摘要:

The influence of the flexoelectric polarization on the nematic surface energy is analyzed. It is shown that if the dielectric constant of the substrate is lower than a critical value the undistorted orientation is no more the one corresponding to lowest energy. The presence of a conducting substrate is also considered. In this case it is shown that by changing the thickness of the dielectric material deposited over the conducting material, a surface order transition is expected. Furthermore, the influence of a finite anchoring energy between nematic and substrate on the critical value of the dielectric constant is discussed.

ISSN:0021-8979    

DOI:10.1063/1.347015

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Arsenic ions have been implanted in (100)Si at an incident energy of 1 MeV to a dose of 1×1015/cm2. Rutherford backscattering measurements with a 1.5‐MeV He‐ion beam have shown that a buried amorphous layer is formed in the Si substrate which is implanted at a low ion‐beam current of 0.8 &mgr;A and that considerable annealing occurs when implantation is carried out at a high ion‐beam current of 2 &mgr;A. The implantation‐induced amorphous layer recrystallizes after annealing above 550 °C, but a high density of lattice defects still remains in the substrate even after annealing at 1000 °C. Defect observations using a cross‐sectional transmission electron microscope have revealed that those defects are located at the two depths corresponding to the initial transition regions where the crystallinity is changed from the amorphous to nonamorphized states in the substrate. In addition, secondary defects also exist in a particular region inside the initial buried amorphous layer. The recrystallization of the buried amorphous layer during post‐implant annealing is initiated not only from the deeper part of the substrate but also from the nonamorphized surface layer. From a series of isothermal annealing studies, it has been shown that the recrystallization rates at 550 °C are 140 and 180 A˚/min on the frontside and backside of the buried amorphous layer, respectively. Electrical profile measurements, using the differential Hall method, have shown that a highly doped, buried conductive layer with a peak carrier concentration of around 2×1019/cm3can be formed by annealing above 800 °C.

ISSN:0021-8979    

DOI:10.1063/1.347193

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Differential Hall measurements at 77 K were done on 150‐keV boron implantedp‐type mercury‐cadmium‐telluride (HgCdTe).n+layers formed as a result of implantation with various doses were very sharp and thicknesses of then+layers were found to depend on boron dose. The sheet carrier concentration tends to saturate above the dose 1×1013cm−2.

ISSN:0021-8979    

DOI:10.1063/1.347016

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Polycrystalline ZnSe thin films were grown by ion‐beam deposition on glass substrates. The crystallinity of ZnSe films grown by ion‐beam deposition is affected by ionization. In particular, at a substrate temperature of 200 °C, there is an abrupt increase in the number of (311) oriented grains. Without ionization, the (111) oriented grains predominate. Transmittance of ZnSe films is improved by ion‐beam deposition at substrate temperatures below 200 °C, in the wavelength range of 460–550 nm near the interband absorption edge. Ion‐beam deposition has a heating effect on the film surface during deposition by ion bombardment, which controls the crystallinity and the optical properties of ZnSe films at low substrate temperature on noncrystalline substrates.

ISSN:0021-8979    

DOI:10.1063/1.346991

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The impurity effects on the creation of Ga vacancies in Si‐doped GaAs grown on a Be‐doped epilayer by molecular‐beam epitaxy were investigated through slow positron beam measurements. Doping of Si impurities enhances the creation of Ga vacancies in GaAs. The experimental results support the theoretical prediction of the creation of Ga vacancies in terms of the change in the Fermi‐level position by the Si doping into GaAs, and also suggest that a Si atom diffuses in GaAs as a neutral complex of SiGa‐VGarather than that of SiGa‐SiAs. The change in theSparameter distribution at the interface between Si and Be‐doped regions is explained by the Be carryforward phenomenon which occurs during the growth of Si‐doped GaAs on a Be‐doped epilayer.

