Center for Correlated Electron Systems


Visualization of polarization, screening charges and ionic transport using atomic force microscopy

October 20, 2016l Hit 779
Date : October 25, 2016 16:00 ~ 17:30
Speaker : Dr. SEUNGBUM HONG (Argonne National Laboratory)
Location : Bldg. 19, Rm. 210

With the invention of scanning tunneling microscopy (STM) and atomic force microscopy (AFM)1,2, researchers started to see atomic structure and manipulate atoms and molecules using nanoscale metallic or silicon tips in both vacuum and ambient conditions3,4. As AFM can detect tiny displacement of the cantilever (< 10 pm) in contact or proximity with the materials surface, any physical parameters coupled with strain could be used to image relevant order parameters (for example, polarization5, magnetization6, and ionic concentration7). Furthermore, conducting AFM opened up local current measurement in conjunction with external stimuli such as heat and photons8, which could be used to detect photovoltaic effect at the nanoscale9.


           As imaging consists of positioning, encoding and decoding of measured data and transducing one form of energy into another, any breakthrough in imaging technology can lead to a new design in information storage devices, imaging sensors or energy storage and harvesting devices10. Consequently, the inventors of SPM have been deeply involved in innovative probe-based data storage devices (e.g., IBM s millipede project), where multiple nanoscale tips read and write data on the thin film surface in microelectromechanical system (MEMS)11,12.


Figure 1. Schematic diagram of scanning resistive probe microscopy. Reprinted with permission from Ref [15]. Copyright 2011, American Chemical Society.

           The dominant trends of advanced materials characterization using SPM can be characterized by high-resolution, high-speed multi-modal, multi-scale, multi-frequency (band excitation) and resonance enhanced and tracking modes13,14. The keys to success include improvement of spatial and temporal resolution as well as invention of new functional imaging such as scanning resistive probe microscopy (see Figure 1) with a field effect transistor embedded in the tip15 or charge gradient microscopy where the electric current induced by the mechanical stimulus can be mapped at high speed16. Here in my talk, I will present our recent thrusts on visualization of polarization, screening charges and ionic transport using piezoresponse force microscopy (PFM), CGM and electrochemical strain microscopy (ESM).