Apparent Temperature Dependence Research Articles

Ion Beam Synthesis of IrSi3 by Implantation of 2 MeV Ir Ions+

ABSTRACTThe formation of a buried IrSi3 layer in (111) oriented Si by ion implantation and annealing has been studied at an implantation energy of 2 MeV for substrate temperatures of 450–550°C. Rutherford backscattering (RBS), ion channeling and cross-sectional transmission electron microscopy showed that a buried epitaxial IrSi3 layer is produced at 550°C by implanting ≥ 3.4 × 1017 Ir/cm2 and subsequently annealing for 1 h at 1000°C plus 5 h at 1100°C. At a dose of 3.4 × 1017 Ir/cm2, the thickness of the layer varied between 120 and 190 nm and many large IrSi3 precipitates were present above and below the film. Increasing the dose to 4.4 × 1017 Ir/cm2 improved the layer uniformity at the expense of increased lattice damage in the overlying Si. RBS analysis of layer formation as a function of substrate temperature revealed the competition between the mechanisms for optimizing surface crystallinity vs. IrSi3 layer formation. Little apparent substrate temperature dependence was evident in the as-implanted state but after annealing the crystallinity of the top Si layer was observed to deteriorate with increasing substrate temperature while the precipitate coarsening and coalescence improved.

A theoretical comparison of the effects of the shape of the pinning potential and a distribution of pinning energies of the apparent pinning energy as measured by magnetic flux creep

In the analysis of magnetic flux creep experiments, it is assumed that, at a given temperature, the pinning energy, which must be overcome by thermal activation, depends on the magnetic induction and its gradient by U(B, Delta B) equivalent to U/sub p/(B)(1-( Delta B/ Delta B/sub max/))/sup n/, where U/sub p/ is the pinning well depth and Delta B/sub max/ corresponds to the critical current density with no thermal activation. Customarily, n is assumed to be unity, and any unusual temperature dependence of U/sub p/ is then ascribed to a distribution of well depths. However, realistic assumptions about the shape of the pinning potential yield 3/2<or approximately=n<or approximately=2, which yields an apparent distribution of well depths in the conventional analysis. Simple models are used to illustrate the characteristics of these two quite different origins for the apparent temperature dependence of well depth obtained from magnetic flux creep rates.

Gas phase reaction rates of N+2 with CH4, O2, and n-H2 at very low temperatures

Using a free jet flow reactor, we have measured the bimolecular rate coefficients for the reactions N+2 with CH4, O2, and n-H2 at temperatures below 15 K. The reaction of CH4 proceeds at a rate which is only slightly faster than the rates at 70 and 300 K, but shows no apparent temperature dependence between 8–15 K. The measurements for the reaction of N+2 with O2 near 10 K indicate a marked increase of the rate coefficient from the room temperature value. The kinetic energy dependence of the rate coefficient for the reaction N+2 with n-H2 resembles the peculiar behavior shown by the reactions of NH+3 and C2H+2 with H2 where a minimum is observed in the rate coefficient. Possible mechanistic implications of such distinct temperature dependences are discussed.

Photoisomerization of diphenylbutadiene in low-viscosity nonpolar solvents: Experimental manifestations of multidimensional Kramers behavior and cluster effects

The photoisomerization of diphenylbutadiene was studied by picosecond absorption spectroscopy over wide pressure and temperature ranges in liquid and supercritical alkanes, CO2, SF6, and He. The reaction shows typical features of a thermal unimolecular reaction on the S1 potential energy surface. The rate can be expressed by a combination of standard unimolecular rate theory and Kramers–Smoluchowski theory. However, multidimensional behavior manifests itself in the transition to the gas phase low pressure range as well as to the high density Kramers–Smoluchowski range: in the former case, the low pressure limit of a unimolecular reaction of the polyatomic molecule is approached; in the latter case, the effective imaginary barrier frequency shows a marked apparent temperature dependence. The experiments also suggest contributions of reactant–solvent cluster interactions, which modify the barrier height even in nonpolar solvents.

