Effects of 3D structure of silsesquioxane moieties on the thermal and optical properties of transparent epoxy/silsesquioxane hybrid materials

Transparent and colorless epoxy/silsesquioxane (SQ) hybrids were prepared by modifying bisphenol-A epoxy resin with two SQ type epoxy resins having different 3D structures, that is, double-decker SQ and cage SQ type epoxy resins. To compare these two hybrids, the cured resin modified with the imperfect ladder SQ epoxy resin was also prepared. The effects of the 3D-structure of the SQ moieties on the thermomechanical, optical and dielectric properties of the cured epoxy/SQ hybrids were investigated. Thus, the refractive index and dielectric constant of the hybrids significantly decreased with an increase in the contents of the SQ moieties. This is due to the introduction of Si atoms with a low atomic polarity and large intermolecular space that was estimated from the difference between the volume of the space surrounded by “Connolly surface” and the van der Waals volume of the SQ moieties. The glass transition temperature, T _g, also decreased with the introduction of the SQ moieties, due to the increase in the intermolecular space. Thus, it was concluded that the performance of the epoxy/SQ hybrids depends not only on the SiO_3/2 content, but also on the 3D structure of the SQ moieties.     

Effects of laser irradiation on the structure and optical properties of ZnO thin films

The effects of laser irradiation on the surface microstructure and optical properties of ZnO films deposited on glass substrates were investigated experimentally and compared with those of thermal annealing. X-ray diffraction (XRD) and atomic force microscopy (AFM) measurements showed that the irradiation treatment with an Ar⁺ laser of 514 nm for 5 min improves the crystalline quality of ZnO thin films through increasing the grain size and enhancing the c-axis orientation, with the effects similar to those of the thermal annealing at 500 °C for 1 h. Laser irradiation was found to be more effective both for the relaxation of the residual compressive stress in the as-grown films and for the modification of the surface morphology. A significant increase in the UV absorption and a widening in the optical band-gap of the films were also observed after laser irradiation.     

偶联剂对聚酰亚胺／纳米Al2O3杂化薄膜结构与性能的影响

将经不同种类硅烷偶联剂改性的纳米Al2O3粒子借助超声波以一定方式均匀分散于聚酰胺酸胶液中,制备聚酰亚胺/纳米Al2O3杂化薄膜,并对该杂化薄膜的微观形貌、分子链有序度、热稳定性、力学性能、电击穿场强进行表征与测试.结果表明,偶联剂种类影响杂化薄膜的分子链有序度,在使用4种偶联剂改性纳米Al2O3制备的PI杂化薄膜中,使用偶联剂KH550的Pl杂化薄膜的热稳定性、力学性能最好;使用AE3012的PI杂化薄膜的电击穿场强最高.     

乙烯基倍半硅氧烷杂化膜的制备及其光学性能

利用溶胶-凝胶法制备了乙烯基倍半硅氧烷(VS)和TEOS改性的乙烯基倍半硅氧烷(VST),以VS和VST为中间体,制备了杂化膜材料m-VS和m-VST,用红外光谱、扫描探针电镜对杂化材料进行了表征,并通过紫外-可见-近红外分光光度计研究了VS和VST膜材料的光学性能.结果表明:m-VS在波长200～300nm的紫外吸收最大,在400～700nm涂膜玻璃片的透光率可提高到90%以上,TEOS质量分数为20%时,杂化膜的增透作用最大,可用于日光温室的透光材料.     

Electronic structure and optical properties of zirconia

The effects of substitutional impurities and oxygen vacancies on the electronic structure and optical properties of cubic zirconia were studied using band-structure calculations. It is shown that oxygen vacancies produce additional states near the Fermi level, whereas impurity atoms make an insignificant contribution to the states in the valence band and at the bottom of the conduction band, and their effect has a predominantly electrostatic character. The mechanisms of the stabilization of the high-temperature ZrO₂ polymorphs are elucidated. The calculation results agree well with x-ray photoelectron spectroscopy and optical data     

Effects of mechanical stress on the transmission properties of optical fiber packaged in a composite structure

Optical circuit boards for system-level interconnection may be fabricated by bonding segments of optical fiber, in the configuration necessary for signal distribution, to a substrate such as a printed wiring board. To measure the effects of mechanical stress on optical transmission, a four-point bend test is applied to prototype optical circuit boards. The results show that flexing a board to a strain of approximately 0.3% leads to a decrease in loss of 0.012 ± 0.002 dB for multimode fiber. Flexing of a thin board, in two directions, around 40-in.- (101.6-cm-) bend-radius mandrels decreases fiber loss by almost 1 dB after 700 cycles. Single-mode fiber bonded to aboard, however, exhibits an increase in loss of 0.11 ± 0.05 dB under an induced strain of 0.3%, a change that is not significant relative to typical loss-per-line budgets in real systems.     

