The role of the substrate material type in formation of laser induced periodical surface structures on ZnO thin films

Laser induced periodical surface structures (LIPSS) are obtained on extended area of zinc oxide thin films by femtosecond laser pulses. The ZnO films deposited by pulsed laser deposition (PLD) technique were irradiated by femtosecond laser beam with 200 fs pulse duration, at 775 nm central wavelength and 2 kHz repetition rate. The irradiation conditions such as laser fluence and scanning speed were varied for each sample. The morphology and the crystalline structure of the LIPSS on ZnO films were investigated by scanning electron microscopy (SEM) and X-ray diffraction (XRD) for different substrates such as fused silica, crystalline SiO2, MgO, Al2O3, or Si wafers with different crystal orientation. The LIPSS appear on all ZnO films, deposited on crystalline substrates, as well as on amorphous substrates. However, more irregular nanostructures, such as bifurcations or nanodroplets were observed on ZnO with MgO, and r-Al2O3 substrates. The ZnO LIPSS are polycrystalline when fused silica, and SiO2 (0 0 0 1) substrates are used.