Direct imaging of hydrogen-atom columns in a crystal by annular bright-field electron microscopy

Abstract

Enhancing the imaging power of microscopy to identify all chemical types of atom, from low- to high-atomic-number elements,would significantly contribute for a direct determinationof material structures. Electron microscopes have successfully provided images of heavy-atom positions, particularly by the annular dark-field method1,2, but detection of light atoms was difficult owing to their weak scattering power. Recent developments of aberration-correction electron optics3,4,5 have significantly advanced the microscope performance, enabling identification of individual light atoms such as oxygen6,7,8,9, nitrogen7,9, carbon9,10,11, boron9 and lithium12,13. However, the lightest hydrogen atom has not yet been observed directly, except in the specific condition of hydrogen adatoms on a graphene membrane14. Here we show the first direct imaging of the hydrogen atom in a crystalline solid YH2, based on a classic ‘hollow-cone’ illumination theory15,16,17,18 combined with state-of-the-art scanning transmission electronmicroscopy. The optimizedhollow-cone condition derived from the aberration-corrected microscope parameters confirms that the information transfer can be extended to 22.5 nm−1, which corresponds to a spatial resolution of about 44.4 pm. These experimental conditions can be readily realized with the annular bright-field imaging in scanning transmission electron microscopy19,20 according to reciprocity21, revealing successfully the hydrogen-atom columns as dark dots, as anticipated from phase contrast of a weak-phase object22.

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Figure 1: Schematic ray diagrams of HCI–TEM/ABF–STEM and PCTF of HCI.
Figure 2: ABF, bright-field and ADF–STEM images of the crystalline compound YH2.
Figure 3: Experimental and simulated ABF intensity.

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Acknowledgements

R.I. was supported as a Japan Society for the Promotion of Science research fellow. E.A. acknowledges support from a Grant-in-Aid for Scientific Research on Priority Areas ‘Atomic scale modification’ from the Ministry of Education, Culture, Sports, Science and Technology of Japan.

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E.A. initiated and designed the research, interpreted the data and wrote the paper. R.I. designed the experiments, analysed the data and carried out computer simulations. E.O., R.I. and E.A. carried out electron microscope experiments. H.S., Y.K. and F.H. contributed to interpretations of ABF imaging.

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Correspondence to Eiji Abe.

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The authors declare no competing financial interests.

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Ishikawa, R., Okunishi, E., Sawada, H. et al. Direct imaging of hydrogen-atom columns in a crystal by annular bright-field electron microscopy. Nature Mater 10, 278–281 (2011). https://doi.org/10.1038/nmat2957

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