摘要:

In this letter the observation by scanning tunneling microscopy of a Au(111) surface reconstruction induced by prolonged annealing of gold films in oxygen (pO2=1 bar) at high temperature (T=800 °C) is reported. At the atomic scale, the surface is characterized by a (&sqrt;3×&sqrt;3)R30° surface structure. In addition, the surface exhibits a long‐range ordered hexagonal superstructure with a periodicity of 80 A˚ and a corrugation of about 0.5 A˚. Convincing evidence is presented that this surface morphology is induced by chemisorption of atomic oxgyen at the Au(111) surface. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.113602

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Fluorine can be naturally incorporated into the silicon oxide (SiO2−xFx) prepared by the liquid phase deposition (LPD) method at 35 °C. Fourier transform infrared and x‐ray photoelectron spectroscopy spectra show that an annealing treatment can change its bond‐structure. Changes in properties accompanying the restructuring are also observed. The annealing also densifies the LPD oxide and reduces its thickness because Si–F intensity decreases and the Si–O–Si intensity increases as annealing temperature increases. ©1995 American Institute of Physics. 

ISSN:0003-6951    

DOI:10.1063/1.113603

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Ti‐48 at. % Al powders of the metastable hexagonal‐closed‐packed solid solution with a grain size of 15 nm were prepared by mechanical alloying. The powders were consolidated to a density of greater than 99.5% by hot isostatic pressing (HIP) at 800 °C. After HIP the material exhibits a globular microstructure of the equilibrium phases &agr;2and &ggr; with a mean grain size of 150 nm. Microhardness measurements show a Hall–Petch type [E. O. Hall, Proc. Phys. Soc. B64, 747 (1951); N. J. Petch, J. Iron Steel Inst.174, 25 (1953)] dependence on grain size. Room temperature compression tests reveal low ductility, but high fracture strengths ≥1800 MPa. On increasing the test temperature the yield strength drops sharply in the temperature range 600–800 °C to very low values. The results indicate that submicron‐grained TiAl alloys can be deformed at much lower temperatures than coarse‐grained material, making them suitable as precursors for net shaping, in particular if high deformation ratios are required. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.113604

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Films of the organic semiconductor 3,4,9,10 perylenetetracarboxylic dianhydride (PTCDA) are deposited at room temperature in ultrahigh vacuum on the (2×4)‐c‐(2×8) As‐terminated, and the (2×1) Se‐passivated (100) GaAs surfaces. The PTCDA deposition on the (2×4)‐c(2×8) surface produces domains randomly oriented in the plane parallel to the interface, giving rise to diffuse ringlike low energy electron diffraction (LEED) patterns. A marked improvement in the PTCDA molecular order is observed for the growth on the Se‐passivated substrate. The resulting LEED patterns are sharp, and indicate that the interface molecular unit cells are azimuthally oriented with respect to the Se‐dimers. The improvement in the crystallinity of the PTCDA layer is attributed to the termination of the chemically active sites by Se and to the smoothness of the Se‐passivated surface. This work provides information as to the conditions under which the quasiepitaxial growth of a lattice mismatched van der Waals film oriented to the substrate can be achieved. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.113605

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Periodic arrays of 150 and 175 nm‐wide GaAs–AlAs quantum wires and quantum dots were investigated, fabricated by electron beam lithography, and SiCl4/O2reactive ion etching, by means of reciprocal space mapping using triple axis x‐ray diffractometry. From the x‐ray data the lateral periodicity of wires and dots, and the etch depth are extracted. The reciprocal space maps reveal that after the fabrication process the lattice constant along the growth direction slightly increases for the wires and even more so for the dots. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.113606

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The infrared (IR) reflection spectra of CdIn2O4films produced by rf reactive sputtering from a Cd‐In alloy target in a reactive Ar+O2atmosphere have been investigated. Experimental results show that IR reflection spectra from CdIn2O4films changed with increasing oxygen concentration and heat treatment, and the results obtained are discussed briefly. ©1995 American Institute of Physics. 

ISSN:0003-6951    

DOI:10.1063/1.113607

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Correlation between growth mode transition and photoluminescence (PL) properties of Si1−xGex/Si quantum wells (QWs) with high Ge composition grown by gas‐source molecular beam epitaxy is investigated. With increasing Ge composition in the QWs, significant deviation from the theoretical calculation is observed forx≳0.4 in the emission energy and the activation energy obtained from the temperature dependence of integrated PL intensity. Transmission electron microscopy reveals emergence of islands forx≳0.4, implying strong correlation with the anomalous PL properties. Observed PL properties are shown to be well explained by the breakdown of two‐dimensional growth. An attempt to grow luminescent QWs with flat interfaces is also presented. ©1995 American Institute of Physics. 

ISSN:0003-6951    

DOI:10.1063/1.113608

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Mean reflection coefficients of plane acoustic waves incident on a liquid‐polycrystals interface are examined experimentally and numerically. The mean reflection coefficient is defined as the complex average value of the reflection coefficient for all the crystals existing in the measurement area. Experiments are performed for a texture controlled low‐carbon steel which can be identified as the transversely isotropic polycrystalline material. The measured reflection coefficient agrees qualitatively with the mean reflection coefficient calculated by the integration of the reflection coefficients for each single crystal on the measurement area. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.113609

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

In this work, it has been shown within the framework of a simple one‐band model how the in‐plane polarized optical interconduction‐subband transitions could simply occur in quantum well structures. A novel approach is proposed for manipulating optical properties through the band‐gap engineering based on the spatial features of wave functions. The underlying physics and consequences for device applications are discussed. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.113610

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

A simple one‐speed solution to the Boltzmann equation is used to evaluate the mobility and diffusion coefficient for carriers in forward‐biased semiconductor barriers. The analysis shows that although the average kinetic energy of carriers remains near thermal equilibrium, the mobility and diffusion coefficient are strongly reduced by the built‐in field. Conventional macroscopic transport equations, which treat the carrier mobility and diffusion coefficient as single valued functions of the kinetic energy will improperly treat transport in forward‐biased barriers. The results are important for the careful analysis of metal–semiconductor and heterojunction diodes. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.113611

出版商:AIP    

年代:1995

数据来源: AIP