镶嵌在氢化氮化硅中纳米非晶硅粒子光吸收的模拟

采用量子限制效应模型对镶嵌有纳米非晶硅粒子的氢化氮化硅薄膜的光吸收进行了理论模拟,探讨了由吸收谱分析给出该结构薄膜光学参数的方法,并通过对不同氮含量样品的讨论给出了量子限制效应和纳米硅粒子表面的结构无序对薄膜光吸收特性的影响规律。分析结果表明,随氮含量的增加,薄膜有效光学带隙增大,该结果与薄膜中纳米硅粒子平均尺寸的减小引起的量子限制效应的增强相关,而小粒度纳米硅粒子比例增加所引入的较高微观结构无序度和较多缺陷将会导致薄膜低能吸收区吸收系数增加。     

Synthesis and photoluminescence studies of silicon nanoparticles embedded in silicon compound films

High-density silicon nanoparticles with well-controlled sizes were grown onto cold substrates in amorphous SiN _x and SiC matrices by plasma-enhanced chemical vapor deposition. Strong, tunable photoluminescence across the whole visible light range has been measured at room temperature from such samples without invoking any post-treatment, and the spectral features can find a qualitative explanation in the framework of quantum confinement effect. Moreover, the decay time was for the first time brought down to within one nanosecond. These excellent features make the silicon nanostructures discussed here very promising candidates for light-emitting units in photonic and optoelectronic applications.      

硅纳米线拉曼光谱的波长选择效应

我们用四种不同波长的激光作为激发源研究硅纳米线的拉曼谱 ,观察到一种反常的现象 ,即拉曼峰的频移、峰宽和非对称系数都依赖于激发光波长。考虑了量子限制效应 ,样品的尺寸分布和共振拉曼散射特性 ,对此反常现象提出了一个合理的解释     

Nanometer-sized Silicon Particles Prepared by Laser Vaporization and Their Photoluminescence

Nanometer-sized silicon particles were prepared by laser vaporization of a silicon target in pure argon ambient at a reduced pressure. The shape and size of the nanoparticles were characterized by transmission electron microscopy. The as prepared nanometer silicon particles exhibit visible luminescence under light excitation and the activated light emissions are found to show a strong dependence on temperature.     

a-Si ∶H/SiO2多量子阱材料制备及其光学性能和微结构研究

利用等离子体增强化学气相沉积技术制备了a-Si ∶H/SiO₂多量子阱结构材料.对a-Si ∶H/SiO₂多量子阱样品分别进行了3种不同的热处理,其中样品经1100 ℃高温退火可获得尺寸可控的nc-Si:H/SiO₂量子点超晶格结构,其尺寸与非晶硅子层厚度相当.比较了a-Si ∶H/SiO₂多量子阱材料与相同制备工艺条件下a-Si ∶H材料的吸收系数,在紫外/可见短波段前者的吸收系数明显增大,光学吸收边蓝移,说明该材料 关键词： 多量子阱 量子限制效应 光学吸收 能带结构     

非晶化与量子限域效应

当材料尺度减小到几个纳米时，材料内部电子结构会表现为分立能级，这就是所谓的量子限域效应。通过晶态和非晶Pd纳米颗粒的单电子隧穿实验发现，在晶态Pd颗粒中能观察到量子限域效应，而在同样大小的非晶Pd颗粒中却没有观察到。考虑到有序／无序结构的静态效应并结合电子散射等动态效应，解释了非晶Pd颗粒实验中没有观察到量子限域效应的原因。这一结果表明，尺寸减小并不足以使纳米体系表现量子行为，原子结构有序度对于决定纳米体系表现经典行为或量子行为具有同等重要作用。     

Nanometer sized Silicon Particles Prepared by Laser Vaporization and Their Photoluminescence

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有机超微粒的制备及其尺寸效应的研究

有机超微粒是国际上刚刚起步的研究领域,是纳米科技领域和有机光电子领域的重要前沿课题.文章从有机功能小分子出发,在制备粒径和形状可控的、高度单分散的纳米超微粒的基础上,首次系统地研究了有机超微粒的电子态随尺寸大小的变化过程.发现有机超微粒和无机超微粒一样具有显著的尺寸效应,而且更具多样性.该项研究工作为探索和比较无机和有机材料介观尺寸效应的异同点这一科学问题奠定了坚实的基础,对于理解有机分子晶体这类传统材料中的基本过程和现象以及开发新型光电材料和器件也极具意义.     

多孔硅的分形结构及其荧光特性

用扫描电子显微镜(SEM)对多孔硅的结构进行了分析.结果显示多孔硅具有分形特性,同计算机模拟结果一致;用荧光光谱仪,研究了多孔硅的荧光特性与激发波长的依赖关系.激发光谱测量结果发现,当激发波长从650 nm变到340 nm时,荧光谱峰位从红端780 nm连续蓝移到500 nm.综合分析说明：正是由于多孔硅的分形微结构以及量子限制效应,导致了多孔硅的荧光特性随激发波长改变的物理现象.     

3C-SiC纳米颗粒量子限制效应的实验证据

报道了关于3C—SiC纳米颗粒量子限制效应的实验证据．将电化学腐蚀3C—SiC多晶靶材得到的多孔材料在水溶液中进行超声处理，制备出发光的3C—SiC纳米颗粒溶液．透射电镜实验表明，所得颗粒直径分布在1-6nm范围，光致发光谱实验给出了存在量子限制效应的实验证据．发光范围在440-460nm．SiC纳米颗粒量子限制效应的发现，为该材料在光电子发光器件中的应用提供了重要的实验基础．     

Dependence of Optical Absorption in Silicon Nanostructures on Size of Silicon Nanoparticles

The amorphous silicon nanoparticles (Si NPs) embedded in silicon nitride (SiN_x) films prepared by helicon wave plasma-enhanced chemical vapor deposition (HWP-CVD) technique are studied. From Raman scattering investigation, we determine that the deposited film has the structure of silicon nanocrystals embedded in silicon nitride (nc-Si/SiNx) thin film at a certain hydrogen dilution amount. The analysis of optical absorption spectra implies that the Si NPs is affected by quantum size effects and has the nature of an indirect-band-gap semiconductor. Further, considering the effects of the mean Si NP size and their dispersion on oscillator strength, and quantum-confinement, we obtain an analytical expression for the spectral absorbance of ensemble samples. Gaussian as well as lognormal size-distributions of the Si NPs are considered for optical absorption coefficient calculations. The influence of the particlesize-distribution on the optical absorption spectra was systematically studied. We present the fitting of the optical absorption experimental data with our model and discuss the results.     

包埋于氮化硅薄膜中的硅团簇的光致发光特性

采用等离子体增强化学气相沉积(PECVD)技术,在低温下制备了富硅氢化氮化硅薄膜。利用红外吸收(IR)谱,光电子能谱(XPS)和光致发光(PL)谱,研究了在不同温度下退火的薄膜样品的结构和发光特性。在经过低温退火的薄膜中观测到一个强的可见发光峰。当退火温度较高时,随着与硅悬键有关的发光峰消失,可见发光峰位发生了蓝移。讨论了退火对薄膜中硅团簇的形成及其对发光的影响。根据Raman谱,计算了氮化硅薄膜中硅团簇的尺寸大小。通过实验结果和分析,我们认为PL谱中较强的室温可见发光峰来自于包埋于氮化硅中的硅团簇。     

多孔硅的形成与发光

本文综述了有关多孔硅(Porous Silicon,简称PS)某些新近的研究成果,包括多孔硅的形成、光致发光和电致发光,着重介绍多孔硅的形成和发光过程的量子尺寸效应.     

量子受限效应和对称性效应对硅光子晶体禁带的影响

光子晶体不仅可以用来调控自发辐射, 还可以用来控制光的传输和局域. 采用平面波展开法进行模拟计算, 分析硅背景下的二维正方、三角晶格光子晶体散射基元的形状和空间取向对光子禁带的影响. 计算结果表明: 对称性和量子受限效应之间的竞争是导致光子晶体禁带宽度发生变化的原因.     

表面键合对硅(111)量子面电子结构的影响

将纳米硅薄膜看成理想的一维限制的量子面结构,通过第一性原理计算研究了不同厚度的硅(111)量子面的能带结构及态密度。随着量子面厚度的变化,在Si—H键钝化较好的量子面结构上,其带隙宽度变化主要遵循量子限制效应规律。当在表面掺杂时,模拟计算表面含Si—N键的硅(111)量子面的结果表明:在一定厚度范围内,带隙宽度主要由量子限制效应决定;超过这个厚度,带隙宽度同时受量子限制效应和表面键合结构的影响。保持量子面厚度不变,表面掺杂浓度越大则带隙变窄效应越明显。同样,模拟计算含Si—Yb键的硅(111)量子面的结果也有同样的效应。几乎所有的模拟计算结果都显示:量子面的能带结构均呈现出准直接带隙特征。     

Optimum Quantum Yield of the Light Emission from 2 to 10 nm Hydrosilylated Silicon Quantum Dots

Optimizing the light‐emitting efficiency of silicon quantum dots (Si QDs) has been recently intensified by the demand of the practical use of Si QDs in a variety of fields such as optoelectronics, photovoltaics, and bioimaging. It is imperative that an understanding of the optimum light‐emitting efficiency of Si QDs should be obtained to guide the design of the synthesis and processing of Si QDs. Here an investigation is presented on the characteristics of the photoluminescence (PL) from hydrosilylated Si QDs in a rather broad size region (≈2–10 nm), which enables an effective mass approximation model to be developed, which can very well describe the dependence of the PL energy on the QD size for Si QDs in the whole quantum‐confinement regime, and demonstrates that an optimum PL quantum yield (QY) appears at a specific QD size for Si QDs. The optimum PL QY results from the interplay between quantum‐confinement effect and surface effect. The current work has important implications for the surface engineering of Si QDs. To optimize the light‐emission efficiency of Si QDs, the surface of Si QDs must be engineered to minimize the formation of defects such as dangling bonds at the QD surface and build an energy barrier that can effectively prevent carriers in Si QDs from tunneling out.     

Preparation and characterization of PbS nanoparticles in AOT micellar medium

The preparation of PbS nanoparticle is important in material science. Due to its predominant ionic character and low optical band gap (0.41 eV), it shows quantum confinement effect up to a larger size domain compared to other well studied semiconductor materials, such as ZnS and CdS, having predominantly covalent character. In this report, we present a simpler method of preparation of nanosized PbS in micellar medium of the surfactant AOT and spectrophotometric, fluorimetric, light scattering and electron microscopic characterization of the dispersion.     

Preparation, characterization and properties of novel covalently surface-functionalized zinc oxide nanoparticles

Novel covalently surface-modified zinc oxide (ZnO) nanoparticles (NP) (ZHIE) were successfully prepared, which have organic chains composed of hydrophilic amide and urethane linkages, and terminal amino groups on the surfaces, using zinc acetate monohydrate. FTIR spectroscopy, X-ray analysis and TEM observation suggested that the resultant ZHIE NPs have the mean sizes of about 10 nm in diameters, the organic chains linking the amino groups in the terminals and wurtzite crystal structure. UV-vis absorption spectrum of the ZHIE NPs in methanol showed maximum absorption band at 348 nm, supporting the TEM observations. Photoluminescent spectrum measurements depicted that the ZHIE NPs show broad visible emission band on the basis of trapped-electron emission. Cytotoxicity and phagocytosis assays suggested that the ZHIE NPs are noncytotoxic, and the ZHIE-labeled zymosan particles derived by conjugation of the ZHIE NPs with zymosan are internalized into the cells and generate fluorescence based on the ZHIE NPs.     

Multipeak-structured photoluminescence mechanisms of as-prepared and oxidized Si nanoporous pillar arrays

Silicon dominates the electronic industry, but its poor optical properties mean that it is not preferred for photonic applications. Visible photoluminescence (PL) was observed from porous Si at room temperature in 1990, but the origin of these light emissions is still not fully understood. This paper reports that an Si nanocrystal, silicon nanoporous pillar array (Si-NPA) with strong visible PL has been prepared on a Si wafer substrate by the hydrothermal etching method. After annealing in O₂ atmosphere, the hydride coverage of the Si pillar internal surface is replaced by an oxide layer, which comprises of a great quantity of Si nanocrystal (nc-Si) particles and each of them are encapsulated by an Si oxide layer. Meanwhile a transition from efficient triple-peak PL bands from blue to red before annealing to strong double-peak blue PL bands after annealing is observed. Comparison of the structural, absorption and luminescence characteristics of the as-prepared and oxidized samples provides evidence for two competitive transition processes, the band-to-band recombination of the quantum confinement effect of nc-Si and the radiative recombination of excitons from the luminescent centres located at the surface of nc-Si units or in the Si oxide layers that cover the nc-Si units because of the different oxidation degrees. The sizes of nc-Si and the quality of the Si oxide surface are two major factors affecting two competitive processes. The smaller the size of nc-Si is and the stronger the oxidation degree of Si oxide layer is, the more beneficial for the luminescent centre recombination process to surpass the quantum confinement process is. The clarification on the origin of the photons may be important for the Si nanoporous pillar array to control both the PL band positions and the relative intensities according to future device requirements and further fabrication of optoelectronic nanodevices.     

Thermo-Optic Switch using Fluorinated Silicon Oxide and Organic Spin-on-Glass Films

A thermo-optic switch in a thin-film optical waveguide was investigated. Fluorinated silicon oxide (SiOF) and organic spin-on-glass (SOG) films were used as core-layer and clad-layer, respectively, in the waveguide structure. The SiOF films were formed at 23#x00B0;C by a liquid-phase deposition (LPD) technique using a supersaturated hydrofluosilicic acid (H₂SiF₆) aqueous solution. Thermal coefficients of the refractive indices for LPD-SiOF and organic SOG films formed on silicon (Si) substrates were #x2212;4.0 #x00D7; 10^#x2212;6/#x00B0;C, #x2212;60 #x00D7; 10^#x2212;6/#x00B0;C at the wavelength of 632.8 nm, respectively. A high extinction ratio of 15 dB was obtained for this switch at the applied voltage of 12.8 V.