基于半导体光放大器垂直双泵浦对偏振复用正交相移键控信号波长变换的性能研究

针对偏振复用相位调制信号的全光波长变换特性问题,基于半导体光放大器中四波混频效应,建立了对偏振复用正交相移键控信号的全光波长变换理论模型.根据理论分析,建立了仿真系统,仿真结果表明:泵浦光与信号光之间的频率间隔、偏振复用信号中的一个信号与一号泵浦光的偏振夹角对系统转换效率和信号质量有影响;波长转换过程中交叉相位调制产生的相位噪音会对信号质量有影响,且当泵浦光功率较大、泵浦光功率远大于信号光功率时,交叉相位调制效应的影响较小,仿真结果与理论分析一致.本文研究方法和相关结论对其它偏振复用信号基于半导体光放大器四波混频效应的波长变换研究有一定的参考价值.     

双光反馈半导体激光混沌系统的外腔反馈强度对延时特征的影响

通过构建一个双光反馈半导体激光混沌系统,本文实验研究了双腔之间不同反馈强度对系统混沌输出的延时特征的影响.结果表明:固定一个腔的反馈量,而适当调节另一个腔的反馈强度,可实现对混沌输出延时特征的良好抑制.同时,在延时反馈特征抑制较好的情况下,还存在时间漂移（即从混沌输出所提取的特征延时与系统真实延时之差）明显增大的现象.因此采用双光反馈半导体系统可以很好地隐藏激光混沌的延时参量,从而显著提升其在相关领域的表现性能.     

Al~(3+)诱导的金纳米粒子静电自组装及其SERS表征

通过Al 3+静电诱导实现了金纳米粒子(Au NPs)的一维(1D)或二维(2D)程序可控自组装。我们的研究发现,静电组装形成的Au NPs组装体(Au NAs)的尺寸、形貌及其表面等离子体共振(SPR)性质与Al 3+的浓度密切相关,随着Al 3+浓度的增加,Au NPs由孤立的Au纳米粒子组装成一维或二维的纳米阵列。同时,与孤立Au NPs相比,Au NAs因存在更多的"热点"而具有更好的SERS活性,并可以通过调节Al 3+的浓度来调控Au NAs的SERS活性。     

Resonant Raman scattering in CdSxSe1−x nanocrystals: effects of phonon confinement,composition, and elastic strain

Optical phonon modes, confined in CdS_xSe_1−x nanocrystal (NC) quantum dots (≈2 nm in radius) grown in a glass matrix by the melting‐nucleation method, were studied by resonant Raman scattering (RRS) spectroscopy and theoretical modeling. The formation of nanocrystalline quantum dots (QDs) is evidenced by the observation of absorption peaks and theoretically expected resonance bands in the RRS excitation spectra. This system, a ternary alloy, offers the possibility to investigate the interplay between the effects of phonon localization by disorder and phonon confinement by the NC/matrix interface. Based on the concept of propagating optical phonons, which is accepted for two‐mode pseudo‐binary alloys in their bulk form, we extended the continuous lattice dynamics model, which has successfully been used for nearly spherical NCs of binary materials, to the present case. After determining the alloy composition for NCs (that was evaluated with only 2–3% uncertainty using the bulk longitudinal optical phonon wavenumbers) and the NC size (using atomic force microscopy and optical absorption data), the experimental RRS spectra were described rather well by this theory, including the line shape and polarization dependence of the scattering intensity. Even though the presence of a compressive strain in the NCs (introduced by the matrix) masks the expected downward shift owing to the phonons' spatial quantization, the asymmetric broadening of both Raman peaks is similar to that characteristic of NCs of pure binary materials. Although with some caution, we suggest that both CdSe‐like and CdS‐like optical phonon modes indeed are propagating within the NC size unless the alloy is considerably heterogeneous. Copyright © 2011 John Wiley & Sons, Ltd.     

Electron beam induced in-vacuo Ag deposition on TiO2 from ionic liquids

The present work describes electron beam induced Ag deposition from [BMIM][BF₄] ionic liquid containing AgBF₄ on anatase TiO₂ surfaces. The procedure is directly performed in the ultra high vacuum chamber of a scanning electron microscope (SEM). Based on the experiments with reference surfaces (Au and amorphous TiO₂) that do not show successful Ag deposition, it is proposed that the deposition mechanism is of pseudo-photocatalytic nature.     

