摘要:

A high‐voltage vacuum spark emitting a continuum in the vacuum ultraviolet was triggered by the particles originating from a dense plasma produced by a laser beam focused onto a nearby solid target. The emitted radiation was used to observe absorption processes in the same laser plasma. Because of the fast transient phenomena occurring in this plasma, the delay‐time before spark breakdown had to be minimized. With the particular device used, the minimum delay‐time between laser pulse and continuum emission was found to be about 200 nsec with a jitter time of the order of 20 nsec. This delay‐time is too long to allow numerous observations of absorption by singly charged ions, but the applicability of the method to absorption studies on neutral species was demonstrated. Examples of absorption spectra from atoms of beryllium and magnesium are discussed.

ISSN:0021-8979    

DOI:10.1063/1.1659177

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The unified charged‐particle interaction operators of Kihara and Aono have been used in the system of kinetic equations for a partially ionized, nonisothermal gas in a magnetic field. It has been assumed that the coupling between the kinetic equation of the electrons and those of the heavy species is weak, as it is always the case in MHD‐generator plasmas. It has been demonstrated that the new theory introduces essential corrections to the values of transport coefficients calculated by other theories of nonisothermal plasmas. Simplified calculation methods for electron transport coefficients have been proposed, which are based on the exact results given by this theory.

ISSN:0021-8979    

DOI:10.1063/1.1659178

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The trapping and thermal reemission of 100–300‐eV Ar+and Kr+ions at a polycrystalline nickel target have been studied. For Ar+and Kr+the trapping probabilities are, respectively, 0.020 and 0.015 at 100 eV and 0.46 and 0.33 at 300 eV. A continuous temperature increase of the target releases trapped argon discontinuously by thermally activated processes at temperatures corresponding to activation energies of 1.12, 1.31, 1.48, 1.67, 1.83, and 2.13 eV. These energies are compared with activation energies which are determined by others for the removal of defects resulting from radiation damage or cold working of nickel. The lowest three energies are believed to be correlated, respectively, with interstitial migration, vacancy formation, and vacancy migration near the surface. The highest energy may be due to surface recrystallization from dislocations produced by the ion bombardment. The intermediate energies probably correspond to the motion of nickel surface atoms along the ridges of facets formed during the bombardment.

ISSN:0021-8979    

DOI:10.1063/1.1659179

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

Dimensional changes in a variety of pyrolytic carbons irradiated at 900° to 1000°C and at 1200° to 1300°C show that during the irradiation, the rate at which the specimens change dimensions accelerates. The accelerations are most pronounced in dense, isotropic carbon and are accompanied by the generation of pores in the structure, which causes a volume expansion. The data obtained at the lower irradiation temperatures (∼900°C) suggest that the accelerations are due primarily to a degradation in crystal structure that enhances the instability of the crystallites. At the higher irradiation temperatures, increases in anisotropy contribute significantly to the accelerations. The volume expansions, the degradation of the crystal structure, and changes in thermal conductivity are all less for irradiations above 1200° than at 1000°C. These observations, together with the increases in anisotropy, are believed to be manifestations of the fact that the intercrystallite irradiation creep rate is substantially higher at irradiation temperatures above 1200° than at 1000°C. High creep rates provide an effective mechanism which relaxes the stresses that are generated between adjacent, misaligned crystallites during irradiation.

ISSN:0021-8979    

DOI:10.1063/1.1659180

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The problem of fluorescence in slab geometries is solved exactly and analytically to first order. Analytic expressions, whose direct evaluation should be faster and more accurate than current numerical methods, are derived for differential and integral dose and for differential reflection and transmission coefficients, for the single slab case. The basic expressions are then used to obtain the general solution for the dose profile of the multislab problem. The limitations of the first‐order approximation are discussed and illustrated by comparison with Monte Carlo results. It is found that even in a situation especially chosen to ensure the validity of the first‐order approximation, a Monte Carlo calculation reveals the presence of higher‐order effects.

