摘要:

The HF-chemical etching process near theSiO2/Si(111)interface(<1&hthinsp;nm)is investigated by scanning reflection electron microscopy and microprobe Auger electron spectroscopy. The HF etching of theSiO2layer thermally grown on an atomically flatSi(111)-7×7surface progresses in a layer-by-layer manner, and then the final layer of oxide(∼0.3&hthinsp;nm)is removed in a two-dimensional void expansion with the H-terminated Si surface. This very uniform HF etching is thought to reflect the structural anisotropy of theSiO2layer formed near theSiO2/Si(111)interface. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122937

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We report a flexible method for the patterning of organic semiconductors in the submicrometer range, which we have successfully applied to thin films of poly(p-phenylene vinylene) (PPV) prepared on a variety of substrates, such as quartz, indium–tin oxide coated glass, or inorganic dielectric mirrors. The method is based on holographic lithography performed by a corner cube interferometer of our own design and construction, followed by Ar-ion etching. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122938

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The voltage modulation depths,&Dgr;Vof high-Tcdirect current superconducting quantum interference devices (SQUIDs) with resistors connected in parallel with their inductances were investigated. Both the junctions and resistors in the SQUIDs were fabricated using focused electron-beam irradiation. The effect of varying the resistor value (using focused ion-beam trimming) and the screening parameter&bgr;L(by varying the temperature and hence the junction critical current) were studied. Significant enhancement of&Dgr;Vrelative to an equivalent unshunted SQUID for&bgr;Lvalues up to 50 was observed, and the most effective shunt resistor value was found to be approximately equal to the junction resistance. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122939

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The voltage–current characteristics of a superconducting coil, made of multifilamentary silver-sheathedBi2Sr2Ca2Cu3O10+&dgr;tape, are investigated. We find that a small ac currentIacsuperimposed on a relatively large dc currentIdccauses a significant increase in the coil dc voltage, approximately proportional toIdc,Iac2,and the ac frequency. We attribute this effect to the nonlinear magnetoresistance of the coil, and discuss its significance in power applications of highTcsuperconducting coils, such as fault current limiters and superconducting magnetic energy storage devices. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122940

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Bi2Sr2Ca2Cu3Ox(Bi-2223) tapes were processed by the standard powder-in-tube technique, but small amounts ofUO4were added prior to processing. Both U-doped and undoped tapes were subsequently exposed to a reactor spectrum of neutrons. Whereas the undoped materials show moderate enhancements of the critical current densitiesJcdue to the pinning action of the fast-neutron-induced collision cascades,Jcin the U-doped tapes increases by factors of 10–20 due to thermal-neutron-induced fission of235Uand the subsequent formation of fission tracks. Since the enhancements are particularly pronounced, when the magnetic field is applied perpendicular to the tape surface, the characteristicJcanisotropy is strongly reduced in a certain field range. At the same time, the irreversibility field at 77 K is doubled for both field orientations. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122941

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The quantum efficiency and current and voltage responsivities of fast hot-electron photodetectors, fabricated from superconducting NbN thin films and biased in the resistive state, have been shown to reach values of 340, 220 A/W, and4×104&hthinsp;V/W,respectively, for infrared radiation with a wavelength of 0.79 &mgr;m. The characteristics of the photodetectors are presented within the general model, based on relaxation processes in the nonequilibrium electron heating of a superconducting thin film. The observed, very high efficiency and sensitivity of the superconductor absorbing the photon are explained by the high multiplication rate of quasiparticles during the avalanche breaking of Cooper pairs. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122942

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We have grown highly oriented lead zirconate titanate [Pb(Zr,&hthinsp;Ti)O3or PZT] films on oxidized silicon substrates using a thin MgO buffer layer (7–70 nm thick). Ferroelectric nonvolatile memory field-effect transistors (FETs) were successfully fabricated using themetal/PZT/MgO/SiO2/Sistructure in conjunction with radio-frequency sputter deposition of PZT and MgO films. The fabricated devices show excellent performance in ferroelectric polarization switching and memory retention. The results indicate that a thin MgO buffer serves well not only as a template layer for the growth of oriented PZT films on amorphous substrates, but also as a diffusion barrier between a ferroelectric and a substrate during device fabrication, protecting theSiO2/Siinterface and the FET channel region. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122943

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Exchange interactions between the holes confined in arrays of strained quantum dots subject to compressive and tensile strain are shown to lead to ferrimagnetic arrangement of magnetic moments. Using example of strainedIn1−xGaxAsquantum dots on InP substrate, it is shown how magnetic properties of a semiconductor material can be engineered without resorting to doping with magnetic ions, and the Curie temperature is estimated to be of the order of 25 K. Potential applications in information storage and processing are considered. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122944

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

A hybrid magneto-optical magnetometer and optical microscope has been designed and constructed for probing the magnetic properties of submicron nanomagnets. 10-nm-thick square nanomagnets have been fabricated individually and in small arrays fromNi80Fe14Mo5(“supermalloy”) by electron-beam lithography. Hysteresis loops with a good signal-to-noise ratio have been obtained fromindividualnanomagnets as small as 400 nm and from (5 &mgr;m)2arrays of nanomagnets ranging in size from 500 to 75 nm. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122945

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We report the unusual transport properties found inLa2/3MnO3−&dgr;thin films onAl2O3 (11¯02).Powder x-ray diffraction shows that the film has a mixture of perpendicular (110) and (001) crystal orientations. Unlike epitaxial or polycrystallineLa1−xMnO3−&dgr;samples, in which the peak resistance temperatureTpshifts toward a higher temperature under the influence of magnetic field, theTpof this particular film remains almost the same even in fields up to 5 T. The film becomes insulating at a low temperatureTm(∼45&hthinsp;K),but the trend is reversed by the applied magnetic field. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122946

出版商:AIP    

年代:1998

数据来源: AIP