Preparation and optical properties of sol–gel derived photo-patternable organic–inorganic hybrid films for optical waveguide applications

Photo-patternable TiO₂/organically modified silane hybrid films were prepared by combining a low-temperature sol–gel technique with a spinning–coating process. A ridge waveguide pattern was fabricated by ultraviolet light irradiation through a mask placed contact with the hybrid film in direct. Optical properties and photochemical activity of the hybrid film, including refractive index, thickness, propagation mode, and propagation loss, were studied and monitored by a prism coupling technique and Fourier transform infrared spectroscopy. The change of transmittance with exposure time was also observed by ultraviolet–visible spectroscopy. These results indicate that the hybrid film is potential application for fabrication of photonic devices by ultraviolet light irradiation. The structure of ridge waveguide pattern was characterized and studied by scanning electron microscope and surface profiler. The fabrication process of the as-prepared photosensitive hybrid film as compared with traditional binary mask has a great amount of advantages of cost-effective, simple, and smooth surface over non-photosensitive material methods.     

TiN_x电子结构与光学性质的第一性原理计算

利用第一性原理计算了TiNx体系中不同N含量(x=0、0.5、0.6和1)所对应TiNx晶胞结构的电子结构和光学性质。计算结果表明,TiNx均具有典型的金属性,随着N含量的增加,TiNx金属性减弱;精确计算了TiNx(x=0、0.5、0.6和1)晶体的介电函数和反射率函数,得出的计算结果与现有的理论吻合得较好,该结果为TiNx材料在分子原子尺度上的进一步设计及其应用提供了理论依据。     

Substrate effects on the structure and optical properties of GaN epitaxial films

The phase composition and luminescent properties of GaN films grown by molecular beam epitaxy on (0001) sapphire and 6H-SiC substrates were studied. The films grown on SiC were found to consist only of the hexagonal phase and contain a lower concentration of impurities. Grains of cubic GaN, as well as donor and acceptor impurities, were found in the GaN film grown on sapphire. The formation of impurity centers is caused by the diffusion of oxygen and aluminum from the sapphire substrate during crystal growth.     

CrSi2能带结构和光学性质的第一性原理研究

采用基于第一性原理的密度泛函理论（DFT）赝势平面波方法，对CrSi2的能带结构、态密度和光学性质进行了理论计算，能带结构计算表明CrSi2属于一种间接带隙半导体，禁带宽度为0．353eV,其能态密度主要由Cr的3d层电子和Si的3p层电子的能态密度决定；计算了CrSi2的介电函数、反射率、折射率及吸收系数等。经比较，计算结果与已有的实验数据符合较好。     

Effect of neutron irradiation on the structure and optical properties of fused SiO<Subscript>2</Subscript>

The effect of fast-neutron irradiation on the structure of fused silica has been studied by IR reflection spectroscopy in a wide range of neutron fluences, from 10¹⁷ to 10²¹ n/cm². The spectral characteristics of the bending and stretching modes of the bridge bonds in silica have been shown to be nonlinear functions of neutron fluence. The kinetics of radiation-induced changes in the optical properties of silica in the UV through visible spectral region have been analyzed in relation to those in its structure and microscopic characteristics. A strong correlation has been found between the dose dependences of the optical and structural properties of silica, such as the 465-nm luminescence intensity, the intensity and position of the amorphous halo, the reflectivity and frequency of the IR bands at 1125 and 480 cm^?1, the density of the material, and its ionic polarizability. We assume that there is a threshold dose in the range 10¹⁹ to 10²⁰ n/cm² which produces sharp changes in the optical and structural properties of SiO₂ due to a transition to a metamict-like state. An analytical expression has been derived for the radiation-induced changes in the intensity of the first halo. The driving force and mechanism of the radiation-induced structural changes in fused SiO₂ have been tentatively identified.     

Electronic structure and optical properties of Al-doped ZnO

Impure ZnO materials are of great interest in optic and electronic applications. In this work, the effects of Al-doping on the electronic structures of ZnO system are investigated in detail. We find that the crystal structure strains significantly due to the introduction of Al impurity. On the other hand, the electronic band structures show that the position of the Fermi level moves upwards and the bands split near the band gap due to the introduction of Al. This is attributed to the interaction between Al3p and Zn4s orbital, which tend to drive the system towards semimetal. Photoluminescence (PL) studies indicate that the Al-doped ZnO samples have a high density of defects. This can be explained qualitatively by the above analysis on electronic structure.     

Electronic structure and optical properties of thorium monopnictides

We have calculated the electronic density of states (DOS) and dielectric function for the ThX (X = P, As and Sb) using the linear muffin tin orbital method within atomic sphere approximation (LMTO-ASA) including the combined correction terms. The calculated electronic DOS of ThSb has been compared with the available experimental data and we find a good agreement. The calculated optical conductivity for ThP and ThAs is increasing monotonically, while for ThSb a sharp peak has been found at 6–5 eV. Unfortunately there are no experimental data to compare with calculated optical properties, we hope our calculations will motivate some experimentalists.     

