Volume 27, Issue 8, 01 August 1956
Index of content:

Effects of Low‐Energy Gas Discharges on Evaporated Metal‐Semiconductor Contacts
View Description Hide DescriptionExposure of the surface of chemically clean 5 ohm‐cm germanium to a low‐energy gas discharge prior to evaporating onto it a platinum diode produced results dependent on the gas used. Exposure of n‐type material to an oxygen or nitrogen discharge destroyed rectification completely; exposure to a hydrogen or argon discharge not only maintained it but tended to counteract the effect of the former gases. These results indicate that such oxygen and nitrogen bombardment lower the effective barrier, making the surface more n‐type, but hydrogen and argon bombardment make it more p‐type. This can be explained by the introduction of gas‐dependent interface states.

High‐Frequency Gas Discharge Breakdown in Neon‐Argon Mixtures
View Description Hide DescriptionBreakdownelectric fields in a wave guide at 9500 Mc/sec frequency are presented for a number of neon‐argon mixtures at various pressures. The argon percentage is found to have a large influence on the breakdownelectric field, just as Penning found for the dcdischarge. For each argon concentration, only one minimum is found in the curves giving breakdown field as a function of pressure. This result contrasts with the two minima found in the dcdischarge for some neon‐argon mixtures. This can be explained by the difference between the efficiency of energy transfer from the electric field to the electrons in the dc case and the high‐frequency case. The relation between the concentration of argon and the breakdown fields is discussed. The influence of electric field distortions and the standing‐wave ratio in the wave guide are investigated.

Adhesion and Contact Error in Length Metrology
View Description Hide DescriptionAn account is given of experimental studies of the nature of the strong adhesive contact between finely finished steel and glass surfaces when a trace of liquid exists between them. These surfaces are of the kind that are of practical use in length metrology where this adhesive action or ``wringing'' is of considerable importance.
The dimensional effects of the thin film between the surfaces have been measured by multiple‐beam interferometry and the nature of the adhesive contact has been further studied by measuring tangential forces and electrical characteristics.
The experimental evidence suggests that there is no liquid film effectively separating the surfaces but that the strong adhesive action induced by the presence of the liquid introduces a dimensional contact error. This error is likely to be positive or negative, depending on the degree of contact between the surfaces. Provided the adhesion is good the contact error is not greater than ±0.01μ. Where such an error is undesirable in high precision length metrology it is better to avoid the use of this adhesive contact.

Measurement of the Image Rotations Produced by the Lenses of a Magnetic Electron Microscope
View Description Hide DescriptionA method of measuring the amount of rotation produced by the lenses of a three‐stage electron microscope is described and the application of the results to stereo‐electron microscopy discussed.

Time Dependence of Mechanical Breakdown Phenomena
View Description Hide DescriptionA phenomenological theory of the time dependence of mechanical breakdown phenomena is presented which is applicable to creep failure of oriented polymeric filaments under tensile stresses. In using the theory, one makes assumptions about the distribution of breaking times in ensembles of filaments which are bearing constant loads and then proceeds to calculate the distribution of lifetimes under other stress histories, e.g., loads increasing linearly with time and sinusoidal loads. The a priori assumptions used here permit a calculation of the dependence of observed tensile strengths on both the sample size and the rate of loading. Experiments involving drawn 66 nylon monofilament yarn are cited to illustrate how the parameters which describe the average lifetime under dead load behavior of a yarn may be used to calculate its tensile strength distribution when measured with a constant rate of loading apparatus.

Flow of Immiscible Fluids in Porous Media: Exact Solution of a Free Boundary Problem
View Description Hide DescriptionA mathematically exact solution is obtained of a two‐dimensional free boundary problem arising in the flow of two immiscible fluids in porous media. The particular problem dealt with concerns the ``fingering'' of water toward a line of equally‐spaced oil wells that penetrate a thin, dipping sand. The solution is obtained by use of the hodograph plane and complex variable theory.

Time Changes in Thin Films of BaTiO_{3}
View Description Hide DescriptionThe decrease of dielectric constant with time under an applied alternating field, less than the coercive field, has been studied in films of BaTiO_{3} between 1 and 3 microns thick. The phenomenon may be interpreted as being associated with the process of switching the domains to a position more nearly parallel to the applied field.

Motion of Electrons and Holes in Photographic Emulsion Grains
View Description Hide DescriptionThe use of simultaneous pulses of light and voltage to study the motion of electrons and holes in photographic grains and the role played by these charge carriers in the formation of the latent image is discussed. The electric field displacement of conduction electrons forming print‐out as well as latent‐image silver is shown by electron micrographs of the grains. Also, results on the motion of positive holes are presented. It is possible to show at the print‐out level that this carrier is mobile; although it may be that the hole is displaced at the latent‐image level, this behavior has not been demonstrated. The light and voltage pulses used for the exposures are analyzed and related to electron displacement. Indications are that when electrons are forced to the grain surface by an electric field, they are trapped in a time less than 1 μsec.

