摘要:

Hole carrier densities and Raman spectra were measured in polycrystalline silicon doped with boron. After increasing the annealing temperature and the dopant dose, spectral broadening was observed in the high‐energy side of the Si peak. The fraction of boron at the substitutional position was estimated by the intensity ratio between the Si‐B local mode and the Si optical phonon mode. This ratio was proportional to the hole carrier densities, and, as a result, estimation of the hole carrier densities was also possible. Raman scattering is applicable for the estimation both of boron at the substitutional position and of hole carrier densities.  

ISSN:0021-8979    

DOI:10.1063/1.351621

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

We use the asymmetry of beam coupling with respect to the orientation of the polar axis in a nominally undoped barium titanate crystal to determine the electro‐optic and absorptive ‘‘gain’’ in the usual beam‐coupling geometry. For small grating wave vectors, the electro‐optic coupling vanishes but the absorptive coupling remains finite and positive. Positive absorptive coupling at small grating wave vectors is correlated with the light‐induced transparency of the crystal described herein. The intensity and grating wave vector dependence of the electro‐optic and absorptive coupling, and the light‐induced transparency are consistent with a model incorporating deep and shallow levels.

ISSN:0021-8979    

DOI:10.1063/1.351622

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

The analysis of transient photoluminescence measurements and extraction of carrier recombination lifetimes in GaAs and AlGaAs double heterostructures is discussed. In contrast to recently reported claims, it is demonstrated that even in regions where the measured decay curves show single exponential behavior, the slopes do not, in general, correspond to any single physical carrier lifetime such as the minority‐carrier lifetime. A series of measurements over a range of incident optical intensities is required to extract such lifetimes.

ISSN:0021-8979    

DOI:10.1063/1.351623

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

The asymmetric wiggler, inserted since the end of 1990 on the Super‐Aco storage ring in Orsay, has been built to produce a high rate and high flux of circularly polarized soft x rays in the 100–3000 eV range. This insertion device is particularly well suited to measure x‐ray absorption spectra corresponding to dipole transitions towards electronic orbitals that are directly responsible for magnetism (3dstates of first row transition metals, 4fstates of rare earths). In this article we report the first magnetic circular x‐ray dichroism spectra obtained with this insertion device. They exemplify the wide prospects of this experimental setup.

ISSN:0021-8979    

DOI:10.1063/1.351624

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

The electron impact ionization coefficient, &agr;n, in bulk silicon, was extracted using a new method that is applicable for the low‐electric fields. In this method, &agr;ncan be simply estimated from the multiplication factor of ann‐type static induction transistor, and a structurally determined depletion layer thickness. Values of &agr;n, as low as 1×10−4cm−1, have been obtained at 300 and 77 K, and they agreed approximately with previously reported data that covered relatively high electric fields.

ISSN:0021-8979    

DOI:10.1063/1.351625

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

It is demonstrated explicitly that the collective‐current concept in atomic mixing, as formulated by Collins, is equivalent with the homogeneous‐relaxation model proposed by Hofer and Littmark. Both schemes lead to the balance equation of Sigmund, Oliva, and Falcone. The relation to Titov’s model of high‐fluence ion implantation is clarified.

ISSN:0021-8979    

DOI:10.1063/1.351626

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Thermomagnetic measurements were used to determine the oxidation kinetics of bulk and powdered Nd‐Fe‐B magnets under a pressure of 1 Pa in the 360–600 °C temperature range. Those conditions are roughly similar to those undergone by sintered or rapidly quenched magnets during heat treatment. The first step of the oxidation kinetics obeys a parabolic law for bulk magnets and a cubic one for powders, with activation energies in the range 65–78 and 35–50 kJ/mol, respectively. Some anomalies in these patterns related to time or temperature are discussed.

