Optical and photoconductivity properties of ZnO thin films grown by pulsed filtered cathodic vacuum arc deposition

High quality transparent conductive ZnO thin films with various thicknesses were prepared by pulsed filtered cathodic vacuum arc deposition (PFCVAD) system on glass substrates at room temperature.The high quality of the ZnO thin films was verified by X-ray diffraction and optical measurements. XRD analysis revealed that all films had a strong ZnO (200) peak, indicating c-axis orientation. The ZnO thin films are very transparent (92%) in the near vis regions. For the ZnO thin films deposited at a pressure of 0.086 Pa (6.5 × 10⁻⁴ Torr) optical energy band gap decreased from 3.21 eV to 3.19 eV with increasing the thickness. Urbach tail energy also decreased as the film thickness increased.Spectral dependence of the photoconductivity was obtained from measurements of the samples deposited at various thicknesses. Photoconductivities were observed at energies lower than energy gap which indicates the existence of energy states in the forbidden gap. Photoconductivities of ZnO thin films increase with energy of the light and reach its maximum value at around 2.32 eV. Above this value surface recombination becomes dominant process and reduces the photocurrent. The photoconductivity increases with decreasing the film thickness.     

真空绝热板部件真空出气性能及机理分析

真空绝热板是近几年发展起来的一种超级绝热材料,其内部真空度的保持是维持其低导热系数的关键因素.真空绝热板中的表面隔膜及内部芯材的真空出气是破坏板内部真空环境引起其绝热性能下降的主要原因之一,本文重点对不锈钢、AF及MF类表面隔膜以及气相二氧化硅和泡沫类芯材的真空出气性能及真空出气途径机理进行了系统的分析,在此基础上提出了降低部件真空出气的有效途径,为优化真空绝热板整体性能奠定了基础.     

石墨烯中Dirac费米子量子输运特性研究

利用紧束缚模型的方法研究了石墨烯中Di-rac费米子的势垒相关输运特性,分析了石墨烯中Di-rac费米子的势垒透射率与其入射角度、入射能量、势垒高度和势垒厚度等对应关系。通过理论分析和数值计算表明,石墨烯中Dirac费米子的隧穿系数随矩形势垒的高度和厚度的变化都呈现出明显的振荡效应,隧穿系数与入射角度依赖关系证实了Klein效应。在一定参数下,Dirac费米子的势垒透射率随Dirac费米子入射能量的变化经历从0～1的突变,显示良好的电导开关效应,该效应在微电子器件中将有很好的应用前景。     

真空绝热板热工性能的研究

介绍真空绝热板的构造及加工工艺，对其高效绝热热工性能进行理论分析及实验数据测试，运用数理统计及计算机数值模拟的方法分析其热工性能随自身参数及制造工艺的变化规律，提出产品生产、施工及使用中应注意的问题和改进的意见。     

真空电渣重熔的冶金特性

真空电渣重熔具有脱氧性能好,防止金属氧化等许多优异的冶金特性.本文通过对真空电渣重熔与普通电渣重熔、气体保护熔炼和真空电弧熔炼等冶金特性的分析对比,找出真空电渣重熔的冶金特性,表明发展真空电渣重熔的意义.     

Tight focusing properties of hybridly polarized vector beams

We theoretically investigate the tight focusing properties of hybridly polarized vector beams. Some numerical results are obtained to illustrate the intensity, phase, and polarization of tightly focused hybridly polarized vector beams. It is shown that the shape of the focal pattern may change from an elliptical beam to a ring focus with increasing radial index. The phase distribution around the tightly focused ring is shown to be the helical phase profile, indicating that the radial-variant spin angular momentum of hybridly polarized vector beams can be converted into the radial-variant orbital angular momentum.     

Optical properties of nano-silicon

We investigated the optical properties of silicon clusters and Si nanocrystallites using photolumine-scence (PL) and Raman scattering technique. Broad luminescence band in the red region was observed from Si-doped SiO₂ thin films deposited by co-sputtering of Si and SiO₂ onp-type Si (100) substrates, annealed in Ar and O₂ atmosphere. Nanocrystalline Si particles fabricated by pulsed plasma processing technique showed infrared luminescence from as grown film at room temperature. Raman spectra from these films consisted of broad band superimposed on a sharp line near 516 cm⁻¹ whose intensity, frequency, and width depend on the particle sizes arising from the phonon confinement in the nanocrystalline silicon. We also performed PL, Raman and resonantly excited PL measurements on porous silicon film to compare the optical properties of Si nanostructures grown by different techniques. An extensive computer simulation using empirical pseudo-potential method was carried out for 5–18 atoms Si clusters and the calculated gap energies were close to our PL data. Paper presented at the 5th IUMRS ICA98, October 1998, Bangalore.     

