Growth of Graphene Films on Pt(111) by Thermal Decomposition of Propylene
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Graphene is a single atomic layer of graphite. Several methods for producing graphene have been found, the first being the mechanical exfoliation from a graphite crystal. In this study we attempt to produce single-layer graphene by decomposition of propylene on the surface of Pt(111). Platinum has a face centered crystal structure, and the (111) plane forms a closepacked layer of atoms, which has a hexagonal symmetry. Graphene crystallizes in the honeycomb structure, which also has a hexagonal symmetry. Therefore, the Pt(111) surface has the proper symmetry for the growth of epitaxial graphene layers. Furthermore, platinum is a natural catalyst for the decomposition of organic molecules. The goal of this project was to form graphene films by catalytic decomposition of propylene at a low enough temperature to prevent the solvation of carbon into the bulk of the platinum, which would cause multilayer graphene formation upon cooling of the crystal.</p> <p>Two methods of growing graphene films were attempted: a) deposition of a propylene layer at low temperature (room temperature or at -175 °C) followed by annealing and b) deposition of propylene on the platinum crystal that was held at high temperature (475 °C). The deposition of propylene on Pt(111) at room temperature was found to form a p(2x2) overlayer from the low energy electron diffraction measurements. Upon annealing, the p(2x2) overlayer dissapeared and a ring structure associated with graphene was found to form at 700°C. Deposition of propylene at -175 °C resulted in an increase in difuse background with no p(2x2) diffraction pattern being observed. Annealing to 700 °C also produced a ring structure associated with graphene. Dosing propylene at 475 °C resulted in an almost total loss of the Pt(111) diffraction pattern for doses beyond a few Langmuir. Since carbon has a solubility of 0.5 atomic percent at 500 °C, the carbon atoms from the dissociated propylene are most likely diffusing into the surface region of the platinum. Because a temperature of 700 °C is needed to order the graphene overlayer, it was determined that the relatively high solubility of carbon in platinum below 700 °C prevents the formation of self-terminated single-layer graphene.