摘要:

A recently formulated porous interface layer model is employed to study the influence of bond defects particularly due to the presence of voids in interface zones on Lamb wave propagation in a laminate made of two identical fiber‐reinforced laminas. The model is developed making use of the mathematical theory of linear elastic materials with voids to describe the interface zone−the adhesive with its minute separation from the adherent laminas. Theoretical Lamb‐mode dispersion spectra in a symmetric bilaminate made of boron fiber‐reinforced aluminum sheets are obtained and compared with those obtained assuming perfect bond condition. It is hoped that the model will facilitate ultrasonic nondestructive evaluation of bond strengths in composite laminates.

ISSN:0021-8979    

DOI:10.1063/1.350414

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

A complete dislocation analysis on a large number of grown‐in dislocations was performed on wafers taken from three different semi‐insulating liquid encapsulation Czochralski GaAs single crystals. By determining the Burgers vector, line direction, and habit plane of nearly 800 dislocations a decision could be made on dislocation type, dislocation generation, and multiplication mechanisms. Taking into account possible dislocation reactions between stress‐induced glide systems all detected glide systems could be explained. The influence of post‐growth annealing on both dislocations and arsenic precipitates was also investigated. Little effect was found on dislocations. Arsenic precipitates, however, showed a different distribution in size and significant effects on fine structure giving information on their nucleation and growth mechanisms.

ISSN:0021-8979    

DOI:10.1063/1.351346

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

The mechanical effects due to the application of multiple laser pulses to thin metallic films are studied. Particular attention is paid to systems involving thin aluminum films deposited on an insulating substrate such as silica. This film/substrate combination is widely employed in silicon semiconductor technology. In building such devices laser energy is sometimes used for the purpose of cutting conducting lines, while in other applications it is used to effect linking between two levels of metallization. Both processes have been greatly facilitated by employing a multiple‐pulse scheme. The mechanism responsible for this effect is discussed and it is shown how the present model leads to a good agreement between the measured and calculated quantities.

ISSN:0021-8979    

DOI:10.1063/1.351347

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

The epitaxial realignment of undoped and As doped polysilicon films onto crystalline silicon substrates induced by high‐temperature rapid‐thermal annealing has been investigated. It is shown that the realignment mode and the kinetics of the process are intimately related to the microcrystalline structure of the layers under investigation, to the morphology of the native oxide film present at the interface, and to the presence of As atoms dispersed in the deposited layers. For layers having fine grain dimensions, compared to the film thickness, the realignment takes place via the motion of the crystal‐polysilicon interface towards the surface. This is observed in undoped layers and in layers which have been subjected to a high‐temperature anneal before As doping. The preimplant anneal disrupts the interfacial oxide film and reduces the thermal cycle needed to complete the realignment of the polysilicon layers. In layers which have not experienced any thermal treatment before As doping, it is seen that the grain size first increases to dimensions on the order of the film thickness, and the realignment transformation then proceeds by lateral growth of epitaxial columns in a manner similar to secondary grain growth. The kinetics of both realignment modes are thermally activated and the atomic limiting processes have been tentatively identified to be As diffusion in bulk Si for As doped layers and Si self diffusion for undoped films. The effect of the microcrystalline structure on the realignment kinetics is attributed to its relationship with the driving force governing the realignment transformation.

ISSN:0021-8979    

DOI:10.1063/1.351348

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Amorphous Si films containing crystal seeds can be converted to a polycrystal by an ion beam with heating at 350 °C on silica glass substrates, and the density of the crystal grain is almost the same as that of the initial seed. However, the size and density of the crystal seed decrease when the ion irradiation is performed without external heating. The average grain size in the completely crystallized film can be controlled by decreasing the crystal seed density before crystallization. The growth process of crystal grains (average grain diameterRand standard deviation &sgr;R) is reported and the gradient &Dgr;&sgr;R/&Dgr;Ris estimated to be about 0.15. A model calculation is performed to estimate the gradient on the assumption that the growth rate is governed by the plane (111) crystallization and the calculated value is 0.05.

