【作者】 陈辉辉；

【导师】 胡俊青；

【作者基本信息】 东华大学 ， 材料物理与化学， 2011， 硕士

【摘要】 多孔硅由于新奇的发光性能及其在光电器件方面的应用,引起了纳米科技界的极大兴趣,其主要是通过化学刻蚀的制备方法获得。随着半导体纳米科技的发展,单晶多孔硅纳米线已经通过化学刻蚀制备出来,并且具有优良的光电性能,可用于光催化基底及活性纳米光电器械。但是,研究表明单晶硅片的掺杂浓度决定了硅纳米线的表面粗糙度及其孔结构,只有高掺杂的硅片(N型硅片电阻：0.008-0.02Ω·cm；P型硅片电阻率：<0.005Ω·cm)经过化学刻蚀后才能获得多孔结构。目前,以低掺杂单晶硅片为原材料通过化学刻蚀方法获得多孔硅纳米线仍然是一个挑战。本文采用化学刻蚀方法制备了低掺杂多孔硅纳米线、硅纳米线和多孔硅,并对样品进行形貌和结构表征,测试纳米材料相应的电学性能、光学性能和超疏水性能,探讨了低掺杂多孔硅纳米线可能的生长机理和分析其电学性能的提高。本论文的主要研究结果如下：(1)采用化学刻蚀方法,以低掺杂单晶硅片N-(100)作为硅源,通过调节刻蚀液组成、刻蚀温度及刻蚀时间,可使硅片表面获得不同微观结构的多孔硅纳米线,硅纳米线的表面有很多纳米孔。利用扫描电镜(SEM)、透射电镜(TEM)、高分辨透射电镜(HRTEM)和选区电子衍射(SAED)等测试手段进行相应的分析和表征,表明得到的低掺杂多孔硅纳米线是单晶结构,且表面没有被氧化,并进一步对产物的形成机理进行了阐述。同时,考察了H2O2对硅纳米线表面成孔的均匀性和密度的影响,当H2O2浓度愈大,硅纳米线的表面愈粗糙,局部区域有可能被横向贯穿。(2)考察了低掺杂多孔硅纳米线的电学性能,利用TEM-STM测量样品台,在透射电子显微镜内,通过移动,将低掺杂多孔硅纳米线连接到金悬臂和铂悬臂的两端,构成肖特基势连接,在硅线的两端施加-10V到10V的电压,获得相应的I-V数据,对比分析了低掺杂多孔硅纳米线和无孔硅纳米线的电学性能。实验结果表明：无孔硅纳米线的电流变化范围仅从-1.5nA到1.5nA；多孔硅纳米线的电流变化值从-4.5nA到4.5nA。在相同的加压条件下,多孔硅纳米线的电流变化范围大约是无孔硅纳米线的3倍,多孔硅纳米线的电学性能得到改善,导电能力增强,拓展了硅在纳米光电器件方面的应用。(3)采用化学刻蚀方法,以低掺杂单晶硅片P-(100)作为硅源,通过调节刻蚀液的组成及刻蚀温度,在硅片的表面获得不同形貌的硅纳米材料：多孔硅和硅纳米线阵列。在室温的条件下可获得多孔硅；在加热的条件下,能够获得大面积垂直于硅衬底的硅纳米线阵列,采用SEM分析纳米银的形貌以及硅纳米线阵列的微观结构,考察了硝酸银的浓度和刻蚀时间对硅纳米线形貌的影响。该法获得的硅纳米线反应活性高,可以作为制备硅纳米颗粒的硅源,在HF和HNO3的刻蚀酸液中,可获得硅纳米颗粒。(4)考察了一维硅纳米线的光致发光性质,在470nm的光激发条件下,分散在乙醇溶液中的硅纳米线在548nm处发出很强的绿光,量子限制效应引起了光致发光；具有一定粗糙度的纳米线阵列结构,通过化学气相沉积法,240℃条件下,在硅片的表面沉积一层二甲基硅油(PDMS),化学改性后的硅纳米线阵列结构接触角达到155°,转变为超疏水性；在单晶硅片表面沉积同样一层二甲基硅油,接触角达到100°。实验结果表明：不同的微观结构形貌直接影响着固体表面的润湿性能。更多还原

