摘要:

An accurate method to calibrate a commercial atomic force microscope (AFM) with commercial cantilevers for surface stress measurements was investigated. The bending of commercial rectangular cantilevers of the AFM was measured by laser beam deflection under a concentrated load mode and a bending moment mode. Good agreement between the experimental results and the theoretical predictions was obtained. The accurate calibration of the deflection angle for &Dgr;&sgr; was possible with the rectangular cantilever by taking into account the dependence of the deflection angle on the laser spot position,a,on the cantilever. The cyclic voltammogram and the electrocapillary curve were measured in the double layer region of a gold thin film on the rectangular cantilever. In addition, it was concluded that a fairly good measurement of &Dgr;&sgr; by triangular cantilevers was also possible as long as the deflection angle measurement was carried out with the same triangular cantilever at the same laser spot positiona.The change in surface stress due to electrochemical oxygen and hydrogen adsorption was also studied on gold and platinum deposited on rectangular cantilevers. In these cases, the change in reflectance of the cantilevers by electrochemical reactions had to be taken into account for accurate calibration. The discussion described here will be also useful for other stimuli, such as pH, that cause the cantilever bending. ©1997 American Institute of Physics. 

ISSN:0021-8979    

DOI:10.1063/1.365306

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The current induced in the human body when exposed to an incident electromagnetic field with the electric vector parallel to the length of the body and the magnetic field perpendicular to the chest was determined in an earlier study with the arms in close contact with the body. The analysis is now extended to the case when both arms are raised by an arbitrary angle. Formulas are derived for the current in the arms and the body when the latter is far from the earth, when it is barefoot on wet earth, and when it is standing on the earth with rubber-soled shoes. The current in the arms is shown to consist of two parts, that induced by the component of the incident electric field parallel to the arms and that generated in them by their connection to the body. The current in the body is significantly increased as the arms are raised. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365308

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A new and effective method for developing ultralow-loss glasses for long-distance optical fiber systems is presented. The idea is based on the observed strong effect of a very small amount of alkaline or alkaline-earth impurities on structural relaxation of “frozen-in” density fluctuations. Efficiency of this method is demonstrated in the case of silica glass withNa2Oof less than 50 wt. ppm, where the light scattering loss was reduced by 13&percent; by the addition of only10 wt. ppm (≈1×10−3 mol &percent;) Na2O.Various problems in developing ultralow-loss fiber materials in multicomponent glasses are avoidable in this method, since concentrations of dopants are very small. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365309

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Intersubband carrier lifetimes and population ratios are calculated for three- and four-level optically pumped terahertz laser structures. Laser operation is based on intersubband transitions between the conduction band states of asymmetricGaAs-Ga1−xAlxAsquantum wells. It is shown that the carrier lifetimes in three-level systems fulfill the necessary conditions for stimulated emission only at temperatures below 200 K. The addition of a fourth level, however, enables fast depopulation of the lower laser level by resonant longitudinal optical phonon emission and thus offers potential for room temperature laser operation. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365310

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We present the application of a general Green function formalism to the study of near- and far-field scattering of an incident acoustic plane wave by a perturbation (an inhomogeneity) existing at the planar surface of a substrate. The perturbing element will be a supported wire which, in principle, can have an arbitrary shape and composition. Considering the case of shear horizontal vibrations, we discuss for a wire of parabolic section the behavior of the scattered field as a function of frequency&ohgr;, of material parameters, and of incidence angle. At normal incidence, typical behaviors depend on the relative impedance and sound velocity of both materials. For an oblique incidence, there are a large variety of cases depending on &ohgr; and on material parameters; one typical behavior will be the predominance of a scattered wave towards the specular reflection direction. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365355

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

This paper analyzes the small strain elasticity of fluid saturated porous media and the influence of the fluid static pressure, or pore pressure, on their isotropic constitutive properties. The porous medium is modelled as a lattice assembly of monodisperse spheres that interact through Hertz contacts. The size of the spheres and hence the matrix volume at zero solids stress are shown to be influenced by the pore pressure. Consequently, the structural pressure generated by elastic Hertzian contact deformations is shown to depend on both the volume occupied by the matrix and the pore pressure. This result is then generalized for random assemblies of spheres by using an isotropic constitutive law that is realistic for dry sands. The present findings suggest that the contributions of pore pressure and structural pressure to the total stress do not have a constant weighting as is often assumed, but one that is sensitive to the deformation state of the matrix. The theory also captures the characteristic loss of matrix stiffness during liquefaction at sufficiently elevated pore pressures. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365311

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Plasma-based ion implantation of a square bar is modeled using a particle-in-cell plasma simulation for three different size bars. When the sheath width is significantly greater than the bar width, it is found that the incident ion dose is largest at the center of the bar and decreases precipitously at the corners. When the sheath width is comparable to the bar width, the incident dose is largest near to, but not at, the corners. It may be possible to optimize dose uniformity by straddling these two regimes. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365312

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The influence of ultraviolet (UV) illumination on the formation of hydroxyl radicals in dielectric barrier discharges (DBD) in mixtures ofAr/O2/H2O(79/18/3) will be presented. The UV is provided from a spectrally calibrated, commercial low pressure mercury lamp while the irradiance power of the discharge cell has been previously determined. First, the filamentary character of the DBD is shown by measurement of the relative intensity of the transitionOH(A2&Sgr;→X2&Pgr;, 0-0)with integrated emission spectroscopy as a function of the absolute water concentration at different energy densities coupled into the gas. Then, the influence of UV illumination on the hydroxyl emission is shown by time-gated and time-resolved emission spectroscopy ofOH(A2&Sgr;→X2&Pgr;).The results of the combined process is an increased total emission but reduced emission for each microdischarge. This result corresponds to an increase in the number of microdischarges which is supported by the measurement of the microdischarge current. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365313

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A discharge heated inductively by resonant absorption of electron cyclotron waves discharge is modeled in a planar geometry. The simulation algorithm is based on a kinetic particle-in-cell (PIC/MC) simulation of the plasma properties; the electromagnetic field is calculated macroscopically using the Appleton–Hartree theory for the dielectric tensor. The results are checked against a simplified analytical theory and experimental data by B. Pfeiffer [J. Appl. Phys.37, 1624,1628 (1966)] for a 15 mTorr argon discharge. As a result, we show that an inhomogeneous density profile in the discharge strongly affects the electromagnetic fields in the plasma. Power deposition is calculated both in and outside of the resonance. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365314

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

To clarify the orientational memory site in the hydrogen disproportionation desorption recombination process ofNd2Fe14B-based anisotropic magnets, high resolution transmission electron microscopy (HRTEM) characterization of hydrogen disproportionated structure ofNd13.0Fe67.9Co11.0Ga1.0Zr0.1B7.0has been performed. In particular, crystallographic orientations of disproportionated products relative to that of parent or originalNd2Fe14Bhave been carefully analyzed using partially disproportionated samples. No apparent orientational coherency exists between the disproportionated products of &agr;-Fe,Fe2B,andNdH2and the parentNd2Fe14B.However, nanoscaleNd2Fe14Bparticles of 10 to 100 nm in diameter have been detected by HRTEM to be densely present within the disproportionated mixture. Lattice fringe observation has also revealed that the crystallographic axes of theNd2Fe14Bparticles are nearly parallel to those of the originalNd2Fe14B.It is thus suggested that theseNd2Fe14Bparticles be the orientational memory site upon the recombination, which recovers the original orientation leading to the anisotropy formation. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365315

出版商:AIP    

年代:1997

数据来源: AIP