表面金属化对多孔硅光特性的影响(英文)

在室温下使用过滤阴极真空电弧系统在多孔硅表面沉积大约10纳米左右厚度的铜、铝和钛薄膜,并且在真空下800度退火10分钟.多孔硅层是通过电化学腐蚀硅制得.X射线光电子谱、荧光谱,光吸收谱和X射线衍射谱的研究表明退火后,沉积铜和钛的样品出现明显的光吸收红移和硅2p电子能级移动.这是由于在多孔硅表面形成铜和钛的硅化物而引起的晶体场和电子传输变化所造成的.     

硅的阳极氧化研究——多孔硅的制备及其发光机制

评介了阳极氧化方法制备多孔硅（Ｐｏｒｏｕｓ Ｓｉｌｉｃｏｎ）的工艺，讨论了多孔硅的形貌及发光机制。     

多孔硅的制备方法和成核机制

目前多孔硅研究已经成为众多研究者关注的热点之一，它在微电子机械、激光器、探测器、传感器、燃料电池，太阳能电池等许多领域具有巨大的应用替力。首先陈述了常见的多孔硅制备方法，其中超声声空化物理化学综合法将光致发光峰半峰宽压缩至3．8mm的报告振奋人心。随后引出比较流行的3种多孔硅成核机制模型，量子限制模型得到大多数的认可。最后，分析了最近国内外多孔硅的研究和应用情况，并指出尺寸厚度精确可控、机械硬度高、孔隙分布均匀、发光稳定性高的多孔硅依然是制备工艺追求的目标。     

钴钝化多孔硅的制备及其场发射特性研究

采用化学染色腐蚀法在Co(NO3)2 和HF酸组成的腐蚀液中制备了钴钝化多孔硅,其表面形貌由垂直于表面分布的尺度为0.5~1.5μm 的硅尖组成,部分硅尖顶端还有0.1~0.5μm的圆形孔洞,硅尖的面密度约为1.0×108 个/cm2,多孔硅层厚度约为2μm。XPS分析结果表明,钴原子仅存在于多孔硅表面非常薄的一层内。其场发射具有较好的可靠性和可重复性,开启场强一般为2.3V/μm 左右,场强为5.4V/μm时,亮点均匀而且密集,发射电流密度达到30μA/cm2 左右。     

热氧化多孔硅制备及其干涉特性研究

采用电化学阳极氧化法制备彩色薄层多孔硅,经高温热氧化处理后形成稳定的热氧化多孔硅.研究电化学制备条件对热氧化多孔硅的干涉效应和光学厚度的影响,分析热氧化处理前后多孔硅的稳定性.结果表明,在可见光波长范围内,所制备的热氧化多孔硅反射光谱出现一定规律性的干涉条纹,表现出明显的反射干涉现象;随阳极氧化时间、电流密度和HF浓度增大,热氧化多孔硅光学厚度呈增大趋势,当阳极氧化时间为30s、电流密度为520mA/cm2、v(HF):v(C2H5OH)为2:1～5:2时,制备的热氧化多孔硅干涉条纹均匀且光学厚度较大;热氧化处理后,多孔硅结构中的Si-Hx键被Si-O键所取代,其反射干涉特性非常稳定.     

多孔硅基热敏薄膜的制备与性能

对MEMS用具有绝热性能的多孔硅基底上沉积的热敏感薄膜进行了研究．首先用电化学方法制备多孔硅,分别在多孔硅基底和硅基底上通过溅射镀膜方法沉积氧化钒、Cu、Au热敏薄膜,测试多孔硅基底和硅基底上的氧化钒及金属薄膜电阻的热敏特性．结果表明,在多孔硅基底表面沉积的热敏薄膜具有与硅基表面热敏薄膜同样的热敏特性且表现出更高的灵敏度;此外,对沉积在不同制备条件得到的多孔硅上的氧化钒薄膜电阻热敏特性进行比较,发现随着孔隙率和厚度的增加,多孔硅的绝热性能提高,其上沉积的氧化钒薄膜电阻热敏特性增强．     

发光多孔硅的制备及其电化学成膜机制研究

研究了阳极氧化法制备多孔硅的工艺，表面形貌及电化学成膜机制。     

多孔硅的场发射特性研究

多孔硅是一种很有前途的场发射材料,研究多孔硅的场发射有着实际的意义.模仿制备了具有弹道电子发射的特殊结构的多孔硅,测试了其场发射性能,比较了腐蚀电流逐渐变小所制备的多孔硅与腐蚀电流不变所制备的多孔硅的场发射性能,发现前者是提高场发射性能的一种有效方法.     

多孔硅制备及在太阳能电池中的应用研究进展

多孔硅是通过对单晶硅片进行电化学腐蚀或适当的化学腐蚀而形成的一种纳米结构半导体材料。多孔硅纳米材料因其巨大的表面积、可调谐的光学性质和良好的相容性,被广泛应用于电子器件、生物传感、化学传感、药物传递、生物芯片等诸多领域。当前研究的挑战主要在于开发更简单高效的多孔硅纳米材料合成方法以及提高其在实际应用中的表现。综述了多孔硅纳米材料的制备方法及其光致发光在太阳能电池领域中的应用。     

Functionalization control of porous silicon optical structures using reflectance spectra modeling for biosensing applications

Modeling and experimental reflectance spectra of porous silicon single layers at different steps of functionalization and protein grafting process are adjusted in order to determine the volume fraction of the biomolecules attached to the internal pore surface. This method is applied in order to control the efficiency of the chemical functionalization process of porous silicon single layers. Using results from single porous silicon layer study, theoretical microcavity is simulated at each step of the functionalization process. The calculated reflectance spectrum is in good agreement to the experimental one. Therefore the single layers study can be applied to multilayer structures and can be adapted for other optical structures such as waveguides, interferometers for biosensing applications.     

