In Situ STM Observation of Self-assembled Monolayers of 2-Amino-6-purinethiol on Au(111) Electrodes

Abstract

In situ scanning tunneling microscopy (STM) was employed to study self-assembled monolayers of 2-amino-6-purinethiol on Au(111) in a sodium perchlorate solution (PH 6.6). In situ STM images disclosed that the 2-amino-6-purinethiolate monolayer consisted of molecularly ordered domains. Ordered molecular rows were predominantly aligned to the directions of the Au(111) atomic rows, and the 2-amino-6-purinethiolate molecules were vertically oriented through S and N atoms onto the Au(111) surface with the purine ring nearly parallel to the Au(111) atomic rows. Bright protrusions were also observed in places of the ordered monolayers, suggesting that differently oriented 2-amino-6-purinethiolates existed in the monolayer. The molecules in the protrusion adsorbed through S and other N atoms with an orientation of the purine ring slightly standing up to the surface normal. It was demonstrated for the first time that in situ STM revealed the molecular orientations and surface morphology of the 2-amino-6-purinethiolate monolayer in solution.