Speaker
Description
ZnO is a multifunctional transparent conductive oxide (TCO) with many scientific and technologic uses. They include, among others, applications in biomedicine, photonics, sensing or photocatalysis. These applications could benefit in many cases from the use of large-area, electrically anisotropic surfaces (i.e. optically transparent surfaces with alternating highly conductive and highly resistive regions). It has recently been shown that such anisotropies can be induced in other TCO´s, particularly ITO1 and FTO2, by structuring the material surface with fs-laser pulses leading to the formation and of coherently-propagated low spatial frequency (LSF) Laser Induced Periodic Structures (LIPSS).
We have analyzed the role of the carrier density of the material (ne) in the formation and coherent propagation of LIPSS in ZnO films grown by Pulsed Laser Deposition (PLD) ad-hoc doped with small amounts of Yb2O3 (below 5 at. %). This induces n-type conductivity but enables preserving the functional properties of pure ZnO. For ne > 1019 cm-3 coherent propagation of LSF-LIPSS can be successfully achieved upon irradiation with 350 fs and longer pulses at 1030 nm, and laser scan speeds well above 1 m/s.
The ablation mechanism (ZnO sublimation at the LIPSS valleys), and the large melting temperature of ZnO make though the thermal conductivity of the substrate, the film thickness and the irradiation pulse duration to play a determining role in configuring the resulting morphology of the LIPPS propagated over large areas, very especially in avoiding film cracking to preserve the film conductivity along the LIPSS.
Processed surfaces can show conductivities along the LIPSS about hundred times larger than transversally. This enables the development large area applications based on LIPSS-structured surfaces, like gas sensing, or electrothermal transparent devices
Notes and References
1 Lopez-Santos, C., et al, Anisotropic Resistivity Surfaces Produced in ITO Films by Laser-Induced Nanoscale Self-Organization. Adv. Opt. Mater. 2021, 9 202001086. https://doi.org/10.1002/adom.202001086
2 Gomez-Munoz, G., et al., Formation and Coherent Propagation of Laser Induced Periodic Surface Structures (LIPSS) upon Fs-Laser-Irradiation of Fluorine-Doped Tin Oxide: Control, Potential Applications and Challenges. https://doi.org/10.1021/acsami.6c06535