摘要:

The transformation of graphite to diamond by impact‐produced shock waves has been examined using a gas gun to launch projectiles onto graphite and a graphite‐metal mixture. Analysis of the mechanism of transformation is complicated by the post shock graphitization of most of the diamond produced. It is argued that the previously proposed models of shock‐wave transformation are incomplete and a revised model of assisted diffusion in a highly defective lattice is proposed to explain the observations.

ISSN:0021-8979    

DOI:10.1063/1.327873

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

We have carried out self‐diffusion studies along grain boundaries in polycrystalline Pb specimen in the temperature range of 70–200 °C. Pb203radioactive isotope (half life of 52.1 h) was used as a tracer, and precision microtome serial sectioning and high‐efficiency gamma counting techniques were employed. The combined diffusion parameter &dgr;Dbin Pb grain boundaries is expressed by the Arrhenius relation &dgr;Db=(6.1±0.9)×=10−9 exp(−0.46±0.01 eV/kT)(cm3/sec) .

ISSN:0021-8979    

DOI:10.1063/1.327874

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

An expression relating the temperature dependence of the Gibbs free energy of a defect process (such as formation, migration, or activation) to the thermoelastic properties of a crystal which has recently been shown to follow from a purely general thermodynamical basis has been applied to analyze self‐diffusion measurements in tungsten. It is shown that the high‐temperature bulk modulus can be predicted up to the melting point from the measured diffusion. Additionally, as an example for the accordance of diffusion and elastic data, the slight curvature in the Arrhenius plot of the diffusion coefficient of potassium as well as its activation volume are shown to follow from thermoelastic experiments.

ISSN:0021-8979    

DOI:10.1063/1.327875

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

Predeposition of tin has been used as the sole dopant source to produce exponentially decreasing free‐donor profiles in molecular‐beam epitaxial GaAs films. The incorporation was found to be first order with respect to surface tin concentration and have an effective activation energy of −1.35±0.1 eV, which does not agree with a Schottky barrier model of incorporation. Films with such profiles were used to fabricate power FET structures which demonstrated good linearity. Source‐to‐drain series resistances have also been reduced by supplemental doping under the contact regions and by degenerate Ge doping of the surface regions, followed by uninterrupted growth of thin epitaxial Ge overlayers for nonalloyed tunnel‐contact metallizations.

ISSN:0021-8979    

DOI:10.1063/1.327876

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

The arrangement of tungsten atoms (0.2–4 monolayers) evaporated onto W(110) has been studied with LEED and work‐function measurements in ultrahigh vacuum. For temperatures ofT=300–430 K island growth has been derived from rings, which are visible at characteristic energies, around each spot of the LEED pattern. By increasing substrate temperature the islands coalesce in the [001] direction. ForT=520–800 K the surface shows microfacets with step edges in the [11¯0] direction. Step‐free epitaxial growth has been observed atT=950 K. The decrease of work function during evaporation confirms the formation of islands and facets. The average dipole moment per edge atom has been determined by combination of LEED and work‐function data. Quantitative evaluation of the LEED pattern yields the distance between islands, size of islands, and number of rows of atoms per terrace. The results show that the LEED pattern provides information on epitaxial growth which is not available with any other technique.

ISSN:0021-8979    

DOI:10.1063/1.327877

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

The conductivity, permittivity, dielectric loss, and electrolytic polarization of solvent‐refined coal dispersions are measured with respect to frequency (10–105Hz), to concentration in the range from solids‐free liquid to nearly dry solid, and to some extent temperature in the range 290–313 K. Some measurements are also made on the oil, asphaltene, carbene, and insoluble carboid/mineral fractions isolated from centrifuge sediment and supernatant liquid. Washed insoluble matter samples having bulk mineral ash contents from 3 to 63% are also examined, using optical and scanning electron microscopy and surface analysis via electron spectroscopy. The asphaltenes, and to a lesser extent the carbenes, are distributed between the liquid and the particle phases; the latter contains all of the carboids, covering a core of mineral matter. Electrolytic polarization at the electrodes gives the ion concentration, which is about 1.7×10−9molar for the liquid. Conductivity probably involves both ionic and electronic mechanisms, with the former arising mainly from alphaltenes. The presence of particulate matter decreases the conductivity and electrolytic polarization compared to the solids‐free liquid; this is particularly marked up to about 8% solids concentration and is likely to reflect association of acidic asphaltene and basic carbene ionizable species at the outer surfaces of the particles. Induced surface polarization of this associated ionic species, for which the maximum surface charge density is about 1.8×1010charges/cm2, appears to be responsible for the increased permittivity in the presence of solids. The frequency dependence of the conductivity and permittivity correspond to Cole‐Cole dielectric relaxation, and suggest a narrow size distribution, with a mean of about 5 &mgr;m in diameter, for the relaxing species. The temperature dependence of conductivity and permittivity indicate that the concentration and mobility components of the activation energies are nearly equal. A small electrophoretic separation and a larger low‐frequency dielectrophoretic separation of particles and fluid are predicted.

ISSN:0021-8979    

DOI:10.1063/1.327878

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

We present an investigation of the low‐temperature piezoluminescence of the (D °X) complex in GaAs1−xPx(Te) in the composition range associated with the direct‐indirect crossover (x?0.45). Both the composition dependence and the uniaxial‐stress dependence of the low‐temperature luminescence peaks are satisfactorily described in the effective‐mass approximation if one takes into account all &Ggr;1candX1cband extrema. The participation of &Ggr; andX1cBloch functions in the wave function of the neutral donor bound excitons is then deduced versus composition.

ISSN:0021-8979    

DOI:10.1063/1.327879

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

A simple analytical method is put forward in this paper, enabling one to extract quantitative information about an arbitrary energetic distribution of traps for current carriers from a single experimental space‐charge‐limited current‐voltage characteristic. The applicability of the method is illustrated with computer‐simulated characteristics, calculated for various typical distributions of traps. The effect of the nonstability of the current, nonuniformity of the spatial distribution of traps, and temperature on the accuracy of the determination of the parameters of traps is briefly discussed.

ISSN:0021-8979    

DOI:10.1063/1.327880

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

The transient photoinduced transmission change under intense band‐gap light irradiation was investigated in amorphous chalcogenide thin films. Spectral distribution, temperature dependence, and the relation with the photocurrent of the change were examined. It appears that the change is due to the excitation of electrons trapped in normally unoccupied states near the valence band edge.

ISSN:0021-8979    

DOI:10.1063/1.327881

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

We have studied the photoconductivity of atactic polystyrene at room temperature under both positive and negative polarity (of the unilluminated electrode). There is a maximum in the response under 5.2‐eV uv illumination. If this illumination is sufficiently intense, the total current may have positive polarity even with negative voltage polarity. This is due to the fact that the photocurrent is always positive, due to the diffusion of holes. This may be understood in terms of the Onsager model of geminate generation and recombination. The microscopic phenomena underlying the behavior are discussed as is the applicability of the Onsager model to other polymers.

ISSN:0021-8979    

DOI:10.1063/1.327882

出版商:AIP    

年代:1980

数据来源: AIP