摘要:

Films of fcc Ni3Al with suppressed short‐range order (SRO) were prepared by physical vapor deposition of Ni3Al onto room‐temperature substrates. Extended electron energy‐loss fine‐structure spectra were obtained from both Al Kand Ni L23edges. After the samples were annealed for various times at 150 °C, a moderate growth of SRO was observed in the first‐nearest‐neighbor environments of both the Al and Ni atoms. As prepared, these fcc Ni3Al materials, and presumably others having similar heat evolutions as measured by differential scanning calorimetry, have a high degree of chemical disorder. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359463

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Microstructural study of theC49–TiSi2toC54–TiSi2polymorphic transformation has been performed to elucidate microstructural evolution and possible mechanism of the phase transformation. It has been shown that the nucleation of theC54–TiSi2is heterogeneous, and preferentially takes place at triple grain junctions or grain boundaries. The interphase interfaces betweenC49 andC54 disilicides are often ragged with incoherent characteristics. The growth of theC54 phase is found to proceed by advancing the highly mobile incoherent interfaces in all directions toward the heavily faultedC49 phase. No rigorous orientation relationships are found between the two phases. The microstructural features of the transformation bear some massive characteristics. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359464

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Thermal stress in GaN epitaxial layers with different thicknesses grown on sapphire substrates by metalorganic vapor phase epitaxy using an AlN buffer layer was investigated. Biaxial compressive stress in the GaN layer, due to the difference in the thermal expansion coefficients between GaN and sapphire, was obtained by measuring the curvature of wafer bending, and the observed stress agreed with the calculated stress. In Raman measurements, theE2phonon peak of GaN was found to shift and broaden with the stress as a consequence of the change of the elastic constants with strain. The frequency shift &Dgr;&ohgr; (in cm−1) was obtained for the first time, given by the relation: &Dgr;&ohgr;=6.2 &sgr;, where the biaxial stress &sgr; is expressed in GPa. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359465

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Differential Hall measurement and secondary ion mass spectrometry have been used to characterize the influences of room temperature Si implantation and annealing on the electrical properties ofn‐layers formed by direct implantation into liquid‐encapsulated‐Czochralski grown, Fe‐doped InP substrates. The Si activation is affected by the background Fe level. The anneal‐time influenced the electron mobility near the channel‐substrate interface. Mobility degradation at the interface, present with customary anneal, could be avoided using long time anneal. The mobility changes have been correlated with the changes in the Fe distribution near the interface. The customary anneal‐time introduced an Fe accumulation behindRm, the maximum of the Si profile, followed by an Fe depletion. However, after long time anneals an Fe depletion was created between theRmandRm+2dRpof the Si profile and the Fe accumulation shifted behindRm+2dRp.

ISSN:0021-8979    

DOI:10.1063/1.359466

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We present a study on the nature of diffusion of copper inp‐type porous silicon. The diffusion of evaporated copper in porous silicon and deposition of metal ions in aqueous solution through the porous network was measured by monitoring the metal concentration depth profile as a function of time using Auger electron spectroscopy. We observed that increasing metal penetration from copper evaporated samples correlates with quenching of photoluminescence, in agreement with previous ion quenching results. We extracted a diffusion coefficient from Auger concentration depth profiles which was seven orders of magnitude lower than that expected for diffusion of copper in bulk crystalline Si at room temperature. Deposition of ionic species cannot be characterized as a simple diffusion process. The observed deposition rates were strongly dependent on the solution concentration. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359606

