摘要:

The Mo¨ssbauer effect in57Fe has been used to study carbide phases appearing during the tempering process of an alloy steel containing 1.33 wt.% Si, 1.13% wt. Mn, and 0.38 Wt.% C. Carbides were chemically extracted from the samples which had been isothermally tempered for 2 h at various temperatures. Carbides obtained from samples tempered at 300° and 400°C were identified as &egr; and &khgr; phases, respectively. The &egr; carbide has an isomer shift (I.S.) of 0.18 mm/sec relative to &agr; iron and an effective hyperfine field (Hn) of 162 kOe at 300°K. The &khgr; carbide has an I.S. of 0.28 mm/sec relative to &agr; iron andHnof 179 kOe at 300°K. Carbides precipitated at and above 500°C were found to have the orthormbic cementite structure, with a composition of (Fe1−xMnx)3C. As the tempering temperature increases from 500° to 700°C the Curie temperature changes from 440° to 270°K, andxincreases from 0.02 to 0.10. Curie points and extrapolated values ofHn(0) were found for all the carbides in question. The early stages of tempering in which transition carbides appear are explained as being controlled by the elastic strain. The elastic binding energy between an interstitial carbon atom and a substitutional silicon atom can then be estimated. Other phases which were found in the chemically extracted samples after tempering the alloy at a low temperature, were identified as oxyhydeoxides and iron gel. In a sample tempered at 700°C the carbide was detected in the steel matrix and compared with the same carbide after chemical extraction.

ISSN:0021-8979    

DOI:10.1063/1.1660082

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

Charge transport and photoconductivity in As2S3amorphous films have been investigated at a temperature of 25°C. It is found that holes are the mobile carriers in As2S3whereas electrons are quite immobile in the material. The photoconductivity is mainly governed by the product of the photogeneration efficiency and the schubweg of the generated holes. Both of these quantities are electric field dependent. Carrier transport is essentially dominated by bulk trapping. The traps are distributed in energies above the hole conduction states. The release rate of the trapped charges varies since the rate is an inverse function of the trap energy. A theoretical model describing the transport process is presented to account for the experimental results. The photogeneration efficiency as a function of electric field at high fields (greater than 105V/cm) has been determined for incident photon energies of 2.5–3.1 eV. The generation efficiency is observed to decrease in the same manner as the absorption coefficient with decreasing photon energy in the light wavelength range 4000–5000 Å.

ISSN:0021-8979    

DOI:10.1063/1.1660083

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

A treatment is given of the one‐dimensional problem of beam‐plasma interaction, including the effects of plasma and beam thermal velocities and momentum transfer collisions in the plasma. The conditions under which the Landau damping due to the plasma is negligible are first investigated. Neglecting this damping, a weak‐beam approximation to the dispersion relation is derived, and conditions for its validity are established. Expressions are derived for the maximum temporal and spatial growth rates in the limits of cold and hot beams, and few and many collisions. The growth rates given by the weak‐beam approximation are compared with those calculated from the full dispersion relation. The transition from a cold to a hot beam is discussed in terms of the topology of the roots of the dispersion relation, and also in terms of the location of the phase velocities of the most unstable waves relative to the bump in the distribution.

ISSN:0021-8979    

DOI:10.1063/1.1660084

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

Total transmitted electron energy spectra have been constructed from measurements of electron energy spectra at various emission angles for targets of Al and Au of thicknesses of from 0.2 to 0.6 of the range in these materials. Bombarding energies of 1.0 and 2.5 MeV were used for beams of perpendicular incidence to the targets. Angular distributions of transmitted electrons are shown. At 1.0 MeV, total transmitted electron energy spectra are constructed from measurements in which incident electron beams were used to simulate an electron flux of intensity varying as the cosine of the angle of incidence. Targets of Al, Sn, and Au were used. Comparisons are made to calculated spectra from ETRAN 15 of Berger and Seltzer.

ISSN:0021-8979    

DOI:10.1063/1.1660085

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

Electron spin resonance studies have been made of natural diamond crystals electron‐irradiated at room temperature. A radiation‐induced spectrum is identified as arising from a new anisotropicS=1 center. TheS=1 center is characterized by:g1=2.0026, g2=2.0021, g3=2.0016; D1=∓27(10−4 cm−1), D2=∓25(10−4 cm−1), D3=±51(10−4 cm−1). Associated with each resonance line are four sets of weaker lines which are ascribed to hyperfine interaction with13C (I=½, 1.1% abundant) at four nonequivalent sets of sites. The identity of the defect has not yet been established.

