Si/C/H ReaxFF reactive potential for silicon surfaces grafted with organic molecules

Abstract

In this work, we developed Si/C/H ReaxFF force field for the study of the functionalization and decomposition of alkyl monolayers on silicon surface. The parameterization was performed based on the main reactions involved in the decomposition of alkyl layers on small silicon clusters. The decomposition mechanisms observed in the molecular dynamics (MD) simulations were validated by the comparison of ReaxFF energy barriers for the elementary steps of the main mechanisms with density functional theory (DFT) calculations. Activation energy barriers obtained from the MD simulations from Arrhenius plots are in excellent agreement with the values calculated from DFT. The trends in the pre-exponential factor with the alkyl chain length follow the predictions of transition state theory. The results confirm that the main decomposition mechanism of the alkyl chains is the alkene elimination to the gas phase after a β-hydride abstraction by silyl radicals, which are formed in a previous step. The ReaxFF force field was used to comparatively investigate the alkyl surface coverage of Si(111), Si(100)-2 × 1 and "half-flat" Si(100) surfaces as a function of the alkyl chain length, showing good agreement with reported experimental values. Both the DFT and ReaxFF MD calculations predict that decyl monolayers with coverages as high as 0.8 are thermodynamically stable at moderate temperatures.