Index of content:
Volume 31, Issue 6, 01 June 1960
31(1960); http://dx.doi.org/10.1063/1.1735780View Description Hide Description
Internal frictionmeasurements made as a function of strain amplitude on deformedsodium chloride single crystals were followed by elastic modulusmeasurements made during x irradiation of the same crystals. Etch pit densities were also determined. These data were used to evaluate the constants in a theory, proposed by Granato and Lücke in 1956, which permits the calculation of the average length of the dislocation segments, L, which vibrate under an applied alternating stress. An independent determination of the magnitude of L was made from the elastic modulus data using a method developed by Gordon and Nowick.
It is concluded that the theories tested in this paper give a useful representation of dislocation damping phenomena in sodium chloride and permit use of internal frictionmeasurements for the continuous observation of dislocations.
31(1960); http://dx.doi.org/10.1063/1.1735782View Description Hide Description
A theory is developed for the spectrum of electrical noise due to electron transitions between several quasi‐isolated groups of states, in the general case where each group may carry part of an electric current. It is applied to the noise due to transitions between valleys of the conduction band of germanium, and the possibility of observing this noise is discussed using the data of Weinreich, Sanders, and White on the frequency of intervalley transitions.
31(1960); http://dx.doi.org/10.1063/1.1735783View Description Hide Description
An analysis is given on the influence of bulk recombination within the base region of a mesa‐type drift transistor. The minority carrier transport efficiency is established for a solid cylinder base region and also for a simplified one‐dimensional structure. A comparison of the two minority carrier transport equations shows the approximate analysis will result in a negligible error when applied to practical semiconductor devices.
31(1960); http://dx.doi.org/10.1063/1.1735784View Description Hide Description
Several analyses of the transport of cathode shot noise through a space‐charge‐limited diode at microwave frequencies have been published to date. Each of these analyses has been beset by inconsistencies arising from assumptions of monovelocity perturbation flow, direct or reflected. A new method of analysis of diode flow eliminating this problem has been developed. Numerical results based on this method are presented here. Attention is restricted to the now classical problem of one‐dimensional longitudinal confined flow.
The magnitude and variation with distance of the so‐called beam noise invariants is shown for a range of diode operating conditions. These calculated results, based for economy on an approximate static flow model, essentially substantiate the qualitative expectations suggested by prior analyses, and fit what little experimental data are available.
The method of analysis employed in the calculation of the numerical results comprises a linear multistream formulation, based on representation or approximation of the perturbation particle density for the noise flow as a composite of singular impulse streams, N in number, along characteristic trajectories in the velocity‐distance phase space. The set of N coupled first‐order linear differential equations resulting is solved by simultaneous numerical extrapolation.
31(1960); http://dx.doi.org/10.1063/1.1735785View Description Hide Description
The equations describing the flow of a power‐law non‐Newtonian fluid on a rotating disk have been solved in general form. This makes it possible to calculate how the shape of an initial surface contour will vary with time and to investigate the possibility of producing uniform films by applying the materials to a rapidly spinning disk. It is shown that the latter process, which has potential industrial applications, has a much better chance of succeeding if the fluid is Newtonian than if it is not, in the sense that whereas for a Newtonian substance centrifugation will smooth out irregularities in the surface contour, for a non‐Newtonian fluid even an initially uniform film thickness will be deformed by rotating the plate.
31(1960); http://dx.doi.org/10.1063/1.1735786View Description Hide Description
A study has been made of the photovoltaic effect in Cu–CdS cells and related systems, associated with undiffused metal‐semiconductor junctions. The photovoltaic current has been shown to result from the photoemission of electrons from the coppermetal into the CdS crystal. Direct evidence is presented for this conclusion, and the conditions required for the photoemission process to occur are demonstrated by several experiments. Important factors contributing to the efficiency of Cu–CdS photovoltaic cells of this type are: (a) the optical properties of copper, (b) the rectifying contact between the metal and CdS, (c) the good conductivity and high optical transparency which can be achieved in CdS crystals, and (d) the favorable relation between the work function of copper and the electron affinity of CdS.
31(1960); http://dx.doi.org/10.1063/1.1735787View Description Hide Description
It has been established that when silicon is heated above 1300°K in a borosilicate glass vacuum system from 1011 to 1015 acceptors per cm2 are normally added to the silicon surface, even though the glass walls remain at room temperature. The acceptor diffuses into the surface upon heating forming a p layer several microns deep.
There is strong evidence that the acceptor is boron from the borosilicate glass envelope. The transfer to the silicon is believed to occur through volatilization of boron oxides by water vapor.
