摘要:

Lattice constants of GaAs layers grown by molecular beam epitaxy were examined by using the high resolution x‐ray diffractometer. For highly doped samples (up to 9×1018cm−3of free‐electron concentration) we observed an increase of the lattice constant with respect to the undoped layers. Since substitutional silicon atoms decrease the lattice constant of GaAs, the results are explained by the influence of free‐electrons via the deformation potential of the &Ggr; minimum of the conduction band. The best fit to our diffractometric data was obtained for the band‐gap deformation potential equal to −8.5 eV. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.115181

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The thermal and plasma‐assisted nitridation of GaAs(100) using NH3has been examined employing x‐ray diffraction, Auger electron spectroscopy, and atomic force microscopy to characterize the nitrided films. All thermally nitrided films were composed of a mixture of hexagonal and cubic GaN, whereas the addition of plasma excitation produced films purely of the cubic structure. Thicknesses of the thermally nitrided films, up to 7000 A˚, increased with both increasing temperature and nitridation time. The plasma‐assisted process holds promise for the formation of templates for homoepitaxial growth of cubic GaN. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.115182

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The oxide superconductor Bi1.7Pb0.3Sr2−xAgxCa2Cu3Oyhas been synthesized under the ordinary pressure. The x‐ray diffraction spectra of these specimens show the presence of only 2212 phase whenx<0.4, and the transition temperature achieved 99 K. With thexincrease, the structure of sample transfers to 2223 phase. The investigation indicates that substitution of Sr2+by Ag1+increases the distance between layers. This may respond toTcincrease in 2212 phase and 2223 phase form at a relatively low temperature. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.115183

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

This letter reports the nitridation of GaAs surfaces using N2through a hot tungsten filament. After nitridation, GaAs cap layers were grown by molecular beam epitaxy to form GaAs/GaN/GaAs structures. For these structures, we determine the sheet nitrogen atom concentration by secondary ion mass spectrometry analysis. The sheet nitrogen atom concentration is proportional to the square root of the N2pressure, indicating that N2molecules are decomposed into nitrogen atoms to adsorb on the GaAs surfaces. The activation energy of this decomposition process is 3.6±0.4 eV. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.115184

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

YBa2Cu3O7−&dgr;thin films patterned in the form of a meander line resonant structure, are used as a sensitive probe of vortex dynamics at microwave frequencies. The experiments enable highly sensitive measurements of the complex microwave surface impedanceZs(&ohgr;,T,H) of YBa2Cu3O7−&dgr;as a function of applied dc magnetic field, temperature, and frequency. TheZs(H,T) versusHdata yield direct experimental results for the vortex viscosity and pinning force constant, which are compared with microscopic theory. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.115166

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The formation of YBa2Cu3O7−y(YBCO)/BaTiO3(BTO)//SrTiO3(STO) (100) and BTO/ YBCO//STO(100) bilayer structures is demonstrated for the construction of a superconductor ferroelectric field transistor. The resulting films of the bilayers have highlyc‐axis oriented structure. Epitaxial YBCO films formed on the BTO//STO(100) have a zero resistance temperature of 88.9 K. The surface morphology of the epitaxial BTO films on the YBCO//STO is very smooth with a mean surface roughness of 32 A˚. Moreover, the Au/BTO/YBCO structures have been fabricated, and the dielectric constant and remanent polarization of BTO layer are obtained to be 180 and 3.5 &mgr;C/cm2at 77 K, respectively. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.115167

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Colossal magnetoresistance in excess of 106% has been obtained (at 110 K,H=6 T) in epitaxially grown La–Ca–Mn–O thin films. The as‐deposited film exhibits a substantial magnetoresistance value of 39 000%, which is further improved by heat treatment. The magnetoresistance is found to be strongly dependent on film thickness, with the value reaching the maxima at ∼1000 A˚ thickness, and then reduced by orders of magnitude when the film is made thicker than ∼2000 A˚. This behavior is interpreted in terms of lattice strain in the La–Ca–Mn–O films. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.115168

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

20 keV N+ions have been implanted on57Fe enriched Fe films and RF deposited on glass and NaCl substrates with various fluences up to 3.0×1016N+/cm2. Conversion electron Mossbauer spectroscopy and transmission electron microscopy measurements performed at room temperature on the as‐implanted samples reveal the presence of &agr;‐Fe, &agr;′‐martensite, and &egr;‐Fe3−xN phases. &agr;″‐Fe16N2is only detected after a subsequent annealing at 220 °C; &agr;′‐martensite with a low nitrogen content appears as the precursor of &agr;″, The additional nitrogen content needed for this process is supplied by the &egr; phase. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.115169

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Nanostructured isotropic Nd–Fe–B magnets with enhanced remanence were produced by hot compaction of mechanically alloyed Nd–Fe–B powders at temperatures of about 600 °C. Phase formation occurred during hot pressing without significant grain growth. The microstructure is a two phase nanocomposite of hard magnetic Nd2Fe14B and soft magnetic &agr;‐Fe with an average grain size of about 20 nm. These small dimensions allow effective exchange interactions between hard and soft magnetic grains and result in an enhancement of the remanence by more than 30% above the Stoner–Wolfarth limit expected for noninteracting single domain particles. So far, the best results are a remanence of 1.0 T, an energy density of 121 kJ/m3, and a coercivity of 4.2 kA/cm for a Nd–Fe–Co–Si–B magnet. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.115170

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Ge0.5Si0.5strained‐layerpinphotodiodes, in which multiple strained layers serve as the absorption region, have been fabricated. These devices exhibit an optical response at wavelengths beyond 1.3 &mgr;m at normal incidence. The measured external quantum efficiencies at an applied bias of 4 V are 17% at 0.85 &mgr;m and 1% at 1.3 &mgr;m, respectively. Excellent electrical characteristics evidenced by the avalanche breakdown at 20 V have also been demonstrated. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.115171

出版商:AIP    

年代:1995

数据来源: AIP