posted on 2007-10-10, 00:00authored byRobin L. Hayes, Mark E. Tuckerman
Understanding the chemical reaction mechanisms governing how small organic molecules attach
to semiconductor surfaces can lead to new strategies for creating specific surface patterns such as single
adduct monolayers. In this study, room-temperature ab initio molecular dynamics simulations of one and
two 1,3-cyclohexadiene (CHD) molecule(s) reacting with the Si(100)-2×1 surface reveal that adducts form
via a carbocation-mediated two-step mechanism. Dimer flipping can either promote or prevent bond formation
depending on how the CHD approaches. CHDs often travel past several Si dimers before finding the proper
local environment. The resulting intermediate can persist for more than 4 ps, allowing the second bond to
form with any adjacent Si dimer. The additional reactive site accounts for a large portion of the discrepancy
between the predicted thermodynamic and observed experimental product distribution. Surface adducts
protect a 5.6 Å region, direct unbound CHD exploration, and can cause adjacent dimers to flip.