湿化学法制备硅纳米线阵列及其光电化学产氢性能分析

为了探究不同方法条件下制备的硅纳米线阵列电极产氢性能异同,文中分别采用了两步金属辅助催化无电刻蚀法、一步金属辅助催化无电刻蚀法以及阳极氧化法来制备硅纳米线阵列用作为光电分解水电池光阴极材料。通过FESEM、XRD和UVVis-IR DRS等手段对实验样品的形貌、晶型、减反性表征,发现相比于其他2种方法所得硅纳米线样品,两步金属辅助催化无电刻蚀法制备的硅纳米线结构晶型保持更好,表面缺陷更少。光电化学测试表明两步金属辅助催化无电刻蚀法制备的硅纳米线光电化学性能表现最优,其光电流密度值是一步法的4倍,阳极氧化法的40倍;转移电荷电阻仅是一步法制备的硅纳米线阵列阻值的1/3,阳极氧化法制备的1/1 000。     

硅纳米线阵列的制备及其光电应用

近年来,硅纳米线阵列在宽波段、宽入射角范围内优异的减反射性能及其在光电领域的巨大应用前景引起了相关研究者的广泛关注。本文综述了国内外硅纳米线阵列的制备及其在光电应用方面的最新研究进展。关于硅纳米线阵列的制备方法,主要从"自下而上"和"自上而下"两大类出发,分别阐述了模板辅助的化学气相沉积法、化学气相沉积结合Langmuir-Blodgett技术法和金属催化化学刻蚀法,其中重点介绍了目前使用最为广泛且操作简单的金属催化化学刻蚀法的步骤、机理及控制参数。关于硅纳米线阵列在光电领域的应用,主要阐述了硅纳米线阵列在光电探测器、常规太阳能电池、光电化学太阳能电池、光催化分解水制氢、光催化降解有机污染物方面的应用。最后,从硅纳米线阵列在实际应用中面临的提高光电转换效率和避免硅纳米线阵列腐蚀以提高器件的稳定性等问题出发,展望了硅纳米线阵列的表面修饰及修饰后的性能研究是未来硅纳米线阵列光电应用研究的主要方向之一。     

基于宏观金属辅助化学刻蚀制备硅纳米线的研究

分别利用镀银的硅衬底和铂丝电极作为原电池反应中的阴极和阳极,基于金属辅助化学刻蚀采用宏观原电池的方法制备硅纳米线,深入研究了该法制备硅纳米线阵列的机理。通过改变电连接、镀银、刻蚀参数、硅衬底和光照等实验条件,系统地研究了所得硅纳米线形貌与其对应短路电流的关系,实验发现短路电流与硅纳米线长度有一定的对应关系。文章中所提出的模型旨在从根本上解决金属辅助化学刻蚀制备硅纳米线的机理。最后对这种方法所具有的潜在应用价值进行了展望和讨论。     

多孔硅/TiO2纳米线光阳极的制备及其光电催化性能

使用金属辅助化学刻蚀(MACE)法与水热法,改变贵金属粒子的刻蚀时间,制备不同n型多孔硅/TiO_2纳米线光阳极。通过扫描电镜(SEM)和X射线衍射仪(XRD)对光阳极样品进行表征,结果显示多孔硅宏孔的尺寸会随着刻蚀时间延长而增大,由0.1μm变化到0.4μm,多孔硅表面长有TiO_2纳米线为金红石相及少量锐钛矿相。测试结果显示刻蚀35 min的多孔硅/TiO_2样品具有最高的减反射率,在模拟太阳光下具有较高的光电流(光电流密度)活性,且在1.5 V外加偏压下具有最高的光电催化活性。这是由于刻蚀35 min的多孔硅基底具有优异的减反射性能,同时多孔硅与Ti O_2纳米线复合形成光阳极之后具有异质结效应和窗口效应,使得多孔硅/TiO_2纳米线光阳极具有优异光电化学性能。     

硅纳米线阵列电极作为细胞色素c传感器的研究

利用化学刻蚀法由p型硅片制备了硅纳米线阵列,经过表面去氧化层处理后,制备了检测蛋白质细胞色素c的电化学传感器.实验表明,硅纳米线阵列电极对细胞色素c有良好的电化学响应,并且在低浓度条件下具备线性响应的特点.根据与未经表面处理的硅纳米线阵列电极的实验结果相对比,提出了细胞色素c所具备的羧基末端与硅纳米线阵列电极表面的Si-H相互作用从而改善传感性能的检测机理.     