Electrical properties of vacuum annealed CdS films

Cadmium sulphide (CdS) films were evaporated in vacuum on glass substrates maintained at room temperature. These films were later annealed in vacuum at temperatures in the range 30 to 300° C. The variation of d.c. electrical conductivity was studied in the temperature range 100 to 300 K. While the conductivity data in the range 100 to 150 K were observed to follow Mott's variable range hopping process, the conductivity in the high-temperature region (150 to 300 K) could be explained by Seto's model.     

Optical properties of metal phthalocyanines

In this study, optical properties of phthalocyanines of five metals, i.e., cobalt, nickel, iron, copper, and manganese, have been discussed in the energy (E) range of 1.5–4.1 eV. Utilizing the available data of refractive index (n) and extinction coefficient (k) of these materials in the literature, the related optical properties such as the real (ε₁), imaginary (ε₂) parts of the complex dielectric constant (ε), and reflectivity (R) are calculated. Interpretations for the energies corresponding to the peaks in ε₂ are explained in terms of the Penn gap (E _P). High-frequency dielectric constant (ε_∞) values corresponding to four models, i.e., the conventional Lorentz model, modified Lorentz model, relaxed Lorentz model, and the dual Lorentz model are used to determine E _P. It is found that the E _P values corresponding to the conventional and dual Lorentz models are in good agreement with the average of energy peaks in the R-E and the ε₂-E spectra. The oscillator energy (E ₀) and the dispersion energy (E _d) of these materials have been determined utilizing the Wemple–DiDomenico model. The calculated values of (a) E ₀ are generally in good agreement with the Penn gap E _P, the average of the energy peaks in the R-E and the ε₂-E spectra and (b) E _d are comparable to those in the literature for CoPc and NiPc.     

Optical properties of ZnO nanostructures

We present a review of current research on the optical properties of ZnO nanostructures. We provide a brief introduction to different fabrication methods for various ZnO nanostructures and some general guidelines on how fabrication parameters (temperature, vapor-phase versus solution-phase deposition, etc.) affect their properties. A detailed discussion of photoluminescence, both in the UV region and in the visible spectral range, is provided. In addition, different gain (excitonic versus electron hole plasma) and feedback (random lasing versus individual nanostructures functioning as Fabry-Perot resonators) mechanisms for achieving stimulated emission are described. The factors affecting the achievement of stimulated emission are discussed, and the results of time-resolved studies of stimulated emission are summarized. Then, results of nonlinear optical studies, such as second-harmonic generation, are presented. Optical properties of doped ZnO nanostructures are also discussed, along with a concluding outlook for research into the optical properties of ZnO.     

Optical properties of polymer nanocomposites

Nanomaterials have emerged as an area of interest motivated by potential applications of these materials in light emitting diodes, solar cells, polarizers, light-stable colour filters, optical sensors, optical data communication and optical data storage. Nanomaterials are of particular interest as they combine the properties of two or more different materials with the possibility of possessing novel mechanical, electronic or chemical behaviour. Understanding and tuning such effects could lead to hybrid devices based on these nanocomposites with improved optical properties. We have prepared polymer nanocomposites of well-defined compositions and studied the optical properties of powders and their thin films. UV-vis absorption spectroscopy on nanocomposite powders and spectroscopic ellipsometry measurements on thin films was used to study the effect of interfacial morphology, interparticle spacing and finite size effects on optical properties of nanocomposites. Systematic shift in the imaginary part of the dielectric function can be seen with variation in size and fraction of the gold nanoparticle. The thickness of the film also plays a significant role in the tunability of the optical spectra.     

Optical properties of nanocrystalline ceria

We believe that, for the first time, the UV-visible optical reflectivity of nanocrystalline ceria with various particle sizes has been measured, and their optical absorption characteristics have been studied by Kramers-Kronig transformation. The wide absorption band in the 200-480-nm range consisted of two narrow bands. This wide band was designated as the charge transfer of O(2p)-Ce(4f) while both narrow bands, which overlapped in this wide band, were due to the well-known (2)F(5/2)-(2)F(7/2) spin-orbit splitting of the Ce 4f(1) state. With a decrease in the particle sizes of the samples, the bandwidth expanded distinctly and a red shift in the wide band was observed. On the other hand, the band gap between the narrow bands showed a remarkable increase. All of these phenomena resulted from the effects of quantum size and the interface of nanostructured materials.     

Optical properties of polycrystalline films

We investigate the optical properties and intermolecular coupling of para-hexaphenyl polycrystalline films by site-selective spectroscopy, time-resolved photoluminescence and photoinduced absorption measurements. Our results point to (i) a short-range orientational and energetic disorder and (ii) the molecular character of the light emission, with no evidence of intermolecular excited states.     

Optical properties of Zhang-Rice states

We present inhomogeneous Hartree-Fock plus RPA calculations of the optical absorption in La₂CuO_4+y. We obtain good agreement with experiment with a LDA parameter set and show also results with an optimized parameter set that fits the observed optical bands. The midinfrared band is explained in terms of renormalized p — d transitions related to Zhang-Rice singlet states. By comparing optical properties with other experiments we can draw a scenario for the occurrence of anomalous Fermi liquid behavior in optimally doped samples.