交替刻蚀制备有序锯齿形硅纳米线阵列及其光学性能研究

采用金属催化化学刻蚀法(MCCE),以金属Ag为催化剂,在HF与H_2O_2体系中通过交替刻蚀在P(111)硅衬底上制备出锯齿形硅纳米线阵列。利用扫描电子显微镜对硅纳米线的形貌进行了表征,研究了HF浓度与H_2O_2浓度对纳米线刻蚀方向的调控作用。选取不同的HF与H_2O_2浓度配比,分别对硅基底各向同性刻蚀与各向异性刻蚀进行调控,使得刻蚀方向对溶液浓度的变化能够快速响应。在溶液Ⅰ([HF]=2.3mol/L,[H_2O_2]=0.4mol/L)与溶液Ⅱ([HF]=9.2mol/L,[H_2O_2]=0.04mol/L)中交替刻蚀,制备出刻蚀方向高度可控的大规模锯齿形硅纳米线。利用紫外-可见分光光度计对锯齿形硅纳米线的减反射性能进行研究,结果表明,其表现出优异的减反特性,最低反射率为5.9%。纳米线形貌的高度可控性使其在微电子器件领域也具有巨大的应用前景。     

金属辅助化学刻蚀法制备硅纳米线的研究进展

硅纳米线(Si NWs)由于具有独特的一维结构、热电导率、光电性质、电化学性能等特点,被广泛应用于热电与传感器件、光电子元器件、太阳能电池、锂离子电池等领域。金属辅助化学刻蚀法(MACE)是制备Si NWs的常用方法之一,具有操作简便、设备简单、成本低廉和高效等优点,可大规模商业化应用,因而近年来被广泛研究。金属辅助化学刻蚀制备硅纳米线的过程可以分为两步:首先在洁净的硅衬底表面沉积一层金属(Ag、Au、Pt等)纳米颗粒,以催化、氧化它附近的硅原子;然后利用HF溶解氧化层,从而对硅晶片进行刻蚀,形成纳米线阵列。然而,这种简单高效的制备硅纳米线的方法存在一些难以控制的缺点:(1)金属纳米颗粒聚集、相连后造成Si NWs之间的缝隙比较大,从而导致Si NWs密度较低;(2)由于金属纳米颗粒沉积的随机性,在硅晶片表面分布不均匀,不仅导致刻蚀出的纳米线直径范围(50～200 nm)较宽,而且使制得的纳米线阵列排列无序且间距不易调控;(3)当刻蚀出的硅纳米线太长时,范德华力等作用会造成纳米线顶端出现严重的团簇现象。针对常规法存在的一些问题以及不同的器件对硅纳米线的形貌、类型和直径等的要求,近年来的研究主要集中在如何减少纳米线顶端团簇、调控纳米表面粗糙度和直径、低成本制备有序硅纳米线等方面。目前一些改进常规金属辅助化学刻蚀的方法取得了进展,比如:(1)用酸溶液或UV/Ozone对硅晶片预处理,在表面形成氧化层,可以使纳米线的均匀性得到改善并增大其密度(从18%提高到38%);(2)使用物理气相沉积法在硅晶片表面沉积一层金属纳米薄膜,然后再刻蚀,这种方法能够减少纳米线顶端团簇和有效调控纳米线直径;(3)利用模板法(聚苯乙烯小球模板、氧化铝模板、二氧化硅模板和光刻胶模板等)可以制备出有序的硅纳米线阵列。本课题组用离子束刻蚀的方法制备了直径范围可以控制在30～90 nm的聚苯乙烯小球模板,为小尺寸有序硅纳米线的制备打下了坚实的基础。本文简要介绍了常规MACE的原理和制备流程,总结了硅晶片的类型、刻蚀溶液的浓度、温度和刻蚀时间等因素对Si NWs形貌、尺度、表面粗糙度、刻蚀方向以及刻蚀速率的影响,用相关的机制解释了H2O2过量时刻蚀路径偏离垂直方向的机理以及刻蚀速率随溶液浓度变化的原因,重点综述了氧化层预处理、物理法沉积贵金属纳米薄膜、退火处理和模板法等改进方法在减少纳米线顶部团簇、改善均匀性、制备有序且直径和间距可控纳米线中的研究进展。     