ISSN:0021-8979    

DOI:10.1063/1.346992

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Thin native oxide films on Si(100) have been previously shown to be decomposed by exposing the film surface to synchrotron radiation (SR) in the vacuum‐ultraviolet region. In this study, photoemission and photon‐stimulated desorption (PSD) experiments are performed to investigate the synchrotron‐radiation‐induced decomposition of a native oxide film on Si(100). For mass analysis of the PSD ions, the time‐of‐flight method is utilized. Si 2pcore‐level and valence‐band photoemission spectra demonstrate that the native‐oxide decomposition preferentially takes place on the thin parts of the native oxide film which are terminated with Si—OH and Si—H bonds. It is shown that the native‐oxide decomposition is accompanied by desorption of H+and O+ions. The H+PDS ion yield decreases exponentially with increasing the exposure time of SR, whereas the O+PSD one first increases with the exposure time, and subsequently decreases with the exposure time after the H+PSD ion yield substantially drops. The behavior of the O+PSD ion yield is explained in terms of the photon‐induced Si—O bond breaking reaction promoted by removing surface hydrogen atoms through the H+PSD process in which a Si—H bond and the O—H bond in a Si—OH bond are ruptured.

ISSN:0021-8979    

DOI:10.1063/1.346993

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The variations of Raman spectra for Si‐implanted (100) GaSb with various doses and energies were investigated. Samples implanted at room temperature showed disorder or amorphous layer. In order to heal the damage layer, furnace annealing as well as rapid thermal annealing were used. We got a better structural recovery with increasing the annealing temperature or time, and rapid thermal annealing showed better results in comparison with conventional furnace annealing. The relative intensities of longitudinal optical phonons from Raman spectra by rapid thermal annealing samples were compared with those of unimplanted GaSb. It is found that a better recovery of damage layer is formed comparable to an unimplanted wafer when the annealing temperature is 600 °C for 30 s.

ISSN:0021-8979    

DOI:10.1063/1.346994

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

n‐type GaAs specimens have been annealed in sealed quartz ampoules and characterized with electron‐beam‐induced current and photoresponse measurements, deep‐level transient spectroscopy, and photoluminescence spectroscopy. By correlating changes in the concentrations of defects with minority‐carrier diffusion length (Lp) it is shown that the dominant recombination center in this material is a hole trap termed HCX (Ev+0.29 eV). Increases inLpof up to a factor of 3, which can be achieved by proximity annealing at 950 °C for 16 h, are related to the loss of As from the specimen surfaces during the early stages of annealing. The beneficial effect of the annealing is associated with a limited source diffusion process since the total amount of As loss is determined by the ratio of the ampoule volume to the GaAs surface area. Proximity protection of the surfaces is necessary to prevent the generation of a Ga vacancy‐related hole trap HCZ (Ev+0.57 eV).

ISSN:0021-8979    

DOI:10.1063/1.346995

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Three techniques have been combined to correlate interface morphology and optical properties of single AlAs‐GaAs quantum wells grown by molecular beam epitaxy (MBE) with and without growth interruption at the inverted (GaAs on AlAs) interface. Surface recovery and interface formation were monitoredinsituby reflection high energy electron diffraction, optical properties were assessed by photoluminescence excitation (PLE) spectroscopy and the results compared with a Monte Carlo simulation of MBE growth, extended to evaluate PLE linewidths. Criteria for linewidth reduction have been established and interface morphology described.

ISSN:0021-8979    

DOI:10.1063/1.346970

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Measurements of the acoustic quality factor (reciprocal internal friction) of commercial aluminum alloys 2090, 5056, and 6061 in a torsional vibrational mode at a frequency of 1 kHz in the temperature range from 50 mK to 300 K are reported. The temperature dependence of the mode frequency, which is a measure of the shear modulus of the material, is also given. The quality factor (Q) of all alloys exhibited the highest values at the lowest measurement temperature. A heat‐treated sample of the 5056 alloy gave the highestQof 6.5×107at 53 mK. MaximumQvalues of 8.9×106in 2090 and 6.5×106in 6061 were observed. Internal friction mechanisms which may explain the measuredQvalues are discussed. The results provide support for the planned construction and operation of very sensitive 50‐mK aluminum‐alloy bar gravity‐wave detectors.

ISSN:0021-8979    

DOI:10.1063/1.346971

出版商:AIP    

年代:1990

数据来源: AIP