摘要:

We consider the chain ofNspheres contacting each other with an area and study the change of the magnetic behaviors of this chain by the contact area. Critical fieldHcrifor the discontinuous jump of the magnetization and coercive forceHcby both the parallel rotation and fanning mechanisms, and uniaxial magnetic anisotropy constantKudue to the shape of the chain are found to increase, reach the maximum value, and decrease with an increase in the contact area. The ratios of the maximum value to the value at the point contact forHcri,Hc, andKuare also found to increase with an increase in the number of the spheres.

ISSN:0021-8979    

DOI:10.1063/1.336612

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The incorporation mechanisms of residual impurities in GaAs layers grown by molecular‐beam epitaxy has been investigated by high‐resolution photoluminescence (PL) spectroscopy at 2 K. A systematic study of near‐band‐edge emissions of undoped GaAs layers grown at a wide range of growth temperatures (Tg), 470–750 °C, demonstrates that PL spectra related with residual impurities are significantly dependent uponTg. It was found that maximum emission intensity of free exciton is obtained atTg∼550 °C, and the minimum impurity incorporation is established atTgof 550–650 °C.

ISSN:0021-8979    

DOI:10.1063/1.336559

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

We present results made with a new apparatus for the study of localized field emission (FE) sites on broad‐area cathodes. The apparatus is centered around a UHV field emission scanning microscope, consisting of a micromanipulator allowing precision cathode motion, a rotatable holder for broad and microtip anodes, and a fast high‐voltage regulator allowing constant‐current measurement of a distribution of both weakly and strongly emitting sites. Also included are aninsituscanning electron microscope, and a facility forinsitumicrofocus Auger analysis as well as scanning Auger microscopy. Samples can be high‐temperature annealed without removal from UHV. These tools have been used to study the effects of heat treatment (HT) up to 2000 °C on the FE from nonanodized and anodized Nb cathodes. We find that HT at 800–900 °C increases the density of field emitters at a given electric field. HT atT>1000 °C reduces the density, while atT≥1400 °C a drastic decrease of the emission occurs. We have repeatedly obtained surfaces of cm2size which do not emit at 100 MV/m. If such an emission‐free surface is heat treated again at 800 °C, new emitters appear. Typically, the physical size of the field emitters is a few &mgr;m, although in some cases a larger particle was found and in others no feature was seen at 0.5‐&mgr;m resolution. A large variety of elements is associated with these particles. We discuss in particular the nature and origin of three types of emitters: (1) sulfur containing particles, (2) carbon particles, both of which were identified as new emitters after a 800 °C HT, and (3) FE sites which are especially resistant against HT.

ISSN:0021-8979    

DOI:10.1063/1.336560

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Laser‐induced damage study of transparent conducting coatings of tin oxide prepared by spray pyrolysis has been made using a dyeQ‐switched Nd:glass laser emitting 25‐ns (FWHM) pulses at 1062 nm. For comparison tin oxide films prepared by chemical vapor deposition (CVD) method and indium tin oxide (ITO) prepared by the reactive rf sputtering method have also been damage tested. The study reveals that the spray pyrolysis method yields good electrical and optical quality films with a damage threshold value of 5.2±0.3 J/cm2. Though CVD technique provides the highest damage threshold coatings (14.2±0.6 J/cm2), their electrical characteristics and uniformity are inferior to rf‐sputtered ITO films which have the best electrical properties and the lowest damage threshold values (1.3±0.1 J/cm2).

ISSN:0021-8979    

DOI:10.1063/1.337033

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Activation of implanted dopant in Si is investigated as a function of ion energy during rapid thermal annealing (RTA). It is shown that the fraction of dopant incorporated on the lattice site by RTA decreases as the implant energy increases. This is attributed to clustering or precipitation of the dopant during RTA as a result of fast diffusion of the dopant in the amorphous layer produced by implantation. The increased thickness of the amorphous layer at higher implant energies allows sufficient time for clustering before the amorphous layer recrystallizes. Similar behavior is observed for electrically inactive impurities. In this work, the diffusion of Ge was investigated to gain insight into the transient, greatly enhanced diffusion of certain dopants during RTA that has been reported. No enhancement in the diffusion of Ge was observed which is shown to be consistent with a model proposed to explain the enhanced diffusion for dopants.