硅基径向纳米线阵列的制备及其机理研究

采用金属辅助化学刻蚀(MACE)的方法在硅衬底上制备出尺寸可控、表面光滑的硅纳米线阵列.利用扫描电子显微镜等检测仪器对所制备的硅纳米线样品进行了表征,研究了附银时间和双氧水浓度等工艺参数对硅纳米线生长的影响.结果表明,在附银时间为60 s、双氧水浓度为1.0 mol/L条件下,能够得到较为均匀、规则的硅纳米线阵列.此外,探讨了银辅助刻蚀硅纳米线的形成机理.     

无电金属沉积法硅纳米线阵列的制备研究

采用无电金属沉积法在硅衬底上制备出了大面积规整的硅纳米线阵列,并对其形貌控制的影响因素和形成机理进行了研究。用扫描电子显微镜(SEM)、X射线衍射仪(XRD)对硅纳米线阵列和相应银枝晶的形貌和结构进行了表征。结果表明,硅纳米线阵列的形貌受水热体系中溶液配比、温度和时间的影响,在温度为50℃、HF和AgNO3浓度分别为4.6和0.02mol/L的条件下,容易得到大面积排列规整的硅纳米线阵列,并且硅纳米线的长度为30～50μm,直径为200nm左右。无电金属沉积法为硅纳米线及其阵列的制备提供了一种设备简单、条件温和的制备方法。     

电催化金属辅助化学刻蚀法制备硅纳米线/多孔硅复合结构

量子限制效应使硅纳米线具有良好的场致发射特性,结合多孔硅的准弹道电子漂移模型可提高场发射器件的性能。传统的金属辅助化学刻蚀法制备硅纳米线的效率较低,本研究在传统方法的基础上引入恒流源,提出电催化金属辅助化学刻蚀法,高效制备了硅纳米线/多孔硅复合结构。在外加30mA恒定电流的条件下,硅纳米线的平均制备速率可达308nm/min,较传统方法提升了173%。研究了AgNO₃浓度、刻蚀时间和刻蚀电流对复合结构形貌的影响规律;测试了采用电催化金属辅助化学刻蚀法制备样品的场发射特性。结果显示样品的阈值场强为10.83 V/μm,当场强为14.16 V/μm时,电流密度为64μA/cm²。     

HF酸刻蚀ZSM-5/PDMS膜渗透汽化透醇性能研究

采用HF酸对3种MFI型沸石(ZSM-5,silicalite-1)进行刻蚀,通过SEM和TEM对刻蚀前后沸石的表面和本体形貌进行了表征,发现酸刻蚀造成沸石表面出现微米级孔洞,但本体仍保留了规则的孔道结构。将刻蚀后的ZSM-5填充至聚二甲基硅氧烷(PDMS)中制备了复合膜,用于乙醇/水混合物的分离,研究了沸石硅铝比、HF酸浓度、操作温度和料液浓度对复合膜渗透汽化分离性能的影响。研究发现HF酸处理,可以有效地提高ZSM-5/PDMS膜的分离因子,由12.3最高上升至16.8([EtOH]=5wt%,50℃),渗透通量稍有下降;随着操作温度的升高,复合膜渗透通量增大,分离因子在50℃达到极大值;料液中乙醇浓度提高,复合膜渗透通量增大,分离因子减小。     

超声雾化热分解法制备超细SnO2粉体及其形貌和粒度控制

以SnCl4·5H2O为原料,采用喷雾热分解法制备超细SnO2粉体,结果表明,通过控制反应炉温、前驱体溶液浓度、载气流量,选择合适的添加剂可以有效调控粉体的粒度与形貌.当反应条件为温度600℃、前驱体盐溶液浓度0.4mol/L、载气流量124L/h和柠檬酸浓度0.004mol/L,得到的SnO2颗粒大小在1.4μm左右,粒度分布均匀,结晶度高,球形度好.     

