硅在HF溶液中阳极溶解的研究

Uhlir及Turner早在50年代就已发现^[1,2],硅在HF溶液中阳极极化时,阳极电流大于某一特定值硅表面会发生电抛光反应,而低于这个值硅表面则会形成一层不同颜色的多孔硅层.1990年Canham发现多孔硅层在室温下有光致发光现象^[3],受到科学界的高度重视,在世界范围内掀起了研究多孔硅的热潮^[4].众多的研究表明,多孔硅的发光性能与其微孔的多少、大小和分布密切相关.但多孔硅要发展成为可实用的光电子材料,首先必须制备出微孔分布均匀,孔径及孔深可控的多孔硅材料.这就有必要弄清多孔硅的形成机理^[5],了解硅在HF溶液中的溶解过程及机理.为此,本文对不同掺杂浓度不同导电类型的(111)晶面单晶硅在HF溶液中的电流-电压(I-V)、电容-电压(C-V)特性进行了研究,并对这些特性进行了分析.     

氧化钒/多孔硅/硅结构的微观形貌、纳米力学及温敏特性

采用电化学腐蚀法在硅基片表面形成多孔硅, 利用直流对靶反应磁控溅射方法在不同电流密度条件下制备的多孔硅样品表面上溅射沉积了VOx薄膜, 获得了氧化钒/多孔硅/硅(VOx/PS/Si)结构. 采用场发射扫描电镜(FESEM)观测多孔硅及VOx/PS/Si结构的微观形貌, 采用纳米压痕仪器测量VOx/PS/Si结构的纳米力学特性, 通过电阻-功率曲线分析研究其温度敏感特性. 实验结果表明, 在40和80 mA·cm-2电流密度下制备多孔硅的平均孔径分别为18和24 nm, 用显微拉曼光谱法(MRS)测量其热导率分别为3.282和1.278 kW·K-1; VOx/PS/Si结构的电阻随功率变化的平均速率分别为60×10⁹和100×10⁹ Ω·W-1, VOx/PS/Si结构的显微硬度分别为1.917和0.928 GPa. 实验结果表明, 多孔硅的微观形貌对VOx/PS/Si结构的纳米力学及温敏特性有很大的影响, 大孔隙率多孔硅基底上制备的VOx/PS/Si 结构比小孔隙率多孔硅基底上制备的具有更高的温度灵敏度, 但其机械稳定性也随之下降.     

疏水多孔硅制备及其对水中有机污染物的吸附

以硅酸钠为硅源,盐酸为催化剂,三甲基氯硅烷(TMCS)为表面改性剂,经溶胶-凝胶和表面改性过程制备出一种疏水性多孔硅材料.采用傅里叶变换红外(FTIR)光谱仪、接触角分析仪、氮气物理吸附仪和扫描电子显微镜(SEM)对其结构和性质进行表征.结果表明:所制备的多孔硅具有分等级孔道结构(中孔-大孔),比表面积为566m2·g-1,孔体积高达2.28cm3·g-1,多孔硅与水的接触角为156°,显示出超疏水特征.对甲苯、汽油、柴油和润滑油的吸附量均可高达自身质量的14倍,丰富的孔道使其在几分钟内即可达到饱和吸附.这种多孔硅在汽油/水混合体系中对汽油具有较高的选择性,同时具有良好的再生能力.经正己烷萃取再生后,多孔硅仍能基本保持初始吸附容量.此方法制备的多孔硅材料在吸附分离污水中的有机物和溢油处理方面具有很好的应用前景.     

新型甲醛多孔硅复合传感器的制备

构建了一种简便、快速检测甲醛的新型钯-多孔硅(Pd-PS)复合传感器.采用水热腐蚀法制备多孔硅,通过扫描电镜表征其表面微结构.对多孔硅腐蚀条件进行了优化,得出多孔硅的最佳制备条件.多孔硅经化学浸渍法在其表面掺杂金属钯,进而制成了钯-多孔硅复合传感器.当此传感器被置于含甲醛的混合气体中时,可高选择性结合甲醛气体分子,并产生电信号,其强度与甲醛浓度相关,通过万用表检测其电信号,进而分析其气敏性能.检测结果表明,此传感器对甲醛气体敏感,且表现出良好的选择性,对乙醇、氨气、甲醇和丙酮不敏感.此传感器对甲醛浓度的检测范围在0.1～ 6.0 mg/m3之间,检出限为0.1 mg/m3,检测时间为3 min.     

