摘要:

An experimental method for determining the diffusivity of point defects as a function of hydrostatic pressure has been developed by using synchrotron-radiation topography. In this method, the diffusivity can be obtained fromin situobservations of dislocation climb under hydrostatic pressure. The climb motion of dislocations is caused by a rapid change in temperature which introduces supersaturation (or undersaturation) of the point defects. The method has been applied to ice, and diffusion coefficients of self-interstitials were successfully determined up to 100 MPa.

ISSN:0950-0839    

DOI:10.1080/09500839108206593

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Model experiments have been conducted on a series of alumina samples in which the microstructures have been tailored to conform to the classical configurations depicted in the models of final-stage sintering. Simultaneous measurements of sintered density, grain size, pore number density and pore size distribution were made as a function of sintering time at constant temperature (18500C). The data conformed to a model of grain-boundary-diffusion-controlled densification. Atom flux equations for grain-boundary diffusion transport and lattice diffusion transport were deduced from the data. The number of pores per unit volume was identified as the most critical factor influencing densification kinetics.

ISSN:0950-0839    

DOI:10.1080/09500839108206594

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

The mechanical stress in thermal SiO2–Si structures exposed to a radiofrequency hydrogen plasma has been investigated. It was found that the compressive oxide stress is released and a small tensile stress appears, which is consistent with a previously observed annealing of a built-in oxide charge. This result applies for oxides with a thickness of about 40nm and above and an oxidation temperature in the range of 850 to 1050°C

ISSN:0950-0839    

DOI:10.1080/09500839108206595

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

The microstructure of as-received and post-annealed SiC whiskers were investigated by transmission electron microscopy. In the as-received SiC whiskers, the thinner β-SiC parts were jointed with the one-dimensional disordered parts by {111}, twin boundaries. After annealing, β-SiC parts became coarser than the one-dimensional disordered parts at 1900°C and then disappeared at 2000°C.

ISSN:0950-0839    

DOI:10.1080/09500839108206596

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

A new misfit dislocation multiplication process has been observed for the first time in InxGa1−xAs/GaAs strained-layer superlattices (withx<0.20). Transmission electron microscopy reveals that this process is based on the occurrence of interactions between perpendicular 60° misfit dislocations with identical Burgers vectors and cross-slip events on the resulting dislocation configurations. The last stage of the process involves the operation of Frank-Read sources that emit glissile dislocations into the {111} planes; parts of the half-loops which develop towards the superlattice are parallel to the interface and are then new misfit dislocations.

ISSN:0950-0839    

DOI:10.1080/09500839108206597

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

The utility of Patterson transforms applied to higher-order Laue zone (HOLZ) reflections in convergent-beam electron diffraction (CBED) patterns from unknown crystal structures is discussed. For HOLZ diffraction from molecular Bloch states located on subsets of atom strings, the transforms contain sharp peaks defining accurate interatomic vectors. As an example, the HOLZ Patterson transforms for two metastable Al–Ge phases are described, where the rhombohedral phase (space group R&3bar;c) is probably isostructural with Zn4Sb3and a monoclinic phase (space group P21/c) has a new polyanionic structure with tetrahedral coordination of Al by Ge.

ISSN:0950-0839    

DOI:10.1080/09500839108206598

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

We report, for the first time, the formation of the icosahedral phase (i-phase) in rapidly quenched Ti73-xV27Sixalloys, where 13 ≤ × ≤ 25. Transmission electron microscopy (TEM) lattice image studies show that the i-phase occurs with b.c.c. phase of large unit cell. Diffraction studies demonstrate that the two phases are coherently related; the cubic ⟨001⟩ directions are parallel to three of the two-fold icosahedral axes, the ⟨111⟩ directions are parallel to the threefold icosahedral axes and the ⟨530⟩ cubic directions are nearly parallel to the fivefold directions. The b.c.c. lattice constant, a0= 12·98 Å, is related to he quasilattice constant, 4·72 Å, suggesting different projections from the same six-dimensional cubic lattice. These observations demonstrate the similarity of these two structures. A determination of the atom locations in this crystalline phase should provide information of the atomic positions in the icosahedral phase.

ISSN:0950-0839    

DOI:10.1080/09500839108206599

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

A new tetragonal phase with lattice parametersa=9·07 Å andc=21·9 Å has been discovered by electron diffraction. The space group determined by combining conventional and convergent beam electron diffraction is I4/mmm. The approximate composition obtained from X-ray dispersive analysis is Al80Cu5Fe15. It coexists with an incommensurate composite phase which consists of two subcells. The sublattice parameters area1=a,c1≈1/7c=3·14 Å anda2=a1/$$2,c2=3·71 Å. The structural and compositional relationships between the incommensurate phase and the commensurate phase are discussed.

ISSN:0950-0839    

DOI:10.1080/09500839108206600

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

The travelling wave technique was used to measure the drift mobility of photoexcited carriers in a-Si:H from 1·6 to 300 K. Above 100 K the drift mobility increases with temperature as expected from multiple trapping theories. Below 100K the measured signal increases with decreasing temperature reaching values that, if interpreted as drift mobility, exceed 07middot;2 cm2V−1s−1at 1·6 K. The results are qualitatively consistent with the large drift mobilities measured at low temperatures by the time-of-flight technique. The drift mobility increases linearly with travelling wave frequency below l00 K but is independent of frequency above 100 K. However, the interpretation of the low-temperature signal as drift mobility is in doubt because the sign of the signal below 100 K, which should indicate the sign of the dominant carrier, is instead determined by the orientation of theyaxis of the LiNbO3plate used to generate the travelling wave. This indicates a heretofore unknown interaction of the travelling wave with the semiconductor that is dominant below 100 K.

ISSN:0950-0839    

DOI:10.1080/09500839108206601

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

ISSN:0950-0839    

DOI:10.1080/09500839108206602

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor