Self-Assembly of n-Alkanethiolate Monolayers on Silver Nanostructures: Protective Encapsulation

Abstract

Electrochemically synthesized silver nanostructures having dimensions 200-1000 A in diameter and 20-50 A high were prepared on graphite surfaces using the scanning tunneling microscope (STM). These nanostructures were stable while immersed in aqueous solutions containing small (0.5 mM) concentrations of Ag + during repeated STM imaging at small sample-negative biases for at least 1 h. Upon exchange of the silver plating solution for pure water, dissolution of the nanostructure occurred within 30 min, irrespective of the applied imaging bias up to ±200 mV. The anodic dissolution of silver nanostructures in pure water was strongly inhibited following the formation of an n-alkanethiolate self-assembled monolayer (SAM) on the silver surface, demonstrating that molecular self-assembly provides a method for the protective, and chemically selective, encapsulation ofreactive nanometer-scale structures on solid surfaces. In contrast, self-assembly was not observed following the exposure of silver nanostructures to long-chain n-alkylamines or carboxylic acids and these prospective ligands provided no protection from dissolution of the nanostructure in pure water.