Structure-related infrared optical properties of BaTiO3 thin films grown on Pt/Ti/SiO2/Si substrates

BaTiO₃ thin films with different thickness have been grown on Pt/Ti/SiO₂/Si substrates by a modified sol-gel method. X-ray diffraction analyses show that the BaTiO₃ thin films are polycrystalline. The crystalline quality of the films is improved with increasing thickness. The infrared optical properties of the BaTiO₃ thin films have been investigated using an infrared spectroscopic ellipsometry in the wave number range of 800-4000 cm⁻¹ (2.5-12.5 μm). By fitting the measured pseudodielectric functions with a three-phase model (Air/BaTiO₃/Pt), and a derived classical dispersion relation for the thin films, the optical constants and thicknesses of the thin films have been simultaneously obtained. The refractive index of the BaTiO₃ thin films increases and on the other hand, the extinction coefficient does not change with increasing thickness in the entirely measured wave number range. The dependence of the refractive index on the film thickness has been discussed in detail and was mainly due to both the crystalline quality of the films and packing density. Finally, the absorption coefficient was calculated in the infrared region for applications in the pyroelectric IR detectors.     

优序理论与平面分析(Ⅱ)

Let RE_λ(q) denote the GF for reverse plane partitions of shape λ with part restiction (i.e., the parts in ith row do not exceed n_i). Combining domination method with the techniques of combinatorial computation, we obtain the follo wing determinant expression.     

Electrochromism by polarization of semiconducting ionic materials

Electrochromic effects are observed by employing a single mixed ionic and electronic conducting layer in-between two transparent electronic leads. Besides the simplicity of the arrangement, the advantage is the displacement of ions only within one phase rather than across phase boundaries as required by conventional devices. The applied voltage controls the compositions at the two interfaces according to Nernst's law independent of ions being majority or minority charge carriers. Appropriate materials are intrinsic conductors in the unpolarized transparent state which become n-type and p-type conducting at the negative and positive electrode side, respectively. Several materials have been investigated, such as lithiated tungsten oxide and lithium/tantalum co-doped tungsten oxide. Paper presented at the 1st Euroconference on Solid State Ionics, Zakynthos, Greece, 11–18 September 1994.     

Photon correlation spectra of poly(phenylmethyl siloxane) under high pressures

We report polarized photon correlation measurements of bulk poly(phenylmethyl siloxane) (PPMS) with a molecular weight of about 2500 at different pressures from 1 to 1750 bar and temperatures between 269 and 308 K. In the Frequency range accessible by present-day digital correlators, the time correlation function can measure a slow q²-dependent diffusional process due to local concentration fluctuations and a fast α-mode structural relaxation process. The mean characteristic times of the two processes approach each other at low temperatures and high pressures, in contrast to the behavior of the α- and β-relaxation times. We should be cautious in relating the mean characteristic times for the structural relaxation process obtained by different experimental techniques, such as Brillouin scattering and photon correlation spectroscopy, because of the differnces in the probe emphasis and the extremely broad frequency distribution of such relaxation processes.     

重离子碰撞中产生的K介子的末态作用

推广了RVUU模型,计入了K介子的平均场势和K与核子的末态重散射.并用它模拟了每核子1GeV入射能量的两个Ca核碰撞的阈下K⁺产生.讨论了K⁺矢量势和K⁺末态重散射效应对K介子的末态性质的影响.计算结果表明,排斥的矢量势,与K⁺的末态重散射相似,明显地影响了末态K⁺动能谱,导致了实验室系中具有大动量的K⁺产额的增大.然而,排斥的K⁺矢量势的计入可观地减少了K⁺的末态重散射的影响.这说明,为了合理地评价K⁺能谱和角分布,K⁺同核子的这些末态作用都是不能忽略的.     

Synthesis and crystal structure of 5-methyl-5,10-dihydrophenarsazine

The X-ray crystal structure of 5-methyl-5,10-dihydrophenarsazine, C₁₃H₁₂NAs, has been determined. The crystals are orthorhombic, space group P2₁2₁2₁, a = 8.511(4), b = 5.690(1), c = 23.535(9) Å, V = 1139.7(1.0)A³, and Z = 4. Least-squares refinement converged to R = 0.049 and Rw = 0.045. The central ring is in a boat conformation and the 5-methyl group is in the axial position with respect to the central ring. The folding angle between the planes of the two benzo rings is 154.1(4)°.     

Noise analysis of refractive index profile measurements of an optical fibre and preform by deflection function techniques

It is shown that many of the existing index profiling methods for optical fibre and preform are related to one another through the deflection function from which the index profile is reconstructed. These methods are classified into direct deflection function measurement, integral (or phase) measurement, and differential (or intensity) measurement. The deflection function from the integral method is obtained by measuring the phase distribution of the exit rays followed by numerical differentiation. Thus the reconstructed index profile has Gaussian noise. The deflection function from the differential method is obtained by measuring the light intensity distribution followed by a numerical integration. This process enhances low frequency noise but suppresses high frequency noise. The noise from direct method behaves in the similar manner as in the differential method except that it is less pronounced. Studies of the choice of methods for profiling of preform, multimode fibre and single mode fibre are also given.     

Excimer laser ablation of thin gold films on a quartz crystal microbalance at various argon background pressures

Received: 21 June 1996/Accepted: 9 December 1996