金属辅助化学刻蚀法制备硅纳米线及应用

金属辅助化学刻蚀是近些年发展起来的一种各向异性湿法刻蚀,利用该方法可以制备出高长径比的半导体一维纳米结构。 本文综述了金属辅助化学刻蚀法可控制备硅纳米线的最新进展,简要概述了刻蚀的基本过程与机制,重点阐述了基于不同模板的金属辅助化学刻蚀可控制备高度有序、高长径比的硅纳米线阵列的具体流程与工艺,并介绍了其在锂离子电池、太阳能电池、气体传感检测和仿生超疏水等方面的潜在应用,探讨了目前存在的问题及其今后的研究发展方向。     

双层分等级TiO_2纳米线制备及其光伏性能研究

采用两步溶剂热反应制备了底层为分等级锐钛矿的TiO_2纳米线阵列,上层为分等级锐钛矿的TiO_2纳米线薄膜的双层结构电极.通过XRD和SEM对其组成和形貌进行了表征,并考察了纳米线薄膜对染料敏化太阳电池(DSSC)光伏性能的影响.实验结果表明,分等级锐钛矿的TiO_2纳米线作为DSSC的光阳极,光电转换效率为4.39%,其效率高于光滑的TiO_2纳米线光阳极电池效率(2.07%).     

TiO2纳米管阵列光电催化氧化处理氨氮废水

用电化学阳极氧化法制备了高度有序的钛基二氧化钛纳米管阵列薄膜。用场发射扫描电镜(FE-SEM)、X射线衍射(XRD)表征样品的形貌与晶型特征。以二氧化钛纳米管阵列为光阳极,石墨为对电极,测试了不同pH值和外加偏压条件下的光电流响应和光电催化氧化降解NH4Cl水溶液(以N计,100 mg·L-1)的效率。结果表明:所制备的TiO2纳米管阵列具有锐钛矿和金红石的混晶结构,且主要晶型为锐钛矿。光电流响应的强弱与光电催化氧化效率的高低相对应,降解氨氮废水的最佳条件为pH=11,偏压为1.0 V。     

n-型多孔Si/TiO2纳米线异质结构的制备及光电化学性能

采用光辅助电化学腐蚀法制备了n-型多孔硅衬底, 再采用水热法在其表面生长TiO₂纳米线制得了三维n-型多孔Si/TiO₂纳米线异质结构. 通过X射线衍射、 扫描电子显微镜和X射线能量散射等表征证实了n-型多孔Si/TiO₂纳米线异质结构的形成. 紫外-可见漫反射光谱测试结果表明, n-型多孔硅与TiO₂纳米线的复合提高了紫外-可见波段的光吸收. 光电性能测试结果表明, 3个样品中n-型多孔Si/TiO₂纳米线异质结作为光电极的光电流最高, 这说明n-型多孔Si/TiO₂纳米线作为光电极具有更高的光电化学分解水性能.     

