摘要:

The layer compounds WS2and MoS2were exfoliated into single layers suspended in solution, and conditions were adjusted to produce a new homogeneous structure that is believed to be built of alternating layers of WS2and MoS2recrystallized in a 1Tstructure. Evidence for this is provided by the observation of a new hexagonal structure with expanded lattice spacings relative to the identical lattice spacings of the original materials and the fact that if the Mo:W ratio differs from 1:1, the x‐ray diffraction shows that some of the original WS2or MoS2phase is present. The catalytic activity of the alternating layer material is extremely high for the methanation reaction. It is observed and concluded that the alternating material is made up of fine particles, and a model of flocculation is presented to explain why in this material the particles are so fine.

ISSN:0021-8979    

DOI:10.1063/1.345661

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The electrical properties and structural defects of Te‐doped GaAs grown in space have been investigated by using various techniques. The experimental results confirm that the microgravity conditions offer some advantages for the melt growth of III‐V compound semiconductor materials; improvements of homogeneity and perfection as well as purity of the space GaAs single crystal are expected.

ISSN:0021-8979    

DOI:10.1063/1.345662

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The emission of Si, SiCl, Cl, Cl2, CCl, Cl+, and Cl+ 2has been observed in a CCl4rf discharge in the presence of Si(100) in a plasma etching system. Spectral intensities have been recorded over a wide range of process gas flow rates and rf powers. These data have been analyzed to show that (i) SiCl emission from theA˜ state arises through chemiluminescent reactions of metastable (1S) Si and (ii) the species which leaves the Si surface in the etching process is SiClx(x=0, 1, or 2) rather than SiCl3or SiCl4. To arrive at these conclusions, detailed chemical models are examined and shown quantitatively to reproduce our observed variations of emission with flow and power.

ISSN:0021-8979    

DOI:10.1063/1.345663

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Enhanced oxidation of ZnS and ZnSe semiconductor surfaces has been observedinsituduring electron irradiation in a high‐resolution electron microscope. The phase present at the surface region has been identified as ZnO by optical diffractogram and selected area electron diffraction techniques. For ZnS oxidation, both hexagonal ZnO having a random orientation and cubic ZnO in perfect epitaxial relationship with the bulk ZnS were observed. Enhanced oxidation of ZnSe to ZnO has also been observed under electron beam irradiation. However, only the hexagonal form was observed. The oxidation rates for both ZnS and ZnSe depended on electron flux but was independent of orientation. A model in which the oxidation process is limited by diffusion through the oxide film is proposed. By electron irradiation the diffusion rate is enhanced presumably by a nonthermal process.

ISSN:0021-8979    

DOI:10.1063/1.346098

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Metastable single‐phase, NaCl‐structure, polycrystalline Ti0.5Al0.5N alloy films have been shown to exhibit much better high‐temperature (750–900 °C) oxidation resistance than polycrystalline TiN films grown under similar conditions. The Ti0.5Al0.5N alloys, &bartil;3 &mgr;m thick, were deposited at temperatures between 400 and 500 °C on stainless‐steel substrates by dc magnetron sputter deposition in mixed Ar+N2discharges with an applied negative substrate biasVsof either 0 or 150 V. Oxidation in pure O2initially occurred at a rate that varied parabolically with time. The oxide overlayers consisted of two partially crystalline sublayers, the upper one Al‐rich and the lower one Ti‐rich, with no measurable N concentrations in either. Inert‐marker transport experiments showed that oxidation proceeded by the simultaneous outward diffusion of Al to the oxide/vapor interface and inward diffusion of O to the oxide/nitride interface. The oxidation rate constant K increased with oxidation temperatureToxat a rate much higher than would be predicted from a simple exponential dependence due to changes in the oxide microstructure (increased crystallinity) with increasingTox. AtTox≥850 °C, O transport became the rate‐limiting step. After oxidation times, ranging from 6 h at 750 °C to 7 min at 900 °C, oxide crystallites, exhibiting a tetragonal rutile TiO2structure, were observed inVs=0 samples to grow at an accelerated rate up through cracks in the oxide overlayer. The formation of these crystallites was postponed until a much later stage in oxide‐overlayer development for samples grown withVs=150 V.

