Modification of ZnO thin films induced by high-density electronic excitation of femtosecond KrF laser

Abstract

The effect of laser irradiation on nanoscale morphology of ZnO thin films has been studied in the regime of high-density electronic excitation. A femtosecond KrF laser (248 nm, 450 fs) was used to irradiate the films prepared by solgel (SG) and pulsed laser deposition (PLD) methods with fluences below ablation threshold and above that of Mott density. This regime corresponds to electron-hole plasma (EHP) creation, resulting in a specific nanostructuring of monocrystalline ZnO surfaces. A strong nanoscale modification of thin films in the domain of laser fluences 105  mJ/cm2<E<180  mJ/cm2 has been evidenced. While PLD films maintain a smooth surface with nanoholes arranged in straight and zig–zag lines (similar to ZnO monocrystals) surrounded by domains of ∼100  nm size, SG films show the flake-like structure with an open porosity. This behavior can be related to the density of the prepared films.