【作者】 常彦龙；

【导师】 王春明；

【作者基本信息】 兰州大学 ， 分析化学， 2007， 博士

【摘要】 本论文在p型单晶硅[p-Si（100）]和多孔硅（PS）基底上，用电化学方法制备了Ag、Au、Pd、Pt、Ru、Ni和Co的纳米功能薄膜，探讨了该功能薄膜在电化学催化和微反应器等方面的应用前景。用原子力显微镜（AFM）、扫描电子显微镜（SEM）系统地表征了所制薄膜材料的表面形貌；用电子色散能谱仪（EDS）分析了薄膜材料的组成；用循环伏安（CV）、线性扫描伏安（LSV）、开路电位～时间（Ocp～t）、电流～时间（Amperometric i～t）、交流阻抗（IMP）和差示脉冲伏安法（DPV）等电化学方法分析了功能薄膜的性能和金属在p型硅上的沉积机理。论文主要内容如下：1．p-Si（100）的阳极特性。金属浸入沉积时，金属离子的阴极还原和硅的阳极溶解同时进行，因此，首先用线性扫描伏安（LSV）和交流阻抗（IMP）研究了p-Si（100）在HF和NH₄F溶液中的阳极溶解行为。I～V曲线显示，p-Si（100）在阳极氧化过程中出现两个电流峰J₁和J₃，分别对应硅在F^-溶液中的直接溶解和间接溶解，溶解价分别是2和4。本实验中，金属浸入沉积的混合电位都小于2.0 V，低于J₁对应的电位，因此硅的溶解价是2。阻抗谱显示，在所测频率段，出现一个容抗弧，此容抗弧来自硅的空间电荷层，说明硅的溶解由电化学反应所控制。2．多孔硅的制备。采用HF溶液中直流腐蚀的方法。腐蚀液为体积比1∶1的40％HF和CH₃CH₂OH（无水），电流密度为40 mA·cm^-2，腐蚀时间30 min。将制得的多孔硅在10％HF中浸泡8小时去除表面土黄色层，露出金属亮色的底层，荧光检测表明，在386 nm的激发波长下，多孔硅发射峰的波长为441 nm，用2.5nm狭缝，荧光光强达877.7 cd。制得的多孔硅平均孔径约2.5μm，深度1.7μm，是一种大孔、浅孔结构。3．单晶硅表面金属薄膜的制备。在HF溶液中，用浸入沉积的方法在单晶硅表面制备了贵金属Ag、Au、Pd和Pt的薄膜。实验表明，Ag和Pd的沉积都是瞬间成核，而Au和Pt是逐渐成核，晶核的生长都服从3D岛状模式。沉积机理主要是局部池腐蚀（Local-cell corrosion），即金属离子的还原和硅的氧化不是在同一位置发生的，硅氧化产生的电子可以通过硅基体和已沉积物传递。在相同的条件下，Pd薄膜的溶出峰电流比其他3种大1个数量级。用化学镀的方法在Pd活化的单晶硅表面用NiSO₄+NH₂NH₂镀浴制备了Ni薄膜，用开路电位～时间（Ocp～t）方法和电流～时间（i～V）曲线探讨了硅表面化学镀Ni的热力学和动力学特性。4．多孔硅表面金属薄膜的制备。在HF酸性溶液中，用浸入沉积的方法在多孔硅表面制备了Ag、Au、Pd和Pt的薄膜；在NH₄F碱性溶液中，用浸入沉积的方法在多孔硅表面制备了Ni、Co和Ru的多孔薄膜。不同的沉积行为取决于溶液的pH值、体系的混合电位、硅的阳极溶解速率、金属离子的络合状态和还原电位。Ni²⁺／Ni，Co²⁺／Co，Ru³⁺／Ru的还原电位均负于H⁺／H₂的还原电位，在HF溶液中，优先析氢，干扰了金属的沉积；NH₄F溶液中，H⁺／H₂的还原电位降低，硅的溶解速率加快，金属离子的络合物M（NH₄）_xⁿ⁺形成，因此不能在HF中沉积的金属元素可以在NH₄F中沉积。5．用化学镀的方法在未经活化的多孔硅表面制备了15μm厚的镍膜后再用电镀增厚至200μm，镀层在10％的HF溶液中浸泡10分钟后超声剥离，得到镍厚膜，SEM形貌显示，镍膜完全填充了多孔硅，但与多孔硅的结合强度低，结合面显示出了光滑的环形微流道，可以用作微换热器元件，具有潜在的应用价值。6．金属在多孔硅表面的沉积具有位置选择性。实验发现，贵金属优先在多孔硅的孔边上生长，Ag沉积10 s后，孔边上的沉积量是孔底部的4.6倍，而多孔硅的形貌基本不变，Au、Pd和Pt具有类似的特性，可以用来制备带催化剂的微反应器。Ni、Co和Ru在多孔硅表面沉积时在填充大孔的同时，会产生微孔，形成高比表面积的催化膜，具有潜在的工业应用价值。更多还原

