摘要:

The relative photoluminescence intensities of band‐to‐band and band‐to‐acceptor radiative recombination were measured as a function of temperature.p‐Type cadmium‐doped epitaxial GaAs was studied. The samples that were used had carrier concentrations in the range of 5×1017to 3.5×1016/cc as determined from Hall measurements at 300°K. Over the temperature range 40° to 150°K the two emission peaks were sufficiently resolved so that accurate intensity measurements could be made. The temperature dependence of the band‐to‐acceptor luminescence intensity is in agreement with theoretical estimates of the inverse lifetime for this recombination mechanism. The variation of the diffusion of photoexcited minority carriers as a function of temperature must be considered in order to relate the band‐to‐band luminescence with the lifetime for the mechanism. Minority carrier diffusion theory analysis suggests that the good agreement obtained between theory and experiment for the band‐to‐acceptor luminescence occurs because the total lifetime and the diffusion coefficient have similar temperature dependence in the temperature range studied.

ISSN:0021-8979    

DOI:10.1063/1.1709947

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

The self‐diffusion of tritium in artificially and naturally grown ice monocrystals, parallel and perpendicular to the optical axis, was studied between −2.5° and −35.9°C. The plane‐source solution to Fick's second law was used in treating the data. An anisotropy of ≈ 12% was observed. The activation energy was found to be 0.62 eV for all cases andD0≈ 10 cm2/sec. Based on the experimental data, it is concluded that the diffusion takes place by a vacancy mechanism, and that entire H2O molecules are diffusing, i.e., molecular diffusion occurs. Theoretical calculations using the atomic‐diffusion theory and Zener's theory forD0are in excellent agreement with the experimentally determined diffusion coefficient.

ISSN:0021-8979    

DOI:10.1063/1.1709948

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

Using a three‐fluid model, wave equations are developed for the disturbances due to current sources in a partly ionized gas. The formal solutions to the wave equations are obtained for an elementary current source. The power radiated from the source is given in terms of these solutions and, for the special case in which the electrons are much hotter than the other two constituents, the radiated power is determined in detail.

ISSN:0021-8979    

DOI:10.1063/1.1709949

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

For strong homogeneous fields the ideal loop and solenoid elements of a prototype system may be expanded into thick cylindrical coils whose current density is (a) uniform or (b) inversely proportional to the cylindrical radius. Error coefficients of the zonal harmonic series for field or gradient that are cancelled in any given prototype continue to vanish as the elements are expanded, even to fusion, if at each stage the coil boundaries are adjusted by an iterative method. This involves the use of (a) the harmonic source functionsUn* or (b) the Legendre functionsPn; either set is best computed by a recursion formula. An alternative method based on Lyle's principle requires no iterations and only trivial calculations. Though it also is valid for systems of any order, it can only expand a set of loops into coils with square cross sections of limited area. Also, the true null coefficients are replaced by small residues proportional to 4th and higher powers of the section dimensions when the second method is used.The number of tabulated prototype systems of the 6th and 8th orders is increased to more than 200. Since multiply infinite sets of prototypes can be computed for every order higher than the 8th, univariate tables would be inadequate and only a few illustrative examples of such systems are given. Some 150 thick‐walled systems of the 6th or 8th order are listed in several tables, but such a selection can only suggest the wide range of possibilities. These systems have more degrees of freedom than do the corresponding prototypes, and even the 6th order is multivariant. At the 8th order and beyond, the growing redundancy of variables permits the design of systems with a common current density in all coils and with all section dimensions proportional to a set of small integers. Systems of order 4nhave paired coils with gaps for lateral access, an advantage that is lacking in the 6th‐order designs.Efficient computer programs have been written to design systems of all the types so far enumerated, including multiple sets of both prototypes and fully adjusted systems of thick coils for orders from 8 to 20 in steps of 4. Since adequate tabulation of results is ruled out by their diversity and sheer bulk, in view of the wide range of potential applications the programs themselves must be considered the basic research tool. They will be described in detail elsewhere.As a measure of field inhomogeneity, including contributions from all orders and from both axial and radial field components, the concept of total vector error is developed. The tables include error limits for all systems, and some 40 systems or their error contours are shown in the figures.

