• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.40-40
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• 2010

Employing synchrotron radiation based photoemission spectroscopy (PES) and scanning tunneling microscopy (STM), our group have investigated Si surfaces, various graphenes and molecular nanolayers. In this talk, I introduce recent results on the surface related systems. All experiments have been performed at the surface science beamlines, 3A2 and 7B1, in Pohang Accelerator Laboratory, where high resolution PES (HRPES) and angle resolved PES (ARPES) are available. Metals or molecules are adsorbed and sometimes extreme ultraviolet is irradiated onto surfaces to give them special functions. I show several examples for surface functionalzation and how to characterize solid surface using the analysis techniques. In particular, lots of ARPES and STM data are provided from graphenes, a strong candidate for replacing Si and conducting oxide currently used in many electronic and optical devices.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.28 no.9
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• pp.1270-1275
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• 2004

Standard positive photoresist techniques were adapted to generate nano-scale patterns of gold substrate using self-assembled monolayers (SAMs) and femtosecond laser. SAMs formed by the adsorption of alkanethiols onto gold substrate are employed as very thin photoresists, Alkanethiolates formed by the adsorption of alkanethiols are oxidized on exposure to UV light in the presence of air to alkylsulfonates. Specifically, it is known that deep UV light of wavelength less than 200nm is necessary for oxidation to occur. In this study, ultrafast laser of wavelength 800nm and pulse width 200fs is applied for photolithography. Results show that ultrafast laser of visible range wavelength can replace deep UV laser source for photo patterning using thin organic films. Femtosecond laser coupled near-field scanning optical microscopy facilitates not only the patterning of surface chemical structure, but also the creation of three-dimensional nano-scale structures by combination with suitable etching methods.

• The Journal of Korean Academy of Prosthodontics
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• v.40 no.4
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• pp.323-334
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• 2002

The purpose of this study is to investigate which current densities and etching times will result in an optimal etching depth and surface roughness when an Ni-Cr-Be alloy is etched with 30% perchloric acid($HClO_4$). For this study, observations were made by means of an optical three-dimensional surface roughness measuring machine and a scanning electron microscope. The etchings took place under the following conditions using current densities of $300mA/cm^2\;450mA/cm^2,\;600mA/cm^2$ and $750mA/cm^2$, and using etching time of three, five, six, seven and nine minutes. Under the conditions, the experiments reached the following conclusions. 1. When the current density is above $450mA/cm^2$ and the etching time is longer than five minutes, the etching depth increased as the current density and etching time increased. And the surface roughness was significantly influenced by the interaction of the current density and etching time. 2. Under the etching conditions of $600mA/cm^2$ and five minutes, the optimal etching depth for a resin cement space and the highest surface roughness for mechanical retention were obtained. The etching depth and surface roughness were $32.86{\mu}m$ and $7.90{\mu}m$, respectively. 3. Observations under the scanning electron microscope showed that both the corrosion at the grain boundary and the corrosion within the grain occurred on the etched surface. It was also observed that the corrosion at the grain boundary became more severe as the current density and etching time increased. In addition. at higher current densities and longer etching times general corrosion appeared.

• Journal of the Korean institute of surface engineering
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• v.52 no.5
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• pp.265-274
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• 2019

Formation behavior of PEO (Plasma Electrolytic Oxidation) films on AZ31 Mg alloy was investigated under application of 310 Hz AC as a function of $Na_3PO_4$ concentration from 0.02 M to 0.2 M. Film formation voltage and in-situ observation of arcs generated on the specimen surface were recorded with time, and surface morphologies of the PEO films were investigated using optical microscopy, confocal scanning laser microscopy and scanning electron microscopy. PEO film formation voltage decreased linearly with increasing $Na_3PO_4$ concentration which is attributed to the increase of solution pH. PEO films were grown uniformly over the entire surface in $Na_3PO_4$ solutions between 0.05 M and 0.1 M. However, non-uniform PEO films with white spots were formed in $Na_3PO_4$ solutions containing more than 0.1 M. Thickness and roughness of PEO films on AZ31 Mg alloy increased linearly with increasing $Na_3PO_4$ concentration and their increasing rates appeared to be much higher under 1 M than above 1 M. The experimental results suggest that phosphate ions can contribute to the formation of PEO films but higher $Na_3PO_4$ concentration more than 1 M results in local damages of PEO films due to repeated generation of white arcs at the same surface site of AZ31 Mg alloy.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2012.11a
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• pp.127-128
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• 2012

ZnO nanostructures were grown by the hydrothermal method on ZnO seed layers post-heated in the range $350-500^{\circ}C$. The effects of the post-heated ZnO seed layers on the structural and optical properties of the ZnO nanostructures were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD) spectroscopy, and photoluminescence (PL) spectroscopy. The average grain sizes in the ZnO seed layers increased with increasing post-heating temperature, and nano-fibrous structures were observed on the surface of the ZnO seed layers post-heated at $450^{\circ}C$. The ZnO seed layers post-heated in the range $350-500^{\circ}C$ affected the residual stress, lattice distortion in the ZnO nanostructures and the intensity, positions, and full widths at half maximum of the 2-theta and PL peaks in the XRD and PL spectra for the ZnO nanostructures.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.15 no.12
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• pp.1016-1020
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• 2002

