摘要:

Electronic structure of Nd2−xCexCuO4−y(x=0 and 0.15) thin films was examined by x‐ray photoelectron spectroscopy. The films were prepared by rf magnetron sputtering and successive annealing under reducing condition (reduction). The reduced films showed semiconducting and superconducting behaviors depending on the valuex. The Cu, O, and Nd core‐level spectra revealed that the doped electrons were predominantly in CuO2plane of the Nd2CuO4crystal. The Cu core‐level spectra fromx=0.15 films before and after the reduction suggested that the reduction added electrons to Cu4s‐O2pextended conduction band, and strengthened Cu O bond covalency to screen the core hole state by mobile itinerant electrons.

ISSN:0021-8979    

DOI:10.1063/1.346722

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Insitucleaning of GaAs surfaces has been achieved at 350 °C with a novel technique employing hydrogen that is excited and dissociated using a remote Ar discharge. Reconstructed surfaces characteristic of clean, As‐stabilized GaAs surfaces have been observed with reflection high‐energy electron diffraction following the cleaning treatment. Auger electron spectroscopy analyses confirm that such a treatment removes both carbon and oxygen contamination from the surface. X‐ray photoelectron spectroscopy shows the removal of oxygen bonded to both Ga and As on the surface. Emission spectroscopy shows evidence of excited molecular and atomic hydrogen with the downstream‐excitation process.

ISSN:0021-8979    

DOI:10.1063/1.346723

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Amorphous hydrogenated carbon films (a‐C:H) have been deposited using 193‐nm ArF laser‐induced photolysis. The source gas was C2H2(5%), diluted in argon (95%). The substrate temperature was varied between 150 and 350 °C in steps of 50 °C. Infrared spectroscopic analysis yields results on hydrogen content andsp3/sp2carbon bond ratio. For the H/C atomic ratio values near 1.0 and for thesp3/sp2bond ratio values near 10 are obtained. The corresponding values for plasma‐depositeda‐C:H films from C2H2are distinctly lower. Electrical resistivity, refractive index, optical gap, and microhardness have also been determined.

ISSN:0021-8979    

DOI:10.1063/1.346724

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The use of ac stabilization in ferroelectric liquid‐crystal (FLC) devices is commonplace: It enhances the bistability and increases the extinction angles seen in a cell. The mechanism involved in this process is investigated here. Examining the optic tensor profile across an ac‐stabilized FLC layer has revealed that it is very similar to that present under a forward bias dc field. Comparing the dc/dipole and ac/dielectric interaction energies shows conclusively the presence of biaxiality in the dielectric tensor. This biaxiality is measured through the comparison of the ac and dc electric energy densities in a cell.

ISSN:0021-8979    

DOI:10.1063/1.347157

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Diamond particles 10–500 nm in diameter were produced by microwave‐assisted combustion of acetylene in oxygen. Both premixed and diffusion flame configurations were investigated. A mixture of cubic and hexagonal polytypes of diamond were identified. Larger particle sizes were observed at lower reactor pressure and higher C to O atomic ratios. C to O atomic ratios between 0.83 and 1.0 produced crystalline diamond powder while other ratios produced graphite, soot, and amorphous carbon phases. Diamond formation was not observed when reaction pressures were above 150 Torr.

ISSN:0021-8979    

DOI:10.1063/1.346725

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Some possible effects of elastic stress, engendered by epitaxial strain and compositional inhomogeneity, on the kinetics of intermediate phase formation in a planar thin‐film binary diffusion couple are identified. A simple quasistatic approximation to the diffusion equation is used to estimate the thickening rate of the intermediate phases when elastic effects are incorporated into both the diffusion equation and the interfacial boundary conditions for diffusion using the thermodynamics of stressed solids. The various growth regimes of the phases are visualized using a simple graphical representation of the phase growth velocities (phase plot). Growth kinetics are shown to depend on both the strain engendered by and the crystallographic orientation of the substrate. It is also proposed that elastic stresses could influence the sequence of phase formation in thin‐film systems including such observations as the absence of those phases appearing in the equilibrium phase diagram and the initial disappearance and subsequent reappearance of equilibrium phases.

