摘要:

The distributions of vacancy‐type defects and displaced Si atoms in Si(100) produced by the room‐temperature implantation of 1014–101612‐MeV28Si+ions/cm2are measured with low‐energy positron‐ and ion‐beam techniques. The observed damage regions are reproduced by computer simulations. The distribution of displaced Si atoms coincides with the deposited energy distribution in elastic collisions. At the fluence of 1×1016Si+/cm2, no crystalline structure was found in the peak region of the deposited energy at the depth ofz=6 &mgr;m. Saturation of the divacancy concentration was observed at the ion fluences 3×1015Si+/cm2close to the surface (z<0.7 &mgr;m) and 3×1014Si+/cm2deeper in the sample (z>1 &mgr;m). In the regionz<0.7 &mgr;m, the divacancy concentration is a factor of 4 higher than that in the regionz>1 &mgr;m. This is also found in the simulated spatial structure of collision cascades.

ISSN:0021-8979    

DOI:10.1063/1.345709

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

A ferroelectric liquid‐crystal light valve for laser addressing is studied. Surface‐stabilized ferroelectric liquid‐crystal cells are employed, where the liquid crystals have bistable states with respect to molecular alignment. The threshold width of an applied voltage pulse required for ferroelectric switching (polarization reversal) decreases with raising cell temperature for a given pulse height. Laser writing and erasure are successfully performed with this effect. An important feature of this light valve is that the overall erasure can be done certainly, readily, and quickly by applying an appropriate pulse voltage.

ISSN:0021-8979    

DOI:10.1063/1.345710

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

This paper deals with the phase transition behaviors of the mixtures of oleyl cholesteryl carbonate and cholesteryl nonanoate by means of optical and differential scanning calorimetry methods. The iridescent colors were measured by using the spectro multichannel photodetector. The phase diagrams show that the smectic mesophase appears in the whole concentration ranges under cooling, but only exists in heating with concentration less than 60%. The phase transition temperatures of the mixtures increase monotonically with increase of cholesteryl nonanoate (CN) contents. This phenomenon has been interpreted from the viewpoints of molecular configurations. The iridescent colors vary from red to violet as the temperature increases, and in reverse order when cooling. The concentration ranges of the iridescence are in agreement with those of smectic existence. Results also indicate that the color band shifts monotonically toward higher temperatures with an increased concentration of CN. This effect is accompanied by a gradual expansion of the temperature interval of the color band. The temperature dependence of the color shift may be explained with the pretransition of twist or untwist of the helical structures. Reflection bandwidth variations with temperature are also attributable to pretransitional effects. The temperature dependence of selectively reflected light intensity measurements reveals that the sensitivity decreases with increase in the wavelength. Moreover, 50% CN concentration is most sensitive, whether heating or cooling.

ISSN:0021-8979    

DOI:10.1063/1.345807

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

We use simple arguments to fix the range of density of randomly distributed defects over which &pgr; electrons in a graphite sheet are strongly localized, but the underlying two‐dimensional carbon network remains connected. This ‘‘defeated graphite’’ construct leads to simple structural models of both hydrogenated and unhydrogenated amorphous ‘‘diamondlike’’ carbon, which reproduce many important properties of those materials.

ISSN:0021-8979    

DOI:10.1063/1.345808

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Defects introduced by reactive‐ion etching and plasma etching using deuterium have been studied in boron‐doped Si with the photoluminescence (PL) technique. We have observed a set of broad luminescence bands in the below‐band‐gap range between 1.05 and 0.8 eV. These bands change in intensity as well as in photon energy with annealing. This has been studied by isochronal annealing treatments from 75 to 800 °C in steps of 50 °C, each for 30 min. Directly after the plasma treatment we observe overlapping broad bands at liquid‐He temperature, with a peak around 0.9 eV and a half‐width of about 100 meV. There is a large shift of these bands to higher photon energy after the annealing step at 325 °C, peaking at about 0.925 eV with a half‐width of about 60 meV. The intensities of the broad PL bands increase with increasing annealing temperature up to about 375 °C, while they decrease in intensity at higher temperatures. The changes in PL intensity of the broad bands after annealing are shown to be related to the difference in deuterium concentration near the surface, as determined by secondary‐ion mass spectrometry, due to the passivation effect the deuterium has on other competing recombination channels. The samples have not completely recovered after annealing at 800 °C, where a broad PL band at 0.96 eV still remains. PL bands observed in hydrogenated samples containing ‘‘bubbles’’ will also be reported. We attribute all these PL bands to electron‐hole recombination in heavily damaged regions, where electrons and holes can be localized in potential wells caused by the strain from the hydrogen‐induced microscopic defects. This ‘‘strain‐induced intrinsic quantum well’’ model is supported by the temperature and excitation intensity dependence of the broad PL bands.

