摘要:

The heterointerfacep‐CuInSe2/CdS was investigated by soft x‐ray photoelectron spectroscopy. CdS was deposited sequentially in steps onto CuInSe2(011) cleavage planes at room temperature (RT) and at elevated temperatures (≳120 °C). At RT a nonreactive interface to cubic CdS is formed. The valence band and conduction‐band discontinuities are determined to be 0.8 and 0.7 eV, respectively. A band bending of 0.9 eV is deduced for thep‐type substrate. Annealing to temperatures above 120 °C leads to the formation of a CuxS reactive layer at the interface. As a consequence the valence‐band offset and band bending is found to be considerably reduced. The experimentally determined band energy diagram is in agreement with heterojunctions of zincblende‐type semiconductors, and its consequences for solar cells are discussed. ©1995 American Institute of Physics. 

ISSN:0021-8979    

DOI:10.1063/1.359583

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

A new low‐voltage contrast mechanism due to electron‐hole pairs generated in the oxide by an electron beam was observed at electric fields lower than 3.5 MV/cm. This is in addition to the tunneling current microscopy (TCM) contrast mechanism observed at electric fields higher than 3.5 MV/cm. The new contrast mechanism is opposite in sign to the TCM contrast mechanism such that the image of a local thinning defect in the oxide is dark at low bias voltage and bright at higher bias voltage. Good contrast can be obtained at electric field as low as 2.4 MV/cm. Applications include large area imaging of oxide defects and quantitative mapping of small oxide thickness variations. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.358994

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We discuss multiband coupling effects on electronic intersubband single particle excitations (SPE) of infrared (IR) and Raman processes in type I quantum wells (QWs). Interband couplings between &Ggr;c1‐&Ggr;v15, &Ggr;c1‐&Ggr;c15, and &Ggr;c15‐&Ggr;v15bulk band edges are treated within 14‐bandk⋅pfirst‐order perturbation theory. Enhanced band‐mixing effects are observed at Brillouin zone center (k∥=0) because of quantization effects (kz≠0). For zinc‐blende‐type QWs, &Ggr;c15‐&Ggr;v15band‐mixing effects at high‐lying &Ggr;c1conduction subbands contribute (x,y)‐polarized IR andz(x,x)z¯‐ andz(x,y)z¯‐polarized Raman intersubband SPE. Intersubband polarization splittings occur when the QWs are under biaxial strains. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.358995

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

A simplified version of the specific contact resistance measurement scheme of G. K. Reeves [Solid State Electronics23, 487 (1980)] has been developed. Its applicability to semiconducting diamond is demonstrated using four sample types: epitaxial films doped to mid 1019acceptors/cm3on ⟨100⟩ and ⟨110⟩ type IIa substrates; type IIb diamonds 0.25 mm thick, and type IIb diamonds thinned to 0.035–0.05 mm thick. The ohmic contacts were based on a solid‐state annealing process using carbide forming metals. The measured specific contact resistance depends mainly on the doping level in the diamond. Measured values ranged from 8×10−6&OHgr; cm2for heavily doped films to 1×10−2&OHgr; cm2for lightly doped bulk samples. A simple analysis shows that the contacts to highly doped layers are suitable for device applications. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.358996

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

All‐thin‐film SrTiO3/YBa2Cu3O7−x/SrTiO3/Cu structures fabricated on sapphire substrates were used to study large electric field effects in YBCO superconducting films. The YBCO films (∼100 nm) were deposited by off‐axis radio‐frequency sputtering while the top SrTiO3films (∼200 nm) were reactively vacuum deposited at low temperatures to avoid significant deoxygenation of the superconducting YBCO underlayer films. Cu was used in the field‐effect transistor‐type YBCO/SrTiO3/Cu multilayered structures as the gate electrode and as Ohmic contacts for the source and drain electrodes. This avoided probable electroforming processes taking place in the SrTiO3insulating matrices under the large electric fields arising from the applied gate voltages. The YBCO films were polycrystalline withTconsets ∼72–82 K. The gate voltages were found to change both theTcandTcovalues and hence the resistivity of the relatively thick superconducting YBCO layers in the normal and superconducting states. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.358997

