Growth of iron phthalocyanine nanoweb and nanobrush using molecular beam epitaxy

We present a detailed study on the growth and characterization of iron phthalocyanine (FePc) nanostructures using molecular beam epitaxy. FePc films of nominal thickness varying between 30 and 500 nm have been deposited as a function of substrate temperature (25-300 degrees C) and deposition rate (0.02-0.07 nm/s). Several interesting results have been observed. (1) For a growth temperature up to 200 degrees C, FePc grows in a-phase; while at growth temperatures > 200 degrees C formation of P-phase also takes place. (2) Film thickness has a profound influence on the morphology: for thickness <= 60nm well-defined nanorods with crystallographic a-axis orientated normal to the substrate plane are formed, while for higher thicknesses a-axis oriented nanarods coalescence to each other which results in the random grain growth. (3) The morphology of a 60 nm a-phase film, at a growth temperature of 200 degrees C, can be tuned from nanobrush (nearly parallel nanorods aligned normal to the substrate plane) to nanoweb (nanowires forming a web-like structure in the plane of the substrate) by changing the deposition rate from 0.02 to 0.07nm/s. (4) Both alpha-FePc nanobrush and nanoweb morphology turn into polycrystalline beta-phase on annealing at 225 degrees C for prolonged durations. We propose growth mechanisms of nanoweb and nanobrush morphology based on the van der Waals (vdW) epitaxy. (c) 2008 Elsevier B.V. All rights reserved.