摘要:

The adsorption of Cd on Ge(111) was studied with combined RHEED‐MB techniques. The reciprocal lattice of the interface was mapped as a function of absolute adatom density. For low coverages, of the order of 10−3monolayers, the Cd adatoms clustered to form islands which were either static with random orientation with respect to the substrate or mobile ’’spinners’’. At a density of &sgr;=3.2×1014/cm2the islands took on substrate symmetry and formed an incommensurate overlayer having the structure of the basal plane of hcp Cd. The observations are discussed in terms of dangling‐bond densities and the uncertainties in the absolute density determination described.

ISSN:0021-8979    

DOI:10.1063/1.323243

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

Piezoelectric materials often undergo material degradation with the application of severe stress. Consequently, repetitive testing with single samples can be very misleading if the interval between increasing stress levels is too small. In this paper, the autocorrelation analysis technique is used to determine a proper stress increment such that single sample testing is uncorrelated with previous stress exposure, consequently insuring an accurate material evaluation. Five piezoelectric materials were evaluated with electric field to 6.0 kV/cm and hydrostatic pressure to 34.5 MPa (5000 psi). Autocorrelation analysis of the data showed that electric field increments of 1.6 kV/cm and pressure increments of 5.5 MPa (800 psi) were adequate to guarantee valid results while minimizing the number of samples required. It is expected that this autocorrelation analysis technique can be used in other applications where successive measurements are being made and history‐dependent behavior is suspected or known.

ISSN:0021-8979    

DOI:10.1063/1.323244

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

Electric field‐induced deformation is studied in a unique hybrid‐aligned nematic (HAN) cell, in which the director of a nematic liquid crystal (LC) with either positive or negative dielectric anisotropy is varied continuously, lying perpendicular to one substrate and parallel to the other. The experimental results show the absence of threshold field in the birefringence–vs–applied voltage relationship as well as the slow variation of birefringence with voltage; these phenomena are analyzed in terms of the Frank‐Oseen continuum theory. Also, the above characteristics of HAN are demonstrated to have such advantages in multicolor LC display applications as low operating voltage and fairly good color separation together with uniform and bright color generation.

ISSN:0021-8979    

DOI:10.1063/1.323245

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

Photoelectron emission measurements, alternating on the same surface with ellipsometric and surface‐potential‐difference measurements, have been made during cyclic flexure fatigue of aluminum samples. A high cyclic fatigue rate was achieved with a unique electromagnetic drive. Measurements were conducted as a function of strain amplitude and oxide‐film thickness. Argon‐ion bombardment was used to achieve a pure aluminum surface. Most of the measurements, including Auger spectroscopy, were conducted in ultrahigh vacuum. The fatigue‐enhanced optically stimulated electron emission (OSEE or exo‐electron current) increases with strain amplitude or surface roughening and decreases with oxide thickness. The mechanism of emission is discussed in relation to enhanced plasmon coupling due to surface roughening during fatigue cycling.

ISSN:0021-8979    

DOI:10.1063/1.323246

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

Strain‐amplitude–dependent internal friction was measured in pure aluminum under forced vibrations at a frequency of 8.3×10−3Hz. Using a modification of the torsional pendulum apparatus, the effects of time, cold work by bending, and changes in bias stress were investigated at room temperature. The dislocation damping theory by Granato and Lu¨cke adequately describes the results. The frequency range in which this theory has been successfully applied is thus extended several orders of magnitude below the frequencies employed to date in experiments of this kind. Similar work at much higher frequencies by other investigators compares well with the present results.

ISSN:0021-8979    

DOI:10.1063/1.323247

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

The experimental results for the delay time of a signal propagating through a thick fluid layer as a function of thickness is given. A theoretical analysis of the interference of the normal modes of a thick layer is presented and it is shown that the observations of delayed ’’modes’’ are, in reality, beats between many normal modes.

ISSN:0021-8979    

DOI:10.1063/1.323248

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

For a Ge(111) surface irradiated by an electron beam of 1.5‐keV energy and current density of 2 &mgr;A mm−2, it was found that beam‐assisted oxygen adsorption at pressures <10−9Torr always resulted in carbon‐contaminated overlayers and was probably due to dissociation of physisorbed CO. The sticking coefficientsof CO was 0.08. At oxygen pressures ≳10−6Torr, carbon‐free coverages could be formed, even without irradiation.sfor oxygen was 6×10−4for beam‐assisted and 1.5×10−4for nonassisted adsorption. Electron impact desorption followed a first‐order rate equation and the desorption cross section for oxygen was 6×10−20cm2.

ISSN:0021-8979    

DOI:10.1063/1.323249

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

Strain‐rate dependence of acoustic‐emission power and spectra for deformation of aluminum alloys is investigated over a wide frequency range of 100 kHz to 4 MHz. In case of Al‐Cu‐Mg alloy (2024) and pure aluminum (1100), it is found that acoustic‐emission power is proportional to the first power of the plastic strain rate times the gauge length of the specimen. Normalized acoustic‐emission power spectra show no significant change at a given strain depending on the strain rate, though they vary with the strain in early stages of deformation. In case of Al‐Mg alloy (5056), repeated bursts of acoustic emission are recorded accompanied by repeated discontinuous yielding. The mode of inhomogeneous deformation and the pattern of acoustic emission vary with the strain rate.

ISSN:0021-8979    

DOI:10.1063/1.323250

出版商:AIP    

年代:1976

数据来源: AIP

ISSN:0021-8979    

DOI:10.1063/1.323251

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

The optical and electrical characteristics of high‐current discharge in a capillary in helium were studied in the range of initial pressure from 10 to 760 Torr. The discharge current increased to a peak of 8 kA in 1.5 &mgr;sec after breakdown. The duration of the current was about 15 &mgr;sec. Two different types of peak were observed during the temporal changes of arc voltage. No such peaks of arc voltage have ever been observed in free‐burning arcs. To study the cause of these voltage peaks, temporal changes in the emission spectra, electron density, and temperature of the arc were measured and analyzed. One type of voltage peak appears at high initial pressures above 100 Torr and is related to the kink instability which occurs at very high pressures in the capillary. The pressure of the arc is estimated to be 90 atm when the initial pressure is 1 atm. The other type of voltage peak observed at low initial pressures below 100 Torr is attributed to wall evaporation which causes a reduction in the electron temperature in the arc. It has also been proven that local thermodynamic equilibrium (LTE) between the temperatures of heavy particles and electrons and also between the particle densities of singly and doubly ionized helium are not always established in arcs confined in capillaries.

ISSN:0021-8979    

DOI:10.1063/1.323252

出版商:AIP    

年代:1976

数据来源: AIP