|Research:||Correlative Atom Probe Tomography (APT) and |
Transmission Electron Microscopy (TEM) Studies
Analytic and In-situ TEM experiment
|Education:||Seoul National University: Ph. D. in MSE (2010) |
Materials Science and Engineering
2220 North Campus Drive
Evanston, IL 60208
I was born in South Korea and graduated from Korea university in 2001 with a B.S degree in Material Sci.&Eng. Department. After B.S. graduation, I served two year military service as an 123th Commissioned Officer of Republic of Korea Marine Corps (ROKMC). Then I came back to university to start my graduate study in Material Sci.&Eng at Seoul University, with a topic “Effects of stacking fault energy on the microstructure and the twinning mechanism in TwinningInduced Plasticity(TWIP) steel”. During my graduate study I learned a lot relating with in-situ and high resolution (scanning) TEM technics.
I joined the Northwestern university in 2010 as a postdoctoral research associate, and I’ve been studying stress-corrosion cracks in nickel-base alloys. The development of novel correlative approach for site specific atom probe tomography (APT) sample preparation in the analyzed transmission electron microscope (TEM) have synergies for not only sub-nano scale structural but also tens PPM level chemical information. And we are broadening the application to thin ceramic/metal interface, CdTe solar cell, Peroveskite fuel cell, and thin multilayer semiconducting electronic devices. I hope to contribute to a material science society by state-of-art subnano-scale structural and PPM level chemical analyses combining with in-situ experiment.
TEM-APT Correlative Works
Atom probe tomography (APT) is unique analysis tool enables true three-dimensional (3-D) analysis with sub-nano scale spatial resolution. Recent implementations of the local electrode and the laser pulsing have expended the research applications of the APT, but needle-shaped narrow APT specimen still remains a major limiting factor for analyzing material. The novel approach for site specific APT sample preparation in the analyzed TEM sample is introduced to solve the geometrical limitations of a sharpened APT tip and have synergies for not only high resolution structural but also chemical information. Chemical analysis in TEM, energy dispersive X-ray spectroscopy (EDS) and electron energy loss spectrum (EELS), is carried out to compare the compositions of APT results. Grain boundary carbide junction is used to get a precision of position of APT samples in the analyzed TEM sample.
Adiabatic shear band (ASB) in high Ni steel
Adiabatic shear bands (ASBs) are narrow zones of highly localized deformation which are failure prone in high strain rate deformation. The adiabatic conditions in dynamic deformation result in a temperature rise within these bands and as a result there is local softening, which adversely affects work hardening and leads to a marked decrease in the load carrying capacity in these bands. The phase transformation and atomic scale elemental distribution are osberved at adiabatic shear band (ASBs). Even though it possesses excellent static properties, the failure of alloy in deformation localization during dynamic deformation should be tested for alloy selection. Detailed characterization of the deformed adiabatic shear band structures was analyzed by combining electron beam scattering diffraction (EBSD), transmission electron microscopy (TEM) and atom probe tomography techniques (APT).
Tomography study of CVD graphene on Cu substrate
Oxygen and hydrogen atoms and their functional molecules (OH, CO, and CO2) positions' and chemical identities are tomographically mapped in three dimensions in a graphene monolayer film grown on a copper substrate, at the atomic part-per-million (atomic ppm) detection level, employing laser assisted atom-probe tomography.
In-situ and analytical TEM
These enhanced superior formability and strength satisfied the improved safety standards for high energy absorption in the construction and crash resistance in the automotive industry. In twinning-induced plasticity (TWIP) steel, stacking fault energy (SFE) is the key parameter to determine the strengthening mechanism In this study, the generation of mechanical twin was observed by in-situ tensile test in TEM and the effect of SFE was discussed linked with the measured SFE.