摘要:

We have developed a method for evaluating the capacitance created from charges stored in the quantum well. This capacitance is currently calculated by using the formula for a parallel‐plate capacitor. We have shown that the simple formula for a parallel‐plate capacitor is invalid for this estimation. Our method, which is based on the damped resonant tunneling model, predicts that the capacitance due to the charges stored in the well is about two to three orders of magnitude smaller than that previously estimated.

ISSN:0003-6951    

DOI:10.1063/1.104961

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

High quality Fe‐doped semi‐insulating InP epitaxial layers were grown by low‐pressure organometallic vapor phase epitaxy using tertiarybutylphosphine (TBP) and triethylindium (TEI) as the reactant sources. Semi‐insulating InP epitaxial layers with specular surface morphology and low defect density were obtained at TBP partial pressure higher than 0.38 Torr. Electrical measurements on these layers showed the resistivity of TBP‐grown materials to be comparable to that of PH3‐grown materials over a measurement temperature range of 25 to 110 °C. A premature reaction between TEI and TBP was observed upstream from the substrate in which things such as TEI:TBP adducts and/or polymers could have been formed. This reaction occurred under low pressure, high gas flow conditions which effectively suppressed analogous reactions for TEI:PH3. As a result, the growth rate of Fe‐doped semi‐insulating InP layers grown at low pressure with TBP in our reactor decreased by 35% as the V/III ratio was increased from 15 to 46.

ISSN:0003-6951    

DOI:10.1063/1.104962

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

A monolithic GaAs impulse compressor circuit which utilizes soliton wave propagation effects in nonlinear transmission lines has been fabricated. The circuits compress a 20 dBm, 8 GHz sinusoid to a train of 3.9 V peak to peak, 5.5 ps full width at half maximum impulses.

ISSN:0003-6951    

DOI:10.1063/1.104963

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The effect of BeO substitution and addition in the superconducting properties of YBa2Cu3O7−&dgr;superconductors has been investigated by temperature resistance measurements and x‐ray diffraction studies. The results revealed that the substitution or addition of BeO in YBa2Cu3O7−&dgr;does not have much detrimental effect on the superconducting properties. Because of this nonpoisoning behavior, beryllia is suggested as a suitable substrate material for the production of superconducting thin films.

ISSN:0003-6951    

DOI:10.1063/1.104964

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The lateral force interaction between a permanent bar magnet and a large slab of highTcsuperconductor has been investigated at 77 K, under conditions of a constant vertical separation of 2 mm. The restoring force as a function of lateral displacement rises very steeply, and reaches 90% of its saturation value, 5.1 mN, after 1.8 mm. The profile of the force‐displacement curve is in qualitative agreement with the existing theory. A significant quantitative discrepancy is interpreted as due to a theoretical penetration depth exceeding the sample thickness. The lateral magnetic stiffness or spring constant, is found to be independent of displacement away from lateral equilibrium.

ISSN:0003-6951    

DOI:10.1063/1.104965

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Films of the Tl2Ba2Can−1CunO2n+4highTcsuperconductors (n=2 or 3) can be prepared with a high degree of phase selectivity using a combination of metalorganic chemical vapor deposition (MOCVD) and vapor diffusion. Ba‐Ca‐Cu‐O films are first prepared by MOCVD using the volatile metalorganic precursors Ba(hexafluoroacetyl‐ acetonate)2(tetraglyme), Ca(dipivaloylmethanate)2, and Cu(acetylacetonate)2. The ‘‘second‐generation’’ barium precursor exhibits significantly improved thermal stability and volatility over previously used compounds. Thallium is then incorporated into these films by vapor diffusion using a Tl‐Ba‐Ca‐Cu oxide mixture of controlled composition as the source of volatile thallium oxides. Phase control is achieved by a combination of improved stoichiometry of the deposited film, a result of the new Ba source, and annealing with the appropriate oxide mixture. The resultant films consist predominantly of the Tl2Ba2Ca2Cu3Oxor Tl2Ba2CaCu2Oxphase, each having preferential orientation of the crystallite Cu‐O planes parallel to the substrate surface. The films exhibit superconducting onset temperatures of ∼115 K with zero resistance by 93 and 85 K, respectively. Critical current densities for a number of films, estimated by the Bean method, are in the range 104–105A/cm2at 5 K.<lz> <lz> <lz> <lz> <lz> <lz> <lz>

