Argon ion irradiation induced morphological instability of bare and thiol-functionalized Au(111) surfaces

Abstract

Ar ion irradiation-induced changes in the morphology of bare and 1-dodecanethiol self-assembled monolayer (SAM) covered Au(111) surfaces have been investigated systematically. The changes were followed by scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS) measurements while varying the ion charge (Ar⁺,Ar⁴⁺), energy (10–40 keV) and fluency (10¹²–10¹³ ions per cm²). The impact of flame-annealing of the Au(111) surface on subsequent ion bombardment was considered and more prominent related surface morphology changes were noted. The irradiation of Au(111) surfaces generated Au vacancy and adatom islands and caused roughening of step edges. The size and abundance of these islands and the level of deformation on the step edges depended strongly on the ion energy and fluency. In case of the SAM functionalized surface, the gold vacancy islands present on the surface already from the SAM formation were modified, step edges roughened and gold adatom islands formed. Similarly to the bare surface, the level of surface deformation increased as a function of ion energy and fluency. The Ar⁴⁺ irradiation caused on the average slightly larger vacancy islands on the SAM modified surfaces than the Ar⁺ irradiation. Irradiation to fluency of 10¹² ions per cm² mostly maintained standing-up orientation of the thiolates whereas irradiation to higher fluency resulted in reduced surface coverage and flat-lying molecules. As a general trend the DDT covered surfaces were more susceptible for irradiation-induced surface morphology changes than the unmodified Au surfaces.