ZnO纳米线/棒阵列的水热法制备及应用研究进展

氧化锌(ZnO)纳米线/棒阵列的质量决定了所构建光电器件的性能. 为了制备出比表面积更大、垂直性更好以及无根部融合的高质量ZnO纳米线/棒阵列, 本文概述了近几年两步水热法可控制备ZnO纳米线/棒阵列的研究进展, 分别探讨了种子层、生长液和生长方法对纳米线/棒阵列形貌的影响, 详细分析了氨水、六次甲基四胺和聚乙烯亚胺对于促进纳米线/棒阵列生长的作用机理, 提出了通过微流控技术可控制备ZnO纳米线阵列提高纳米线生长效率的方法. 最后介绍了ZnO纳米线/棒阵列的形貌对于提高染料敏化太阳能电池、纳米发电机、气体传感器和场发射器件性能的重要作用, 并对未来两步水热法制备ZnO纳米线/棒阵列的发展趋势进行了展望.     

FTIR spectroscopic studies of the stabilities and reactivities of hydrogen-terminated surfaces of silicon nanowires

Attenuated total reflection Fourier transform infrared (FTIR) spectroscopy was used to characterize the surface species on oxide-free silicon nanowires (SiNWs) after etching with aqueous HF solution. The HF-etched SiNW surfaces were found to be hydrogen-terminated; in particular, three types of silicon hydride species, the monohydride (SiH), the dihydride (SiH(2)), and the trihydride (SiH(3)), had been observed. The thermal stability of the hydrogen-passivated surfaces of SiNWs was investigated by measuring the FTIR spectra after annealing at different elevated temperatures. It was found that hydrogen desorption of the trihydrides occurred at approximately 550 K, and that of the dihydrides occurred at approximately 650 K. At or above 750 K, all silicon hydride species began to desorb from the surfaces of the SiNWs. At around 850 K, the SiNW surfaces were free of silicon hydride species. The stabilities and reactivities of HF-etched SiNWs in air and water were also studied. The hydrogen-passivated surfaces of SiNWs showed good stability in air (under ambient conditions) but relatively poor stability in water. The stabilities and reactivities of the SiNWs are also compared with those of silicon wafers.     

Preparation of well-aligned carbon nanotubes/silicon nanowires core-sheath composite structure arrays in porous anodic aluminum oxide templates

The well-aligned carbon nanotubes (CNTs) arrays with opened ends were prepared in ordered pores of anodic aluminum oxide (AAO) template by the chemical vapor deposition (CVD) method. After then, silicon nanowires (SiNWs) were deposited in the hollow cavities of CNTs. By using this method, CNTs/SiNWs core-sheath composite structure arrays were synthesized successfully. Growing structures and physical properties of the CNTs/SiNWs composite structure arrays were analyzed and researched by the scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction spectrum (XRD), respectively. The field emission (FE) behavior of the CNTs/SiNWs composite structure arrays was studied based on Fowler-Nordheim tunneling mechanism and current-voltage (/-V) curve. And the photoluminescence (PL) was also characterized. Significantly, the CNTs/SiNWs core-sheath composite structure nanowire fabricated by AAO template method is characteristic of a metal/semiconductor (M/S) behavior and can be     

Three-dimensional etching profiles and surface speciations (via attenuated total reflection-fourier transform infrared spectroscopy) of silicon nanowires in NH4F-buffered HF solutions: a double passivation model

