摘要:

We have studied the effects of reducing and oxidizing thermal treatments on truly epitaxial Bi2.1−xPbxSr2.9−yCayCu2O8+zfilms. Films were grown on NdGaO3substrates by liquid phase epitaxy with a very narrow mosaic spread (less than 0.1°). Transport and structural properties were investigated for a number of films after various annealing treatments.Tcis shifted to higher values by reducing treatments and to lower values by oxidizing treatments for all lead concentrations. For all films the maximum range of variationTmaxc− Tmincis about 15 K. However, theTcfor the as‐grown lead doped films is lower relative to the undoped ones. Furthermore, in the case of doped films, the optimum hole concentration (corresponding to the highestTcof 94 K) cannot be reached by reducing treatments. For both doped and undoped films thec‐lattice parameter was found to increase slightly after reducing treatments.

ISSN:0021-8979    

DOI:10.1063/1.352156

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

A new contactless inductive method is used to generate currents in large YBaCuO rings at liquid‐nitrogen temperature up to 100 kHz. With this method the transport current in the ring is directly measured. A study of the current‐voltage curves for currents above the critical current has been made in three rings of fixed size but of different oxygen content. The experimental results indicate the occurrence of the skin effect.

ISSN:0021-8979    

DOI:10.1063/1.352361

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

The growth ofc‐axis oriented Y1Ba2Cu3Oxthin films on an amorphous buffer layer of Y‐ZrO2, deposited on sapphire substrates, was investigated. Both films were grown by a pulsed laser deposition technique. A strong correlation was observed between the properties of Y1Ba2Cu3Oxand the thickness of the buffer layer. ATcof 89 K was obtained for an optimal buffer layer thickness of 9 nm. A model that adequately describes the film growth process was developed. A multilayer system of Y1Ba2Cu3Oxand amorphous Y‐ZrO2was grown and aTcof 87 K for the upperc‐axis oriented layer was measured.

ISSN:0021-8979    

DOI:10.1063/1.352157

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

This letter presents a theoretical approach for calculating the stray magnetic field of the tiny tip used in magnetic force microscopy (MFM). We consider several models for the tip. We demonstrate the advantage of using nonmagnetic tips covered by a magnetic thin film to improve lateral resolution of MFM. The analysis is quantitative and can be directly applied to a real tip that conforms to the shape limitations of our model. The same analysis can be applied to the case of a superconducting sample.

ISSN:0021-8979    

DOI:10.1063/1.352159

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

The magneto‐optical Faraday effect of plastic foils composed of cobalt fine particles fixed by polystyrene was investigated. Colloidal suspensions of the cobalt particles from 5 to 10 nm in diameter were prepared by thermal decomposition of dicobalt octacarbonyl dissolved by toluene. After that, polystyrene was added to the solution. The solution was then dried on glass receptacles, and foils 0.1 to 0.2 mm in thickness were obtained by peeling it off from the receptacles. The Faraday rotation spectra &thgr;F(&lgr;) of the foils were quite different from those of a cobalt film and polystyrene. &thgr;F(&lgr;) varied with the particle size and agglomerate state of particles during solidification.

ISSN:0021-8979    

DOI:10.1063/1.352160

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

The Autler–Townes effect in nuclear magnetic resonance (NMR) and electron paramagnetic resonance has been observed using recently developed Raman heterodyne techniques. The measurements were carried out on the nitrogen‐vacancy color center in diamond, where the3A↔3Eoptical transition was driven by a single mode dye laser at 638 nm while the magnetic transitions in the3Aground state were driven by two rf fields. The measured splittings in the NMR lines were found to be in good agreement with theoretical predictions. Using the Autler–Townes effect, the magnitude of the dipole moments of themI=0↔±1 (mS=0) transitions in the ground state was determined, and found to be the same. Comparison of this latter result with the NMR spectra shows that Raman heterodyne signal intensities are determined by population factors.

ISSN:0021-8979    

DOI:10.1063/1.352161

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Dielectric properties of CaNdAlO4monocrystals, a prospective substrate material for the deposition of high‐Tcsuperconductors, were measured with high accuracy at microwave frequencies from 8 to 40 GHz in the temperature range from 10 to 300 K by measuring the resonant frequencies of a completely filled resonant cavity. The material was found to be highly anisotropic. At 300 K it exhibits the dielectric constant alongcaxis &egr;’c= 17.68, while the dielectric constant in thea‐bplane is &egr;’=19.62, and loss tangent tan &dgr;c&bartil; tan &dgr; &bartil; 5.1× 10−4. Both &egr;’cand &egr;’depend strongly on temperature and their thermal coefficients have opposite signs, apparently a unique property of CaNdAlO4. Below 160 K microwave losses caused by electric field perpendicular to the opticalcaxis increase with decreasing temperature, exhibiting a maximum near 65 K followed by a minimum at 30 K. It is suggested that neodymium ions in CaNdAlO4at lower temperatures become magnetically ordered, causing an increase of magnetic permeability &mgr;’c≳ 1 and a significant increase of magnetic losses at microwave frequencies. A crystallographic phase transition below 60 K cannot also be excluded.

ISSN:0021-8979    

DOI:10.1063/1.352162

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

The standard expression for the excited‐state acceptor concentration in codoped solid‐state materials is modified to include the possibility of nonradiative acceptor deexcitation. The chromium and thulium time‐dependent emission in yttrium aluminum garnet (YAG) is then studied; evidence is given for the identification of the tendency for localized correlated chromium‐thulium pairs in the crystalline material.

ISSN:0021-8979    

DOI:10.1063/1.352163

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

A computer simulation based on the binary collision approximation has been performed to investigate the Si implantation efficiency, the Si depth profile, and the vacancy formation for Si‐implanted GaAs (001) crystals. The results reveal a strong dependence on the incident angle of the Si source. The calculated depth profile of Si agrees well with the experimental results from secondary‐ion mass spectroscopy. The simulated distribution of vacancies is shallower than that of Si atoms. Also, the calculated number of Ga vacancies exceeds that of As vacancies, which suggests that the Si atoms easily occupy the Ga sites and are activated as donors.

ISSN:0021-8979    

DOI:10.1063/1.352164

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Deposition of hydrogenated amorphous silicon (a‐Si:H) films is performed by low‐frequency (50 Hz) plasma‐enhanced chemical‐vapor deposition (PECVD). The results show that the undopeda‐Si:H films deposited at a substrate temperature of 200 °C are high‐quality films comparable to those deposited by conventional rf PECVD at a substrate temperature of 300 °C. The photoconductivity and dark conductivity of the films are 4 × 10−4S/cm and 5 × 10−9S/cm respectively. The activation energy is 0.78 eV and the optical gap is 1.8 eV. Furthermore, it is possible to control the dark conductivity and activation energy by doping with substitutional impurities of boron and phosphorus. These properties are very similar to those of thea‐Si:H films deposited by conventional rf PECVD in the optimum substrate temperature range from 250 to 300 °C. These results show that the 50 Hz PECVD can deposit high‐qualitya‐Si:H films.

ISSN:0021-8979    

DOI:10.1063/1.352165

出版商:AIP    

年代:1992

数据来源: AIP