多孔硅基微型Bragg光学传感器的理论和应用研究

对多孔硅基微型光学传感器的可制备性进行了理论分析,说明只要选择合适的腐蚀条件,采用交替改变电流密度的方法就可以得到折射率随深度交替变化的多层多孔硅结构,即Bragg反射镜,同时可实现了反射谱峰位可调。提出了Bragg反射镜的理论模型,对其布拉格中心波长,半峰全宽以及光强反射率进行了理论计算,得出了高低折射率之比、层数与光强反射率之间的关系,并对实际情况进行了说明。最后,简单介绍了Bragg反射镜在气体/液体传感器及光学微腔中的应用,有一定的应用价值。     

基于多孔硅反射镜的农药浓度测量实验研究

利用脉冲腐蚀法制备了多孔硅Bragg反射镜,分析了反射镜测量农药浓度的原理,搭建了多孔硅反射谱测量系统,实验研究了多孔硅反射镜的光谱图、在不同浓度克百威溶液条件下的多孔硅光谱图以及克百威浓度与多孔硅反射谱峰位变化的关系.结果表明,多孔硅反射镜在不同浓度的克百威溶液下,反射谱峰位将发生红移变化;当克百威浓度在0～0.1 ...     

Cu:Co:SrxBa1-xNb2O6 晶体光折变效应的研究

在SrxBal-xNb2O6 (SBN)晶体中掺进CuO和Co3O4,采用硅钼棒加热体,以Czochralski法生长了CuCoSBN晶体.通过二波耦合光路测试了晶体的光折变性能.CuCoSBN晶体的最大衍射效率为74%,最大折射率变化为7.9×10-5,光折变灵敏度为4.8×10-4cm3/J,并给出了晶体响应时间与光强的关系.利用四波混频光路测试了晶体的自泵浦位相共轭反射率和响应时间.用CuCoSBN晶体作为存储元件, MgFeLiNbO3晶体为位相共轭反射镜,以增益反馈系统,实现关联存储实验.     

Cu∶Co∶Sr_xBa_(1-x)Nb_2O_6晶体光折变效应的研究

在SrxBal-xNb2 O6 (SBN)晶体中掺进CuO和Co3O4,采用硅钼棒加热体 ,以Czochralski法生长了Cu :Co :SBN晶体。通过二波耦合光路测试了晶体的光折变性能。Cu∶Co∶SBN晶体的最大衍射效率为 74% ,最大折射率变化为 7.9× 10 - 5,光折变灵敏度为 4.8× 10 - 4 cm3/J,并给出了晶体响应时间与光强的关系。利用四波混频光路测试了晶体的自泵浦位相共轭反射率和响应时间。用Cu∶Co∶SBN晶体作为存储元件 ,Mg∶Fe∶LiNbO3晶体为位相共轭反射镜 ,以增益反馈系统 ,实现关联存储实验。     

NaOH溶液对多孔硅后处理的研究

用强碱溶液后处理多孔硅的方法常被用来打开表面孔洞,以便生物化学分子更好的进入孔洞而实现传感检测的目的。对于纳米多孔硅,碱溶液处理带来的孔洞直径的增加不可忽视,而对此的相关研究未见报道。本文用浓度分别为1、3和15m mol·L~(-1)的NaOH溶液对多孔硅进行后处理研究,处理时间从1min到30min。用NaOH溶液处理以后的多孔硅,孔径大小会改变,从而孔隙率改变导致多孔硅的折射率改变。测量不同条件下后处理多孔硅的反射光谱时反射谱会发生平移。实验结果表明:单层多孔硅和多层多孔硅,随着处理时间增加,Na OH溶液浓度增大,反射谱波峰会向波长小的方向移动,即发生蓝移。当Na OH溶液浓度达到15m M,浸泡时间达到8min时,多孔硅结构遭到破坏。     

多孔纳米二氧化硅球的制备及其对胰岛素的担载和释放行为

利用实心的二氧化硅纳米微球为原材料,通过用聚乙烯吡咯烷酮进行表面保护,用氢氧化钠对硅球进行溶蚀,制备多孔纳米二氧化硅微球.通过热重分析、扫描电镜及透射电镜对溶蚀的硅球进行表征.结果表明:溶蚀前后,二氧化硅球的外形没有发生实质的变化,但在内部形成了多孔通道.用这种多孔状的纳米硅球对胰岛素进行担载和释放试验发现,经过多孔化处理后,硅球对胰岛素的担载能力增强,释放速率降低,说明经过溶蚀获得的纳米二氧化硅可以作为一种药物的微胶囊载体,在药物控制释放领域有一定的应用前景.     

金辅助化学腐蚀法制备多孔硅及其性能研究

近年来金属辅助化学腐蚀法制备多孔硅逐渐成为研究热点,但该方法存在金属颗粒易团聚、引入模板辅助刻蚀成本高昂等突出问题。为了优化多孔硅的制备技术,降低制备成本,本文研究了基于金颗粒辅助化学腐蚀的多孔硅制备方法。首先采用氯金酸还原法制备了粒径从18～80 nm的带负电荷金颗粒,3-氨基丙基三乙氧基硅烷修饰可以使单晶硅表面带正电荷,通过静电吸附实现了金在硅基底表面均匀、独立的沉积。在含H2O2和HF的刻蚀液中,硅基底被蚀刻成规则的孔状,多孔硅产物膜厚在添加N,N-二甲基乙酰胺作为表面活性剂时达到44. 45μm。此外,刻蚀液组成为ρ=70%(ρ=[HF]/([HF]+[H2O2]))时多孔硅刻蚀速率达到1. 23μm/min,对应的多孔硅/高氯酸钠复合含能材料爆炸光强最大,DSC放热量为1636 J/g。     

锂离子电池多孔硅基复合负极材料的研究进展

概述了多孔硅基负极材料在锂离子电池中的应用,重点介绍了材料结构和复合方式对其电化学性能的影响;分析了导致其循环性能降低的主要原因,指出控制电池循环过程中硅基材料体积变化、抑制SEI膜的增加是改善硅基负极材料循环性能的重要途径. 对多孔硅基复合负极材料的研究进行了展望,提出在纳米化和复合化的基础上,设计特殊孔道结构、制备多孔的硅/碳复合材料是推进硅基负极材料应用的重要研究方向.     

多孔硅发光材料研究进展

综述了多孔硅的制备方法、形成机理和多孔硅的光致发光机制,以及为改善多扎硅的发光特性而采取的一些措施,最后概述了多孔硅发光材料的应用.     

多孔硅的形貌、制备和应用

介绍了近年来制备多孔硅的主要方法,以及多孔硅在光电传感器、发光器件、电池、生物技术等新领域的应用。     

Porous silicon Bloch surface and sub-surface wave structure for simultaneous detection of small and large molecules

A porous silicon (PSi) Bloch surface wave (BSW) and Bloch sub-surface wave (BSSW) composite biosensor is designed and used for the size-selective detection of both small and large molecules. The BSW/BSSW structure consists of a periodic stack of high and low refractive index PSi layers and a reduced optical thickness surface layer that gives rise to a BSW with an evanescent tail that extends above the surface to enable the detection of large surface-bound molecules. Small molecules were detected in the sensor by the BSSW, which is a large electric field intensity spatially localized to a desired region of the Bragg mirror and is generated by the implementation of a step or gradient refractive index profile within the Bragg mirror. The step and gradient BSW/BSSW sensors are designed to maximize both resonance reflectance intensity and sensitivity to large molecules. Size-selective detection of large molecules including latex nanospheres and the M13KO7 bacteriophage as well as small chemical linker molecules is reported.     

Laser interferometry: A measurement technique for diffusion studies in thin polymer films

Laser interferometric techniques have many applications in the area of thin film science and technology due to their sensitivity, simplicity, and low cost. Typically, changes in thickness and/or refractive index of a transparent polymer film sample are detected from changes in film reflectivity, as measured by variations in the intensity of reflected laser light. Diffusion related properties such as solvent uptake/swelling, dissolution, and drying rates are accessible with laser interferometry since each of these processes involves a change in the film's thickness and/or refractive index. The principles and basic experimental considerations common to these three applications will be discussed. Illustrative examples from our lab will include n-methyl-2-pyrrolidone diffusion in polyimide, and methanol diffusion in poly(methyl methacrylate).     

Drying dynamics of polymers films by an interferometric technique

We analyze a simple laser reflectivity measurement as a tool to monitor the drying kinetics of transparent polymer films. The reflectivity signal of a laser beam at normal incidence shows oscillations due to interference arising from multiple reflection of the laser light within the drying film. We develop a model to interpret the reflectivity curves in terms of time evolving refractive indices at the top and bottom of the film. We present results of the drying kinetics of transparent alkyd films on a glass substrate of high refractive index. Data shows a clear hallmark indicating the evolution of the crosslinking process. From the reflectivity curves, the time evolution of the refractive indices at the top and bottom is obtained. Assuming a linear-gradient of the refractive index along the depth of the film the average refractive index and consequently the film thickness as a function of time are estimated. Clear features in the time evolution of the refractive indices and thickness, correlate well with qualitative “dust”, “touch” and “fingerprint” drying times. Additionally, we present some preliminary results for water based latex binders, where scattering of light is present, showing that this simple optical technique could be extended for studying latex film formation.     

Tunneling times of acoustic phonon packets through a distributed Bragg reflector

The longwave phenomenological model is used to make simple and precise calculations of various physical quantities such as the vibrational energy density, the vibrational energy, the relative mechanical displacement, and the one-dimensional stress tensor of a porous silicon distributed Bragg reflector. From general principles such as invariance under time reversal, invariance under space reflection, and conservation of energy density flux, the equivalence of the tunneling times for both transmission and reflection is demonstrated. Here, we study the tunneling times of acoustic phonon packets through a distributed Bragg reflector in porous silicon multilayer structures, and we report the possibility that a phenomenon called Hartman effect appears in these structures.     

Robust,low haze and graded porous anti-reflective glass by Tailoring the Nanostructures

Low haze and anti-reflective glass has high potential applications in automobile and optoelectronic fields. Etching is a novel and effective method to fabricate gradient refractive index anti-reflective layer on glass surface. However, the gradient layer on glass surface prepared by the etching method usually characterizes rough porous structure, and the structural defect results in high haze and low abrasion resistance to restrict its applications. In this paper, a hydrothermal etching method has been explored to prepare anti-reflective glass. It has demonstrated to be a new and facile method successfully to tailor the porous nanostructure of gradient refractive index layer and largely decrease the haze of the glass, by adding complex compound in the etching solution. Compared with the etching solution containing NaOH, adding the complex compound of C₆H₅Na₃O₇ in the etching solution has the advantage to overcome the defects. The grain diameter of the graded porous anti-reflective film decreases from ~63 nm to ~18 nm, the etched film thickness increases from 0.44 μm to 1.55 μm, the haze decreases drastically from 23.76% to 1.00%, the reflectivity decreases from 5.88% to 1.08% and the abrasion resistance greatly increases. However, when changing the complex compound from C₆H₅Na₃O₇ to Na₂HPO₄, the haze is 23.44% and has no effect on decreasing haze. Structural characterizations show that the grain size in the porous gradient layer can be easily tailored by changing the ion radius of complex anion in the etching solution, and the optical properties can be controlled. The paper provides new insights into the nanostructures and the preparation approach of anti-reflective glass.     

Glass Inhomogeneity Measurement Using the Shelyubskii Method

Inhomogeneity in glass can be measured in terms of the variance of the refractive index distribution by using the Shelyubskii method. In the method, the transmission of an optical cell containing glass particles immersed in a nearly matching refractive index liquid is measured. Transmission can be measured accurately and reproducibly as a function of wavelength with a conventional spectrophotometer. The primary source of errors, hitherto, has been the Raman-Shelyubskii theory to relate the transmission to the refractive index variance by using interference optics principles. It is shown that a common Shelyubskii experiment can be described more cogently by a theory based on the principles of geometric optics. A Monte Carlo simulation of light ray tracing through the optical cell containing glass particles with a random distribution of refractive index was conducted. The fraction of intensity collected within the acceptance angle of the spectrophotometer, identified as the transmission, agrees well with the measured data. A glass inhomogeneity meter based on the simulation experiments is described.     

Modulation of Transmission Spectra of Anodized Alumina Membrane Distributed Bragg Reflector by Controlling Anodization Temperature

We have successfully prepared anodized alumina membrane distributed Bragg reflector (DBR) using electrochemical anodization method. The transmission peak of this distributed Bragg reflector could be easily and effectively modulated to cover almost any wavelength range of the whole visible spectrum by adjusting anodization temperature.     

Novel-stratified low reflectivity anti-reflective coatings derived from self-assembly of high refractive index nanoparticles

We describe new anti-reflective multilayer optical coatings formed from a single liquid coating solution in a single coating step. The nanoparticles in these coatings self-organize as the liquid coating dries on the substrate. The self-assembly of the nanoparticles results in the formation of a two-layer dielectric stack composed of alternating high and low refractive index layers. For the first time, using this process, an ultra-low reflectivity film can be inexpensively and simply formed using high refractive index titanium oxide nanoparticles and a low refractive index fluoropolymer. These films can be made scratch or abrasion resistant by the inclusion of silane coupling agents and low refractive index nanoparticles.     

Study of the omnidirectional photonic band gap for dielectric mirrors based on porous silicon : effect of optical and physical thickness

ABSTRACT: We report the theoretical comparison of the omnidirectional photonic band gap (OPBG) of one-dimensional dielectric photonic structures, using three different refractive index profiles: sinusoidal, Gaussian and Bragg. For different values of physical thickness (PT) and optical thickness (OT), the tunability of the OPBG of each profile is shown to depend on the maximum/minimum refractive indices. With an increase in the value of the maximum refractive index, the structures with the same PT, showed a linear increment of the OPBG; in contrast to the structures with the same OT, showing an optimal combination of refractive indices for each structure to generate the maximum OPBG. An experimental verification was carried out with a multilayered dielectric porous silicon structure for all the three profiles.     

Polymer nanoparticle-based porous antireflective coating on flexible plastic substrate

Increased using of plastic optical elements has generated a need for applying antireflection coatings onto plastic substrates. In this paper we reported a facile method to preparing porous thin films on plastic substrates by spin-casting poly (methyl methacrylate) (PMMA)/polystyrene (PS) mixed latices, followed by selectively removing PS particles. The refractive index of the porous coating is directly related to its porosity which could be controlled by varying mixing fraction of the sacrificial PS particles. The obtained porous thin films exhibited excellent anti-reflective (AR) performance over visible range with minimum reflection of 0.02%. The powerful control on refractive index and the versatility of this method makes it practicable to prepare antireflective coating on various plastic substrates with optimal performance.