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Open AccessArticle

Crystallization of TiO2 Nanotubes by In Situ Heating TEM

1
King Abdullah University of Science and Technology (KAUST), Biological and Environmental Sciences and Engineering (BESE) Division, NABLA Lab, 23955-6900 Thuwal, Saudi Arabia
2
Department of Applied Science and Technology, Politecnico di Torino, Corso Duca degli Abruzzi 24, 10129 Torino, Italy
*
Authors to whom correspondence should be addressed.
Nanomaterials 2018, 8(1), 40; https://doi.org/10.3390/nano8010040
Received: 27 September 2017 / Revised: 12 December 2017 / Accepted: 11 January 2018 / Published: 14 January 2018
(This article belongs to the Special Issue ZnO and TiO2 Based Nanostructures)
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Abstract

The thermally-induced crystallization of anodically grown TiO2 amorphous nanotubes has been studied so far under ambient pressure conditions by techniques such as differential scanning calorimetry and in situ X-ray diffraction, then looking at the overall response of several thousands of nanotubes in a carpet arrangement. Here we report a study of this phenomenon based on an in situ transmission electron microscopy approach that uses a twofold strategy. First, a group of some tens of TiO2 amorphous nanotubes was heated looking at their electron diffraction pattern change versus temperature, in order to determine both the initial temperature of crystallization and the corresponding crystalline phases. Second, the experiment was repeated on groups of few nanotubes, imaging their structural evolution in the direct space by spherical aberration-corrected high resolution transmission electron microscopy. These studies showed that, differently from what happens under ambient pressure conditions, under the microscope’s high vacuum (p < 10−5 Pa) the crystallization of TiO2 amorphous nanotubes starts from local small seeds of rutile and brookite, which then grow up with the increasing temperature. Besides, the crystallization started at different temperatures, namely 450 and 380 °C, when the in situ heating was performed irradiating the sample with electron beam energy of 120 or 300 keV, respectively. This difference is due to atomic knock-on effects induced by the electron beam with diverse energy. View Full-Text
Keywords: TiO2 amorphous nanotubes; high resolution transmission electron microscopy; in situ transmission electron microscopy; amorphous-crystalline phase transition; electron beam effects; anodic oxidation TiO2 amorphous nanotubes; high resolution transmission electron microscopy; in situ transmission electron microscopy; amorphous-crystalline phase transition; electron beam effects; anodic oxidation
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Casu, A.; Lamberti, A.; Stassi, S.; Falqui, A. Crystallization of TiO2 Nanotubes by In Situ Heating TEM. Nanomaterials 2018, 8, 40.

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