摘要:

X‐ray photoelectron spectroscopy (XPS) examines only a thin surface layer (<5 nm) that may not be representative of the bulk. We separated the information from the surface and bulk by using laser‐deposited superconducting films that have nearly atomically flat surfaces for which quantitative analysis formalisms exist. The chemical compositions of highTc(90 K) and highJc(>106A/cm2) Y‐Ba‐Cu‐O films on SrTiO3(001) substrates were examined. From the relative intensities of the surface and bulk components of the Ba(3d) and Ba(4d) spectra taken at different take‐off angles and different escape depths [using Al K&agr; (1486.6 eV) and Mg K&agr; (1253.6 eV) excitations], we have determined the nonsuperconducting surface layer thickness to be 1 nm and the layer composition to be BaCuO2. The surface layer thickness for a superconducting film only 8 nm thick was also 1 nm. By detecting the substrate Ti signal through this film, and ruling out a high density pinholes, we provide evidence that the XPS data contain information from the superconducting phase. A polycrystalline pellet scraped in vacuum had a surface layer only 0.4 nm thick. Since typical photoelectron escape depths are about 2 nm, about 80% of the detected signal originates in the bulk. The surface layer contains Cu2+and oxygen with a photoelectron binding energy of 531 eV.

ISSN:0021-8979    

DOI:10.1063/1.345834

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The physical and electromagnetic properties of Y‐Ba‐Cu‐O superconductors synthesized with BaO2(barium peroxide) have been studied. A comparison of reactions with BaCO3and BaO indicates that the peroxide promotes formation and strong alignment of platelet grains in planes normal to thecaxis, yields material with larger grain sizes and aspect ratios, reduces the synthesis reaction time by over half, increases the volume fraction of material that goes superconducting (Meissner effect), and facilitates metallic conduction in the normal state. Critical current densities of 1.1×104A/cm2at 77 K have been observed in peroxide‐synthesized material. These beneficial effects may be due to the low melting temperature of BaO2(450 °C), and the elimination of residual unreacted BaCO3, BaO, and/or C.

ISSN:0021-8979    

DOI:10.1063/1.345835

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Artificially layered niobium‐titanium (Nb‐Ti) films with various thickness ratios (3/1–1/3) and periodicities (2–100 A˚) are made in an argon or in a mixed argon/nitrogen atmosphere by a dc magnetron sputtering method. Films with small periodicities (less than 30 A˚) have an artificial superlattice structure (ASL) with crystallographic coherence between constituent layers, where Nb and Ti grow epitaxially on the closest planes. The crystallographic structures of films are bcc with the (110) plane parallel to the film for films with the same or a thicker Nb layer than a Ti layer, and hcp with the (001) plane parallel to the film for films with a thinner Nb layer than a Ti layer. Films with large periodicities have an artificial superstructure (ASS) with only periodic stacking of constituent layers. Films deposited in the Ar/N atmosphere also have the artificially layered structures of ASL or ASS. The artificially layered structure is thermally stable at temperatures up to 500 °C. The superconducting properties of the films depend strongly on the periodicity and thickness ratio of Nb and Ti layers. The dependence of the transition temperature on the periodicity and thickness ratio is qualitatively explained by a proximity effect with a three‐region model. Films with periodicities less than 20 A˚, composed of the same or a thicker Nb layer than a Ti layer, show high transition temperatures (above 9.3 K). The highestTcof about 13.6 K is obtained in the film composed of monatomic layers of constituents deposited in an Ar atmosphere including 30 vol % N.

ISSN:0021-8979    

DOI:10.1063/1.345809

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

A study was made on the effects of elements substituted into the Cr layer on a CoNiCr/Cr sputtered hard disk. Among the various elements tried, Si, Gd, Ce, and Cu were found to increase the coercive force in the film. For Si and Gd, alloy targets of Cr‐Si and Cr‐Gd were prepared, and the deposited films indicated an increase of the coercive force by about 150 Oe over those without Si or Gd element.

ISSN:0021-8979    

DOI:10.1063/1.345810

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Transmission electron microscopy has been used to characterize the rhombohedral 5:19 phase (R3¯m) in a stoichiometric (Sm0.75Pr0.25)5Co19alloy. In some regions, strain‐induced contrast was observed in the 5:19 phase. By contrast analysis, this strain contrast was associated with a displacement vector of the type (1)/(3) [011¯0]. In other regions where the strain‐induced contrast was significantly reduced, faults with the crystal structure of hexagonal (Sm,Pr)2Co7(2:7H) phase (P63/mmc) were observed. The formation of the faults is believed to release elastic energy within the 5:19 phase. In the interface regions between the 5:19 phase and the minor component hexagonal 2:7Hphase, it was found by lattice imaging that the 5:19 and 2:7Hplates are superimposed with a commoncdirection. The orientation relationship between the 5:19 and 2:7Hphases is given by [0002]2:7H∥[0003]5:19Rand [112¯0]2:7H∥[112¯0]5:19R.

