Titanium dioxide thin films are obtained by CVD on low temperature substrates (60±210 C) using perpendicular irradiation from a long pulse 308 nm excimer laser. Titanium tetra-isopropoxide is used as the precursor in an oxygen-containing atmosphere with a total pressure in the chamber of 10 mbar. An empirical law describing the growth rate as a function of the experimental parameters (substrate temperature and laser fluence) is derived. The deposited thickness is proportional to the number of photons and has an Arrhenius dependence on the substrate temperature. Low growth rates per pulse (less than 0.1 nm per pulse) obtained allow a good control of the deposited thickness, while the use of high laser repetition rates leads to high temporal growth rates (up to 100 nm min ±1 ).
Titanium dioxide thin films are obtained by CVD on low temperature (60±210 C) substrates using perpendicular irradiation from a long pulse XeCl excimer laser (308 nm). The precursor, tetra-isopropoxide titanium, is used in an oxygen-containing atmosphere with a total pressure of 10 mbar in the chamber. X-ray photoelectron spectroscopy (XPS) analyses show that the chemical composition of the film, independent of the deposition parameters, is TiO 2 with some additional surface carbon contamination. Depending on deposition parameters, the film crystallinity varies between amorphous, anatase, and rutile. Numerical temperature simulations and sample characterization show that the crystalline state of the deposited material evolves from amorphous to anatase to rutile with an increase in the laser-induced temperature. Additionally, substrate temperature and laser repetition rate strongly influence the phase-transition behavior.
Light induced chemical vapor deposits of titanium dioxide are achieved on poly͑methyl methacrylate͒ substrates from titanium tetraisopropoxide with a long pulse ͑250 ns͒ 308 nm XeCl excimer laser, using a mask imaging setup. Similarly to other results obtained on nonpolymeric substrates, localized deposits are achieved in the irradiated area, and the deposited thickness is precisely controlled. This paper focuses on the limitations of the process on polymeric substrates due to laser induced thermal effects. Based both on experimental results and theoretical laser induced temperature rise simulations, the laser induced heating is shown to be responsible for (i) the limitation of the used laser fluence to values below 20 mJ cm Ϫ2 pulse Ϫ1 so as not to damage the substrate, (ii) the appearance of cracks in the deposited films above a certain thickness, and (iii) the amorphous state and the 9% carbon contamination of the deposited material which is obtained at the imposed low fluences.Light induced chemical vapor deposition ͑LICVD͒ using excimer lasers in perpendicular irradiation was demonstrated to allow the deposition of titanium dioxide from titanium tetraisopropoxide and oxygen at low substrate temperatures, even room temperature. 1-3 However, LICVD on highly temperature-sensitive substrates like polymers are rarely described. Tokita and Okada 1 are, to the best of our knowledge, the only researchers to claim deposition on polymer ͑polypropylene͒ substrates, but they did not give any further details on the process. Deposition of titanium dioxide thin films on polymers is of industrial interest for different applications, e.g., optical coatings. Some successful techniques are described in the literature, like sol-gel, 4 pulsed laser deposition, 5 radio frequency magnetron sputtering, 6 reactive ion beam assisted deposition, 7 and vacuum arc deposition. 8 LICVD is a very interesting alternative as it allows direct patterning of the deposits and precise control of the deposited thickness, as we already showed on inorganic substrates. 9,10 In this work, we report the feasibility of LICVD deposition on poly͑methyl methacrylate͒ ͑PMMA͒ and evidence the limitations of the technique due to laser induced thermal effects. Experimental and TheoreticalDeposition techniques.-A precise description of our homemade LICVD reactor was reported elsewhere. 9 Briefly, a long pulse ( ϭ 250 ns) XeCl excimer laser ( ϭ 308 nm) irradiates perpendicularly the PMMA substrate placed on a temperature-controlled plate ͑60°C͒. Titanium tetraisopropoxide ͑TTIP, kept in a bubbler at 30°C͒ is brought in the chamber by an oxygen carrier gas flow ͑43 standard cubic centimeters per minute ͑sccm͒, line temperature: 60°C͒ while a nitrogen flow ͑150 sccm͒ is directed onto the window to prevent deposition on it. The total pressure in the chamber is kept at 10 mbar. A freestanding mask is imaged on the substrate by a single lens. The laser energy per pulse is measured by a pyroelectric detector and regulated by an attenuator. In this process, the deposit...
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