Microfabrication by UV femtosecond laser ablation of Pt, Cr and indium oxide thin films

We demonstrate the direct deposition of Pt, Cr and In2O3 microstructures on glass using a femtosecond laser assisted technique. A metal (Pt, Cr) or oxide (In2O3) source film is first deposited on an optically transparent quartz carrier and is brought in intimate contact with a receiver glass substrate using an especially designed vacuum cell. An ultrashort excimer laser pulse ablates the source film at the quartz/film interface and results in the forward-transfer deposition of material onto the nearby glass receiver. The morphology of the ablated and transferred features was studied by means of scanning electron and atomic force microscopies. It was found that the good adhesion of the pre-deposited source film on the quartz substrate and the intimate contact between the source and receiver glass are two critical factors for achieving efficient transfer printing. The optimal deposited morphology in terms of spatial resolution and dispersion was produced using 30–40 nm and 50–60 nm thick source films of metals and In2O3 respectively. In addition, the laser fluence had to be just above the threshold for printing (Epr). This was 150±20 mJ/cm2 for Pt, Cr and 60±20 mJ/cm2 for the In2O3. Fluences greater than Epr lead to the development of crater like features with excessive spread on the periphery rim. Similar behaviour was observed for micro-prints obtained using a backward-transfer configuration. Sub-micron Pt dots were obtained from a 30 nm thick Pt source film, irradiated with a 3 μ×3 μm spot at a fluence of 150 mJ/cm2. The production of these sub-micron dots was possible due to limited thermal diffusion and sharp ablation threshold existent in fs laser processing.