Structural properties of iron phthalocyanine thin films on solid surfaces by drop casting deposition

Iron phthalocyanine (FePc) is a p-type organic semiconductor and it has potential applications in optoelectronics, organic magnets and catalysts. The performance of the FePc-based devices essentially depends both on the properties of the FePc molecule and on the morphology of the organic thin films formed by FePc molecules. Here, using atomic force microscopy, we studied the structural properties of FePc thin films prepared with different solvents by drop-casting method. We observed the formation of large three-dimensional aggregates on Si substrates for the high-solubility solvents, while separated two-dimensional islands and multilayer islands are formed for low-solubility solvents. An identical interlayer distance of 4.3 nm is measured in such multilayer islands, suggesting a repeated unit including four molecular layers that are stacked along the direction normal to the molecular plane of FePc inclined to the ac plane with an angle of 47.7°. Meanwhile, nanorods and short linear chains along three directions are formed on graphite and mica surfaces. Our work shows that both the solvents and the substrates can exert great impact on the thin film structure that is very valuable for the preparation of high-quality FePc thin films and devices.