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91.
A survey of previous studies on vacuum deposited metal films shows that in high frequency measurements, explicit reference
to the effect of air-exposure is not made. The present work on bismuth films (in-situ and air-exposed) at dc and rf frequencies, carried out mainly to study the air-exposure effect, shows that in-situ
dc and rf and exposed rf all show nearly the same resistivity for thick continuous films. But air-exposed dc film resistances, when compared to in-situ
dc resistances, show that the grain boundary reflection coefficient, R
gin Mayadas-Shatzkes model changes from 0·2 to 0·6. This is shown to be due to the grain boundary oxidation. The result is
substantiated by rf measurements. 相似文献
92.
The electrical properties of sets of simultaneously grown p-type polycrystalline Si films, deposited by SiH4 pyrolysis on polycrystalline high-purity alumina substrates and B-doped during growth, were determined by Hall-effect measurements
in the temperature range 77-420K as functions both of impurity doping concentration N (~10l5 to ~1020cm−3) and average grain size (≈1 to ≈125μm) in the film. Room temperature data showed rapidly increasing resistivities and rapidly
decreasing free-carrier concentrations for doping below a critical concentration Nm and distinct mobility minima at that concentration, with the value of Nm being larger the smaller the average grain size. Measurements as a function of sample temperature showed the intergrain barrier
height Eb, decreasing from a maximum value of ~0.4eV at the critical concentration to very small values (~0.01eV) for concentrations
above 1019cm−3, with a functional dependence close to Eb ∝l/N1/2 and Eb for any given concentration being larger the smaller the average grain size. Results are interpreted in terms of the grain-boundary
trapping model. Trapped carrier densities in the grain boundaries were calculated to range from ~5×l011cm−2 at N≈Nm to ~5×l012cm−2 for N>1019cm−3, the density being higher the smaller the grain size, and evidence was found for an energy distribution of traps in the Si
bandgap, rather than a fixed density at a single discrete energy level. The observed relationship between Nm and average grain size nearly coincides with that of the model for films with ~lμm grain size but sharply departs from it
for larger grain sizes, indicating probable applicability of the model for grain sizes up to that range.
aThis work was supported by the U.S. Department of Energythrough its San Francisco Operations Office under Contract DE-AC03-79ET23045
and monitored by the Solar Energy Research Institute, Golden, CO.
bThese results were first described at the 22nd Electronic Materials Conference, Ithaca, NY, June 21–27, 1980, Paper No. M4. 相似文献
93.
E. L. Gurvitch 《Journal of Optimization Theory and Applications》1976,20(1):65-79
In the present paper, we discuss the isoperimetric problems for domains with partly known boundaries, i.e., the problem of determining a domain that minimizes the capacity functional in the class of plain double-connected domains having the same fixed area and outer boundary. The formulas for capacity variations obtained in this paper allows us to formulate necessary conditions.It is proved that the convexity of the fixed outer boundary implies the convexity of the inner boundary corresponding to an optimal domain. Then, we discuss the case where the fixed part of the boundary is a square.Further, we consider similar problems with more complicated functionals. We introduce the concept of a minimal function in the class of equimeasurable functions. This concept allows us to unify the approach to all of these problems. At the end, we produce a hypothesis that, if proved, would enable us to characterize the shape of the optimal domains in the isoperimetric problems mentioned above.The author wishes to express his appreciation to Dr. K. A. Lurie for his help and unceasing attention. 相似文献
94.
High-spatial energy dispersive X-ray (EDX) microanalysis has been applied in order to reveal changes of chemical composition accompanying the formation of the lamellar structure due to discontinuous precipitation reaction in Al-22at.% Zn alloy. The line-scans performed in the reaction zone have shown that the region left behind the grain boundary (GB) after its displacement from the original position is solute depleted, similar to the de-alloying case of diffusion induced grain boundary migration. This enables the allotriomorphs to be transformed into solute-rich lamellae and development of lamellar + structure, especially if the GB moves in the direction perpendicular to its original location. If the direction of movement is strongly inclined to the original location of the GB, the growth usually stops after a short period of time, mainly due to formation of the precipitation free zone (PFZ) ahead of the reaction front. The detailed EDX examination revealed that there is a sharp change in solute content at the lamella/PFZ and PFZ/matrix alloy interfaces. The solute content in the PFZ is lower than in the neighbouring lamella and it corresponds to the equilibrium state. Therefore, one can suppose that the PFZ is formed due to backward movement of the reaction front in order to consume the excess of solute atoms stored in the lamellae in comparison with the equilibrium state. As soon as the equilibrium state is attained within the PFZ, the growth of the colony is completed. 相似文献
95.
