LANS Informal Seminar: Seungbum (Daniel) Hong

Seminar Title: Visualizing the behavior of polar domains and screening charges under electric and mechanical fields
Speaker: Seungbum (Daniel) Hong, Materials Scientist, Argonne National Laboratory

Date/Time: 2015-09-16 15:00
Location: Bldg 241 rm D172

Description:
In this talk, I will introduce our work related to visualization of polarization domains and screening charges using atomic force microscopy (AFM). Polarization, the dipole moment per unit volume, forms domains, which are the basic building blocks for information storage devices using dielectric or ferroelectric materials. By using the fact that polarization is coupled with the piezoelectric strain, we can map the polarization domains through decoding the amplitude and phase of the out-of-plane and in-plane vibrations of the AFM tip over the region of interest.
The boundary between polarization domains is called domain boundary, of which motion contributes to the capacitance of the materials. As the mobility of domain boundary determines the speed of polarization switching, identifying the slow and fast directions of the domain boundary motion will guide the ideal geometry for ferroelectric capacitors as high frequency information storage element.
Polarization domains are screened by either external or internal screening charges, and the interaction between the polarization domains and the screening charges can lead to various interesting phenomena including unexpected local polarization switching. By applying mechanical pressure and moving the external screening charges using the AFM tip, we are able not only to visualize the underlying polarization domain at high speed but also to study the unscreened polarization domains at room temperature. I will present the recent results related to the rescreening kinetics of external screening charges on polarization domains using charge gradient microscopy. Lastly, I will discuss potential collaboration area with LANS.