Introduction: Titanium Dioxide (TiO2) is a semiconductor that can be found under Brookite, Rutile and Anatase phases, where the former has gained relevance due to its photocatalytic features, high chemical stability, low toxicity/cost, and strong oxidizing capacity under UV light [1]. Exposing TiO2 to UV light leads to the production of indirect electronical transition that enables the formation of reactive species, with free radical hydroxyl (HO) and superoxide (O2) that promotes decomposition of organic contaminants [2]. Two techniques will be compared. Atomic Layer Deposition (ALD) is physical and requires two vapor precursors injections inside a chamber separated by the purge of an inert gas, and each precursor saturates the surface of the substrate leading to the formation of the TiO2 thin film. Hence, the ALD methodology is considered a stepped self-limiting technic [3], where the thickness of the thin film relies on the number of deposited cycles under half vacuum pressure conditions (0.1 torr). Sol-Gel is a chemical technique applied at room temperature and atmospheric pressure conditions, where simultaneous reactions are produced: hydrolysis and condensation [4]. Initially, the hydrolysis requires a metallic precursor (titanium alkoxide), solvents and acidification of the solution, which results in the formation of Titanium Hydroxides and the condensation process finally leads to the Titanium Dioxide synthesis [5]. In this work, TiO2 thin films are generated over glass substrates previously cleaned through DI water, 2propanol and acetone. For ALD the Titanium Alkoxide Tetraisopropyl Orthotitanate (Ti[OCH(CH3)2]4) was taken as precursor, and vaporized water for the formation of TiO2; under a Ni atmosphere at 20 sccm, with 1100 cycles (20 nm thick), a working temperature fixed at 200 C and pressure of 2.45x10-1 torr. For Sol-Gel, the solution was also prepared using Ti[OCH(CH3)2]4, but with ethanol (CH3CH2OH), acetic acid (CH3COOH), H2O2 and DI water, as explored in [5-7]. Solution is spin coated over hydrolyzing substrate (H2SO4 + H2O2 in 3:1 concentration. Manufactured films from both techniques, were taken to an annealing process at 450 C and 550 C, under a Ni atmosphere with a gas flux of 4000 sccm during 1 hour. The characterization of TiO2 thin films was realized before and after the annealing process, starting from X-Ray Diffraction (XRD) to the crystallin phase of the TiO2 anatase on each treatment, in order to measure the intensity of the phase in the plane (101) with an angle of 25.16±0.2° (Fig. 1) [2]. Also, the absorption spectrum was measured using the Lambert-Beer Law [8] and the bandgap energy by direct gap of the semiconductor was estimated as a function of temperature (Fig. 2); moreover, the morphology of the films surface was observed with the Scanning Eletron Microscopy (SEM) technique and the elemental analysis of the films by energy dispersive X-ray spectroscopy (EDX). Finally, the resistivity was measured using the Van der Pauw 4-point technique and the charge mobility was analyzed with Hall effect (Fig. 2). References [1] A. Ibrahim, W. Phoohinkong, W. Mekprasart, and W. Pecharapa, Mater. Today Proc., vol. 5, no. 5, pp. 10903–10909, 2018. [2] R. Katal, S. Masudy-Panah, M. Tanhaei, M. H. D. A. Farahani, and H. Jiangyong, Chem. Eng. J., vol. 384, no. October 2019, p. 123384, 2020. [3] V. Pore, A. Rahtu, M. Leskelä, M. Ritala, T. Sajavaara, and J. Keinonen, Chem. Vap. Depos., vol. 10, no. 3, pp. 143–148, 2004 [4] Brinker C. Jeffrey, p. 462, 1990. [5] M. B. Tahir, K. Nadeem, M. Hafeez, and S. Firdous, Indian J. Pure Appl. Phys., vol. 55, no. 10, pp. 716–721, 2017. [6] M. Urbonavicius, S. Varnagiris, S. Sakalauskaite, E. Demikyte, S. Tuckute, and M. Lelis, Catalysts, vol. 11, no. 7, 2021. [7] C. Villanueva Jaramillo, A. M. Pedroza, J. C. Salcedo, A. K. Carrascal Camacho, and A. E. Florido Cuellar, pp. 1–125, 2011. [8] G. L. Tian, H. B. He, and J. Da Shao, Chinese Phys. Lett., vol. 22, no. 7, pp. 1787–1789, 2005.

Atomic Layer Deposition (ALD) and Sol-Gel Techniques Comparison from the Perspective of TiO2 Thin-Films Fabrication

AA: Semiconducting Oxide Thin Films and Transistors

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Atomic Layer Deposition (ALD) and Sol-Gel Techniques Comparison from the Perspective of TiO2 Thin-Films Fabrication

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