A systematic study of the etching behavior, in terms of three-dimensional profiles, of one-dimensional (1-D) silicon nanowires (SiNWs) in NH(4)F-buffered hydrofluoric acid (BHF) solutions of varying concentrations and pH values and the surface speciations of the resulting etched SiNW surfaces, as characterized by attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectroscopy, is reported. It was found that SiNWs are stable only in relatively narrow pH ranges of the BHF solutions. The results are rationalized in terms of a "double passivation" model. When SiNWs are etched in BHF solutions with pH values of 1-3, the surfaces are passivated with hydrogen (inner layer) giving rise to surface moieties such as Si-H(x) species (x = 1-3); at high HF concentrations, the H-terminated Si surfaces are covered with a hydrogen bonding network of HF and related molecules (oligomers, etc.), providing an outer-layer passivation. When SiNWs are etched in BHF solutions with pH values of 11-14 (by adding a strong base such as NaOH), the surfaces are oxygen-terminated with surface moieties such as Si-(O(-))(x)() species (x = 1-3); at high NH(4)F concentrations, the negatively charged Si surfaces are stabilized by NH(4)(+) ions via ionic bonding, again providing outer-layer passivation. In BHF solutions with pH values of 3-11, the surface speciation, consisting of Si-(OH)(x)(O(-))(y) (x + y = 1-3) species, is unstable and etched away rapidly. The surface speciations of SiNWs etched in various BHF solutions were explored via ATR-FTIR spectroscopy. It was found that, while etching SiNWs with HF-rich BHF solutions with pH < 4 gave rise to Si-H(x)() surface species, no surface Si-H(x) species were observed with SiNWs etched in BHF solutions with pH >/= 4 (HF/NH(4)F /= 4 on the other. These two factors, among others, contribute to the rapid hydrolysis of the surface Si-H(x)() species (and the etching of the SiNWs), particularly in BHF solutions with low HF/NH(4)F ratios and high pH values (pH >/= 4).     

硅纳米线的化学气相沉积法合成

硅纳米线是近十几年来在纳米科学与技术领域快速发展的一种重要材料．通过精细的结构设计与材料合成,硅纳米线在生物传感、锂离子电池、太阳能电池和光电化学等领域展示出良好的应用前景．化学气相沉积（CVD）法是一大类重要的自下而上合成硅纳米线方法．本文简介了CVD法合成硅纳米线的主要进展,包括具有单一结构和复合结构的硅纳米线的合成．其中,单一结构的硅纳米包括本征（无掺杂）、掺杂和超长的硅纳米线;复合结构的硅纳米线包括轴向异质结、径向异质结、转折结构和树枝状结构的硅纳米线．     

SiO-Au法制备硅纳米线

在低真空的CVD系统中直接热蒸发SiO粉末并以金为催化剂在硅衬底上制备出大量长达几十微米的硅纳米线(SiNWs), 通过X 射线衍射谱(XRD)、场发射扫描电子显微镜(FESEM)、透射电子显微镜(TEM)、选区电子衍射仪(SAED)和Raman光谱等技术对硅纳米线进行形貌及结构分析. 实验结果表明, 在不同生长温度下制备得到的硅纳米线质量不同, 其中在700 ℃温区生长的硅线质量最好; 与晶体硅Raman的一级散射特征峰(TO)520.3 cm−1相比, 纳米硅线的Raman特征峰(TO)红移至514.8 cm−1.     

Synthesis and characterization of silicon nanowires on mesophase carbon microbead substrates by chemical vapor deposition

Silicon nanowires (SiNWs) have been fabricated by chemical vapor deposition at ambient pressure using SiCl(4) as a silicon source and mesophase carbon microbead powder as a substrate without any templates and/or metal catalysts. The SiNWs have a crystalline core with a very thin amorphous SiO(x) sheath. The obtained SiNWs are homogeneous with average diameters below 50 nm and lengths up to micrometers. Temperature and time effects on the growth of SiNWs were systematically studied. Higher reaction temperatures and longer reaction times resulted in larger diameters and higher yields of SiNWs. SiNWs with a better crystallinity can be obtained at higher temperatures and longer reaction times. The obtained SiNWs were characterized by field-emission scanning electron microscopy, X-ray diffraction, Raman spectroscopy, and transmission electron microscopy.     

Aligned Pt-diamond core-shell nanowires for electrochemical catalysis

Heavily boron-doped diamond electrode has been applied as a robust substrate for Pt based catalyst. However, by simply applying a planar electrode the effective surface area of the catalyst is limited. In this article we for the first time prepared vertically aligned Pt-diamond core-shell nanowires electrode in a convenient and scalable method (up to 6-inch wafer size). The diamond nanowires are first fabricated with reactive ion etching with metal nanoparticles as etching masks. The following Pt deposition was achieved by DC sputtering. Different amounts of Pt were coated on to the nanowires and the morphology of the core-shell wires is characterized by SEM and TEM. The catalytic oxygen/hydrogen adsorption/desorption response are characterized by cyclic voltammetry. The results show that the active Pt surface area is 23 times higher than a planar Pt electrode, and 4.3 times higher than previously reported on Pt nanoparticles on diamond by electro-deposition. Moreover, this highly active surface is stable even after 1000 full surface oxidation and reduction cycles.     