Diffraction by a Wide Slit
View Description Hide DescriptionThe problem of diffraction of scalar waves by an infinite conducting plane with a slit is investigated. Approximate expressions for the near and far fields, taking into account the interaction between the edges, are derived in terms of the well‐known solutions for the field produced when an isolated conducting half‐plane is excited by (a) a plane wave, and (b) a line source. Results of numerical calculation are given for the case of a plane wave normally incident on the slit. Twelve values of slit width ranging from 0.96 to 2.5 wavelengths are considered. A comparison of transmission coefficients is given. It is found that the new approximate solution agrees well with the exact solution, and provides a significant correction to the noninteraction solution. The accuracy increases with the slit width, so that the result is useful in the range where interaction cannot well be neglected but where the exact solution converges so slowly that computation is impracticable.

Avalanche Breakdown Voltage in Silicon Diffused p‐n Junctions as a Function of Impurity Gradient
View Description Hide DescriptionA method is presented for controlling the reverse breakdown voltage (V_{B} ) in a silicon graded junction. The significant process parameters are shown to be resistivity, time of diffusion, and temperature of diffusion. For a constant resistivity, V_{B} increases with the fourth root of the time of diffusion and with the square root of the depth of diffusion as predicted by theory. Statistical analysis shows that the mean breakdown voltage for a large group of units can be predicted within 2%. The method fails for very low or high resistivity material.

Two‐Dimensional Motion of Idealized Grain Boundaries
View Description Hide DescriptionTo represent ideal grain boundary motion in two dimensions, a rule of motion of plane curves is considered whereby any given point of a curve moves toward its center of curvature with a speed that is proportional to the curvature. A general theorem is deduced concerning the change of area enclosed by such a curve. Three families of curves are found that obey the curvature rule of motion while undergoing the shape preserving transformations of uniform magnification, translation, and rotation respectively. Pieces of these curves represent the steady shapes of idealized grain boundaries under certain symmetrical conditions.

On the Transient Behavior of Semiconductor Rectifiers
View Description Hide DescriptionThe time dependent behavior of semiconductor surface barrier and point contactdiodes has been calculated for small variations. (It is assumed here that the surface barrier lies on a semiconducting pellet with uniform cross section. If, on the contrary, the contact area is small compared with the semiconducting surface, like the case considered by Borneman, Schwartz, and Stickler [J. Appl. Phys. 26, 1021–1028 (1955)], then the analysis given for a point contact applies.) It is pointed out that these rectifying barriers have an ac admittance of the form in which G _{0} is the slope of the dc characteristic curve, C_{b} the barrier capacitance, ω and j the angular frequency and √−1, respectively, and τ the recombination time of minority carriers. The dimensionless constant Γ equals the injection ratio γ with surface barriers, but represents γr _{0}(L+r _{0})^{−1} with point contacts where r _{0} is the effective contact radius, and L the diffusion length of minority carriers. The constant conductance is related only to electrons with surface barriers (it is assumed that the semiconductor is n‐type and that the rectifying contact emits holes), but with point contacts it is associated with both electrons and holes. The frequency dependent conductance is due only to holes in either case. Compared with the conductance the barrier capacitanceC_{b} ordinarily plays a more dominant role in the frequency dependence of point contacts than with surface barriers, because the value of Γ is r _{0}(L+r _{0})^{−1} times its value with surface barriers, and normally r _{0}≪L.
The barrier voltage response f(t) to an impulse current has been calculated. Although the expression f(t) is complicated, it may be approximated under representative conditions (depending on bias and nature of the contact) by one of the following functions: e^{−t}, e^{t} erfct ^{½}, or {[1–2C(t)] cost+[1–2S(t)] sint} with time t in appropriate units. The functions C(t) and S(t) are the Fresnel integrals defined by the equation .
A special case of large amplitude behavior, the open circuit voltage decay following the interruption of forward current is also treated. It is found that with surface barriers, the open circuit decay time depends on recombination time of minority carriers, their penetration depth beyond the barrier in the semiconductor, and the injection ratio. With point contacts the decay time depends primarily on the product of the injection ratio and contact radius.

Oscillating Glow Discharge Plasma
View Description Hide DescriptionThe plasma potential, electron temperature, and electron concentration have been measured as functions of both time and position in the positive column of an argon glow discharge with moving striations using a plane circular probe 0.25 mm in diameter that could be saturated in the electron collecting region. It is found that (1) the radial distribution of charge is that predicted by the ambipolar diffusion theory, (2) in each cycle, close to the time of the negative striation, the potential at all points in the positive column decreases sharply, (3) no increase in electron concentration occurs at the time of the negative striation. It is concluded that the positive striations move from anode to cathode as a result of ionization in front of the charge maximum combined with diffusion and drift of the charges radially and longitudinally. When the ionization function necessary to produce the observed striation motion is calculated from the observed charge concentrations, it is found to agree closely with the observed light emission of the discharge.

Charged Right Circular Cylinder
View Description Hide DescriptionA new method permits the calculation of the electric field surrounding a charged conducting surface of revolution without the use of orthogonal functions. Detailed formulas show how to find the charge density on a right circular cylinder with any desired precision. The numerical examples worked out give the maximum deviation of the actual surface from that of a true cylinder of diameter d to be −0.0015d, −0.00037d, −0.00017d, +0.0016d, and +0.014d for length to diameter ratios ¼, ½, 1, 2, and 4, respectively. The capacitance calculation gives an accuracy of one part in 30 000 for the ratios ½, 1, and 2. A capacitance formula is worked out which is accurate to one part in 1000 over the ratio range 0 to 4. Additional formulas indicate the method of solution for the bodies in longitudinal and transverse electric fields and the extension of two‐body problems such as the thick plate parallel plate capacitor. A way to calculate the flow about bodies of revolution is indicated. Digital computers are well suited to this method as no function tables are needed.

Controlled Field Emission in Hexane
View Description Hide DescriptionThe current‐voltage relationship for dielectric liquids consists of two portions, usually in superposition: at lower voltages a current of ions flows; at higher voltages, field emission sets in. The field‐emission current depends on the material of the cathode, but not simply on its work function. The current may be altered by changing the thickness of the cathodesurface layer or the gas adsorbed upon the surface. When the ion content of the liquid is raised, not only the ionic current, but also the field‐emission portion of the current increases.
Controlled field‐emission currents have been produced.

Electrical Cleanup of Gases in an Ionization Gauge
View Description Hide DescriptionObservations have been made on the electrical cleanup of different gases in a Bayard‐Alpert ionization gauge. It has been found that the ion current striking the wall of such a gauge is 5 to 10 times that reaching the ion collector. It is therefore possible to account for a maximum pumping speed of 0.1 to 0.2 l/sec due to ion pumping at the gauge walls. The maximum pumping speed observed was 0.1 l/sec for nitrogen. It was found that the maximum pumping speed for nitrogen remained the same when the inner wall of the ion gauge was covered with a thin metal deposit or Aquadag. An expression has been derived on the basis of ion pumping which describes the observed cleanup.

Excitation and Separation of Pure High‐Order Modes in Large High‐Q Cavities
View Description Hide DescriptionIn order to extend the range of cavity resonance techniques a successful method has been developed for the suppression of undesired modes of a densely populated cavity spectrum. It is based on the nodal properties of the usual simple solutions of the wave equation. The analytic continuation of any such solution may be regarded as a master mode pattern which defines an infinite variety of elementary cavities or cells all having one frequency in common. These properties provide the basis for a novel principle in the design of cavity‐coupling systems. By suitable choice of a ``complex'' of these elementary cells, devices can be obtained with remarkable transducing, filtering, or suppressing properties. An experimental test of the foregoing ideas has been made in which it was possible to excite a well‐separated very high order TE _{0mν} mode in a large cylindrical cavity, at a frequency of 20 000 Mc. The observed Q for this preferred mode was of the order of one million. As an additional test quantitative experiments have been performed on a special type of complex cavity in which the number of elementary cells could be varied.

Switching Time in Ferroelectric BaTiO_{3} and Its Dependence on Crystal Thickness
View Description Hide DescriptionThe switching time t_{s} and the switching current i _{max} have been measured as a function of applied field E and of the size of the sample. It has been observed that the ``activation field'' α for the nucleation of new domains is inversely proportional to the thickness of the sample. This behavior can be explained by assuming a surface layer. The thickness of this layer has been calculated to be of the order of 10^{−4} cm. The same way we can explain the thickness dependence of the 60‐cycle coercive field strength. Furthermore, it has been found that the switching time depends to a first approximation linearly on the thickness of the sample if the field E is kept constant. This can be explained by assuming a domain wall motion primarily in the forward direction or by assuming a nucleation mechanism. The maximum velocity of the domain growth was found to be of the order of the velocity of sound. The switching time does not depend on electrode area.

Effect of Pressure on Glass Structure
View Description Hide DescriptionThe anelastic response of a glass structure to pressure is examined in terms of the random‐network hypothesis. The analysis is based upon the premise that an asymmetrical distribution of bond lengths characterizes the randomness of the network. It is found that the effect of pressure is to change the amount of skewness and therefore the average bond length which determines the density. Two kinds of persisting density changes are found. One is reversible and is called densification, and the other is irreversible and is called compaction. Experimental results for Corning 7052 glass show that both densification and compaction exist for combinations of the p, T, τ conditions, 3800 to 6600 atmos, 100–300°C, 15 min—1 week. These experiments also show that the kinetics of the densification process agree qualitatively with that predicted by the theory.

Effect of Growth Imperfections on the Strength of Aluminum Single Crystals
View Description Hide DescriptionThe effect of growth imperfections on the critical resolved shear stress is investigated for high‐purity (99.99+%) aluminumsingle crystals as compared with strain‐anneal crystals. An apparatus for measuring strains of the order of 0.2 μin. is described. Using etch pits as an index, the critical resolved shear stress is found to be inversely proportional to the growth imperfections for a range of etch pit density ρ of 5 to 25×10^{4}/cm^{2}. An elastic range is demonstrated; and prior plastic deformation is found to lower Young's modulus. The results are interpreted in terms of dislocation theory.