【Abstract】 In this thesis, the functional nano-films of Ag, Au, Pd, Pt, Ru, Ni and Co on p-Si（100） and porous silicon （PS） were prepared by electrochemical techniques. Thepromising application in electrochemical catalysis and microreactor were discussed.The morphologies of films were characterized with Atomic Microscope （AFM） andScanning Electron Microscopic （SEM）, while’ its compositions were analyzed byElectron Dispersive Spectroscopy （EDS）. The properties of films and mechanism ofmetal deposition were investigatedby electrochemical technologies, such as CyclicVoltammeter （CV）, Linear Sweep Voltammeter （LSV）, Open Circuit Potential～time（Ocp～t）, Amperometric i～t, A.C. Impedance （IMP） and Differential PulseVoltammeter （DPV）. The main issues of this thesis were described as follows:1. The anodic properties of p-Si （100）. Metal ion reduction accompanies anodicdissolution of silicon, so the anodic dissolution behaviors of p-Si （100） wereinvestigated firstly by LSV and IMP in HF and NH₄F solution separately. Two currentpeaks J₁ and J₃ occurred on i～V curves which separately mean direct dissolution（dissolution valence is 2） and indirect dissolution （dissolution valence is 4） of silicon.The mixed potentials of redox reaction in this experiment are less than 2.0 V andbelow the potential of J₁, so the dissolution valence of silicon is 2 during metaldeposition. A single capacitive loop arising from space charge layer was occurred onNyquist plots at measured frequencies, which showed that the dissolution of siliconwas controlled by electrochemical reaction.2. The preparation of porous silicon （PS）. A macro-porous silicon template withporous size ofΦ2.5μm×1.7μm fabricated by anodizing p-Si（100） in HF （40％）:CH₃CH₂OH （absolute）=1:1（volume ratio） bath at current density of 40 mA·cm^-2 for30 min and then immersed into 10％HF solution for 8 h to remove the khaki surfacelayer for baring the bright bottom. Fluorescence showed that the emission wavelength was 441 nm under the excitated wavelength of 386 nm, and the fluorescence intensitywas 900 cd with 2.5 nm narrow gap.3. The preparation of metal films on p-Si （100）. The Ag, Au, Pd and Pt films werefabricated by immersion deposition on p-Si （100） in HF bathcontaining noble metalsalt. Experiments revealed that the nucleation of Ag and Pd were instantaneous whileAu and Pt were progressive, and the nuclei growth obeyed 3D island model. Metaldeposition mechanism was mainly local-cell corrosion type, the reduction of metal ionand oxidation of silicon occurred not at same location, electron produced by oxidationof silicon can transfer through silicon substrate and pre-deposits. At same conditions,the stripping peaks of Pd deposits on p-Si （100） are higher one order than that ofothers. Ni films were prepared on Pd-activated p-Si （100） by electroless deposition inNiSO₄+NH₂NH₂ plating bath, and the thermodynamic and kinetic properties ofelectroless deposition were modeling by Ocp～t and Amperometric i～t.4. The preparation of metal films on PS. Ag, Au, Pd and Pt films were prepared on PSby immersion deposition in acidic HF bath, while Ni, Co and Ru films were depositedon PS in alkaline NH₄F bath. The different deposition behaviors were dependent onpH of solution, mixed potential of redox couple, dissolution rate of silicon, complexformation and equilibrium potential of metal ion. The equilibrium potential ofNi²⁺/Ni, Co²⁺/Co and Ru³⁺/Ru are more negative than H⁺/H₂ in HF solution, so thehydrogen evolution disturbed the deposition of metal. But in NH₄F solution, theequilibrium potential of H⁺/H₂ was more negative, the dissolution rate of silicon wasincreased; and the metal complex M（NH₄）_xⁿ⁺ was formed, so those that can notreduced in HF bath can deposit on silicon in NH₄F bath.5. A thick Ni template with thickness of 200μm was fabricated by electroplating afterpre-deposited 15μm Ni layer by electroless deposition on PS. And then peeled offfrom PS by ultrasonic after dipping in 10％HF solution for 10 min. SEM morphologies showed that Ni deposits filled the pores completely, however, theadhesion between Ni layer and PS substrate was low. Ni template exhibits manysmooth orbicular microchannels on its interface and presents promising application infabricating microheater.6. Position-selective metal deposition on PS. Experiments showed that noble metalpreferentially deposited on pore borders than bottoms of PS. The ratio is about 4.6 forAg deposits at 10 s, while the morphologies of PS almost remained original; Au, Pdand Pt had similar cases. This character can be used to fabricate low-cost microreactorcompositive with catalyzer. Micro-porous materials of Ni, Co and Ru with higherspecific surface area were fabricated while the macro-pores of PS were filled withdeposits. Those materials present promising application in industrial catalyzer.更多还原