Oriented Attachment and Nanorod Formation in Atomic Layer Deposition of TiO₂ on Graphene Nanoplatelets

Abstract

Understanding the spontaneous organization of atoms on well-defined surfaces promises to enable control over the shape and size of supported nanostructures. Atomic layer deposition (ALD) boasts atomic-scale control in the synthesis of thin films and nanoparticles. Yet, the possibility to control the shape of ALD-grown nanostructures remains mostly unexplored. Here, we report on the bottom-up formation of both linear and V-shaped anatase TiO2 nanorods (NRs) on graphene nanoplatelets during TiCl4/H2O ALD carried out at 300 °C. NRs as large as 200 nm form after only five ALD cycles, indicating that diffusional processes rather than layer-by-layer growth are behind the NR formation. In particular, high-resolution transmission electron microscopy reveals that the TiO2 NRs and graphene nanoplatelets are in rotational alignment as a result of lattice matching. Crucially, we also show that individual nanocrystals can undergo in-plane oriented attachment.

Atomic Layer Deposition of ZnO on InP Quantum Dot Films for Charge Separation, Stabilization, and Solar Cell Formation

“…TiO 2 films produced at growth temperatures suitable for preserving the QD properties are amorphous . The absorption spectrum and photoconductance of a 27 nm (99 cycles) thick film are shown in Figure S1 in the Supporting Information.…”

“…While the same charge separation could occur as in ZnO coated films, the amorphous TiO 2 has a low mobility resulting in little enhancement of the carrier transport in composite films. If the deposition temperature were increased to yield more crystalline TiO 2 this could possibly result in a larger enhancement of the measured mobility . However, the QDs have a greater risk of sintering or morphological changes with increased temperature .…”

“…[58][59][60] TiO 2 films produced at growth temperatures suitable for preserving the QD properties are amorphous. [61] The absorption spectrum and photoconductance of a 27 nm (99 cycles) thick film are shown in Figure S1 expected bandgap; however, the photoconductance is at the lower limit of the measurement, corresponding to a mobility of 2 × 10 −4 cm 2 (V s) −1 , hence more focus is placed on ZnO due to its superior optoelectronic properties, when grown with AP-ALD.…”

“…If the deposition temperature were increased to yield more crystalline TiO 2 this could possibly result in a larger enhancement of the measured mobility. [61] However, the QDs have a greater risk of sintering or morphological changes with increased temperature. [40,65] Therefore, ZnO appears to be the material of choice for the formation of type II heterojunction via ALD infilling.…”

Subnano Surface Engineering of TiO2 Nanoparticles by PET Molecular Layer Deposition: Tuning Photoactivity and Dispersibility

“…The MLD experiments were carried out in a custom-built fluidized bed reactor operating at atmospheric pressure ( Fig. 1), as described elsewhere (35). The system consists of a glass column (internal diameter of 2.5 cm and height of 50 cm) resting on a double motor Paja PTL 40/40-24 vibration table to assist fluidization of the TiO 2 nanoparticles.…”