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Abstract:The Raman spectroscopy method was used for structural characterization of TiO 2 thin films prepared by atomic layer deposition (ALD) and pulsed laser deposition (PLD) on fused silica and single-crystal silicon and sapphire substrates. Using ALD, anatase thin films were grown on silica and silicon substrates at temperatures 125-425 • C. At higher deposition temperatures, mixed anatase and rutile phases grew on these substrates. Post-growth annealing resulted in anatase-to-rutile phase transitions at 750 • C in the case of pure anatase films. The films that contained chlorine residues and were amorphous in their as-grown stage transformed into anatase phase at 400 • C and retained this phase even after annealing at 900 • C. On single crystal sapphire substrates, phase-pure rutile films were obtained by ALD at 425 • C and higher temperatures without additional annealing. Thin films that predominantly contained brookite phase were grown by PLD on silica substrates using rutile as a starting material.

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Graphene as a single-atomic-layer material is fully exposed to environmental factors and has therefore a great potential for the creation of sensitive gas sensors. However, in order to realize this potential for different polluting gases, graphene has to be functionalized -adsorption centers of different types and with high affinity to target gases have to be created at its surface. In the present work, the modification of graphene by small amounts of laser-ablated materials is introduced for this purpose as a versatile and precise tool. The approach has been demonstrated with two very different materials chosen for pulsed laser deposition (PLD) -a metal (Ag) and a dielectric oxide (ZrO2). It was shown that the gas response and its recovery rate can be significantly enhanced by choosing the PLD target material and deposition conditions. The response to NO2 gas in air was amplified up to 40 times in the case of PLD-modified graphene, in comparison with pristine graphene, and it reached 7-8% at 40 ppb of NO2 and 20-30% at 1 ppm of NO2. The PLD process was conducted in a background gas (5 x10 -2 mbar oxygen or nitrogen) and resulted in the atomic areal