摘要:

Optical polarization in orderedGaInP2alloys has been studied by low-temperature photoluminescence. A perturbative theory that includes the effects of lattice mismatch, substrate misorientation, and excitonic transitions has been developed for making quantitative comparisons between experimental results and theoretical predictions. We show that to obtain quantitative information about ordering from the polarization of near-band-gap transitions, all of the above-mentioned effects should be taken into account. This study demonstrates that the electronic and optical properties of a monolayer superlattice formed by partial ordering in theGaInP2alloy can be well described by a simple perturbative Hamiltonian, i.e., a quasicubic model. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364390

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The high temperature optical properties of cadmium telluride have been studied at temperatures up to 1104 K by measurement of the incandescence spectra from a wafer of that material. These measurements provided information equivalent to that of a transmission experiment and allowed the optical absorption spectra of the material to be determined using a theoretical expression for the refractive index and its dispersion with wavelength modified to account for the effect of temperature. This analysis required only a knowledge of the temperature dependence of the fundamental gap of cadmium telluride. Absorption by intrinsic carriers was not found to be significant at photon energies in the region of the fundamental gap even at such elevated temperatures and accordingly the near band-edge absorption was clearly discernable. As is typical in II-VI compound semiconductors, a disorder related exponential absorption (Urbach) tail was observed below the fundamental (mobility) gap and it was to such values of the absorption coefficient that this experiment was sensitive for the relatively thick sample used here. The absorption data were well fitted by assuming the energy gap to have a linear temperature coefficient of−0.34±0.02meV K−1and determining the absorption spectra self-consistently with that temperature dependence. At very low values of absorption, however, the condition of the sample surface dominated the spectra. Such measurements may have application in thein situmonitoring of the bulk growth of CdTe by vapour phase techniques, providing information regarding temperature, structural disorder, and surface stoichiometry. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364371

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The optical absorption of syntheticReS2andReSe2single crystals is reported over a temperature range from 25 to 300 K. Analysis reveals that the absorption edges ofReS2andReSe2are indirect allowed transitions. The indirect band gaps at various temperatures are determined and their temperature dependence is analyzed by the Varshni equation [Physica34, 149 (1967)] and an empirical expression proposed by O’Donnel and Chen [Appl. Phys. Lett.58, 2924 (1991)]. The parameters that describe the temperature dependence of energy gaps of these two materials are evaluated and discussed. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365357

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Normal spectral emissivity of Si melt in visible and infrared regions was determined by the direct measurement of thermal radiations from the melt and a blackbody cavity which was located close to the melt. The spectral emissivity slightly decreases with wavelength. The emissivity slightly changes with temperature. The spectral emissivity values in visible and in infrared region are 0.27 and 0.21, respectively. The wavelength dependence of the emissivity can be interpreted by a dielectric response of free electrons in the melt. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364418

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

In this article we report on surface scattering experiments at graphite as to model the interactions at divertor surfaces in tokamaks and conversion electrodes in negative ion sources. The formation of negative and positive hydrogen ions on a graphite surface during positive hydrogenous ion scattering at a projectile energy of 400 eV is observed. A remarkably highH−andH+ion fraction, both varying between 10&percent; and 30&percent; of all scattered particles, is found during scattering of positive hydrogenous ions. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364419

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

There is growing interest in the applications of wavelets as basis functions in solutions of integral equations, especially in the area of electromagnetic field problems. In this article we apply a wavelet expansion to the solution of the three-dimensional eddy current modeling problem based on the volume integral method. Although this method shows promise for eddy current modeling of three-dimensional flaws, it is restricted by the computing power required to solve a large linear system. In this article we show that applying a wavelet basis to the volume integral method can dramatically reduce the size of the linear system to be solved. In our approach, the unknown total field is expressed as a twofold summation of shifted and dilated forms of a properly chosen basis function that is often referred to as the mother wavelet. The wavelet expansion can adaptively fit itself to the total field distribution by distributing the localized functions near the flaw boundary, where the field change is large, and the more spatially diffused functions over the interior of the flaw where the total field tends to be smooth. The approach is thus best suited to modeling large three-dimensional flaws where the large number of elements used in the volume integral method requires extremely large memory space and computational capacity. The feasibility of the wavelet method is discussed in the context of the physical nature of eddy-current modeling problems. Numerical examples using both Haar wavelets and Daubechies compactly supported wavelets with periodic extension are given. The results of the wavelet method are also compared with experimental results from a cylindrical flat-bottom hole in an aluminum plate. These numerical examples and comparisons indicate that the wavelet method can greatly reduce the numerical complexity of the problem with negligible loss in accuracy. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364420

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We have modified the properties of diamondlike atomic-scale composite (DLASC) material of various thicknesses (5–70 &mgr;m) by means of cw Ar-ion laser annealing using a focused beam (∼2 &mgr;mspot size). These DLASC films [amorphous “diamondlike/quartzlike”a-(C:H/Si:O)] constitute a novel class of diamond-related materials. The laser annealing effects were investigated by micro-Raman scattering. The structure of these films can be altered locally from amorphous to nanocrystalline depending not only on the parameters of the annealing process (annealing time, laser intensity) but also the mechanical properties (hardness, stress) of the films. For comparison purposes we also measured the effects of thermal annealing. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364421

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Two methods for producing Si-oxide barriers upon which crystalline Si layers can be grown are presented. One method entails oxide island nucleation on a clean vicinal Si(001) surface. The second method makes use of void formation in ultrathin oxides on the Si(100) surface at elevated temperatures. Either method results in an oxide barrier which is porous and the exposed Si within these pores can serve as a way to seedc-Si overgrowth. We demonstrate that it is feasible to grow crystalline Si overlayers on top of such porous oxide barriers, while on the continuous Si-oxide surface, only amorphous or nanocrystalline Si layer overgrowth can be achieved. The controlled oxide growth and Si overgrowth on the oxide can find possible applications in Si-based resonant tunneling devices, optoelectronics, and other Si-based nanoelectronics. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364422

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The bulk properties and stochastic pore geometry of finite-thickness fiber webs are studied using a realistic model for the sedimentation of flexible fibers [K. J. Niskanen and M. J. Alava, Phys. Rev. Lett.73, 3475 (1994)]. The resulting web structure is controlled by a dimensionless numberF=Tfwf/tf,whereTfis fiber flexibility,wffiber width, andtffiber thickness. The fiber length(≫wf,tf)is irrelevant. With increasing coveragec¯,a crossover occurs atc¯=c0≈1+2Ffrom a vacancy-controlled two-dimensional (2D) structure to a pore-controlled 3D structure. The 3D structures are isomorphic in that the pore dimensions are exponentially distributed, with the decay rate dependent only onF.©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364423

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Films of Ti dioxide, mixed Ti–Ce oxide, and Ce dioxide were produced by reactive dc magnetron sputtering. Electrochemical lithiation was probed by chronopotentiometry, cyclic voltammetry together with optical transmittance recording, and impedance spectroscopy. Evidence was found for inserted electrons being accommodated inCe 4fstates; this contention was supported by preliminary results from x-ray absorption fine-structure spectroscopy. These electrons do not produce luminous electrochromism. The variation of the chemical diffusion coefficient of Li, with film composition and Li content, was also studied. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364424

出版商:AIP    

年代:1997

数据来源: AIP