A Scanning Tunneling Microscopy Study on Atomic Carbon and Nitrogen on Pt(111)

In this thesis, a microscopic picture on the structure of atomic carbon and nitrogen on Pt(111) is provided via scanning tunneling microscopy (STM). Moreover, using graphene as a template, fabrication of Pt nanoclusters is discussed according based on the unique property of the graphene/Pt(111). In addition, manipulation of individual atoms/molecules is investigated on nitrogen covered Pt(111) by low temperature (LT) STM. Carbon on metal surfaces forms graphene with periodically arranged superlattices when annealed to elevated temperatures, which is manifested as moiré patterns in the STM images. Different rotational domains of graphene on Pt(111) are observed due to a weak interaction between the graphene and the Pt substrate. The multitude of moiré patterns on Pt(111) results in the unique behavior in the formation of Pt nanoclusters on graphene/Pt(111), where Pt nanoclusters form one-dimensional chains along moiré boundaries. Atomic nitrogen is present in two well-ordered phases, (2 × 2) and (√3 × √3)R30°, at high coverages, where it occupies the fcc-hollow sites in both phases. Hydrogenation of the (2 × 2)-N layer forms scattered NH molecules and islands of NH, which is presumably due to the direct and indirect channel for H2 dissociative adsorption on N covered Pt(111). Induced by tunneling electrons, NH(ND) dissociation and H(D) hopping are observed, which are both found to be vibration-mediated reactions as revealed by the action spectroscopy (AS). NH bond breaking occurs when the stretching mode of N‒H is activated. Hopping of H atoms is triggered when the Pt‒H stretch mode is activated and is coupled to the hindered translational mode. Substituting hydrogen by deuterium reveals that the reaction rate of ND dissociation is reduced due to a smaller tunneling rate. D hopping with excitation energy larger than 245 meV indicates an over-the-barrier mechanism, while the reaction rate is attributed to intermode transition. With energy smaller than the hopping barrier, which is the case of exciting the ν(Pt-D) mode, hopping rate is greatly reduced as tunneling of D is involved.