31(1960); http://dx.doi.org/10.1063/1.1735788View Description Hide Description
Paramagnetic susceptibilities of Fe and Fe‐Si alloys (5.75, 6.82, 9.45, 12.65, 14.70, 18.11, 20.85, and 24.38 at. % Si) have been measured up to 1200°C. At high temperatures the paramagnetic susceptibilities of bcc Fe‐Si alloys obey the Curie‐Weiss law, possibly indicating that the contribution due to s‐dexchange interactions is small in comparison with the temperature dependent paramagnetism. The effective Bohr‐magneton number of Fe from the high‐temperature region is independent of Si content up to about 14 at. % Si. At higher Si concentrations, gradual decrease in the effective Bohr‐magneton number occurs. According to the paramagnetic susceptibility measurements, the α‐γ transition in iron takes place at 910±3°C. Assuming that the critical temperatures for chemical ordering as given by Glaser and Ivanick are correct, our measurements indicate that the paramagnetic susceptibility, within the experimental error, is not influenced by the destruction of the superlattice above 13 at. % of Si.
31(1960); http://dx.doi.org/10.1063/1.1735789View Description Hide Description
A new method of producing thin layers of indium antimonide is described. This consists of suddenly squashing a drop of molten indium antimonide between two optical flats and allowing it to cool.
Large area, self‐supporting specimens of 10‐μ thickness have been prepared in this way and their properties examined. Although these layers are polycrystalline, their electrical and optical properties are in good agreement with the single‐crystal materials from which they were obtained.
31(1960); http://dx.doi.org/10.1063/1.1735790View Description Hide Description
Germanium layers have been formed on single‐crystal Ge substrates by the thermal decomposition of GeI2. The single‐crystal nature of the layers has been established by x‐ray and electron diffraction examination and by electrical measurements. The deposition process is described briefly. The crystal growth rate varies with crystal direction, and under certain conditions Gewhiskers appear. The layers as deposited are generally n type; ρ ranges from 1 to 5 ohm‐cm and μH from 1200 to 2700 cm2/v‐sec at room temperature. A donor level is found approximately 0.2 ev below the conduction band, with a concentration of active centers of about 1016/cm3. Heat treatment at 550°C gradually converts the layers to p type, for which ρ is 10 to 40 ohm‐cm and μH 1500 to 2400 cm2/v‐sec at room temperature; an acceptor level is found at about 0.05 ev above the valence band, with a density of active centers of 1014 to 1015/cm3. The layers can be doped intentionally to produce either conductivity type, permitting fabrication of junction devices. Although iodine and other impurity atoms are considered, it is concluded that interstitialGe atoms and lattice vacancies, occurring in unequal numbers at the time of deposition, are the most likely source of the donor and acceptor levels, respectively, and of the observed heat treatment properties.
31(1960); http://dx.doi.org/10.1063/1.1735735View Description Hide Description
In order to gain some insight in the problem of space charge neutralization of ion beams we make use of a previous calculation to discuss the unidimensional flow of positive ions in a tube where both ions and electrons issue from an emitter surface but only ion current is collected by means of an accelerating electrode. The resulting ion flow can be neutralized to varying degrees by the electrons present. We find that even in the absence of collisional interactions the potential distribution in the tube may closely resemble the electrode sheath and positive column structure familiar to glow discharges. This is the situation to be expected whenever the ion current has values far in excess of that predicted from a zero degree of neutralization space charge limited theory.
Measurement of Elastic Constants of RbBr, RbI, CsBr, and CsI by an Ultrasonic cw Resonance Technique31(1960); http://dx.doi.org/10.1063/1.1735736View Description Hide Description
An ultrasonic cw resonance technique for the measurement of the velocity of sound in solids is described. The end correction due to the presence of the transducer and coupling film can be calculated from consideration of a transmission‐line equivalent circuit. An experimental comparison is made of the cw and two pulse techniques over the frequency range 5 to 45 Mc. Application of the cw resonance technique is made to the measurement of the room‐temperature adiabatic elastic constants of single crystals of RbBr, RbI, CsBr, and CsI. A tabulation of the important elastic properties of these crystals is presented.
31(1960); http://dx.doi.org/10.1063/1.1735737View Description Hide Description
An investigation has been made of the cleanup of inert gases by a gas discharge. The cleanup of rare gases in a tube in which metal is being sputtered is governed largely by two factors. First, the rate at which the metal is sputtered, and second, the potential of the surface on which the metal lands. At small negative or positive potentials on the surface collecting sputteredmetal there is a slow cleanup rate caused by uncharged species being buried by sputteredmetal. At more negative potentials burial of ions becomes important, and cleanup is much more rapid. Recovery has been effected by heating to the evaporation temperatures of the metal. As the metalevaporates the buried gas is liberated. Hundreds of equivalent monolayers of argon have been cleaned up with only a total recovery of about one equivalent monolayer by heating at 1500°C. This shows that even with a forced ``solubility'' of the order of one per cent we find no evidence for significant diffusion of argon in metals. An electrode collecting ions at a uniform current density over the surface will have a net cleanup rate of zero on that surface after the initial cleanup of a small amount of gas. After the initial disappearance of some gas, resputtering will occur liberating the cleaned up gas as fast as it is being cleaned up.
