Two-dimensional electron gas or hole gas (2DEG or 2DHG) and their functionalities at artificial heterostructure interfaces have attracted extensive attention in recent years. Many theoretical calculations and recent experimental studies have shown the formation of alternating 2DEG and 2DHG at ferroelectric/insulator interfaces, such as BiFeO3/TbScO3, depending on the different polarization states. However, a direct observation based on the local charge distribution at the BiFeO3/TbScO3interface has yet to be explored. Herein we demonstrate the direct observation of 2DHG and 2DEG at BiFeO3/TbScO3interface using four-dimensional scanning transmission electron microscopy and Bader charge analysis. The results show that the measured charge state of each Fe/O columns at the interface undergoes a significant increase/reduction for the polarization state pointing away/toward the interface, indicating the existence of 2DHG/2DEG. This method opens up a path of directly observing charge at atomic scale and provides new insights into the design of future electronic nanodevices.
The atomic structure at the interface between two-dimensional (2D) and three-dimensional (3D) materials influences properties such as contact resistance, photo-response, and high-frequency electrical performance. Moiré engineering is yet to be utilized for tailoring this 2D/3D interface, despite its success in enabling correlated physics at 2D/2D interfaces. Using epitaxially aligned MoS2/Au{111} as a model system, we demonstrate the use of advanced scanning transmission electron microscopy (STEM) combined with a geometric convolution technique in imaging the crystallographic 32 Å moiré pattern at the 2D/3D interface. This moiré period is often hidden in conventional electron microscopy, where the Au structure is seen in projection. We show, via ab initio electronic structure calculations, that charge density is modulated according to the moiré period, illustrating the potential for (opto-)electronic moiré engineering at the 2D/3D interface. Our work presents a general pathway to directly image periodic modulation at interfaces using this combination of emerging microscopy techniques.
- Publication Date:
- NSF-PAR ID:
- 10215323
- Journal Name:
- Nature Communications
- Volume:
- 12
- Issue:
- 1
- ISSN:
- 2041-1723
- Publisher:
- Nature Publishing Group
- Sponsoring Org:
- National Science Foundation
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