【作者】 叶为春；

【导师】 王春明； 高鸿钧；

【作者基本信息】 兰州大学 ， 分析化学， 2008， 博士

【摘要】 本论文研究了硅基贵金属膜材料的制备、形貌控制及其在光学、电学及催化等性能的应用研究。应用电化学方法如循环伏安法（CV）、电化学直流极化法及开路电位时间曲线（Ocp-t）,以及扫描电子显微镜（SEM）、原子力显微镜（AFM）、X射线光电子能谱（XPS）、X射线衍射（XRD）、拉曼光谱等技术来研究所制膜材料的性质和分析金属的沉积机理,实现了由“材料制备”、“材料组成形貌分析”到“材料应用”的交叉、系统性研究。论文的主要内容如下:1.应用循环伏安法研究沉积在硅表面的Ag的阳极溶出行为,开展银在0.01mol/L AgNO₃溶液对单晶硅微污染情况的研究。结果表明Ag的沉积速率是相当快的,几乎1s内就能完成。进一步计算沉积1s,10min及1h后硅表面金属银的表面覆盖量（Γ）,得出在该溶液硅表面得到的Ag层仅为一个单层。（参见第二章）2.电化学直流极化法和开路电位时间曲线（Ocp-t）技术研究了不同HF浓度下Ag在硅表面的无电沉积行为。这两种电化学测试结果及AFM结果都证明了HF浓度的增加促进硅表面能级的下降,进而有利于Ag的3D生长。本文根据混合电位理论推导了开路电位下降斜率(K_{-ΔE（OCP）/t})公式,并应用K_{-ΔE（OCP）/t}的大小来评价金属沉积速率的快慢。K_{-ΔE（OCP）/t}值与ICP-AES结果作了比较,表明沉积速率随HF浓度的增加而增加,但不是线性关系。最后应力（Stress）产生与释放机制用来解释实验结果。（参见第二章）3.用金属无电沉积技术在NH₄F-AgNO₃溶液50℃下,既制备有序树枝状Ag纳米晶又同时得到浅层多孔硅纳米层。自组装定位微观电解池模型和极限扩散聚合（diffusion-limited aggregation,DLA）过程解释Ag树枝纳米结构的生成过程,认为Ag树枝纳米结构是由于VW层小的纳米粒子连续不断的聚集生长而得到的。浅层均匀的多孔硅纳米结构显示了室温下可见光发光特性。表面增强拉曼散射光谱（SERS）的研究证明了这种负载在多孔硅表面的树枝状Ag膜是很好的SERS活性基体,具有高的拉曼增强效应。（参见第三章）4.枝状分级的Ag纳米树枝通过简单的置换反应制备,即将HF-AgNO₃溶液滴在硅表面即可。实验中观察到树枝结构生长中的形貌多样性;Ocp-t曲线现场记录了硅/溶液的界面开路电位的表面,以揭示结构演变的过程;XRD表征所得沉积物的晶体结构;定位生长方向的选择取决于固/液界面能的理论和取向连接机理用于解释树枝结构生长中存在形貌多样性的现象。最后以罗丹明B（RB）为探针分子研究了这种树枝纳米Ag膜的SERS活性,表明这种简单的置换方法是制备SERS活性基底一种很有效的方法,可用于传感、选择性检测。（参见第三章）5.首先在HF-HAuCl₄溶液50℃下用无电沉积技术制备硅基有序树枝状纳米Au膜,然后在其表面自组装2-巯基萘单分子膜。以铁氰化钾为电子转移探针试剂,单分子膜的电化学实验表明2-巯基萘分子并不能完全阻隔电子在Au膜与铁氰化钾间的转移;0.5mol/L NaOH溶液中的电化学脱附实验证明2-巯基萘分子是以形成Au-S键的化学吸附形式自组装在Au膜上。表面增强拉曼散射光谱证明树枝状纳米Au基底的自组装2-巯基萘单分子膜具有很高的表面拉曼增强效应。（参见第三章）6.应用无电沉积技术在HF溶液制备了VW结构和树枝结构的W掺杂Ag膜。通过比较与仅含有金属Ag相应结构的膜材料的沉积行为,发现在所得的Ag-W二元组成体系中Ag的沉积生长起主导作用,并不受钨酸根离子大的影响;提出了W元素掺杂的理论模型,即W元素的掺杂是在Ag的沉积过程中通过钨酸根二聚体中的O原子与金属银的化学吸附—形成Ag-O化学键而实现的。CV用于检测Ag与O间的化学键作用力的大小。高温空气中退火实验表明了所得到的Ag-W二元组成物质具有良好的抗氧化能力。（参见第四章）7.应用电沉积法导电玻璃（ITO）基体制备Pd/WO₃组成膜材料,电解液为50mmol/L过氧化钨溶液+5wt.%十二烷基硫酸钠（SDS）+5mmol/L PdCl₂。膜材料的形貌和组成由扫描电子显微镜、能量散射能谱、X射线光电子能谱（XPS）和X射线衍射分析和表征。WO₃对电催化氧化肼化合物的增强效应进行了研究,在Pd/WO₃-ITO电极上肼氧化峰电流达10μA,是Pd-ITO电极的1.7倍,后者仅为62μA,主要原因归结于WO₃的添加对Pd纳米粒子起到很好的分散作用。（参见第五章）8.循环伏安法用于电沉积硅基体Ag-W膜材料。不同SDS含量下Ag-W的电化学沉积行为及所得沉积物的微观结构分别进行了比较,发现当SDS含量达5wt.%时SDS由于沉淀作用大大地改善了Ag-W膜的微观结构;XPS表明所得沉积物中W元素的含量达3.4%,O/W原子比约为3.0;XPS和XRD结果证明了Ag-W膜在350℃下空气中不会被氧化。最后研究了膜材料的电阻率与沉积循环圈数的关系。（参见第五章）更多还原

【Abstract】 This thesis describes the preparation of noble metal films on silicon substrates, morphological control and the studies of their properties such as optical,electrical and catalytic properties.The properties of the films and metal deposition mechanism were investigated by using electrochemical methods involving cyclic voltammetry（CV）,an electrochemical direct current polarization method and open circuit potential-time （Ocp-t）technique,scanning electron microscopy（SEM）,atomic force microscopy （AFM）,X-ray photoelectron spectroscopy（XPS）,X-ray diffraction measurement （XRD）,Raman spectroscopic analysis,etc.Some important results obtained are described as follows:1.The microcontamination process of silver onto p-type crystalline silicon（111）in a solution of 0.01 mol/L AgNO₃ at room temperature was investigated by studying the anodic stripping behavior using cyclic voltammetry（CV）.This result shows that the rate of Ag deposition is rapid and that deposition is almost fully accomplished within 1 s.Calculating the surface coverage（F）for 1 s,10 min,or 1 h immersion based on the CV curves demonstrated that the silver layer was only a monolayer.