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 (C 60) 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 carbonbased materials, ranging from π-conjugated systems (graphenes) to synthesized species, e.g., carbides such as silicon carbide (SiC). To this goal, C 60 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 C 60 physisorption, or kinetically by using supersonic molecular beam epitaxy techniques. In this work, aiming at demonstrating the growth of SiC thin films by C 60 supersonic beams, we present the experimental investigation of C 60 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 C 60-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 C 60 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), C 60 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.

2D Material Armors Showing Superior Impact Strength of Few Layers

“…Usually, the terms appearing in the total energy expression are parameterized to reproduce accurately high-level electronic structure calculations for several different bonding conditions. In this way, the transferability of these precalculated terms (the so-called Slater–Koster matrix elements) to different chemical environments and physical conditions as well as a considerable reduction (around 2 orders of magnitude) of the computational cost of this approach with respect to full DFT simulations , are generally obtained. Because of this substantial speed gain, DFTB can be used to simulate systems larger than those accessible by full DFT, to follow their dynamics for longer time scales, and to test how the tuning of the DFTB parameters affects the impact dynamics at an affordable computational cost.…”

“…From a methodological point of view, approaches beyond molecular dynamics (MD) based on classical force fields have not yet been widely used for studying the impact properties of 2D nanomaterials owing to their high computational cost with increasing size of the system. Notable exceptions have been reported in modeling analogous problems, in which intermediate kinetic energy regimes (around tens of eV) were used to achieve the epitaxial growth of silicon carbide − and graphene , via buckyball beams impacting on silicon or metallic substrates.…”

“…Notable exceptions have been reported in modeling analogous problems, in which intermediate kinetic energy regimes (around tens of eV) were used to achieve the epitaxial growth of silicon carbide [27][28][29] and graphene 30,31 via buckyball beams impacting on silicon or metallic substrates.…”

Multiscale Investigation of Oxygen Vacancies in TiO2 Anatase and Their Role in Memristor’s Behavior

“…For these scattering problems, it is customary to divide the space into left-hand, center, and right-hand regions, where the former and latter represent the “leads” and the central part is the “device”. Owing to the much lower computational cost of DFTB with respect to other ab initio methods, − larger supercells can be used to perform the calculation of charge transport properties. The device region is a 6 × 2 × 1 supercell, having 144 atoms, obtained by using the unit cell lattice vectors computed by Dolgonos et al and optimizing the atomic positions.…”

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

“…In a previous work, concerned with SiC growth induced by SuMBE of C 60 on Si(111), we demonstrated that substrate temperature has very limited effect on cage breaking mechanisms. 43 Thus, we decided to perform DFT simulations at RT. Details on these simulations and the parameters used are given in Section 2.2.1.…”