一种太阳电池纳米陷光结构的制备方法

提出了一种利用石墨纳米颗粒作为掩膜,通过金属辅助刻蚀来制备具有低反射率的太阳电池纳米陷光结构的方法。用该方法制得了一种表面覆盖有纳米线和纳米孔的太阳电池纳米陷光结构。结合金属辅助刻蚀的机制和这种陷光结构的形成原理,分析了石墨纳米颗粒和H2O2浓度对陷光结构形貌的影响,并讨论了陷光结构的形貌对样品陷光性能的影响。最后,制得了在300～1100nm波长范围内平均反射率仅为3.6%的太阳电池陷光层。     

单晶黑硅微结构对其反射率影响的研究

采用Ag辅助化学腐蚀法在不同H2O2浓度、腐蚀温度和腐蚀时间条件下制备了单晶黑硅微结构,并系统地研究了这种微结构对表面反射率的影响规律。采用场发射扫描电子显微镜对样品形貌进行了观察,并利用分光光度计对样品的表面反射率进行了测试,最终采用陷光模型对黑硅微结构与其反射率的关系进行了深入分析。发现当腐蚀液为7.8mol/L HF和0.6mol/L H2O2混合液、腐蚀温度为20℃以及腐蚀时间为90s时,所制备黑硅的腐蚀深度为900nm,其表面平均反射率为0.98%(400~900nm)。     

水热法合成Bi25FeO40纳米粉体的研究

本文以Fe(NO3)39H2O和Bi(NO3)35H2O为起始物料,NaOH为沉淀剂和矿化剂,利用水热合成技术制备了Bi25FeO40纳米粉体.利用XRD、SEM和TEM等分析测试手段对所制得Bi25FeO40粉体的物相组成和晶粒形貌等性质进行了研究,并详细讨论了水热反应温度、反应时间和矿化剂浓度等对晶体生长和粉体制备的影响.结果表明,采用这种低温水热技术制备出的产品为纯的Bi25FeO40陶瓷粉体,在微观结构上呈现出三角锥和立方体结构,最佳工艺条件为[Fe]=[Bi]=0.2mol/L,矿化剂[NaOH]=0.5mol/L,在180℃水热反应24h.     

Porosity control in metal-assisted chemical etching of degenerately doped silicon nanowires

We report the fabrication of degenerately doped silicon (Si) nanowires of different aspect ratios using a simple, low-cost and effective technique that involves metal-assisted chemical etching (MacEtch) combined with soft lithography or thermal dewetting metal patterning. We demonstrate sub-micron diameter Si nanowire arrays with aspect ratios as high as 180:1, and present the challenges in producing solid nanowires using MacEtch as the doping level increases in both p- and n-type Si. We report a systematic reduction in the porosity of these nanowires by adjusting the etching solution composition and temperature. We found that the porosity decreases from top to bottom along the axial direction and increases with etching time. With a MacEtch solution that has a high [HF]:[H(2)O(2)] ratio and low temperature, it is possible to form completely solid nanowires with aspect ratios of less than approximately 10:1. However, further etching to produce longer wires renders the top portion of the nanowires porous.     