ISSN:0021-8979    

DOI:10.1063/1.1659181

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

It is shown that the small‐signal behavior ofn‐type GaAs can be described in the approximation of displaced Maxwellian distribution functions in terms of five field‐dependent relaxation constants &Ggr;kwhich are defined as the eigenvalues of the matrix controlling the change with time of the electron temperatures, the drift velocities, and the population ratio. For the frequency dependence of these quantities and the mobility, expressions of the formk=15Cki&ohgr;−&Ggr;kresult, where theCkdepend only on the bias field. Hence the frequency limit for negative differential mobility is derived, having a maximum value of 200 GHz. Furthermore the frequencies of the plasma modes are calculated as a function of the bias field and the electron concentration. Two of the six plasma modes are oscillatory (especially for large electron density); one of the relaxation‐type modes (the soft mode) is shown to give rise for current‐controlled instability of the infinitely extended semiconductor for bias fields which belong to negative slope of the static characteristic.

ISSN:0021-8979    

DOI:10.1063/1.1659182

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The ternary‐phase diagram of GaAsSb has been calculated using Darken's quadratic formalism for a ternary liquid and assuming a regular solid solution. Liquid epitaxial layers of GaAsxSb1−xhave been grown in the range 0.75>x>1 on {100} and {111} GaAs substrates. Results are in excellent agreement with the calculated phase diagram. Variation of bandgap with composition of the layer has been determined by transmission, photoemission, and x‐ray fluorescence experiments. The data were fitted to a curve of the formEG=A+Bx+Cx2, whereA=0.725 eV,B=−0.32 eV, andC=1.02 eV. Graded bandgap layers have been obtained, with gradients of 700 eV/cm near the substrate interface and 25 eV/cm for thick layers. For use as high‐efficiency photoemitters, the samples were dopedptype by the addition of elemental Zn to the melt. Cesium and oxygen surface layers were used to lower the work function. Quantum yields of 0.1%–0.2% at 1.06 &mgr; were obtained. Field assisted photoemission in a graded bandgap sample has been calculated and demonstrated experimentally.

ISSN:0021-8979    

DOI:10.1063/1.1659183

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

After repeated switching, ferroelectric ceramic plates will exhibit aging evident in hysteresis loops as a marked decrease in remanent polarization (Pr) and an increase in coercive field (Ec). A hot‐pressed ceramic having a composition of 65% lead zirconate‐35% lead titanate with 2 at.% lanthanum and having a grain size 2 &mgr; or less was used to study the effects of various electrode materials. The source disks were polished down to a thickness of 25, 37, or 63 &mgr; and square plates 2.5 mm on edge were cut for testing. Prior to the application of the electrodes, the square plates were annealed in air at 700°C for 10 min and cooled slowly to room temperature. Electrodes were then applied as opposing disks 1.5 mm in diameter on the surfaces of the plates. A Sawyer‐Tower circuit was used to observe hysteresis loops formed on an oscilloscope at a frequency of 60 Hz, and occasionally at 600 Hz. Maximum applied voltage corresponded to approximately 3Ec. Results were obtained for vapor plated electrodes of Al, Cr&sngbnd;Au, Pb, PbO&sngbnd;Ag, Sn&sngbnd;Ag, Ag, Ga, and In. For all but the In electrodes, a large decrease ofPrwas evident by 107cycles. The In electrodes yielded lower values ofEc(approximately 8 kV/cm) and the value ofEcdid not increase appreciably over the test period. After 109cycles,Prhad decreased by only 14% for the In electrodes.

ISSN:0021-8979    

DOI:10.1063/1.1659184

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The photoemission of both electrons and holes from aluminum into thin layers of ``plasma‐grown'' aluminum oxide has been observed. The threshold energies for these processes are found to be 2.0±0.2 eV for electrons and 3.1±0.2 eV for holes. An approximate energy band diagram of the Al&sngbnd;Al2O3interface based on these values is presented.

ISSN:0021-8979    

DOI:10.1063/1.1659185

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

An exact uniform theory is given for theI‐Vcharacteristic of longp‐i‐ndiodes with one trapping level. This theory does not assume a constant recombination lifetime or quasi‐neutrality, as did all previous treatments of this problem. As limiting cases, the theory gives the cube law at high injection levels, the square law for the semiconductor regime and the Ashley—Milnes regime. The theory is applied to the acceptor level of Au in Si for which case numerical solutions are given.

ISSN:0021-8979    

DOI:10.1063/1.1659186

出版商:AIP    

年代:1970

数据来源: AIP