P. Zieba 《Interface Science》2003,11(1):51-58
The paper summarizes recent experiments on diffusion at migrating grain boundaries (GBs) occurring during discontinuous reactions, like discontinuous precipitation (DP) and diffusion induced grain boundary migration. Analytical electron microscopy was used for measurements of the solute concentration across individual solute-depleted lamellae. These data combined with information on the growth velocity and the thickness of an individual lamella allowed the determination of the local values of the diffusivities of the moving reaction front of the DP cell in Al–Zn, Ni–Sn, Cu–In and Co–Al alloys. The obtained diffusivities and activation energies are very similar to the relevant parameters of stationary GBs. This allows us to conclude that there is no significant difference in the rates of diffusion along migrating and stationary GBs in the systems investigated. It is therefore believed that the diffusivity values of the moving reaction front of the DP reaction can be a source of reliable information on interfacial diffusion characteristics, especially in systems and/or at temperatures where radiotracer data are not readily available. 相似文献
96.
Wetting of 975 grain boundaries (GB's) by liquid Cu in an iron-based alloy has been studied as a function of the five macroscopic degrees of freedom (DoF's) of grain boundary character. In addition, models of GB energy in terms of all five DoF's, and of anisotropic solid-liquid interfacial energy have been developed. The experimentally observed wetting behavior is interpreted in terms of the model, and it is shown that reasonable overall agreement is obtained between experimental results and model predictions. 相似文献
97.
The atomistic simulation results presented in Part I for SrTiO3 (310) symmetrical tilt grain boundary (STGB, the so-called = 5 GB with 36.8° symmetrical misorientation about [001]) are analyzed in the context of available experimental studies. In particular, atomic imaging studies of SrTiO3 GBs via high resolution TEM and incoherent Z-contrast STEM imaging; and determination of oxygen positions by combining electron energy loss spectroscopy (EELS) and bond-valence-sum rules, are compared with simulation results. The atomistic simulation data on the GB energies are compared with relative experimental estimates obtained via a novel approach of faceting of focused ion beam (FIB) induced microvoids.While there are considerable differences in details of simulation and experimental results, some basic trends seem to emerge about the core structural framework of GBs in SrTiO3. The paper highlights the limitations of both, experimental and simulation techniques, and argues in favor of synergistic use of diverse experimental and simulation approach to determine the atomic structure and properties of GBs. 相似文献
98.
回顾介绍了葛庭燧院士的生平和他在科学研究、人才培养方面所作出的贡献,展示了他的高尚情操,分析了他取得卓著成就的原因. 相似文献
99.
采用电沉积方法在表面活性剂和电解液的界面制备了硫化镉纳米膜.通过对不同电解液体系和表面活性剂体系中纳米硫化镉膜沉积情况进行比较发现,相同条件下采用硫代乙酰胺体系为电解液,蓖麻油类为表面活性剂可以在液/液界面制备硫化镉纳米膜.考察了表面活性剂种类、电解液浓度和温度及溶液的pH值对制备硫化镉纳米膜的影响,确立了制备纳米膜的最佳工艺条件:氯化镉浓度为4 mmol·L-1,硫代乙酰胺浓度为12 mmol·L-1,槽压5 V,pH值为4.8,蓖麻油/十六醇的用量为0.06 ml·cm-2.实验表明,最佳工艺条件下制备的硫化镉纳米膜晶粒粒径均匀、平均粒径在30 nm左右,近似球形,将在非线性光学材料领域有特殊的应用前景. 相似文献
100.