摘要:

HoBa2Cu3Oxthin films with a zero resistivity temperature of 63 K are successively grown on a Si substrate, at a substrate temperature as low as 550 °C using reactive evaporation with microwave‐discharged oxygen plasma. The films are polycrystalline and consist of grains with radii of about 100 nm without microcracks. No significant interdiffusion between the substrate and film is observed by x‐ray diffraction or secondary ion mass spectrometry depth profiles. However, a transmission electron microscopy study reveals that two kinds of amorphous interlayers are formed between the film and substrate: a Ba‐excess diffusion layer and a silicon oxide layer.

ISSN:0021-8979    

DOI:10.1063/1.347044

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

A Ba2YCu3O7−yhighTcsuperconductor degrades with time in air. In this paper we discuss the early stage of the degradation from a microscopic standpoint by using transmission electron microscopy (TEM). It has been shown by a high resolution TEM that the degradation has two modes. One is the formation of amorphous and polycrystalline phases, the latter of which are perhaps BaCO3. It has been clarified that the origin of the formation of the amorphous and polycrystalline phases is the reaction of Ba2YCu3O7−yphase with the water vapor, and the polycrystalline phase is formed sequentially after the formation of the amorphous phase. The other is the formation of planar defects which are introduced between Ba‐O and Ba‐O layers even in dry air. It is thought that the planar defects are formed to relax the strain energy of the dislocation caused by the migration of ions.

ISSN:0021-8979    

DOI:10.1063/1.347045

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Nominal ZnTlBaCuO4.5, CdTlBaCuO4.5, and HgTlBaCuO4.5samples have been prepared under different conditions and have been studied by resistance and ac‐susceptibility measurements compared to nominal TlBaCuO3.5samples. In general, the ZnTlBaCuO4.5samples required less strict heating conditions to reach zero resistance near liquid nitrogen temperature; the CdTlBaCuO4.5samples had lowerTc; the HgTlBaCuO4.5samples showed slightly improvedTcat certain conditions. In contrast to La2−xSrxCuO4, Zn‐addition did not significantly depressTcof TlBaCuO. This observation is worthy to be investigated further. Hardness of the ZnTlBaCuO4.5and CdTlBaCuO4.5samples was greatly increased, which could have importance in the practical applications of these materials.

ISSN:0021-8979    

DOI:10.1063/1.347020

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The erase and write processes in single layer direct‐overwrite magneto‐optic recording materials were investigated utilizing a stroboscopic microscope system with 10‐nsec time resolution. The effects of thermal magnetization reduction are addressed and limited by image subtraction techniques. With this technique the erase process is shown to be a collapse process which occurs during heating, rather than cooling. Galvanometer driven beam scanning is utilized to write and erase ‘‘stripe’’ domains at velocities up to 5 m/s. Scanning write and scanning continuous beam erase are investigated stroboscopically, providing surprising new data on these processes. The erase process for a ‘‘stripe’’ domain is shown to proceed from the end of the domain, and in front of the approaching erase laser beam. Jitter in the leading edge of the written domain is observed, and may be responsible for the noise levels observed in these materials. The data indicate that the erase process is driven by a combination of temperature and temperature gradient. The write behavior can be explained by either a post‐laser pulse nucleation or by movement of the trailing domain wall.

ISSN:0021-8979    

DOI:10.1063/1.347021

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Oxide layers grown on surfaces of gas‐evaporated Si particles as small as 100 A˚ have been investigated. Results of high‐resolution electron microscopy and x‐ray photoemission spectroscopy show that the native oxide layer (SiOx) is about 20 A˚ thick and its chemical compositionxis around 1.2. When the particles are annealed in air at 400 °C, the thickness of the oxide layers remains almost the same while the compositionxincreases up to 2 as the annealing time increases. The evolution of the oxide takes place during the first 15 min of annealing. Due to the increase inx, the infrared absorption band in the region of Si‐O‐Si stretching vibration shifts to higher frequencies and increases in intensity. A comparison of experimental infrared spectra with those calculated by an effective medium theory suggests that the observed large width of the absorption band is caused by the particle aggregation.

