摘要:

The interface between evaporated aluminum and poly(p‐phenylenevinylene) (PPV) was studiedinsituusing x‐ray photoelectron spectroscopy (XPS). PPV has potential for use in electroluminescent devices, and Al can be used as the electron‐injecting electrode. Aluminum was deposited on the PPV surface and the evolution of the chemical interactions at the interface was monitored using XPS. It was observed that the evaporated aluminum atoms react with the oxygen‐containing groups present as impurities on the surface of PPV to form Al‐O‐C linkages. The Al atoms also interact with the &pgr; system of the polymer, which, based on the changes in the valence‐band spectrum, results in the disruption of the conjugation along the polymer chain in the near surface region. In contrast to recently published work by E. Ettedgui, H. Razafitrimo, K. T. Park, Y. Gao, and B. R. Hsieh [J. Appl. Phys.75, 7526 (1994)], no polymer band bending is observed. Shifts of the Al 2pmetallic peak as a function of coverage are attributed to cluster growth of the deposited film. ©1995 American Institute of Physics. 

ISSN:0021-8979    

DOI:10.1063/1.359206

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Experimental observations have revealed a significant scatter in the spheroidization wavelength in solid rods and rod‐shaped inclusions. Using a finite difference method, the role of multiharmonic initial conditions, where the wavelength and amplitude vary with position, is investigated as a cause of the scatter. When the initial amplitude of the radius perturbation is small relative to the radius of the perturbation, the waves with their wavelengths at the maximum growth rate are shown to evolve with little scatter. As the initial amplitude increases, however, a large magnitude of scatter in the growing wavelength is observed due to wave/wave interactions. A simplified, analytical model is also proposed to describe the nonlinear wave/wave interaction between two waves. Based on this model, it is found that the stability of one wave can be affected by the other, and that a new wave can be generated. A wave stability diagram is constructed to predict the stability of a given wave. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359207

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Highly oriented polydiacetylene thin films were prepared by epitaxial polymerization of vacuum deposited monomer 5,7‐dodecadiyne 1,12 diol bis{[(4‐butoxy carbonyl) methyl] urethane} (4‐BCMU) on friction‐transferred poly(tetrafluoroethylene) (PTFE) substrates. Detailed structural and morphological studies were performed using UV‐dichroism measurements, optical and transmission electron microscopy, and suggest that 4‐BCMU grows epitaxially on PTFE as a result of a near perfect lattice matching. The oriented monomer layer is converted by photopolymerization into a highly oriented polymer layer with a unique poly(4‐BCMU)/PTFE chain to chain orientation and a well defined ac contact plane. Annealing of the monomer layer, prior to photopolymerization, is shown to strongly enhance the final degree of ordering of the polydiacetylene thin films. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359208

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Electron emission from deep states in the intrinsic layer of a‐Si:H p‐i‐n structures was investigated by post‐transit time‐of‐flight photocurrents in space‐charge‐limited current mode. The emission timetEfrom the deep levels is thermally activated for temperatures above 250 K. The frequency pre‐factor &ngr;0(attempt‐to‐escape frequency) varies between 1011Hz and 1013Hz, with the corresponding activation energiesEain the range of 0.42 to 0.52 eV for our samples. A Meyer–Neldel relation between &ngr;0andEais observed. Below 250 K,tEbecomes less temperature sensitive. The density of states in the upper part of the gap is evaluated from the current in the post‐extraction regime. At low temperature, the resolved distribution of gap states becomes inconsistent with higher‐temperature data, similar to what is observed by standard post‐transit photocurrent analysis. Possible mechanisms for the observed behavior of both thetEand the density of states are discussed: re‐trapping, hopping‐assisted release from deep states, the shift of transport energy with temperature and the energy dependence of the attempt‐to‐escape frequency. The shift of transport energy with temperature can partially explain the temperature dependence of the measured &ngr;0and the density of states. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359521