A large-area hybrid metallic nanostructure array and its optical properties

A process for fabricating a large-area hybrid metallic nanostructure array is presented. The structures consist of an array of metal capped dielectric nanopillars and an array of metallic holes, each possessing its individual optical properties. The plasmon response of such structures can be viewed as the collection of plasmons from two geometries to form an interacting system. Experimental results show two peak values in the extinction spectrum for p-polarized incident light. The two peaks in the extinction spectrum were shifted to longer wavelength and shorter wavelength respectively with the addition of absolute ethanol on the structure surface. The narrowest extinction peak appears at normal incidence.     

Mg2Si电子结构及光学性质的研究

采用基于第一性原理的赝势平面波方法系统地计算了Mg2Si基态的电子结构、态密度和光学性质。计算结果表明Mg2Si属于间接带隙半导体，禁带宽度为0．2994eV；其价带主要由Si的3p以及Mg的3s、3p态电子构成，导带主要由Mg的3s、3p以及Si的3p态电子构成；静态介电常数ε1（0）=18．89；折射率n0=4．3460；吸收系数最大峰值为356474．5cm^-1；并利用计算的能带结构和态密度分析了Mg2Si的介电函数、折射率、反射率、吸收系数、光电导率和能量损失函数的计算结果，为Mg2Si的设计与应用提供了理论依据。     

Effects of cryogenic grinding on soft-tissue optical properties

Optical properties obtained from spectrophotometer measurements of reflectance and transmittance were determined for both frozen-ground and intact soft tissues. The tissues used in these experiments were calf aorta, rat jejunum, and rabbit sciatic nerve. Tissue specimens from each tissue type were frozen in liquid nitrogen and then ground with a pestle and mortar into a fine powder. A tissue paste formed once the powder returned to room temperature. The tissue paste was then sandwiched between glass slides for spectrophotometer measurements. For comparison, the optical properties of the intact specimens were also measured. Total transmission and diffuse reflection were obtained on a Varian Cary 5E spectrophotometer (400-850 nm). Absorption and reduced scattering coefficients of the tissues were determined with the Inverse Adding Doubling method. Our results suggested that within the 400-nm to 850-nm spectrum, optical properties of the ground tissue approximated intact tissue within limits of experimental error.     

Effect of hybrid woven fabrics structure on their electrical properties

The aim of this study is to investigate the influence of hybrid textile woven fabric structure on the electrical resistivity. Weave structure was varied by varying the weave pattern and the conductive yarn density in the woven fabrics. Electrical surface and volume resistivity were measured and compared to the fabric structural properties. Results showed that not only the conductive yarns percentage has an important effect on the electrical resistivity but also the weave structure. The most influencing structural parameter on surface resistivity was the woven fabric surface profile as it controls the contact quality between the conductive yarns and the measuring electrodes. A high surface resistivity was noticed when the contact quality was poor. When this contact quality was good, a linear correlation was found between surface electrical resistivity and the cover firmness factor, the apparent conductive fiber surface area as well as the conductive yarn floating length of the woven structures.     

多孔ZnO薄膜结构与光学性能研究

采用sol-gel提拉法,以聚乙二醇(PEG2000)为模板剂,醋酸锌为前驱体,乙醇为溶剂,二乙醇胺为络合剂,在玻璃基片上生长了多孔ZnO薄膜,利用SEM和紫外分光光度计分析了多孔ZnO薄膜的表面形貌和光学性质。研究了涂膜层数,模板剂加入量对多孔ZnO薄膜结构和透射率的影响。实验结果表明:随着涂膜层数的增加,薄膜的透射率有减小的趋势;当镀膜层数一定时,加入PEG2000后,有利于ZnO多孔结构的形成,在一定范围内,孔尺寸随PEG加入量的增加而增大,薄膜的紫外-可见光透射率随PEG加入量的增加而减小。     

Fabrication and optical properties of photochromic compound/clay hybrid films

A cationic spiropyran iodide derivative (SPI) was synthesized as a photoresponsive compound, and SPI/montmorillonite clay hybrid films were prepared using ion- and guest-exchange intercalation methods. When the ion-exchange method was applied to clay with a low cation-exchange capacity (CEC), intercalation of SPI into clay interlayers did not occur. Using the clay with a high CEC, SPI was intercalated into clay interlayer and the interlayer distances were elongated. Upon UV and visible light irradiation, SPI in hybrid film photoisomerized reversibly and the interlayer distance also changed reversibly. On the other hand, intercalation by the guest-exchange method using cethyltrimethylammoniumbromide (CTAB) as a pre-exchanging reagent was independent on the CEC. After the addition of SPI, the CTAB in the clay interlayers was exchanged for SPI, but a partial CTAB remained in the interlayer. SPI in the hybrid films prepared by the guest-exchange method photoisomerized reversibly without any change in interplanar distance due to the coexisted CTAB.