摘要:

A low‐pressure magnetically confined argon arc discharge was used in a mass spectrometer ion source to study low‐energy (0–100 eV) sputtering of polycrystalline copper. Target bombarding ion current densities ranged from 60–200 &mgr;A/cm2. Neutral particles were studied. Cu atoms and Cu2molecules were detected. The mass ratio of analyzed Cu2molecules to Cu atoms increased with bombarding ion energies to about 5½% at ion energies of 100 eV. Target voltages for appearance of Cu atoms and Cu2molecules were − 19 and − 50 V, respectively. No Cu3molecules were detected; if they were present, it was estimated that the ratio189Cu3to63Cu is less than 0.09%. The method has been found to be promising for the study of neutral particles in low‐energy sputtering. Yield curves agree well with results of other observers; sensitivities of 7×10−4atoms/ion were attained, and this figure can be improved.

ISSN:0021-8979    

DOI:10.1063/1.1713576

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

For an exact solution of the Bragg equation it is necessary that there be a one‐to‐one correspondence (equivalence) between the angular measure &thgr; and the wavelength measure &lgr;. Because the aberrations inherent in all x‐ray diffraction profile measurements distort the profile, it is necessary to correct any given measure (peak, centroid, etc.) for all aberrations. The only angular measure of powder diffractometer profiles that can be corrected to a high degree of accuracy is the centroid. To realize the greater accuracy inherent in the centroid method, accurate centroid spectral wavelengths are required. Centroids of CuK&agr; and FeK&agr; two‐crystal spectrometer profiles prepared by Bearden have been calculated and corrected for axial divergence, distortions arising from variation in absorption across the spectral distributions, crystal asymmetry, and other factors. To determine the centroid wavelength it is necessary to truncate the profile; equivalence of &lgr; and &thgr; is maintained by truncating the powder and spectral profiles in the same manner. Four methods for systematically truncating the profiles have been published; the methods are evaluated and the superiority of one of the methods is demonstrated. It is shown that the centroid wavelength is a function of integration (wavelength) range, primarily as a result of inclusion or exclusion of theK&agr; satellite group within the truncated profile. The two‐crystal spectrometer profiles are compared with models based on a Cauchy distribution. The necessity for additional spectral data before reference centroid wavelengths can be established is discussed.

ISSN:0021-8979    

DOI:10.1063/1.1713577

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

The afterglow following pulsed dc excitation of neon can be explained by the requirement that the electron temperature must decrease before electron‐ion recombination followed by radiative transitions can take place. This conclusion is supported by the suppression of afterglow by simultaneously applied rf power. The absence of negative absorption rules out energy level population inversion and stimulated emission.

ISSN:0021-8979    

DOI:10.1063/1.1713578

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

A substantial lowering of the work function of a tungsten Langmuir probe immersed in an argon plasma in a discharge tube is observed. The mechanism is thought to be similar to the Schottky effect. The electron temperature measurement is lowered about 30%, in a particular discharge condition, as the probe goes from room temperature to 2000°C. The charge number density measurement, by saturation electron current appears to be higher by 15%, and that by ion saturation current appears to be higher by almost one order of magnitude. This phenomenon can also account for the discrepancy of the ratio of ion and electron saturation current obtained by previous authors and this author.

ISSN:0021-8979    

DOI:10.1063/1.1713579

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

High‐power lasers encounter increasing losses of stored energy from stimulated emission by once‐through avalanches of photons as higher powers are sought. This occurs even without resonance buildup. Even in the simple geometry of a thin rod, a satisfactory analysis would require elaborate machine calculation. A very crude model has, however, produced rough results from which some guidance is obtainable.The model exhibits the expected linear increase of outgoing photon flux near the end of the rod and the huge depletion of excited atom population away from the rod equator. A criterion has been developed for the maximum useful excitation relative to emission parameters, rod length and rod cross section. It is concluded that this excitation level is fairly insensitive to aspect ratio (radius/length) but that internal reflection from the rod cylindrical surface can markedly lower this level by increasing the effective aspect ratio enormously.

