Fabrication of micro/nano crystalline ITO structures by femtosecond laser pulses

A method is proposed for the fabrication of micro/nano crystalline indium tin oxide (c-ITO) structures using a Ti:Sapphire laser with a repetition rate of 1 kHz and a wavelength of 800 nm. In the proposed approach, an amorphous ITO (a-ITO) thin film is transformed into a c-ITO micro/nano structure over a predetermined area via laser beam irradiation, and the residual a-ITO thin film is then removed using an etchant solution. The fabricated c-ITO structures are observed using scanning electron microscopy (SEM) and cross-sectional transmission electron microscopy (TEM). The observation results show that the use of a low repetition rate laser induces a high thermal cycling effect within the ITO film and therefore prompts the formation of micro-cracks in the c-ITO structure. In addition, it is shown that as the laser power approaches the ablation threshold of the a-ITO thin film, nanogratings and disordered nanostructures are formed along the center lines of the c-ITO patterns formed using linearly polarized and circularly polarized laser beam irradiation, respectively. The nanogratings are found to have a period of approximately 200 nm (i.e. one-quarter of the irradiation wavelength), while the nanostructures have an average diameter of approximately 100-160 nm.