Overtone atomic force microscopy studies of decagonal quasicrystal surfaces

The surface of a decagonal Al-Ni-Fe quasicrystal was investigated by overtone AFM, a special type of force modulation microscopy (FMM), where the cantilever is driven at a frequency higher than the fundamental flexural mode of the cantilever in contact with the surface. The resonance behaviour of the cantilever sample system was studied with finite element analysis (FEA). Using the excitation frequency of a torsional vibration of the cantilever, an image contrast could be obtained, which is dominated by the shear stiffness of the material. Differently orientated decagonal grains, as well as lamellae structures of different phases could be resolved on the quasicrystalline specimen. It is shown that the elastic anisotropy of the material gives rise to the contrast formation in overtone microscopy.