摘要:

Poly(vinylidene fluoride) form II is transformed to polar II under a high electric field. Servet and Rault [J. Phys. (Paris)40, 1145 (1979)] found few weak so‐called superlattice spots on the fiber diagram of polar II. In the present study these spots are clarified to arise from a new form, which is considered to be the intermediate structure between polar II (TGTG¯)nand form I (T)n, a conformationally incommensurate structure.

ISSN:0021-8979    

DOI:10.1063/1.344963

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The interactions of deuterium with ion‐irradiated SiO2on Si were investigated during annealing in D2gas and vacuum over the temperature range 373–1273 K. The uptake and release of D by the oxide layer were monitored using the ion‐induced nuclear reaction D(3He,p)4He. Results were analyzed in terms of a new mathematical model which describes the diffusion of atomic D and molecular D2in conjunction with trapping at irradiation defects via SiD and OD bonding. The combined body of experimental data on release is quantitatively described by the model using fitted binding enthalpies of 2.8 eV for the Si‐D interaction and 3.2 eV for the O‐D coupling. The model predicts a relationship between the activation barriers for trapping and detrapping which is in semiquantitative agreement with the experimental data on uptake. The same relationship is obeyed by independently reported results on the hydrogen passivation and reactivation of Si‐dangling‐bond defects at the SiO2‐Si interface.

ISSN:0021-8979    

DOI:10.1063/1.344964

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

A qualitative analysis of the mechanical response caused by smooth attenuating wave fronts and by continuous attenuating wave fronts degrading in rate‐dependent media is performed by an underdetermined system of equations, that is, by equations of conservation of mass and momentum only. Degradation is defined as the decrease of the number of partial waves in a smooth wave front or of independent waves in a continuous wave front. For the smooth wave front the inceptive wave front with which the degradation commences is a wave that is composed of four partial waves found previously and named a contraction wave, mesocontraction waves I and II, and a rear rarefaction wave. The analysis reveals one possible degradation process that is caused by another rarefaction wave which first follows the rear wave and then outruns the rear wave, mesocontraction waves II and I in sequence. The continuous wave degrades from the inceptive continuous wave front which is composed of four independent waves found previously and named a contraction wave, degenerate contraction waves I and II, and a rear rarefaction wave. The analysis indicates that degradation from the inceptive wave front to the contraction wave is possible to progress in six different patterns. In short, the degradation can occur through six different processes. Each process gives rise to four different sets of strain, particle velocity, and stress profiles, and accordingly four different types of stress‐strain paths and four different types of stress‐particle velocity paths. The stress‐strain paths induced during some of the processes are similar to the paths in sandstone computed by Seaman using the Lagrangian analysis. The stress‐particle velocity paths induced during some of the processes are also similar to the paths in LASL graphite computed by Seaman.

ISSN:0021-8979    

DOI:10.1063/1.344965

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The molecular structural changes induced in sputtered fluoropolymer film by tribological effects is pursued using polarized micro‐Fourier‐transform‐infrared (micro‐FTIR) spectroscopy. Hydrogenation of the carbon radicals produced by CF or CC bond cleavage is detected in the mildly rubbed region, together with C&squflg;C bond formation. Polarization measurements reveal that a rigid C&squflg;C‐bond‐rich framework is oriented along the sliding direction in a hardly rubbed region. This rigid carbon framework involves CF bonds with low polarizability. This structure greatly contributes to stable lubrication with a low friction coefficient, after the fluctuating lubrication characteristics that occur in the early rubbing stage have stabilized. These molecular structures are decomposed into C 3/4 C and C&squflg;C&squflg;C bonds through further elimination of CF moieties by abrasive hard rubbing by all means. Finally, they extremely decompose into amorphous carbon and metal carbide under severe conditions involving the reactive metals which appear after the film molecules are worn out.

ISSN:0021-8979    

DOI:10.1063/1.344966

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

An expression in the literature has been used to determine the spall strength of materials from measurements of the surface velocity on reflection of a nonsteady shock wave. It uses initial density, the sound speed, and the difference between the initial surface jump‐off velocity and the minimum in the velocity seen when the spall shock reaches the surface. Workers using the expression have found it necessary to choose the sound speed carefully in order to get reasonable results. It is shown that this is due to the inadequacy of the acoustic approximation used to represent the release isentrope. Approximation of the release isentrope by the Hugoniot makes it unnecessary to use special velocities and gives better agreement with experiment.

