摘要:

By measuring the axial profiles of thermal wall loading and radiation output in a dc vortex‐stabilized arc, it has been shown that the vortex significantly influences the energy transport in the arc. The arc was operated at 225 A in an argon vortex at a pressure of 5.5 atm. The measurements show that there is a rapid onset of thermal wall loading immediately adjacent to the upstream electrode. Furthermore, there is a significant amount of thermal wall loading upstream of the arc column, which is found to scale with the flowrate through the vortex. This fact, taken together with observations of the tracks produced by tungsten droplets on the arc wall, and photographs of the electrode regions indicate that reverse axial flow exists in the core of the arc vortex. Near the electrodes there is a region of locally increased thermal wall loading and radiation output, but between these regions there exists a region where the wall loading and radiation are axially invariant. In this region the measured wall loading is as much as 100% larger than that predicted using laminar heat transport. The scaling of this wall loading with gas flowrate in the vortex has been measured, and it has been shown that if the data are extrapolated to the no‐flow condition, the wall loading is in much better agreement with the laminar heat transport model. The existence of turbulence or Taylor–Go¨rtler vorticies in the stabilizing gas flow are proposed as mechanisms for the enhanced thermal wall loading.

ISSN:0021-8979    

DOI:10.1063/1.341223

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

A collisional‐radiative (C‐R) model for high‐temperature air is developed. Ionization and recombination coefficients are presented for electron temperatures between 1.0 and 3.0 eV and electron densities between 1016and 1019cm−3. For an assumed airlike mixture of 80% nitrogen and 20% oxygen, these results are compared with C‐R coefficients of nitrogen and oxygen plasmas developed separately and show little difference. The inclusion of charge‐exchange effects does not alter the coefficients. Saha decrements for air are used to delineate the onset of local thermodynamic equilibrium (LTE) for the above conditions. These thresholds are compared to other criteria and show some difference. Finally, ratios of spectral line intensities are presented in terms of the Saha decrements as a means of diagnosing high‐temperature air discharges, such as lightning channels, without requiring LTE.

ISSN:0021-8979    

DOI:10.1063/1.341224

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

The evolution of the electron acoustic signal has been measured for Be‐ and Si‐doped GaAs and Ga0.28Al0.19In0.53As layers with doping levels from1017to 1020at. cm−3. The samples have also been analyzed by cathodoluminescence spectroscopy for near‐band‐edge transition and deep level emission. The results are explained by the reduction of the mean free path of phonons, giving rise to a lattice thermal conductivity decrease. Meanwhile, the electronic part of the thermal conductivity of these compounds is found to be nearly negligible.

ISSN:0021-8979    

DOI:10.1063/1.341225

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

The density and microhardness of the system Se100−xSbx(wherex=5, 10, and 15 at. %) were determined at room temperature using the stepwise method. The values of the density and microhardness increase with time of annealing, temperature of annealing, and Sb content. The energy required for the crystallization processes was calculated from the density as 31.82, 39.8, and 49.7 K cal/mol for the samples Se95Sb5, Se90Sb10, and Se85Sb15, respectively. On the other hand, these energies are given by 43.76, 49.72, and 54.7 K cal/mol, using the microhardness data. The dimensional nature of the growth process has been looked for through the determination of thenexponent of the Avrami rate equation. The value of the ‘‘n’’ exponent of the Avrami rate equation indicates that the crystals grow in a one‐dimensional way.

ISSN:0021-8979    

DOI:10.1063/1.341451

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

Stresses induced in a silicon wafer by mask edges or recessed oxides may be studied by the means of x‐ray topographs. The contrast of such topographs has been previously studied using the Blech and Meieran theory [J. Appl. Phys.38, 2913 (1967)] for the stresses and Kato’s theory [Acta Crystallogr.16, 282 (1963)] for the diffraction. Simulations using Takagi’s equations [S. Takagi, Acta Crystallogr.15, 1131 (1962)] show that this model is not correct: the magnitude of stresses is too large and should lead to additional fringes in the image. This could not be predicted using Kato’s theory where the interaction between the wavefields and the most deformed areas of the crystal is underestimated. It suggests that a relaxation occurs along the surface to decrease the value of the stresses.

ISSN:0021-8979    

DOI:10.1063/1.341452

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

Dislocation loops and precipitates in an arsenic‐rich GaAs crystal have been studied by transmission electron microscopy to investigate their formation mechanism and establish their relationship to point defects. The precipitates are identified to be hexagonal arsenic phases having a simple orientation relationship with the GaAs matrix. Detailed analyses of the loops indicate that they are composed of two separate defects lying on (111) planes: a faulted loop and a perfect loop. It is proposed that the loops are formed by condensation of excess arsenic interstitials followed by clustering of excess Ga vacancies and subsequent generation and movement of Shockley partial dislocation(s). The faulted loop is interpreted as an hcp arrangement of arsenic atoms. This model supports the hypothesis that arsenic interstitials and Ga vacancies coexist in GaAs at high temperatures although arsenic interstitials initiate the formation of arsenic‐related dislocation loops. Implications concerning the formation process of the EL2 deep‐level defect are also discussed.

ISSN:0021-8979    

DOI:10.1063/1.341453

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

This paper deals with an extension of the well‐known case of the harmonic oscillation of a nonkinked dislocation line to the case of both harmonic and anharmonic oscillations of a dislocation line in the presence of a moving kink. The one‐kinked dislocation is considered as the unbounded, nondissipative sine‐Gordon system, and the mixed, one‐soliton one‐periodic solutions of the sine‐Gordon equation, recently obtained by applying the method of Riemann theta function, are used for this purpose.

ISSN:0021-8979    

DOI:10.1063/1.341454

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

Silicon wafers with and without a protective thermal oxide were implanted with oxygen at 150 keV with doses of 1.6–2.0×1018cm−2. Transmission electron microscopy and secondary‐ion mass spectroscopy were used to study the silicon layer above the implanted buried oxide. A regular array of spheroidal bubbles, postulated to be filled with oxygen gas, was observed only in the samples that were not protected by the oxide. The bubbles were aligned in individual columns whose orientation matched the direction of the implantation. The origin and kinetics of their formation are discussed. A model for column formation involving the overlap of ionization thermal spikes is proposed. It is also proposed that the observed phenomenon is a solid‐state analog of the bubble chamber effect.

ISSN:0021-8979    

DOI:10.1063/1.341455

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

Based on the solution of an internal crack, we have investigated the elastic interaction of a screw dislocation and cracks emanating from an elliptic hole by using a conformal mapping technique. We have derived the stress field, the image force on the dislocation, the stress intensity factor at the crack tip, and the crack extension force. From the image force, we find the unstable equilibrium positions of dislocation. It is possible to form a plastic zone from the region containing the unstable equilibrium position by collecting dislocations. By extending the concept of the unstable equilibrium position, we also develop the dislocation emission criterion. It is found that the critical applied stress for dislocation emission is dependent on the geometry of the crack. In addition, we also find that the elliptic hole prefers to emanate double cracks. Finally, it is worthwhile to mention that the mapping function cannot be arbitrarily chosen.

ISSN:0021-8979    

DOI:10.1063/1.341456

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

The lattice trapping effect of a crack in solids with layered structure has been studied with a double‐chain model. It is shown that the difference in physicomechanical properties between different atomic planes has significant influence upon this effect, and the stress range for stability of a crack can be enhanced by increasing the difference. This perhaps, provides a way for the lattice trapping effect to be made observable by appropriately synthesizing solids with superlattices of special design.

ISSN:0021-8979    

DOI:10.1063/1.341458

出版商:AIP    

年代:1988

数据来源: AIP