Correlative Analysis of the Dimensional Properties of Bipyramidal Titania Nanoparticles by Complementing Electron Microscopy with Other Methods

Abstract

In this paper, the accurate determination of the size and size distribution of bipyramidal anatase nanoparticles (NPs) after deposition as single particles on a silicon substrate by correlative Scanning Electron Microscopy (SEM) with Atomic Force Microscopy (AFM) analysis is described as a new measurement procedure for metrological purposes. The knowledge of the exact orientation of the NPs is a crucial step in extracting the real 3D dimensions of the particles. Two approaches are proposed to determine the geometrical orientation of individual nano-bipyramides: (i) AFM profiling along the long bipyramid axis and (ii) stage tilting followed by SEM imaging. Furthermore, a recently developed method, Transmission Kikuchi Diffraction (TKD), which needs preparation of the crystalline NPs on electron-transparent substrates such as TEM grids, has been tested with respect to its capability of identifying the geometrical orientation of the individual NPs. With the NPs prepared homogeneously on a TEM grid, the transmission mode in a SEM, i.e., STEM-in-SEM (or T-SEM), can be also applied to extract accurate projection dimensions of the nanoparticles from the same sample area as that analysed by SEM, TKD and possibly AFM. Finally, Small Angle X-ray Scattering (SAXS) can be used as an ensemble technique able to measure the NPs in liquid suspension and, with ab-initio knowledge of the NP shape from the descriptive imaging techniques, to provide traceable NP size distribution and particle concentration.

Small-angle X-ray scattering: characterization of cubic Au nanoparticles using Debye's scattering formula

“…The time-saving approach of implementing Debye's equation in CDEF further allows us to introduce fit parameters of the particle shape, which enable users to obtain more detailed information on the measured nanoparticles. In terms of 'steady-shape' particle evaluation, moreover, CDEF has also been coupled with a Markov chain Monte Carlo algorithm to additionally reveal uncertainty estimates of the assumed size distribution of bipyramidal TiO 2 nanoparticles (Crouzier et al, 2021).…”

Customizing New Titanium Dioxide Nanoparticles with Controlled Particle Size and Shape Distribution: A Feasibility Study Toward Reference Materials for Quality Assurance of Nonspherical Nanoparticle Characterization

“…The approach followed here to develop a sample preparation protocol able to guarantee the distribution of single nanoplatelets deposited parallel onto a substrate succeeded only partially. Further developments in both directions, 1) measurement of nanoplatelet thickness in SEM-in-STEM based on the mass-thickness determination, [64] and/or correlative analysis with AFM; [65] and 2) representative, that is, statistical measurement of the arbitrarily oriented nanoplatelets in powder form in the SEM mode, are necessary. Artificial intelligence approaches for the automated and reliable identification and size analysis of the nanoplatelets could help to resolve this task.…”

“…It should be noticed that the geometrical orientation of the bipyramides as deposited in this case either lies on a particle facet or lies parallel with the substrate. Exact quantification approaches are given in detail in the study by Crouzier et al [65] ; and 4) The superior contrast of STEM-in-SEM with respect to the mass thickness contrast enables a more accurate reading of the particle boundaries, however, without knowledge of the exact 3D orientation of the particles on the substrate. Correlative approaches such as SEM and atomic force microscopy (AFM) or SEM with STEMin-SEM and transmission Kikuchi diffraction (TKD) [65,66] have a decisive contribution in extracting accurate full 3D information of the nonspherical nanoparticles.…”

Metrological Protocols for Reaching Reliable and SI-Traceable Size Results for Multi-Modal and Complexly Shaped Reference Nanoparticles

“…To obtain a fair description of the two elongated materials, the bipyramidal NPs (nPSize03) and the nanorods (nPSize07), two parameters are necessary: the length of both structures and the side of the square base and the section, respectively. For determining the nano-bipyramid parameters by SAXS, a specific model integrating a comprehensive description of the geometry was used [ 32 ].…”