Nano-Patterning by Diffraction Mask-Projection Laser Ablation

Nanostrcutures attached to a substrate promise optical and electronic applications.Moreover, applications for nanodots in various probing techniques are also aspired.So far, however, the fabrication process of most nanostructures is still very complex and often too costly for industrial use.An alternative, versatile, and fast process is laser ablation of a thin film using diffraction maskprojection.A pulsed excimer laser (wavelength 248 nm) is sent through a phase mask.The phase mask modulates the phase of the incident beam and provokes distinct diffraction maxima.Using a Schwarzschild reflection objective, the resulting interference pattern is demagnified and illuminates a thin film.When the ablation threshold of the underlying substrate clearly exceeds that of the thin film, the film is ablated at positions where the intensity is in excess of the ablation threshold of the film while the substrate remains unchanged.Different shapes of nanostructures can be fabricated this way.Applying about 1 J/cm 2 , metal nanodots (gold, nickel and others) and gratings (titanium) were fabricated with this technique using a checkerboard mask.This method is in principle applicable to every combination of thin film and substrate material, as long as the ablation threshold of the substrate is high enough in comparison to the film ablation threshold.