Splitting and shift of hot magnetophonon resonance peaks in a two-dimensional electron gas

The splitting of the magnetophonon resonance peaks in a two-dimensional electron system is investigated as function of the electric field (or average electron velocity) for different values of the broadening of the Landau levels. We found that for small broadening the maxima in the magnetophonon oscillations are split into two peaks. A new physical interpretation is presented for this splitting which is based on the separate contributions of LO-phonon absorption and emission processes. A shift of the resonance maxima is found when the broadening of the Landau levels is large. A new explanation is given for the apparent temperature and electron density dependence of the optical phonon frequency in heterostructures as determined from magnetophonon resonance experiments. A mechanism is proposed which is able to produce the observed shift in the resonant position and which is consistent with an interaction with the optical phonon mode of the bulk material.

Quantitative infrared methods for the measurement of crystallinity and its temperature dependence: polyethylene

Vibrational spectroscopic methods are widely used to characterize semicrystalline polymers in terms of crystallinity. The temperature coefficient of crystallinity, an important and fundamental quantity, is seldom determined for lack of a sensitive method. In this paper, we describe an infrared approach to the measurement of the temperature coefficient of crystallinity. We start from the well-known observation that the integrated intensities of the bands in the spectrum of a semicrystalline polymer change with temperature. It is also known, though less appreciated, that only part of the change is due to changes in crystallinity, the remaining part being due to changes in the intrinsic intensity of the bands. We outline a method for separating these overlapping effects. The method has been applied to a variety of semicrystalline polyethylene samples. The temperature coefficients are found to be highly dependent both on the temperature and on the morphology of the sample. In addition we report crystallinity measurements on a solution crystallized low molecular weight (A& = 13 600) sample, discuss the origin of an apparent anomalous temperature dependence of band intensity cited in the literature, and offer quantitative evidence that the temperature dependence of specific volume is, at temperatures above 0 C, largely determined by partial melting.

Effect of a sudden temperature increase on creep of aluminum at high temperature

Temperature change tests have been done during steady-state creep of polycrystalline aluminum to obtain some fundamental information on the activation energies for parameters related to high-temperature deformation. By the direct passing of a current through a specimen, a temperature increase of 5–20 K was achieved within 0.1–1 s. Immediately after the temperature rise, the creep rate was higher than that expected under the assumption that the activation energy for creep Qc was equal to that for self-diffusion, QD. The apparent Qc immediately after the temperature rise was about 175 kJ/mol. The creep rate became gradually lower and reached, within 1–2 s, the value expected from the relation, Qc ≒ QD = 135 kJ/mol. The experimental results have been discussed by taking into account the apparent temperature dependence of recovery and work-hardening rates during steady-state creep of pure metals. It is concluded that creep structure depends on temperature even under an identical σ/E condition. Upon raising the temperature, the structure related to strain hardening changes very rapidly, whereas the structure related to recovery changes gradually. This difference in changing rates between structures related to strain-hardening and those related to recovery results in a large apparent Qc at an early stage after a temperature rise. In individual tests, the temperature dependence of structure affects in an opposite way the recovery rate and the strain-hardening rate so that Qc is still equal to QD.

Deuterium kinetic isotope effect in the thermal decomposition of 1,3,5-trinitro-1,3,5-triazacyclohexane and 1,3,5,7-tetranitro-1,3,5,7-tetraazacyclooctane: its use as an experimental probe for their shock-induced chemistry

An isothermal thermogravimetric analysis (TGA) study of the decomposition of RDX, HMX and the respective deuterated analogues, RDX-d/sub 6/ and HMX-d/sub 8/, has been carried out. In RDX, a kinetic isotope effect (KIE) (K/sub h//K/sub d/) of 1.5 was observed for the first time in the temperature range 199-216/sup 0/C. In the HMX decomposition, an isotope effect of approx.2.0 was consistently obtained in the temperature range 237-282/sup 0/C with no apparent temperature dependence. In both substances the KIE produced a small but definite decrease in shock sensitivity measured by the exploding metal foil method. These results indicate that the rate-determining steps in the processes of thermal decomposition and the chemical process of initiation are likely to be the same. Thus, the kinetic isotope effect served as a novel experimental probe to test the similarity, or otherwise, of the rate-limiting steps of the slow decomposition and the rapidly accelerating reactions of the initiation. Possible rate-limiting steps and reaction mechanisms are discussed.