ISSN:0021-8979    

DOI:10.1063/1.351627

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

We report a system capable of obtaining Raman spectra during growth of carbon films in a hot filament reactor. A gated, multichannel detection system was used to discriminate against the high levels of background radiation produced by the hot substrate and the hot filament. The ability to detect and distinguish between diamond and nondiamond carbon films during growth is shown. Diamond was grown on silicon substrates at 925 °C, with a filament temperature of 2100 °C and with CH4/H2ratios between 0.002 and 0.008. A nondiamond carbon film was produced with CH4/H2ratio of 0.016. In order to estimate the sensitivity of the system to detect diamond during growth, the average particle size and fractional coverage of the substrate were determined when a diamond Raman signature was first observed. Currently, the system is capable of detecting diamond particles about 0.5 &mgr;m in diameter covering about 3/4 of the surface.

ISSN:0021-8979    

DOI:10.1063/1.352330

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Heteroepitaxial growth of 3C‐SiC on Si substrates by gas source molecular beam epitaxy was investigated. Both Si(001) and Si(111) surfaces were carbonized using a C2H2gas molecular beam to convert the surface region into single crystalline 3C‐SiC prior to crystal growth. The supply of C2H2was started at 400 °C, and the substrate temperature was raised at a rate of 7 °C/min. An amorphous‐like layer was observed at 870 °C. Raising the temperature at a rate of 2 °C/min from 870 to 970 °C, a single crystalline 3C‐SiC layer was obtained. In the case of Si(001), increase of C2H2supply resulted in improvement of crystallinity, because of a thin (∼50 A˚) 3C‐SiC layer formed at an early stage of carbonization, which prevented outdiffusion of Si atoms. The thickness of the 3C‐SiC layer did not increase for prolonged time of carbonization after formation of the thin layer. In the case of Si(111), the increase of C2H2supply resulted in a thicker layer of 3C‐SiC with a rough surface, because the channels of Si outdiffusion were not sealed off. Epitaxial growth of 3C‐SiC was carried out using alternate supply of Si2H6and C2H2gas molecular beams on 3C‐SiC layers obtained by carbonization under optimum conditions. Single crystalline 3C‐SiC layers were obtained at 1075 °C, both on (001) and (111) surfaces.

ISSN:0021-8979    

DOI:10.1063/1.351628

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Multilayer poly(p‐phenylene biphenyltetracarboximide) (BPDA‐PDA) polyimide films of 172 &mgr;m total thickness (11.4 &mgr;m per layer) were prepared from the poly(amic acid) precursor solution through repetition of a spin‐coat/softbake/cure process. Wide‐angle x‐ray diffraction results indicate that the polyimide molecules in the multilayer films are highly ordered along the chain axes as well as in the lateral direction and furthermore are highly oriented in the film plane as observed in a single‐layer film of 11.4 &mgr;m thickness. The multilayer films showed the same dynamic mechanical properties and glass transition behavior (Tg= 330 °C) as a single‐layer film. For the multilayer films both the in‐plane dielectric constant (&egr;’XY) and out‐of‐plane thermal‐expansion coefficient (&agr;Z) were measured using time‐domain spectroscopy and conventional thermal mechanical analysis, respectively. The &egr;’XYat room temperature was 3.69 (±0.08) over a frequency range of 0.35–2.50 THz. A similar &egr;’XYis predicted at frequencies of ≤0.35 THz. In contrast to the &egr;’XY, a relatively lower out‐of‐plane dielectric constant (&egr;’Z) was observed: &egr;’Z= 2.96–3.03 (±0.02) at 1 MHz, depending on moisture content in the film. The dielectric loss &egr;‘Zat 1 MHz was 0.011–0.014 (±0.001), depending on moisture content. The measured &agr;Zwas 74 ppm/°C over the temperature range of 25–150 °C, which was much higher than &agr;XY= 2.6–5 ppm/°C. Consequently, large anisotropic &egr;’and &agr; have been observed in the in plane and out of plane of the thermally imidized BPDA‐PDA films. The anisotropic &egr;’and &agr; were caused by high in‐plane orientation of the polyimide molecules highly ordered along the chain axes in the films.

ISSN:0021-8979    

DOI:10.1063/1.351629

出版商:AIP    

年代:1992

数据来源: AIP