ISSN:0021-8979    

DOI:10.1063/1.344967

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The correlation between the surface crosshatched morphology and the interfacial misfit dislocations in strained III‐V semiconductor heteroepitaxy has been studied. The surface pattern is clearly seen on samples grown at high temperature (520 °C) and those with small lattice‐mismatched (f<2%) systems. A poorly defined crosshatched morphology was found on layers grown at relatively low temperature (400 °C). As the lattice mismatch of the strained layer becomes larger than 2%, a roughly textured surface morphology is commonly observed in place of actual cross‐hatching. Few threading dislocations are observed in the strained layer when the crosshatched pattern develops. It is also noted that the surface crosshatched pattern develops after the majority of the interfacial misfit dislocations are generated. The result suggests that the surface crosshatch pattern is directly related to the generation of interfacial misfit dislocations through glide processes.

ISSN:0021-8979    

DOI:10.1063/1.344968

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Epitaxial alignment has been obtained by means of grain growth in polycrystalline films deposited on single‐crystal substrates. A theory for epitaxial grain growth is outlined and results given for experiments on Au, Al, Cu, and Ag films on vacuum‐cleaved NaCl, KBr, KCl, or mica. Epitaxial grain growth provides a fundamentally different alternative to conventional epitaxy, and can lead to very thin films with improved continuity and crystalline perfection, as well as non‐lattice‐matched orientations.

ISSN:0021-8979    

DOI:10.1063/1.344969

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Results obtained by x‐ray diffractometry, topography, and curvature measurements made with a quadruple‐crystal x‐ray diffractometer used in (+,−,+) setting and as a Lang system are reported. About 0.1‐mm‐thick semi‐insulating (SI) (Cr‐compensated) andn‐type wafers with dimensions ∼10×10 mm2or less were used. The metallizations were (i) Ge‐Ni‐WSi2‐Au and (ii) Ge‐Au‐Ni‐WSi2‐Au, with layer thicknesses as follows: Ge: 20 nm; Au: 5 nm; Ni: 10 nm; WSi2: 100 nm; and Au: 100 nm. Both types of metallizations were deposited onn‐type crystals, whereas only the second type was used with SI wafers. Diffraction curve half‐widths of the wafers without deposits were in the range 15–22 arcsec (SI) and 18–30 arcsec (ntype). Radii of curvature (R) were around 6 and 3 m for SI andn‐type crystals, respectively. Topographs showed low defect density. Metallization decreased the level of perfection and enhanced curvature. Diffraction curve half‐widths increased up to 155 arcsec (SI) and 180 arcsec (ntype). High‐strain field and bandlike features were observed in topographs, indicating nonhomogeneous distribution of strain.Rvalues decreased to 0.8 m (SI) and 0.3 m (ntype). These correspond to stress values of 1.7×1010and 4.5×1010dyn cm−2, respectively. Anisotropy inRvalues was studied by changing diffracting planes. Lattice planes parallel to the metallization were also curved, but in small regions the degree of perfection was high. The five‐layered metallization produced more stress inn‐type crystals in comparison to the other deposit.

ISSN:0021-8979    

DOI:10.1063/1.344970

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

We have used transmission electron microscopy to investigate CdTe(111) grown on GaAs(100) by molecular‐beam epitaxy. The loop structure previously observed by photoluminescence microscopy has been identified as the boundary between twinned microcrystallites that extend from the CdTe/GaAs interface to the CdTe surface. When viewed along the growth axis, these boundaries between the columnar twins appear as loops and segments. Surface roughness of the GaAs substrate contributes to the initial growth of twinned material. This leads to competitive growth between the twins and the creation of the observed columnar twins.

ISSN:0021-8979    

DOI:10.1063/1.344971

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The formation and release of hydro‐ and deuterocarbons from pyrolytic graphite bombarded with 6‐keV H+3ions and subsequently with 6‐keV D+3ions as well as vice versa have been investigated using a quadrupole mass spectrometer (QMS) at a target temperature of 500 °C. For both cases the signal intensities of masses 17 (CHD2,CH3D) and 19 (CHD3) first increased and then decreased with increasing the fluence of subsequent bombardment. A similar tendency was also observed in those of masses 29 (C2H3D, C2HD2) and 31 (C2HD3). These results indicate that the mixing of hydro‐ and deuterocarbons, forming CHmDnand C2HmDn, occurs during the subsequent bombardment. A simple calculation of QMS signal intensities has been performed, assuming that the fully saturated hydro‐ and deuterocarbons (CH4, C2H2, and C2H4types) are formed and then released, and that their radicals are only produced through cracking in the ion source of QMS. The calculated results qualitatively agreed with the measured ones. They suggest that the mixing of hydro‐ and deuterocarbons becomes maximum when the product of the local H and D concentrations has the maximum value, and that the mixing mainly takes place around the depth at which the H and D profiles mostly overlap.

ISSN:0021-8979    

DOI:10.1063/1.344972

出版商:AIP    

年代:1990

数据来源: AIP