ON THE METALLIC CONDUCTIVITY OF DOPED POLYPYRROLE FILM

Polypyrrole films doped with BF4-,HSO4- and ClO4- were prepared by electrochemical method. Electrical conductivities of these samples and their temperature dependences were measured by four-probe method and VSC (voltage shorted compaction) method respectively. Experimental results indicate that the apparent temperature dependence of the conductivity as obtainted by the usual four-probe method, exhibits the character of typieal semiconductor, this feature is due to the contact resistance in the interblock or intergranular regions of the film. The measurement cannot reflect the true conductivity intrinsic to the doped polypyrrole film. However, the method devi-ced to short circuit the intergranular contact resistance does actually show the metallic temperature dependence of the conductivity of doped polypyrrole film, its conductivity increases with decreasing temperatures.When the polypyrrole film doped with BF4- was .partially reduced electrochemi-cally to a room temperature conductivity of 6-9 (Ω·cm)-1, the film exhibit a metal-semiconductor transition at 100 K as obtained by VSC measurement. IR-spectra indicates that the polypyrrole chain undergo certain structural changes during the electrochemical reduction process.

Internal Loss of InGaAsP/InP Buried Crescent (λ=1.3 µm) Laser

The temperature dependence of the internal loss α of the InGaAsP/InP buired crescent (λ=1.3 µm) laser is presented in the temperature range 20∼80°C. α is about 18 cm-1 and no apparent temperature dependence of α is observed in this temperature range. This indicates that the temperature-sensitive behavior of the threshold current in 1.3 µm laser is not due to the internal loss. The decrease in the external quantum efficiency with increasing temperature is attributed to the decrease in the internal quantum efficiency, which is possibly caused by some leakage current.

The effect of void density on the dislocation bias

Recent experimental work on the void-swelling characteristics of FV548 steel during irradiation is analysed, and it is shown that the dislocation bias for interstitial condensation p is a function of the void density N v , decreasing from 4̃0% when N v is 10 19/m 3 to 0̃.5% when N v is 10 23/m 3. This dependence on N v is responsible for most of the apparent temperature dependence of the bias. In addition to affecting N v , the temperature imposes a maximum void growth rate, which decreases as the temperature is reduced, and because of this, high swelling rates cannot be obtained at low temperatures even when N v is low. The full effect of the void-density dependence of p is therefore only visible at high temperatures.

The effects of surface scattering upon resistivity

It is shown how surface scattering may lead to substantial deviations from Matthiessen's rule. Using an angularly dependent surface scattering parameter as modelled by Soffer (1967), limit expressions for surface scattering in foils and wires are presented for both high and low kappa regions, where kappa is the ratio of the foil thickness, d, or wire radius, a, to the bulk electron mean free path, lambda infinity . From considerations for general values of kappa it is shown that surface scattering, at temperatures where the residual resistivity dominates, simply enhances the bulk temperature dependence. For higher temperatures for which the bulk resistivity varies as T5 the surface scattering can lead to an apparent T2 dependence. Further, it is shown that only for very thick samples or high temperatures where kappa >>1 is it possible to use a simplifying expression of the form rho - rho infinity =3/8 rho infinity lambda infinity /t, for the resistivity of foils or wires, where t is d or a. For most experiments the full theory is necessary to deduce rho infinity lambda infinity ; consequently virtually all previous determinations of this parameter are erroneous. Moreover, because of the influence of the surface scattering on the apparent temperature dependence of the resistivity, even of relatively thick material, several of the 'bulk' temperature dependences previously deduced for pure materials are almost certainly in error.

Internal loss of InGaAsP/InP buried crescent (λ = 1.3 μm) laser

The temperature dependence of the internal loss α of the InGaAsP/InP buried crescent laser is presented in the temperature range 20–80 °C. α is about 18 cm−1, and no apparent temperature dependence of α is observed in this temperature range. This indicates that the temperature-sensitive behavior of the threshold current in InGaAsP/InP long-wavelength lasers is not due to the temperature dependence of internal loss. The decrease in the external quantum efficiency with increasing temperature is attributed to the decrease in the internal quantum efficiency.

