摘要:

The effects of electron beam irradiation on luminescence and microstructure ofn‐type porous silicon (PS) have been investigated, using cathodoluminescence (CL) in the scanning electron microscope (SEM), and electron energy loss spectroscopy in the transmission electron microscope (TEM). In the SEM, the CL rapidly decreased with irradiation. It could be fully restored by boiling the samples in de‐ionized water. In the TEM, freshly restored PS emerged as Si nano‐crystallites embedded in an unstable silicon oxide. The effect of irradiation was to suppress the oxide, and also, in the case of proximity of carbon from the foil holding the sample, to change the crystallite composition to &bgr;‐SiC. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.113886

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We report the demonstration of demultiplexing of 150 fs pulses, without pulse breakup, in an AlGaAs nonlinear directional coupler operated at photon energies below half the band gap energy of AlGaAs. ©1995 American Institute of Physics. 

ISSN:0003-6951    

DOI:10.1063/1.113887

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

A thin palladium layer (∼40 A˚) was selectively formed on top of amorphous silicon films before annealing and the effects of palladium layer on the crystallization behavior of the amorphous silicon films were investigated. It was observed that the amorphous silicon right under the Pd layer could be crystallized to grain sizes of several hundred angstroms by annealing at 500 °C. In addition, the area between the Pd thin pads, patterned by lithography, was found to be crystallized to grain sizes of a few tens of microns in length by the same annealing. Such lateral crystallization was found to reach more than 100 &mgr;m in some cases. The lateral crystallization phenomenon might be useful for the fabrication of low temperature polycrystalline‐Si thin film transistors, providing large‐grained Si films. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.113888

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Incorporation of Fe in YBa2Cu3O7−&dgr;matrix during its epitaxial growth on (001) LaAlO3by pulsed excimer laser ablation is examined. It is shown that oxygen pressure during deposition plays a critical role in the incorporation process and that a low‐temperature postsynthesis annealing is essential for complete substitution. Clustering of iron atoms and its control via the anion controlled reactions are identified as the key features in this context. It is also shown by using atomic force microscopy that Fe incorporation influences the surface morphology. These issues are of importance in the formation of cationic defects in multicomponent thin films. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.113889

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Strong Fiske type resonance peaks have been observed in current–voltage curves ofmtsp;YBa2Cu3O7step edge junctions onmtsp;LaAlO3substrates. We determined effective shunting capacitances from the voltages of the resonances. These data compare well with those obtained from the McCumber constantmtsp;&bgr;c. Typical values of the shunting capacitance per unit area for these junctions were estimated to be in the range of 20–30mtsp;fF/&mgr;m2. The surface resistance normalized to 1 GHz at the conjugating junction interfaces was estimated to be in the range of 1–3 &mgr;&OHgr;. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.113890

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We have measured the noise of YBa2Cu3O7−&dgr;superconductor‐normal‐superconductor (SNS) junctions whose high normal‐state resistances and characteristic frequencies make them suitable for THz frequency mixers. By directly measuring the 1 GHz power spectral density delivered to a low‐noise 50 &OHgr; radiometer system, the noise could be measured over a wide range of dc voltage and temperature, without complications due to 1/fnoise, and without invoking any specific model. At a physical temperature of 4 K, the lowest noise junction had an available noise temperature of 31±2 K, corresponding to an effective noise temperature of the normal resistance of 9 K. The effective noise temperature of the normal resistance is approximately equal to the physical temperature at high temperatures, but approaches a limiting value at low temperatures, implying an excess current noise of unknown origin.

ISSN:0003-6951    

DOI:10.1063/1.113891

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We have imaged the magnetic domain structure of several heterogeneous CoxAg1−xalloys by using scanning electron microscopy with polarization analysis. These images show that extended domain structures exist in both the as‐deposited samples and in samples annealed at moderate temperatures. This suggests that a significant fraction of the cobalt in these materials does not contribute to the giant magnetoresistance. Only those samples annealed at 600 °C and containing less than 40% cobalt by volume show no domain structure. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.113892

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Three‐dimensional atom probe (3DAP) was employed to study nanoscale compositional heterogeneities in Co‐22 at. %Cr sputter‐deposited thin films. Compositional fluctuations were visualized on a nanometer scale through a 3D reconstruction of collected atoms. Transmission electron microscopy observations of the same specimen area of before and after 3DAP analysis made it possible to scale the analyzed volume precisely. The resulting data show that a Co‐22 at. %Cr thin film sputter deposited at elevated temperature was composed of two phases with a lamellarlike structure, one phase was ferromagnetic containing approximately 90 at. %Co, and the other was paramagnetic, containing approximately 60 at. %Co. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.113893

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The influence of sample preparation on the resistivity and magnetoresistance (MR) behavior of doped manganese oxides has been studied. Two systems, Nd0.7Sr0.3MnO3−&dgr;and La0.67Ba0.33MnO3−&dgr;thin films, have been chosen for this study. The former has the largest reported MR ratio at 60 K and the latter has a large MR ratio at room temperature. Two processes, deposition at a high temperature and annealing at a high temperature, have opposite influences on the resistivity behavior of these films. The results suggest that oxygen stoichiometry and diffusion are important factors in causing the behavior observed in doped manganese oxide films. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.113894

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Equiatomic CoPt and FePt alloy films were deposited by cosputtering at substrate temperatures between 25 and 640 °C. Those deposited at high temperatures (≥400 and ≥520 °C for FePt and CoPt, respectively) contained ordered intermetallic compounds with theL10crystal structure while those deposited at lower temperatures were chemically disordered. Deposition on single crystal [001] MgO and [0001] Al2O3resulted in [001] and [111] oriented films, respectively, for all deposition temperatures. Ordered alloys have out‐of‐plane magnetic easy axes and modified magneto‐optic Kerr rotation spectra relative to the disordered case. A difference in the Kerr rotation spectrum is observed between ordered, but not disordered, [001] and [111] films. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.113895

出版商:AIP    

年代:1995

数据来源: AIP