摘要:

The steady rate of heat conductionQfrom a heated sphere maintained at a constant temperature different from that of a surrounding two‐phase medium, which consists of an array of spherical particles of thermal conductivity &agr;kand a matrix of conductivityk, is determined by a method of multipole expansion toO(&fgr;4), where &fgr; is the volume fraction of the particles in the array, and by a lubrication analysis for highly conducting and closely packed arrays. The results of the two analyses are combined to obtain estimates ofQthat are expected to be accurate over the complete range of &agr; and &fgr;. These results are compared with the predictions of an effective‐medium theory, and it is shown that the predictions of this theory are quite accurate over a rather wide range of &agr;, 0<&agr;<103, for the case of a simple cubic array, even at its maximum allowable volume fraction, but differ by as much as 60% for the case of a face‐centered cubic array.

ISSN:0021-8979    

DOI:10.1063/1.344981

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

In this paper a two‐dimensional model of fluid and heat flow in weld pools is considered and a solution methodology is presented that is based on a perturbation expansion with the Prandtl number as a small parameter. This allowed us to determine the temperature field efficiently and by using it to determine the location of the phase front to map the molten region into a semicircular region in which the Boussinesq form of the Navier–Stokes equations were solved. Doing so allows the domain to be represented with a much smoother phase boundary than is usual in phase change problems. The flow in the weld pool made with a moving laser shows vigorous convection on the solidification side of the weld pool and crowding of the isotherms on the melting side.

ISSN:0021-8979    

DOI:10.1063/1.344982

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The rate of particle generation in a SiH4/NH3rf discharge has been studied as a function of the discharge operating parameter space, electrode geometry, and power supply coupling mode. Measurements of the bulk quantity of particles produced in the discharge reveal that the mode of coupling (capacitive or dc) as well as the electrode temperature significantly affects particle generation rates. Laser light scattering measurements made as a function of the plasma power density indicate that particle generation abruptly ceases at a threshold value sufficient to induce spark breakdown at the cathode. Based on these observations, it is shown that particle growth in plasmas can be modeled entirely as a heterogeneous process. The initiation of particle growth is shown to be consistent with an electron surface desorption model involving vibrational excitation of surface clusters. Propagation of growth in the gas phase is shown to be consistent with an eliminative ion‐molecular condensation reaction, and the pressure dependence of this mechanism is exploited to estimate a value for the rate constants for SiH4and NH3condensation in SiN:H particle growth.

ISSN:0021-8979    

DOI:10.1063/1.344983

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The measurement method of Hg 6p 3P0,1,2state densities using the 8s 3S1–6p 3P0,1,2lines of less absorption has been developed, and the Hg 6p 3Pstate densities on the tube axis in the low‐pressure positive‐column Ar‐Hg discharge of 12 mm inner diameter used for the mercury lamp have been measured.

ISSN:0021-8979    

DOI:10.1063/1.344984

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Previous theoretical studies assumed that the energy loss of a colliding electron has a discrete value for dissociative excitation of molecular oxygen. In the calculation of the rate coefficients for oxygen atom yields using the Boltzmann equation, the previous reports have used discrete energy loss values of 6.1 eV forA3&Sgr;+uand 8.4 eV forB3&Sgr;−u. In this paper, we take account of the fact that the excitation toB3&Sgr;−uhas a continuum energy loss spectrum and describe the effects on calculated swarm parameters that are important in the simulation of ozonizer discharges. It can be seen that the use of a continuum electron energy‐loss spectrum as opposed to a discrete electron energy loss associated with excitation to theB3&Sgr;−ustate makes no significant difference in the calculated values of electron swarm parameters in oxygen. We also calculate the ozone yield as a function ofE/Nobtained from the analysis of the energy balance equation. In this case, the partial cross section for dissociation viaB3&Sgr;−uassuming a continuum electron energy‐loss spectrum can have significant effects on the atomic oxygen yields at differentE/N.

