Femtosecond Laser Induced Periodic Surface Structures on ZnO Thin Films

Laser Induced Periodic Surface Structures (LIPSS) were obtained on ZnO thin films deposited on sapphire substrate. The structures were creaded by scanning the sample surface with a focalised femtosecond laser beam in air. The period and depth of the structures were measured by Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM). The dependence of the morphology of the periodic structures on the experimental conditions such as laser fluence, laser polarisation and laser scanning speed, were investigated. Ripples with 150 nm period, spaced by grooves with 50 nm width and about 100 nm depth have been obtained on large area by multiple scanning of the sample surface. Such microprocessing method suggests a possible technique to produce nanogratings, micropolarisers, or nanopatterned surfaces for micro-sensors.