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TiO2 nanorods in the brookite phase, having a mean size of 5 nm×50 nm, were prepared through a chemical route. The nanorods were dissolved in pure to luene (0,016 wt % TiO2). The solution was frozen at the liquid-nitrogen temperature and used as a target for the matrix-assisted pulsed laser evaporation (MAPLE) process. Target irradiation was accomplished with a KrF excimer laser (λ=248 nm,τ=20 ns), operated at fluences from F=25 to 350 mJ/cm2. Films were deposited at the repetition rate of 10 Hz using 6000 laser pulses. Film thickness resulted to be ∼ 100 nm at the highest fluence. It was not possible to use a higher number of laser pulses due to the melting of the target (~ 5 mm thick with a diameter of ~ 2.5 mm), even if continuously refrigerated at the LN temperature. Several substrates were used to fully characterize the deposited layers: single-crystal Si wafers, silica slides, Cu carbon-coated grids and alumina interdigital slabs. High-resolution scanning and transmission electron microscopy investigations evidenced the formation of quite rough films incorporating individually distinguishable TiO2 single nanorods. Crystalline spheres were also detected in films, starting from the threshold fluence of 50 mJ/cm2 . Surface density and dimension of the spheres increase with increasing laser fluence. The sphere formation process and the target melting are discussed and attributed to nanosize effects. Films were positively tested as resistive sensors towards very low NO2 concentrations (≅ 1 ppm).
Institute of Electronics, Bulgarian Academy of Sciences
Publication date: 
1 Jan 2011

Anna Paola Caricato, M Belviso, Pantaleo Davide Cozzoli, Maura Cesaria, A Luches, MG Manera, Maurizio Martino, R Rella, A Taurino

Biblio References: 
Pages: 1-1
19 th International Conference on Advanced Laser Technologies–ALT’11