Emerging Leaders Program

Ellen Williams Distinguished Postdoctoral Fellowship
Research Topic: Time-Domain Nanoscience

Nanoscale Imaging of Fast Electrochemistry

Advisor(s):

John Cumings, Department of Materials Science and Engineering

Research Description

The selected candidate will work to develop high-speed imaging capabilities in electrochemical environments using transmission electron microscopy (TEM). Existing efforts at the University of Maryland are developing robust platforms for TEM imaging of specimens in liquid environments, and the candidate will extend these toolsets by developing further capability for ultrafast imaging. The measurement techniques developed will be directly applied to the science of electrode materials for high-power and high-capacity lithium batteries.

Progress Upate:

Researcher - Dr. Kai He, John Cumings Group
Website

9/3/2011
Kai He was appointed as an Ellen Williams Distinguished Postdoctoral Fellow in Department of Materials Science and Engineering at University of Maryland in January 2011. He has been working on the in-situ study of nanoscale devices using transmission electron microscopy, especially on electron holography studies of new nanostructures to observe electric and magnetic fields in devices during operation. The progress made during this fellowship appointment includes the following aspects.

1. Functionalization of electron holography
Electron holography is a unique technique based on transmission electron microscopes, where both intensity and phase information can be retrieved from electron waves passing through a specimen, so that to provide quantitative visualization of the electronic and magnetic fields inside the sample with nanometer spatial resolution. Kai’s primary objective is to apply this functionality on our electron microscope as a powerful toolset and develop a protocol to allow users to perform this technique. Currently, off-axis electron holography is operational on the JEOL 2100F TEM in NISP Lab at UMD, with field-of-view of 40-2600nm, and spatial resolution of 0.2-13nm.

2. Investigation of electric fields in electrically-biased systems
In the emerging energy technologies, various nanostructured materials have been used in energy harvesting and storage devices. As for devices to generate or store the electrical energy, these nanostructures are operated under electrically-biased environments. Therefore, it is of great importance to perform direct observation of the electric fields within working devices. Kai is working on projects involving devices consisting of p-n junction silicon nanowires and carbon nanotubes, in which Si NWs (or CNTs) are in-situ biased inside the TEM so that the electric fields can be observed by detecting corresponding phase shifts using electron holography.

3. Domain-wall motion in
Magnetic domain-wall (DW) motion has been actively studied due to its importance in fundamental physics as well as applications for next-generation memory and logic devices. Kai is studying on DW motion inside lithographically-patterned NiFe nanowires. The experiments are carried out inside TEM, where DW motion induced by spin-polarized current and/or magnetic field can be observed using Lorentz microscopy and electron holography. Devices with different designs have been studied, including current-induced DW motion in individual nanowires and magnetic-field-driven DW motion in a large scale identical nanowire arrays. Preliminary results will be presented at the 56th annual conference on magnetism and magnetic materials.