摘要:

A unique microwave plasma chemical vapor deposition (MPCVD) technique was employed to produce multiply twinned diamond films with quintuplet wedges. Biased nucleation, nonbiased growth, and high methane/hydrogen ratio (≳5%) were used to prepare the multiply twinned diamond films. The growth parameter &agr; was carefully controlled to be close but larger than 3/2 to allow the multiply twinned particles with quintuplets to outgrow the parent face to form the secondary crystals with uniformly distributed particle sizes and smooth surface. Since there is no need to suppress the natural growth of twins in vapor‐grown diamond, higher growth rate was achieved. Excellent field emission properties of such films compared to the normal MPCVD diamond films were also obtained. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117331

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We report the Rutherford backscattering spectroscopy/channeling studies of epitaxial grown Ag films on Si(100) substrates irradiated with fast ions (12C++,19F++,28Si++) in the energy range between 0.5 and 4 MeV at 200 and −150 °C. The quality of the Ag films is improved considerably by ion irradiation. Irradiation with 0.5 MeV28Si ions to 2×1016/cm2at 200 °C, for example, reduces the channeling minimum yield from 55% to 6% at the Ag surface. The improvement of crystalline quality is brought about by a decrease in mosaic spread in the Ag film. Also, it is found that the higher the crystallinity, the more radiation‐induced defects are produced. The mechanism involved in the irradiation‐induced improvement is discussed. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117332

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We have developed a simple tapping mode in atomic force microscopy using a capacitive electrostatic force. In this technique, the probe‐to‐sample distance is modulated by the capacitive force between tip and sample induced by a sinusoidal bias applied to the conductive probe instead of a conventional mechanical vibration. The electrostatic force versus distance curve of the probe indicates that it is necessary to use a rather stiff cantilever to prevent the snapping of the tip into the surface due to the adhesive force at the surface. We have succeeded in obtaining topographic images of a conductive surface as well as a soft polystyrene sample with a low tracking and lateral force through this method. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117333

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

A simple model is presented for rectangular cantilevers when vibrating in various media. The mass of the surrounding medium affected by the motion of the lever is calculated. It depends on the dimensions of the lever, on the excited mode, and on the density of the medium. Although the viscosity of the media is not taken into account, the resulting predictions for the resonance frequencies agree well with experimental data obtained for levers in air and water up to the seventh harmonic. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117334

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Time‐resolved photoluminescence (PL) has been employed to study the optical transitions and their dynamic processes and to evaluate materials quality of InGaN epilayers grown by metalorganic chemical vapor deposition. Our results suggest that the PL emissions in InGaN epilayers result primarily from localized exciton recombination. The localization energies of these localized excitons have been obtained. In relatively lower quality epilayers, the localized exciton recombination lifetime &tgr;, decreases monotonically with an increase of temperature. In high quality epilayers, &tgr; increases with temperature at low temperatures, which is a well‐known indication of radiative exciton recombination. Our results demonstrate that time‐resolved PL measurements uniquely provide opportunities for the understanding of basic optical processes as well as for identifying high quality materials. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117335

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The formation of donor–acceptor pairs was detected by perturbed &ggr;&ggr; angular correlation spectroscopy. In ZnSe, ZnTe, and CdTe crystals doped with the donor111In and one of the acceptors N, P, As, or Sb the strength of the electric field gradient shows a systematic correlation of the bond length between the respective acceptor and the neighboring cation. For N acceptors, an inward relaxation of the neighboring cations is concluded to occur. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117336

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Distinctly different exciton properties in pseudomorphic and strain relaxed ZnCdSe/ZnSe structures grown on GaAs are demonstrated. For pseudomorphic or partly strained structures temperature stability of photoluminescence depends on the distance from the ZnCdSe quantum well to GaAs/ZnSe interface and less on confinement energies. Densities of two‐dimensional localized states and averaged localization energies, as seen by excitons, are determined from the photoluminescence kinetics measurements. These values are compared with the ones reported for contemporary GaAs/AlGaAs structures. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117337

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

A newly developed porous glass, nanochannel glass, was used to fabricate uniform, high‐density GaAs and InAs micro‐ and nanowires with high aspect ratios. The fabrication process utilized reactions between organogallium and organoindium compounds with arsine to produce polycrystalline GaAs and InAs with crystallite sizes of approximately 50–130 A˚ when annealed at 400–500 °C. At the higher annealing temperatures, the InAs wires exhibited an increase in surface porosity and grain size, whereas the GaAs wires maintained a uniform, smooth texture. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117338

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Dislocations and traps inp‐InGaAs/GaAs lattice‐mismatched heterostructures are investigated by cross‐section transmission electron microscopy (XTEM) and deep level transient spectroscopy (DLTS). The misfit dislocations and threading dislocations observed by XTEM in different samples with different In mole fractions and different InGaAs layer thicknesses over all satisfy the Dodson–Tsao plastic flow critical layer thickness curve. By comparing the XTEM and DLTS results, we identify that the threading dislocations in bulk layers introduce three hole trap levels H1, H2, and H5 with DLTS activation energies of 0.32, 0.40, and 0.88 eV, respectively, and one electron trap level E1 with a DLTS activation energy of 0.54 eV. The misfit dislocations in the relaxed InGaAs/GaAs interface induce a hole trap level H4 with a DLTS activation energy of 0.67–0.73 eV. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117339

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The effects of vacuum annealing on the optical absorption spectra in the visible and infrared ranges, photoluminescence intensity, and concentration of paramagnetic centers in free‐standing porous silicon films were investigated in a temperature range of 100–600 °C. It was found that heat‐induced hydrogen desorption decreased the porous silicon band gap, which suggests that band‐gap energy depends on hydrogen coverage of nanoparticles. The annealing also leads to increasing concentration of defects that were identified as silicon dangling bonds. The energy distribution of the dangling‐bond states was estimated from the absorption spectrum. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117340

出版商:AIP    

年代:1996

数据来源: AIP