ISSN:0003-6951    

DOI:10.1063/1.104966

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

High quality epitaxial YBa2Cu3O7−x(YBCO) superconducting thin films (0.3 &mgr;m thick) were grown on the closely lattice and thermal expansion matched substrate, LaAlO3, which has low dielectric loss. The YBCO layers were prepared,insitu, by a microwave plasma‐enhanced metalorganic chemical vapor deposition process. The films, which had mirror‐like smooth surfaces, were deposited at a substrate temperature of 730 °C with a partial pressure of 2 Torr of N2O. The electrical resistance and magnetic susceptibility versus temperature of the as‐deposited films show metallic behavior in the normal state and sharp superconducting transitions withTc(R=0) of 88 K. Critical current densities measured on patterned bridges were 5×105A/cm2at 78 K for the films deposited on LaAlO3. X‐ray diffraction measurements indicate that films grow epitaxially in the plane of the substrate with axis perpendicular to the substrate surface.

ISSN:0003-6951    

DOI:10.1063/1.104973

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The microstructure of the highTcphase (Tc∼111 K) in the Sb‐Pb‐Bi‐Sr‐Ca‐Cu‐O system has been determined using transmission electron microscopy. Its crystal structure belongs to the superspace groupNBbmb11¯1, NBb2b111,PBbmb11¯1orPBb2b111with subcell lattice parametersa=5.411(1) A˚,b=5.411(1) A˚, andc=37.22(6) A˚. The highTcphase has a modulated structure withb‐axis wavelengths 26.9 and 36.1 A˚. Stacking faults along thecaxis in the highTcphase are much less numerous than in the Bi‐Sr‐Ca‐Cu‐O system, but comparable to the Pb‐Bi‐Sr‐Ca‐Cu‐O system. Sb substitution for Ca may affect the internal strain of the crystal.

ISSN:0003-6951    

DOI:10.1063/1.104944

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Transparent ZnO with an optical index of refractionn∼2 is a suitable candidate for a dielectric enhancement layer in a magneto‐optical disk. Surprisingly, sputtering a Pt/Co multilayer on a ZnO layer not only increased the optical Kerr rotation but also increased the magnetic coercivity and improved the rectangular magnetic loop shape. Sputter etching the dielectric surface prior to the metal deposition also improved magnetic properties.

ISSN:0003-6951    

DOI:10.1063/1.104945

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The angular distribution of photoelectrons produced by laser‐induced four‐photon excitation in gold metalic targets is reported. Laser‐target interaction time effects have been investigated by using two Nd:YAG lasers emitting at 1.06 &mgr;m pulses of 35 ps and 20 ns duration. Both lasers produced four‐photon electron angular distributions of 9°±2° full width at half maximum. This width was independent from the intensity of the picosecond laser up to the breakdown threshold at a laser intensity of 1.4 GW/cm2. In contrast, the distribution produced by the nanosecond pulses was broadened at intensity levels higher than 60 MW/cm2, which is indicative of a significant contribution from thermionic emission. These results are compared to those obtained by D. Charalambidis, E. Hontzopoulos, C. Fotakis, Gy. Farkas, and Cs. To´th [J. Appl. Phys.65, 2843 (1989)], for single photon excitation by using a KrF excimer laser.

ISSN:0003-6951    

DOI:10.1063/1.104946

出版商:AIP    

年代:1991

数据来源: AIP