摘要:

The possibility of describing transient phenomena associated with flow and consolidation of solids, such as stress relaxation or physical aging, in terms of a kinetic mechanism comprising spontaneous and induced events is discussed. The starting point is the differential equationdn˙/dt=−an˙[1−(b/a)n˙], withndenoting the number of relaxed entities andn˙=dn/dt(a,bare constants,tis time), yielding ann˙(t) function reminiscent of a Bose–Einstein distribution. The correspondingn(t) relation describes the linear variation ofnwith log t, and the exponential dependence ofn˙ onn, as often found experimentally. Replacingn˙ in the starting equation by the relative raten˙/nyields a power‐law‐typen˙(n) dependence. A further modification, where the induction termn˙/nis not linear but raised to a power ≳1, finally produces a generalized version of the stretched exponential. When interpreted formally in terms of a spectrum of relaxation times &tgr;, all three equations produce response functions with discrete &tgr; distributions, provideda≠0.

ISSN:0021-8979    

DOI:10.1063/1.351998

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

The hard x‐ray photoacoustic signal intensities of copper have been measured at an x‐ray absorption near‐edge structure (XANES) region as functions of sample thickness (from 5 to 300 &mgr;m) and modulation frequency (from 5 to 50 Hz). It is shown that the photoacoustic signal intensities show maxima at the sample thickness close to 10 &mgr;m for each modulation frequency. The x‐ray photoacoustic signal varies fromf−1.0( fdenotes modulation frequency) up to 20 &mgr;m sample thickness, whereas it varies fromf−0.5beyond a 20 &mgr;m sample thickness, which is not consistent with the Rosencwaig–Gersho theory for the photoacoustic effect in solids.

ISSN:0021-8979    

DOI:10.1063/1.351999

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

The recrystallization and dopant activation in the BF2+implanted samples with a 110 keV/5×1015cm−2condition into a Si substrate and annealed with different heating rates to various preset temperatures for zero holding time have been studied. A higher heating rate yielded a higher carrier mobility and a better crystallinity. A statistical model was proposed to characterize the dopant activation. The activated dopant concentrationnwas expressed as &ggr; exp(−Ea/kT). The pre‐exponential term &ggr; is a function of critical temperatureTc, due to a finite melting point of Si, and heating rate. Both the effective activation energyEaandTcvalues decreased with increasing heating rate. With increasing heating rate, the &ggr; term rapidly decreased at low rates due to the shortened effective annealing time, but showed slight increase at high rates due to the decreasedTcvalue. Low heating rates facilitated the dopant activation via the &ggr; term, while high heating rates enhanced the activation efficiency via theEaterm.

ISSN:0021-8979    

DOI:10.1063/1.352000

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

The activation volume &Dgr;Vfor chemical diffusion in Ag50Au50alloy has been determined from the pressure dependence of the rate of decrease in amplitude of composition‐modulated thin films. Based on resistivity measurements, it is argued that the technique yields the bulk chemical diffusion coefficient, in close agreement with the experimental results. Eight measurements of the diffusion coefficient were made, four as a function of temperature (237–309 °C) at atmospheric pressure and four as a function of pressure (0–0.85 GPa) at constant temperature (269.5 °C). The samples, 2000–3000‐A˚‐thick multilayers of alternating silver and gold, with periods between 72 and 160 A˚, were made with a newly built UHV sputter‐deposition apparatus. The bulk chemical interdiffusion activation energy (1.5 eV) and activation volume (0.72 &OHgr;) agree with those expected from other interdiffusion and tracer measurements.

ISSN:0021-8979    

DOI:10.1063/1.352001

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Undoped69GaAs/71GaAs isotope superlattice structures grown by molecular beam epitaxy onn‐type GaAs substrates, doped by Si to ∼3×1018cm−3, have been used to study Ga self‐diffusion in GaAs by disordering reactions. In the temperature range of 850–960 °C, the secondary ion mass spectrometry (SIMS) measured Ga self‐diffusivity values showed an activation enthalpy of 4 eV, and are larger than previously compiled Ga self‐diffusivity and Al‐Ga interdiffusivity values obtained under thermal equilibrium and intrinsic conditions, which are characterized by a 6 eV activation enthalpy. Characterizations by SIMS, capacitance‐voltage (C‐V), and transmission electron microscopy showed that the as‐grown superlattice layers were intrinsic which turned intoptype with hole concentrations of ∼2×1017cm−3after annealing, because the layers contain carbon. Dislocations of a density of ∼106–107cm−2were also present. However, the factor responsible for the presently observed larger Ga self‐diffusivity values appears to be Si out‐diffusion from the substrate, which was determined usingC‐Vmeasurements. Out‐diffusion of Si decreases the electron concentration in the substrate which causes the release of Ga vacancies into the superlattice layers where they become supersaturated. This Ga vacancy supersaturation leads to enhanced Ga self‐diffusion in the superlattice layers.