化学蚀刻法制备纳米硅线作为高能锂离子电池的负极

采用金属催化剂诱导化学蚀刻法首先在单晶硅片上制备出具有高长径比的纳米硅线阵列, 然后通过超声振荡法将硅线阵列破碎为纳米硅线粉体, 最后将其作为锂离子电池的负极材料, 系统研究了金属银催化剂制备过程和各向异性化学蚀刻过程对硅片表面形貌特征的影响, 发现银催化剂在蚀刻过程出现溶解/再沉积现象。通过优化AgNO₃、HF、H₂O₂等试剂的浓度, 在大面积范围内得到了高长径比的纳米硅线阵列。借助超声波的作用将硅线从硅片上切割下来, 制备成纳米硅线负极进行了充放电循环测试, 观察到标准的硅锂合金/去合金化反应平台, 前五次循环的比容量均超过1800 mAh/g。     

金刚石线锯切割多晶硅片表面制绒工艺研

晶体硅片的制绒技术是太阳能电池制造工艺中的关键步骤。本研究以工业中酸制绒方法为基础, 研究了腐蚀时间、浓度对绒面结构以及反射率的影响。此外, 还采用金属催化化学腐蚀法进行制绒, 选用氢氟酸和硝酸银作为腐蚀液。而且对两种制绒方法效果进行了对比。研究获得的最优绒面结构及反射率结果的实验条件为: 氢氟酸浓度4.6 mol/L、硝酸银浓度0.02 mol/L, 室温下反应90 min, 得到的平均反射率为8%, 远低于目前多晶硅片制绒生产标准。     

Anisotropic characteristics and morphological control of silicon nanowires fabricated by metal-assisted chemical etching

Low-cost fabrication methods enabling the morphological control of silicon nanowires are of great importance in many device application fields. A top-down fabrication method, metal-assisted chemical etching, is proved to be a feasible solution. In this paper, some novel approaches based on metal-assisted chemical etching, alkaline solution etching, and electrochemical anodic etching are presented for fabricating micro- and nano-structures, which reveal the anisotropic characteristics of metal-assisted chemical etching in silicon. A new model is proposed to explain the motility behavior of Ag particles in metal-assisted chemical etching of silicon. It is shown that Ag particle forms a self-electrophoresis unit and migrates into Si substrate along [100] direction independently. Diameter and length control of silicon nanowires are achieved by varying Ag deposition and etching durations of metal-assisted chemical etching, respectively, which provide a facilitation to achieve high-aspect-ratio silicon nanowires at room temperature in a short period. These results show a potential simple method to microstructure silicon for devices application, such as solar cells and sensors.     

失活钒钛基SCR催化剂性能表征及其再生

主要研究了钒钛基脱硝催化剂失活机理及再生。采用SEM、EDS、XRD、BET等手段对国内某家燃煤火电厂运行20000h的SCR脱硝催化剂进行表征,然后使用0.5mol/L的硫酸和0.01mol/L的氢氟酸对运行过的催化剂进行了清洗再生并通过烟气模拟-催化剂活性测试系统考察了催化剂的脱硝活性。结果表明,相比于新鲜催化剂,运行后的催化剂活性明显下降,孔容和比表面积有所下降,其表面存在着组成复杂的飞灰,飞灰主要成分为SiO2;采用0.01mol/L氢氟酸溶液清洗能够明显恢复催化剂的脱硝活性,这是因为氢氟酸可以有效清除失活催化剂表面的SiO2。     

Microfabrication of SiN membrane nanosieve using anisotropic reactive ion etching (ARIE) with an Ar/CF4 gas flow

We have designed, fabricated, and characterized a low-stressed silicon nitride (SiN) membrane nanosieve (100 microm x 100 microm) using an anisotropic reactive ion etching (ARIE) combining with gas mixture, thus maintaining compatibility with the complementary metal-oxide semiconductor integrated circuit (CMOS IC) processes. The holes pattern of this nanosieve membrane was precisely controlled under 30 nm diameter by the electron beam writing. By employing mainly anisotropic reactive ion etching plus diffusion to the depth direction, the etch holes size was controlled to be the same with patterns on the e-beam resist (ER). This nanosieve membrane has proper mechanical strength withstanding up to one bar of transmembrane pressure. And it can endure harsh treatments such as high temperature up to 800 degrees C. In addition, it is inert to a number of strong chemicals including the piranha (H2SO4 + H2O2) solution, highly-concentrated potassium hydroxide (KOH), hydrogen fluoride (HF), hydrogen chloride (HCI), and nitric acid (HNO3).     

