摘要:

First-principles molecular orbital methods and gradient-corrected density functional calculations on silicon clusters are used to study possible pathways for the initial oxidation of Si (100)-2×1. In these reactions, the adsorbed hydroxyl oxygen inserts into the dimer Si–Si bond to form a suboxide (&trpbnd;Si–O–Si&trpbnd;) surface structure. The reaction typically follows a two-step pathway involving an intermediate energy minimum. In the case of an ideal surface with full water coverage, the reaction is exothermic by 1.3 eV and the overall reaction barrier is estimated at 2.4 eV. However, an alternative pathway involving a dangling bond site lowers the activation barrier to 2.1 eV. The implications for the oxidation reaction rates are discussed as well as possible alternative pathways. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122013

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Wurtzite GaN films were grown on silicon nitride buffer layers formed on Si (111) substrates by radio frequency plasma-assisted molecular beam epitaxy. Reflection high energy electron diffraction, Auger electron spectroscopy, transmission electron microscopy, and photoluminescence results indicate that the single crystalline wurtzite GaN was grown on the buffer layers of amorphouslike silicon nitride formed on Si (111) substrates by taking the following relationship with the substrate: GaN [0001]//Si [111] and GaN (1¯1¯20)//Si (11¯0). Both faces of the silicon nitride buffer layer were found to be flat and sharp, the thickness of the buffer layer (1–1.5 nm) being constant across the interface. Efficient bound exciton emission was observed at 3.46 eV. The growth technique described was found to be simple but very powerful for growing high quality GaN films on Si substrates. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122014

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We have observed photoluminescence ofAl1−xInxNfilms. The films were grown on GaN by atmospheric pressure metalorganic vapor phase epitaxy. GaN was grown on ac-plane sapphire substrate with a low-temperature deposited AlN buffer layer. Photoluminescence, absorption, and x-ray diffraction measurements have shown that each spectral peak shifts with alloy compositionxand thatAl1−xInxNheteroepitaxial films are not macroscopically in phase separation and are constituted in the wurzite structure. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122015

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

After obtaining an epitaxially laterally overgrown GaN on sapphire by the metalorganic chemical vapor deposition method, GaN growth was continued up to a thickness of 200 &mgr;m by a hydride vapor phase epitaxy method. The InGaN multi-quantum-well-structure laser diode (LD) was grown on a free-standing GaN substrate, which was obtained by removing the sapphire substrate. The LDs with cleaved mirror facets showed an output power as high as 160 mW under room-temperature continuous-wave (CW) operation. The fundamental transverse mode was observed up to an output power of 80 mW. The lifetime of the LDs at a constant output power of 5 mW was about 180 h under CW operation at an ambient temperature of 50 °C, due to a high threshold current density of 14 kA/cm2. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122016

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We report on the anisotropic polarization of the luminescence observed in ZnSe-based heterostructure lasers. It has been found that light originating from the radiative recombination of electrons and holes confined in the ZnCdSe quantum well of the laser is linearly polarized collinearly to one ⟨110⟩ crystallographic direction after having passed thep-type region of the laser diode. A strong dependence of the laser operation on the two possible ⟨110⟩ directions of cleaved facets is observed. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122017

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

High-energy (1 MeV), ion irradiation of GeSi/Si strained layers at elevated temperatures can cause strain relaxation. This study examines the defects responsible for relaxation and for the evolution of the strain during subsequent annealing. Three distinct annealing stages are identified and correlated with the defect microstructure. In the temperature range from 350 to 600 °C, a gradual recovery of strain is observed. This is shown to correlate with annealing of small defect clusters and the growth of voids. The voids are visible at annealing temperatures in excess of 600 °C, consistent with an excess vacancy concentration in the irradiated alloy layer. In the temperature range 600–750 °C, the strain recovers to a maximum value which is correlated with the ripening of voids, dissolution of alloy layer {113} rodlike defects, and {113} planar interstitial defects in the substrate. At temperatures in the range 750–1000 °C, strain relaxation is observed and is correlated with the growth of intrinsic dislocations within the alloy layer. These intrinsic, looplike dislocations nucleate at the alloy–substrate interface and grow within the alloy layer, toward the surface. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122018

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The effect of ultrathin oxides on nanocrystallites of luminescent porous silicon is studied using infrared, optical, and Auger spectroscopy. Room-temperature oxidation is performed usingH2O2immersion and UV ozone interactions, producing oxides of ∼5 and ∼10 Å, respectively. TheH2O2oxidized sample is optically active, while the ozone oxidized sample is not active. UV–ozone produces a transverse optical Si–O–Si mode blueshifted by∼90 cm−1from bulk oxide, whichH2O2does not produce. Auger SiLVVspectra show an oxidelike signal for UV/ozone samples and a Si-like signal forH2O2samples. We discuss this in terms of different oxidation behaviors that either preserve or break Si–Si dimers that may be responsible for the optical behavior. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122019

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The voltage bias, temperature, and magnetic field dependence of the differential conductance of the interface between a half-metallic ferromagnet and a high-Tcsuperconductor have been studied inDyBa2Cu3O7/La2/3Ba1/3MnO3heterostructures. Below the superconducting transition the differential conductance exhibits a dip at zero bias whose amplitude is a decreasing function of temperature and/or magnetic field. These results are interpreted qualitatively using a picture based on the suppression of Andreev reflection as a consequence of the high spin polarization of the carriers in the half-metallic ferromagnet. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122020

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Single-pulse laser ablation of polyimide was investigated by using focusedUV-Ar+-laser radiation(&lgr;≈302 nm,140 ns⩽&tgr;l⩽50 ms)and atomic force microscopy. The results clearly demonstrate that the ablation rates donotdepend on the total dose only, but depend as well on the duration of the laser pulses,&tgr;l.The experimental results can be interpreted almost quantitatively on the basis of a purely thermal model. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122021

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Ultrahigh density data storage on a novel organic thin film by scanning tunneling microscope (STM) under ambient conditions is demonstrated. The material, N-(3-nitrobenzylidene)p-phenylenediamine (NBPDA), is used for preparing thin film by vacuum evaporation method. Crystalline NBPDA films with electrical bistability are obtained by this method. Recording experiment on the films is made by applying voltage pulses between the STM tip and substrate. The recorded marks are 0.7 nm in size, corresponding to a storage density of1014 bit/cm2.Current–voltage characteristic measurement shows that the resistance of the unrecorded region of the NBPDA films is much higher than that of the recorded region. The mechanism of recording is discussed. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122022

出版商:AIP    

年代:1998

数据来源: AIP