Nanostructuring of Mn(II)Pc thin films by vacuum deposition in a weak magnetic field

Abstract

Manganese phthalocyanine, Mn(II)Pc, is a disc-like paramagnetic molecule whose unusual electronic structure have been studied for decades. However, no credible results on the direct impact of intrinsic molecular magnetism on the solid state properties of Mn(II)Pc are known. In this work, the Mn(II)Pc films were deposited by thermal vacuum evaporation with and without applying an external static magnetic field with a strength of a few tenths of a Tesla to the growth zone. Evolution of the microstructure of the thus formed films was documented using XRD, SEM, AFM and optical methods. In the field-free conditions, the Mn(II)Pc films deposited on the hot substrate are rather smooth, continuous and strongly textured. Large needle-like crystals (whiskers) grow when magnetic field is turned on, without noticeable correlation with the direction of field lines. However, the density of whiskers per unit area increases with increasing field strength. Possible explanations of the growth mechanism include molecular surface diffusion, adsorption energy lowering and Lorentz force but none of them is yet internally consistent.