31(1960); http://dx.doi.org/10.1063/1.1735738View Description Hide Description
Detailed measurements of the fast‐neutron and gamma‐ray bombardment behavior of germanium‐alloy‐transistor current‐gain have been obtained concurrent with exposure. These data indicate that previously reported analyses, which lead to a linear dependence of common‐base current‐gain on fast neutron exposure, yield a good approximation for the npn device, but are not of general validity for the pnpgermaniumtransistor. The extent of departure from the linear approximation depends on the width and conductivity of the base‐region and can be appreciable in many cases of practical interest.
For the pnpgermaniumtransistor it is necessary to take additional account of both changes during bombardment of the minority‐carrier recombination rate at bombardment introduced and initially present recombination centers and changes in the width of the collector junction depletion layer. Observed bombardment curves are in good agreement with an analysis which includes these effects. From initial slopes of the current‐gain bombardment curves, values of the product of fast‐neutron‐exposure times minority‐carrier‐lifetime at bombardment introduced recombination centers are 9.7×107 for 2.7 ohm‐cm p‐type and 14.2×107, 6.0×107, and 1.3×107, for 3.6 ohm‐cm, 1.2 ohm‐cm, and 0.2 ohm‐cm n‐type germanium, respectively, in units of sec‐neutrons/cm2.
31(1960); http://dx.doi.org/10.1063/1.1735739View Description Hide Description
The question of the existence of an intrinsic bias in colemanite above the Curie point is studied and compared with experimental results. It is concluded that a bias does exist above the Curie point and that it is completely responsible for the pyroeffect experimentally observed there. Some formulas are derived, connecting the pyroeffect and the intrinsic bias, and are compared with data available in the literature.
31(1960); http://dx.doi.org/10.1063/1.1735740View Description Hide Description
The current from a beta particle source measured through a thin dielectric cannot be predicted simply from the absorption curve. A model is considered in which the space charge formation in the medium results in a component of current in addition to that of the betas transmitted. Calculations developed from this model give a close approximation to experimental results.
31(1960); http://dx.doi.org/10.1063/1.1735741View Description Hide Description
Single crystals of a number of binary iron‐base alloys were grown, fabricated, and tested for magnetic anisotropy (K 1) and magnetostriction (λ100 and λ111). The additions made to iron included vanadium,molybdenum, germanium, chromium, titanium, and tin. The anisotropy of iron was lowered by the addition elements with the possible exception of tin. On the other hand, λ100 of iron was generally raised by these addition elements. Only titanium and tin lowered λ100; however, titanium had limited solublilty in iron and tin caused embrittlement.
31(1960); http://dx.doi.org/10.1063/1.1735742View Description Hide Description
A geometrical theory is developed for the analysis of surface wave excitation and propagation. The surfaces along which the surface waves propagate may be either curved or flat, and may have either constant or variable properties. The theory is based on the concept of a complex or imaginary ray. The excitation coefficient which enters the theory is determined from the solution of a canonical problem—that of a line source over an impedance plane. Then the theory is applied to the surface wave excited by a line source, on a wedge with variable surface impedance. The result agrees precisely with the asymptotic form of the exact solution. Another application is made to the surface wave excited on a cylinder by a line source. The result also agrees with the exact solution.
31(1960); http://dx.doi.org/10.1063/1.1735743View Description Hide Description
The slowing down of a primary displaced atom of high energy in a solid is investigated in detail. Physically interesting quantities, such as the total distance travelled and the vector distance to the end of the path, are discussed in terms of certain averages for hard core potentials with general dependence of the core radius on energy. These averages are explicitly calculated for a screened Coulomb potential for the purpose of comparison with experimental ranges observed in different metals. Theoretical values for the range can be derived. Comparison with the experimental data gives a value for the screening radius of the interaction potential which is about twice the value originally suggested by N. Bohr.
31(1960); http://dx.doi.org/10.1063/1.1735745View Description Hide Description
The threshold for displacement of the sulfur atom from a lattice point in CdS has been measured to be 8.7 ev. This is accomplished with 115‐kev electrons. This is also the threshold for the production of green edge emission centers and of centers for a red fluorescence band with a maximum intensity at about 7200 A. In crystals which show edge emission before bombardment, the edge emission is removed by electron bombardment in the energy range 2.5 to 200 kev. The red luminescence is not removed by electron bombardment but increases in intensity with bombardment above the threshold. The radiation``annealing'' of the edge emission is accomplished even in crystals which do not thermally anneal. A model is proposed with the sulfur interstitial atom the center for edge emission, and the sulfur vacancy the center for the red emission band.