LAUSR

DOI: 10.1002/admi.201900401 Laser-based patterning performs well in this domain since lasers facilitate contactless, fast, and reliable micromachining over extended surface areas. On the production scale, direct laser ablation of ITO thin films achieves spatial resolutions in the range of 5–50 μm.[14–16] Feature sizes down to the submicron scale can be realized on the laboratory scale; however, industrial use of laser direct writing with submicron resolution is barely viable due to prohibitively long processing times required for pattern formation over extended surface areas.[17–19] An elegant solution for submicron patterning with high throughput is the utilization of laserstimulated self-organization. In particular, a phenomenon called laser-induced periodic surface structures (LIPSS) offers great potential for robust submicron patterning over extended surface areas.[20–22] The formation of LIPSS in ITO has already been demonstrated. Studies concerning this topic were conducted with ultrafast lasers and are primarily focused on alterations of structural and chemical aspects or rather changes of the electrical and optical properties of ITO resulting from LIPSS generation.[23–29] In general, LIPSS are stimulated when a material is subjected to pulsed laser irradiation under conditions that trigger specific light-matter feedback mechanisms. Performed with nanosecond pulsed lasers, this characteristically generates surface ripples featuring periodicities close to the laser wavelength which are currently referred to as low-spatial frequency LIPSS (LSFL).[30] The exact mechanism of LIPSS formation is still under debate. LSFL are currently regarded as the result of interference between incident wave fronts and surface scattered waves or rather surface plasmon polaritons.[31–35] Resulting fringe patterns transpose their periodically alternating photonic flux densities into morphological, structural, and compositional transformations that can give rise to electrical, catalytic, and magnetic surface patterns.[36] In this study, LIPSS are utilized for the rapid patterning of ITO films coated on borosilicate glass. The process is performed by scanning the focused beam of a linearly polarized nanosecond pulsed laser over the substrate. Resultant LIPSS are oriented parallel with regard to laser polarization and feature an average periodicity of 350 nm at normal laser beam incidence. A self-organization phenomenon named laser-induced periodic surface structures (LIPSS) is utilized for pattern formation in indium–tin oxide (ITO) transparent conductive films coated on borosilicate glass. Stripe patterns with periodicities down to 175 nm are created by scanning the focused beam (30 μm spot diameter 1 e−2) of a nanosecond pulsed laser operating at 532 nm wavelength over ITO films. Highly ordered ITO-LIPSS are generated at a pulse duration of 6 ns, pulse frequencies between 100 and 200 kHz, pulse energies around 20 μJ, and laser spot scan speeds in the range of 50–80 mm s−1. Resulting nanopatterns are electrically conductive and feature improved optical transparency as well as stability against strong acids such as hydrochloric acid, sulfuric acid, and even aqua regia. The formation of mixed phases between ITO and silicon is considered to be the origin for the chemical robustness of laser patterned transparent conductive electrodes.