摘要:

Porous GaAs was formed electrochemically onn‐type GaAs(100) in a 0.1 M HCl electrolyte. Scanning electron microscopy revealed feature sizes of the porous structure in the micrometer to nanometer range. The optical properties of the porous material were characterized by photoluminescence (PL) measurements at 295 K. Compared with untreated GaAs, a shift down of the ‘‘infrared’’ PL maximum to ∼840 nm can be observed. An additional ‘‘green’’ PL peak occurs at ∼540 nm that in some samples is readily visible to the naked eye. The ‘‘green’’ and the ‘‘infrared’’ PL are ascribed to quantum confinement effects in GaAs nano‐ and microcrystallites, respectively. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117050

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Analysis of normal incidence spectral reflectivity of excimer laser annealed &agr;‐Si:H shows that the annealed material can be modeled as a stratified system comprising a large‐grained polycrystalline layer, a fine grained polycrystalline layer, and residual amorphous silicon in agreement with transmission electron microscopy. Optically, the large‐grained poly‐Si behaves as single‐crystal silicon and the fine‐grained material is modeled, using effective medium theory, as a mixture of single‐crystal silicon and amorphous silicon. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117051

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We have used a parallel‐plate resonator technique to measure the microwave surface resist‐ anceRsof YBa2Cu3O7−x(YBCO) films on buffered ceramic substrates at around 10 GHz, and studied the correlation between theirRsand materials properties. A 0.4‐&mgr;m‐thick YBCO film (with an in‐plane mosaic spread of 7°) grown on a polycrystalline alumina substrate with an ion‐beam‐assisted‐deposited yttria‐stabilized zirconia buffer layer showed anRsof 1.89 m&OHgr; at 76 K and 0.21 m&OHgr; at 4 K. We have observed a strong correlation between theRsof the samples and the in‐plane mosaic spread of the YBCO films. This correlation can be explained qualitatively in terms of a simple model in which the weak links between the grains of the YBCO film form an electrical network of Josephson junctions.

ISSN:0003-6951    

DOI:10.1063/1.117052

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Ion gettering effect has been observed in high‐temperature superconducting YBa2Cu3O7material. Silicon ions were implanted into the material and subsequent high‐temperature annealing produced ion movement from a low concentration region to a higher concentration region where the damage of the crystal structure is severe. This gettering effect could be used to make a superconductor‐nonsuperconductor‐superconductor trilayer structure within a single YBCO film. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117053

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We describe the use of a miniature microwave Fiske cavity coupled to a Josephson junction oscillator to monitor the dynamic quasiparticle population created in the surrounding superconductor by incident x rays. An expression is obtained for the phase velocities of the TM modes supported by this structure. The design has the advantage of being inherently thick—sufficient to completely absorb low energy x rays and is potentially scalable to a pixilated device with a pixel size 50 &mgr;m in linear dimension. The device represents an alternative strategy to implement the dynamic microwave absorption approach suggested by Gulian and Van Vechten and subsequent variations. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117054

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Series arrays of 365 shunted YBa2Cu3O7−xJosephson junctions on yttria‐stabilized zirconia bicrystals were investigated under microwave irradiation in the K‐band. Sub‐arrays of up to 39 junctions were synchronized to the external microwave power at a temperature of 15 K. Although there was a considerable spread in the critical currents of the junctions and in the microwave bias current distribution, a first Shapiro step with a height of 30% of the total critical current of the sub‐array was obtained by using an external shunt resistor, thus reducing the spread in normal resistances to 5%. Such high‐Tccryoelectronic circuits are applicable for voltage standards and precision digital‐analog converters. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117055

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We report a method that allows the measurement of the absolute size of the magnetic penetration depth &lgr;(T) of large area YBa2Cu3O7−&dgr;films using the two‐coil method where a YBa2Cu3O7−&dgr;film is overlapped with a 1‐&mgr;m‐thick Pb film equivalent in size placed in the gap between the drive and receive coil. The drive coil has fewer counter turns on the top section than the bottom, which is closer to the film, so the film’s edge current would be suppressed and the accuracy that depends on geometry is greatly improved. The transition of the Pb film causes a steplike portion in the mutual inductanceM(T) graph and the resultant step height leads to the absolute value of &lgr;. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117056

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We demonstrate the introduction of high carrier densities into two and three‐dimensional magnetic semiconductor heterostructures that contain large local concentrations of magnetic moments. The use of (ZnSe)m−f(MnSe)fdigital alloys readily allows the fabrication of epilayer samples of moderate Mn composition with carrier concentrations up to ∼1019cm−3. Modulation doping of ZnSe/Zn1−x−yCdyMnxSe quantum wells enables the fabrication of a 2‐D electron gas confined within themagneticregion with sheet concentrations up to ∼6×1011cm−2. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117442

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

YCo2and TbCo2Laves phase compounds were epitaxially grown on (110) W buffer layers by pulsed laser deposition at a base pressure of 5×10−10Torr and a substrate temperature of 500 °C. The films were characterizedinsituby reflection high‐energy electron diffraction, and after deposition by grazing‐incidence x‐ray diffraction and scanning electron microscopy. The relative orientation of the RCo2(111), where R=Y or Tb, and the W(110) planes was found to be unlike any previously observed relationship between fcc and bcc materials. Two in‐plane crystallographic domains of RCo2(111) have been pointed out and are discussed in terms of geometrical lattice matching. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117443

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

It is demonstrated that monolayers of organic molecules (long chain hydrocarbons) as thin as 1.9 nm, deposited by the self‐assembly technique on silicon, form high performance electrically insulating barriers. Their properties are compared with those of silicon dioxide. Leakage current densities through the organic monolayers of the order of 10−8–10−7A/cm2have been obtained. These values are 4–5 decades lower than those for silicon dioxide of equivalent thickness. Larger tunneling barriers for organic monolayers than for silicon dioxide explain these results. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117444

出版商:AIP    

年代:1996

数据来源: AIP