Volume 30, Issue 11, 01 November 1959
Index of content:
30(1959); http://dx.doi.org/10.1063/1.1735025View Description Hide Description
Oxygen has been diffused into silicon at temperatures above 1250°C. The diffused layers have been detected by subjecting the samples to a second heat treatment at 450°C. The donors, which then form from the oxygen, cause the layer to convert to n type. The relationship between donor and oxygen concentrations was established by studying donor formation in crystals of known oxygen concentration. From these results and the electrical properties of the layers, the diffusivity and solubility of oxygen in silicon has been measured. For silicon, in contact with SiO2 (glass), the heat of solution is (2.3±0.3) ev and the diffusivity is given by .
30(1959); http://dx.doi.org/10.1063/1.1735026View Description Hide Description
Permanent and elastic strains in silicon crystals grown by the Czochralski technique have been studied by observing the crystal birefringence. These studies reveal that the presence of birefringence is related to (a) plastic deformation caused by severe thermal gradients which produce forces exceeding the crystal yield force and (b) work damage or externally applied forces. The first source of birefringence has been termed permanent strain since this appears in the crystal as grown and the birefringence pattern cannot be altered by changes in sample geometry. This characteristic is typical of a ``frozen‐in'' strain. A strain‐free sample may also be made birefringent, however, by a work damage such as surface abrasion or sand blasting. Such a birefringent pattern can be altered if the sample geometry is changed. This characteristic, of course, is typical of elastic strain.
Studies made of samples both parallel and perpendicular to the direction of crystal growth revealed birefringence patterns similar to those of naturally anisotropic crystals such as calcite. The patterns indicate the formation of a pseudo‐optic axis in silicon coincident with the growth direction and is caused by the uneven temperature distribution which results in perdominantly uniaxial stress.
Regions of tension and compression have been discovered and their respective magnitudes determined. The calculation of the ``frozen‐in'' tension and compression stresses are based upon experimental determination of the stress‐optic coefficient of silicon. Satisfactory agreement was obtained between frozen‐in stress calculations and measurements of yield stress at elevated temperatures.
30(1959); http://dx.doi.org/10.1063/1.1735027View Description Hide Description
Aluminum was strained in tension under a Geiger‐Müller counter. Both the electron emission associated with plastic deformation and the subsequent delayed emission were observed. An attempt was made to correlate quantitatively the emission rates with the mechanical variables, i.e., strain and rate of deformation. The model used for this correlation links point imperfections formed during deformation with the emission from the oxide surface film.
30(1959); http://dx.doi.org/10.1063/1.1735028View Description Hide Description
Dynamic pyroelectric techniques have been used to study single crystal triglycine sulfate hysteresis loops at room temperature. An apparent polarization bias is observed and is similar to that reported earlier for BaTiO3. The apparent polarization bias can be shifted with the application of a dcelectric field. When precautions are taken to eliminate electrode‐edge effects, the pyroelectrichysteresis loops are always symmetric. The apparent polarization bias is ascribed to electrode‐edge effects as in the case of BaTiO3.
30(1959); http://dx.doi.org/10.1063/1.1735029View Description Hide Description
The influence of plastic deformation upon the linear magnetostriction of hard‐worked nickel has been determined by use of direct measurements of strain in three normal directions and then by measurement of magnetostriction in the same three directions using the method of rotating the specimen 90° for each measurement. This combination of measurements appears to have advantages for the interpretation of magnetostriction in nonisotropic bodies.
The value of magnetostriction at saturation for grade A nickel plastically deformed with an 84% reduction of cross‐sectional area was found to be −33.5±1×10−6. This compares with −35±1×10−6 for annealed nickel of the same quality. The hard‐worked nickel was free of volume magnetostriction of determinable magnitude. It showed inappreciable preferred domain orientation. It did appear to have a small amount of preferred crystalline orientation.
30(1959); http://dx.doi.org/10.1063/1.1735030View Description Hide Description
A statistical approach is used to determine the effect of porosity in ceramicmaterials on their dielectric breakdown strength. The calculated drop in dielectric strength is in good agreement with the experimental data for lead zirconate titanateceramics. The theory shows that the measureddielectric strength in porous materials is a function of the porosity, the void size, and of the dimensions of the test sample.
Development and Comparison of Two X‐Ray Methods for Determining the Crystallinity of Cotton Cellulose30(1959); http://dx.doi.org/10.1063/1.1735031View Description Hide Description
Two x‐ray methods have been developed for determining the crystallinity of cellulose using a Geiger counter spectrometer. The two methods were applied to six native cotton varieties, to a cross‐bred variety, and to two cottons chemically modified with ethylamine. The x‐ray scattering curves for each of the nine samples were compared with those from a highly crystalline sample, a cotton hydrolyzed in HCl, and an amorphous cotton sample to provide a relative measure of crystallinity, or crystalline index.
