scholarly journals Systematic Identification of Activity Cliffs with Dual‐Atom Replacements and Their Rationalization on the Basis of Single‐Atom Replacement Analogs and X‐Ray Structures

2021 ◽  
Author(s):  
Huabin Hu ◽  
Jürgen Bajorath
Keyword(s):  
Single Atom ◽  
X Ray ◽  
Dual Atom ◽  
Systematic Identification ◽  
Activity Cliffs

Practical Estimation of Analytical Sensitivity for EDS in an Intermediate Voltage FEG-STEM

1997 ◽  
Vol 3 (S2) ◽  
pp. 965-966
Author(s):  
M. Watanabe ◽  
D. W. Ackland ◽  
D. B. Williams
Keyword(s):  
Spatial Resolution ◽  
Single Atom ◽  
Acquisition Time ◽  
Analytical Sensitivity ◽  
X Ray ◽  
Quantitative Microanalysis ◽  
Analytical Electron ◽  
Atom Detection ◽  
Electron Microscopes ◽  
Image Position

One of the ultimate objectives for energy-dispersive X-ray spectrometry (EDS) in the analytical electron microscope (AEM) is single-atom detection in thin specimens, as well as quantitative microanalysis with high accuracy approaching ±1% relative. In order to realize the single-atom analysis, the design of the AEM has to be optimized with respect to improvements in spatial resolution and detectability limits. The detectability limit, as defined by the minimum mass fraction (MMF), is given by:where P is the peak intensity of interest, (P/B) is the peak-to-background ratio for that peak, and r is the acquisition time. To improve the sensitivity for analysis, any or all of the variables P, (P/B), and τ should be increased. Intermediate-voltage analytical electron microscopes combined with high brightness field-emission gun (FEG) are expected to improve the MMF, while maintaining high spatial resolution. Additionally, the MMF should also be improved by maximizing the solid angle of X-ray collection.

Photon-recoil imaging: Expanding the view of nonlinear x-ray physics

Science ◽  
2020 ◽  
Vol 369 (6511) ◽  
pp. 1630-1633
Author(s):  
U. Eichmann ◽  
H. Rottke ◽  
S. Meise ◽  
J.-E. Rubensson ◽  
J. Söderström ◽  
...  
Keyword(s):  
Free Electron Laser ◽  
Signal Amplification ◽  
Pulse Propagation ◽  
Wave Functions ◽  
Single Atom ◽  
Experimental Protocol ◽  
X Ray ◽  
Photon Recoil ◽  
Fundamental Process ◽  
Electronic Wave Functions

Addressing the ultrafast coherent evolution of electronic wave functions has long been a goal of nonlinear x-ray physics. A first step toward this goal is the investigation of stimulated x-ray Raman scattering (SXRS) using intense pulses from an x-ray free-electron laser. Earlier SXRS experiments relied on signal amplification during pulse propagation through dense resonant media. By contrast, our method reveals the fundamental process in which photons from the primary radiation source directly interact with a single atom. We introduce an experimental protocol in which scattered neutral atoms rather than scattered photons are detected. We present SXRS measurements at the neon K edge and a quantitative theoretical analysis. The method should become a powerful tool in the exploration of nonlinear x-ray physics.

scholarly journals Systematic identification of target set-dependent activity cliffs

2019 ◽  
Vol 5 (2) ◽  
pp. FSO363 ◽  
Author(s):  
Huabin Hu ◽  
Dagmar Stumpfe ◽  
Jürgen Bajorath
Keyword(s):  
Dependent Activity ◽  
Target Set ◽  
Systematic Identification ◽  
Activity Cliffs

scholarly journals Charge localized atomic Moδ+ site boosting hydrogen evolution in alkaline solution

2020 ◽  
Author(s):  
Maoqi Cao ◽  
Kang Liu ◽  
Yao Song ◽  
Chao Ma ◽  
Yiyang Lin ◽  
...  
Keyword(s):  
Hydrogen Evolution ◽  
Active Site ◽  
Density Functional ◽  
Alkaline Media ◽  
Water Dissociation ◽  
Single Atom ◽  
Alkaline Solutions ◽  
X Ray ◽  
Tafel Slope ◽  
Charge Localization

Abstract Electrochemical water splitting has drawn tremendous interest for the scalable and sustainable conversion of renewable electricity to clear hydrogen fuel and chemicals. However, the sluggishly kinetics of water dissociation step in alkaline solutions restrict severely the application of hydrogen evolution reaction (HER). Here, we designed and prepared cobalt layers with nitrogen modified atomically dispersed Mo sites (N-Mo/Co SAA) to boost the activity of HER. Density functional theory (DFT) calculations demonstrated that the N can induce the asymmetry charge localization of Moδ+ to facilitate the water dissociation. The energy barriers of water dissociation reduced from 0.48 to 0.35 eV by the charge localized Moδ+ site. High resolution transmission electron microscope (HRTEM) and synchrotron X-ray absorption spectroscopy (XAS) measurements confirmed the structure of N modified atomically dispersed Moδ+. Ambient pressure X-ray photoelectron spectroscopy (AP-XPS) measurements assessed the atomically dispersed Moδ+ site is the active site for water dissociation. Thus, the obtained N-Mo/Co catalyst exhibits record activity with 12 mV overpotential to achieve the current density of 10 mA cm− 2 and Tafel slope of 31 mV dec− 1 in alkaline media, which are superior to 32 mV overpotential for 10 mA cm− 2 and 38 mV dec− 1 Tafel slope on best commercial 20 wt% Pt/C sample in the same condition. This design strategy provided a new pathway to boost the activity of single atom alloy (SAA) by regulating the charge localization of the active site precisely at the atomic-level.

scholarly journals A Cobalt-Iron Double-Atom Catalyst for the Oxygen Evolution Reaction

2019 ◽  
Author(s):  
Lichen Bai ◽  
Chia-Shuo Hsu ◽  
Duncan Alexander ◽  
Hao Ming Chen ◽  
Xile Hu
Keyword(s):  
Oxygen Evolution ◽  
Active Site ◽  
Oxygen Evolution Reaction ◽  
Active Sites ◽  
Single Atom ◽  
X Ray ◽  
Highly Active ◽  
Cobalt Iron ◽  
X Ray Absorption

Single atom catalysts exhibit well-defined active sites and potentially maximum atomic efficiency. However, they are unsuitable for reactions that benefit from bimetallic promotion such as the oxygen evolution reaction (OER) in alkaline medium. Here we show that a single atom Co precatalyst can be in-situ transformed into a Co-Fe double atom catalyst for OER. This catalyst exhibits one of the highest turnover frequencies among metal oxides. Electrochemical, microscopic, and spectroscopic data including those from operando X-ray absorption spectroscopy, reveal a dimeric Co-Fe moiety as the active site of the catalyst. This work demonstrates double-atom catalysis as a promising approach for the developed of defined and highly active OER catalysts.

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