（See Chapter 2）2.Electroless silver deposition onto p-silicon（111）from 0.005 mol/L AgNO₃ solutions with different HF concentration was investigated by using an electrochemical direct current polarization method and open circuit potential-time （Ocp-t）technique.The fact that three-dimensional（3D）growth of silver onto silicon is favored with increasing the HF concentration was ascribed to the drop of the surface energy and approved by the two electrochemical methods and atomic force microscopy（AFM）.The drop slope of open circuit potential,K_{-ΔE（OCP）/t},was educed from the mixed-potential theory.K_{-ΔE（OCP）/t}as well as the deposition rate determined by an inductively coupled plasma atomic emission spectrometry（ICP-AES）, increased with the HF concentration,yet was not a linear function.Results were explained by the stress generation and relaxation mechanisms.（See Chapter 2）3.Via electroless metal deposition,well-defined silver dendrites and thin porous silicon（por-Si）layers were simultaneously prepared in ammonia fluoride solution containing AgNO₃ at 50℃.A self-assembled localized microscopic electrochemical cell model and a diffusion-limited aggregation mode were used to explain the growth of silver dendrites.The formation of silver dendritic nanostructures derives from the continuous aggregation growth of small particles on a layer of silver nanoparticles or nanoclusters（Volmer-Weber layer）.Thin and homogeneous nanostructure por-Si layers displayed visible light-emission properties at room temperature.The investigation of the surface-enhanced Raman scattering（SERS）revealed that the film of silver dendrites on por-Si was an excellent substrate with significant enhancement effect.（See Chapter 3）4.Hierarchical silver dendritic nanostructures were prepared at room temperature via a simple replacement reaction by dropping a droplet of HF-AgNO₃ solution on silicon wafers.The morphological diversity of the resulting dendritic structures was observed.Open circuit potential-time（Ocp-t）curve was used to record in situ the variation of the open circuit potentials of silicon/electrolyte,which reflected the structural evolution process.The crystal structures of the deposits were characterized by X-ray diffraction（XRD）.Results were interpreted in term of the theory that orientation selection in dendritic evolution is determined by the anisotropy of the solid-liquid interfacial energy and the oriented attachment-based aggregation mechanism.The silver dendrites show significant SERS effect as probed with Rhodamine B（RB）.The ease of the approach to prepare SERS-active substrates makes it very promising in sensing and detection oriented applications.