Effect of chemically modified tips on STM imaging of 1-octadecanethiol molecule

The effect of chemically modified tips on STM imaging was investigated. An electrochemical technique was used to prepare a monolayer of sulfur and iod ine on the apex of STM tips. The chemically modified STM tips were first em ployed to image a 1-octadecanethiol (1-C18H37SH) adlayer on a highly orient ed pyrolytic graphite (HOPG) surface. The images acquired with S-modified t ips could ascertain the structural detail of thiol groups of the adsorbed m olecules, while that acquired with I-modified tips appeared in a low resolu tion. The contrast variations of STM images are attributed to the changes o f electronic states of the tips.