Etching and Growth: An Intertwined Pathway to Silver Nanocrystals with Exotic Shapes

Two‐faced nanocrystals : Rapid addition of a second aliquot of silver nitrate during a polyol synthesis led to the formation of anisotropically truncated octahedrons as a result of oxidative etching and overgrowth of silver nanocubes. Three adjacent faces of the nanocube grew more rapidly than the three other faces, generating a non‐centrosymmetric structure (see picture).

     

Solar-driven electrochemically assisted semiconductor-catalyzed iodide ion oxidation. Enhanced efficiency by oxide mixtures

Oxidation of iodide ion from an air-saturated solution under natural sunlight (900±50 W m⁻²) on the surfaces of TiO₂, ZnO, Fe₂O₃, MoO₃ and CeO₂ enhances by 6 to 12-fold on application of a cathodic bias of −0.2 to −0.3 V (vs NHE) to the semiconductors; light, the semiconductor and dissolved oxygen are essential for iodine generation. The semiconductors under an anodic bias of +0.2 to +0.3 V (vs NHE) fail to oxidize iodide ion from air-saturated solution under sunlight. Under cathodic bias, semiconductor mixtures like TiO₂-ZnO, TiO₂-Fe₂O₃ and ZnO-Fe₂O₃ show enhanced photocatalytic activity, indicating improved charge separation in oxide mixtures. The mechanism of photocatalysis under cathodic bias is discussed.      

基于单分散氟化物纳米晶的成核生长模型

在纳米介观尺度范围内实现对材料尺寸与形貌的调控,是纳米材料合成、制备、功能化及其应用的关键,对认识并解纳米晶的成核与生长规律具有重要意义.基于单分散氟化物纳米晶合成提出的扩散控制动力学模型(DCK,diffusion-controlled kinetic)和表面化学热力学模型(SCT,surface chemical thermodynamics)旨在探讨纳米晶的成核与生长规律.本文围绕纳米晶的成核、生长机理,在综述前人工作的基础上,归纳和总结了上述模型,有望对纳米晶的可控合成提供理论指导与借鉴.     

纳米晶取向接合生长动力学研究及其在量子点发光性质调控中的应用

对晶体生长机制、动力学与微结构衍化的认识是实现纳米材料的尺寸和形貌可控制备的基础．以表面溶解沉积为特征的奥斯特瓦尔德熟化（0R）理论常用来解释传统的晶体生长过程．在该生长模式下,纳米晶体的生长呈现出小颗粒溶解而大颗粒逐渐长大的特征．在纳米材料体系,近来还发现了一种重要的新的晶体生长模式——“取向接合（OA）”机制,在该机制下,两个晶格取向一致的初级纳米颗粒可通过直接接合和结构调整,从而长成一个新的晶体．这一机制已被证实在许多纳米材料体系中广泛存在,并对所合成的纳米材料的形貌、微结构具有非常显著的影响,在构筑新型纳米结构方面具有潜在的优势．本文我们首先回顾了OA生长机制的认识历程和这一机制对材料科学的重大意义;进而,基于我们的研究工作系统介绍了OA生长动力学模型的建立与发展,进一步阐述了这一机制的微观过程及其对材料内部缺陷的特殊影响,深入地分析和讨论了表面包裹的强弱、表面作用的性质对OR机制和OA机制的抑制和调控作用;基于上述表面包裹可调控纳米材料的生长机制的认识,我们结合近期研究结果,从动力学角度分析了量子点的生长机制与其发光特性的内在关联,阐明了表面包裹调控量子点的发光性质的本质原因,为制备不同发光特征的量子点及理解其发光性质衍化规律提供了重要的理论指引．     

水相CdTe纳米晶的合成、生长机理和应用研究

纳米晶在生物检测、光电器件、光波导、可调激光器等领域有着广泛的应用前景．本文以CdTe为例,对近年来水相纳米品合成和生长机理方面的研究进展作了简要的归纳和论述．水相合成纳米晶具有操作简单、价格低廉、在水溶液中稳定性高等优点,并可以通过静电力、范德华力等弱相互作用实现一维、二维甚至三维结构的组装．对纳米晶的生长机理的研究涵盖了热力学主导的Ostwald熟化（Ostwaldripening）机理和动力学控制的聚集机理两个主要方面．文章最后对水相合成CdTe纳米晶的应用进行了总结和展望,