ISSN:0021-8979    

DOI:10.1063/1.346726

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The depletion of thin liquid films due to the combined effect of centrifugation, surface roughness, and air shear is addressed. As a liquid film flows on a horizontal rotating solid surface, it is thinned by both inertial forces as well as by shearing forces at the liquid‐air interface. The equations describing the flow of a thin viscous film over a rough rotating disk are solved by numerical techniques. Depletion histories of the thin film are given for several cases involving both deterministic and random surface asperities. It is noted that surface roughness of a rotating disk markedly enhances the retention of the thin liquid film. The thinner the liquid layer, the more significant is the effect of surface roughness. On the other hand, shearing forces between the free liquid surface and ambient air increase the depletion of the liquid film at a rate that is dependent on the speed of rotation. In general, inertial forces play a secondary role in the depletion of very thin films; the asymptotic limits of liquid retention are strongly influenced by the topographic structures of the surface roughness and the air shear.

ISSN:0021-8979    

DOI:10.1063/1.346727

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The control factors controlling the growth of native silicon oxide on silicon (Si) surfaces have been identified. The coexistence of oxygen and water or moisture is required for growth of native oxide both in air and in ultrapure water at room temperature. Layer‐by‐layer growth of native oxide films occurs on Si surfaces exposed to air. Growth of native oxides onn‐Si in ultrapure water is described by a parabolic law, while the native oxide film thickness onn+‐Si in ultrapure water saturates at 10 A˚. The native oxide growth onn‐Si in ultrapure water is continuously accompanied by a dissolution of Si into the water and degrades the atomic flatness at the oxide‐Si interface, producing a rough oxide surface. A dissolution of Si into the water has not been observed for the Si wafer having surface covered by the native oxide grown in air. Native oxides grown in air and in ultrapure de‐ionized water have been demonstrated experimentally to exhibit remarkable differences such as contact angles of ultrapure water drops and chemical binding energy. These chemical bond structures for native oxide films grown in air and in ultrapure water are also discussed.

ISSN:0021-8979    

DOI:10.1063/1.347181

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

(InAs)m(GaAs)mshort period superlattices (SPSs) have been grown by molecular‐beam epitaxy on InP substrates with their layer indexmvalue systematically changed from 1 to 3. Their structural and electrical property dependencies on the layer indexmvalue have been examined. During the first growth stage for the SPSs, with layer indexmvalues of 2 and 3, two‐dimensional reflection high‐electron energy diffraction growth patterns were observed. The intended periodic structures without misfit dislocation generation were confirmed by x‐ray diffraction and transmission electron microscopy (TEM) measurements. However, the obtained electrical properties were still poor, indicating the existence of a large amount of disorder in the SPSs. On the other hand, though the thickness of consisting binary compounds was as thin as one monolayer, a high‐quality (InAs)1(GaAs)1SPS was obtained. The highly ordered monolayer arrangement for InAs and GaAs was first observed by a TEM lattice image as well as x‐ray diffraction measurement. The obtained electron Hall mobilities for the modulation‐doped N‐AlInAs/(InAs)1(GaAs)1SPS structure were as high as 11 000 cm2/V s at room temperature and 74 000 cm2/V s at 25 K.

ISSN:0021-8979    

DOI:10.1063/1.346729

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

A numerical simulation approach is used to investigate various aspects of dynamic metal powder consolidation. A two‐dimensional continuum model is employed where only a few powder particles, and the interparticle voids, are considered. Consolidation is achieved by introducing large compressive stress waves in type 304 stainless‐steel powder material using a high‐velocity flyer plate. The effects of stress‐wave amplitude on the particle deformation, consolidation rate, and temperature field are discussed based on the results of simulations using projectile impact velocities of 0.5, 1.0, and 2.0 km/s. It is demonstrated that increases in stress‐wave amplitude result in higher surface temperatures leading to more extensive interparticle bonding. The 0.5 km/s impact results in full densification but is insufficient to create particle melting and bonding; the 2.0 km/s impact results in extensive interparticle melting. The effects of simple variations in the initial particle geometry are investigated by considering monosized and bimodal particle distributions and a matrix of identical hollow particles. Because each of these simulations correspond to a different initial density, the results are used to examine the effects of initial void fraction on energy deposition in the powder material during consolidation. It is shown that the average internal energy of the consolidated particles increases substantially as the initial void fraction is increased. In a final simulation, argon is placed in the regions between particles to investigate the effects of interstitial gases on the temperature field during consolidation. Shock compression of the gas results in increased surface temperatures and more extensive interparticle melting; for the materials and consolidation conditions considered, however, it is not a predominant energy deposition mechanism.

ISSN:0021-8979    

DOI:10.1063/1.346730

出版商:AIP    

年代:1990

数据来源: AIP