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The electrical activity of extended lattice defects formed by interstitial oxygen precipitation in silicon is studied. Their impact on diode characteristics and on minority carrier lifetime is addressed for different initial oxygen contents and pretreatments. The carrier traps present in the substrate are studied with deep level transient spectroscopy and with photoluminescence spectroscopy. The obtained electrical results are correlated with those of structural and chemical characterization using cross‐section transmission electron microscopy and Fourier transform infrared spectroscopy. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359209

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Thus far the general theory of the spatial distribution of photocarriers under the presence of a small signal inhomogeneous photocarrier generation has been limited to the one carrier case. In this work the more general and more complicated case of the spatial distribution of the two types of excess carriers is addressed. This distribution is pertinent in particular to the newly developed photocarrier grating (PCG) technique. The above two carrier problem and the PCG technique are discussed in a much broader context than previously given in the literature. A Green’s‐function approach, applied here for the first time, provides a general recipe for the problem of inhomogeneous carrier generation and it gives a better physical insight into the corresponding system by showing how the local carrier concentration is determined by the carrier generation in the entire sample. Hence the mathematical and physical basis for the PCG technique is provided here. The generality and the usefulness of the present approach for the nontrivial carrier generations of the ‘‘single square pulse,’’ the ‘‘square wave,’’ and the ‘‘one period sinusoidal pulse,’’ which have not been considered previously, are demonstrated. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359210

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Polypropylene (PP) samples were treated in an electron cyclotron resonance plasma with several gases and under different treatment conditions (pressure, treatment time, rf potential). The surfaces were chemically characterizedinsituby x‐ray photoelectron spectroscopy (XPS). Changes in the electrical resistance of the surface layer were analyzed by four points measurements. Noble gas plasma treatments led to a great decrease (ten orders of magnitude) of the resistance, whereas reactive gas plasma treatments induced no modification of the resistance. Taking into account that the treated layer corresponds to the ion penetration depth, an estimation gives 0.1 &OHgr; cm for the bulk resistivity of He plasma treated PP. For noble gases, this value depends on the plasma gas and on the ion kinetic energy. The resistance decrease is explained by a dehydrogenation and an increase of carbon–carbon bonds. During reactive gas plasma treatments, the incorporation of new chemical species prevents this graphitization. Correlations of the resistance with XPS measurements and comparisons with literature on high energetic ion treatments allow a better understanding of the effects of the plasma treatment. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359211

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The thermal annealing of light‐induced defects inp‐i‐pandn‐i‐nhydrogenated amorphous silicon (a‐Si:H) structures has been studied at 140 °C under ohmic and single‐carrier injection conditions. The influence of hole or electron injection on steady state defect density and relaxation time of the isothermal defect annealing has been studied. All the experimental results can be qualitatively explained by a simple model in which the creation rate of the defects in intrinsica‐Si:H is proportional to then‐pproduct of the carrier densities, and the annealing rate is proportional to the product of defect density and hole density. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359212

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The dependence of photoluminescence spectra and surface morphology on misfit strain are investigated for highly strained InxGa1−xSb/Al0.35Ga0.65Sb quantum wells grown on GaSb(001) by molecular beam epitaxy. Infrared photoluminescence with a wavelength as long as 1.95 &mgr;m is observed at room temperature from a multiple‐quantum well. The measured photoluminescence wavelength is in good agreement with that calculated by the theory in which strain effects are taken into account for a single‐strained quantum well condition. The photoluminescence intensity decreases remarkably when width of strained quantum well exceeds the critical layer thickness (CLT) that depends on the misfit, i.e., indium content of the well layer. The mechanical‐equilibrium theory of the generation of misfit dislocations predicts the CLT observed successfully. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359213

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

It is shown that photoluminescence emission from AlGaAs/GaAs and InGaAs/GaAs near‐surface quantum wells can be a nonlinear function of the excitation‐power density depending on the surface‐barrier thickness and on the conditions of the barrier‐oxide interface. By studying the rate‐equation system, it is shown that this nonlinear effect is mainly due to the competition between tunneling to surface states and relaxation of photogenerated carriers within the quantum well. The information about surface states that one can obtain from this nonlinear behavior is also discussed. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359214

出版商:AIP    

年代:1995

数据来源: AIP