Joong Jung Kim

Triboelectricity evaluation of single toner particle by electron holography

Understanding electrification is particularly important in materials science since the use of charged particles, e.g., the electrophotographic printer with toner particles, is one of the most successful applications of electrification. However, the charge generation mechanism still remains unclear due to the lack of an appropriate method for evaluating individual fine particles. In this study, we describe an approach for determining the charge of a single toner particle that uses electron holography in combination with a shielding technique. Two long-standing problems in holographic studies—namely, perturbation of the reference electron wave and unwanted charging by illumination—have been overcome by introducing two types of shields in a microscope. Using this method, the amount of charge on a single toner particle was determined, and the surface charge distribution was found to be inhomogeneous. Furthermore, an in situ observation of triboelectricity was conducted inside the microscope.

Electron holography study for two-dimensional dopant profile measurement with specimens prepared by backside ion milling.

The visualization of two-dimensional dopant profiles and the quantitative analysis of the built-in potential across the p-n junction, DeltaV(p-n), by electron holography were carried out with specimens prepared from the backside ion milling method combined with the focused ion beam technique. It was possible to obtain dopant profiling of the large field of view with low surface damage and gradually changed thickness. From the quantitative analysis using the phase information of electron holography and the thickness information of electron energy-loss spectroscopy, DeltaV(p-n) was estimated to be about 0.78 V assuming that the thickness of the dead layer on both surfaces is 50 nm, which is to show the difference of within 12% from the calculated value. It demonstrates that the backside ion milling method is a very promising specimen preparation technique for the reliable and quantitative analysis of dopant profiling with electron holography.

Electron holography for improved measurement of microfields in nanoelectrode assemblies

An approach to investigate the electric field distribution and field-emission property of a single crystal tungsten oxide (WO3) nanowire by electron holography technique is presented, which solves the problems encountered in the traditional reconstruction of the holograms, the so-called perturbed reference wave. We proposed this unique method to meticulously illustrate the status of the surroundings of a single crystal nanowire under biased conditions. This paves the way to precisely quantifying the electric and magnetic field distributions for nanostructures as well as nanodevices.

Determination of Orbital Location of Electron-Induced Secondary Electrons by Electric Field Visualization

The electric field around positively charged biological specimens is studied by electron holography. By the amplitude reconstruction process for holograms, the orbits of electron-induced secondary electrons are clarified on the nanometer scale. It is found that the stationary orbit of secondary electrons can be directly located without disturbing their motions under the condition that the current of secondary electrons in stationary orbit is considerably larger than that of incident electrons. The experimental conditions for the induction of the stationary orbit of secondary electrons are discussed, and furthermore the theoretical basis of the orbital location of secondary electrons through electric field visualization is discussed in the framework of quantum mechanics.

Characterization of the charging effect in a ZrO2 sintered body by Ga ion beam irradiation.

The charging effect in a ZrO2 sintered body was investigated by using scanning ion microscope (SIM) images. In this study, we report interesting features caused by the charging effect in the ZrO2 sintered body during the Ga ion beam irradiation: a bright contrast with a distorted net shape appears around the positively charged specimen. From this feature in the SIM image, it is clarified that the Ga ion beam is strongly deflected and the wide area of the internal parts of the focused ion beam machine is irradiated by the Ga ion beam, depending on the extent to which the specimen is charged. We discuss the mechanism of the characteristic charging effect through observing SIM images by varying the intensity of the Ga ion beam.

Electron Holography on Charging Effect in Non-Conductive Materials

The charging effects on non-conductive materials due to electrons irradiation were investigated by electron holography. The phenomena that the charging effects were more enhanced with an increase in the incident electron density were visualized through the direct observations in the electric potential distribution around the specimens. In addition, through the comparison between the electron holography results and the simulations, we were able to obtain the quantitative results indicating the amount of charges accumulated during electron irradiation.