摘要:

Hg1−xCdxTe metal‐insulator‐semiconductor (MIS) devices withx&bartil;0.22 often exhibit very short storage times that are determined by minority‐carrier dark currents. This study describes a novel system, for measuring the fast collapse of such devices. The measurement and modeling of the dark current during the fast collapse process is presented. A quantitative correlation is noticeable between the experimental results and theoretical calculations which assume that thermal‐trap‐assisted tunneling is the dominant dark process. The results demonstrate the importance of trap‐assisted tunneling in narrow band‐gap HgCdTe, and that this process causes short storage times.

ISSN:0003-6951    

DOI:10.1063/1.105988

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

A study of the levitation forces related to superconducting bearing design was conducted on free‐sintered and melt‐textured Y1Ba2Cu3O7−&dgr;(YBCO) materials. Comparisons were made between free sintered, variously oriented, and randomly oriented melt‐textured materials. Magnetic force measurements were also conducted on oriented YBCO before and after neutron irradiation. A magnetic bearing of new design utilizing the phenomenon of flux pinning was then fabricated using melt‐textured YBCO with permanent magnets and a speed of 135 000 rpm was achieved. Rotational dissipation and magnetic stiffness measurements were performed on the bearing prototype.

ISSN:0003-6951    

DOI:10.1063/1.105989

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

We report on large in‐plane anisotropic transport properties observed in epitaxial Bi2(Sr,Ca)3Cu2Oxfilms grown on tilted (001)SrTiO3substrate. By tilting the surface normal axis about 4° toward [111]SrTiO3, regular steps and terraces were formed on the substrate surface and perfect alignment of filmbaxis with incommensurate modulation along [110]SrTiO3was realized. The filmcaxis was perpendicular to the (001)SrTiO3terrace, thus the filmcaxis grew tilted 4° toward [111] from surface normal due to the surface inclination. In those epitaxial configurations, the in‐plane resistivity along the step direction(&rgr;[110]) involved the contribution from thec‐axis(&rgr;c) component, and we observed the large resistivity anisotropy betweena‐ andb‐ direction of the film. The transport alongaaxis(&rgr;a) showed a low resistivity with metallic temperature dependence while the resistivity along the step direction(&rgr;[110]) was higher and semiconductive. The ratio of &rgr;c/&rgr;a≊ 104estimated in this experiment agrees well with the anisotropy observed in the bulk single crystal.

ISSN:0003-6951    

DOI:10.1063/1.105990

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

We report the successful synthesis of superconducting YBa2Cu3O7−&dgr;(YBCO) (100) thin films with alignment of the in‐planecaxis. These films were grown on single crystal NdGaO3(110) substrates. The twofold symmetry of the substrate surface is believed to lead to anisotropic alignment of the in‐planecaxis of the epitaxial YBCO (100) film. X‐ray diffraction studies indicate that over 80% of the film grew epitaxially with the YBCO [100] perpendicular to the substrate surface, and YBCO [001] aligned along one pseudo‐cubic axis of the NdGaO3. The superconductivity onset of the film was measured to be 89 K by ac susceptibility.

ISSN:0003-6951    

DOI:10.1063/1.105991

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The resistivity of the Bi‐Sr‐Ca‐Cu‐O thin films deposited by MOCVD (metalorganic chemical vapor deposition) has been investigated. Samples of thickness from 5 to 300 nm have been studied. Zero resistance temperatures (Tc0) for all samples were about 70 K. For all samples,Tc0was nearly independent of magnetic fields up to 6 Tesla applied parallel to the film surface. In contrast,Tc0decreased significantly in fields applied perpendicular to the film surface. We suspect this difference to originate in the nonpenetration of flux quanta (due to the large effective lower critical field for thin film in the parallel field case) and in the potential barrier to flux penetration at the surface of the thin films in addition to the natural anisotropy of the Bi‐based superconductors.

ISSN:0003-6951    

DOI:10.1063/1.105992

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Room‐temperature measurements of the reversible relaxation of the initial magnetic permeability have been performed in rapidly solidified Fe73.5Cu1Nb3Si13.5B9ribbons at different stages of the transformation from the amorphous to the nanocrystalline phase. The intensity of the relaxation is observed to practically disappear in the nanocrystalline alloy. This result may modify the current views about the structural defects responsible for the magnetic‐permeability relaxation in amorphous ferromagnets.

ISSN:0003-6951    

DOI:10.1063/1.105993

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Permanent nanometer structures were fabricated on chemically prepared Si by chemical activation of loosely bound hydrocarbon clusters triggered by voltage pulses across the tunneling gap of a scanning tunneling microscope. Current‐voltage measurements show that the fabrication process results in a local transition from a Schottky junction behavior to a MIS junction behavior, indicating the formation of topographic structures. Our experimental results indicate that the size and density of the clusters and the shape of the tunneling tip are important factors of the process. An example of parallel fabrication is presented.

ISSN:0003-6951    

DOI:10.1063/1.105994

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

High resolution transmission electron microscopy in conjunction with optical diffractometry have been applied to identify the formation of an amorphous interlayer as well as to detect the presence of Ti5Si3, Ti5Si4, TiSi, and C49‐TiSi2in the interfacial reactions of ultrahigh vacuum (UHV) deposited Ti thin films on atomically clean (111)Si. The discovery of the formation of an amorphous interlayer and as many as four different silicide phases in the initial stages of interfacial reactions of UHV deposited Ti thin films on silicon by high resolution techniques necessitates a modification of the existing theory of the silicide formation in thin‐film reactions.

ISSN:0003-6951    

DOI:10.1063/1.105995

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Diamond films grown by rf plasma‐enhanced chemical vapor deposition in dilute CO, CF4, and CH4(diluent H2) mixtures have been examined by cathodoluminescence (CL) in a transmission electron microscope to assess the incorporation of optically active impurities and defects. The details of the CL spectra are found to be dependent on the different gas mixtures and are correlated with the different film microstructures. Dislocation‐related bandACL due to closely spaced donor‐acceptor (D‐A) pairs was observed from both the CO and CH4‐grown films, but was absent in the CF4‐grown material. BandACL due to widely separated (D‐A) pairs was seen in all samples but was especially dominant in the CF4‐grown film. Emission due to a di‐Si interstitial impurity was observed in CO‐ and CF4‐grown films but was absent in the CH4‐grown material.

ISSN:0003-6951    

DOI:10.1063/1.105996

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Micrometer size patterns of copper phthalocyanine derivatives were fabricated from 1,2,4,5‐tetracyanobenzene (TCNB) by a selective chemical vapor deposition method. Copper films were patterned on silicon wafers by photolithography and wet etching techniques, sealed in a glass tube with TCNB, and heated at different temperatures. Controlling the treatment temperature, selective chemical vapor deposition was achieved to produce copper phthalocyanine thin films on the copper patterns. After thermal annealing of the deposited film in vacuum, the films were converted to a polymer of the copper phthalocyanines.

ISSN:0003-6951    

DOI:10.1063/1.105997

出版商:AIP    

年代:1991

数据来源: AIP