【作者】 杭弢；

【导师】 毛大立；

【作者基本信息】 上海交通大学 ， 材料学， 2010， 博士

【摘要】 微纳米阵列材料,由于其特殊的表面微纳米结构、高化学活性等,决定了它在催化、光学、磁学、电子学等方面表现出良好的功能特性,在微电子、新能源、医疗器械、化工、军事等领域具有广阔的应用前景,已成为当今研究的热点之一。但目前制备微纳米阵列结构材料的方法多为光刻法、模板法等,设备昂贵,工艺复杂,加工尺寸有限,极大地限制了它在各个领域的应用。因此,开发工艺简单、成本低廉的新型制备方法是当前研究的重要课题之一。本文基于电化学沉积原理,提出了一种无模板制备表面微纳米阵列材料的新方法——定向电结晶法;通过对镍微纳米针锥阵列材料的制备工艺研究,探索了定向电结晶方法的可行性;借助电化学方法和显微分析等手段,系统研究了镍微纳米针锥阵列材料的定向电结晶机理;表征了该材料的基本特性,并对其在电子封装材料中的应用进行了尝试性研究。在制备方面,通过镀层表面形貌的对比,对筛选出的两种金属主盐及四种结晶调整剂进行了定向电结晶可行性的研究,结果表明在氯化物镀液中添加含胺(铵)基的结晶调整剂可获得镍微纳米针锥晶,证实了定向电结晶的可行性,确定了镍定向电结晶的镀液体系。在此基础上详细研究了各种电沉积条件对微纳米针锥阵列形貌及尺寸的影响,表明溶液温度升高有利于微纳米针锥阵列的形成、提高电流密度会减小微纳米针锥的尺寸,改变沉积时间可以获得不同尺寸的针锥晶阵列,通过电沉积条件的适当选择,实现了镍微纳米针锥阵列尺寸在50 nm到1500 nm范围内的可控制备。为探索定向电结晶机理,研究了镀液中结晶调整剂与镍离子的络合形态和电沉积过程的电化学行为。镀液紫外可见光谱及电极反应数据表明结晶调整剂中的铵根与镍离子在溶液中不发生络合,并排除了扩散传质导致针锥形成的可能性。进一步研究发现定向电结晶初期按瞬时形核三维生长方式进行,镍微纳米针锥阵列的电沉积过程存在着中间产物,结晶调整剂主要通过在电极表面吸附,参与电极表面的电化学反应影响电结晶过程,并形成阻滞作用从而引起阻抗谱中低频区的容抗弧。最后提出了该反应的等效电路模型,模拟结果与实验结果具有较好的一致性。通过XRD、FE-SEM、HRTEM等分析技术对针锥晶的微观结构进行了表征。结果表明,沉积初期镀层呈现(111)织构。随着晶体的长大,镀层逐渐向(110)织构转变,并最终形成具有[110]取向的针锥晶阵列。发现了大部分微纳米针锥晶呈现出五棱锥形貌,推测其为以[110]为取向轴,(100)为侧面,(111)面为孪晶面的多重孪晶结构。针锥晶的生长可用单螺旋位错理论解释,台阶边界能的各向异性导致棱锥的产生。根据螺旋生长理论,推导出微纳米针锥的长径比与螺旋生长电流密度的平方根成正比,而结晶调整剂则可能通过阻碍生长台阶的平行扩展而促使针锥晶向上生长。本文还对镍微纳米针锥阵列材料的几种主要性能进行了表征。该材料的比表面积比普通镀镍层表面高2倍以上;在整个紫外可见光范围内,微纳米针锥阵列结构的反射率都低于10%,具有很好的吸光性能;镍基纳米针阵列材料的易磁化轴平行于基底表面,其矫顽力远大于块状镍金属的矫顽力。在溅射Cu玻璃基片上制备的镍微纳米针锥阵列显示了良好的场发射性能;利用分步沉积法制备的微纳米针锥分级结构的镍薄膜具有超疏水特性。最后对微纳米针锥阵列材料在电子封装领域的实际应用做了尝试。在引线框架表面引入微纳米针锥阵列结构,利用其较大的比表面积且可与封装树脂产生物理镶嵌咬合作用,从而增强引线框架与封装树脂间结合力达两倍以上,提高了电子产品的可靠性。同时,拉力测试和可焊性测试的结果表明,微纳米针锥阵列结构对引线框架与金线键合的强度影响不大,且该结构引线框架的可焊性良好。这些研究表明微纳米针锥阵列材料可提高镀钯引线框架的可靠性,具有广阔的应用前景。更多还原

