TiO 2 –SiO 2 nanocomposite thin films deposited by direct liquid injection of colloidal solution in an O 2 /HMDSO low-pressure plasma

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Abstract
TiO 2 nanoparticles (NPs), 3 nm in size, were injected inside a very-low-pressure O 2 plasma reactor using a liquid injector and following an iterative injection sequence. Simultaneously, hexamethyldisiloxane (HMDSO) vapor precursor was added to create a SiO 2 matrix and a TiO 2 –SiO 2 nanocomposite (NC) thin film. Both the liquid injection and vapor precursor parameters were established to address the main challenges observed when creating NCs. In contrast to most aerosol-assisted plasma deposition processes, scanning/transmission electron microscopy (S/TEM) indicated isolated (i.e. non-agglomerated) NPs distributed in a rather uniform way in the matrix. The fraction of the TiO 2 NPs inside the SiO 2 matrix was estimated by SEM, spectroscopic ellipsometry (SE), and x-ray photoelectron spectroscopy. All techniques provided coherent values, with percentages between 12% and 19%. Despite the presence of TiO 2 NPs, SE measurements confirmed that the plasma-deposited SiO 2 matrix was dense with an optical quality similar to the one of thermal silica. Finally, the percentage of TiO 2 NPs inside the SiO 2 matrix and the effective refractive index of the NCs can be tuned through judicious control of the injection sequence.

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