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The Morphology of TiO2 Nanotube Arrays Grown from Atomically Peened and Non-Atomically Peened Ti Films

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The growth of TiO2 nanotube arrays (TNTAs) on non-native substrates is essential for exploiting the full potential of this nanoarchitecture in applications such as gas sensing, biosensing, antifouling coatings, low-cost solar cells, drug-eluting bimedical implants and stem-cell differentiators. The direct formation of anodic TNTAs on non-native substrates requires the vacuum deposition of a thin film of titanium on the substrate followed by subsequent electrochemical anodization of the film. In this report, we studied the effect of atomic peening on the formation of Ti thin films on technologically important non-native substrates. We compared the structure and morphology of evaporated and sputtered Ti films, and correlated them to the morphology of the vertically oriented TiO2 nanostructures that resulted subsequent to anodization of those films. We calculated a minimum value of 1.33 eV/atom for the energy of refkected neutral Ar species arriving at the substrate when a chamber pressure of 1 mTorr is used during the sputter deposition of Ti. Previous approaches relied on substrate heating to elevated temperatures during Ti thin film deposition or ion-beam assisted Ti thin film deposition as a prerequisite to form TiO2 nanotube arrays (TNTAs). We demonstrated TNTAs on a variety of substrates at room temperature using both evaporated and sputtered Ti films without recourse to ion-beam sources. Evaporated Ti films were found to possess small grain size and high local surface roughness, which resulted in nanotubes with extremely rough sidewalls. Ti thin films formed by Ar+ ion sputtering at commonly used chamber pressures of 7–20 mTorr at substrate temperatures ranging from room-temperature to 250 °C possessed a highly rough surface and three-dimensional grains, which precluded the formation of ordered nanotubes upon anodization due to highly non-uniform pore nucleation processes. In contrast, Ti thin films sputtered at low chamber pressures of 0.8–2 mTorr had a low surface roughness due to the atomic peening process. Such films, even when deposited at room temperature, resulted in ordered nanotube arrays upon anodization.

Keywords: DC Sputtering; Electron Beam Evaporation; Ion Beam Sputtering; Polymeric Substrates; Si Wafers; Vacuum Deposition; Zone Models

Document Type: Research Article

Affiliations: Department of Electrical and Computer Engineering, University of Alberta, Edmonton, AB, T6G 2V4, Canada

Publication date: July 1, 2017

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  • Journal for Nanoscience and Nanotechnology (JNN) is an international and multidisciplinary peer-reviewed journal with a wide-ranging coverage, consolidating research activities in all areas of nanoscience and nanotechnology into a single and unique reference source. JNN is the first cross-disciplinary journal to publish original full research articles, rapid communications of important new scientific and technological findings, timely state-of-the-art reviews with author's photo and short biography, and current research news encompassing the fundamental and applied research in all disciplines of science, engineering and medicine.
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