The physical and chemical properties of nanophase materials rely on their crystal and surface structures. Transmission electron microscopy (TEM) is a powerful and unique technique for structure characterization. The most important application of TEM is the atomic-resolution real-space imaging of nanoparticles. This article introduces the fundamentals of TEM and its applications in structural determination of shape-controlled nanocrystals and their assemblies. By forming a nanometer size electron probe, TEM is unique in identifying and quantifying the chemical and electronic structure of individual nanocrystals. Electron energy-loss spectroscopy analysis of the solid-state effects and mapping the valence states are even more attractive. In situ TEM is demonstrated for characterizing and measuring the thermodynamic, electric, and mechanical properties of individual nanostructures, from which the structure−property relationship can be registered with a specific nanoparticle/structure.

Transmission Electron Microscopy of Shape-Controlled Nanocrystals and Their Assemblies

We elucidate the atomic and electronic structure of graphene oxide (GO) using annular dark field imaging of single and multilayer sheets and electron energy loss spectroscopy for measuring the fine structure of C and O K-edges in a scanning transmission electron microscope. Partial density of states and electronic plasma excitations are also measured for these GO sheets showing unusual π* + σ* excitation at 19 eV. The results of this detailed analysis reveal that the GO is rough with an average surface roughness of 0.6 nm and the structure is predominantly amorphous due to distortions from sp3 C−O bonds. Around 40% sp3 bonding was found to be present in these sheets with measured O/C ratio of 1:5. These sp2 to sp3 bond modifications due to oxidation are also supported by ab initio calculations.

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Atomic and Electronic Structure of Graphene-Oxide

Molecular structure determination by electron microscopy of unstained crystalline specimens.

Suspended gold nanowires were made in an ultra-high vacuum. The finest of them was 0.6 nanometer in diameter and 6 nanometers in length. By high-resolution electron microscopy, they were shown to have a multi-shell structure composed of coaxial tubes. Each tube consists of helical atom rows coiled round the wire axis. The difference between the numbers of atom rows in outer and inner shells is seven, resulting in magic shell-closing numbers.

https://science.sciencemag.org/content/sci/289/5479/606.full.pdf

Synthesis and characterization of helical multi-shell gold nanowires

A dynamical theory of X-ray and electron diffraction for a distorted crystal which has been briefly explained elsewhere (Acta cryst. 15 (1962) 1311) is presented in more detail. The fundamental equations for both the X-ray and electron cases are deduced from the Maxwell or the Schrodinger equations, respectively, inside crystalline media which may contain distortions. A method of solution of the equations using the Riemann function is given together with the following general results; (1) the intensities and integrated intensities, with respect to the incident angle, of the transmitted and diffracted rays at a point on the exit surface are given by integrals over the entrance surface, (2) a theoretical basis for the column approximation in the electron case is provided, (3) the intensities of the X-ray projection topographs (traverse pattern) is not dependent upon the type of the incident waves but upon the total intensity to which the crystal is exposed. The limit of the applicability of the present theo...

A Dynamical Theory of Diffraction for a Distorted Crystal

The scattering of electrons by three-dimensional potential fields, and, in particular, the potential fields associated with a crystal lattice, is considered in terms of the new approach to physical optics proposed by Cowley & Moodie.

J. M. Cowley

Papers

The scattering of electrons by atoms and crystals. I. A new theoretical approach