（See Chapter 3）5.Gold films with well-defined dendritic nanostructure on a silicon substrate were firstly fabricated by using electroless deposition technique from aqueous HF solution containing HAuCI4 at 50℃.And then the gold films were self-assembled with 2-naphthalenethiol.Using potassium ferricyanide as an electron transfer probe,the electrochemical behavior of the resulting monolayers showed that 2-naphthalenethiol self-assembled monolayers（SAMs）failed to block the electron transfer（ET）between the gold film and potassium ferricyanide.Electrochemical desorption of SAMs in 0.5 mol/L NaOH solution revealed that 2-naphthalenethiol molecules were adsorbed on gold films by chemisorption resulting in forming Au-S bonding.Surface enhanced Raman scattering spectroscopic observations confirmed that the SAMs adsorbed on Au dendrites had significant enhancement effect.（See Chapter 3）6.Volmer-Weber（VW）film and dendritic nanostructure film of W-doped Ag were prepared by using electroless deposition from hydrofluoride solution.Compared with the deposition of the corresponding structure of only silver,the results show that the growth of silver is leading and can not be changed essentially by tungstate ions in the Ag-W binary system.A doping mode of W element was proposed,i.e.,the doping of W may occur during silver deposition through chemisorption—chemical bonding of oxygen atoms of tungstate dimer with silver.Cyclic voltammetry was employed to determine the chemical bonding energy between silver and oxygen.Annealing at high temperature in air revealed that the Ag-W composites had good anti-corrosion in air. （See Chapter 4）7.Pd/WO₃ composite film on indium tin oxide（ITO）glass was prepared by electroplating in a solution of 50 mmol/L tungsten-peroxo complex+5 wt.%SDS with 5 mmol/L PdCl₂.The structure and composition of the synthesized Pd/WO₃ composites were characterized by scanning electron microscopy combined with energy dispersion spectroscopy,X-ray photoelectron spectroscopy and X-ray diffraction.The promotional effect of WO₃ for the electrocatalytic activity for hydrazine oxidation was investigated.The peak current of Pd/WO₃ ITO glass electrode reached up to 106μA,which was 1.7 times as high as that of a Pd-ITO glass electrode（62μA）under the same working conditions.It might be mainly attributed to the good dispersion of palladium nanoparticles on WO₃ supports.（See Chapter 5）8.An electrodeposition process using cyclic voltammetry（CV）for preparing Ag-W films on p-type silicon（100）wafers is described.The electrochemical behaviors and microstructural properties of Ag-W deposits were compared in different concentration of sodium dodecylsulfate（SDS）.It was found that SDS functioned as precipitation action to silver ions and promoted strongly the microstructure of Ag-W films as its concentration amounted to 5 wt.%.X-ray electronspectroscopy（XPS）investigation demonstrated that the concentration of tungsten was 3.4%and the O/W atom ratio was about 3.0 for Ag-W deposits.XPS and X-ray diffraction（XRD）measurements certified that the silver coating was not corroded at temperatures up to 350℃in air.Finally,the resistivity of the films with the CV cycle number was analyzed.（See Chapter 5）更多还原