Interfacial rearrangements and strain evolution in the thin film growth of ZnPc on glass

We report on the characterization of the growth of vacuum-deposited zinc phthalocyanine (ZnPc) thin films on glass through a combination of in situ grazing incidence x-ray scattering, x-ray reflectivity, and atomic force microscopy. We found that the growth at room temperature proceeds via the formation of two structurally unique substrate-induced interfacial layers, followed by the growth of the gamma-ZnPc polymorph thereafter (thickness approximate to 1.0 nm). As the growth of the bulk gamma-ZnPc progresses, a substantial out-of-plane lattice strain (approximate to 15% relative to gamma-ZnPc powder) is continually relaxed during the thin film growth. The rate of strain relaxation was slowed after a thickness of approximate to 13 nm, corresponding to the transition from layer growth to island growth. The findings reveal the real-time microstructural evolution of ZnPc and highlight the importance of substrate-induced strain on thin film growth.