摘要:

An electromagnetic explanation is given in earlier experimental evidence for the possibility of exciting acoustic signals by a transient electric field in an electrolyte. The theory is in agreement with experimental observations of acoustic signals excited by some elementary electric signals. The described mechanism can be applied to the construction of ultrasonic transducers operating in liquids or in living tissues. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117295

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Since ulrahigh frequency (UHF) plasma has a low electron temperature (less than 2 eV) and uniform density, the effects of electron confinement due to the sheath potential barrier or the plasma potential distributions are less prominent than with electron cyclotron resonance plasma or inductive coupled plasma. Consequently, with no magnetic fields, the pulsed UHF plasma discharge cannot be maintained. To confine electrons at the afterglow in the pulsed UHF plasma, multiple‐cusp magnetic fields are required on the chamber wall. Under this condition, the pulsed UHF plasma can be maintained even at a pulse interval of 40 &mgr;s and can significantly improve the etching rate and etching selectivity. That is, electron confinement with magnetic fields plays a very important role for the generation of negative ions at the afterglow in a pulse‐time‐modulated plasma. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117296

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Positron annihilation spectra of arsenic‐ and gold‐implanted silicon are compared with spectra from bulk samples of arsenic and gold. Spectra with strongly reduced background intensities were recorded using a two detector coincidence system with a variable‐energy positron beam. It is shown that features in the high‐momentum region of the spectra (∼514–520 keV) can be identified with particular elements and that this identification is independent of structure, i.e., whether the element forms the bulk or is an implanted impurity. Proportionality between the intensity of characteristic spectral features and the fraction of annihilating positrons is also demonstrated, using the native oxide on a silicon wafer as a test case. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117297

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We have observed a conversion of step configuration of 3.5° miscut Si(001) surface after depositing several monolayers of Ge by using a scanning tunneling microscope. For a 3.5° miscut Si(001) surface, terraces are spaced by double‐atom height steps and all dimer rows, either on the upper terrace or on the lower terrace of a step, are normal to the step edge, defined as single‐domain (1×2) surface. After depositing 2 ML of Ge, the surface is still single domain, but dimer rows have changed their direction, running parallel to the step edge and single domain (2×1) appeared. The reason for such conversion is attributed to the strain that existed on the epilayer of Ge. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117298

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

In the search for a correlation between the magnetism and the microstructure of ultrathin films, straightforward layer‐by‐layer growth is desirable. The thermal deposition of Fe onto Cu(111), however, does not result in this growth mode. In this letter, we compare the initial growth of Fe on Cu(111) prepared by pulsed laser deposition (PLD) with thermally deposited Fe/Cu(111) using scanning tunneling microscopy (STM). In PLD, from the beginning there is two‐dimensional nucleation and growth, in contrast to the initial bilayer nucleation and growth found for thermal deposition. Therefore, it is shown by STM that PLD grown films exhibit greatly improved layer‐by‐layer growth. The different experimental results are interpreted in terms of the very high deposition rate during PLD. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117299

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

An approach is developed to describe the evolution of threading dislocation (TD) densities in lattice‐mismatched epitaxial films. TD ensembles are treated in close correspondence to chemical species in chemical reaction kinetics. ‘‘Reaction rate’’ equations are derived for changing TD density with increasing film thickness for first‐ and second‐order reactions. Selective area growth is an example of a first‐order reaction. TD annihilation, fusion, and scattering are examples of second‐order reactions. Analytic models are derived for TD behavior in relaxed homogeneous buffer layers, selective area growth, and strained layers. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117300

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Based on infrared spectra and protonic conductivity measurements, we propose a model of hydrogen ion migration in K1−yLiyTa1−xNbxO3doped crystals and use it to obtain a theoretical estimate of the diffusion constant pre‐exponential factorD0that is in reasonable agreement with the experimental result. This model shows that the transition energy of the second, and higher, overtone(s) of the [OH] vibration can be higher than the activation energy of hydrogen ion migration. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117301

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

High resolution electron energy loss spectroscopy was used to observe variations in the vibrational states of amorphous carbon films with differences in preparation methods. Diamondlike films made by pulsed laser deposition (PLD) exhibit differences in the weighted phonon density of states relative to sputtered films. These differences are due to an increase of fourfold bonded atoms in the PLD films and are in qualitative agreement with theoretical calculations for amorphous carbon networks. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117302

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Surfaces of GaN films have been investigated with photoemission spectroscopy. The measured valence band is in good agreement with band structure calculations and correlates well with tunneling luminescence measurements performed on the same samples. The effect of N depletion on band structure is explored, clarifying disagreements in previous photoemission measurements. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117303

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We investigated the temperature dependence (10–180 K) of the photoluminescence (PL) emission spectrum of self‐organized InAs/GaAs quantum dots grown under different conditions. The temperature dependence of the PL intensity is determined by two thermally activated processes: (i) quenching due to the escape of carriers from the quantum dots and (ii) carrier transfer between dots via wetting layer states. The existence of different dot families is confirmed by the deconvolution of the spectra in gaussian components with full width half maxima of 20–30 meV. The transfer of excitation is responsible for the sigmoidal temperature dependence of the peak energies of undeconvoluted PL bands. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117304

出版商:AIP    

年代:1996

数据来源: AIP