Jung Ho Yoo

Corrosion behavior of PVD-grown WC–(Ti1−xAlx)N films in a 3.5% NaCl solution

Abstract WC–(Ti 1− x Al x )N coatings of stepwise changing Al concentration (WC–Ti 0.86 Al 0.14 N, WC–Ti 0.72 Al 0.28 N, and WC–Ti 0.58 Al 0.42 N) were deposited on AISI 1045 substrate by high-ionization sputtered PVD method. The Al concentration could be controlled by using evaporation source for Al and fixing the evaporation rate of the metals (WC alloy and Ti). The corrosion behavior of WC–(Ti 1− x Al x )N coatings in deaerated 3.5% NaCl solution was investigated by electrochemical corrosion tests and surface analyses. Particular attention was paid to the effects of Al target power density on the film properties related to the corrosion behavior. The measured galvanic corrosion currents between coating and substrate indicated that WC–Ti 0.72 Al 0.28 N coating showed the best resistance of the coating tested. The results of potentiodynamic polarization tests showed that this coating had passivation and lower porosity. This indicated that this coating is effective in improving corrosion resistance. In electrochemical impedance spectroscopy, the WC–Ti 0.72 Al 0.28 N coating showed one time constant loop and the increased polarization resistance of coating relative to other samples. The better corrosion performance of WC–Ti 0.72 Al 0.28 N coating is due to the modified compactness, porosity and adhesion of the coating layer.

On the corrosion behavior of multilayered WC–Ti1−xAlxN coatings on AISI D2 steel

In the present work, multilayered coatings with alternate layers of WC-Ti and WC-Ti 1-x Al x N were deposited for use as wear-resistant and corrosion-resistant surfaces. Ti and TiN base layers were deposited on the substrate prior to the multilayers. WC-Ti 1-x Al x N coatings with variable Al content (i.e., Al target power density) were deposited onto a steel substrate (high-speed steel; HSS) by the cathodic arc deposition method. The Al content could be controlled using an evaporation source for Al and fixing the evaporation rate of the other target sources. Four kinds of WC-Ti 1-x Al x N coatings were prepared (WC-Ti 0.6 Al 0.4 N, WC-Ti 0.53 Al 0.47 N, WC-Ti 0.5 Al 0.5 N and WC-Ti 0.43 Al 0.57 N). The corrosion behavior of WC-Ti 1-x Al x N coatings in deaerated 3.5% NaCI solution was investigated by electrochemical corrosion tests and surface analyses. Particular attention was paid to the effects of Al content on the coating properties related to the corrosion behavior. The galvanic corrosion current measured between the coating and substrate showed a low value. The results of potentiodynamic polarization tests indicated that the WC-Ti 0.43 Al 0.57 N coating with lower porosity enhanced the corrosion resistance. In electrochemical impedance spectroscopy measurements, the WC-Ti 0.43 Al 0.57 N coating showed two time constants and decreased the charge transfer resistance of the coating (R et ). Multilayered coatings were analyzed by EDS and XRD techniques to evaluate the crystal structure and compound formation behavior. Surface and cross-sectional morphology of the films was observed using SEM. In addition, scratch tests were performed to measure film adhesion strength.

Microstructural Analysis of Si-Ti-Fe Alloy Anode Materials for Li-ion Secondary Batteries

For improving anode materials in Li-ion batteries, the Si system has been noted by many researchers because it has higher energy density and capacity than the graphite anode material used currently. However, the life cycle of the Si anode tends to decrease due to the remarkable volume expansion which is caused by insertion of Li ions when the cell is charged. In this study, we controlled the size of active Si particles, which are dispersed in the inactive matrix, down to several tens of nm as active materials by adding heterogeneous elements. To understand the reaction mechanism of active Si dispersed in the inactive matrix, we analyzed the microstructure of the Si-Ti-Fe alloy using high resolution transmission electron microscopy and energy dispersive X-ray spectroscopy. The volume expansion behavior was improved by employing the TiFeSi2 matrix and refining the active Si particle size, and life performance of the Li-ion batteries was enhanced. (Received September 28, 2012)

Two-dimensional dopant profiling in semiconductor devices by electron holography and chemical etching delineation techniques with the same specimen

The electron holography and chemical etching delineation techniques were successfully employed to assess two-dimensional (2D) dopant profiles in semiconductor devices. The results obtained from both techniques with the same specimen were precisely compared and discussed in order to evaluate the performance limits of these techniques. It was demonstrated that both techniques are very effective in obtaining reliable 2D dopant profiles in nanodevice.

Graphene growth from reduced graphene oxide by chemical vapour deposition: seeded growth accompanied by restoration.

Understanding the underlying mechanisms involved in graphene growth via chemical vapour deposition (CVD) is critical for precise control of the characteristics of graphene. Despite much effort, the actual processes behind graphene synthesis still remain to be elucidated in a large number of aspects. Herein, we report the evolution of graphene properties during in-plane growth of graphene from reduced graphene oxide (RGO) on copper (Cu) via methane CVD. While graphene is laterally grown from RGO flakes on Cu foils up to a few hundred nanometres during CVD process, it shows appreciable improvement in structural quality. The monotonous enhancement of the structural quality of the graphene with increasing length of the graphene growth from RGO suggests that seeded CVD growth of graphene from RGO on Cu surface is accompanied by the restoration of graphitic structure. The finding provides insight into graphene growth and defect reconstruction useful for the production of tailored carbon nanostructures with required properties.

Transmission electron microscopy study of microstructural properties and dislocation characterization in the GaN film grown on the cone-shaped patterned Al2O3 substrate

Growing a GaN film on a patterned Al2O3 substrate is one of the methods of reducing threading dislocations (TDs), which can significantly deteriorate the performance of GaN-based LEDs. In this study, the microstructural details of the GaN film grown on a cone-shaped patterned Al2O3 substrate were investigated using high-resolution transmission electron microscopy and weak-beam dark-field techniques. Various defects such as misfit dislocations (MDs), recrystallized GaN (R-GaN) islands and nano-voids were observed on the patterned Al2O3 surfaces, i.e. the flat surface (FS), the inclined surface (IS) and the top surface (TS), respectively. Especially, the crystallographic orientation of R-GaN between the GaN film and the inclined Al2O3 substrate was identified as

A study of the perpendicular magnetic microstructure of the L10 FePt epitaxial film using electron holography

[\overline 1 2\overline 1 0]_{{\rm GaN}} \hbox{//}[\overline 1 101]_{{\rm R - GaN} \,{\rm on}\,{\rm IS}} \hbox{//}[\overline 1 100]_{ {{\rm Al}} _{\rm 2} {\rm O}_{\rm 3}}

Precise Comparison of Two-dimensional Dopant Profiles Measured by Low-voltage Scanning Electron Microscopy and Electron Holography Techniques

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Towards the plasmonic nanopore for single molecule analysis

(\overline 1 012)_{{\rm GaN}} \hbox{//}(1\overline 1 02)_{{\rm R - Ga}\,{\rm Non}\,{\rm IS}} \hbox{//}(\overline {11} 26)_{ {{\rm Al}} _{\rm 2} {\rm O}_{\rm 3}}

Nanopore integrated with Au clusters formed under electron beam irradiation for single molecule analysis

. In addition, a rotation by 9° between