Atomic-Number (Z)-Correlated Atomic Sizes for Deciphering Electron Microscopic Molecular Images

TL;DR

This paper introduces Z-correlated atomic radii models that improve the interpretation of atomic-resolution TEM images by correlating atomic number with atomic size, aiding in deciphering molecular structures.

Contribution

It proposes novel Z-correlated atomic radii models for AR-TEM imaging, accounting for noise conditions, to enhance molecular structure estimation from TEM images.

Findings

Good correlation between atomic number and atomic size in TEM images.

Development of two parameter sets for high-noise and low-noise imaging conditions.

Models facilitate easier interpretation of TEM images compared to conventional molecular models.

Abstract

With the advent of atomic-resolution transmission electron microscopy (AR-TEM) achieving sub-{\AA}ngstrom image resolution and submillisecond time resolution, an era of visual molecular science where chemists can visually study the time evolution of molecular motions and reactions at atomistic precision has arrived. However, the appearance of experimental TEM images often differs greatly from that of conventional molecular models, and the images are difficult to decipher unless we know in advance the structure of the specimen molecules. The difference arises from the fundamental design of the molecular models that represent atomic connectivity and/or the electronic properties of molecules rather than the nuclear charge of atoms and electrostatic potentials that are felt by the e-beam in TEM imaging. We found a good correlation between the atomic number (Z) and the atomic size seen in TEM images when we consider shot noise in digital images. We propose here Z-correlated (ZC) atomic radii for modeling AR-TEM images of single molecules and ultrathin crystals, with which we can develop a good estimate of the molecular structure from the TEM image much more easily than with conventional molecular models. Two parameter sets were developed for TEM images recorded under high-noise (ZCHN) and low-noise (ZCLN) conditions. The new molecular models will stimulate the imaginations of chemists planning to use AR-TEM for their research.