Study of structures at the boundary and defects in organic thin films of perchlorocoronene by high-resolution and analytical transmission electron microscopy

摘要

Both the periodic and non-periodic structures of perchlorocoronene (C_(24)Cl_(12)) crystals were characterized by high-resolution transmission electron microscopy (HRTEM), electron diffraction (ED), electron energy-loss spectroscopy (EELS), and energy-filtered transmission electron microscopy (EFTEM). The HRTEM images at the boundary of the C_(24)Cl_(12) crystals exhibit the flexibility of defect structures, where molecules align to compensate for the discontinuity between two different domains. Emphasized by the filtered images, it was found that the non-periodic regions are created everywhere with a small electron beam irradiation (~10~6 electrons nm~(-2)) and then spread over the entire regions to completely destroy the periodic structures after a higher electron dose (~2 x 10~6 electrons nm~(-2)). The effect of the electron beam irradiation was monitored by ED, EELS, and EFTEM, where periodic structures and content elements are well preserved up to 10~6 electrons nm~(-2), but chlorine atoms decreased with a much higher electron dose. This is explained by the breakage of the C-Cl bond to detach chlorine atoms, confirmed by energy-loss near the edge structures (ELNES) of carbon π* peaks and chlorine loss at the edge of the specimen, as well as by theoretical simulation. The detachment of chlorine is localized at the peripheral edge around a hole confirmed by core-loss EFTEM imaging.