The interaction of C60 on Si(111) 7 × 7 studied by supersonic molecular beams: Interplay between precursor kinetic energy and substrate temperature in surface activated processes

Abstract

Buckminsterfullerene (C60) is a molecule fully formed of carbon that can be used, owing to its electronic and mechanical properties, as “clean” precursor for the growth of carbon-based materials, ranging from π-conjugated systems (graphenes) to synthesized species, e.g., carbides such as silicon carbide (SiC). To this goal, C60 cage rupture is the main physical process that triggers material growth. Cage breaking can be obtained either thermally by heating up the substrate to high temperatures (630°C), after C60 physisorption, or kinetically by using supersonic molecular beam epitaxy techniques. In this work, aiming at demonstrating the growth of SiC thin films by C60 supersonic beams, we present the experimental investigation of C60 impacts on Si(111) 7 × 7 kept at 500°C for translational kinetic energies (KEs) ranging from 18 to 30 eV. The attained kinetically activated synthesis of SiC submonolayer films is probed by in situ surface electron spectroscopies (X-ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy). Furthermore, in these experimental conditions, the C60-Si(111) 7 × 7 collision has been studied by computer simulations based on a tight-binding approximation to density-functional theory. Our theoretical and experimental findings point toward a kinetically driven growth of SiC on Si, where C60 precursor KE plays a crucial role, while temperature is relevant only after cage rupture to enhance Si and carbon reactivity. In particular, we observe a counterintuitive effect in which for low KE (below 22 eV), C60 bounces back without breaking more effectively at high temperature due to energy transfer from excited phonons. At higher KE (22 < K < 30 eV), for which cage rupture occurs, temperature enhances reactivity without playing a major role in the cage break. These results are in good agreement with ab initio molecular dynamics simulations. Supersonic molecular beam epitaxy is thus a technique able to drive material growth at low-temperature regime.