摘要:

Measurements of the photoacoustic (PA) effect in properly oriented triglycine sulfate (TGS) crystals from 30 to 60 °C show clearly the ferroelectric phase transition in this crystal manifested by the pronounced thermal expansion anomalies. The same method is generally applicable to similar phase transitions.

ISSN:0003-6951    

DOI:10.1063/1.106243

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

DopplerS‐parameter measurements have been performed on low‐pressure chemical vapor deposited (LPCVD) Si3N4samples. Annealing of the samples at 1000 °C for times up to 1 h resulted in a decrease of both theSparameter and the positron diffusion length of the silicon nitride. The diffusion length recovers after reimplantation of deuterium, but theSparameter remains low. The data are discussed using a model also applied to understand some electrical properties of the LPCVD nitride.

ISSN:0003-6951    

DOI:10.1063/1.106218

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

It is demonstrated for the first time that photodarkening in colored filter glasses is associated with apparent growth of CdSxSe1−xmicrocrystallites. This is thought to be due to the attraction of impurity ions around the microcrystallites. Both aQ‐switched Nd3+:YAG laser and a hybrid mode‐locked dye laser are used as the light sources. Microcrystallite growth is directly observed by transmission electron microscopy and by field‐emission scanning electron microscopy. Growth is also inferred from local changes in color and measured absorption spectra.

ISSN:0003-6951    

DOI:10.1063/1.106219

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The morphology of the nucleation and growth surfaces of oxygen‐acetylene combustion deposited diamond thin films has been studied using scanning electron microscopy. The diameters of both nucleation cells and growth surface grains have been measured and analyzed statistically. The general shape of the distributions is found to change from nucleation to growth surface for each film. The frequency distribution of cells is generallynormal, whereas, the distribution for the growth surface is found to be always lognormal. The change in shape of the distributions from normal for the nucleation surface to lognormal for the growth surface can be explained from a stochastic theory of growth.

ISSN:0003-6951    

DOI:10.1063/1.106220

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

We have studied the evolution of the surface topography of neon‐bombarded gold films, from the initial stages of sputter damage to the removal of several layers. Energy‐dependent sputter yields and crater size distributions are derived from scanning tunneling microscope (STM) images which show the progressing surface erosion. A surprising duality in the behavior of surfaces prepared by deposition of atoms (growth) and ‘‘deposition of vacancies’’ (erosion) is revealed.  

ISSN:0003-6951    

DOI:10.1063/1.106221

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The composition dependence and room‐temperature metastability of the paramagnetic nitrogen dangling‐bond center is amorphous silicon nitride suggest that its energy level lies close to the Np&pgr; states, in agreement with theoretical calculations.

ISSN:0003-6951    

DOI:10.1063/1.106222

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Vertical electrical transport in the heterostructure hot‐electron diode is considered theoretically. We present a simple dynamical model which consistently explains the measured S‐shaped negative differential conductivity in the current‐voltage characteristics. The model predicts a new type of self‐sustained 60 GHz voltage oscillations between tunneling and thermionic emission if the sample is driven by a dc voltage source having a resistor in series and a capacitor in parallel.

ISSN:0003-6951    

DOI:10.1063/1.106223

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The effect of hydrogen passivation on the photoluminescence of Si‐rich superlattices is investigated. The as‐grown samples show many defect‐related luminescence signals and several additional luminescence peaks believed to originate from the superlattice. The background luminescence along with the dislocation and defect lines are found to be passivated by the hydrogen atoms. The intensity of the superlattice peak increases after passivation and its phonon replica, initially submerged in the background and defect luminescence signals, is highlighted. After a subsequent temperature annealing in N2, the background luminescence is increased as hydrogen outdiffuses but the superlattice main peak decreases, perhaps due to the change of the carrier lifetime.

ISSN:0003-6951    

DOI:10.1063/1.106224

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

We have measured transport properties in an AlGaAs/AlxGa1−xAs, triangular quantum well whose energy spectrum has been varied by means of gate bias. We have observed several nonlinear effects in the lateral conductance arising at positive gate voltages as the increasing Fermi level is moved toward the lowering energy positions of the excited subbands in the quantum well. We interpret our results in terms of electron population of the excited subbands in which electrons possess low mobility. Finally, we find new features at high lateral voltages which are considered to be an evidence of previous predicted electrophonon resonance.

ISSN:0003-6951    

DOI:10.1063/1.106225

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

We present electrooptic modulation results on [100], [211]A and [211]B oriented InGaAs/GaAs multiple quantum wells. Internal electric fields are generated by a combination of strain, due to lattice mismatch, and the piezoelectric properties of III‐V semiconductors in the [211] structures. These fields have opposite orientation in the [211]A and [211]B samples. They do not occur in the [100] samples. The total electric field is a superposition of the strain‐generated field, the built‐in field from thep‐njunction and any externally applied field. We show that whereas in the conventional [100] structures the exciton energy is a quadratic function of applied field, the strain‐generated fields cause a linear shift in the exciton resonance with applied field in the [211] structures. In addition, the direction of the excitonic shift is opposite in the [211]A and [211]B samples, because the sign of the strain‐generated fields are opposite for these samples.

ISSN:0003-6951    

DOI:10.1063/1.106226

出版商:AIP    

年代:1991

数据来源: AIP