ISSN:0021-8979    

DOI:10.1063/1.345784

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

A new type of Monte Carlo algorithm to calculate packing fraction and general particle dispersion characteristics for arbitrary random packs of spherical particles is presented. Given arbitrary quantities of arbitrary sizes with arbitrary mass densities, the algorithms calculate the close random packing fraction. If desired, they can return the position and type of each particle in the pack. Since every detail of the positions and types of particles in the pack is known, any pack characteristic can be calculated. The algorithms use a dimension‐reducing trick to turn a computationally intractable problem into a tractable one. Planned extensions and improvements of the algorithms are discussed.

ISSN:0021-8979    

DOI:10.1063/1.345785

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Chromium thin films were prepared by a sputter‐deposition system in which substrates were arranged semicircularly against a chromium target. Structures and compositions of the films were investigated by x‐ray diffractometer, x‐ray photoelectron spectroscopy, electron probe microanalyzer, and scanning electron microscope. It was found that oxygen content in the films was highest at the opposite side of the target and was lowest at the position of 60° or 75° off with respect to the target normal. At the latter position, (110)‐preferred orientation and enlargement of the bcc chromium lattice were observed. Although cracks were generated in the films deposited at the opposite side of the target, no cracks were generated in the films deposited at the oblique direction. These results on the chromium films could be explained in terms of the bombardment effect by the reflected argon atoms whose energy was a function of the scattering angle.

ISSN:0021-8979    

DOI:10.1063/1.345786

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

A novel technique for examining corona processing variables in thin‐film organic second‐order nonlinear optical materials is discussed. Positive and negative polarity dc‐coronas were used to pole doped glassy polymer filmsinsituat room temperature in air, helium, and nitrogen environments to create materials capable of second harmonic generation (SHG). Films are poled in the beam path and are continuously sampled. For a given atmosphere and poling time, films poled in a positive corona show greater SHG intensities than those poled with negative coronas. The temporal stability of the SHG intensity for films poled with a positive corona increases from air to nitrogen to helium, and for a negative corona is similar in nitrogen and helium atmospheres, and less stable in air. Possible mechanisms are discussed.

ISSN:0021-8979    

DOI:10.1063/1.345787

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The microstructure and electrical properties of calcium‐modified barium titanate ceramics of compositions (Ba1−xCax)TiO3have been investigated. From the influence of the CaO content and stoichiometry on the said characteristics of the materials, it is concluded that the cationic ratio, &agr;=(Ba+Ca)/Ti, is the predominant factor affecting the resistance of materials against the reducing sintering atmosphere. The electrical properties, including resistivity and dielectric dispersion, can be completely preserved when the sintering atmosphere is switched from air to H2/N2, but only for samples with values of &agr; greater than unity. The formation of a hexagonal BaTiO3−&dgr;phase, which consumes the oxygen vacancies, is presumed to be the factor that improves the resistance of these materials against the reducing sintering atmosphere.

ISSN:0021-8979    

DOI:10.1063/1.345788

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The effect of hydrogen dilution on deposition ofa‐SiC:H from silane/ethylene mixtures has been investigated by analyzing deposited films using optical absorption and x‐ray photoelectron spectroscopy (XPS) measurements. Film deposition rate and stoichiometry are found to be sensitive to the hydrogen dilution rate and it is proposed that ethylene decomposes through a two stage reaction with atomic hydrogen. Films with similar stoichiometries deposited using different combinations of ethylene, silane, and hydrogen and are found to have the steepest optical absorption edge when the ethylene/silane ratio is low and when the hydrogen partial pressure fraction is at 80%–85% of the total pressure. XPS measurements show that the density of SiC bonds increases as the slope of the optical edge becomes steeper.

ISSN:0021-8979    

DOI:10.1063/1.345789

出版商:AIP    

年代:1990

数据来源: AIP