Photochemical reaction based on a nonadiabatic transition by an optical near-field observed in chemical vapor deposition

Optical chemical vapor deposition using an optical near-field (NFO-CVD) was used to fabricate nanometric Zn dots under a nonadiabatic photochemical process. In the nonadiabatic photochemical process, the molecular vibration states in the reacting molecule (zinc-bis(acetylacetonate):(Zn(acac)2)) are excited optically. We investigated the dependency of the deposition rate on the separation between the top of the deposited Zn dot and the apex of the fiber probe. With separations from 5 to 17 nm, the reaction and dissociation rates increased as the separation decreased, i.e., narrowing the separation increases the overlap integration of the wave functions between the ground and excited states of the molecular vibration mode. With separations narrower than 5 nm, the reaction rate decreased rapidly due to the decreasing supply of molecules to the narrow space between the substrate and the fiber probe. This experimental result strongly supported the nonadiabatic photochemical process.