多孔硅薄膜上铜微晶的形成

以氯化铜水溶液作电解液,在发光多孔硅薄膜表面上电沉积铜.SEM观测和计算机图像处理结果表明:电沉积之后,在多孔硅薄膜上形成了一些或实心或中空的等边三角形铜微晶,沉积后的多孔硅薄膜的分形维数从2.608降为2.252,其表面由粗糙变为光滑.与物理方法制作相比,这是一种机械强度和导电性能都更加良好的多孔硅薄膜.     

多孔硅上银纳米粒薄膜的制备及其表面增强红外光谱

通过简便的化学沉积法在多孔硅上制备银纳米粒薄膜用于表面增强红外光谱检测。通过Ag⁺与多孔硅表面的SiHx发生氧化还原反应将银纳米粒子沉积在多孔硅表面。红外探针分子溶解于无水乙醇中进而被均匀分散在多孔硅表面,实验结果显示：对氨基苯硫酚、对氨基苯甲酸和对氟苯硫酚3个探针分子的红外峰分别最大增强了10、85和21倍。银纳米粒的大小和形状等物理特性、探针分子是否有与银表面进行强结合的基团和芳烃结构、以及表面选律等因素影响表面增强红外的吸收效应。     

介孔硅与大孔硅的结构、电学和气敏特性

采用双槽电化学腐蚀法在P型单晶硅表面制备两种多孔硅.根据它们的孔径将它们分为介孔硅和大孔硅.使用扫描电子显微镜(SEM)观察两种多孔硅表面和断面形貌,介孔硅和大孔硅的表面化学键用傅里叶变换红外(FTIR)光谱仪来研究,通过I-V特性测试表征两种多孔硅电学特性,随后在室温下测试其气敏特性.结果表明:介孔硅具有较高的气体灵敏度,大孔硅具有较好的气体响应恢复特性.介孔硅对NO2气体具有较好的选择性,大孔硅对NH3气体具有较好的选择性.     

多孔硅表面性质导致电致发光的进一步论证

用荧光分光光度法现场监测多孔硅在阳极偏压下于溶液中的电致发光行为 ,该电致发光行为主要取决于多孔硅本身的表面性质 .将电致发光实验后的多孔硅样品再次电解 ,并再次进行电致发光实验 ,发现其发光性能明显改善 ;实验表明 ,多孔硅在阳极偏压下的液相电致发光机制是由表面的Si_H键氧化向导带注入电子 ,并与阳极偏压注入的价带空穴进行复合而发光 ;此外 ,还发现了多孔硅于溶液中在阳极偏压下电压调制的可见光发射行为 ,并以量子限制效应对该现象进行了解释     

量子限制效应对多孔硅液相电致发光的影响

着重研究多孔硅在阴极偏压下过硫酸铵溶液中电压调制的电致发光现象 .随阴极偏压的增大 ,电致荧光峰位蓝移 ,荧光强度增大 ,同时发现定电压下 ,发生电致发光随时间的衰减伴随着光谱的红移现象 .通过红外光谱、AFM及电化学等手段对电致发光的电位调制机理及荧光衰减机制进行了研究 ,结果表明电致发光与光致发光具有相同的起源 ,电压选择激发不同粒径的多孔硅 ,而导致了发光峰值能量的电位选择性 .在电致发光过程中 ,强氧化剂向多孔硅注入空穴使其表面氧化导致小粒径的硅晶逐渐被剥落 ,使光谱高能部分首先衰减出现了随时间的电致发光红移现象 .这些结果支持量子限制效应在多孔硅液相电致发光中起着重要作用     

多孔硅于甲酸-甲酸钠溶液阳极偏压下的电致发光研究

用荧光分光光度法现场监测了多孔硅于甲酸-甲酸钠溶液阳极偏压下的电致发光行为。发现该体系的电致发光峰值随着阳极偏压增大而发生蓝移;发光峰能量值与阳极偏压呈良好的线性关系,其斜率与多孔硅在阴极偏压下电致发光的结果一致。扫描探针技术研究表明：多孔硅的表面形貌明显地影响其发光性质。提出了多孔硅在甲酸-甲酸钠溶液中阳极偏压下的电致发光与多孔硅表面的Si-H键的氧化作用有关的发光机理。发现了多孔硅于甲酸-甲酸钠溶液中在阳极偏压下电压调制的可见光发射行为,并用量子限制效应对该现象进行了解释。     