ISSN:0021-8979    

DOI:10.1063/1.1713580

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

A uniform magnetic field is compressed in a circuit containing two semi‐infinite slabs of constant conductivity &sgr;. The separationlof the slabs decreases uniformly according tol=l0−vt. An equation involving the magnetic Reynolds numberRm=&sgr;&mgr;0l0vis derived for the magnetic field in the gap. Expressions are given for the magnetic and electric fields everywhere up to the instant of collision. These expressions are evaluated for several values ofRmand it is found that the ratio of Joule energy density to magnetic energy density at the surfaces of the slabs is fairly close to unity throughout the motion. ForRm»1 it is shown that the maximum magnification of the initial field is approximatelyRm/8.

ISSN:0021-8979    

DOI:10.1063/1.1713581

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

The results and experimental details ofS‐band noise figure and noise spectra measurements made on electron beams that yield traveling‐wave‐tube noise figures below 4 dB are presented. A simple technique involving the observation of the change in noise figure with electron gun‐helix separation in a special traveling‐wave tube (TWT) is employed. A positive correlation between current and velocity fluctuations contributes heavily to the reduction of noise in the ultralow‐noise TWT. This conclusion supports the general results, but not necessarily the details of the theory of noise on multivelocity beams. In contrast to the theoretical assumption that the important source of multivelocity flow is the cathode temperature, the measurements give evidence that, in the ultralow‐noise TWT, the flow of importance is due to transverse beam slippage in the finite beam that produces what may be termed a ``quasi‐multivelocity'' flow with a velocity spread which may be wide enough to mask the thermal spread. The measurements also raise the possibility that a cyclotron wave‐space‐charge wave interaction occurring beyond the cathode‐first anode space contributes to the noise behavior.

ISSN:0021-8979    

DOI:10.1063/1.1713582

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

Electroluminescent GaAs diodes have been shaped as truncated cones with thep‐njunction at the apex to direct a large fraction of the radiation toward the base of the cone within the critical angle for transmission. Devices having an efficiency at 77°K of 8% have been fabricated. Efficiency is defined here as the radiant power out the base per unit electrical power input. It is calculated that improved devices of this type will have efficiencies of about 18%.

ISSN:0021-8979    

DOI:10.1063/1.1713583

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

Lamellar thickness, melting temperature, and density were measured for bulk polyethylene crystallized by the application of a fixed pressure to molten polymer at different temperatures. Melting temperature varied from 135.2° to 139.2°C, and density varied from 0.9759 to 0.9842 g/cc. Small‐angle x‐ray diffraction yields two maxima which apparently are not first and second orders of diffraction. Electron micrographs of fracture surfaces exhibit lamellae, which support the suggestion that the lamellar thickness is the shorter of the two dimensions (469≤L1≤981 Å and 193≤L2≤440 Å) corresponding to the diffraction maxima. However, the functional relationship of both dimensions to melting temperature and density are in accord with existing or easily derived equations. Analysis of these data, together with the result obtained from paraffin data, yields an equilibrium melting temperature of 141.9±1.7°C. Dimensions of the unit cell did not vary with lamellar thickness.Single crystals of polyethylene were collected into mats and heated at a fixed temperature under various pressures. The observed effect of pressure was to limit the fold period attained during heat treatment. The data suggest that the refolding process follows a relationship which describes crystallization from the melt.

ISSN:0021-8979    

DOI:10.1063/1.1713584

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

The free volume theory of diffusion for hard spheres, earlier developed by Cohen and Turnbull, is modified for simple van der Waals type liquids. The modified theory fits the self‐diffusion data for argon, krypton, and xenon fairly well and predicts glass transition for these liquids at approximately one‐third of their normal boiling points. It is found that a more accurate model for the free volume diffusion in liquids should include a redistribution energy for voids arising from the nonlinear behavior of the pair potential. The agreement found by Cohen and Turnbull between their hard sphere theory and the self‐diffusion data of some large organic molecules is interpreted as evidence that the simple Lennard‐Jones potential does not accurately describe their interaction with each other. This situation is reflected in the failure of these molecules to obey the same corresponding states relationship as the simple liquids of argon, krypton, and xenon.

ISSN:0021-8979    

DOI:10.1063/1.1713585

出版商:AIP    

年代:1964

数据来源: AIP