TEM analysis allows picturing the catalyst morphology at the nanoscale, defining shape, size and size distribution of nanostructured materials. Pushing forward the resolution, a new set of information could be extracted in order to fully describe the catalyst down to the nanoscale. The local nanocrystalline structure could be disclosed learning about particle interactions, fine structure, crystalline orientation and morphology of nano-hetero structure and junction.  HRTEM images along with related FFT analysis could be used also to reveal material composition through the single crystalline pattern identification.

On the left side: 'LACTIC ACID FROM GLYCEROL BY ETHYLENE-STABILIZED PLATINUM-NANOPARTICLES' W. Oberhauser, C. Evangelisti, C. Tiozzo, F. Vizza and R. Psaro - ACS Catal.,6, 2016,1671

One of the most powerful tools included in the TEM/STEM methodologies is the local elemental analysis and maps at the nanoscale. The ISTEM microscopy allows two analysis mode: TEM-EELS analysis and maps (ESI electron spectroscopy image) and STEM-EDS (Energy Dispersive Spectroscopy). The first one could map a large number of elements giving information on the oxidation state, structure and the elemental map information is related to TEM morphology. The second use the X-ray generated by the interaction between the material and the electron beam. The EDS analysis allows collecting fast survey of elemental composition, semi-quant analysis and to map single elements in STEM mode.

on the left side: ‘HIGHLY ACTIVE NANOSTRUCTURED PALLADIUM-CERIA ELECTROCATALYSTS FOR THE HYDROGEN OXIDATION REACTION IN ALKALINE MEDIUM’ H. A. Miller, F. Vizza, M. Marelli, A. Zadick, L. Dubau, M. Chatenet, S. Geiger, S. Cherevko, H. Doan, R. K. Pavlicek, S. Mukerjee, D. R. Dekel - Nano Energy, 33, 2017, 293

In STEM mode, the electron beam is focused in a spot (with size less than 1 nm) and used to scan the sample point o point. Tha transmitted information is then collected by a high angle annular dark-field (HAADF) detector in order to reconstruct the image where the contrast is ruled over by the atomic number (Z-Contrast) highlighting the presence of tiny metal NPs or enhancing the contrast of different materials in a heterostructure. Changing the associated camera length is possible to move in a crystalline-ruled over contrast mode, enhancing the crystalline phases vs. amorphous one. STEM mode could be coupled with EDS mapping and analysis in order to elucidate elemental analysis at the nanoscale. STEM could be coupled also with a special tomo-holder in order to collect 2D projection images series at incremental tilts and reconstruct the 3D tomographic volume, collecting information about the internal and external material structure.

Electron diffraction in TEM, or better Selected Area Electron Diffraction (SAED), is a crystallographic methodology inside TEM that takes advantage of the interaction electron/matter and the resulting transmitted diffracted electron beam. An electron diffraction pattern is composed by spot or crystal reflex that satisfy the diffraction condition of the crystal structure. Single crystal will provide neat spot pattern, whereas polycrystalline system will provide bright ring patterns. SAED could be used (as X-ray diffraction) to identify crystal structure, different phases, crystal defects and measure lattice parameters Thanks to the SAED aperture, is possible to limit the investigated area to small portion or even single nanocrystals, giving a unique space resolved diffraction.

SEM could be used to picture the sample down to micro- and nano-scale. Using secondary electron (SE) the fine surface morphology could be revealed and could be extremely useful to analyze hierarchical or anchored nanostructures such as electrodes or particle loaded monolith. Moreover, ESEM or low vacuum mode available with the XL-30 SEM allows the direct analysis of non-conductive and semiconductor material without any coating treatment (i.e. gold or graphite coating). These coating treatments could hide the fine sample's nanofeatures or modify the sample morphology. The use of back-scattered electrons (BSE) decrease the resolution but allows the detection of different elements due to their dependence on the element atomic number (Z). The BSE images could be successfully used to highlight the presence of nanostructured metal nanoparticle, hardly detectable with the sole SE signal. SEM could be coupled with EDS methodology in order to analyze the local elemental composition and produce elemental maps at the micro- and nano-scale.