Atom-by-atom structural and chemical analysis by annular dark-field electron microscopy

Abstract

Direct imaging and chemical identification of all the atoms in a material with unknown three-dimensional structure would constitute a very powerful general analysis tool. Transmission electron microscopy should in principle be able to fulfil this role, as many scientists including Feynman realized early on. It images matter with electrons that scatter strongly from individual atoms and whose wavelengths are about 50 times smaller than an atom. Recently the technique has advanced greatly owing to the introduction of aberration-corrected optics. However, neither electron microscopy nor any other experimental technique has yet been able to resolve and identify all the atoms in a non-periodic material consisting of several atomic species. Here we show that annular dark-field imaging in an aberration-corrected scanning transmission electron microscope optimized for low voltage operation can resolve and identify the chemical type of every atom in monolayer hexagonal boron nitride that contains substitutional defects. Three types of atomic substitutions were found and identified: carbon substituting for boron, carbon substituting for nitrogen, and oxygen substituting for nitrogen. The substitutions caused in-plane distortions in the boron nitride monolayer of about 0.1 A magnitude, which were directly resolved, and verified by density functional theory calculations. The results demonstrate that atom-by-atom structural and chemical analysis of all radiation-damage-resistant atoms present in, and on top of, ultra-thin sheets has now become possible.

Direct visualization of reversible dynamics in a Si6 cluster embedded in a graphene pore

“…Atom-by-atom chemical analysis was performed based on quantitative intensity analysis of the deconvolved ADF image. The intensity from the impurity atoms is about 3.83 times the intensity obtained from the carbon atoms, which is close to the Z 1.6 ratio of 1:3.87 for Z ¼ 6 (C) and Z ¼ 14 (Si), respectively 29 . Furthermore, electron energy-loss spectroscopy analysis from a substitutional impurity atom with the same ADF image intensity ratio indicates that the impurities are Si atoms 30 .…”

Electron radiation damage mechanisms in 2D MoSe2

“…Modern transmission electron microscopes (TEM) allow imaging materials at a single atom resolution with acceleration voltages in the range of 20-300 kV [1][2][3] , foremost thanks to the practical realization of aberration correctors (AC) for transmission electron microscopy 4,5 . However, high electron doses are required for achieving a high enough signal to noise ratio for accurate detection of the atom position in the image.…”

Review of massively parallel DNA sequencing technologies

“…Another novel technique for DNA uses transmission electron microscopy to directly visualise strands of DNA that have been suitably modified with heavy metal atoms to distinguish the bases (Krivanek et al 2010). This method is being developed and commercialised by several companies, including Halcyon Molecular and ZSGenetics.…”