ISSN:0021-8979    

DOI:10.1063/1.344985

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Ion implantation, employing Si, Ar, and Cu ions in the energy range from 275 to 600 keV, was used to form amorphous silicon layers buried in a crystalline matrix. Different layer geometries were produced, with 150–620‐nm‐thick amorphous layers, separated from the surface by 120–350‐nm‐thick crystalline layers. Crystallization of the amorphous layers was induced by 32‐ns pulsed ruby laser irradiation. Real‐time reflectivity and conductivity measurements indicate that internal melting can be initiated at the amorphous‐crystalline interface, immediately followed by explosive crystallization of the buried layer. Channeling and cross‐section transmission electron microscopy reveal that in both Si(100) and Si(111) samples explosive crystallization proceeds epitaxially with twin formation, the twin density being higher in Si(111) than in Si(100). The measured crystal growth velocities range from 15 to 16 m/s, close to the fundamental limit for crystalline ordering at a Si liquid‐crystalline interface. Computer modeling of heat flow and phase transformations supports the experimental data.

ISSN:0021-8979    

DOI:10.1063/1.346076

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The amorphization and recrystallization of tin‐ion‐implanted gallium arsenide were studied by cross‐sectional transmission electron microscopy. Amorphization occurred in the sample implanted at a dose of 1014ions/cm2. The interface between the amorphous region and the crystalline matrix is not flat. The amorphous region recrystallizes epitaxially with microtwin formation at 673 K. The amorphous‐crystalline interface in the sample implanted at a dose of 1016ions/cm2is flat. In the deep region of this sample a solid‐phase epitaxial growth without microtwin formation is observed after annealing at 673 K. These structural changes were compared with the nuclear energy loss (damage energy) distribution simulated by thetrimcode. It is concluded that the amorphization of the sample implanted at a dose of 1014ions/cm2is induced by the accumulation of damage energy; on the other hand, the amorphization of the sample implanted at a dose of 1016ions/cm2cannot be explained only by this process. The contribution of stress at the amorphous‐crystalline interface is suggested.

ISSN:0021-8979    

DOI:10.1063/1.344959

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The influence of wafer rotation on implanted dose uniformity was investigated using thermal‐wave measurement to realize highly uniform ion implants into a (001) wafer. It was found that conically rotating ion implantation is an effective way to scramble the scanning ion beam during implantation by using an electrostatic‐scan implantation system with a specially designed wafer station. Furthermore, two‐fold ion implantation was employed to correct the dose inhomogeneity caused by the variation of the tilt angle across a wafer. Based on these considerations, a high dose uniformity of less than 1% across a wafer was achieved.

ISSN:0021-8979    

DOI:10.1063/1.344960

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Complete amplitude‐displacement‐frequency spectra for a lever of an atomic force microscope have been measured and used to determine surface forces in air. Two ac techniques were used to measure the shift in resonant frequency of the Ni lever, as a function of separation from a mica surface. A strong, short‐range force was observed for freshly prepared surfaces, implying a van der Waals interaction. A weak, long‐range force was observed after exposure of the surfaces for some hours, suggestive of a capillary interaction. The long‐range force appeared to contain a nonconservative element which increased on approach to the surface. The results have implications for surface‐force determinations by single tip displacement scans, and for imaging with force microscopes.

ISSN:0021-8979    

DOI:10.1063/1.344961

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

A buried layer of GaAs was formed in single‐crystal silicon by dual implantation of extremely high doses of As+plus Ga+at 200 keV, followed by furnace annealing. The layer consists of polycrystalline grains with random orientation. Rapid thermal annealing, in the presence of oxygen, does not result in the formation of GaAs. Instead, Ga and As migrate to the surface to form an oxidized layer, which is separated from the underlying silicon by a thin layer of SiO2. Analysis of the samples with single implants of Ga+or As+indicates the oxides formed to be Ga2O3and As2O2. Samples implanted with As+alone have essentially dislocation loops after annealing, while those implanted with only Ga+have mostly microtwins and precipitates. Up to 88% Ga and 62% As from the single implants and 31% As and Ga from the dual implants are lost during annealing. This is probably due to the migration of the implanted species to the surface and the subsequent formation of volatile oxides. However, such outward migration does not result in redistribution or broadening of the implanted species.

ISSN:0021-8979    

DOI:10.1063/1.344962

出版商:AIP    

年代:1990

数据来源: AIP