摘要:

So-called “anode activation” is shown to entail the growth of metallic fibers with nanometric dimensions. These fibers grow from dendritic deposits comprised of carbon and chromium, and thus chromium is a major component. They are confined inside thin-wall carbon nanotubes, with their diameter defined by the inner diameter of the host nanotube. This growth behavior reflects a template-mediated type of fiber growth. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119811

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The dynamics of a vibrating cantilever with an attached tip in contact with a solid is treated analytically. The tip length is shown to be crucial in determining the resonant response. The finite tip size changes the boundary conditions for the flexural motion, rendering the cantilever-tip-sample combination more rigid and implicating both the normal and lateral stiffnesses of the sample in the analysis. This is confirmed in an experiment with a silica sample, a sapphire tip, and a silicon cantilever. The theory has implications in the field of quantitative analysis with atomic ac force microscopy. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120547

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The suppression effect of oxygen on Si incorporation in homoepitaxial diamond films grown by microwave assisted chemical vapor deposition is investigated by secondary ion mass spectrometry. The Si depth profile in the multilayered diamond films continuously synthesized with different oxygen addition shows that Si incorporation decreases with increasing oxygen addition into the plasma. A change in the interfacial composition at the quartz glass due to oxygen-promoted surface chemistry may be the origin of this suppression effect. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119812

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Amorphous carbon films are prepared by plasma-assisted chemical vapor deposition. Resistivity of the films is measured from 300 down to 8 K showing a negative temperature coefficient of resistivity. An increase of room temperature conductivity from102S cm−1to a value of about104S cm−1is found at a pressure of 2 GPa. At a fixed pressure of 0.5 GPa, the films show a positive temperature coefficient of conductivity in the range from 300 to 200 K, followed by a very weak dependence of temperature down to 15 K. At a pressure of 2 GPa a positive temperature coefficient of resistivity is observed in the range between 300 and 15 K. The metallic behavior of the carbon films under high pressure is explained using electronic structure. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120425

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The mechanism of room-temperature (RT) intrinsic optical transition in high quality and purity GaN epilayer grown by metalorganic chemical vapor deposition (MOCVD) has been investigated. Our results show that the band-to-band instead of excitonic transition is the dominant transition in MOCVD grown GaN epilayer at RT. This conclusion is supported by the observation of the excitation intensity dependence of the photoluminescence emission peak position and by a model calculation. The band-to-band transition energy at RT at the limit of low carrier concentration has been determined to be 3.429 eV. Since the band-to-band transition is the dominant optical transition at RT, it thus suggests that the electron-hole plasma is most likely responsible for gain in GaN blue lasers similar to the case in other III–V semiconductor lasers. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119813

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A systematic investigation of GaAs layers grown at low temperatures was carried out by means of positron annihilation. The vacancy defects in undoped as-grown material were identified to be mainly Ga vacancies(VGa)by comparing the annihilation parameters to those of Ga vacancies in highly Si-doped GaAs. The characteristicSparameter for positron annihilation in Ga vacancies was determined to beS(VGa)=1.024(1).TheVGaconcentration increases up to1018 cm−3by decreasing the growth temperature to 200 °C. The vacancy concentration can account for the compensation ofAsGa+antisites as was previously assumed. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119814

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We report on a high bandwidth measurement of the transient intersubband photocurrent of a GaAs/AlGaAs multiple quantum-well infrared photodetector (QWIP). The photocurrent is excited via tunable subpicosecond infrared pulses. The response time of the detector has a full width at half-maximum of 18.5 ps and a rise time of 14.5 ps, which is limited by the electrical circuit. The decay time of the photocurrent response exhibits a significant dependence on the applied voltage, with increasing decay times for increasing bias voltages. From the experimental data, we conclude that the intrinsic response time of a QWIP is less than 7 ps. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119815

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Photoluminescence spectra of porous silicon prepared with electro-chemical etching, were analyzed using a simple model based on a statistical distribution of particle size. It was found that the size of nanoparticles, obeys the logarithmic normal distribution in all the porous silicon investigated here. This model also explains the dependence of the photoluminescence spectrum on the excitation energy. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119816

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

By using the technique of noncollinear nearly-degenerate four-wave mixing, ambipolar diffusion coefficients and carrier lifetimes were directly determined for a compressively-strained InGaAsP multiple quantum well semiconductor optical amplifier operating at 1.3 &mgr;m. A diffusion coefficient of8.0 cm2/sand a carrier lifetime of 1.33 ns, were obtained at the amplifier current density of 1.88kA/cm2.The current-density dependent measurements show that the diffusion coefficient will drop with increasing amplifier pumping current, which is consistent with the prediction of the conventional semiconductor theory. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119817

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We have investigated the intrinsic modulation response ofGaxIn1-xP/AlGaInPquantum well lasers. The differential gain resulting from the measurement of the frequency response, is in good agreement with calculations based on a 6-bandkp-theory and direct measurements of the optical gain. We find a maximum value of3.8×10−16cm2for a strongly compressively strained sample, which is less than in InGaAs lasers according to the larger effective masses. The maximum bandwidth we observed is 9.3 GHz at −3 dB. We show that the bandwidth is limited by catastrophic optical damage and not by intrinsic mechanisms. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119818

出版商:AIP    

年代:1997

数据来源: AIP