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Anisotropic resistivity surfaces produced in TCO-ITO films by fs-laser induced self-organization in the nanoscale
Carmen Lopez-Santos1'2, Daniel Puerto3, Jan Siegel3, Manuel Macias-Montero3, Camilo Florian3, Jorge Gil-Rostra1, Víctor López-Flores1, Ana Borras1, Agustín R. González-Elipel,
Javier Solis3
1-Nanotechnology on Surfaces Group, Institute of Material Science of Seville (US-CSIC), Américo Vespucio
49, Seville 41092, Spain
2- Departamento de Física Atómica, Molecular y Nuclear, Facultad de Física, University of Seville, Reina
Merdedes, s/n, Seville 41012, Spain 3- Laser Processing Group, Institute of Optics (IO-CSIC), Serrano 121, Madrid 28006, Spain
j.solis@io. cfmac. csic.es
Transparent conducting oxides (TCOs) are materials with a comparably low optical absorption in the visible region of the spectrum which makes them particularly suitable for key applications in information technologies (organic light emitting diodes, flat panel displays, etc.) and energy harvesting (photovoltaics, low emissivity coatings, etc.). Among them, in spite of the scarcity of In, Indium Tin Oxide (ITO) still plays a very important role, especially in niche applications where the chemical stability in water solutions is a decisive factor (electrochemical sensors).
In this work we demonstrate the production of highly anisotropic resistivity surfaces by high repetition rate fs-laser irradiation of ITO films at 1030 nm [2]. Electrical anisotropy appears as a consequence of the formation of Laser Induced Periodic Structures (LIPSS) at the material surface. Still, the formation of LIPSS in this case involves a novel mechanism associated to the dynamical modification of the material composition at the laser exposed regions. LIPSS [3] have been coherently extended over large areas (cm-sized regions). We have identified two main optimized processing conditions (Fig.1). At the lower fluences, the material at the LIPSS ridges remains essentially unmodified while only partial ablation is observed at the valleys. In this case, the structures show a longitudinal conductivity twice the transverse one, and a resistivity similar to that of the pristine ITO film. At higher fluences, nearly complete ablation at the valleys of the LIPSS, and strong ablation at their ridges, accompanied by a preferential In-loss, lead to an insulating structure in the direction transverse to the LIPSS and conductive in the longitudinal one. The compositional changes induced as laser pulses accumulate, condition the LIPSS evolution and thus the result of the structuring process. Strategies to further improve the achieved anisotropic resistivity results are also provided.
Fig.1 (Upper row) EDX maps and cross-sectional SEM images of LIPSS induced at low and high fluence in ITO films by fs-laser processing. (Lower row) Resistivity measurements in (left) macro- and (right) micro-scale configuration of the same structures.
[1] K. Ellmer, Nat. Photonics 2012, 6, 809
[2] C. Lopez-Santos, D. Puerto, J. Siegel, M. Macias-Montero, C. Florian, J. Gil-Rostra, V. Lopez-Flores, A. Borras, A. R. Gonzalez-Elipe, J. Solis, Adv. Opt. Mater. 9, 2001086 (2020).
[3] J. Bonse, S. Hohm, S. V. Kirner, A. Rosenfeld, J. Kruger, IEEE J. Sel. Top. Quantum Electron. 2017, 23, 9000615
