摘要:

A one‐dimensional analysis of the anode boundary layer of an atmospheric pressure, high intensity argon arc reveals substantial deviations from local thermodynamic equilibrium (LTE) in this layer. The temperature of the heavy species approaches the temperature of the anode in the immediate vicinity of the anode surface, whereas the electron temperature remains sufficiently high to ensure the required electrical conductivity. Temperature and density gradients in the anode boundary layer contribute substantially to the electric current flow so that the potential drop across the boundary layer becomes negative. The main voltage drop, which is in the order of 1 V, is essentially confined to the sheath at the bottom of the boundary layer overlying the anode surface. The thickness of this sheath is several orders of magnitude smaller than the anode boundary layer and the potential drop in the sheath is also negative. Therefore, the anode fall becomes negative for the entire parameter range covered in this paper, in contrast to the results of previous theories. This finding affects the anode energy balance as well as the interpretation of indirect (calorimetric) anode fall measurements which is important for the design of arc gas heaters.

ISSN:0021-8979    

DOI:10.1063/1.328063

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

The x‐ray absorption spectra of Ge and of Br in NaBr have been measured to pressures of 52 and 21 kbars, respectively, in a boron carbide and diamond anvil cell in which pressure was measured via the ruby‐fluorescence technique. Although Bragg peaks from the diamond anvil reduced the accuracy, atomic spacings in both materials could be determined by extended x‐ray absorption fine‐structure (EXAFS) analysis. Changes in the nearest‐neighbor separations in NaBr, and Ge to at least 40 kbars, agreed with literature values, indicating that the EXAFS phase shifts are quite insensitive to such pressures. In addition the near‐edge peak positions in the NaBr spectra appeared to readily shift with pressure, which suggests that NaBr may be quite suitable as a pressure standard in future work of this type.

ISSN:0021-8979    

DOI:10.1063/1.328064

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

An ultrasonic technique previously developed for studying dewetting and cumulative internal damage in filled polymers, such as solid rocket propellents, has been improved. The previous theoretical treatment is here expanded to include internal vacuoles of general spheroidal (rather than spherical) shape. Experimental measurements of sound speed and attenuation in a solid propellant material are utilized together with the modified theoretical model to calculate the internal damage parameters of effective vacuole size and number density as functions of applied uniaxial tensile strain. Results obtained from the model near the point of material failure are in excellent agreement with those provided by independent microscopic observations made on several rupture surfaces of propellant samples stressed to failure.

ISSN:0021-8979    

DOI:10.1063/1.328065

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

The conditions of the growth of single crystals of CdTe produce marked changes in their thermal conductivities. This study shows the influence of some specific parameters of the growth conditions: (i) material purity, and (ii) growth temperature and growth rate on the microprecipitate concentration (S?1014cm−3witha?100 A˚) in CdTe obtained by the ’’traveling heater method’’. An upper limit of the homogeneity region is deduced that takes into account all the defects, including nonelectrically active ones.

ISSN:0021-8979    

DOI:10.1063/1.328066

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

Extendedn‐type layers have been produced in semi‐insulating GaAs by the activation of Si implanted to atomic concentrations as low as 6×1016cm−3. Active layers were obtained in two types of undoped (no intentional dopants introduced during the growth process) semi‐insulating GaAs. These were bulk GaAs grown by the liquid encapsulated Czochralski method and epitaxial layers grown by chemical vapor deposition. Three terminal transferred‐electron devices were fabricated in a completely planar geometry. Gunn domain triggering by the gate resulted in dc negative resistance current dropback between 20% and 40%. High‐frequency negative resistance was observed in the 2–7 GHz range.

ISSN:0021-8979    

DOI:10.1063/1.328067

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

By bombarding GaAs wafers with thermal neutrons it has been possible to introduce a specific constant donor concentration. The radiation damage caused by bombardment can be annealed at temperatures below 800 °C. A room temperature electron mobility of 3900 cm2/Vs has been achieved at an impurity concentration of 5×1017cm−3. The doping ofn−‐type layers shows, in addition to the expected doping effect, that then−‐type layer is compensated near the semi‐insulating substrate.

ISSN:0021-8979    

DOI:10.1063/1.328068

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

The strain distribution in boron implanted, laser annealed silicon has been investigated using x‐ray Bragg reflection profiles. The 400 Bragg reflection profile from implanted, laser annealed silicon was analyzed, using the dynamical theory of scattering for distorted crystals, to obtain the strain distribution in the implanted layer as a function of depth. The depth distribution of the strain for an implantation dose of 1×101635 keV B+/cm2, followed by a 1.6 J/cm2ruby laser pulse, was found to have a magnitude of −5.8×10−3near the surface and was found to decrease rapidly for depths greater than 0.2 &mgr;m. The shape of the depth distribution of the strain was found to be essentially the same as that for the boron distribution after laser annealing.

ISSN:0021-8979    

DOI:10.1063/1.328069

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

The energy and force of interaction of an extended screw dislocation with spherical and tetragonal defects were calculated for several fcc metals using anisotropic and isotropic elasticity theories. It is shown that anisotropy has a large effect on the magnitude of interaction energy and interaction force, as well as on the shape of the energy‐distance and force‐distance curves. The maximum value of the interaction energy was always smaller in the anisotropic case than in the isotropic case. But the maximum resisting force to dislocation motion due to defect‐dislocation interaction is not always smaller in the anisotropic crystal. Computation of the hardening coefficient at 0 °K for several fcc metals indicates that tetragonal defects cause significantly larger hardening than spherical defects.

ISSN:0021-8979    

DOI:10.1063/1.328070

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

A thermal anneal technique is proposed to effectively remove electron beam irradiation damage in metal‐nitride‐oxide semiconductor structures. Using a high‐temperature (800–950 °C) H2anneal treatment the SiO2layer is impregnated with hydrogen after the nitride deposition. This leads to very low surface state densities for both thick‐oxide and thin‐oxide devices. After irradiation the device is given a mild heat treatment at 450 °C in an inert ambient. A complete removal of the radiation‐induced fixed charges and surfaces states is observed. The effectiveness of the high‐temperature H2anneal is most pronounced for thin‐oxide MNOS structures. The technique is shown also to be effective in case of other types of ionizing radiation.

ISSN:0021-8979    

DOI:10.1063/1.328071

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

Polycrystalline TZM alloy samples have been irradiated at room temperature with helium ions of energy from 75–350 keV in high vacuum. Irradiation parameters such as ion energy, total dose, and ion flux were varied, and the surfaces were examined in a scanning electron microscope. The critical dose for blister formation was found to lie between 4 and 7×1017ions cm−2and is independent of the beam flux in the range 6.7×1013–2×1015ions cm−2 s−1. However, within this flux range the average blister diameter increases with the flux and the blister number density, and the exfoliation maximizes at an intermediate flux. Blister‐cover thickness for TZM is found to be less than that for molybdenum, although the average blister diameter for the two materials differs only at the highest energy used. When the TZM surface is successively bombarded with varying ion energies, blistering is reduced compared to monoenergetic helium bombardment, but this reduction is not as substantial as for pure molybdenum.

ISSN:0021-8979    

DOI:10.1063/1.328072

出版商:AIP    

年代:1980

数据来源: AIP