectrometer for the temperature programmed reaction experiments. A single reaction limited CO2 peak is observed in the 320–340 K temperature range over a wide range of initial atomic oxygen and molecular CO coverages, suggesting that a single reaction mechanism dominates. The activation energy for CO2 formation ranges from 166 kJ/mol (40 kcal/mol) for small surface concentrations of reactive adsorbed atomic oxygen and CO (0.4×1014/cm2) to 68 kJ/mol (17 kcal/mol) for larger surface concentrations of reactive adsorbed atomic oxygen and CO (2.5×1014/cm2). Low energy electron diffraction results indicate that adsorbed atomic oxygen forms islands ...

Diffusivity of oxygen in silicon at the donor formation temperature

Abstract: We present data on oxygen diffusivity in silicon for the temperature range 270–400 °C. The diffusivity is determined from the recovery kinetics of a stress induced dichroism in the 9‐μm oxygen infrared absorption band. We combine our data for well dispersed oxygen (i.e., crystals heat treated at 1350 °C for 20 h), with Mikkelsen’s recent mass transport work at higher temperature to obtain the diffusivity, D=0.17 exp (−2.54/kT), for the range 330–1240 °C. We have also found that the oxygen atomic hopping times can be as much as 100 times faster in crystals that have not received the 1350 °C heat treatment.

Elastic properties of a single-crystal forsterite Mg2SiO4, up to 1,200 K

Abstract: Elastic moduli of forsterite were measured between 300 and 1,200 K (≃ 1.6 times the Debye temperature) by the Rectangular Parallelepiped Resonance method. All the moduli decrease regularly with temperature. A summary of the results is as follows: temperature derivatives of elastic moduli, - ∂C ij /∂R in MPa/K whereC si =(C jj +C kk −2·C jk )/4; (i, j, k=1, 2, 3;i ≠j ≠k), and ρ is density in kg/m3. These data permit for the first time the calculation of elastic and thermal properties well into the classical range far above the Debye temperature. We find, for example, that the elastic constants, including the bulk moduls, closely follow standard equations throughout the measured temperature range. This information aids extrapolations up to the melting point. This data, coupled with thermal expansivity data permit the computations of thermal anharmonic parameters of minerals forT>θ.

The influence of morphology and molecular weight on ductile-brittle transitions in linear polyethylene

Abstract: The tensile behaviour of linear polyethylene was examined over a wide range of temperatures. Samples were prepared from low and medium molecular weight polymer with different morphologies, by varying the initial crystallization conditions. It was found that the temperature of the ductile-brittle transition was markedly different for different samples. In particular, low molecular weight polymer crystallized at a low degree of of supercooling, showed brittle behaviour over most of the temperature range, with a ductile-brittle transition near to room temperature. Rapidly quenched material, where the degree of supercooling is high, showed a very low ductile-brittle transition temperature, especially in high molecular weight polymer. The reasons for these differences in behaviour are discussed both at a phenomenological level and in terms of known structural differences between the different materials examined.

Incorporation rates of gallium and aluminum on GaAs during molecular beam epitaxy at high substrate temperatures

Abstract: Gallium arsenide, aluminum arsenide, and aluminum gallium arsenide epitaxial layers were grown by molecular beam epitaxy in the substrate temperature range 590–720 °C. The incorporation rates of Ga and Al in this temperature range were studied by means of thickness measurements. The growth rates of GaAs and AlxGa1−xAs were observed to be dependent on growth temperature above 640 °C while the AlAs growth rate was observed to be independent of growth temperature in the range investigated. The reduction of the GaAs growth rate at a growth temperature above 640 °C was found to be lessened by the presence of minute amounts of Al and excess As. For the fixed Ga flux and a growth temperature of 700 °C the GaAs growth rate and the Ga contribution to the growth rate of Al0.3Ga0.7As were 0.50 and 0.89 times their low temperature values, respectively, while at 680 °C these values were 0.88 and 0.99, respectively.

Stability and electrical transport properties of amorphous Ti1-xNix alloys

Abstract: Amorphous alloys of the type Ti1-xNix were prepared by means of melt spinning in the concentration range 0.25

Hydrogen diffusion in aluminium at high temperatures

Abstract: The diffusion of hydrogen in aluminium has been measured by the permeation method using a quadrupole mass spectrometer. Hydrogen was introduced by gas phase charging in the temperature range of 300-400 degrees C, and by electrochemical charging at room temperature. It was found that the diffusivity of hydrogen depends on the relative concentration of vacancies to the dissolved hydrogen concentration. The activation energy for the diffusion of hydrogen was found to be 0.61-0.62 eV at high temperatures where the concentration of vacancies was much higher than that of dissolved hydrogen. The value is near the migration energy of a vacancy in aluminium. On the other hand, at room temperature where the hydrogen showed a diffusivity considerably larger than that extrapolated from high temperatures. These facts suggest that hydrogen in aluminium migrates together with a vacancy at high temperatures due to a large binding energy between them.

