Burt David P, Wilson Neil R, Janus Ulrich, Macpherson Julie V, Unwin Patrick R
Department of Chemistry, University of Warwick, Coventry, UK.
Langmuir. 2008 Nov 18;24(22):12867-76. doi: 10.1021/la8003323. Epub 2008 Jun 18.
The effect of AFM probe geometry on diffusion to micrometer-scale reactive (electrode) interfaces is considered. A disk-shaped substrate electrode was held at a potential to reduce a species of interest (aqueous Ru(NH 3) 6 (3+)) at a diffusion-controlled rate and the current response during AFM imaging provided information on local mass transport to the interface. This approach reveals how the AFM probe influences diffusion to a reactive surface, which is of importance in more clearly delineating the conditions under which in-situ AFM can be treated as a noninvasive probe of surface processes involving mass transport (e.g., electrode reactions and crystal dissolution and growth). An assessment has been made of three types of probes: V-shaped silicon nitride contact mode probes; single beam silicon probes; and batch-fabricated scanning electrochemical-atomic force microscopy (SECM-AFM) probes. Two disk electrodes, (6.1 microm and 1.6 microm diameter) have been considered as substrates. The results indicate that conventional V-shaped contact mode probes are the most invasive and that the batch-fabricated SECM-AFM probes are the least invasive to diffusion at both of the substrates used herein. The experimental data are complemented by the development of simulations based on a simple 2D model of the AFM probe and active surface site. The importance of probe parameters such as the cantilever size, tip cone height, and cone angle is discussed, and the implications of the results for studies in other areas, such as growth and dissolution processes, are considered briefly.
研究了原子力显微镜（AFM）探针几何形状对微米级反应性（电极）界面扩散的影响。将圆盘形基底电极保持在一定电位，以扩散控制速率还原目标物质（水合Ru(NH₃)₆³⁺），AFM成像过程中的电流响应提供了局部物质传输到界面的信息。这种方法揭示了AFM探针如何影响向反应性表面的扩散，这对于更清晰地描绘原位AFM可被视为涉及物质传输的表面过程（如电极反应、晶体溶解和生长）的非侵入性探针的条件非常重要。对三种类型的探针进行了评估：V形氮化硅接触模式探针；单束硅探针；以及批量制造的扫描电化学原子力显微镜（SECM-AFM）探针。考虑了两个圆盘电极（直径分别为6.1微米和1.6微米）作为基底。结果表明，传统的V形接触模式探针侵入性最强，而批量制造的SECM-AFM探针在本文使用的两种基底上对扩散的侵入性最小。基于AFM探针和活性表面位点的简单二维模型进行模拟，对实验数据进行了补充。讨论了探针参数（如悬臂尺寸、针尖锥高和锥角）的重要性，并简要考虑了结果对其他领域（如生长和溶解过程）研究的影响。