Hybrid heterojunction solar cell based on organic-inorganic silicon nanowire array architecture

Silicon nanowire arrays (SiNWs) on a planar silicon wafer can be fabricated by a simple metal-assisted wet chemical etching method. They can offer an excellent light harvesting capability through light scattering and trapping. In this work, we demonstrated that the organic-inorganic solar cell based on hybrid composites of conjugated molecules and SiNWs on a planar substrate yielded an excellent power conversion efficiency (PCE) of 9.70%. The high efficiency was ascribed to two aspects: one was the improvement of the light absorption by SiNWs structure on the planar components; the other was the enhancement of charge extraction efficiency, resulting from the novel top contact by forming a thin organic layer shell around the individual silicon nanowire. On the contrary, the sole planar junction solar cell only exhibited a PCE of 6.01%, due to the lower light trapping capability and the less hole extraction efficiency. It indicated that both the SiNWs structure and the thin organic layer top contact were critical to achieve a high performance organic/silicon solar cell.     

Etching behavior of silicon nanowires with HF and NH4F and surface characterization by attenuated total reflection Fourier transform infrared spectroscopy: similarities and differences between one-dimensional and two-dimensional silicon surfaces

A systematic study of the etching behavior of one-dimensional (1-D) Si nanowires (SiNWs) in various HF and NH4F etching solutions is reported. The concentration and pH dependences of the etching time (which is inverse to the "stability") of the SiNWs in these solutions were investigated. A V-shaped bimodal etching curve was observed for HF solutions with concentrations of 0.5-40%. Specifically, SiNWs exhibit high stability in both low (0.5%) and high (40%) concentrations of HF solution, with the lowest stability (i.e., fastest etching rate) occurring at 2% (1 M) HF solution. With NH4F, the time needed to totally etch away the SiNWs sample decreases with increasing concentration (from 1-40%). The opposite is true when the pH of the NH4F solution was maintained at 14. These surprising results were rationalized in terms of "passivation" of the SiNW surfaces by HF or related molecules via hydrogen bonding for Si-H-terminated surfaces in HF solutions (with low pH values) and by NH4(+) ions via ionic bonding for Si-O(-)-terminated surfaces in NH4F solutions (with high pH values), respectively. Furthermore, it was found that SiNWs are stable only in relatively narrow pH ranges in these solutions. When SiNWs are etched with HF, the stability range is pH = 1-2 where the surface moieties are Si-H(x) species (x = 1-3). When SiNWs are etched with NH4F, the stability range is pH = 12-14 where the surface moieties are mainly Si-(O-)x species (x = 1-3). These rationales were confirmed by attenuated total reflection Fourier transform infrared spectroscopy measurements, which showed that, while etching SiNWs with HF gave rise to Si-H(x) surface species, no Si-H(x) species were observed when SiNWs were etched with NH4F. The latter finding is at odds with the corresponding results reported for the two-dimensional (2-D) Si wafers where etching with either HF or NH4F produces Si-H(x) species on the surface. This difference suggests either that the etching mechanisms for NH4F versus HF are different for SiNWs or, more likely, that the Si-H(x) surface species produced in NH4F solutions are so unstable that they are hydrolyzed readily at pH > 4. The similarities and differences of the etching behaviors and the resulting surface speciations between the 1-D SiNWs and the 2-D Si wafers suggest that the nanoscale structures as well as the low dimensionality of SiNWs may have contributed to the rapid hydrolysis of the surface Si-H(x) species in NH4F solutions, especially at high pH values.