Understanding and Controlling Nucleation and Growth of TiO₂ Deposited on Multiwalled Carbon Nanotubes by Atomic Layer Deposition

Abstract

Controlled deposition of thin conformal oxide films on carbon nanotubes (CNTs) by atomic layer deposition (ALD) for applications in solar energy and photocatalysis is still challenging, as the early stages of nucleation and subsequent growth are not yet well understood. In this work, we employed ALD to grow TiO2 on multiwalled carbon nanotubes (MW-CNTs). The effects of deposition temperature (120–240 °C), number of ALD cycles (20–750), and surface pretreatment of the MW-CNTs with oxygen plasma on the morphology and crystallinity of the TiO2 were systematically studied using transmission electron microscopy (TEM). By tuning the deposition conditions, controllable nucleation and growth of TiO2 on CNTs was achieved. In particular, high-quality crystalline anatase conforming to the CNTs was obtained with an ALD growth temperature as low as 200 °C. Direct observation using aberration-corrected atomic-resolution TEM imaging at 120 keV revealed an island structure of crystalline TiO x at the very early stage of nucleation, followed by coalesced growth of crystalline anatase at this temperature. The study also paves the way to understand the interface between the two materials on an atomic level.

Atomic Layer Deposition of Titanium Oxide on Single-Layer Graphene: An Atomic-Scale Study toward Understanding Nucleation and Growth

“…The observation of reduced TiO x was also reported previously for ALD of titanium oxide on multiwalled CNTs (MWCNTs) using the same precursors. 20 In addition, an in situ X-ray photoemission spectroscopy (XPS) study of ALD of TiO 2 on a silicon substrate revealed the presence of Ti 3+ at the initial stage, i.e., after only two cycles. 28 However, the amount of reduced TiO x in our sample is believed to be small, probably <1%, beyond the limit of detection of XPS.…”

Titanium Dioxide/Lithium Phosphate Nanocomposite Derived from Atomic Layer Deposition as a High‐Performance Anode for Lithium Ion Batteries

“…Meanwhile, the deposition of TiO 2 by ALD has been well established . TiCl 4 and titanium tetraisopropoxide (TTIP, Ti(OCH(CH 3 ) 2 ) 4 ) are two most common titanium sources, with water as the most widely used oxidizer.…”

Synthesis of Pt@TiO2@CNTs Hierarchical Structure Catalyst by Atomic Layer Deposition and Their Photocatalytic and Photoelectrochemical Activity

“…However, the crystallinity of TiO 2 was hardly observed when the number of cycle was less than 25. According to Zhang’s report [29], the nucleation of TiO 2 ALD was about 20 cycles. The size of TiO 2 nuclei was less than 2 nm when temperatures were 120 °C and 200 °C.…”

“…In the meanwhile, the crystalline particles were also consisted of amorphous shell and crystalline core. The ratio of amorphous shell and crystalline core decreased as ALD cycles decreased [29]. The TiO 2 particles less than 25 ALD cycles were probably too weak to be observed in XRD patterns due to the initial nucleation of TiO 2 .…”