Crystallization of TiO2 polymorphs from RF-sputtered, amorphous thin-film precursors

O Agirseven,A Patterson,L T Schelhas,B P Gorman,J S Mangum,K Diffendaffer,D T Rivella,J Kreb,J E S Haggerty,J D Perkins,P O Berry,J Tate,B R Chen

doi:10.1063/1.5140368

O Agirseven, A Patterson + Show 11 more

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https://doi.org/10.1063/1.5140368

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Abstract

Crystalline TiO2 films of anatase, brookite, and rutile are reproducibly made from amorphous precursors deposited by RF magnetron sputtering, producing large-area, single phase films of uniform thickness. Sputtered amorphous TiO2 precursor thin films follow the general behavior observed for amorphous precursor thin films generated by pulsed laser deposition, namely, that oxygen deficiency is necessary for the formation of brookite and rutile. We quantify the oxygen deficiency and correlate it with the long wavelength optical absorption. We find that the precursor deposition rate is also a contributing factor to phase selection and that brookite and rutile form from films deposited more rapidly and anatase from films deposited more slowly. Sputtered and pulsed laser deposited amorphous precursor films prepared with similar oxygen deficiency and similar thickness result in the same final state after annealing, but the rate for sputtered precursors is slower.

Highlights

TiO2 is a multifunctional transparent semiconductor used in industrial and technological applications such as solar cells, sensors, lithium-ion batteries, ultra-thin capacitors, photovoltaics, photocatalysts, optical waveguides, and filters.1–5 It has a high refractive index, a high dielectric constant, and a wide bandgap
We previously found that amorphous TiO2 films grown by pulsed laser deposition (PLD) annealed to different polymorphs of crystalline TiO2 and that the major factors determining which polymorphs formed were the pressure of oxygen during deposition and the thickness of the precursor film
We were unable to say whether the results were unique to pulsed laser deposition or whether they were transferable to other deposition methods. We address those questions with the results of a similar investigation of sputter-deposited TiO2 amorphous precursor films, which are of uniform thickness over a large area sputtered at different rates and to different thicknesses

Summary

Introduction

TiO2 is a multifunctional transparent semiconductor used in industrial and technological applications such as solar cells, sensors, lithium-ion batteries, ultra-thin capacitors, photovoltaics, photocatalysts, optical waveguides, and filters. It has a high refractive index, a high dielectric constant, and a wide bandgap. TiO2 is a multifunctional transparent semiconductor used in industrial and technological applications such as solar cells, sensors, lithium-ion batteries, ultra-thin capacitors, photovoltaics, photocatalysts, optical waveguides, and filters.. TiO2 is a multifunctional transparent semiconductor used in industrial and technological applications such as solar cells, sensors, lithium-ion batteries, ultra-thin capacitors, photovoltaics, photocatalysts, optical waveguides, and filters.1–5 It has a high refractive index, a high dielectric constant, and a wide bandgap. TiO2 has several polymorphs: rutile is the lowest energy state, while anatase and brookite are both metastable. It is useful to understand whether and how a metastable polymorph can be stabilized. Such knowledge on the TiO2 system could be transferred to other polymorphic material systems

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