The dependence of hydrofluoric acid concentration during anodization on photoluminescence of porous silicon

The mixture of hydrofluoric (HF) acid and ethanol is used as an electrolyte during anodization of silicon. We investigated the effect of the ratio of HF acid to ethanol on photoluminescence. It is concluded that porous silicon anodized with the electrolyte containing 35 or 40% HF acid provides strong photoluminescence. The fact implies the existence of a chemical reaction including ethanol during anodization other than electrochemical reaction.     

Optical sensing of flammable substances using porous silicon microcavities

A porous silicon multilayer, constituted by a Fabry–Pèrot cavity between two distributed Bragg reflectors, is exposed to vapor of several organic species. Different resonant peak shifts in the reflectivity spectra, ascribed to capillary condensation of the vapor in the silicon pores, have been observed. Starting from experimental data, the layer liquid volume fractions condensed in the sensing stack have been numerically estimated. Values ranging between 0.27 (for ethanol) and 0.33 (for iso-propanol) have been found. Time-resolved measurements show that the solvent identification occurs in less then 10 s.     

The dependence of hydrofluoric acid concentration during anodization on photoluminescence of porous silicon

The mixture of hydrofluoric (HF) acid and ethanol is used as an electrolyte during anodization of silicon. We investigated the effect of the ratio of HF acid to ethanol on photoluminescence. It is concluded that porous silicon anodized with the electrolyte containing 35 or 40% HF acid provides strong photoluminescence. The fact implies the existence of a chemical reaction including ethanol during anodization other than electrochemical reaction.     

Simple optical method to determine the porosity of porous silicon films

A simple optical method to estimate the porosity of microporous silicon films is described. The technique relies upon determination of film refractive index via measurement of the incident (Brewster) angle corresponding to a minimum in the intensity of light reflected from the air-film interface. The sample porosity is then obtained using an effective medium model. Porosities obtained using this method show general agreement with those obtained using gravimetric means and, where comparison was possible, excellent agreement with those of similarly-prepared films found by low angle X-ray reflectivity. These results confirm the general applicability of this technique to the determination of microporous silicon film porosity.     

Light-emitting porous silicon

Although porous silicon has been known for more than 35 years, only in 1990 was it recognized that porous silicon shows an increased bandgap and efficient room-temperature photoluminescence in the visible. This paper will give an overview of porous silicon research, with special emphasis on the formation mechanism of microporous silicon in terms of a depletion of holes in the porous region due to quantum confinement and the understanding of the origin of the visible luminescence. The status of research on electroluminescent and other devices based on porous silicon will be discussed, as well as results for other luminescent forms of nanocrystalline silicon.     

Rationally designed porous silicon as platform for optical biosensors

Optical porous silicon multilayer structures are able to work as sensitive chemical sensors or biosensors based in their optical response. An algorithm to simulate the optical response of these multilayers was developed, considering the optical properties of the individual layers. The algorithm allows designing and customizing the porous silicon structures according to a given application. The results obtained by the simulation were experimentally verified; for this purpose different photonic structures were prepared, such as Bragg reflectors and microcavities. Some of these structures have been derivatized by the introduction of aminosilane groups on the porous silicon surface. The algorithm also permits to simulate the effects produced by a non uniform derivatization of the multilayer.     

Crystallite-size-dependent characteristics of porous silicon

Porous silicon prepared with anodic currents of 5 to 30 mA/cm² are characterized for structural and electronic properties of surface using photoluminescence, grazing angle X-ray diffraction, photoconductivity, thermally stimulated exo electron emission and work function measurements. The observed results indicate that with increasing porosity the crystallite size decreases and the amount of silicon hydride and oxide-type species increases, exhibiting a tendency similar to that of hydrogenated amorphous silicon and hydrogenated microcrystalline silicon. Free-standing powder of porous silicon, characterized by bright photoluminescence at 730 nm, showed crystallites of nanometre dimensions under the transmission electron microscope.     

Some new results in porous silicon

Efforts have been made to see the effect of some standard microelectronic processing steps on porous silicon. Our diffusion experiments for making p-n junctions confirm that this material can withstand high temperatures of the order of 800°C to 1000°C. A new technique for photolithography has been suggested to obtain porous silicon in selected areas. Etch stop method to control the thickness of the porous layer and an organic protective layer for porous silicon have also been suggested. Models proposed by other workers to explain luminescence in porous silicon are not sufficient to explain many experimental observations. A hybrid model is suggested.     

Morphology of porous silicon structures formed by anodization of heavily and lightly doped silicon

By computer simulation the growing process of porous silicon under p⁻-Si and p⁺-Si anodization in HF solution is studied. The model of electrochemical etching of p⁺-Si includes the relief selective mechanism, which allows one to establish the relationship between anodization conditions (current density, HF concentration, temperature and doping level) and the topological characteristics of porous silicon (PS). The simulation of p⁻-Si dissolution is based on the model of diffusion limited aggregation (DLA), taking into account the thermal generation of holes and the quantum confinement effect. The various morphology of simulated PS structures exhibits a close resemblance to that of experimental ones formed in p⁺-Si and p⁻-Si wafers. For simulated p⁻-Si-based PS layers the porosity profiles and fractal dimension are calculated. It is shown that PS in p⁻-Si is multifractal with fractal dimension varying monotonously from 0.1 to 3 with size increase.