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Both the critical current intensity at zero applied magnetic fieldIc(T), from nitrogen temperature up to the critical temperature, and the normal‐state resistivity &rgr;n(T) have been measured in granular Bi1.5Pb0.5Sr2Ca2Cu3Oy(BiPbSCCO) superconductors, with different granular characteristics. It is found that the combination [Ic(T)/P][&rgr;n(0)/&rgr;’n], where &rgr;(0) is the residual normal‐state resistivity, &rgr;’nis the temperature derivative andPis the sample’s perimeter, is essentially constant from sample to sample at any temperature. It thus constitutes a universal temperature‐dependent critical current for the polycrystalline BiPbSCCO family. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.358998

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

In this paper we report measurements and theoretical interpretation of the lateral forces which act on YBa2Cu3Oxhigh‐Tcsuperconductors in a magnetic field and on small magnets interacting with the high‐Tcsuperconductors. The results of two types of experiments are described: In the first experiment, disk‐shaped superconductor samples are moved along the symmetry plane of a pair of Helmholtz coils, the movement being perpendicular to the magnetic field of the coils. This measurement leads to the determination of the hysteresis curves of the superconductors. A Bean‐type, critical‐state model is considered in which the high‐Tcsuperconductors are treated as an assembly of microscopic, spherical grains of uniform diameters. By taking the influence of the demagnetizing field and the Lorentz field into account, the magnetic response of the grains is derived. In the second experiment, a small magnet is laterally moved above the surface of a high‐Tcsuperconductor, the axis of the magnet being kept perpendicular to the surface. It is shown that the observed lateral force is well reproduced using the grain model if an effective value of the bulk susceptibility is incorporated. The results are presented for both the sintered and melt‐textured YBa2Cu3Ox, for the latter the effect of demagnetization being more important than for the former. Our treatment makes it possible to evaluate the lateral force using closed expressions without resorting to the numerical solution of the field equations. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.358999

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

A new thermomagnetic recording method using tunneling current in a scanning tunneling microscope as a heating source is proposed. In the experiment, pulse voltage of from 2–8 V with a pulse width of 1 ms is applied to the sample, while the probe position is kept at a bias voltage of 0.2 V and a tunneling current of 0.3 nA. As a result, we have demonstrated that thermally recorded magnetic domains are formed in a Pt/Co multilayered film and minimum domains as small as 0.2 &mgr;m in diameter are observed using a polarized optical microscope. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359000

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We describe the structural and magnetoresistive properties of Ag‐Co and Ag‐Ni granular alloys that were grown epitaxially on MgO{100} substrates. With substrate temperatures in the range 300–400 °C and up to 25 vol% of the ferromagnetic constituent (Co or Ni) x‐ray analyses showed that the Ag matrices were elastically strained (by stretching at the interface with the substrate), but had relaxed lattice constants that were the same as that of pure Ag. This excludes the possibility of significant amounts of dissolved Co or Ni. The Co and Ni precipitates gave lattice spacings that were consistent with somewhat smaller strains. Growth at 200 °C appears to yield only partial precipitation of the Co or Ni, as judged by a 20% reduction in saturation magnetization from the values obtained with growth at 300–400 °C. Replacement of Co by Ni in otherwise similar alloys causes an increase in the size of the ferromagnetic precipitates. This leads to a decrease in surface area that combines with a decrease in saturation magnetization to give substantially smaller magnetoresistance in Ag‐Ni than in Ag‐Co. With both alloy systems, decrease of the substrate temperature leads to decreased precipitate size whose influence is seen in the magnitude of the magnetoresistance, the temperature dependence of the hysteresis, and the rate of approach to saturation with applied magnetic field. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359001

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Samples of vitreous silica with OH content <2 ppm (‘‘dry ’’) or 1200 ppm (‘‘wet ’’) were irradiated with x rays from Cr, Cu, and Mo tubes, and with &ggr; rays from a137Cs source (661 keV). Front surface doses ranged from 51 to 1800 Mrad. For each energy of the photons the number ofE’defects produced per megarad of radiation was higher for the ‘‘wet ’’ samples than for the ‘‘dry ’’ samples. The spatial distribution (depth profile) of theE’defects was measured by spectral‐spatial electron paramagnetic‐resonance (EPR) imaging. Defects produced by the high‐energy137Cs &ggr; rays were uniformly distributed through the 1.0 mm thickness of the samples. For the x rays, the EPR signal intensity decayed with distance into the sample, the decay being strongest for the lowest photon energies. The EPR profile was compared with the spatial distribution of the energy deposition (dose profile). The basic features of the EPR profile are determined by the dose profile, but in some cases there appears to be enhanced defect production near the surface of the sample. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359535

出版商:AIP    

年代:1995

数据来源: AIP