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. Kristin Krantzman has been a collaborator for almost two decades.
Investigation of Carbon Build-Up in Simulations of Multi-Impact Bombardment of Si with 20-keV C60 Projectiles, K. D. Krantzman, C. A. Briner, B. J. Garrison, J. Phys. Chem. A, 118, 8081-8087 (2014) 10.1021/jp4108624
Metal overlayers on an organic substrate
Cluster bombardments of 15 keV C60 on metal–organic interfaces composed of silver atoms and octatetraene molecules were modeled using molecular dynamics computer simulations. Dynamics revealed by the simulations include the formation of holes in the metal overlayers from which underlying organic molecules are sputtered predominantly by a rapid jetlike motion and the implantation of metal atoms and clusters in the underlying organic solid. Both of these processes negatively affect the information depth for cluster bombardment of metal–organic interfaces; therefore, the simulations presented here give a clear picture of the issues associated with depth profiling through metal–organic interfaces. Paul Kennedy is my last PhD student.
Dynamics Displayed by Energetic C60 Bombardment of Metal Overlayers on an Organic Substrate, P. E. Kennedy, Z. Postawa, B. J. Garrison, Analytical Chemistry, 85 2348-2355 (2013) 10.1021/ac303348y This publication contains three animations.
Low energy Ar co-bombardment
The use of cluster beams in secondary ion mass spectrometry enables molecular depth profiling, a technique that is essential to many fields. The success of the technique often hinges upon the chemical nature of the substrate, the kinetic energy and incident angle of the primary cluster ion beam, and the sample temperature. It has been shown experimentally that the quality of depth profiles can be improved with cobombardment by a C60 cluster beam and a low-energy argon (Ar) beam. We present molecular dynamics simulations to elucidate the mechanistic reasons for the improved molecular depth profiles with an aim of understanding whether this cobombardment approach is generally applicable. We conclude that the low-energy Ar beam breaks up the surface topology created by the C60 beam, increasing the sputtering yield and reducing the buildup of chemical damage. The simulations also suggest that an equivalent result could be achieved without the Ar cobombardment by optimizing the conditions of the C60 beam. Zack Schiffer was a high school student who worked in the group for three summers.
Molecular Dynamics Simulations Elucidate the Synergy of C60 and Low Energy Ar Co-bombardment for Molecular Depth Profiling, Z. J. Schiffer, P. E. Kennedy, Z. Postawa, B. J. Garrison, Journal of Physical Chemistry Letters, 2, 2635-2638, (2011) 10.1021/jz201219x