Article pubs.acs.org/JPCA
Investigation of Carbon Buildup in Simulations of Multi-Impact Bombardment of Si with 20 keV C60 Projectiles Kristin D. Krantzman,*,† Clarissa A. Briner,† and Barbara J. Garrison‡ †
Department of Chemistry and Biochemistry, College of Charleston, 66 George Street, Charleston, South Carolina 29424, United States ‡ Department of Chemistry, Penn State University, 104 Chemistry Bldg. University Park, Pennsylvania 16802, United States ABSTRACT: Beams of single C+ ions are used for the incorporation of Si in the synthesis of thin films of SiC, which have a wide range of technological applications. We present a theoretical investigation of the use of C60 cluster beams to produce thin films of SiC on a Si substrate, which demonstrates that there are potential advantages to using C60+ cluster ion beams over C+ single ion beams. Molecular dynamics simulations of the multi-impact bombardment of Si with 20 keV normal incident C60 projectiles are performed to study the buildup of carbon and the formation of a region of Si−C mixing up to a fluence of 1.6 impacts/nm2 (900 impacts). The active region of the Si solid is defined as the portion of target that contains almost all of the C atoms and the height ranges from 3 nm to more than 7 nm below the average surface height. The C fraction in the active region is calculated as a function of fluence, and a simple model is developed to describe the dependence of the C fraction on fluence. An analytic function from this model is fit to the data from the molecular dynamics simulations and extrapolated to predict the fluence necessary to achieve equilibrium conditions in which the C fraction is constant with fluence. The fraction of C atoms at equilibrium is predicted to be 0.19, and the fluence necessary to achieve 90% of this asymptotic maximum value is equal to 4.0 impacts/nm2. with C60+ demonstrate that the results are highly dependent on the incident kinetic energy of the ion beam.7,8 At energies above ∼12 keV, the resulting surface contains both Si and C; at energies below this value, a uniform amorphous carbon layer is deposited on top of the silicon substrate. Simulations predict that ∼50 out of the 60 carbon atoms in C60 implant into the silicon regardless of the incident energy or the chemical composition of the surface, which has been varied from pure Si to SiC to diamond.9 At incident kinetic energies below ∼12 keV, the average sputtering yield is