With fully corrected data the average crystalline index of the six cotton varieties was found to be 68.3 and 78.7% by the correlation and by integral methods, respectively. The crystalline indices of the remaining samples determined by the correlation and by the integral methods are, respectively, cross‐bred cotton (S×P), 54.3 and 77.2%; cotton treated with anhydrous ethylamine, 29.7 and 50.9%; and cotton treated with 75% aqueous ethylamine, 28.3 and 50.3%.
30(1959); http://dx.doi.org/10.1063/1.1735032View Description Hide Description
The dependence of switching rate on the crystal thickness has been measured by Merz and explained by him in terms of a surface layer which has a low dielectric constant, and is about 10−4 cm thick. While not explicitly stated in Merz' original arguments, the layer must have a reversible polarization. If a layer without a reversible polarization is assumed, instead, and the discontinuity of the normal component of polarization at the interface between the layer and the bulk is taken into account, then a much thinner layer (∼1 atomic thickness) will explain the thickness dependence. This layer can be taken to be very lossy, so that it has a relaxation time (for the disappearance of electric fields) short compared to the switching time, and yet the layer will still be completely effective in slowing down domain wall motion.
30(1959); http://dx.doi.org/10.1063/1.1735033View Description Hide Description
When a cloud of highly ionized gas flows across a magnetic field, an emf is produced in the gas which is proportional to the speed of flow. Oscillographic probe measurements have been carried out giving the flow speed as a function of position. By drawing currents from the probes the plasmaresistance can be found at various distances from the plasma generator. The resistance is shown to be due to the motion of positive ions.
30(1959); http://dx.doi.org/10.1063/1.1735034View Description Hide Description
With the aid of a mass spectrometer a study has been made of the gaseous contaminants present when oxygen is exposed to different incandescent filaments. In agreement with others CO and CO2 were the most abundant contaminants found. The amounts of CO and CO2 found, at a given filament temperature and oxygen pressure, were greater for Mo 0.031% C, W 0.012% C, and Re 0.010% C than for Ta 0.001% C. Also at the same oxygen pressure and filament temperature the quantity of CO found was much greater for a carbonized W filament than for any of the other filaments investigated. These results are consistent with the hypothesis that CO and CO2 are produced by the interaction of oxygen with the carbon present in the hot filaments. No evidence was found to indicate that the glass walls contribute to the formation of CO and CO2.
30(1959); http://dx.doi.org/10.1063/1.1735035View Description Hide Description
The diffraction of plane waves by an infinite slit is investigated, with attention drawn to the case of grazing incidence and for wavelengths short compared to the slit width. The wave pattern is time harmonic and two dimensional, with identical behavior in all planes normal to the slit axis. At the coplanar screens bordering the slit, the normal derivative of the wave function is assumed to vanish, for this boundary condition provides a problem with calculable diffraction even at grazing incidence. A useful formulation (Sec. 2) of the boundary value problem involves Fourier transforms of field distributions in the plane of the screens, and enables the transmission cross section of the slit to be directly inferred (Sec. 3). The screen distributions are characterized by a pair of integral equations which allow systematic approximation (Sec. 4) at short wavelengths for arbitrary angle of incidence. A few terms in the asymptotic development of the cross section at oblique incidence are obtained explicitly, and since this development fails at grazing incidence, the analogous terms for the latter case are derived by a limiting process. Lastly (Sec. 5), in the related problem of planewave scattering by an infinite strip, a comparison is made with the variational results based on strip distributions of primary or unperturbed form.
30(1959); http://dx.doi.org/10.1063/1.1735036View Description Hide Description
A study has been made of the time‐dependent heat conduction in a semi‐infinite medium subject to a boundary condition which can involve the temperature in a nonlinear manner. A formulation for the determination of the surface temperature, which is often of greatest physical interest, leads to a nonlinear Volterra integral equation. A simple iterative solution method, with an accuracy suitable for many practical purposes is presented. As an example, the problem of the time‐dependent surface temperature of a body receiving heat according to the Stefan‐Boltzmann law is treated. The analysis is also applicable to physical adsorption or chemisorption processes which occur at the boundary.
30(1959); http://dx.doi.org/10.1063/1.1735037View Description Hide Description
Surface effects may seriously degrade the high frequency performance of a semiconductor junction diode used as a variable reactance element without significantly degrading the diode's dc characteristics. Measurements on both p+n and n+p germanium alloy junction diodes have yielded a diode series equivalent resistance component in excess of the calculated integrated bulk resistance. This excess resistance decreased with frequency approximately as 1/f and for freshly etched devices could be varied by changing the atmosphere surrounding the diode. Those ambients which yielded a maximum surface‐determined junction breakdown voltage also yielded a maximum frequency‐dependent excess resistance. A model which can explain these observations assumes a surface inversion layer contiguous with the alloy junction.