Bioconjugate functionalization of thermally carbonized porous silicon using a radical coupling reaction

The high stability of Salonen's thermally carbonized porous silicon (TCPSi) has attracted attention for environmental and biochemical sensing applications, where corrosion-induced zero point drift of porous silicon-based sensor elements has historically been a significant problem. Prepared by the high temperature reaction of porous silicon with acetylene gas, the stability of this silicon carbide-like material also poses a challenge--many sensor applications require a functionalized surface, and the low reactivity of TCPSi has limited the ability to chemically modify its surface. This work presents a simple reaction to modify the surface of TCPSi with an alkyl carboxylate. The method involves radical coupling of a dicarboxylic acid (sebacic acid) to the TCPSi surface using a benzoyl peroxide initiator. The grafted carboxylic acid species provides a route for bioconjugate chemical modification, demonstrated in this work by coupling propylamine to the surface carboxylic acid group through the intermediacy of pentafluorophenol and 1-ethyl-3-[3-dimethylaminopropyl]carbodiimide hydrochloride (EDC). The stability of the carbonized porous Si surface, both before and after chemical modification, is tested in phosphate buffered saline solution and found to be superior to either hydrosilylated (with undecylenic acid) or thermally oxidized porous Si surfaces.     

Self-assembled Alkylation of Atomically Flat Hydrogen-terminated Silicon (111) Surface By Using Highly Polarized Fluoroalkylsilane

Hydrogen-terminated silicon surface is of technological importance to semiconductor processes such as pre-gate^[1]. Re-contamination and re-oxidation on silicon surface become more stringent issues in order to meet the requirements in the process for producing reduced size IC chips. The modification of silicon surfaces by various strategies has attracted more attention in the past few years^[2-4]. The frequently used techniques to attach functional groups to silicon surfaces are via chemical^[2], photochemical^[3] and electrochemical reactions^[4]. Various ways to attach monlayers to silicon surfaces has been reported, including alkylation of silicon with alkenes, alkyenes, aldehydes, alcohols and Grigard reagents under photoactivated or catalytic reactions. Particularly, porous silicon prepared by chemical or electrochemical treatments has been extensively studied. Preparation of passivated layers on porous silicon surfaces has disadvantages that the silicon surfaces are damaged by reactive agents during the reaction or become porous for attachment of molecules. Recently, self-assembled monolayer of alcohols on porous silicon was reported at modest heating without the aid of catalyst or photoexcitation or potential^[5]. In the paper, we report a novel method to attach highly polarized fluoroalkylsilane on atomically flat Si(111) surface at room temperature and to form a self-assembled monolayer to prevent the silicon surface from re-contamination and re-oxidation.     

Fabrication of highly antireflective silicon surfaces with superhydrophobicity

Highly antireflective porous silicon surfaces with superhydrophobicity were obtained by means of chemical etching and fluoroalkylsilane self-assembly. The results show that wettability and reflectivity of these surfaces strongly depend on the etching method and the resultant surface morphology. All of the four resultant porous silicon surfaces by alkaline etching, acidic etching, thick Pt-assisted acidic etching, and thin Pt-assisted acidic etching can reduce reflectance, but the efficiency differs greatly. Except for the alkaline etching, the porous silicon surfaces produced by the other three etching methods can reach superhydrophobicity after fluoroalkylsilane modification. These differences are due to the different surface morphology and roughness. Moreover, the porous silicon surface produced by thin Pt-assisted acidic etching presents abundant holes and particles with diameters ranging from nanometers to submicrometers. This morphology enables the porous silicon surface to own a very low reflectance value that is averaged to be about 3% over the whole experimental photon wavelength spanning 300-800 nm.     

Effects of Ultraviolet Illumination and Pre-treatments on Porous Silicon Formation

Although porous silicon is readily formed by anodizing silicon wafers in HF-based solutions, its application in silicon-based optoelectronic devices is greatly limited due to its poor stability and low luminescence yield. It is well recognized that the nature of silicon wafers and the fabrication condition parameters significantly influence uniformity, stability and optical properties of porous silicon. In this work, the ultraviolet illumination and pre-treatments were investigated for porous silicon formation. The surface morphologies and optical properties of the samples were also studied.     