Ru thin films were etched using CF/$_4$O$_2$ plasma in an ICP (inductively coupled plasma etching) system. The maximum etch rate of Ru thin films was 168 nm/min at a CF$_4$/O$_2$ gas mixing ratio of 10 %. The selectivity of SiO$_2$ over Ru was 1.3. From the OES (optical emission spectroscopy) analysis, the optical emission intensity of the O radical had a maximum value at 10% CF$_4$ gas concentration and drcrease with further addition of CF4 gas, but etch slope was enhanced. From XPS (x-ray photoelectron spectroscopy) analysis, the surface of the etched Ru thin film in CF$_4$/O$_2$ chemistry shows Ru-F bonds by the chemical reaction of Ru and F. RuF$_{x}$ compounds were suggested as a surface passivation layer that reduces the chemical reactions between Ru and O radicals. From a FE-SEM (field emission scanning electron microscope) micrograph, we had an almost perpendicular taper angle of 89$^{\circ}$.>.

• Korean Journal of Materials Research
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• v.28 no.2
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• pp.101-107
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• 2018

Li-incorporated ZnO thin films were deposited by using ultrasonic-assisted spray pyrolysis deposition (SPD) system. To investigate the effect of Li-incorporation on the performance of ZnO thin films, the structural, electrical, and optical properites of the ZnO thin films were analyzed by means of X-ray diffraction (XRD), field-emssion scanning electron microscopy (FE-SEM), Hall effect measurement, and UV-Vis spectrophotometry with variation of the Li concentraion in the ZnO sources. Without incorporation of Li element, the ZnO surface showed large spiral domains. As the Li content increases, the size of spiral domains decreased gradually, and finally formed mixed small grain and one-dimensional nanorod-like structures on the surface. This morphological evolution was explained based on an anti-surfactant effect of Li atoms on the ZnO growth surface. In addition, the Li-incorporation changed the optical and electrical properties of the ZnO thin films by modifying the crystalline defect structures by doping effects.

• Journal of the Optical Society of Korea
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• v.13 no.3
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• pp.392-397
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• 2009

We designed a wavelength interrogation-based surface plasmon resonance (SPR) biosensor to detect avian influenza DNA (AI-DNA). Hybridization reactions between target AI-DNA probes and capture probes immobilized on a gold surface were monitored quantitatively by measuring the resonance wavelength in the visible waveband. The experimental results were consistent with numerical calculations. Although the SPR detection technique does not require the DNA to be labeled, we also evaluated fluorescently-labeled targets to verify the hybridization behavior of the AI-DNA. Changes in resonance were found to be linearly proportional to the amount of bound analyte. A wavelength interrogation-type SPR biosensor can be used for rapid measurement and high-throughput detection of highly pathogenic AI viruses.

• Tribology and Lubricants
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• v.7 no.2
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• pp.61-66
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• 1991

The frictional and wear characteristics of non-asbestos friction materials made of four different fibers (carbon, aramid, ceramic and glass) have been investigated at elevated temperature using High Frequency Friction Tester. On the basis of the experimental results, friction and wear phenomena of four different non-asbestos fibers were caused by lattice layer film of carbon, polymeric transfer film of aramid, abrasion of ceramic and adhesion of glass fiber under each contact junction. The surface analysis of the worn specimens and counter parts after tests were observed using Scanning Electron Microscope and Optical Microscope.

• Journal of the Optical Society of Korea
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• v.12 no.2
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• pp.98-102
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• 2008

Optical Coherence Tomography (OCT) is an important noninvasive medical imaging technique that can reveal subsurface structures of biological tissue. OCT has demonstrated a good correlation with histology in sufficient resolution to identify morphological changes in articular cartilage to differentiate normal through progressive stages of degenerative joint disease. Current OCT systems provide individual cross-sectional images that are representative of the tissue directly under the scanning beam, but they may not fully demonstrate the degree of degeneration occurring within a region of a joint surface. For a full understanding of the nature and degree of cartilage degeneration within a joint, multiple OCT images must be obtained and an overall assessment of the joint surmised from multiple individual images. This study presents frequency domain three-dimensional (3-D) OCT imaging of degenerative joint cartilage extracted from bovine knees. The 3-D OCT imaging of articular cartilage enables the assembly of 126 individual, adjacent, rapid scanned OCT images into a full 3-D image representation of the tissue scanned, or these may be viewed in a progression of successive individual two-dimensional (2-D) OCT images arranged in 3-D orientation. A fiber-based frequency domain OCT system that provides cross-sectional images was used to acquire 126 successive adjacent images for a sample volume of $6{\times}3.2{\times}2.5\;mm^3$. The axial resolution was $8\;{\mu}m$ in air. The 3-D OCT was able to demonstrate surface topography and subsurface disruption of articular cartilage consistent with the gross image as well as with histological cross-sections of the specimen. The 3-D OCT volumetric imaging of articular cartilage provides an enhanced appreciation and better understanding of regional degenerative joint disease than may be realized by individual 2-D OCT sectional images.