Silicon Carbide (SiC) is a semiconductor with unique physical/chemical properties ideally suitable for hard and protective coatings, optoelectronics and sensing. It is the most promising alternative to Si for electronic devices working at high power/high frequency or in prohibitive conditions. A new perspective is now being pursued for SiC as material for biomedical applications, thanks to its good biocompatibility. Since it is also the substrate for synthesizing high quality Graphene, SiC is expected to be one the most promising interface for Graphene-based electronics.
Despite the use of different growth approaches, SiC synthesis of high quality/low defects crystalline films still represents an open challenge. One of the most critical parameters is the material processing temperature, typically higher than 1100 K, which is a harmful source of undesirable side-growth processes and high production costs.
SiC heteroepitaxy on Si is interesting for the cubic (3C) polytype synthesis, having potentially the best electrical properties. The epitaxy is critically affected by the high lattice/thermal mismatches between SiC and Si, leading to creation of defects. Usually, a lower synthesis T corresponds to lower defects density in the carbide film. Molecular Beam Epitaxy (MBE) has demonstrated to be a viable approach to 3C-SiC/Si synthesis at about 1200 K, using buckminsterfullerene (C60) as C precursor.
IMEM in Trento we demonstrated the room T (300 K) synthesis of nanocrystalline 3C-SiC on the Si(111)7×7 surface by kinetic activation based on the Supersonic Molecular Beam Epitaxy (SuMBE) approach with C60. Undergoing an aerodynamic acceleration in vacuum, the C60 translational kinetic energy (KE) reaches values up to 60 eV, inducing, chemical/physical out of equilibrium, processes during film growth with hyperthermal molecular beams. In situ electron spectroscopies (UPS, XPS, LEED) and ex situ microscopies (AFM, TEM) demonstrate the presence of crystalline nanoislands of 3C-SiC and a kinetic energy threshold for the synthesis process of about 35eV for C60.
Furthermore, we simulate the C60-Si(111)7×7 collision by Density Functional Theory (DFT) and we show that the cage rupture at the observed kinetic energies requires to go beyond the Born-Oppenheimer (BO) approximation and the use of non-adiabatic molecular dynamics (NA-MD) to intertwine the electronic and nuclear motion.
This work has been published on the Journal of the American Chemical Society (http://dx.doi.org/10.1063/1.4774376) and received the cover of the Journal of Chemical Physics. Our study paves the way for the creation of high quality/defect free 3C-SiC thin film, achieving islands coalescence in a codeposition scheme with different supersonic beams of Si and C precursors.
Immagini:
