Visualizing single atom dynamics in heterogeneous catalysis using analytical in situ environmental scanning transmission electron microscopy
PHILOSOPHICAL TRANSACTIONS OF THE ROYAL SOCIETY A-MATHEMATICAL PHYSICAL AND ENGINEERING SCIENCES
Authors: Boyes, Edward D.; LaGrow, Alec P.; Ward, Michael R.; Martin, Thomas E.; Gai, Pratibha L.
Abstract
Progress is reported in analytical in situ environmental scanning transmission electron microscopy (ESTEM) for visualizing and analysing in real-time dynamic gas-solid catalyst reactions at the single-atom level under controlled reaction conditions of gas environment and temperature. The recent development of the ESTEM advances the capability of the established ETEM with the detection of fundamental single atoms, and the associated atomic structure of selected solid-state heterogeneous catalysts, in catalytic reactions in their working state. The new data provide improved understanding of dynamic atomic processes and reaction mechanisms, in activity and deactivation, at the fundamental level; and in the chemistry underpinning important technological processes. The benefits of atomic resolution-E(S)TEM to science and technology include new knowledge leading to improved technological processes, reductions in energy requirements and better management of environmental waste. This article is part of a discussion meeting issue 'Dynamic in situ microscopy relating structure and function'.
Nontrivial paired states in novel topological superconductors
JOURNAL OF ALLOYS AND COMPOUNDS
Authors: Radmanesh, S. M. A.; Ebrahimi, S. A. Seyyed; Diaconu, A.; Liu, J. Y.
Abstract
We report on the superconductive paired states in TbPdBi, beta-type FeSe and CaSn3 single crystals through temperature dependence of magnetic penetration depth analysis down to 0.040 K. For half-Heusler TbPdBi, in ultra-low temperature region we traced the T-3 power-law behavior of penetration depth indicating the nodeless topological superconductivity with anisotropic gap structure which was confirmed with the analysis of superfluid density. That highlights the role of thermally activated quasi-particles in the pairing mechanism of TBPdBi for which the variation of Delta lambda(T) wanders off the renown quadratic behavior of penetration depth. In FeSe the contribution of London depth was described with a power law (n approximate to 2.4) and the superfluid density fitted well with two-band d + d model in which the values of both gaps are substantially smaller than the gap size expected by the isotropic BCS model, due to the nodeless anisotropic gap symmetry. In CaSn3, temperature variation of magnetic penetration depth exhibited linear behavior which is ascribed to the topologically nontrivial electronic states. Also, fitting the results of superfluid density exhibited features of multiband pairing allowing the nodal gap in the electronic states which is in good agreement with the expectation of London penetration depth. The complex superconducting order parameter is suggestive of two-dimensional spin singlet or mixing singlet-triplet pairing states behind the signatures of superconductivity in CaSn3. The mechanisms of pairing symmetry uncovered by the temperature dependence of penetration depth study of TbPdBi, FeSe and CaSn3 meet the requirements for topological superconductivity. (C) 2020 Elsevier B.V. All rights reserved.