摘要:

In this letter we report the molecular beam epitaxial growth and characterization of InAs/GaSb superlattices grown on semi-insulating GaAs substrates for long wavelength infrared detectors. Photoconductive detectors fabricated from the superlattices showed photoresponse up to 12 &mgr;m and peak responsivity of 5.5 V/W with Johnson noise limited detectivity of1.33×109 cm Hz1/2/Wat 10.3 &mgr;m at 78 K. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119906

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Scanning electron microscopy dark voltage contrast (DVC) was used to define quasi-Fermi energies in a siliconp-njunction either under illumination or forward bias conditions. Quantitative DVC measurements have proven to be a precise method of locating quasi-Fermi levels (QFLs) in any operating device. By simultaneously using light and electron beams we have obtained accurate measurements of the position of QFLs by DVC in an illuminatedp-njunction. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119907

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We have observed step-flow growth of Si on sapphire, for the first time, by gas-source molecular beam epitaxy using ultrasmooth sapphire substrates, and self-formed Si quantum wires were fabricated on the substrates. The wires were aligned along the substrate steps and formed uniformly with 50 nm width and 1 nm height. Visible photoluminescence from the wires was observed at 9 and 300 K. The optical properties of the wires were very similar to those observed in conventional porous silicon and other nanostructured silicon. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119908

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We report strong evidence for coherent modes of moving Josephson vortices in mesas patterned on the surface ofBi2Sr2CaCu2Oxsingle crystals. The vortex flow current–voltage curves are characterized by a sharp up-turn and the appearance of multiple branches as the current is ramped up and down at a fixed magnetic field and temperature. These results are consistent with weakly damped motion of Josephson vortices in which different coherent modes can occur in a close stack of Josephson coupled multilayers. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119909

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The direct transformation of the energy of an incident high-energy photon into a measurable potential difference within an absorbing metal is investigated. Experimental evidence is presented that the effect arises from the inherent energy dependence of the electronic density of states, rather than from a simple temperature excursion. The similarities between the results on Al andYBa2Cu3O7samples indicate that the effect is universal in nature. We assert it may be used as the basis of a fast, energy resolving, individual photon detector for the ultraviolet radiation and x-rays. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119910

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A model is presented for magnetic dissipation imaging and magnetic force gradient imaging obtained with a vibrating ferromagnetic tip and a ferromagnetic thin film sample. Results of calculations are compared to recent experiments and show good agreement using known bulk values for the magnetic parameters of tip and sample. We suggest that oscillations of domain wall width result in magnetoelastic emission of phonons. These phonons carry energy from the tip, leading to image contrast at domain walls. We also discuss the energy dissipation resulting from eddy current losses in the tip and sample. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119911

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

New “112” phases,LnBaCo2O5.4,with an ordered oxygen deficient perovskite structure, derived from theYBaFeCuO5-type were studied forLn=Eu,Gd. The appearance of giant negative magnetoresistance in this structural type is demonstrated. Resistance ratioR0/R7 Treaches at least 10 at 10 K, i.e., is significantly larger than those observed in the other cobalt perovskites, such asLa1−xSrxCoO3.These properties are linked to an original magnetic behavior of these materials that exhibit two types of transition—antiferromagnetic to ferromagnetic, and ferromagnetic to paramagnetic—asTincreases. This magnetic behavior may be related to a possible I.S. and L.S. spin ordering of trivalent cobalt in pyramidal and octahedral coordinations, respectively. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119912

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We have fabricated perovskiteLa1−xKxMnO3(x=0.14and 0.2) thin films onSrTiO3(100) by e-beam/thermal coevaporation. From the electrical and magnetic studies, we found a simultaneous occurrence of the paramagnetic to ferromagnetic state and insulating to metallic state, as predicted by the double exchange theory. The magnetoresistance is relatively small compared to that of the divalent cation dopedLa1−xAxMnO3in fields up to 5 T. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119913

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We report a sevenfold improvement in the rate of contamination resist formation over previous experiments by using metastable neon atoms for nanolithography. Chemically assisted ion beam etching was used to transfer the resist pattern into the substrate. We demonstrate the fabrication of 50-nm-wide features in GaAs with well-defined edges and an aspect ratio>2:1.These are the best resolution and highest aspect ratio features that have been achieved with metastable atom lithography. The resist formation rate by the metastable neon atoms and the etch selectivity of the contamination resist with GaAs were measured. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119914

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Field emission has been measured from a series of tetrahedrally bonded amorphous carbon (ta-C) films produced by the filtered cathodic vacuum arc. The threshold field and current densities achievable have been studied as a function of theirsp3content and of nitrogen incorporation. Typical undoped ta-C films are found to have a threshold field of 10–20 V/&mgr;m, decreasing with increasingsp3content, and optimally nitrogen doped films exhibit threshold fields as low as 3–5 V/&mgr;m. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119915

出版商:AIP    

年代:1997

数据来源: AIP