Understanding water film assisted CO intercalation underneath Ir(111) supported graphene

Abstract: The aim of this project is to use scanning tunneling microscopy (STM) to investigate how a super-dense phase of OH and H2O, intercalated between graphene flakes and their Ir(111) substrate, facilitates intercalation of CO underneath the graphene flakes at ultra high vacuum (UHV) conditions. The structure and growth of pristine graphene flakes on Ir(111) is discussed and the formation of dense islands of OH and H2O formed below the graphene flakes upon exposure to O2 and H2, is studied using STM. It is shown that these dense OH-H2O islands are primarily formed along the Ir(111) step edges, below the graphene flakes. Saturating the surface with CO after forming the OH-H2O islands leads to digital intercalation of the graphene flakes where the flakes are either fully intercalated by CO or not at all. By lowering the CO exposure partly, CO-intercalated graphene islands are imaged with STM and these images reveal that the CO intercalation phase spreads out from the OH-H2O islands located at the Ir(111) step edges. This observation suggest a mechanism for the CO intercalation in which CO diffuses along the Ir(111) step edges into dense OH-H2O islands and from there spreads out under the graphene flakes.