Direct Imaging of Atomic-Scale Surface Structures of Brookite TiO₂ Nanoparticles by Frequency Modulation Atomic Force Microscopy in Liquid

Abstract

1Direct imaging of atomic-scale surface structures of TiO 2 nanoparticles is a promis-2 ing method for understanding the detailed mechanism of their photocatalytic activities. 3 Atomic force microscopy (AFM) is one of the analytical tools used for direct imaging 4 of surfaces, but atomic-scale AFM studies of TiO 2 nanoparticles in a liquid have not 5 been reported. Here, we report two methods for fixing of TiO 2 nanocrystals: an elec-6 trostatic method and a cross-linking method. Both methods enabled visualization of 7 subnanoscale surface structures of brookite TiO 2 nanoparticles in a liquid by frequency 8 modulation AFM (FM-AFM). The FM-AFM imaging results and density functional 9 theory molecular dynamics calculations suggest that the subnanoscale structures in the 10 FM-AFM images can be explained by the arrangement of the surface topmost atoms 11 or their hydration structures on the brookite TiO 2 (210) surface. Our results open 12 up various possibilities for studying atomic-scale surface structures of nanoparticles in 13 liquids by AFM.14

Local Cross-Coupling Activity of Azide-Hexa(ethylene glycol)-Terminated Self-Assembled Monolayers Investigated by Atomic Force Microscopy

“…The FM-AFM measurements were performed at 25 °C in an aqueous solution of 50 mM sodium chloride (NaCl, 38979, Sigma-Aldrich). The salt concentration can contribute to achieving sub-nanometer scale FM-AFM images, as previously reported …”

“…Commercially available cantilevers (160AC-NG, Opus, MikroMasch) with a nominal spring constant of 26 N/m were used. Before each FM-AFM measurement, the AFM tip was coated with Si (30 nm thick) using a magnetron sputter coater (Q150TS, Quorum Technologies) to enhance the reproducibility of molecular-resolution AFM imaging in liquid, as reported in previous studies. , The cantilever oscillation was excited at a resonance frequency using the photothermal excitation method. This excitation was achieved using a laboratory-built setup and a commercially available oscillation controller (Nanonis OC4.5, SPECS GmbH).…”

“…The salt concentration can contribute to achieving sub-nanometer scale FM-AFM images, as previously reported. 42 Infrared Reflection-Absorption Spectroscopy. The chemical compositions and confirmation of the CuAAC reaction on the N 3 -EG 6 -SAM surfaces were determined via in situ infrared reflectionabsorption spectroscopy (IR-RAS) measurement using a Fouriertransform infrared (FT-IR) spectrometer (FT/IR 6300, JASCO).…”

Photo-sensitive 2D Arrangement of −OH/H2O on Brookite TiO2(210)

“…This acidic condition gives a positive charge to the brookite particles and prevents their aggregation. 37 The solution was vortexed for 5 min and sonicated for 5 min by an ultrasonic homogenizer (UX-050, Mitsui Electric). Immediately after sonication, 100 μL of the solution was deposited on a cleaved mica substrate (01877-MB, SPI Supplies) and left for 10 min for the adsorption of nanocrystals.…”

Atomic-scale topography of rutile TiO2(110) in aqueous solutions: A study involving frequency-modulation atomic force microscopy

“…The application of this technique to metal oxides was reported for mica, 8,9 sapphire, 10 clay and aluminosilicate minerals, [11][12][13] SrTiO 3 , 14 and brookite TiO 2 . 15 One study resolved ridges and trenches, but not individual atoms, parallel to the [001] axis on TiO 2 (110) immersed in pure water. 16 The stoichiometric (110) truncation involves four atomic species when prepared in a vacuum.…”