ISSN:0021-8979    

DOI:10.1063/1.352002

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

A theoretical model was proposed to calculate the stress in the multilayer heterostructures such as multiple quantum well and strained quantum well structures. The model was derived under consideration of the difference between crystalline parameters such as the lattice constant and thermal expansion coefficient of the composed crystal layers. In this model, each composed crystal layer is divided into many imaginary thin layers. The face force and strain balance was considered over all the imaginary thin layers with coherent interfaces. Using this model, the stress in the lattice‐matched InP/In0.53Ga0.47As and strained InP/In0.82Ga0.18As multilayer heterostructures was calculated at 600 °C. In the multilayer, the compressive stress in the In0.53Ga0.47As and In0.82Ga0.18As layers is always larger than the tensile stress in the InP layers. The stress in the InxGa1−xAs layers decreases as the thickness of the InxGa1−xAs layers increases, and it increases by adding InP thick layers on the one side or both sides of the multilayer. The tangential and perpendicular lattice constants in the multilayer were calculated using this model. The perturbation of the InP lattice becomes smaller and that of the InGaAs lattice becomes larger by adding the thick InP layers. It is found from these results that the total stress at the InP/InGaAs heterointerface depends on only the lattice misfit, but the share of the total stress depends strongly on the structure.

ISSN:0021-8979    

DOI:10.1063/1.352003

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Structural studies on highly conductive thin films of pentacene (PEN) were carried out by x‐ray and electron diffraction methods. The ultrathin film before and after doping with iodine was confirmed to consist of single crystalline domains, and the lattice parameters were determined. Drastic elongation along thecaxis as a result of doping was observed, while thea‐bplane did not change during doping. The intercalation of iodine molecules between molecular layers of PEN was confirmed.

ISSN:0021-8979    

DOI:10.1063/1.352004

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Submonolayer coverages of Au on GaAs(001) substrates prepared by variousexsituchemical cleaning procedures using low‐energy ion scattering techniques are investigated. This research is compared with previous results for 1 ML of Au deposited on Si(111). A comparison of the energy spectra showed substantial broadening in the Li+backscattering ion peak from Au deposited on GaAs, as compared to the Au on Si. Li+impact collision ion scattering spectroscopy (ICISS) results showed that the gold formed an ordered overlayer above the Si surface, which was thermally stable to 500 °C. Even for depositions on room‐temperature GaAs(001), shadowing of Au by substrate atoms at low scattering angles showed that Au penetrated below the GaAs surface. The estimate of the average penetration depth into the room‐temperature substrate is two to three atomic planes of the GaAs crystal. An ICISS experiment showed that the Au atoms sampled by the ion beam were not ordered on lattice sites, but appeared to occupy multiple and/or random positions within the substrate. Upon annealing to 300 °C, the gold atoms were more ordered, but did not penetrate significantly further into the GaAs. At higher annealing temperatures, the Au either diffused further into the substrate or became incorporated in islands, and occupied favored subsurface sites.

ISSN:0021-8979    

DOI:10.1063/1.352355

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Reflection high‐energy electron diffraction (RHEED) oscillations that continued up to three cycles were observed during metalorganic molecular‐beam epitaxial growth of CdSe on a ZnSe buffer grown on a GaAs substrate, showing two‐dimensional layer‐by‐layer growth despite the large lattice mismatch (6.85%). Based on this result, we could definitely control the growth of CdSe/ZnSe strained‐layer single quantum wells with well widths of 1–3 monolayers and of short‐period superlattices underinsituRHEED monitoring. Optical properties strongly demonstrated the successful formation of well‐defined structures consisting of these highly strained II‐VI semiconductor multilayers.

ISSN:0021-8979    

DOI:10.1063/1.352005

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Diffraction from totally relaxed, partially relaxed, and unrelaxed strained‐layer superlattices is considered in the light of the similar rocking curves obtained by convergent‐beam electron diffraction and x‐ray diffraction. Diffraction of the superlattice can be described by an intensity expression given in terms of the strains and thicknesses of the superlattice bilayer. It is shown that the intensity profile of a reflection of a given superlattice depends on the difference of the tensile and compressive strains, i.e., the oscillating strain, of the superlattice bilayer. The oscillating strain of the superlattice bilayer, to a very good approximation, is independent of the state of strain in the step model of the superlattice. The insight gained leads to the understanding and prediction of the general form of the rocking curve of a superlattice from its growth parameters, although simulation of the rocking curve is still needed in order to obtain accurate structural parameters.  

ISSN:0021-8979    

DOI:10.1063/1.352006

出版商:AIP    

年代:1992

数据来源: AIP