ISSN:0021-8979    

DOI:10.1063/1.351349

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Thermal stability of polycrystalline NiSi2on high‐dose BF+2‐, Si+‐, B+‐, F+‐, As+‐, and P+‐implanted (001) Si has been studied by both cross‐sectional and plan‐view transmission electron microscopy as well as by sheet resistance measurements. The surface coverage and grain size of polycrystalline NiSi2were found to be significantly influenced by the implantation species in silicon substrate. In Si+‐, B+‐, As+‐, and P+‐implanted samples, agglomeration of NiSi2became very severe after 800 °C, 1‐h annealing. The average grain sizes were larger than 0.5 &mgr;m. In contrast, almost full surface coverage was found in F+‐ and BF+2‐implanted samples after 900 °C, 1‐h annealing. The growth of laterally uniform NiSi2and resistance to agglomeration at high temperatures in BF+2‐ and F+‐implanted samples are attributed to the retardation of the growth of NiSi2grains by the presence of fluorine bubbles at the grain boundaries. Sheet resistance data were found to correlate well with the morphological and microstructural observation.

ISSN:0021-8979    

DOI:10.1063/1.351350

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

The electrical activity of Zn in heavily doped InP crystals grown by the liquid‐encapsulated Czochralski technique has been studied through annealing experiments. When the wafers were annealed at 650 °C, the saturated hole concentration increased as the cooling rate after the heat treatment increased. Annealing at 400 °C led to a reduction in the saturated hole concentration, which was not dependent on the cooling rate after the heat treatment. Some defect reactions at 400 °C would account for this phenomenon. The experimental results of the saturation of the hole concentration may be explained in terms of a defect state whose nature depends on the Fermi level position, as has been suggested by Walukiewicz [Appl. Phys. Lett.54, 2094 (1989)].

ISSN:0021-8979    

DOI:10.1063/1.351351

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

X‐ray diffraction study of smectic‐C* layer orientation in surface stabilized cells filled with fluorinated ferroelectric liquid crystals show chevron layer structure. The chevrons remain unperturbed up to a field of 12.5 × 106V/m while optical observations suggest uniform switching at low fields, and nucleation and growth mediated switching at high‐field strengths.

ISSN:0021-8979    

DOI:10.1063/1.351352

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

The damage in epitaxial CoSi2films 500 nm thick grown on Si(111) produced by room‐temperature implantation of 150 keV28Si were investigated by 2‐MeV4He channeling spectrometry, double‐crystal x‐ray diffractometry, and electrical resistivity measurements. The damage in the films can be categorized into two types. In lightly (heavily) damaged CoSi2the damage is in the form of point‐like (extended) defects. The resistivity of lightly damaged CoSi2films rises with the dose of implantation. Electrical defects correlate well with structural ones in lightly damaged films. The resistivity of heavily damaged films flattens off while the structural defects continue to rise with the dose, so that resistivity no longer correlates with structural defects. Upon thermal annealing, lightly damaged films can fully recover structurally and electrically, whereas heavily damaged films do so only electrically. A residual structural damage remains even after annealing at 800 °C for 60 min.

ISSN:0021-8979    

DOI:10.1063/1.351325

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Solidification of selected Mn‐Al‐C alloys during containerless levitation and rapid quenching has yielded the first report for a ferromagnetic metastable &tgr; (L10) phase formed directly from the melt. Complete solidification to &tgr; phase was interrupted by the competitive evolution of an equilibrium &egr; phase during recalescence. The amount of undercooling required to produce the metastable ferromagnetic &tgr; phase in a Mn0.55Al0.433C0.017alloy during solidification was estimated as approximately 470 K based on differential thermal analysis results. When the alloy carbon content was increased to 3.4 at. % (i.e., Mn0.55Al0.416Co0.034alloy), a transition in structure development occurred so that the samples exhibited &ggr;2phase formation as well as &tgr; and &egr; phases. Both microstructural observations and x‐ray diffraction examination were used to guide the interpretation and the analysis of solidification pathways. The attainment of the high liquid undercooling required to nucleate the metastable &tgr; phase from the melt may be facilitated by containerless processing.

ISSN:0021-8979    

DOI:10.1063/1.351326

出版商:AIP    

年代:1992

数据来源: AIP