芘分子共价修饰的硅纳米线制备及其发光性能表征

将功能分子共价链接于硅纳米线表面,是发展硅纳米线性能,获得新的硅纳米线器件材料的重要手段.但是对硅纳米线表面的修饰却存在产生不可控制的表面氧化层的缺点,因此有必要发展一种温和的新方法.本文通过羟基(—OH)与硅纳米线表面Si—H键反应生成Si—O—C键,从而在硅纳米线表面引入功能分子.并通过芘醇分子在硅纳米线表面的固定化,证明了这一方法能够温和地实现对硅纳米线表面的共价键修饰.     

Preparation and characterization of pore-wall modification gradients generated on porous silicon photonic crystals using diazonium salts

One-dimensional photonic crystals (rugate filters) constructed from porous silicon were modified by the chemical hydrosilylation of terminal alkenes (decyl, 10-carboxydecyl, and 10-hydroxydecyl) in the presence of a concentration gradient of diazonium salt initiators. The concentration gradient was generated by vertically orienting the Si wafer containing the porous Si layer in an alkene solution and then introducing the diazonium salt at the bottom edge of the wafer. Slow diffusion of the salt led to a varying density of grafted alkene across the surface of the porous layer. The modified surfaces were end-capped with methyl groups by electrochemical grafting to impart improved stability and greater hydrophobicity. The surface modified with 10-carboxydecyl species was ionized by deprotonation of the carboxy groups to increase the hydrophilicity of this porous silicon surface. The pore-wall modification gradients were characterized using attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) and scanning electron microscopy (SEM) with energy-dispersive spectroscopy (EDS). The more hydrophilic portion of the gradient changes color when water infiltrates the porous nanostructure because of a shift in the stop band of the photonic crystal. The more hydrophobic portion of the gradient excludes water, although mixtures of water and ethanol will infiltrate this region, depending on the concentration of ethanol in the mixture. A simple visual sensor for small quantities of ethanol in water, capable of detecting ethanol concentrations of between 0 and 8% with a resolution of 1% is demonstrated.     

Iminodiacetic acid derivatized porous silicon as a matrix support for sample pretreatment and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry analysis

Iminodiacetic acid (IDA)-1,2-epoxy-9-decene has been synthesized and covalently linked to the surface of porous silicon wafer through a photochemical reaction. The negatively charged carboxylic acid groups on the porous silicon wafer are capable of binding oppositely charged species from sample solutions through electrostatic interactions. This allows the removal of contaminants prior to matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) by simply washing the porous silicon surface. The carboxylic acid end groups on porous silicon can be used to selectively bind and concentrate target species in sample solutions. Furthermore, Fe(3+)-IDA-derivatized porous silicon was prepared to specifically and effectively concentrate phosphopeptides from the tryptic digests of phosphoproteins, followed by MALDI-MS analysis.     

PEGylation of porous silicon using click chemistry

Porous silicon has received considerable interest in recent years in a range of biomedical applications, with its performance determined by surface chemistry. In this work, we investigate the PEGylation of porous silicon wafers using click chemistry. The porous silicon wafer surface chemistry was monitored at each stage of the reaction via photoacoustic Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy, whereas sessile drop contact angle and model protein adsorption measurements were used to characterize the final PEGylated surface. This work highlights the simplicity of click-chemistry-based functionalization in tailoring the porous silicon surface chemistry and controlling protein-porous silicon interactions.     

Amide-Functionalized Porous Carbonaceous Anode Materials for Lithium-Ion Batteries

Porous carbonaceous anode materials have received considerable attention as an alternative anode material, however, there is a critical bottleneck as it suffers from a large irreversible specific capacity loss over several initial cycles owing to undesired surface reactions. In order to suppress undesired surface reactions of porous carbonaceous anode material, here, we suggest a simple and convenient two-step surface modification approach that allows the embedding of an amide functional group on the surface of a porous carbonaceous anode, which effectively improves the surface stability. In this approach, the porous carbonaceous anode material is firstly activated by means of strong acid treatment comprising a combination of H₂SO₄ and HNO₃, and it is subjected to further modification by means of an amide coupling reaction. Our additional systematic analyses confirm that the acid functional group effectively transforms into the amide functional group. The resulting amide-functionalized porous carbon exhibits an improved electrochemical performance: the initial discharge specific capacity is greatly reduced to less than 2,620 mA h g⁻¹ and charge specific capacity is well still remained, indicating stabling cycling performance of the cell.