TY - JOUR
T1 - Real-space charge-density imaging with sub-ångström resolution by four-dimensional electron microscopy
AU - Gao, Wenpei
AU - Addiego, Christopher
AU - Wang, Hui
AU - Yan, Xingxu
AU - Hou, Yusheng
AU - Ji, Dianxiang
AU - Heikes, Colin
AU - Zhang, Yi
AU - Li, Linze
AU - Huyan, Huaixun
AU - Blum, Thomas
AU - Aoki, Toshihiro
AU - Nie, Yuefeng
AU - Schlom, Darrell G.
AU - Wu, Ruqian
AU - Pan, Xiaoqing
N1 - Funding Information:
Acknowledgements Our experimental work was supported by the US Department of Energy (DOE), Office of Basic Energy Sciences, Division of Materials Sciences and Engineering under grant DE-SC0014430. TEM specimen preparation and sample thickness fitting were partially supported by the US National Science Foundation (NSF) under grant number DMR- 1506535. DFT studies were supported by the US DOE (grant number DE-FG02-05ER46237) and the National Energy Research Scientific Computing Center (NERSC). Growth of BiFeO3 films at Cornell University was supported by the National Science Foundation (Nanosystems Engineering Research Center for Translational Applications of Nanoscale Multiferroic Systems) under grant number EEC-1160504, and film growth at Nanjing University was supported by the National Basic Research Program of China (grant number 2015CB654901). TEM experiments were conducted using the facilities in the Irvine Materials Research Institute (IMRI) at the University of California at Irvine. We thank H. Sawada from Jeol Ltd. for help with experiments.
Publisher Copyright:
© 2019, The Author(s), under exclusive licence to Springer Nature Limited.
Copyright:
Copyright 2019 Elsevier B.V., All rights reserved.
PY - 2019/10/14
Y1 - 2019/10/14
N2 - The distribution of charge density in materials dictates their chemical bonding, electronic transport, and optical and mechanical properties. Indirectly measuring the charge density of bulk materials is possible through X-ray or electron diffraction techniques by fitting their structure factors1–3, but only if the sample is perfectly homogeneous within the area illuminated by the beam. Meanwhile, scanning tunnelling microscopy and atomic force microscopy enable us to see chemical bonds, but only on the surface4–6. It remains a challenge to resolve charge density in nanostructures and functional materials with imperfect crystalline structures—such as those with defects, interfaces or boundaries at which new physics emerges. Here we describe the development of a real-space imaging technique that can directly map the local charge density of crystalline materials with sub-ångström resolution, using scanning transmission electron microscopy alongside an angle-resolved pixellated fast-electron detector. Using this technique, we image the interfacial charge distribution and ferroelectric polarization in a SrTiO3/BiFeO3 heterojunction in four dimensions, and discover charge accumulation at the interface that is induced by the penetration of the polarization field of BiFeO3. We validate this finding through side-by-side comparison with density functional theory calculations. Our charge-density imaging method advances electron microscopy from detecting atoms to imaging electron distributions, providing a new way of studying local bonding in crystalline solids.
AB - The distribution of charge density in materials dictates their chemical bonding, electronic transport, and optical and mechanical properties. Indirectly measuring the charge density of bulk materials is possible through X-ray or electron diffraction techniques by fitting their structure factors1–3, but only if the sample is perfectly homogeneous within the area illuminated by the beam. Meanwhile, scanning tunnelling microscopy and atomic force microscopy enable us to see chemical bonds, but only on the surface4–6. It remains a challenge to resolve charge density in nanostructures and functional materials with imperfect crystalline structures—such as those with defects, interfaces or boundaries at which new physics emerges. Here we describe the development of a real-space imaging technique that can directly map the local charge density of crystalline materials with sub-ångström resolution, using scanning transmission electron microscopy alongside an angle-resolved pixellated fast-electron detector. Using this technique, we image the interfacial charge distribution and ferroelectric polarization in a SrTiO3/BiFeO3 heterojunction in four dimensions, and discover charge accumulation at the interface that is induced by the penetration of the polarization field of BiFeO3. We validate this finding through side-by-side comparison with density functional theory calculations. Our charge-density imaging method advances electron microscopy from detecting atoms to imaging electron distributions, providing a new way of studying local bonding in crystalline solids.
UR - http://www.scopus.com/inward/record.url?scp=85075192624&partnerID=8YFLogxK
U2 - 10.1038/s41586-019-1649-6
DO - 10.1038/s41586-019-1649-6
M3 - Journal article
C2 - 31610544
AN - SCOPUS:85075192624
SN - 0028-0836
VL - 575
SP - 480
EP - 484
JO - Nature
JF - Nature
ER -