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

A model is presented that explains the yield stress and hardness enhancements that have been observed in superlattice thin films. The stress required for dislocations to glide across layers with different shear moduli was calculated using an expression that accounts for core effects and all interfaces in trapezoidal or sawtooth composition modulations. The predicted strength/hardness enhancement increased with increasing superlattice period &Lgr;, before reaching a saturation value that depended on interface widths. A second mechanism, where dislocations glide within individual layers, was important at large &Lgr; and gave a decrease in strength/hardness with increasing &Lgr;. The combination of these two mechanisms gives a strength/hardness maximum versus &Lgr; in good quantitative agreement with experimental results for nitride and metal superlattices. The results indicate that superlattice strength/hardness depends strongly on interface widths and the difference in shear moduli of the two components for &Lgr; values below the maximum, and on the average shear modulus for larger &Lgr;. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359467

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Stability and formation kinetics of TiN and silicides in Ti/Si3N4and TiN/Si diffusion joints have been investigated. Reactions in the diffusion couples were studied experimentally in the temperature range between 950 and 1100 °C. Isothermal sections and activity diagrams of the Ti‐Si‐N system were calculated using the recent thermodynamic data. Both the thermodynamic calculations and experimental results indicate that TiN and Si react with each other and form TiSi2and even Si3N4if the activity of nitrogen is high enough. Similarly, results from the Ti/Si3N4couple were in good accordance with calculated phase equilibria. The experiments carried out in vacuum ampoules and in a vacuum furnace showed that the gas phase has a strong effect on the reactions. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359468

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The semimetal‐semiconductor HgTe/CdTe (p‐type) graded heterostructures were formed by the epitaxial growth of HgTe on ⟨111⟩‐oriented CdTe substrates using metal‐organic chemical‐vapor‐deposition. These graded heterostructures are lattice matched, have a high degree of structural perfection, and the semimetallic HgTe provides both the high electron affinity and high carrier concentration required for ohmic contacts. Unlike the abrupt HgTe/CdTe heterostructure which is rectifying due to the valence‐band offset and interface charges that reside on the polar surfaces of ⟨111⟩‐oriented CdTe, the graded heterostructures form ohmic contacts. The contact specific resistance can be as low as 0.4 &OHgr; cm2and is determined by the transmission line method on HgTe/Ti/Au stripes processed by ion‐beam milling (on CdTe bulk with resistivity of 10 &OHgr; cm). The contacts are characterized electrically by current‐voltage and dynamic resistance‐voltage characteristics. Auger depth profile and morphology of contacts grown on the A and B faces are compared. Double‐crystal rocking curves characterize the structural perfection of the heterostructure. Numerical calculation of the band diagram of the graded heterostructure, which is reported, indicates that the contact resistance may be strongly affected by the grading width as well as the exact distribution of the doping level across the heterostructure. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359469

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The growth kinetics of an amorphous interlayer (a‐interlayer) formed by solid‐state diffusion in ultrahigh‐vacuum‐deposited polycrystalline V thin films on (001)Si have been investigated by conventional and high‐resolution transmission electron microscopy. The growth was found to follow a linear growth law initially in samples annealed at 430–465 °C. The growth then slows down and deviates from a linear growth law as a critical thickness of thea‐interlayer is reached. The activation energy of the linear growth and maximum thickness of thea‐interlayer were measured to be 1.1±0.3 eV and 4.5 nm, respectively. The correlations among differences in atomic size and electronegativity between metal and Si atoms and activation energy of the linear growth, critical and maximuma‐interlayer thickness, the calculated free‐energy difference in forming the amorphous phase, as well as atomic mobility in Ti/Si, Zr/Si, Hf/Si, Ta/Si, Nb/Si, and V/Si systems are discussed. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359470

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

A laser‐based ultrasonic technique, impulsive stimulated thermal scattering (ISTS), is used to characterize the acoustic waveguide behavior in a series of silicon‐supported and free‐standing polyimide bilayer structures. The experimental results demonstrate that multilayer structures are characterizable using ISTS measurements. In addition, simulations of acoustic waveguide behavior in coatings with very thin interfacial layers adjacent to the substrate and in films with continuously changing elastic properties are presented. The results indicate depth‐profiling possibilities using ISTS. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359471

出版商:AIP    

年代:1995

数据来源: AIP