摘要:

Arsenic ions (As+) and Boron ions (B+) were implanted into silicon (Si) at energies such that their respective projected ranges differ. In the implanted Si, the overlapping population of implanted As and B atoms occurred in the region in Si almost midway between their projected ranges near the surfaces after annealing. The only region in Si with As atoms concentration more than three times as large as the B atom concentration becamen type.

ISSN:0021-8979    

DOI:10.1063/1.348610

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Equation‐of‐state data and corresponding first‐principles theory for the metals Al, Cu, Mo, and Pb are reported over the shock pressure range 0.4–2.4 TPa (4–24 Mbar). Strong shock waves were generated by nuclear explosions and a two‐stage light‐gas gun. The experimental data occur in the hot liquid‐metal regime, where condensed‐matter theory applies but with unusually large thermal components to the equation of state.

ISSN:0021-8979    

DOI:10.1063/1.348611

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

It has been clarified in an earlier work [Y. Sano, J. Appl. Phys.65, 3857 (1989)] that the locations of attenuating peaks in smooth strain, particle velocity, and stress profiles in a smooth plane‐wave front differ, that is, the order of peak precedence is stress, particle velocity, and strain. As a result of the precedence order, the wave front composed of elementary waves such as a contraction waveC, mesocontraction waves I and II, and a vice‐rarefaction waveRwas formed. That the process is degraded by another rarefaction waveRbwhich first follows the waveR, and then outruns the wavesR, II, and I in sequence, has also been proved. [Y. Sano, J. Appl. Phys.67, 4072 (1990)]. After the completion of the degradation process, the wave front, i.e., the waveC, may attenuate little, but steepen. This paper extends the process under consideration to include the steepening process during which the waveCapproaches a steady state. In addition to this extension, stationary phenomena in strain, particle velocity, and stress‐time profiles are shown to be able to take place in the degradation process. It is one of the main purposes of this paper to show through the phenomena that the response caused by the wave fronts during the process will be unsteady and nonequilibrium. Furthermore, universal properties of the stress‐particle velocity paths are clarified. The properties involve concavity or convexity of the path curves produced by the wavesC, I, II, andR. Universal properties of the stress‐strain paths such as concavity, convexity, or inflection of the path curves by the wavesC, I, II, andRare also clarified. Through the behavior of the stress‐particle velocity and stress‐strain paths having the properties mentioned above, it is also shown that the response caused by the waves will be unsteady and nonequilibrium. The stationary phenomena, the universal properties, and the stress‐particle velocity and stress‐strain behaviors are compared with the previous experiments and computational data. Another main purpose of this paper is to confirm through comparison the occurrence of the elementary waves and the degradation process in the experiments.

ISSN:0021-8979    

DOI:10.1063/1.348612

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

We have investigated the saturation phenomenon of the free carrier concentration inp‐type GaAs and InP single crystals doped by zinc diffusion. The free hole saturation occurs at 1020cm−3for GaAs, but the maximum concentration for InP appears at mid 1018cm−3. The difference in the saturation hole concentrations for these materials is investigated by studying the incorporation and the lattice location of the impurity zinc, an acceptor when located on a group III atom site. Zinc is diffused into the III‐V wafers in a sealed quartz ampoule. Particle‐induced x‐ray emission with ion‐channeling techniques are employed to determine the exact lattice location of the zinc atoms. We have found that over 90% of all zinc atoms occupy Ga sites in the diffused GaAs samples, while for the InP case, the zinc substitutionality is dependent on the cooling rate of the sample after high‐temperature diffusion. For the slowly cooled sample, a large fraction (∼90%) of the zinc atoms form random precipitates of Zn3P2and elemental Zn. However, when rapidly cooled only 60% of the zinc forms such precipitates while the rest occupies specific sites in the InP. We analyze our results in terms of the amphoteric native defect model. We show that the difference in the electrical activity of the Zn atoms in GaAs and InP is a consequence of the different location of the Fermi level stabilization energy in these two materials.

ISSN:0021-8979    

DOI:10.1063/1.348613

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The reaction between nitrogen gas and the series of R2Fe17intermetallic compounds is studied by thermopiezic analysis on micron‐size powders. Nitrogen diffusion in the range 300–550 °C can be represented by an activated interstitial diffusion processD=D0e−Em/kTwithD0=1.95×10−10m2 s−1and an activation energyEm=0.81 eV. This stage of the nitrogenation reaction leads to the formation of R2Fe17N3−&dgr;nitrides which have structures related to those of the parent compounds. Heating above about 800 °C leads to complete disproportionation of the compounds into a mixture of rare‐earth nitride and iron.