ISSN:0021-8979    

DOI:10.1063/1.345811

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The compositional and magnetic properties of iron‐nitride thin films deposited by dc reactive magnetron sputtering under various nitrogen partial pressure conditions have been investigated by x‐ray diffraction, Mo¨ssbauer and Auger electron spectroscopy as well as magnetic measurements. The x‐ray diffraction patterns indicate a mixed phase composition.57Fe Mo¨ssbauer spectroscopy shows that part of the nitrogen atoms are randomly distributed on interstitial sites with the formation of nonstoichiometric compounds. The excessive width of the Mo¨ssbauer lines indicates the degree of disorder of the different iron nitride precipitates. The nitrogen concentration as a function of depth is obtained by sputter‐etched Auger electron spectroscopy. Furthermore, the ferromagnetic films show moderate saturation magnetization and coercivities at room temperature as compared with pure iron thin films.

ISSN:0021-8979    

DOI:10.1063/1.345812

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

A novel technique was detecting two orthogonal in‐plane magnetization components is presented. This technique utilizes the magneto‐optical Kerr effects to sense the two components. These components of magnetization are parallel and perpendicular to the plane of incidence of the light beam. The ability to sense two components, individually or simultaneously, is a result of the disparity in the longitudinal and transverse Kerr effects. Based on the Frensel reflection coefficients of these two effects, an anlysis is presented describing this dual component sensitivity. The physical conditions are given for simultaneous and individual detection of the two in‐plane magnetization components. To substantiate this analysis, magneto‐optical measurements are made on single‐crystal Fe films. The results are discussed in the context of dual component sensitivity.

ISSN:0021-8979    

DOI:10.1063/1.345813

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Silica substrates were implanted with titanium ions, in the +1 charge state, to nominal doses of 1×1016, 3×1016, and 6×1016ions/cm2at an energy of 160 keV and a current of 2.5 &mgr;A/cm2. The implanted ion depth profiles were measured by backscattering techniques. Components in the vacuum ultraviolet absorption and electron paramagnetic resonance (EPR) spectra are attributed to a fraction of the implanted titanium in the Ti3+state. The intensity of the Ti3+EPR component has a Boltzmann temperature dependence between 490 and 5 K. The fraction of implanted titanium ions producing this EPR component ranges from 10% for doses of 6×1016and 3×1016ions/cm2to 38% for a dose of 1×1016ions/cm2. Based on the relative intensities of the Ti3+charge transfer band resolved in optical absorption measurements, the fraction of Ti ions in the 3+ state is larger than the fraction estimated from the EPR spectral component. The Ti3+ions not contributing to the EPR spectra are assumed to be antiferromagnetically (or speromagnetically) coupled. The linewidth of the EPR component decreases with increasing implantation dose. The value for the exchange integral for the paramagnetic fraction of implanted titanium ions is approximately (1.3±0.4)×10−6eV. The fraction of Ti3+ions antiferromagnetically coupled increases with increasing ion concentration. Thus a smaller fraction of Ti3+ions are detected by EPR as the implantation dose is increased. A greater fraction of the titanium ions are incorporated in the SiO2glass substrate in the Ti3+state by ion implantation than are introduced in the 3+ state by other techniques such as fusion, reduction of Ti4+, and flame hydrolysis.

ISSN:0021-8979    

DOI:10.1063/1.345814

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Rapid thermal processing as a post‐oxidation annealing (POA) process is of considerable influence on the quality of thin thermal oxides: The number of defect‐related oxide failures is reduced, together with a slight reduction of the intrinsic oxide quality, but to a degree that is of no importance as regards reliability aspects. According to our investigations, it is important that POA is performed after poly‐Si deposition and doping, whereas POA after poly‐Si patterning is found to be an undesirable process. Infrared spectroscopy indicates stress relaxation caused by the POA treatment, but no change of the SiO2/Si‐interface roughness could be observed by high‐resolution electron microscopy. This relaxation process was accompanied by the creation of electron traps. Constant‐current investigations indicated an enhanced electron trapping in the oxides after POA. This electron trapping increased with increasing POA temperature. The reduced defect‐related oxide failures after POA are attributed to a retarded runaway of the injection current by negative space charges.

ISSN:0021-8979    

DOI:10.1063/1.345815

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The changes of the refractive index of As2S3and As2S5films deposited on glass substrates upon CO2laser irradiation have been studied. The possibility of writing with the CO2laser a waveguiding channel in As2S3is demonstrated.

ISSN:0021-8979    

DOI:10.1063/1.345816

出版商:AIP    

年代:1990

数据来源: AIP