摘要:

In this article, we use Monte Carlo methods to study the interaction of high power laser pulses with electrons in the conduction band of semiconductors. The laser field is represented by a sinusoidal electric field which tends to cause an oscillatory motion in the electrons. The scattering of electrons from the lattice force the electrons to lose phase coherence with the field. The approach is applied to silicon. We use the approach to examine the carrier energy distribution and material breakdown due to the transfer of energy from the laser to the electrons followed by impact ionization. The impact ionization coefficient, &agr;, and its dependence on the laser frequency and field strength is examined and compared to the values in a dc field. In general, the ac value is smaller than the dc value, but at low frequencies and high field strengths, the ac impact ionization coefficient approaches the dc value at the same rms field value. The importance of collisions in the energy transfer process is elucidated. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364037

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Electrical and photoelectrical properties of GaSb Schottky diodes obtained by evaporating gold metal dots on sulphur treated or chemically etched surfaces of Te-dopedn-GaSb crystals (grown from melt by Czochralski method), with Hall carrier density in the range of 1.8–6.5×1017cm−3, were studied. J/V characteristics with an ideality factor ranging between 1.17 and 1.22 were measured on Schottky diodes prepared on sulphur passivated surfaces. After image force effect correction, photoelectric determination of the barrier height (q&Fgr;b=0.598±0.006 eV) has been found to be independent of the surface treatment and, in the case of the sulphur-treated diodes, in good agreement with the value obtained throughC−2vs reverse bias measurements (q&Fgr;b=0.6±0.01 eV). Through spectral response analysis of Schottky diodes, an estimation of minority carrier diffusion length value is given. A major role of sulphur passivation on preparation of Schottky barrier with good and well reproducible electrical properties is confirmed. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364065

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

In this article, we present the transport properties of W/C multilayers which are generally studied for their optical properties (X-ray mirrors). For the thinnest tungsten layers the magnetoresistance is clearly governed by weak localization. We point out the importance of electron-electron interactions. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364038

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The physical properties and charge trapping behavior of rapid thermal N2O-oxynitrided (RTON) and rapid thermal NH3-nitrided (RTN) ultrathin SiO2films have been investigated. The results of secondary-ion-mass spectrometry and Fourier transform infrared reflection measurements indicate that although nitrogen atoms are incorporated into the RTON and RTN films, only the RTN film shows a large number of NH bonds in the bulk SiO2. Using an analytical model, the number of oxide charge traps, the capture cross section, and the charge trap generation rate for the RTON and RTN SiO2films were determined. Under high-field stress, the RTON SiO2film has a much smaller number of electron and hole traps and a lower electron trap generation rate, resulting in a larger charge-to-breakdownQBDvalue compared to that of pure SiO2film. In contrast, a large number of electron traps which originate from NH and SiH bonds is present in the RTN film. The differences in the charge trapping phenomena and oxide breakdown characteristics are strongly related to the chemical bonding state in the bulk oxide. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364039

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Simple formulae for the kinetic inductance of coupled superconducting microstrip lines in odd mode and even mode have been derived by using the conformal mapping technique. Based on the simple formulae, the geometrical effects of kinetic inductance in odd mode and even mode are analyzed and compared with those of magnetic inductance. The coupling effects of two proximity microstrip lines caused by the kinetic inductance are also studied. The kinetic inductance is dominant for smaller geometrical sizes but is less important than the magnetic inductance for larger geometrical sizes. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364040

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

In this paper, we show that torsional as well as flexion modes can be excited rather naturally in a magnetoelastic bimorph. This behavior is in contrast with that of usual piezoelectric bimorphs in which only flexion modes can be excited. We describe experimental results on the torsional resonances of bimorphs composed of a glass substrate and a highly magnetostrictive thin film of (TbDy)(FeCo)2and show how basic linear piezomagnetic constants may be extracted from the resonance data. Finally, we discuss some possible applications of torsional resonance in magnetoelastic bimorphs. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364014

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Anhysteretic magnetization is the magnetization that results if a constant bias field and an alternating field with decreasing amplitude are applied simultaneously to a ferromagnetic sample. Both anhysteretic magnetization and magnetization curves were measured on strips of iron shielding material in two cases where the product of the demagnetization factor and magnetization is much smaller than or comparable with the external field. The influence of demagnetizing fields on the measured effective anhysteretic permeability can be described neither by “normal’’ shearing of the magnetization curve nor by a dependence predicted by Ne´el for anhysteretic permeability. A crucial role in Ne´el’s theory is played by so-called “frozen magnetization.’’ During anhysteretic magnetization an increasing fraction of the magnetization ceases to follow the applied alternating field and remains fixed. Comparison with Preisach models suggests that deviation from normal behavior is connected with a gradual rather than an instantaneous buildup of frozen magnetization. It is concluded that Ne´el’s theory gives a qualitative but not a quantitative explanation of the dependence of anhysteretic permeability on demagnetizing fields in the material investigated. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364009

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

To investigate the behavior of the magnetization in a single-domain disk with a uniaxial magnetocrystalline anisotropy, the assumption is made that the magnetization changes its direction by the magnetization curling mode. In this mode, the deviation &thgr; of the spin from thezaxis at(r,&fgr;,z)in the cylindrical coordinate is given by &thgr;=a0+a1(r/R)+a2(r/R)2+a3(r/R)3, whereRis the radius of the disk anda0–a3are coefficients. An equilibrium spin configuration is obtained for a given applied fieldHby finding a set of values ofa0–a3that minimize the magnetic energy of the disk. Carrying out this procedure for variousH, a hysteresis loop and the coercive force are obtained. It is found that the configuration in which the spins deviate from thezaxis can be stable and, therefore, the hysteresis loop is not rectangular, even though an applied field is along thezaxis. The deviation is larger for the spins near the lateral surface of the disk, and the spins near the center do not incline easily. Moreover, for a large magnetocrystalline anisotropy and a large diameter, the magnetization changes its direction upward and downward alternately withr. The nucleation field calculated with the present model agrees well with that of the curling mode in an oblate spheroid. ©1997 American Institute of Physics.   

ISSN:0021-8979    

DOI:10.1063/1.364067

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Fine powders of ZnFe2O4with an average particle size of 10 nm and inversion parameter of 0.21 were synthesized by the aerogel procedure. Portions of the powders were calcined in air at 500 and 800 °C and other portions were ball-milled for 10 h. The materials were characterized by x-ray diffractometry, vibrating sample, and SQUID magnetometry, Mo¨ssbauer spectrometry, and low temperature calorimetry. Upon calcination the powders underwent significant changes in grain size, inversion parameter, and hence magnetic properties. The magnetic state of the as-produced and calcined samples is best described as disordered and highly dependent on temperature. Upon ball-milling the grain size varied widely and the inversion parameter attained a value of 0.55. The magnetic properties of the ball-milled sample are similar to those of ferrimagnetic MgFe2O4powders having comparable grain size and inversion parameters. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364068

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We have synthesized hcp-Co fine particles with the average diameter of less than 50 nm by sputtering Co in a somewhat high inert gas pressure. A nearly perfect hcp phase can be stabilized by increasing sputtering gas pressure and decreasing sputtering power in contrast to conventional preparation conditions. Magnetic measurements have revealed the clear relation of coercivity with the volume ratio of hcp phase. That is, the increase in the hcp phase considerably enhances the coercivity. Appearance of the hcp phase seems to be related to the promotion of allotropic phase transformation in Co initiated by lattice defects within each particle. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364041

出版商:AIP    

年代:1997

数据来源: AIP