CRSS of disordered and ordered Cu3Au single crystals containing SiO2particles Correlation with the Orowan stress

Abstract Single crystals of Ou3Au containing SiO2 particles, oriented for single slip on (111)[101], and suitably heat-treated to have either an ordered or a disordered matrix, have been tested in compression in the range of temperatures 77–373 K. The quenching stresses generated at the particles, owing to the differences in the thermal expansion coefficients of Cu3Au and SiO2, were shown to have a significant effect on the CRSS of the disordered crystals, leading to an apparent temperature dependence of the Orowan stress. The effect was much less pronounced for the ordered crystals. After calculating the magnitude of this effect for the disordered samples, good agreement was obtained between the experimentally observed increment in the CRSS and the theoretically predicted Orowan stress. The agreement between theory and experiment for the ordered crystals was also satisfactory, assuming that the superlattice dislocations bypass the particles as a unit. TEM examination of (111) sections showed Orowan-type ...

Effects of Vaporization and Temperature in Gas/Liquid Relative Permeability Experiments

Abstract Liquid vaporization can influence the results of unsteady, external gas-drive relative permeability experiments. At elevated temperatures, liquid vaporization may affect (1) displacing gas mixture volume, (2) displacing gas mixture viscosity, and (3) volumetric liquid saturation calculated from a material balance. Approximate methods are presented to correct laboratory displacement data for the effect of liquid vaporization on displacing gas mixture volume and viscosity. An approximate method also is presented to evaluate the magnitude of liquid saturation reduction caused by liquid vaporization. By use of a modified Jones and Roszelle1 calculation procedure, equations are developed to describe the dynamic displacement of liquid water by nitrogen gas at elevated temperatures. A conventional analysis of three displacement experiments demonstrated the apparent temperature dependence of gas relative permeability. Use of the proposed method indicated that corrected gas and water relative permeability curves are not strongly temperature dependent for the artificially consolidated sandstone cores used in this study.

Reply to 'Comment on empirical photoionisation thresholds'

For comment see ibid., vol.14, p.L713 (1981). For original paper see ibid., vol.14, p.1255 (1981). The disagreement between Noras (1981) and Ridley and Amato (1981) over the interpretation of photoionisation curves seems, as far as physics is concerned, slight indeed. Everyone would probably agree that a detailed numerical curve-fitting is likely to be a more precise method than drawing best straight lines from experimental data. Unfortunately a detailed numerical curve-fitting is useful only if the theoretical model is accurate. No such model exists for the photoionisation of deep-level impurities. The paper of Ridley and Amato was written very consciously with this in mind, and consequently it adopted the simple empirical approach of drawing best straight lines to model data. The results obtained, particularly the existence of an apparent temperature dependence of threshold, are not disputed by Noras.

Optical transitions via the deep O donor in GaP. II. Temperature dependence of cross sections

A detailed experimental study of temperature dependence of optical cross sections for the GaP: O one-electron state for $Tl300$ K is presented. Broadening effects on the edge as well as temperature shift of the deep-level binding energy and spectral variations of the measured cross section with temperature are treated. In our purely optical data from bulk material the overall broadening of the edge for ${\ensuremath{\sigma}}_{p1}^{0}(h\ensuremath{\nu})$ and ${\ensuremath{\sigma}}_{n1}^{0}(h\ensuremath{\nu})$ is well explained (\ensuremath{\sim}15% accuracy) by absorption of configuration-coordinate phonon quanta in the optical transitions, apart from an anomalous behavior below 30 K. The 0.9-eV O level is nearly pinned to the valence band below 175 K ($\frac{\ensuremath{\Delta}{E}_{i}}{\ensuremath{\Delta}{E}_{g}}=0.90\ifmmode\pm\else\textpm\fi{}0.10$) while above this temperature $\frac{\ensuremath{\Delta}{E}_{i}}{\ensuremath{\Delta}{E}_{g}}$ seems to decrease gradually. The temperature-dependent spectral behavior of the cross sections seems to be due to the presence of two different levels related to the one-electron O state where the new level is situated 80\ifmmode\pm\else\textpm\fi{}20 meV above the previously established 0.9-eV level. The apparent temperature dependence of the part of the cross sections associated with the 0.9-eV level is described in terms of a thermal activation energy of 0.4 meV.