【Abstract】 Porous Si has been extensively investigated for its lighting emitting properties and potential applications in optoelectronics. Usually, porous Si is synthesized by applying a voltage bias to a Si substrate immersed in hydrofluoric (HF)-containing aqueous or organic solutions or by chemical etching. With advancement of the semiconductor nanotechnology, based on the above synthetic method for producing porous Si, a metal-assisted deposition and chemical sacrificial etching process has been exploited to fabricate single-crystalline porous Si arrays, which show excellent optical properties and may be useful as photocatalytic substrates or active nanoscale optoelectronic devices for energy harvesting, conversion, and biosensing. It is found that the doping level of the Si wafers is a key factor determining the surface roughness or porous structures of the Si nanowires, and only the Si wafers with highly or heavily doped p-typed wafers (resistivity:< 0.005Ω·cm) and n- typed wafers (resistivity:0.008-0.02Ω·cm) can be etched to produce porosities inside them. So, the fabrication of the porous Si nanowires from lightly doped Si wafers by the above described chemical etching method has not yet been accomplished and remains a challenge. Porous silicon, silicon nanowires and lightly doped porous silicon nanowires with various morphologies were successfully fabricated using a chemical etching method. The morphologies and crystal structure of the as-synthesized products were characterized in detail. Photoluminescence properties, electrical measurements and superhydrophobic properties were also carefully carried out. The main results are summarized as follows:(1) Lightly doped porous silicon nanowires with different microstructure morphologies have been fabricated on silicon wafer via the chemical etching method, through controlling the composition of etching solution, etching temperature and etching time. The morphology and crystal structure of the as-synthesized samples were characterized by SEM, TEM, HRTEM, SAED in detail. Si lattice fringes are continuous between the surface and the interior of the as-fabricated lightly doped porous Si nanowire, indicating that the surface of this Si nanowire is not native oxide and Si lattice integrity is not destroyed at the surface of the nanowire during the etching process. In addition, the formation mechanism of the product was seriously studied. An addition of H2O2 into the etchant played a significant role in the density and homogeneity of the lightly porous Si nanowires. An increase of the concentration of H2O2 will enhance the etching of the Si nanowire. The etching to this products partly penetrated the nanowires in the lateral direction.(2) The electrical measurements of lightly doped silicon nanowires were carried out using a new STM-TEM holder. The relative X, Y, and Z positions of the gold cantilever and a platinum cantilever with a mounted si nanowire were adjusted through the nanoscale precision piezodriven manipulation of the silicon nanowires inside the TEM, so as to build a silicon nanowire bridge between the gold and platinum cantilever. Silicon nanowire with a lower work function than those of platinum and gold makes a schottky contact between them. Both non-porous silicon nanowires and porous nanowires with the voltage range from -10 to 10V for 4000 milliseconds and I-V data were obtained. The current value of porous silicon nanowires varies from-4.5 to 4.5nA, while the current value of nonporous silicon nanowires varies from-1.0 to 1.5nA. The range of the current variation of porous silicon nanowires is-3 times as large as those of non-porous silicon nanowires at the same applied voltage. It is stated that the porous silicon nanowires possess improved electrical property and significantly increase conductance, compared with non-porous silicon nanowires. The porous silicon nanowires may expand opportunities for nanoscale optoelectronic devices, energy harvesting, conversion and sensors.(3) Porous silicon and silicon nanowires arrays with different morphologies have been prepared on the surface of the Si wafer via a chemical etching, through controlling the etching solution and etching temperature. Porous silicon was obtained at room temperature; straight and vertical Silicon nanowire arrays were obtained when heating. The morphology of nano-scale silver and silicon nanowire arrays were revealed in detail by SEM imaging. The effects of silver nitrate concentration and etching time on the morphologies of silicon nanowires were also studied. The as-synthesized silicon nanowires can be used as original silicon in order to prepare silicon nano-particles owing to its high activity.(4) The photoluminescence properties of the resulting silicon nanowires were seriously investigated. Using the excitation of 470nm laser beam from a diode laser, the silicon nanowires dispersed in ethanol solution apparently emitted a strong green emission band centered at 560nm. The PL emission can be attributed to the quantum confinement. Detailed experiments have been carried out to investigate the wetting behavior of silicon surfaces. Both the starting silicon wafer and the silicon nanowires substrates were coated with a polydimethysiloxane (PDMS) film via a vapor deposition technique, heating at 240℃. The modified silicon wafer was hydrophobic with a contact angle of 100°. However, the modified silicon nanowires combined with a contact angle of 155°became superhydrophobic. The contrast results suggest that different microstructure morphologies made a great impact on the wetting properties of solid surfaces.更多还原