ISSN:0021-8979    

DOI:10.1063/1.1709950

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

A perturbation procedure is introduced to solve for the probability amplitudes of a system of coupled spins under the action of two rf magnetic fields; one a large saturating signal, the other a relatively weak one. The power absorbed when the saturating signal connects two states in the system is affected by the presence of the second signal connecting two other states especially if both signals have one state in common. The mixing of these states by the saturating signal can become large enough in some instances that it becomes meaningless to speak in terms of population differences and rate equations for these levels. It is further shown that the effect of the intermediate levels is to cause a shift in the resonance frequency for these levels. For widely spaced levels this ``intermediate'' effect may be neglected, but for closely spaced levels it can become appreciable.A four‐level system is used to illustrate the method. Relaxation effects are neglected.

ISSN:0021-8979    

DOI:10.1063/1.1709951

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

The effects of fairly high densities of extrinsic stacking faults (&agr; approximately as large as 0.3) and twins (&bgr; approximately as large as 0.15) on the coercive force,Hc, of thin (less than 700 Å) ferromagnetic Fe‐Co‐Ni films are studied.Once the effects of strain and small crystallite size onHcare eliminated, it can be shown that stacking faults and twins increase theHc, stacking faults having a larger effect than the twins. The introduction of the faults was achieved by sputtering onto ``unclean'' substrates, which gave an initial small‐crystallite‐size layer of about 100 Å, where the crystallite size gradually increased to that found on ``clean'' substrates. At the intersection of the two layers, there was a layer of faults extending about 200 Å into the larger‐crystallite‐size film. The x‐ray technique used to evaluate thickness variation of faults is described.

ISSN:0021-8979    

DOI:10.1063/1.1709952

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

A capillary wave of the appropriate wavelength will cause a jet to break up into a stream of uniform‐sized droplets. In this paper, a theoretical expression for droplet size, radius, and spacing in terms of the jet parameters and applied frequency is derived and verified experimentally. For a given jet radius and velocity, the droplet size can be varied from its minimum value,rmin, to approximately 1.6rminby varying the driving frequency. Also, a theoretical expression for the charge on droplets resulting from the disintegration of a charged jet is shown to agree with the measured value of droplet charge.

ISSN:0021-8979    

DOI:10.1063/1.1709953

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

Dielectric constant and dissipation factor at 1 kHz for films formed by vacuum evaporation of silicon monoxide have been measured as a function of deposition rate and residual oxygen pressure. The dielectric properties are found to depend strongly on the ratio of molecular‐impingement rates at the substrate of O2and SiO. A model based on changes in the film of the concentrations of Si, SiO, and Si2O3is proposed to explain the dielectric behavior. The model is compared to optical data reported by other workers.

ISSN:0021-8979    

DOI:10.1063/1.1709954

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

The six third‐order moduli of GaAs have been determined by measurement of ultrasonic wave velocities (time delays) as a function of applied stress. The adiabatic values (in units of 1012dyn/cm2) at 25°C and for zero electric field are very similar to those previously obtained for Si and Ge, as can be seen from the following table:ModulusGaAsGeSiC111−6.22±0.06−7.10−8.25C112−3.87±0.03−3.89−4.51C123−0.57±0.06−0.18−0.64C144+0.02±0.09−0.23+0.12C166−2.69±0.06−2.92−3.10C456−0.39±0.09−0.53−0.64.

ISSN:0021-8979    

DOI:10.1063/1.1709955

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

The stress and displacement fields of an edge dislocation that climbs with a uniform velocity are derived. This solution has application for the determination of the stress and displacement field arising from the anomalous edge component of a moving partial dislocation. The climb motion of the anomalous edge component does not involve diffusion of point defects and is not restricted to slow velocities. The self‐energy of a climbing edge dislocation also is determined. It is found that the self‐energy diverges as (1−V2/c2)−1/2, whereVis the dislocation velocity andcis the transverse sound velocity when the dislocation velocity approaches the slow sound velocity. This divergence is not as strong as that of the gliding edge dislocation [which is (1−V2/c2)−3/2].

ISSN:0021-8979    

DOI:10.1063/1.1709956

出版商:AIP    

年代:1967

数据来源: AIP