Unveiling the formation pathway of single crystalline porous silicon nanowires

Porous silicon nanowire is emerging as an interesting material system due to its unique combination of structural, chemical, electronic, and optical properties. To fully understand their formation mechanism is of great importance for controlling the fundamental physical properties and enabling potential applications. Here we present a systematic study to elucidate the mechanism responsible for the formation of porous silicon nanowires in a two-step silver-assisted electroless chemical etching method. It is shown that silicon nanowire arrays with various porosities can be prepared by varying multiple experimental parameters such as the resistivity of the starting silicon wafer, the concentration of oxidant (H(2)O(2)) and the amount of silver catalyst. Our study shows a consistent trend that the porosity increases with the increasing wafer conductivity (dopant concentration) and oxidant (H(2)O(2)) concentration. We further demonstrate that silver ions, formed by the oxidation of silver, can diffuse upwards and renucleate on the sidewalls of nanowires to initiate new etching pathways to produce a porous structure. The elucidation of this fundamental formation mechanism opens a rational pathway to the production of wafer-scale single crystalline porous silicon nanowires with tunable surface areas ranging from 370 to 30 m(2) g(-1) and can enable exciting opportunities in catalysis, energy harvesting, conversion, storage, as well as biomedical imaging and therapy.     

Optical properties of black silicon prepared by wet etching

In this paper, the optical properties of black silicon have been studied. The black silicon samples were fabricated by alkaline etching and metal assisted etching. The micro-columns and nanopores on the silicon surface were obtained in KOH and Au-induced HF/H₂O₂ solution, respectively. The height and diameter of micro-columns prepared by KOH etching is about 470?nm and 2?μm. In the Au-induced HF/H₂O₂ etching, the metallic nuclei behave as a cathode and their surrounding area acts as an anode, resulting in nanopores with diameters ranging from 80 to 120?nm. These microstructures formed in the etching process directly affect the optical properties of black silicon such as reflectance, transmittance and absorptance. According to the measurement of integrating sphere detector, the absorptance of the black silicon produced by wet etching remains roughly 90% from 250 to 1,000?nm wavelength, which is almost 150% of the absorptance of conventional silicon. However, the reflectance of black silicon is less than 13% and the transmittance is less than 4%.     

Integrated freestanding single-crystal silicon nanowires: conductivity and surface treatment

Integrated freestanding single-crystal silicon nanowires with typical dimension of 100 nm × 100 nm × 5 μm are fabricated by conventional 1:1 optical lithography and wet chemical silicon etching. The fabrication procedure can lead to wafer-scale integration of silicon nanowires in arrays. The measured electrical transport characteristics of the silicon nanowires covered with/without SiO(2) support a model of Fermi level pinning near the conduction band. The I-V curves of the nanowires reveal a current carrier polarity reversal depending on Si-SiO(2) and Si-H bonds on the nanowire surfaces.     

化学腐蚀工艺对激光选区熔化成形TC4钛合金表面粗糙度的影响

采用化学腐蚀技术解决激光选区熔化(Selective laser melting, SLM)成形钛合金表面黏附粉末导致表面粗糙的问题,系统研究了腐蚀溶液成分及工艺参数对SLM成形TC4钛合金表面粗糙度的影响。研究结果表明,腐蚀液的成分配比与腐蚀时间是主要的影响因素,随着HF/HNO3体积比的减小,样品表面粗糙度降低效果减弱。当HF/HNO3=1/4时,随着腐蚀时间的增加,样品表面粗糙度显著降低,但当腐蚀时间过长时会造成对基体的损伤。当HF∶HNO3体积比=1∶4,腐蚀时间为9 min时,样品表面粗糙度为2.52μm,同时腐蚀处理过程对样品的尺寸影响较小(降低0.12 mm),此时达到一个最佳状态。