Advanced Materials Research Vol. 1035

Abstract: Coherent pre-illumination technique is proposed to improve the pulsed holographic recording characteristics of polyvinyl alcohol (PVA) /acrylamide green-sensitive photopolymer. By optimizing the pre-illumination parameters such as pre-illumination energy density and pre-illumination delay time, the photosensitivity and diffraction efficiency of photopolymer under pulsed holographic recording are improved effectively. For the coherent pre-illumination energy density of 2mJ/cm², total pre-illumination energy of 50mJ/cm², the diffraction efficiency of 85% can be obtained with holographic exposure of 35mJ/cm². For the coherent pre-illumination delay time of 20seconds, the diffraction efficiency of 60% is obtained with holographic exposure of 17.5mJ/cm². The photosensitivity is successfully improved about 8 times compared with other reported results, it has good application prospects in the measurements of high-speed transient processes.

Abstract: Two thiophene derivatives 4,4'-di (thiophen-2-yl) biphenyl and 4,4'-di (thiophen-2-yl) -2-nitrobiphenyl ,which were used as monomers for preparing poly (4,4'-di (thiophen-2-yl) biphenyl) (DPBT) and poly (4,4'-di (thiophen-2-yl)-2-nitrobiphenyl) (DPNT) by ferric chloride oxidation polymerization, were synthesized via Suzuki reaction with 4,4'-dibromobiphenyl as the raw material. UV-vis absorption spectra, fluorescence spectra, photoluminescence spectra and electrochemical properties of the polymers were recorded and used for calculating the band-gap (E_g), HOMO orbital energy (E_HOMO) and LUMO orbital energy (E_LUMO) of the polymers. The calculation results indicated that attaching an electron-withdrawing group such as-NO₂ to the main chain can lower band-gap and increase the maximum absorption wavelength.

Abstract: The structure and properties of the Ge_xAs_xS_100-2x have been studied by ab initio molecular dynamics simulation. By calculating the pair distribution functions, bond angle distribution functions, we analyze the structure and properties of the alloys. Calculations show that Ge and As are all well combined with S atoms. When x is smaller than 25.0 the binding increases with x , when x is larger than 25.0 the binding decreases with increasing x . The intervention of As atom does not affect the GeS₂ formation in Ge₄₀As₄₀S₈₀

Abstract: Laser induced plasma is a relatively complex process which is closely related to many factors. In this paper, using a short pulse Nd:YAG laser and CCD photoelectric detection system, the variation of laser focus position effected by spectral intensity, the ratio of signal to background as well as the self-absorption of the plasma spectral lines with the standard spectra sample of aluminum for analysis samples was studied. Results show that: when the laser focus position is about 5mm under the surface of the sample, the relative intensity and the ratio of signal to background of the spectral lines are the strongest, and the spectral lines are sharp without obvious self-absorption.

Abstract: In order to realize the macroscopic objects invisible in the visible region, according to the law of refraction, total internal reflection law and symmetry reduction transformation method, a new type of visible light stealth cloak was designed. The cloak was prepared using the ordinary homogeneous and isotropic glass materials, which can guide the light around the hidden region, and the direction of propagation of light has not changed. Thus the macroscopic object achieve the perfect stealth. The invisible cloak in air environment for arbitrary polarized visible light have stealth features, easy processing, low cost, has potential application value.

Abstract: To solve more and more serious electromagnetic radiations, electromagnetic wave absorption cement were prepared by introducing carbon black and glass fiber as composited absorbing reagent, wich can be useful in building anechoic chamber and other electromagnetic radiation protection to buildings. The results showed that the absorption properties were improved compared with single absorbing agent such as carbon or glass fiber. the lowest reflection loss of-11.3dB was obtained at 18 GHz of 5wt.% carbon black and 9wt.% glass fiber filled cement with thickness of 20mm. The increase of thickness separately can not improve the absorption properties.

Abstract: Graphene-bismuth oxide composite were fabricated through a facile hydrothermal method. The SEM, XRD, EDS, FTIR were performed to characterize the morphology, composition, structure and surface functional groups. It was found that the Bi₂O₃ evenly spread on the surface of graphene. What is interesting is that two kinds of bismuth oxide can be generate in an experiment. One is spherical Bi₂O₃ with a diameter of 1~2 μm, the other is about 40 nm particle-size growed on the surface of the graphene. The possible growth mechanism was discussed. Under UV-pulsed illumination, graphene-Bi₂O₃ composite electrodes can produce an extracurrent of about 52.92 μA/cm² under 0.3 V bias voltage, this value is higher than the existing report, indicating potential applications in optoelectronic devices. The possible reasons are explained.

Abstract: NiO-SiO₂ composite photonic crystals were fabricated by the self-assembly and the spin coating method. First, the SiO₂ monodisperse colloidal spheres were fabricated by the Storber method and the opal structure was obtained by the vertical deposition method. After spin coating and sintering, the electrochromic material NiO was infiltrated in the opal template. The obtained NiO-SiO₂ composite photonic crystal was characterized by X-ray diffraction (XRD), and the morphologies of SiO₂ opals and the composite structures were characterized by SEM. The reflection spectra were measured and revealed that the periodic arrays exhibit a photonic band gap in the (111) direction.