摘要:

A method of making an ohmic contact to a semiconductor that does not inject minority carriers at high current densities has been found. This surmounts difficulties and limitations of previously reported experiments. Utilizing this technique, the high field current‐voltage characteristic ofp‐type germanium was measured at several temperatures from room temperature to liquid helium temperatures, a wider range than previously reported. From these data, one can compute the drift velocity (and drift mobility) as a function of electric field and also estimate the amount of heating that will occur when a square pulse of current is passed through ap‐type germanium sample immersed in liquid helium.

ISSN:0021-8979    

DOI:10.1063/1.1735253

出版商:AIP    

年代:1959

数据来源: AIP

摘要:

Since the initial work of Brillouin, interest in long, dense electrom beams with a uniform velocity profile has increased steadily. Notable contributions have been made by Samuel and Harris. In this paper, the general member of this class of beams is derived. Various special cases become the equilibrium systems of current interest. In addition to these known systems, the analysis leads to new possibilities. One of these is of particular interest in that it is the first of this group of beams in which the axial velocity is important to the balance of forces on the electrons. The new beam has properties ideal forM‐type interaction and should be of considerable future importance.

ISSN:0021-8979    

DOI:10.1063/1.1735254

出版商:AIP    

年代:1959

数据来源: AIP

摘要:

Since the small‐angle x‐ray scattering intensity can be expressed as a Fourier integral, the techniques of asymptotic expansion of Fourier integrals can be used to calculate the small‐angle x‐ray scattering at relatively large scattering angles. Some asymptotic expansion techniques which are often useful are described. The relation between the scattered intensity at relatively large angles and the characteristic function and its derivatives is discussed. The scattered intensity for both prolate and oblate ellipsoids of revolution is calculated to provide examples of asymptotic expansion methods, and the resulting expressions are evaluated numerically. The behavior of the scattered intensity at relatively large scattering angles for platelet particles of negligible thickness is described.

ISSN:0021-8979    

DOI:10.1063/1.1735255

出版商:AIP    

年代:1959

数据来源: AIP

摘要:

Rotating collector measurements, made at a pressure of 10−5mm Hg, yielded cosine distributions for all experimental conditions. Data were obtained for gas‐covered and partly gas‐covered target surfaces, for several beam incidence angles, and for ion energies of 40, 400, and 825 ev. It is postulated that the identical cosine distributions observed for both kinetic and potential ejection are caused by the existence of isotropic angular distributions for both mechanisms within the metal. A general expression is given for the angular distribution of emission from an arbitrarily shaped surface. This expression is a function of the fundamental angular distribution associated with a single element of area on that surface and the orientation distribution of the elements of area.

ISSN:0021-8979    

DOI:10.1063/1.1735256

出版商:AIP    

年代:1959

数据来源: AIP

摘要:

The high intensity of the anomalously transmitted x‐ray beam depends upon the coincidence of the nodal planes of the x‐ray wave field with one set of atomic planes within the crystal when the crystal is set for Laue diffraction. If there is any structural defect within the crystal which causes some of the atoms of the crystal to deviate from their normal location in perfect planes, these atoms will no longer be at the nodes of the x‐ray wave field and by their absorption they will reduce the transmitted intensity.The present paper shows how this effect may be employed to measure the amount of microstrain present in nearly perfect germanium crystals. It is found that some apparently dislocation free crystals show a greater degree of crystalline imperfection than crystals with a finite dislocation count.

ISSN:0021-8979    

DOI:10.1063/1.1735257

出版商:AIP    

年代:1959

数据来源: AIP

摘要:

We have measured the carrier density as a function of temperature inn‐type germanium which has been plastically deformed by bending, and find that it can be accounted for on the basis of Read's theory if the dislocation acceptor level lies 0.18 to 0.20 ev below the conduction band. The analysis indicates that the dislocation density introduced by plastic bending is about 8 times the theoretical equilibrium density that would correspond to zero internal stress. We observe that the mobility for current flow along the bending axis is the normal mobility, which indicates that the dislocations are parallel to the bending axis, although they may zig‐zag with line segments along (110) type directions. The mobility perpendicular to the bending axis is in qualitative agreement with the theory given by Read, although the theory tends to underestimate the reduction of mobility below 50°K. We have extended Read's theory to the case where the current flows along the bending axis and the magnetic field is perpendicular to the bending axis.