Thermal Oxidation of Reactively Sputtered Titanium Nitride and Hafnium Nitride Films

Abstract: The oxidation behavior of reactively sputtered and thin films was investigated for oxide formation in dry and wet oxidizing ambient in the temperature range of 425°–800°C. For both cases, formation of a single‐oxide phase, rutile for oxidized and monoclinic for oxidized , was observed. The oxidation process is thermally activated, and it has a parabolic time dependence, except in the case of wet oxidized where nonuniform oxidation behavior was observed. The parabolic time dependence of the oxide growth is attributed to a transport‐controlled process which is limited by the diffusivity of the oxidant in the oxide. The dry oxidation of is much faster than the dry oxidation of at a given temperature. The oxidation rate is always higher in a wet than in a dry ambient.

Defects and Cation Diffusion in Magnetite (V): Electrical Conduction, Cation Distribution and Point Defects in Fe3‐δO4

Abstract: Electrical conductivity in magnetite has been studied experimentally as a function of temperature and oxygen activity between 560 and 1400°C. The results indicate that above TC (=575°C) an octahedral site small polaron mechanism is dominant over the entire temperature range (Ea = 0.1136 eV). By comparing data on electrical conductivity and thermoelectric power, a second (small polaron) mechanism (Ea = 0.714 eV) is detected at elevated temperatures. Additionally, equilibrium constants for the cation vacancy formation are derived from fitting the conductivity isotherms as a function of oxygen activity. These agree well with values determined thermogravimetrically.

X-ray study of the low-temperature phase transitions in LiKSO4

Abstract: Lattice parameters of LiKSO4 have been measured in the temperature range 155–300 K with an X-ray single-crystal Bond diffractometer. Below 180 K LiKSO4 transforms on cooling into an orthorhombic phase. Above this temperature there is a broad range of an intermediate hexagonal phase which depends on the real structure of the sample and differs considerably on cooling and on heating. The anomalies in the physical properties of LiKSO4 reported in the literature have been explained. The crystal structure of the low-temperature and intermediate phase, as well as the mechanism of the phase transitions, are suggested and discussed.

X-ray diffraction study of subgrain misorientation during high temperature creep of tin single crystals

Abstract: Creep tests in the high temperature range (0.68 Tm-0.94 Tm, where Tm is the melting temperature) have been performed on high purity tin single crystals with the [100] direction as the tensile axis. Above the transition temperature, about 0.84 Tm (150 °C), the creep activation energy was found to be almost equal to the self diffusion energy. Below the transition temperature the creep activation energy is about half of the self diffusion energy and has a value of the order expected for dislocation pipe diffusion. A method based on X-ray rocking curves was developed to measure subgrain misorientation angles of crept specimens. The average subgrain misorientation angles for specimens crept at 70 °C and 100 °C increased continuously with creep strain at rates a factor of 20 to 40 smaller than that predicted by a cross-slip controlled process. The average subgrain misorientation angles at a given strain decrease slightly with increasing temperature. However, no abrupt change of the angle was observed at the transition temperature. It was concluded that a cross-slip controlled mechanism cannot control below the transition temperature. Instead, our results lend support to Sherby and Weertman’s argument that dislocation climb controls creep over the entire high temperature regime.

Thermophysical properties of polycrystalline PbS, PbSe, and PbTe in the temperature range 300 700 K

Abstract: Thermal properties (thermal conductivity λ, thermal diffusivity a, and specific heat capacity c p of polycrystalline PbS, PbSe, and PbTe were measured in the temperature range 300–700 K. The electrical conductivity was also measured for the three substances. Lattice, electronic and bipolar components of thermal conductivity are much larger than the electronic part. The specific heat capacity is observed to increase slightly with temperature.

Cation Self-Diffusion in Cr2O3

Abstract: Self-diffusion of 51Cr was measured both parallel to and perpendicular to the c axis in single crystals of Cr2O3 as a function of oxygen partial pressure at 1490° and 1570°C. The oxygen-partial-pressure dependence of the diffusivity indicates that cation self-diffusion occurs by a vacancy mechanism. The values of the self diffusion coefficients determined in this experiment are about 104 times smaller than those previously reported in this temperature range.

Thermal conductivity of toluene in the temperature range 35–90°C at pressures up to 600 MPa

Abstract: New, absolute measurements of the thermal conductivity of liquid toluene are reported. The measurements extend over the temperature range 35–90°C and the pressure range 0.8–600 MPa. A new analytic evaluation of the contribution of radiation in an absorbing emitting fluid to the measurement process is presented. This analysis indicates that the thermal conductivity determined in a transient hot-wire instrument is the radiation-free value. As a consequence it is possible to assert that the overall uncertainty in the experimental data is one of ± 0.3%. A comparison of the data with the results of independent measurements by the same technique shows that the various sets of data are consistent within their mutual uncertainty.

Kinetics and Mechanism of Hydrocarbon Formation in the System C2H2/O/H at Temperatures up to 1300 K

Abstract: The consumption of O atoms and the formation of CO, C3H4 (Propyne and Propadiene), C4H2 (Butadiyne) and other hydrocarbons in the system C2H2/O with and without added H atoms has been studied in the temperature range 295–1300 K, p = 2.7 mbar. Both the rate of formation and the yield of C3H4 in C2H2-rich mixtures increases with higher temperature. The rate of C4H2 formation increases but the maximum concentration remains constant up to 500 K. The results can be described quantitatively through a slightly modified mechanism of 30 reactions that had been proposed previously for the reaction at room temperature.