Surface Mobility and Nucleation of a Molecular Switch: Tetraaniline on Hematite

Understanding the dynamics of organic thin film formation is crucial to quality control in organic electronics and smart coatings. We have studied the nucleation and growth of the reduced and the oxidized states of phenyl-capped aniline tetramer (PCAT) deposited on hematite(1000) surfaces by physical vapor deposition. The fully reduced PCAT molecules form 2D islands on the surface, whereas the fully oxidized molecules form 3D islands. Through scaled island size distribution, it was found that the critical island sizes, i, for the reduced and oxidized molecules are i = 4 and 5, respectively. From the dependence of the island density on substrate temperature, the activation energies for the diffusion of the molecules away from the critical cluster were calculated to be 1.30 and 0.55 eV, respectively. At low temperatures, the reduced and the oxidized PCAT molecules form compact islands on the surface. At higher temperatures, the reduced islands become dendritic, whereas the oxidized islands become slightly d...