Nanometer-scale electrochemical synthesis of materials using a scanning tunneling microscope.

摘要

In this dissertation, I have developed an electrochemical STM technique for nanometer-scale synthesis of materials on highly ordered pyrolytic graphite (HOPG). The method is unique to deposit nanostructures of various materials with high lateral precision. The mechanism of nanostructure formation was experimentally decoupled into pit formation and metal deposition. Experimental evidence suggested that metal layer deposited by underpotential deposition (UPD) was dominating metal source for the growth of metal nanostructure. This technique allowed solution exchange to deposit two different metals and monitor spontaneous electrochemical reactions on a nanometer scale. The technique was employed to determine the thickness of self-assembled n-alkanethiolate monolayer on silver nanostructures and provide direct evidence regarding the position of the STM tip with respect to the sample surface. The stability of metal nanostructures was investigated under various conditions. It was found that metal nanostructures were generally stable in their own plating solution and unstable in pure water. The anodic dissolution of silver nanostructures in pure water was strongly inhibited following the formation of n-alkanethiolate self-assembled monolayer on the silver surface. The developed method has potential applications to synthesis of more complex materials such as binary materials. An initial attempt was made to electrochemically synthesize semiconducting cadmium selenide nanostructures using a modification of the metal deposition method.