摘要:

A saturation voltage method is described for determining the unified surface-anchoring energy, which has been proposed theoretically by Sugimura and co-workers [Phys. Rev. E,52, 681 (1995)], at the interface of nematic (4-pentyl-4′-cyanobiphenyl) and its alignment layer (polyvinyl cinnamate). The method proposed can be employed as a standard measure of this energy without any additional numerical calculation. A conventional measurement method of an optical retardation from a liquid crystal slab is used to estimate the saturation voltage. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120727

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

(TiO2)x−(Ta2O5)1−xthin films were prepared with radio-frequency magnetron sputtering deposition in this study. The dielectric constant measured from these films appears to critically depend on the amount ofTiO2incorporated into the film and post-anneal condition. The composition dependence was found similar to that reported on(TiO2)x−(Ta2O5)1−xbulk. The highest value of dielectric constant is about 55 for aTiO2content of 8&percent; and annealing at 800 °C. Compared to pureTa2O5thin films, significant enhancement in dielectric constant is obtained by adding small quantity ofTiO2.©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120746

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The resonant wavelengths and mode radii of the dominant and certain higher orderTEMmpmodes supported by an oxide apertured vertical cavity surface emitting lasers are determined using a scalar variational formula. The reflectivity of the Bragg mirrors and the photon lifetime are calculated for each mode and both are found to decrease with decreasing oxide aperture diameter and increasing mode number. The aperture diameter, thickness, and axial position in the cavity, together with the refractive index contrast ratio used in the Bragg mirrors, are shown to be important in controlling the suppression of higher order modes. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120728

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The effect of the growth interruption time during the growth of InGaAs/InAlAs quantum well structures is shown to have a significant effect on both the interband transitions, as determined by photoreflectance, and the electrical properties of the as-grown structure. The results show that, for increasing growth interruption time, the quantum well heterointerfaces become more abrupt and the carrier mobility increases, thereby demonstrating that long interruption times are preferable for the growth of high quality rectangular quantum well structures. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120729

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The monoatomic hydride layer on silicon was used as a prototype for resistless electron beam lithography. Arbitrary patterns with linewidths below 60 nm have been achieved. The variation of the linewidth with electron energy, electron dose, and substrate thickness was studied to determine the mechanisms that govern surface hydrogen desorption and subsequent pattern formation. Unlike in resist based lithography, no resolution enhancement was observed with decreasing substrate thickness. The experimental data in combination with Monte Carlo simulations of the backscattered and transmitted electrons suggest that surface hydrogen desorption and pattern formation are not strongly related to the backscattered electrons and the secondary electrons (energies <50 eV) associated with the backscattered electrons. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120730

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Nanoscale GaN dots were successfully formed onAlxGa1−xN/6H-SiC(0001)surfaces by gas-source molecular beam epitaxy. It was found that the growth mode can be changed by introducing Si before GaN growth, where the Si is believed to play an important role in the change of theAlxGa1−xNsurface free energy. Without introducing Si, the GaN growth mode was two dimensional and (1×3) reconstruction was observed. The growth mode of GaN was changed from two-dimensional to three-dimensional by introducing Si on theAlxGa1−xNsurface.In situreflection high-energy electron diffraction and atomic force microscopy observations were used to monitor and characterize the growth processes and surface morphology. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120731

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Ap-i-nresonant tunnel diode is designed and investigated using photoluminescence (PL) spectroscopy. The device is based on anAl0.4Ga0.6As/GaAsgraded-index waveguide heterostructure enhanced by aperiodic-superlattice injectors for simultaneous resonant injection of electrons and heavy holes. The bias-dependent study of photocurrent, electroluminescence (EL) and PL show strong resonance behavior in the optical intensity confirming the field-dependent resonant injection of the excited states in the emission layers. Pronounced voltage-current bistability due to injection efficiency leads to multiple-wavelength EL and lasing action. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120732

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We show that optical reflectivity measurements can be used to evaluate the part of aNH3flux which reacts with a Ga-terminated GaN surface or with a Ga-flux simultaneously impinging on the surface, as in standard molecular beam epitaxy situation. At least for temperatures not exceeding 700 °C, the ratio of the reacted part of theNH3flux to the incident flux can be assimilated to theNH3cracking efficiency. Being nearly zero below a threshold temperature of 450 °C, it increases with temperature but remains low(∼4&percent;)explaining why an exceptionally high V/III flux ratio is necessary to grow GaN usingNH3.©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120733

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Polycrystalline diamond films have been found to displayp-type surface conductivity. No bulk impurity is added to the films; thep-type characteristics of the undoped diamond are thought to be due to a surface or near surface hydrogenated layer. Carrier concentrations within the range1017–1019 cm−3have been measured; control over the carrier concentration can be achieved by annealing the “as-grown” films in air. For a given annealing temperature a stable carrier concentration arises. The Hall carrier mobility has been explored and a value of>70 cm2/Vshas been measured for a film with a carrier concentration of∼5×1017 cm−3,the highest reported for polycrystalline thin film diamond and equivalent to boron doped single crystal diamond. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120734

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Intense ultraviolet photoluminescence centered at 370 nm was observed from magnetron-sputtered silicon oxide films after they were annealed at about 1000 °C inN2atmosphere. This photoluminescence is found to be associated with the formation of nanocrystal silicon particles in the specially structuredSiO2,which highly resembles the oxide layer of porous silicon. The luminescence centers at the interface between the nanocrystal silicon particles and theSiO2matrix are responsible for the strong ultraviolet luminescence. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120735

出版商:AIP    

年代:1998

数据来源: AIP