ISSN:0021-8979    

DOI:10.1063/1.336561

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Hard carbon films were produced by the rf glow discharge plasma decomposition of hydrocarbon gases diluted with H2gas at relatively low temperature and low pressure. Optical emission spectra were measured during the deposition of the carbon films, and the correlation between the carbon film’s properties and the plasma’s condition was examined. From these results, H radicals were considered to contribute to the formation of hard carbon films. These were examined by transmission electron microscopy, and were found to be predominantly amorphous. The existence of diamond grains was confirmed in the amorphous phase. A relatively large diamond grain in the order of 10 &mgr;m was obtained under the conditions of a gas mixture ratio of 70% and a gas pressure of 5×10−3Torr.

ISSN:0021-8979    

DOI:10.1063/1.336562

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

We present experimental evidence that during rapid deformation of at least some crystalline and polymeric solids heat is generated at unexpectedly high temperatures beginning essentially at the moment deformation begins. The heat was observed by fast infrared sensors. Both the initial infrared emissions and the apparent blackbody temperatures were far in excess of what can reasonably be accounted for by the conventional picture that distributes the energy due to deformation over the bulk of the solid. It appears that the origins of these high temperatures are associated with mechanical processes that effectively concentrate the energy of deformation into small local regions within the sample. These local hot spot regions are most likely associated with shear bands and possibly fracture sites in the deforming crystal.

ISSN:0021-8979    

DOI:10.1063/1.336563

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

We report experimental results of an oxygen precipitation study carried out using Czochralski silicon wafers. A two‐step anneal scheme was employed: a lower‐temperature step (at 650 or 750 °C for 0–128 h) for SiO2precipitate nucleation and a higher temperature step (at 1050 °C for 0–64 h) for growth. The oxygen precipitation rate is monitored by measuring the interstitial oxygen (Oi) concentration in the silicon lattice. We have found that (i) a precipitation retardation phenomenon exists for wafers that received prolonged nucleation annealing treatment (from 2 to 16 h), and (ii) this retardation phenomenon gives way to a precipitation recovery phenomenon for wafers that received still longer nucleation annealing treatment (for 8–128 h). We also describe a nuclei dissolution model to explain the retardation/recovery phenomena. The dissolution proceedsagainstan Oisupersaturationwhich would normally drive the nuclei into growth.The most important aspects of the model are (i) the dissolution occurs at the onset of the high‐temperature growth anneal step, (ii) the factor directly opposing the Oisupersaturation and leading to the nuclei dissolution process is attributed to a large supersaturation of silicon self‐interstitials (Isupersaturation), essentially also generated at the onset of the growth anneal step, (iii) the generation of theIsupersaturation is associated with a nuclei/precipitate polymorph change again occurring at the onset of the growth anneal step. The fundamental physical cause leading to these phenomena is theexigent‐accommodation volume(orexigent volume) associated with precipitate growth. This model can explain the present results and is consistent with many other experimental results. We then examine the relevance of the exigent‐volume factor with nucleation issues such as its effect on ramping, the effect of carbon, the existence of multiple polymorphs of SiO2, multiple nucleation paths, and a nucleation incubation phenomenon. We believe contributions of the exigent‐volume factor to the nucleation phenomena generally exist.

ISSN:0021-8979    

DOI:10.1063/1.336564

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

First reports on the characteristics and applications of GeO2‐SiO2glass films formed by laser‐induced chemical vapor deposition (CVD) are presented. At a low temperature (200–300 °C), solid solutions of ternary compounds can be obtained by laser‐induced CVD. It is shown that these GeO2‐SiO2ternary films were applicable to planar optical waveguides.

ISSN:0021-8979    

DOI:10.1063/1.336565

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

We have grown high‐purity GaAs on (100), (311)A, and (311)Borientations by molecular‐beam epitaxy (MBE). While undoped GaAs grown on (100) and (311)Aare typicallyptype, growth on (311)Borientation has yieldedntype with a liquid‐nitrogen electron mobility of 1.3×105cm2 V−1 s−1, which is among the highest mobilities reported for MBE‐grown materials. Low‐temperature photoluminescence showed well‐resolved impurity bound exciton peaks consistent with electrical results. The possible incorporations of impurities, especially carbon, are discussed. Our work demonstrates that the previously reported undopedp‐type GaAs(100) are compensated.

ISSN:0021-8979    

DOI:10.1063/1.336566

出版商:AIP    

年代:1986

数据来源: AIP