Experimental Studies of Surface Transport Aspects of Electrodeposition and Corrosion

CTS-9527497这项工作的目标是开发和应用一种方法来测量固-液界面电极上的表面扩散。该方法使用伏安法、微分电容和表面二次谐波产生(SHG)。所研究的体系包括金(111)上的铅和银(111)上的氯、铅或铜。在邻近金(111)上的实验使用纯伏安测量来获得梯级和台阶上的相对覆盖率；这种分配与稀溶液中的沉积速率的依赖关系给出了表面扩散的间接测量。表面扩散的直接测量。直接测量银(111)上的表面扩散使用表面倍频，这是一种能够选择亚单层的非线性吸附光学探头；这些实验有两种类型：测量表面衍射光栅的衰变和测量一维浓度阶跃的衰变。第一种技术使用激光诱导热解吸(LITD)来创建衍射光栅，并使用倍频来监测其由表面扩散引起的衰减率。第二种技术包括通过LITD或通过屏蔽真空蒸发来创建阶跃浓度分布，其衰减由SHG监测。对衰变的Boltzmann-Montano分析给出了描述宏观电沉积过程所需的依赖于覆盖率的扩散系数。通过两种电化学方法：溶出伏安法和微分电容，将倍频信号与表面覆盖率进行了经验关联。表面扩散是电沉积和电溶解的基本步骤之一，在某些工业场合是限速的。然而，这一现象很少被研究，因为它在实验上是不可访问的。这项研究旨在纠正这一点，最终目标是将表面扩散和成核的微观信息纳入贵金属互连和电接触的亚半微米电沉积的特征尺度(形态)模拟中。***

ABSTRACT CTS-9527497 The goal of this effort is to develop and apply a methodology to measure surface diffusion on electrodes at the solid-liquid interface. The approach uses voltammetry, differential capacitance, and surface second harmonic generation (SHG). Systems studied include lead on gold (111) and chlorine, lead, or copper on silver (111). Experiments on vicinal gold (111) use a purely voltammetric measurement to obtain the relative coverage on terraces and steps; the dependence of this partitioning on the deposition rate from dilute solutions gives an indirect measure of surface diffusion. Direct measurements of surface diffusion. Direct measurements of surface diffusion on silver (111) use surface SHG, a nonlinear optical probe of adsorption capable of submonolayer selection; these experiments are two types: measurement of the decay of a surface diffraction grating, and measurement of the decay of a one-dimensional concentration step. The first technique employs laser-induced thermal desorption (LITD) to create a diffraction grating and uses SHG to monitor its rate of decay, which is caused by surface diffusion. The second techniques involves creation of a step concentration profile, either by LITD or by masked vacuum evaporation, the decay of which is monitored by SHG. A Boltzmann-Montano analysis of the decay gives the coverage-dependent diffusivity that is needed to describe macroscopic electrodeposition processes. The SHG signal is related empirically to surface coverage by two electrochemical methods: stripping voltammetry and differential capacitance. Surface diffusion is one of the fundamental steps in electrodeposition and electrodissolution, and is rate-limiting in some industrial situations. Nevertheless, the phenomenon is little studied because it is experimentally inaccessible. This study aims to rectify this with the eventual goal of incorporating microscopic information on surface diffusion and nucleation into feature-scale (morphological) simula tion of sub-half-micron electrodeposition of noble-metal interconnects and electrical contacts. ***