ISSN:0021-8979    

DOI:10.1063/1.1660086

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

The electrical conduction from 4.2°K to room temperature in thin film Ni&sngbnd;NiOx‐metal junctions was studied. Tunneling is the dominant conduction mechanism at low temperature; at high temperature, Schottky thermionic emission dominates. The effective barrier thickness determines at what temperature the conductivity changes from tunneling to Schottky emission. Atomic penetration into the oxide is important, and there appear to be broad transition regions at the metal‐oxide interfaces. Using the conventional models, the barrier heights are approximately 0.2 eV.

ISSN:0021-8979    

DOI:10.1063/1.1660087

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

The occurrence of a high‐resistivity region (ilayer) at the interface ofn‐type GaAs films onn+GaAs substrates has been a recurring problem in the halide synthesis transport growth of these films for microwave devices. Consistent success in the elimination of anilayer in the doping profile has been achieved by deposition of ann+epitaxial film substrate prior to growth of the activenfilm, however the nature and cause of theilayer has remained unknown. It has been proposed by others that theilayer is caused by the presence of an impurity in that region. Under this assumption, a new analytical tool, the Direct Image Mass Analyzer (DIMA, Bell & Howell/CEC) has been used to obtain depth impurity profiles of known impurities through five homoepitaxialn‐on‐n+GaAs film samples. These samples differed in the type of dopants used in the film and substrate, and in the magnitude of theilayers. The data were compared with doping profiles, and an analysis of this comparison has led to the following conclusions: (1) The impurities that are present in these samples include Si, K, Li, C, Na, Fe, F, Cl, and Mn; (2) the presence of anilayer is correlated with the presence of a high concentration (∼1×1021/cm3) of silicon in theilayer region; and (3) the origin of the silicon is probably external to the sample. The hardware of the reactor is a likely source of silicon, and a mechanism is proposed for the transport of the silicon into the growing film.

ISSN:0021-8979    

DOI:10.1063/1.1660088

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

This paper describes the measurement of free carrier decay profiles over the temperature range 7°–300°K for GaP:N, GaP:Bi, CdS:Te, and ZnTe:O following their excitation by pulses of electrons from a Van de Graaff accelerator. Contactless microwave transmission and reflectivity techniques were employed to measure the transient conductivity changes. The studies were made principally to obtain a more complete understanding of the recombination mechanisms previously proposed to be operative in CdS:Te and ZnTe:O on the basis of luminescence decay time data. The gross features of the temperature dependence of the free carrier lifetimes correlate well with the luminescence decay time data. Differential equations, formulated to describe the temperature‐dependent kinetics, were solved by a combination of numerical and analytical methods to obtain the transient luminescence and free carrier decay profiles. The solutions depend very weakly upon certain capture coefficients. The major variable parameter is in both cases the binding energy &egr; of the majority carrier in the Coulomb field of the charged isoelectronic trap. For CdS:Te, with &egr;h=20 meV, good agreement was obtained between the calculated and observed free carrier and luminescence decay profiles, thereby providing good support for the model of the recombination mechanism. For ZnTe:O with &egr;e=20 meV, agreement is adequate for the luminescence profiles, but only semiquantitative for the free carrier decay profiles. Reasons for the discrepancies are discussed. For all the materials, at the lowest temperatures, the results indicate very rapid and stable trapping of the carriers with no evidence of a post‐excitation conductivity. This is in keeping with the occurrence of highly radiative transitions at these temperatures.

ISSN:0021-8979    

DOI:10.1063/1.1660089

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

The contactless microwave reflectivity technique was used to measure the transient free carrier density following the creation by a pulsed electron accelerator of electron‐hole pairs in arsenic‐doped silicon at 7°K. The experiments were directed at providing supporting evidence for the Auger recombination mechanism postulated by Nelsonet al. as being operative in the decay of excitons bound at neutral donors in silicon. The results contrast distinctly with the results of similar experiments on semiconductors containing isoelectronic traps by showing a strong post excitation conductivity. Differential equations, describing the model of Auger decay and including the important effects of residual acceptors, are formulated and solved numerically. At high excitation levels the theoretical profiles depend weakly on unknown capture cross‐sectional parameters and agree well with the experimental profiles. At lower excitation levels, the predicted profiles have a stronger dependence on the values of the unknown parameters, but, assuming reasonable values, good fits to the experimental data are obtained. It is therefore concluded that conductivity associated with Auger electrons has been observed.

ISSN:0021-8979    

DOI:10.1063/1.1660090

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

This paper describes the results of dry thermal oxidation of silicon under uv‐irradiation conditions. A model is proposed to explain the enhanced oxidation and reduced surface‐state charge density that occur under these conditions.

ISSN:0021-8979    

DOI:10.1063/1.1660091

出版商:AIP    

年代:1971

数据来源: AIP