Nickel partitioning between olivine and silicate melt

Partitioning of Ni between olivine and silicate melt has been determined for compositions in the system Fo-Ab-An (1 atm) for temperatures ranging from 1250°C to 1450°C. Nickel concentrations were determined by electron microprobe; concentration levels in the liquids ranged from 0.1% to 0.5%. Platinum capsules or Pt wire loops were used as containers. Equilibrium was evaluated from kinetic considerations and by variation of run parameters; it was documented in one case by a bracketed reversal. No evidence was found for a dependence of the partition coefficient D (Ni in olivine/Ni in liquid) on Ni concentration. D is strongly dependent on melt composition, varying linearly with (1/MgO) at constant temperature. The intrinsic temperature dependence of D is small; the apparent temperature dependence reported in previous studies is largely related to the variation of melt composition with temperature. Our D values determined in the simple system Fo-An-Ab agree well with those reported by Leeman for natural (Fe-bearing) basalt systems. Overall variation of D in our system (and in natural basalts) can be expressed by the regression: D = (124/MgO) − 0.9 Our data are used to evaluate published Ni-MgO relationships in natural basalt series from Kilauea, Crozet, Cape Verde and Baffin Bay. A combination of olivine accumulation and fractional crystallization processes are sufficient to model these series. Using our data, unique “parental” liquids can be specified for each of these series; the MgO content of these liquids varies from 6% to 13%. Basalts with MgO contents greater than these “parental” liquids must be accumulative. The linear Ni-MgO trends, high absolute Ni concentrations, and large spread of Ni contents for the high-MgO basalts argue convincingly against their being “primary” liquids. Models such as those of O'Hara [6,13] and Clarke [24], based on the assertion of primary high-MgO liquids, must therefore be re-evaluated. Because of the high Si/O ratio and low MgO content of island arc andesites, the Ni partition coefficient D may be quite high. Therefore, the relatively low Ni content of such andesites may not be an argument against their derivation as direct partial melts of the mantle.

Concentration Expansion Study of the Randomly Dilute Ising Ferromagnet with Second Neighbor Interaction

The critical properties of the randomly dilute Ising ferromagnet are discussed for the square lattice by the method of concentration expansion. The studies are mostly limited to the investigation of the effects of the second neighbor interaction on the concentration dependence of the Curie temperature T c ( p ) and on the temperature dependence of the critical exponent \barγ(θ) describing the susceptibility divergence. The series obtained is analysed by the root, ratio, and Padé approximant methods, respectively. As for T c ( p ), the previous results are reconfirmed by raising the degree of series expansion. The present calculation gives an apparent temperature dependence of \barγ(θ) and its behavior can be compared with the results previously calculated for some three-dimensional lattices. Furthermore, it is found that the essential feature of \barγ(θ) is not affected by the presence of the second neighbor interaction.

Field dependence of the elastic constantsc 11 andc 33 of paramagnetic rare earth metals

An earlier theory for the magnetic field dependence of the elastic constantsc11 andc33 of paramagnets of hcp structure is extended in three different ways. First, the effect of the principal axial crystal-field term\(\tilde B_2^0 \tilde O_{20} (J_i )\) on the energy eigenstates of each magnetic ion is taken into account. Secondly, a field-dependent part of\(\tilde B_2^0 \) having its origin in the homogeneous strains is shown to yield a contribution toc11 andc33 similar in form to the other contributions. Finally, a contribution toc11 andc33 coming from the part of the magnetoelastic interaction linear in the strains evaluated in second order perturbation theory is calculated. This second order contribution is large and may predominate over the other contributions in certain cases. All three effects lead to “correction terms” to the earlier theory varying as (1/T). This temperature variation is too weak, however, to explain the apparent temperature dependence of the magnetoelastic coupling constants measured by Salama, Melcher and Donoho for terbium and by Kale, Donoho, Pinatti and Ferreira for dysprosium. The unexpectedly strong temperature dependence deduced from their measurements is discussed in the light of the present extensions to the theory, suspicion falling on the susceptibility functionsχz(T) andχ⊥(T) that enter the analysis of the data.