摘要:

The generation of Fourier transforms of a time varying signal by frequency‐dependent beam steering of focused surface acoustic waves (SAWs) is described. This transform is accomplished by using a focusing array of phased SAW interdigital transducers (IDT) to generate, focus, and angularly disperse the acoustic waves according to the input signal frequencies. The spectrum is retrieved at the output by an array of independent SAW IDTs placed along the focal arc. Substrate anisotropy affects SAW diffraction, but need not present a problem when properly accounted for. This paper discusses the rationale for the design of the input transducer and its effect on the acoustic diffraction pattern, frequency response, and sidelobe suppression on an anisotropic substrate.

ISSN:0021-8979    

DOI:10.1063/1.336130

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

Experimental results that verify focusing and dispersion with frequency of surface acoustic waves (SAW) by wide‐band phased array of SAW interdigital transducers (IDTs) are presented. The diffraction sidelobes are suppressed by weighting the drive to each IDT using capacitive taps.

ISSN:0021-8979    

DOI:10.1063/1.336131

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

The spatial variation of the optogalvanic (OG) signal resulting from visible laser irradiation of rare‐gas positive column discharges has been investigated for the case of standing striations. The OG signal was observed to periodically change polarity as the laser was scanned transversly across the bright and (relatively) dark regions of the column. Transitions involving the3P2,0metastable levels were found to be everywhere opposite in polarity to those originating on freely radiating levels. The effects of trapped resonance level emission, and collisions of the second kind involving metastables are proposed to be important in determining the OG signal polarity for excitation in certain discharge regions.

ISSN:0021-8979    

DOI:10.1063/1.336132

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

The etch rate of Si with F atoms was measured by the use of F2microwave plasma over a range of discharge pressures between 2.7×10−2and 17 Pa. Fluorine atom concentration in the plasma was determined over the same pressure range by means of both gas‐phase titration and actinometry using Ar gas. A Si surface etched at 1.0×10−1, 5.3×10−1, 1.3, and 5.3 Pa was analyzed with XPS without exposing the surface to room air. A linear relation was obtained between the Si etch rate and the F atom concentration at discharge pressures between 2.7×10−2and 2.7 Pa. The reaction probability of F atoms with Si to yield SiF4was determined from the linear relation to be 0.1 for a Si surface at about 300 K. When the discharge pressure was higher than 1.3 Pa, the surface became rather strongly oxidized by O atoms resulting from residual gases. This surface oxidation results in a slight saturation of the Si etch rate at about 10 Pa.

ISSN:0021-8979    

DOI:10.1063/1.336133

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

The depth profiles of bulk stacking fault radius formed under the annealed specimen surface of Czochralski silicon wafers have been obtained. It is clearly shown that the depth profiles have been well predicted by the theoretical result. The curve fitting gives the diffusion coefficient of the responsible point defects expressed byD=257 exp[−(2.84±0.66)eV/kT] in the temperature range between 1080 and 1270 °C. It is strongly suggested that vacancies, not self‐interstitials, dominate the growth of the bulk stacking faults.

ISSN:0021-8979    

DOI:10.1063/1.336134

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

This paper reports on the effect of low energy He+ion‐beam bombardment upon the structure of pyrene thin films formed on quartz substrates. Films are prepared by vacuum evaporation during ion bombardment at room temperature. The structure of the film is controlled by the kinetic energy and current density of the ions. The colorless and transparent crystalline films preferentially oriented with their {001} plane parallel to the substrates are obtained by bombardment of 350 to 500 eV, 60 nA/cm2He+ions. Ion‐beam irradiation of the higher ion current density enhances intermolecular chemical reactions and, as a result, a crystalline polymer with its {001} plane parallel to the substrate is produced.

ISSN:0021-8979    

DOI:10.1063/1.336135

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

We present a crystallization study of melt‐spun Co‐Zr metallic glasses. The primary crystallization products are all metastable or unstable except around the equiatomic composition where the stable phase CoZr is produced. Alloys at the composition Co25Zr75show a crystallization characteristic that is dependent on heating rate.

ISSN:0021-8979    

DOI:10.1063/1.336136

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

The uniform and reproducible activation of silicon, ion‐implanted directly into GaAs substrates, is often difficult to achieve. Epitaxial GaAs buffer layers have been used as an alternative implantation media which offers improved electrical characteristics. The characteristics of Si implanted GaAs buffer layers grown by the metalorganic chemical vapor deposition technique are presented here. The influence of the gas phase stoichiometry, a key determinant in the electrical properties of the layer, on the characteristics of the Si implanted and capless annealed layers was studied over the implantation dose range of 3×1012to 1×1014cm−2at an implant energy of 150 keV. The electrical activation, mobility, deep‐level concentration, and impurity distribution both prior to and after the implant and anneal were determined through optical and electrical characterization techniques. Undoped GaAs grown by this technique provides reproducible high levels of implant activation. Implantation into thick buffer layers allows the study of the implant and anneal processes free from the complicating influence of the GaAs substrate.

ISSN:0021-8979    

DOI:10.1063/1.336137

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

SiOxNycapped infrared rapid thermal annealing was investigated for activating high dose (>7×1013cm−2) Si implants in GaAs. The SiOxNyencapsulation resulted in enhancement in electrical activation. An electron concentration as high as 9×1018cm−3was obtained by 1120 °C, 5‐sec annealing using an SiOxNyencapsulant with 1.75 refractive index. Nonalloyed ohmic contacts were formed by depositing AuGe‐Ni on a heavily dopedn‐type layer activated by this technique, where a 9×10−5&OHgr; cm2specific contact resistance was obtained. Furthermore, low‐temperature (300 °C) alloying significantly improved a specific contact resistance to as low as 6×10−6&OHgr; cm2while keeping a smooth morphology. These techniques, including low‐temperature alloying, are promising for GaAs and its heterostructure device applications.

ISSN:0021-8979    

DOI:10.1063/1.336138

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

The present study is focused on the distributions in particle size produced in dynamic fragmentation processes. Previous work on this subject is reviewed. We then examine the one‐dimensional fragmentation problem as a random Poisson process and provide comparisons with expanding ring fragmentation data. Next we explore the two‐dimensional (area) and, less extensively, the three‐dimensional (volume) fragmentation problem. Mott’s theory of random area fragmentation is developed, and we propose an alternative application of Poisson statistics which leads to an exponential distribution in fragment size. Both theoretical distributions are compared with analytic and computer studies of random area geometric fragmentation problems, including those suggested by Mott, the Voronoi construction, a variation of the Johnson–Mehl construction, and several methods of our own. We find that size distributions from random geometric fragmentation are construction dependent, and that a conclusive choice between the two distributions cannot be made. A tentative application of the maximum entropy principle to fragmentation is discussed. The statistical theory is extended to include a concept of statistical heterogeneity in the fragmentation process. Finally, comparisons are made with various, dynamic fragmentation data.

ISSN:0021-8979    

DOI:10.1063/1.336139

出版商:AIP    

年代:1985

数据来源: AIP