ISSN:0021-8979    

DOI:10.1063/1.345664

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The use of x‐ray diffraction techniques for studying twin microstructure and particle‐size analysis of (111) CdTe and (111) ZnTe layers grown by metalorganic chemical vapor deposition on GaAs substrates is demonstrated. Two types of twins, lamella and double positioning, were identified, both composed of small particles (domains). A procedure is presented for the determination of the particle thickness and width as well as the lamella thickness. CdTe(111)Blayers are typically characterized by a two‐dimensional growth mechanism, smooth surface appearance, relatively high growth rate, and lamella twin structure. On the other hand, the (111)A‐oriented layers (CdTe and ZnTe) exhibited a three‐dimensional growth mechanism, rough surfaces, low growth rates, and double‐positioning twins with a preferred twin orientation of the substrate.

ISSN:0021-8979    

DOI:10.1063/1.345665

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

High throughput, low‐temperature deposition, sharp interfaces, and selective deposition with direct ion‐, electron‐, and photon‐beam‐controlled techniques are some of the key driving forces for the development of superconducting thin films by metalorganic chemical vapor deposition (MOCVD) technique. In this paper we report on the electrical and structural properties of Y‐Ba‐Cu‐O (YBCO) films deposited by MOCVD on yttrium‐stabilized zirconia (YSZ) and BaF2/YSZ substrates using a single‐stepinsituprocessing method which requires no further annealing. YBCO films deposited on BaF2/YSZ substrates have zero resistance at 80 K. The films were characterized by energy dispersive x‐ray analysis, x‐ray diffraction, scanning electron microscopy, and transmission electron microscopy. The films on BaF2/YSZ substrates exhibited textured growth having both thecandaaxis perpendicular to the substrate. The use of BaF2as a buffer layer suggests three‐dimensional integration of high‐temperature superconducting thin film for hybrid superconductor/semiconductor devices as well as superconductor switches and other related devices.

ISSN:0021-8979    

DOI:10.1063/1.345666

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Epitaxial silicon wafers having an epitaxial layer of 110 &mgr;m thickness were nucleation annealed at 750 °C for times up to 72 h. This was followed by 16‐h growth anneal at 1050 °C. After the annealing sequence, the minority‐carrier lifetime of the epitaxial layer was characterized using the pulsed metal‐oxide‐semiconductor capacitance‐time transient analysis. A significant improvement in the generation lifetime of the epitaxial layer of the samples which received the nucleation anneal was observed. In contrast, the nucleation anneal appeared to have no effect on the recombination lifetime. From the experimental results, the electronic defects responsible for the limitation of the recombination lifetime of a thin epitaxial layer were hypothesized to be the complexes of metallic impurity and boron originating in the heavily doped substrate region of the epitaxial wafer.

ISSN:0021-8979    

DOI:10.1063/1.345667

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Modern high‐energy magnetic materials such as samarium‐cobalt and neodymium‐iron‐boron require very large magnetizing fields to achieve full saturation. In some cases the recommended magnetizing field is as high as 40 kOe. Such a field is readily achievable in a large solenoid, and unidirectional magnetization is easily accomplished. Many applications, such as motors and linear actuators, however, require multipole magnets. The problem of designing custom fixtures for multipole magnetization has often been considered more of an art than a science. This paper shows that by mathematically modeling the capacitor discharge magnetizer and the fixture the problem can be solved with reasonable predictability. Two different multipole fixture designs are presented along with the experimental results. The basic equations are presented and used to predict the magnetic‐field intensity inside the fixtures. It is shown that optimum performance is achieved when the resistance of the fixture is equal to the parasitic resistance of the magnetizer. Finite‐element analysis is also used as part of the design process. The experimental results have been achieved using a high‐voltage, low‐energy capacitor‐discharge magnetizer and air core fixtures. The magnetization patterns that are produced are very sharp and well defined.

ISSN:0021-8979    

DOI:10.1063/1.345668

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

A vertical amorphous silicon thin‐film transistor that has a very short channel length that is determined by deposition, not lithography, is described. These transistors have a field‐effect mobility of approximately 0.5 cm2/V s, an effective channel length of 1.5 &mgr;m, and a dynamic range of over five orders of magnitude. A method for suppressing excessive leakage currents and improving the saturation of the output characteristics by a novel current‐blocking technique is shown. A two‐dimensional computer program is used to analyze these devices and guide their design and optimization. Unlike a conventional thin‐film transistor, the current path is primarily parallel to the electric field created by an insulated gate electrode. These vertical transistors are easy to fabricate, compatible with large‐area processing techniques, and have suitable terminal characteristics for use in practical circuits.

ISSN:0021-8979    

DOI:10.1063/1.345669

出版商:AIP    

年代:1990

数据来源: AIP