摘要:

The temperature distribution and evolution of metal field‐ion emitters under pulsed and continuous‐wave (cw) laser irradiation are obtained numerically using implicit alternating direction method. For the cw laser irradiation, the temperature distribution in the emitter reaches a steady‐state value after approximately 2 &mgr;s of laser heating. The peak temperature of the tip apex reached depends almost linearly on the incident energy flux of the laser beam, and also on the cone angle of the emitter. For the fast laser pulse, both the waveform and the spatial intensity variation of the laser beam are considered. The numerical result is found to differ only slightly from that obtained by assuming a square shape of the laser pulse. The feasibility and advantages of using a laser beam as a means of heating the emitter in the study of single atom surface diffusion and adatom‐adatom interaction, laser‐induced silicide interface formation, and other studies with the Atom Probes and Field Ion Microscope are also discussed.

ISSN:0021-8979    

DOI:10.1063/1.336527

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The time dependence of particle size (e.g., mean volume) in normal grain growth, bubble growth, and late‐stage coarsening is deduced from a statistical self‐similarity (SSS) hypothesis, according to which consecutive configurations of the system in the self‐similar mode are geometrically similar in a statistical sense, and from the scaling characteristic ofv˙, the rate of change of the volume of a given particle. It is shown that ifv˙ scales asv¯&agr;under uniform magnification, wherev¯ is the mean particle volume and &agr; a constant depending on the controlling kinetics and geometry of the system, thenv¯1−&agr;is a linear function of the time. Values of &agr; are obtained for a number of cases. The treatment is free of many of the approximations and geometrical simplifications used in most theories. Evidence for the SSS hypothesis is discussed. Special new results are obtained for two‐dimensional bubble and idealized grain growth that should be testable by computer simulation or by observation of a well‐behaved soap‐bubble array.

ISSN:0021-8979    

DOI:10.1063/1.336528

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

For the first time Raman microprobe experiments have been made to measure the space‐resolved temperature distribution induced in silicon‐on‐sapphire by a stationary elliptical Gaussian laser beam. The algorithm [J. Appl. Phys.57, 965 (1985)] for solving the nonlinear heat equation in a two‐layer structure has been also extended to include the temperature dependence of laser power absorbed besides the temperature dependencies of thermal conductivity and diffusivity. The problems involved in applying the numerical calculations to the experimental situation are discussed. The numerical calculations of temperature distributions based on the present algorithm are found to give a good agreement with the present Raman microprobe results.

ISSN:0021-8979    

DOI:10.1063/1.336529

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Calculated optical absorption spectra of colloidal copper particles in photochromic glasses containing both copper halides and cadmium halides are presented. Comparison with available experimental data supports the previously suggested colloidal darkening mechanism. The dielectric constant of the copper particles is obtained from the bulk one by applying either the mean‐free‐path correction or the quantum size effect correction. It is shown that, using the available experimental data, no conclusion about the superiority of either correction can be drawn.

ISSN:0021-8979    

DOI:10.1063/1.336530

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Lateral electromigration of Cu+in a Cu2−&agr;S/CdS solar cell induced by light generated current causes variation in composition of copper sulfide leading to increased sheet resistance and power losses of the device. These effects have been studied in short‐circuit mode by fine probe measurements of lateral potential distribution and are clearly evident inI‐Vcharacteristics. The theory of mixed ionic‐electronic transport in copper sulfide explains steady‐state logarithmic potential distribution between grid wires and correctly predicts its kinetics which depend on Cu+diffusion coefficient in Cu2−&agr;S and grid density. The effects of grid defects on cell degradation are also demonstrated.

ISSN:0021-8979    

DOI:10.1063/1.337031

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Reported in this paper are the results of an experiment to produce high‐powerKu‐band (12–18 GHz) microwave radiation from a backward wave oscillator (BWO) driven by a relativistic electron beam. Experimentally measured output power was about 250 MW at 12.5 GHz and 100 MW at 14 GHz. A description of the slow wave structure is given along with theoretical predictions of the vacuum waveguide dispersion relations. The diagnostics to determine the frequency and power of the device are described. Finally, comparisons between the experimentally measured frequency and power, and the analytic and numerical simulations of the BWO are made.

ISSN:0021-8979    

DOI:10.1063/1.336531

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Grady’s model of the dynamic fragmentation process, in which the average fragment size is determined by balancing the local kinetic energy and the surface energy, is modified to include the stored elastic (strain) energy. The revised model predicts that the strain energy should dominate for brittle materials, with low fracture toughness and high fracture‐initiation stress. This conclusion is not borne out, however, by limited experimental data on brittle steels, even when the kinetic‐energy density is small compared with the strain‐energy density.

ISSN:0021-8979    

DOI:10.1063/1.336532

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

We have developed a monolithically integrated external feedback laser utilizing a pair of stop‐cleaved double channel planar buried heterostructure lasers emitting at 1.3 &mgr;m. The external feedback is provided by the stop cleaved facet of the second cavity. A sidemode rejection ratio of 200 : 1 has been obtained with a laser having a 250‐&mgr;m cavity length and an external resonator length of 200 &mgr;m. Since both lasers are fabricated in a self‐aligned structure, this device may prove to be a powerful scheme for injection locking to reduce dynamic linewidth.

ISSN:0021-8979    

DOI:10.1063/1.336482

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The steady‐wave features of the plastic shock wave in low carbon steel are explored with manganin stress gauges. We show that at the low stress range (20–45 kb) these waves are not steady and that the corresponding Bland numbers are much lower than unity, as expected for nonsteady waves.

ISSN:0021-8979    

DOI:10.1063/1.336483

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

We have attempted to experimentally detect a nonlinear reflection in mixtures of cholesteric and cholesteric/nematic liquid crystals induced by Nd:YAG laser pulses. At power densities of up to 4 MW/cm2(532 nm) and 8 MW/cm2(1064 nm) we have not observed any optically induced pitch dilation or distortion in these media.

ISSN:0021-8979    

DOI:10.1063/1.337029

出版商:AIP    

年代:1986

数据来源: AIP