Influence of Vacancies and Grain Boundaries on the Diffusive Motion of Surface Rolling Molecules
A Nemati and HN Pishkenari and A Meghdari and SS Ge, JOURNAL OF PHYSICAL CHEMISTRY C, 124, 16629-16643 (2020).
Molecular machines and surface rolling molecules show great potential to accomplish different tasks in several fields, such as bottom-up assembly and nanomanipulation. Many researchers have investigated molecular machines, most of which was on a flat single-crystal substrate. In this paper, we studied the influence of vacancies in different sizes on the motion of a nanocar, a nanotruck, and C-60 on a gold substrate at different temperatures by employing classical all-atom molecular dynamics. At the temperature of 200 K, a hole or vacancy appears as a repellent obstacle in the path of C-60, and at higher temperatures, C-60 can enter this hole. Although C-60 has enough energy to escape single- atom vacancies at 400 K or higher temperatures, larger holes become permanent traps for C-60. We also studied the nanocar motion at the temperature range of 400-600 K. A nanocar has a flexible chassis, which provides short-range freedom for fullerene wheels. The impact of a hole on nanocar motion is almost similar to C-60. The nanocar is capable of releasing itself from a 1-atom hole; however, it cannot escape larger holes. Becoming trapped inside holes at temperatures of 500 and 600 K disrupts the diffusive motion of the nanocar. A nanotruck has a relatively rigid chassis, which limits the motion of the wheels. As a result, a 9-atom or larger hole appears as an impenetrable obstacle blocking the nanotruck path. We can conclude that irregularities and vacancies in grain boundaries can drastically affect the surface rolling molecules. In certain conditions, C-60 can pass over the grain boundary. However, holes in the grain interface will most likely prevent the free movement of nanocars by either repelling or trapping them. Therefore, a single-crystal substrate is essential for the uninterrupted motion of nanocars, C-60, and other similar surface rolling molecules. The repellent effect of holes can be utilized to direct the diffusive motion of nanocars and guide them in a desired path in certain conditions. Since nanocars and C-60 get trapped inside holes in some situations, we can employ this effect to build a two-dimensional (2D) pattern of C-60 molecules and nanocars or fix them in place for more precise experimental investigations.
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