【Abstract】 The micro-nano array materials, owing to their unique structure, large specific surface area, high chemical activity etc., have shown special characteristic in optics magnetics and electronics. They are widely used in microelectronics, new energy, medical instrument, chemistry, military and many other fields. However, only a few methods were developed to fabricate micro-nano array materials, and most of them are AAO template-based methods or LIGA photolithography, which are complicated and costly in manufacturing process. And the dimension of the structures is limited to the available templates.In this dissertation, a novel method named directional electrodeposition is presented, which is low-cost and easy for application. The technique of directional electrodeposition method to fabricate nickel nanocones array is studied in details. The microstructure as well as the deposition mechanism of the nanocone is investigated by extensive structural characterization and electrochemical techniques. The basic properties of this material are also characterized, and its potential application in microelectronic packaging is raised as well. The main contents and conclusions are shown as follows:First, the morphologies of the deposits obtained from two metal main salts and four additives were compared, and the additive containing ammonium was found to be an effective crystallization agent in nickel chloride solution to fabricate nickel nanocone array by directional electrodeposition method. And through the study on the influence of the crystallization agent concentration, the prescription of the bath can be obtained. The deposits obtained in many different depositing conditions were compared. The solution temperature, current density as well as the deposition time was found to be the main factors influenced on the morphology of nanocones array. Thus the cones size can be varied from 50 to 1500 nm in height by controlling the deposition conditions.The influences of crystallization agent and solution temperature to the nickel deposition were discussed by studying the plating bath and basic electrochemical behaviors of the nickel nanocones array deposition. The calculated apparent active energy of the reaction confirmed that the reduction process was not controlled by dispersion. The initial stage of nickel nanocones electrocrystallization follows the mechanism of three dimension instantaneous nucleation growth. The electrochemical impedance spectroscopy indicates that nickel nanocones electrodeposition occurs in two steps; the low frequency capacitive loop may be due to the inhibition of nickel electrodeposition by adsorbed crystallization agent. The mechanism and equivalent circuit of nickel electrodeposition were proposed on the basis of the analysis of electrochemical impedance spectroscopy. Meanwhile, the kinetics law of nickel electrodeposition was investigated by means of steady-state polarization to confirm the proposed reaction mechanism.The microstructures of the nanocones were characterized by field-emitting scanning electron microscope (FE-SEM), X-ray diffraction (XRD) and Transmission Electron Microscope (TEM), etc. The results indicated that the nickel deposits’preferred orientation is changed from (111) to (011) texture. A single nanocone is pentagonal symmetric, which is supposed to be a multiple twinning crystallite with (110) orientation axis, (100) sides and twinning at each corner of the (111) planes. The growth mechanism of the nanocones by this method may be explained by the single screw dislocation growth theory. According to the theory, it can be concluded that the aspect ratio of the nanocones is proportional to the square root of the current density. And the propagation of the step edge might be blocked by adsorbed crystallization agent to promote up growth of the nanocones.The characteristics of nickel nanocones array material were also investigated in this dissertation. The results show that the Ni nanocones array materials have 3 times larger specific surface area than the common plain surface. UV-Vis reflection spectrum shows that the reflection rate of nanocones array structure is below 10% in the entire UV-visible range, indicating a good absorption performance; Ni nanocones array material is demonstrated to have the easy axis of magnetization paralleled to the substrate plane. The coercivity of this material is much higher than that of bulk nickel metal. The nickel nanocones array shows very good field emission properties. The nickel film with micro-nano cones array hierarchical structure fabricated by two-step electro-deposition, shows super-hydrophobic characteristic without any chemical modification.Finally, the nanocones array was attempted to apply to electronic packaging. The nanocones array structure was introduced into the Pd pre-plated leadframe (PPF). The adhesion between the epoxy resin molding compound (EMC) and the nanocone-arrayed PPF was three times higher than that of the conventional PPF, and PPFs with taller and steeper nanocones had greater bonding strength with the resin. The increased surface area and the physical keying effect play important roles in this adhesion strengthening between the Pd-PPF and the resin. This approach offers a promising alternative for the synthesis of novel Pd PPF and contributes to solving the problem of weak adhesion between Pd PPFs and EMC. The Au wire bonding strength and the solderability of the nanocones array Pd PPF were also tested. The results showed that both the Au wire bonding strength and the solderability of the nanocones Pd PPF were comparable with the conventional Pd PPF and could reach the industry requirement well. These results indicate that the nanocones arrayed Pd PPF can meet the high reliability requirements, especially for the automobile industry.更多还原