摘要:

The nature of the atomic structure and the characteristics of both line and planar defects in decagonal quasicrystals of as‐cast Al62Cu20Co15Si3were studied by means of conventional diffraction contrast and high‐resolution electron microscopy. Two types of dislocations were observed. The magnitude and direction of the Burgers’ vector of type A dislocations and the Burgers’ vector direction of type B dislocations were determined. The direction of the displacement vector of the planar faults was defined.

ISSN:0021-8979    

DOI:10.1063/1.353347

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Molecular hydrogen is alternately introduced into and removed from the gate oxide of irradiated metal‐oxide‐semiconductor field‐effect transistors at room temperature by changing the ambient between forming gas (10/90% H2/N2) and nitrogen. Using charge pumping, it is observed that H2causes a simultaneous buildup of interface states and decrease of trapped positive charge. The results are explained by a reaction sequence in which H2is cracked to form mobile H+, which under positive bias drifts to the Si/SiO2interface, and reacts to produce a dangling‐bond defect. The rate limiting step over most of the time domain studied is the cracking process. Two types of cracking sites are modeled by molecular orbital calculations: oxygen vacancies (E’centers) and broken bond hole traps (BBHTs). Initial‐ and final‐state energies, as well as the activation energies, are calculated. The calculations indicate that the latter is the more likely H2cracking site. The combined experimental and theoretical results suggest that at least 15% of the trapped positive charge is at sites similar to the BBHT sites. Implications of the model and similarities between interface‐state formation by cracked H2and irradiation are discussed.

ISSN:0021-8979    

DOI:10.1063/1.353348

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Glass particles, having nominal radii of approximately 20 &mgr;m, were deposited onto polyurethane substrates, which had been overcoated with a 5‐&mgr;m‐thick thermoplastic layer, and the surface‐force‐induced contact radii were measured using scanning electron microscopy. It was found that the size of the deformations depends only on the modulus of the coating and not on the modulus of the underlying substrate. The measured contact radii were found to scale with the Young’s modulus of the substrate for the uncoated polyurethane substrates according to the predictions of the JKR model [K. L. Johnson, K. Kendall, and A. D. Roberts, Proc. R. Soc. London Ser. A324, 301 (1971)]. However, the contact radii on the overcoated substrates appear to be more accurately predicted by the DMT theory [B. V. Derjaguin, V. M. Muller, and Yu P. Toporov, J. Colloid Interface Sci.53, 314 (1975)].

ISSN:0021-8979    

DOI:10.1063/1.353349

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Strength of TiB2under plane shock wave loading is assessed in terms of its spall threshold and the shear stress sustained by it under shock compression to 60 GPa. The results of experiments support the thesis that the observed cusp in TiB2at 4.5–7.0 GPa is of mechanical nature and its effect is to decrease the spall threshold values at stresses above the cusp but below the accepted Hugoniot elastic limit (HEL) value of 13–17 GPa. A comparison of shock Hugoniot data on two different TiB2obtained from Grady [Dynamic Material Properties of Armor Ceramics, Sandia Laboratories, SAND 91‐0147. UC‐704 (1991)] and the adiabats constructed from high pressure ultrasonic wave velocity measurements show that these materials sustain increasing shear stresses with increasing values of shock stress. For example, results of data analysis on the denser TiB2show that it sustains around three times the shear stress at 60 GPa than at its HEL, i.e., 17 GPa.

ISSN:0021-8979    

DOI:10.1063/1.353350

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The electrorheological (ER) properties of a model system consisting of oxidized metal particles in an insulating oil are analyzed. It is suggested that previous dc experiments on such systems have failed to reveal strong ER activity because of conductivity effects. Recent experiments by Inoue at 50 Hz excitation appear to have nearly obtained the ultimate strength of the metal‐particle system studied.

ISSN:0021-8979    

DOI:10.1063/1.353351

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The structure of layered materials or substances with depth‐dependent properties is often difficult to investigate with conventional optical or acoustical methods. Since the photoacoustic technique is based on thermal waves, which have other transmission and reflection properties than optical or acoustical waves, it can provide information on samples for which other methods fail. In this work, a straightforward numerical calculation of the photoacoustical signal for samples with a one‐dimensional layered optical and thermal structure is described. An inversion procedure, based on the nonlinear least‐squares fit routineminuitis shown to be very effective for obtaining depth information from the frequency dependence of the photoacoustic signal.

ISSN:0021-8979    

DOI:10.1063/1.353352

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Studies of the diffusion of Ge, Sn, As, and Sb in Si at high donor concentrations provided by phosphorous doping have been performed. It is found that for donor concentrations,CDbelow ∼2×1020cm−3, the diffusivity depends linearly onCD; for doping concentrations above ∼2×1020cm−3, however, the diffusivity increases dramatically with increasing donor concentrations. This behavior has been successfully modeled within the vacancy–percolation model, and it is concluded that collective phenomena play a significant role at high donor concentrations.

ISSN:0021-8979    

DOI:10.1063/1.353324

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The diffusion of P in Si–TaSi2eutectic and silicon single crystal specimens was investigated at a concentration of about 1019atoms cm−3in the temperature range of 767–1227 °C. No definite distinction can be made between diffusion of P in the eutectic structure and in silicon. A nonlinear Arrhenius plot was obtained, indicating a P diffusion enhancement at the lower temperature range. From the linear portion of the Arrhenius line drawn through all the experimental points, an activation energy and pre‐exponential factor of 3.75 eV and 5.7 cm2 s−1were derived, respectively.

ISSN:0021-8979    

DOI:10.1063/1.353325

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Out‐diffusion of oxygen in Czochralski silicon wafers annealed at 1000 and 1200 °C under a hydrogen ambient is studied with secondary ion mass spectroscopy (SIMS). The oxygen diffusivity, 1.41×102 exp(−3.1 eV/kT) cm2 s−1, obtained from fitting the oxygen SIMS profile is significantly larger than normally expected. This hydrogen enhancement effect is found at temperatures much higher than those reported (<500 °C) in literature, and is attributed to the direct interaction between in‐diffused hydrogen and interstitial oxygen atoms. Estimation of the oxygen diffusivity made from hydrogen solubility and diffusivity data is in reasonable agreement with the experimental result. It is suggested that the intrinsic/internal gettering may benefit from the enhancement effect as well as a very low surface oxygen concentration, which is also observed in this work, due to hydrogen treatment.

ISSN:0021-8979    

DOI:10.1063/1.353326

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Diamond was deposited on synthetic graphite, highly oriented pyrolytic graphite and on substrates covered with graphite powder. Scanning electron microscopy and transmission electron microscopy were used to examine the samples. A strong preference for nucleation of diamond on the edges of the graphite sheets was observed. The graphite and the diamond have a preferential orientation relationship in which the diamond (111) plane is parallel to the graphite (0001) plane, and the diamond [11¯0] direction is parallel to the graphite [112¯0] direction. This orientation means that the puckered hexagons in the diamond (111) plane retain the same orientation as the flat hexagons in the original graphite sheet. We conclude that the diamond can nucleate with an epitaxial relationship to the graphite. Some of the edges of the graphite sheets may have been converted to diamond by the atomic hydrogen.  

ISSN:0021-8979    

DOI:10.1063/1.353327

出版商:AIP    

年代:1993

数据来源: AIP