Crystallization of TiO2 Nanotubes by In Situ Heating TEM

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.

In Situ TEM Crystallization of Amorphous Iron Particles

“…On the other hand, thickness limitations do not affect the XRD, which can successfully account for bigger particles during size measurement. Finally, similarly to what reported in our previous work [22] and in [36,37], an electron beam contribution to the crystallization cannot be neglected a priori, since in principle it could further promote the fast growth of crystal domains once their nucleation kicks off. Indeed, the electron beam energy is well-known to promote atomic displacements by knock-on effect; i.e., a further support to the atomic motion needed for the crystal domains' growth.…”

“…In this work we report on the first in situ transmission electron microscopy (TEM) study of the crystallization of amorphous iron sub-micron and nanoparticles prepared following the synthetic method where the trivalent iron cations were reduced by using NaBH 4 . The crystallization was performed by heating the particles using an ultra-low drift, microelectromechanical system (MEMS)-based in situ TEM sample holder under the high vacuum conditions typical of a TEM equipped with a Schottky electron source, and using an experimental procedure similar to the one we already published for the in situ crystallization of titania nanotubes [22,23]. The results reported herein indicate that the amorphous particles, whose size ranges between 80 and 200 nm, start to crystallize at 550 • C by in situ TEM heating and give rise multi-domain nanocrystals.…”

Emergence and Evolution of Crystallization in TiO2 Thin Films: A Structural and Morphological Study

“…To date, the market demand on TiO 2 -based devices for photocatalysis [1][2][3][4], sensors [5,6], optical reflective coatings for highly innovative 2 of 18 applications [7,8] (innovative mirrors for gravitational wave interferometers, among the others [9][10][11][12]), solar cells [13][14][15], metal insulator semiconductor industry [16], self-cleaning application [17][18][19], water purification processes [20], has been systematically growing, especially for thin films and nanostructures. In addition, a constant effort has been made in setting up reliable computational techniques, mainly based on density functional theory (DFT), to predict and describe the properties of TiO 2 , not only in its crystalline forms, but also in the amorphous phase, as well as to simulate the amorphous to crystalline phase transition [21][22][23]. Indeed, while some applications (optical fibers, displays, solar cells) require amorphous materials [24,25], some others, such as phase-change memory devices, are based on the amorphous to crystalline transition [26].…”

Probing the beam-induced heating effect inside a transmission electron microscope by nanoparticle labels

“…Aside from such notable shape changes, the temperature effect is also very often doubted to play a role in many other behaviors observed in TEM, e.g. the abnormal deformation behaviors of nanoscale metals, semiconductors and oxides [11], the phase transitions in nanowires and nano-belts [12], the reconstruction and recrystallizations in amorphous nanoparticles [13,14].…”