期刊
MICROSCOPY AND MICROANALYSIS
卷 19, 期 4, 页码 1027-1035出版社
OXFORD UNIV PRESS
DOI: 10.1017/S1431927613001505
关键词
STEM; EELS; EFTEM; liquid; in situ; environmental; CuSO4; LiFePO4
资金
- National Science Foundation Materials Research Science and Engineering Centers (MRSEC) program [DMR 1120296]
- Energy Materials Center at Cornell, an Energy Frontier Research Center
- U.S. Department of Energy, Office of Basic Energy Sciences [DESC0001086]
In situ scanning transmission electron microscopy (STEM) through liquids is a promising approach for exploring biological and materials processes. However, options for in situ chemical identification are limited: X-ray analysis is precluded because the liquid cell holder shadows the detector and electron energy-loss spectroscopy (EELS) is degraded by multiple scattering events in thick layers. Here, we explore the limits of EELS in the study of chemical reactions in their native environments in real time and on the nanometer scale. The determination of the local electron density, optical gap, and thickness of the liquid layer by valence EELS is demonstrated. By comparing theoretical and experimental plasmon energies, we find that liquids appear to follow the free-electron model that has been previously established for solids. Signals at energies below the optical gap and plasmon energy of the liquid provide a high signal-to-background ratio regime as demonstrated for LiFePO4 in an aqueous solution. The potential for the use of valence EELS to understand in situ STEM reactions is demonstrated for beam-induced deposition of metallic copper: as copper clusters grow, EELS develops low-loss peaks corresponding to metallic copper. From these techniques, in situ imaging and valence EELS offer insights into the local electronic structure of nanoparticles and chemical reactions.
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