RAPID LASER-INDUCED CRYSTALLIZATION OF THERMOCHROMIC VO2 THIN FILMS
BASSO M. 1,3, COLUSSO E. 1, CARRARO C. 2, NAPOLITANI E. 2, REGOUTZ A. 3, MARTUCCI A. 1
1 University of Padova - Department of Industrial Engineering, Padova, Italy; 2 University of Padova - Department of Physics and Astronomy, Padova, Italy; 3 Department of Chemistry - University College London, London, United Kingdom
The temperature-dependence of the optical properties of vanadium dioxide (VO2) offers great advantages for the thermal regulation of buildings: the employment of smart windows, coated with VO2 thin films, allow a passive regulation of the thermal exchange. A critical aspect of VO2 thin films obtained by wet chemistry concerns the crystallization step. Conventional thermal annealing requires temperatures above 500°C and controlled atmosphere. An alternative is offered by UV laser annealing. In this work, conventional furnace annealing was compared to the photonic curing of an excimer KrF laser. A systematic study of the different crystallization conditions was carried to evaluate the influence of the energy density and the number of pulses on the final properties. The laser-induced crystallization was reached within 60 s irradiation in air at ambient temperature, after a 10 min pre-treatment at 300°C. Threshold laser parameters to induce VO2 crystallization whilst at the same time avoiding surface melting were identified, by combining experimental results with simulations on the temperature distribution during laser irradiation. The thermochromic properties of the lasered thin films were comparable or higher with respect to purely thermally annealed ones.