Thermal and substrate surface energy effects on nanostructure and surface morphology in the ultra-thin copper phthalocyanine film

Abstract

Real time grazing incidence small angle x-ray scattering (GI-SAXS) and x-ray reflectivity measurements were conducted in order to investigate the thermal evolution of the nano-grain structure and surface of 5nm thick Copper(II) Phthalocyanine (CuPc) films. The evolution was strongly influenced by the surface energy of silicon substrate. On the low surface energy (hydrophobic) Si substrate, CuPc nano-grains are randomly distributed and the crystal size did not increase in size upon thermal annealing. Thermal annealing induced a more random distribution of nano-grains with an increase in roughness, and large islands formed by the coalescence of small grains. On the high surface energy (hydrophilic) Si substrate, CuPc film consisted of disk shaped nano-grains of two different sizes. The larger grains showed lateral crystal growth and planarization by thermal annealing, while the smaller grains did not increase in size. Large clusters were observed at high temperature, which were derived by large grains. The different thermal evolution models of CuPc films based on GI-SAXS analysis are consistent with the different temperature behavior of the hole mobilities of organic field-effect transistor (OFET) devices fabricated on both surfaces.