Synthesis of single layer graphene on Cu(111) by C₆₀ supersonic molecular beam epitaxy

Abstract

High-kinetic energy impacts between inorganic surfaces and molecular beams seeded by organics represent a fundamental case study in materials science, most notably when they activate chemical-physical processes leading to nanocrystals growth. Here we demonstrate single-layer graphene synthesis on copper by C60 supersonic molecular beam (SuMBE) epitaxy at 645 °C, with the possibility of further reduction. Using a variety of electron spectroscopy and microscopy techniques, and first-principles simulations, we describe the chemical-physical mechanisms activated by SuMBE resulting in graphene growth. In particular, we find a crucial role of high-kinetic energy deposition in enhancing the organic/inorganic interface interaction, to control the cage openings and to improve the growing film quality. These results, while discussed in the specific case of graphene on copper, are potentially extendable to different metallic or semiconductor substrates and where lower processing temperature is desirable.Non-adiabatic molecular dynamics, Supersonic Molecular Beam Epitaxy.of in-plane carbon-carbon bonds (~ 7.4 eV per carbon atom) and of the graphene edge-metal substrate (~ 7 eV per carbon atom), and the reversibility of the growth dynamics. 1 However, high working temperatures, 3 even in excess of 1000 ºC, are needed in CVD to obtain good quality graphene layers and to initiate the desorption of the hydrogen atoms present in the hydrocarbon precursors. Furthermore, graphene growth by CVD may be critically affected by carbon solubility within the bulk and, finally, by the bond strength between carbon atoms and metal surface. Both these factors depend on process temperature conditions and, typically, CVD single-layer graphene exhibits several defects and polycrystalline structure. 4 Thus, much effort is currently devoted to a better understanding of the growth dynamics on substrate surfaces, to achieve large single-domain dimensions, optimal grain boundary matching and lower processing temperature. 4In this work, aiming at overcoming these issues, we demonstrate the possibility of inducing C60 cage unzipping by supersonic molecular beam epitaxy (SuMBE) on single-crystal (111) and polycrystalline copper surfaces. SuMBE application to graphene growth will be studied by investigating electronic and structural properties of the synthesized C60/Cu thin films and the role of thermal energy in single-layer graphene synthesis by a variety of in-situ and ex-situ experimental methods, such as electron and Raman spectroscopy and scanning microscopy techniques.Furthermore, first-principles simulations based on density functional theory (DFT) will be used: i) to simulate the C60 impact on Cu(111) surface at several kinetic energies (KE); ii) to show the 4 crucial role of non-adiabatic effects on cage breaking; iii) finally, to follow the long-time dynamics after cage rupture leading eventually to graphene formation. RESULTS AND DISCUSSION SuMBE deposition of C60 on copper, core and valence band characterization of the filmsSuMBE has been al...

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