ISSN:0021-8979    

DOI:10.1063/1.347022

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Photoreflectance (PR) spectroscopy has been used to study the surface Fermi level in GaAs by taking account of photovoltaic properties at the semiconductor surface. The PR signal amplitude ‖&Dgr;R/R‖ is proportional to a modulating photovoltageVmgenerated by a modulation light irradiation. To modify the surface potential, the sample was irradiated by a third perturbing light, i.e., a continuous bias lightPb, together with the modulation light. The modulation light power dependence of ‖&Dgr;R/R‖ is extremely sensitive to bias light intensity, surface Fermi level, and temperature. From the analysis of the temperature dependence of ‖&Dgr;R/R‖ on modulation‐light power, the surface Fermi level of 0.47±0.09 eV below the conduction band was determined for a molecular beam epitaxially‐grown GaAs(100).

ISSN:0021-8979    

DOI:10.1063/1.347023

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The optical spectra of a molecular‐beam‐epitaxially grown In0.53Ga0.47As epilayer lattice‐matched on a (100) InP substrate are measured in the visible and infrared regions. The transmittance, reflectance, and their wavelength derivatives (wavelength‐modulation spectra) are measured at room temperature. The spectra were analyzed by a theoretical spectral line‐shape calculation based upon the band structure near the fundamental band gap. The quasidielectric functions and optical constants in the 0.6–3.1 eV range and the critical energiesE0,E0+&Dgr;0,E1, andE1+&Dgr;1are determined by fitting the calculated spectral line shapes to the measured spectra.

ISSN:0021-8979    

DOI:10.1063/1.347024

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

A disordered superlattice, a recently proposed artificially constructed material, is fabricated and photoluminescent properties and optical absorption are investigated. Disorder is intentionally introduced into the period of the superlattice in order to enhance its photoluminescence. The photoluminescent temperature dependences and the optical absorption spectra of Al0.5Ga0.5As bulk alloy, AlAs/GaAs ordered superlattice, and AlAs/GaAs disordered superlattice are studied and compared. The optical absorption spectra suggest that localized states are created in the band tail of the AlAs/GaAs disordered superlattice. The photoluminescence spectra of the disordered superlattice are strongly dependent on the localized states, and the temperature dependence of photoluminescence intensities obeys the same relationIPL∝[1+A exp(T/T0)]−1as that reported for amorphous semiconductors.

ISSN:0021-8979    

DOI:10.1063/1.347025

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Freon 12 is compared to freon 14 as an etchant for patterning of high density superconductive circuits. Both reactive ion and plasma regimes are examined. CCl2F2is observed to be an excellent niobium etchant, offering significant advantages over similar CF4processes. Improvements include a six‐fold increase of Nb:photoresist selectivity, while Nb:SiO2selectivity is increased by over 1400%. Critical dimension control was also enhanced through the reduction of photo to etch bias from between 1. 09 and 0.5 &mgr;m to 0.14 &mgr;m. Diminished photoresist loss and the elimination of photoresist undercut are the reasons for this improvement. SiO2surface texturing is not observed with either of the two etchants. Finally, data are presented that demonstrate the importance of electrode cooling in obtaining etch rate repeatability.

ISSN:0021-8979    

DOI:10.1063/1.347026

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Reactive ion etching of aluminum oxide has been studied in CHF3and SF6plasmas generated by electron cyclotron resonance in conjunction withinsituellipsometric measurement for thickness variation. Because of the involatility of etch products associated with aluminum, purely chemical reactions cannot desorb etch products at room temperatures, and ion bombardment is essential to etch Al2O3through chemically enhanced physical sputtering. The higher the oxygen content in a film, the faster the etch rate, resulting from chemical sputtering due to volatile CO molecules in CHF3plasmas. This dependence on composition is absent in SF6plasma. The threshold ion energy for physi‐chemical sputtering by fluorine‐containing species is estimated to be about 20 eV at room temperature, while the threshold for Ar sputtering is 50 eV. In CHF3plasmas, however, Al2O3exhibits a larger threshold energy at a lower temperature due to passivating species which inhibit sputtering. These passivating species have a very weak binding energy of roughly 0.1 eV, which has been deduced from a temperature dependence of the threshold energy. A patterned sample always shows vertical profile without undercuts.

ISSN:0021-8979    

DOI:10.1063/1.347027

出版商:AIP    

年代:1990

数据来源: AIP