Understanding the Formation of Etching Patterns Using a Refined Monte Carlo Simulation Model

Abstract

Tailor-made additives of acetaminophen were shown to be very effective in changing the etching patterns on the cleaved surface of the single crystal (i.e., the (010) face in an aqueous environment). The shape of the etch pits was “mutated” from a parallelogram to a square shape when the concentration of additives was increased. Monte Carlo simulation was carried out to study the formation mechanism of the square-shaped etch pit. When the intermolecular interactions between acetaminophen on the surface were treated the same as in the bulk, including the adsorption of additive molecules alone failed to align the additive-terminated kink sites perpendicular to the c axis. Therefore, it has been hypothesized that an additive molecule can stabilize a “relaxed” state of molecules on the surface of the crystal that may form stronger interactions with its neighboring molecules along the [102] axis. Such a relaxed state is possible only if the two neighboring sites along the [102] direction are unoccupied by host molecules because of the extra space that would be required for the methyl group's motion. Supporting evidence for the concept was found in the literature.