摘要:

Experimental results are presented on the optical characterization of high‐dose oxygen‐implanted (∼2×1018cm−2, 200 keV) and annealed (6 h, 1300 °C) silicon‐on‐insulator structures by spectroscopic ellipsometry. The ellipsometric sensitivity to variations in the multilayer geometry, induced by small variations in implantation dose, is demonstrated. In the analysis a five‐layer model is used. For the given conditions of sample preparation the results show a linear relation between the thicknesses of the buried oxide layer and the silicon top layer. Additional spectroscopic reflectometry measurements, interpreted by using a simplified two‐layer model, are correlated to the ellipsometric results.

ISSN:0021-8979    

DOI:10.1063/1.349835

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Purified samples of C60and C70are synthesized according to recently published procedures. Desorption with 308 nm laser light from solid C60and C70samples is used as a neutral cluster source to study the ionization and concurrent fragmentation in the gas phase by interaction with intense laser radiation. According to a well‐known classification scheme, the ionization/fragmentation behavior of C60and C70clusters is clearly identified as of class A type. Also, the laser desorption process itself has been investigated by measuring the velocity distributions of laser desorbed neutral C60and C70clusters. Good agreement of the experimental data with a Maxwell‐Boltzmann distribution is found. We conclude that at the applied laser fluences, C60and C70clusters are desorbed by evaporation induced by the incident radiation, providing no fragmentation in the desorption process.

ISSN:0021-8979    

DOI:10.1063/1.349836

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The properties of the plasma waveguide of finite thickness (plasma tube) have been studied. The analysis indicates that, in the case of finite thickness, most of the properties for the plasma waveguide with infinite thickness are retained. At high frequencies, such a plasma tube is still a nondispersive waveguide system. The losses due to the finite thickness of the cladding and the conductivity of the plasma are both small. The decay coefficient decreases with the thickness exponentially. With a thickness equal to the radius of the central core, the attenuation can be as low as 0.1 dB/km.

ISSN:0021-8979    

DOI:10.1063/1.349837

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The characteristics of proton‐exchanged LiNbO3waveguides fabricated using pyrophosphoric acid process are reported. Using this process, high index change waveguides with step profile have been realized. Low‐loss (0.7 dB/cm) channel waveguides have been also obtained by pyrophosphoric acid process. The loss is much lower than that given by conventional benzoic acid process. We show that the reason for low‐loss waveguide fabrication is due to the uniform proton‐exchange formed by this process, compared with the benzoic acid process.

ISSN:0021-8979    

DOI:10.1063/1.349838

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

We have measured the temperature and electric field dependence of the direct current (dc) electrical resistivity of several electro‐optic polymers, in addition to pure polymethyl methacrylate (PMMA) and a commercial acrylate, UV‐15. All the polymers exhibit a decrease in resistivity, to different degrees, with increasing temperature between room temperature and 130 °C. The results show that in a sandwich of multiple layers, the high temperature resistivity mismatch between individual layers results in field concentration in the layer with the highest electrical resistivity. This can be used to explain the enhanced electro‐optic coefficient measured in electro‐optic devices consisting of a sandwich of UV‐15/copolymer/UV‐15. In PMMA, we observed a saddle region in the temperature dependence of resistivity between 67 and 78 °C. Outside the saddle region, the resistivity of PMMA follows an Arrhenius relationship, with an activation energy of 1.0 eV. This saddle region is broadened in the nitro and DCV copolymers. A mechanism in which the motion of side chains hinders the interchain hopping of conducting species is proposed to explain our data.

ISSN:0021-8979    

DOI:10.1063/1.349839

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Single crystals of mixed methyl‐(2,4‐dinitrophenyl)‐aminopropanoate (MAP): 2‐methyl‐4‐nitroaniline (MNA) have been grown from solution using a 40:60 mixture of ethanol and ethyl acetate. Formation of an equimolar complex is confirmed by x‐ray diffraction studies. The complex crystallizes in the monoclinic space groupP21. The lattice parameters area=6.9196(±0.005) A˚;b=7.673(±0.008) A˚;c=18.554(±0.001) A˚; and &bgr;=92.547(±0.006)0.baxis is the unique twofold axis and there are two molecules per unit cell. The molecules stack along thebaxis with MAP atop MNA atop MAP. Details of the molecular orientation are given. The Raman spectra also indicate that the parent molecules are not disturbed in the process of crystallization. The second harmonic generation efficiency of the new material for 1064 nm laser radiation is observed to be the same as that of MAP but lower than that of MNA. The latter is attributed to the absorption at 532 nm in the mixed crystal. The melting point determined by differential scanning calorimetry is 104.30 °C.

ISSN:0021-8979    

DOI:10.1063/1.349840

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Based on general rotationally invariant nonlinear electroelastic equations (energy balance equation and Gibbs function expansion), a complete and deductive derivation of constitutive equations for an electroelastic media upon mechanical or electrical bias has been presented. Bilinear constitutive relations for large quantities have been given and linear, but parametric constitutive formulas for small‐field variables have been derived in the reference or intermediate frame. Equations of motion and boundary conditions in the respective configurations, required to solve dynamical problems, are also reported shortly for completeness. Presented reformulation of constitutive equations may be useful in solving nonlinear problems of electromechanical interactions in crystals, for example in analyzing sensors of nonelectric quantities with electric output or modulators.

ISSN:0021-8979    

DOI:10.1063/1.349841

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Planar solidification in a slab of finite thickness, cooled from below, is addressed. The solid density is supposed to be greater than the liquid density. The fluid flows toward the moving phase‐change front, accompanied by heat transfer in the emerging solid, in the liquid and cavity, resulting due to the contraction of the volume of the material, are analyzed. The Rubinstein transformation, which immobilizes the interface, is modified in order to take the density change into account. It enables one to reduce the problem to that without the density change. Several approximate analytic solutions for transient solidification, some of which are new even for equal solid and liquid densities, are presented.

ISSN:0021-8979    

DOI:10.1063/1.349842

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The spatiotemporal evolution of a pulsed low‐pressure glow discharge is investigated theoretically and experimentally. The discharge is modelled phenomenologically by a reaction‐diffusion equation in which the cathode fall and the negative glow of the discharge are described as a bistable layer. A laterally one‐dimensional discharge is realized experimentally by a hollow cathode discharge in a slotted cathode. With the help of probe measurements, a homogeneous evolution with a laterally uniform current rise and an inhomogeneous evolution starting from special sites and progressing along the cathode are found. The main experimental results are reproduced by model calculations.

ISSN:0021-8979    

DOI:10.1063/1.349843

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

We treat electromagnetic radiation from narrow electrical discharges, with particular emphasis on the asymptotic behavior at high frequenciesf. We show that discontinuities in the discharge current and its derivatives dominate the high‐frequency part of the radiated spectrum. Specifically, when a current discontinuity is present, the envelope of the radiated fields falls off with largefasf −1for almost all observation angles. If the current is continuous but has discontinuities in its first derivatives, then the envelope of the radiated field falls off asf −(1+1/n)at largeffor a range of observation angles. If the discharge current and its first derivatives are continuous, then the radiated fields fall off at least as fast asf −2at largef. The characteristic high‐frequency dependence associated with abrupt current change persists for some large range off, even when current variation is not precisely abrupt. We illustrate the general results with radiation from AWA discharge models (previously referred to as arc welder’s ansatz models) featuring a constant electric field associated with dissipative discharge processes.

ISSN:0021-8979    

DOI:10.1063/1.349844

出版商:AIP    

年代:1991

数据来源: AIP