ISSN:0021-8979    

DOI:10.1063/1.348614

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

A simple and reproducible process for the open‐tube diffusion of zinc from (ZnO)x(SiO2)1−xsource films into GaAs, Al0.2Ga0.8As and GaAs0.6P0.4is reported. (ZnO)x(SiO2)1−xfilms were deposited onto compound semiconductor substrates by metalorganic chemical vapor deposition. A capping layer of SiO2was deposited on top of the source films. The diffusions were performed in flowing nitrogen at 650 °C. Diffusion depths from 0.2 &mgr;m to several micrometers were readily achieved. The diffusion front inn‐type substrates is abrupt and the average hole concentration for diffused layers in GaAs is approximately 8 × 1019/cm3. The dependence of the diffusion depth on the source film composition (x=0.04–x=1.00) is presented. The dependence of the diffusion depth on the source film thickness and the SiO2cap layer thickness is also reported.

ISSN:0021-8979    

DOI:10.1063/1.348587

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

A practical method to determine the ionic diffusion coefficient and activation energy by using quasielastic light scattering (QELS) is presented. It is shown that a temperature dependence curve of the QELS intensity at a fixed frequency can be well fitted by Jonscher’s formula and that the diffusion parameters can be obtained from this curve fitting. This method is successfully applied not only to crystals with high optical quality, as reported earlier, but also to opaque ceramics, which are more important than the crystals from a practical point of view. The composition dependence of the ionic diffusion coefficient is studied in sintered YbSZ to show the usefulness of this method.

ISSN:0021-8979    

DOI:10.1063/1.348588

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Atomistic thermodynamic calculations are performed in order to examine the energetics of self‐diffusion in GaAs. An energetic assessment of the activation enthalpy of the saddle‐point configuration of various modes of vacancy self‐diffusion indicates second‐nearest‐neighbor hopping to be the energetically most favorable mechanism if vacancies are available in equilibrium concentrations. An assessment of the activation entropy indicates that normal diffusion prefactors of magnitudeD0&bartil;10−5–10−1 s, cm2 s−1are consistent with vacancy self‐diffusion by second‐nearest‐neighbor hopping. It is proposed that self‐diffusion experiments characterized by prefactors and activation energies of large magnitude, e.g.,D0&bartil;107–108cm2 s−1andEa≊ 6 eV, involve processes in which surface vacancy generation is inhibited and self‐diffusion is mediated by Frenkel pair generation.

ISSN:0021-8979    

DOI:10.1063/1.348589

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The effect of gas phase oxygen on chemical vapor deposition diamond growth on Pt substrates was studied using x‐ray photoelectron spectroscopy (XPS). Samples were transferred between the diamond growth chamber and an attached ultrahigh vacuum analysis chamber without exposure to air. The time‐dependent evolution of surface carbon species was monitored by interrupting growth at specific times and analyzing the surface with XPS. In this paper we compare samples prepared from four different mixtures of H2/CH4/O2. With low gas phase O/C ratios (≤0.5) diamond growth on Pt proceeds by a three‐step mechanism: (1) decomposition of surface contaminants to form graphitic carbon, (2) conversion of these graphitic species to stable hydrocarbon species, (3) replacement of hydrocarbons with diamond. At higher gas phase O/C ratios (≥0.75) we observed that the Pt surface had less than 1 ML of carbon. In other words, the surface was very clean, and diamond growth did not occur at a measurable rate. However, once diamond is nucleated on the surface under conditions of low oxygen concentration, diamond growth proceeds readily using a high oxygen feed with O/C=1. We conclude that the addition of oxygen affects diamond formation primarily by decreasing the nucleation rate on metals like Pt. Growth rates of existing diamond films are not strongly affected by oxygen.

ISSN:0021-8979    

DOI:10.1063/1.348590

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The microstructure and composition of the SiO2/TiO2analog (codeposited) and digital (thin layer pairs) gradient‐index films were examined by transmission electron microscopy, Auger electron spectroscopy, Rutherford backscattering spectrometry, x‐ray photoelectron spectroscopy, scatterometry, andinsituellipsometry. Both analog and digital structures were amorphous as‐grown. The SiO2was incompletely oxidized at some of the interfaces in the layered structures and in the codeposited films, indicated competition from the TiO2for available oxygen during growth. Digital structures with thin (65 A˚) layers remained well defined after annealing at 900 °C, but their order was completely destroyed by 1100 °C. Structures with thick (500 A˚) layers remained intact up to 1100 °C, with the TiO2crystallizing throughout the layer width. Both anatase and rutile TiO2crystallites were present in the layered and codeposited films after a high‐temperature anneal (T≳650 °C), while only the anatase phase was observed for 300 °C<T<650 °C. The optical scatter of the digital films increased with increasing annealing temperature and layer thickness. TiO2precipitated out of the codeposited films after a high‐temperature anneal; however, the scatter of these films at 0.633 &mgr;m was several orders of magnitude lower than that of the annealed layered films. Codeposited films consisting of greater than ∼60% TiO2displayed form birefringence in the as‐grown state.

ISSN:0021-8979    

DOI:10.1063/1.348591

出版商:AIP    

年代:1991

数据来源: AIP