30(1959); http://dx.doi.org/10.1063/1.1735038View Description Hide Description
The temperature dependence of a semiconductorp‐njunction over a given temperature range can be held to a minimum by using material with a minority carrier lifetimebelow a certain maximum value. The first‐order temperature dependence of the junction currents is then iαe−Eg/2kT , rather than iαe−Eg/kT , over the entire operating temperature range. Calculations applied to gallium arsenide in monograph form show that an optimum lifetime should be practically attainable by controlled doping with recombination‐center impurities. The maximum‐lifetime condition fixes the last remaining degree of freedom in the choice of semiconductor materialproperties for junctiondevice design. The upper operating temperature limit of junctiondevices is calculated for germanium, silicon, indium phosphide, and gallium arsenide.
30(1959); http://dx.doi.org/10.1063/1.1735039View Description Hide Description
The effects produced on luminescence and conductivity in pure CdS crystals by application of electric fields up to ∼1000 v/cm are reported. A shift in the red and green cathodoluminescence peaks of ∼0.1 A/v/cm is observed. After application of the low fields, some crystals required over 90 minutes to recover their ``prefield'' luminescence. Fine structure in the luminescent peaks at room temperature is reported. A V‐I plot shows a sublinear relation in this voltage range for several different levels of irradiation. An explanation of the observations is suggested based on self trapping of electrons.
30(1959); http://dx.doi.org/10.1063/1.1735040View Description Hide Description
The thermal conductivity of clear fused silica was measured over the temperature range 300–2100°K in an experiment which minimized radiative energy transport. This was a steady‐state experiment involving the measurement of the electric current and voltage drop through a fine tungsten wire which was embedded along the axis of a cylindrical silica rod. The wire served both as a heating element and as a resistancethermometer.Thermal conductivities were calculated by graphical evaluation of the rate of change of electric power with temperature at different temperatures. The experiment yielded thermal conductivities between 2.6×10−3 and 2.9×10−3 cal/cm sec°K at room temperature, and between 4.5×10−3 and 5.5×10−3 cal/cm sec°K over the temperature range 1000–2100°K.
30(1959); http://dx.doi.org/10.1063/1.1735041View Description Hide Description
Normal stress phenomena are studied in solutions of some typical high polymers, polystyrene, methylcellulose, and sodium‐carboxymethylcellulose, with a parallel plate instrument. The principle of procedures for separate determination of normal stress components with the parallel plate instrument is briefly described. The normal stress measurements are performed in shearing rates ranging from about 1.0 to 100. The results obtained, together with the flow curves, are discussed in terms of the cross‐elasticity theory and of some molecular bases. It is concluded that polystyrene solutions roughly obey ``Hooke's law in shear,'' while solutions of cellulose derivatives are remarkably ``non‐Hookean in shear.''
30(1959); http://dx.doi.org/10.1063/1.1735042View Description Hide Description
The rolling friction of a hard cylinder over a viscoelastic material is worked out in terms of the bulk properties of the material. It is found that the rolling friction has a maximum at a velocity corresponding to the peak of the relaxation time distribution. Both the load required to maintain the cylinder at constant depth of indentation and the coefficient of friction are dependent on the velocity of rolling. The shape of the rolling frictionversus velocity curve is a first approximation to the distribution curve of relaxation times, indicating that rolling frictionmeasurements can be used to determine the distribution experimentally.
30(1959); http://dx.doi.org/10.1063/1.1735043View Description Hide Description
A theory of rolling friction featuring the importance of elastic hysteresis losses is presented. A simple model of retarded elasticity is chosen to represent the physical properties of the material. A prediction resulting from the theory is that the coefficient of friction for a relatively hard sphere rolling on a softer base material should vary with speed so as to go through a maximum. This relationship resembles closely the variation of mechanical loss with frequency.
The results are not restricted to rolling but also apply to well‐lubricated sliding where shearing forces have been minimized. Although the theory is developed for a material with idealized physical properties, it nevertheless affords a basis for comparing real materials and for predicting their frictional properties in cases where deformation losses are predominant.
30(1959); http://dx.doi.org/10.1063/1.1735044View Description Hide Description
Contrary to the results of previous investigators, it has been found that molecular O2 and N2 have no effect on the ductility of rock salt single crystals. Also, it has been found that air‐aged crystals are brittle in summer and are ductile during a major fraction of the time in winter. Ductile rock salt crystals have been made brittle by subjecting them to ozone, NO, and atomic oxygen atmospheres. It is believed the ozone content of the atmosphere is responsible for the reported effects on brittleness. Other embrittling agents have been found.