【作者】 夏炜炜；

【导师】 沙健； 王业伍；

【作者基本信息】 浙江大学 ， 凝聚态物理， 2013， 博士

【摘要】 硅纳米线阵列具有独特的微结构及量子限域效应,因而呈现出优异的光学及电学性能,近来被广泛应用于太阳能电池、生物传感器、场发射器件及锂离子电池中。通常采用以下方法制备硅纳米线：激光刻蚀、化学气相沉积法、热蒸发、分子束外延等。但这些制备方法工艺相对复杂、制备成本高、很难在硅基底实现硅纳米线阵列的可控生长。近年来,Peng等人报道的金属辅助催化化学腐蚀法由于可以克服上述缺点而备受关注。在金属催化化学腐蚀法中可以通过控制腐蚀液组分及腐蚀时间实现对硅纳米线的直径、长度、晶向及孔隙率等参数的调控。本论文采用金属催化化学腐蚀的方法实现硅纳米线阵列腐蚀方向的控制,并提出相关理论模型,系统研究腐蚀过程中硅纳米线表面形态,最后在腐蚀得到的硅纳米线阵列顶端自组装形成银纳米颗粒,研究该基底的拉曼增强效应等,主要研究工作如下：(1)采用金属辅助催化化学腐蚀法制备硅纳米线阵列。硅纳米线表面自然生成一层无定型的硅氧化物,该壳层无定型SiOx与芯部单晶硅纳米线的晶体结构不完全一致,导致在Si/SiOx界面处产生应力。通过研究发现：硅纳米线表面的Si/SiOx界面处的缺陷类型主要为Pb0型,室温下PL谱中蓝峰407nm(3ev)和红峰656nm(1.9ev)处光致发光峰主要来自于Si/SiOx界面中氧缺陷及氧空位缺陷。通过降低腐蚀速率及硅纳米线表面改性等方式可以有效减小Si/SiOx界面处的缺陷浓度。(2)硅纳米线阵列腐蚀方向的控制及相关理论模型。采用三种常见N型Si(111)、Si(110)、Si(100)作为腐蚀基底,在硅基片上镀上不同长径比的银催化剂颗粒,再利用金属辅助催化法制备硅纳米线阵列。实验结果表明：Si(111)、Si(110)呈现各向异性的腐蚀行为,而Si(100)硅基底的腐蚀方向一直沿着垂直于硅片的方向腐蚀。在实验基础上,我们提出了硅纳米线阵列腐蚀模型。我们认为：金属辅助催化化学腐蚀中同时存在径向与侧向腐蚀行为,当催化剂颗粒长径比较大时侧向腐蚀尤为明显。因此,我们通过调节银催化剂颗粒的长径比可以实现在Si基底上制备与基底保持不同方向的硅纳米线阵列,甚至可以实现在硅基底上制备硅纳米多重“折线”。(3)硅基表面拉曼增强基底。通过调节银纳米颗粒与HAuCl4浓度实现在银颗粒上自组装金纳米结构,并用此基底材料实现了拉曼增强。实验结果表明：在光滑的银纳米颗粒上组装一定数目的金纳米颗粒的基底具有最强的拉曼增强效应,而银纳米颗粒上包裹金纳米层的核壳结构的基底显示最弱的拉曼增强效应。通过本文的研究,我们初步揭示了金属催化化学腐蚀法制备硅线的各向异性腐蚀机理及硅线表面态结构,并制备了基于硅线阵列的拉曼增强基底。在今后的研究工作中,我们将进一步探究硅线表面态结构对其物理性能的影响并拓展硅线的应用领域。更多还原

【Abstract】 Due to the microstructure and quantum confinement, Silicon nanowire arrays have received intensive interests in recent years for their unique electrical and optical properties and potential for device application as solar cell, biosensors, field emission device and lithium-ion battery. Until now, there have been various methods for synthesizing silicon nanowires (SiNWs), such as laser ablation, chemical vapor deposition, thermal evaporation, molecular beam epitaxy. However, these growth process complicated in fabrication and costly in preparation procedures. It is difficult to realize controlled fabrication of silicon nanowire arrays with controllable crystallographic orientation to the substrate surface. Recently, Peng et al. have successfully prepared large-area oriented SiNWs array on silicon utilizing metal-assisted electroless etching method(MacEtch). MacEtch method enables control of various parameters (e.g., diameter, length, crystallographic orientation, and porosity) of SiNWs by adjusting the etchant concentration and etching time. Lager-area uniform SiNW array were prepared by MacEtch. We put forward the related theoretical model to explain the change of etching direction in MacEtch process. The surface state of SiNWs was also discussed in detail. SiNWs arrays coated with Ag nanoparticles act as efficient surface-enhanced Raman scattering (SERS) substrate, which have exhibited distinct surface-enhanced Raman scattering. The main contents are as follows:(1) SiNWs arrays have been fabricated by a metal-assisted chemical etching method. A layer of amorphous shell of SiOx was naturally generated on the surfaces of SiNWs arrays. The shell of amorphous SiOx and the core of the SiNWs show lattice mismatch, which resulted in the tensile stress at the Si/SiOx interface of SiNWs. The Si dangling bond interface center Pbo is the prominent defect at Si/SiOx interface. The surface modification with copper nanoparticles can decrease the concentration of Pbo centers on the surfaces of SiNWs. Photoluminescence (PL) spectra showed that bule peak at407nm (3ev) and red peak at656nm (1.9ev), which were mainly come from oxygen vacancies and oxygen deficiency at Si/SiOx interface.(2) Three types of Si wafers, which were n-type (100), n-type (110) Si, n-type (111) Si, have been used as starting wafers. Ag nanoparticles with different Length/Radius ratio was deposited on silicon wafer surfaces. Our experiments indicated that the Length/Radius ratio of Ag catalysts show different etching behavior on three types of Si substrates. The etching directions of (110) and (111) Si substrates are found to be influenced by the Length/Radius ratio of Ag catalysts, whereases the metal-assisted etching direction of (100)Si substrate was found to be vertical to the surface of (100)Si substrate. On the basis of morphology-dependent etching, we concluded that the radial and lateral corrosion behavior are coexist during the process of metal-assisted chemical etching, especially as Ag catalysts with huge Length/Radius ratio. The direction of the SiNWs arrays relative to the Si substrate can been controlled by adjusting the Length/Radius ratio of Ag catalysts, and with this way we can also achieved multiple zigzag silicon nanowires.(3) A simple and cost-effective chemical method was introduced to assemble Au nanoparticles on smooth Ag spheres for realizing SERS enhancement by the replacement reaction between chloroauric acid and Ag spheres. In addition, the Ag-Au core-shell spheres were fabricated when a certain amount of chloroauric acid was used in the reaction solution. Ag particles decorated with small Au nanoparticles demonstrated the strongest SERS enhancement, while Ag-Au core-shell spheres showed the weakest enhancement.In our study, we revealed the mechanism of anisotropic etching behavior in MacEtch process and made a detailed study about surface states of silicon nanowires. SERS substrates were prepared with SiNW arrays. In future work, we would expand the application fields of SiNW arrays and make the detailed study of the effect of surface states on the physical properties of SiNW arrays.更多还原