ISSN:0021-8979    

DOI:10.1063/1.1735258

出版商:AIP    

年代:1959

数据来源: AIP

摘要:

A study was made of crystallite orientation in cubic ferrites when pressed in a magnetic field. One easy axis orients in the field direction, the other easy axes lying at random in or near a perpendicular plane. Experimental torque curves have the theoretically predicted shape. The magnetic field required for microwave resonance is lower than in the same nonoriented ferrite if the axis of alignment and the field are parallel. This occurs because the anisotropy fieldHais no longer randomly oriented but helps to supply part of the resonant field requirement. Values of saturation magnetization (Ms), anisotropy energy (K), and resonant field (Hr) at 14 775 mc/sec were measured on a series of oriented polycrystalline nickel cobalt ferrites. Values of the measured resonant field are compared with values obtained from Kittel's resonance relation using the independently measured values ofMsandK.

ISSN:0021-8979    

DOI:10.1063/1.1735259

出版商:AIP    

年代:1959

数据来源: AIP

摘要:

Dynamic piezoelectric resonance measurements have been made on single crystals of barium titanate in the temperature range from room temperature to 160°C. In the ferroelectric region (room temperature to 120°C) the material is spontaneously polarized and hence naturally piezoelectric. For this range of temperature results are presented for the elastic compliance coefficientss11Eands11P, the combination (2s12+s66) at constant field and constant polarization, and the piezoelectric coefficientd31as functions of temperature. Above the Curie temperature (120°C) the piezoelectric resonances can be observed only by polarizing the crystal with an external field. From measurements of the resonant frequencies in crystals having their longitudinal axes along the (100) and the (110) direction, and the assumption of the validity of the Cauchy relation (c12=c44), the elastic coefficients at constant polarization have been determined as functions of temperature and polarization from the Curie point to 160°C. The strains induced by the polarization in a stress‐free crystal are shown to be proportional to the square of the polarization, for values of polarization up to one‐third of the spontaneous polarization at room temperature.

ISSN:0021-8979    

DOI:10.1063/1.1735260

出版商:AIP    

年代:1959

数据来源: AIP

摘要:

A filamentary structure has been used to compare the electrical properties of a germanium surface with those of an adjacentp‐njunction intersecting the same surface. Surface charge is varied by field effect plates in the isolated portion of the filament and near the junction. An orderly relation can be found between surface potential variations and changes in the reverse currents across the junction. At low bias, the junction current varies with surface recombination velocity, and for bias near breakdown, the breakdown voltage varies with induced charge at the surface. For inverted surfaces, the low bias current varies rapidly as expected from channel length variations. With inverted surfaces, channel growth leads to large reverse current variations with surface potential, but breakdown voltage becomes independent of surface charge. These variations are considered in terms of simple theory, and device implications are discussed.

ISSN:0021-8979    

DOI:10.1063/1.1735261

出版商:AIP    

年代:1959

数据来源: AIP

摘要:

The kinetic theory for the rate of stress‐assisted precipitation on dislocations is re‐examined in order to extend the work of Cottrell and Bilby. Two approximate expressions are used for the elastic interaction between a solute atom and edge and screw dislocations:V=−Asin&thgr;/randV=−B/r, respectively. The resulting partial differential diffusion equations are integrated numerically to get the time‐dependent rate of precipitation on an isolated dislocation. These results are used to calculate the short‐time part of the precipitation curve for an array of dislocations. Exact steady‐state solutions to the diffusion equations are derived for both interactions and are used with a variational procedure to establish the long‐time part of the curve for a regular array. For very short times the precipitated fractionWis proportional tot⅔as derived by Cottrell and Bilby, but this result is not accurate over the range oftduring which most of the precipitation occurs. The long‐time part of the curve is given accurately byW=1−exp(−t/&tgr;), where &tgr; can be calculated by replacing each dislocation and its stress field by a cylinder with an ``effective capture radius,'' the value of which is calculated for each form of interaction. Complete precipitation curves are obtained for a regular array by combining the short‐ and long‐time results, and it is shown that these are changed but slightly if the array is random. These results differ significantly from a formula suggested by Harper to extend Cottrell and Bilby's work, and they thereby indicate that the interpretation of the precipitation process for carbon in alpha‐iron is not yet entirely established.

ISSN:0021-8979    

DOI:10.1063/1.1735262

出版商:AIP    

年代:1959

数据来源: AIP