Influence of substrate on molecular order for self-assembled adlayers of CoPc and FePc

Self-assembled metal phthalocyanine thin films are receiving considerable interest due to their potential technological applications. In this study, we present a comprehensive study of CoPc and FePc thin films of about 50 nm thickness on technologically relevant substrates such as SiO_x/Si, indium tin oxide (ITO) and polycrystalline gold in order to investigate the substrate induced effects on molecular stacking and crystal structure. Raman spectroscopic analysis reveals lower intensity for the vibrational bands corresponding to phthalocyanine macrocycle for the CoPc and FePc thin films grown on ITO as compared to SiO_x/Si due to the higher order of phthalocyanine molecules on SiO_x/Si. Atomic force microscopy analysis displays higher grain size for FePc and CoPc thin films on ITO as compared to SiO_x/Si and polycrystalline gold indicating towards the influence of molecule–substrate interactions on the molecular stacking. Grazing incidence X-ray diffraction reciprocal space maps reveal that FePc and CoPc molecules adopt a combination of herringbone and brickstone arrangement on SiO_x/Si and polycrystalline gold substrate, which can have significant implications on the optoelectronic properties of the films due to unique molecular stacking.