Improvement of the energy resolution of energy dispersive spectrometers (EDS) using Richardson-Lucy deconvolution

Coincidence Detection of EELS and EDX Spectral Events in the Electron Microscope

Recent advances in the development of electron and X-ray detectors have opened up the possibility to detect single events from which its time of arrival can be determined with nanosecond resolution. This allows observing time correlations between electrons and X-rays in the transmission electron microscope. In this work, a novel setup is described which measures individual events using a silicon drift detector and digital pulse processor for the X-rays and a Timepix3 detector for the electrons. This setup enables recording time correlation between both event streams while at the same time preserving the complete conventional electron energy loss (EELS) and energy dispersive X-ray (EDX) signal. We show that the added coincidence information improves the sensitivity for detecting trace elements in a matrix as compared to conventional EELS and EDX. Furthermore, the method allows the determination of the collection efficiencies without the use of a reference sample and can subtract the background signal for EELS and EDX without any prior knowledge of the background shape and without pre-edge fitting region. We discuss limitations in time resolution arising due to specificities of the silicon drift detector and discuss ways to further improve this aspect.

The change of water content and role of microbe in the sludge drying process

In this study, the pure terephthalic acid sludge was treated by a drying process which was an economical and environmentally method. The water change and metabolic pathways for bacterial community function prediction were analyzed. The microbial community changes were studied by high-throughput sequencing to draw the dynamic succession model. Then multiple statistics was used to determine the key factors of the reduction. The results showed that the main stage of water loss in the PTA sludge drying process was the high temperature period where the water lost by evaporation accounted for more than 90% of the total removal. The main metabolic pathways for bacterial community function were amino acid (7.72%-8.71% of Kyoto encyclopedia of genes and genomes relative abundance and 8.26%-9.51% of Cluster of orthologous groups of proteins relative abundance) and carbohydrate metabolism. The model describing the dynamic succession of microbial communities showed that the dominant bacteria changed from Nitrospira, Novosphingobium and Azohydromonas to Pseudomonas, Paeniglutamicibac and Pelotomaculum. The key factors for water loss were Gemmatimonas, Novosphingobium and Azohydromonas with the correlation coefficients of 0.887, 0.772, 0.783, respectively; the key factors for dry matter loss were Pelotomaculum, total organic matter, dissovlved organic carbon and carbon/nitrogen ratio; the key factors for toxic substance loss were Brevundimonas, Novosphingobium and Gemmatimonas. These results provided theoretical support for the application and demonstration for hazardous waste sludge reduction.

Directly Probing the Local Coordination, Charge State, and Stability of Single Atom Catalysts by Advanced Electron Microscopy: A Review

The drive for atom efficient catalysts with carefully controlled properties has motivated the development of single atom catalysts (SACs), aided by a variety of synthetic methods, characterization techniques, and computational modeling. The distinct capabilities of SACs for oxidation, hydrogenation, and electrocatalytic reactions have led to the optimization of activity and selectivity through composition variation. However, characterization methods such as infrared and X-ray spectroscopy are incapable of direct observations at atomic scale. Advances in transmission electron microscopy (TEM) including aberration correction, monochromators, environmental TEM, and micro-electro-mechanical system based in situ holders have improved catalysis study, allowing researchers to peer into regimes previously unavailable, observing critical structural and chemical information at atomic scale. This review presents recent development and applications of TEM techniques to garner information about the location, bonding characteristics, homogeneity, and stability of SACs. Aberration corrected TEM imaging routinely achieves sub-Ångstrom resolution to reveal the atomic structure of materials. TEM spectroscopy provides complementary information about local composition, chemical bonding, electronic properties, and atomic/molecular vibration with superior spatial resolution. In situ/operando TEM directly observe the evolution of SACs under reaction conditions. This review concludes with remarks on the challenges and opportunities for further development of TEM to study SACs.