We developed a new scanning probe microscopy technique, charge gradient microscopy (CGM), which can be used to study the complex dynamics of polar domain nucleation and growth.
Significance and Impact
CGM can be used to study the complex interactions between surface screening charges, electric dipole moments and ferroelectric domain dynamics.
High-Level Research Details
We collected the current from a grounded CGM probe while scanning a periodically-poled single crystal LiTaO3 thin film on a Cr electrode.
We observed signals from the ferroelectric domains and domain walls, which originate from the displacement current and from relocation or removal of surface charge.
The scraped charge, measured as a current that scales with the scraping rate, induces a charge gradient leading to the immediate relocation of the screening charges from the probe vicinity.
Additional Research Details
Polarization charges of ferroelectric materials are screened by equal amounts of surface charges with opposite polarity in ambient condition. In this study, we showed that scraping, collecting and quantifying the surface screening charges reveals the underlying polarization domain structure at high speeds, a technique we call Charge Gradient Microscopy (CGM).
We collected the current from a grounded CGM probe while scanning a periodically poled lithium niobate (PPLN) single crystal and single crystal LiTaO3 thin film on a Cr electrode. We observed current signals at the domains and domain walls originating from the displacement current and the relocation or removal of surface charges, which enabled us to visualize the ferroelectric domains at a scan frequency above 78 Hz over 10 μm. The scraped charge, measured as a current that scales with the scraping rate, induces a charge gradient that leads to the immediate relocation or refill of the screening charges from the vicinity of the probe. As such, we envision that CGM can be used to study the complex dynamics of domain nucleation and growth induced by a biased tip in the absence of surface screening charges.
Seungbum Hong, Woon Ik Park (Argonne Materials Science Division), Sheng Tong, Andreas Roelofs (Argonne Nanoscience and Technology Division) and Yoshiomi Hiranaga, Yasuo Cho (Tohoku University, Japan).
U.S. Department of Energy, Office of Science, Materials Science and Engineering Division; Department of Energy, Office of Science, Office of Basic Energy Sciences User Facilities
S. Hong, S. Tong, W. I. Park, Y. Hiranaga, Y. Cho, A. Roelofs, Proc. Nat’l Acad. Sci USA 111, 6566 (2014)
The authors acknowledge stimulating discussions with S. Hruszkewycz at Argonne National Laboratory, S. H. Baek at Korea Institute of Science and Technology, Korea, and B. Rodriguez at Trinity College, Ireland. The work was supported by the U.S. Department of Energy, Office of Science, Materials Sciences and Engineering Division and by the Center for Nanoscale Materials, a U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences User Facility under Contract DE-AC02-06CH11357. The CGM and PFM experiments presented in the main text and the CGM/PFM/EFM/C-AFM in ambient-condition experiments presented in the SI Appendix were performed at the Materials Science Division and the vacuum PFM, CGM and SEM experiments presented in the SI Appendix were performed at the Center for Nanoscale Materials and the Electron Microscopy Center. We acknowledge Y.-Y. Choi and J. R. Guest at Argonne National Laboratory for their support in CGM experiments.