• Proceedings of the Korean Society of Precision Engineering Conference
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• 2006.05a
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• pp.475-476
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• 2006

Self-assembled monolayers (SAMs) formed by the adsorption of alkanethiols, HS(CH2)nX, where X is an organic functional group, onto gold surfaces have attracted widespread interest as templates for the fabrication of molecular and biomolecular microstructures. Previously photopatterning has been thought of as being restricted to the micron scale, because of the well-known diffraction limit. So, we have explored a novel approach to nanofabrication by utilizing a femtosecond laser.

• Journal of Institute of Control, Robotics and Systems
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• v.7 no.3
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• pp.218-228
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• 2001

The switched reluctance motor(SRM) has been increasingly used in high-performance servo applications such as electric vehicles, aircraft, and direct-drive robots. The dynamic equations of SRMs are, however, highly nonlinear and this makes it difficult to control SRMs with high performance. In this paper, we propose a new robust current tracking controller for SAMs which can compensate the nonlinear characteristics of SRM(i.e., back-emf and inductance) completely and hence shows perfect tracking performance even with an arbitrary small current control loop gain. Furthermore, even in case that there exist some model uncertainties, our current controller guarantees that the stator currents can track the reference current commands with sufficiently small tracking errors. In order to justify our work, we present the tracking performance analysis and some simulation results.

• Bulletin of the Korean Chemical Society
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• v.25 no.10
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• pp.1531-1537
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• 2004

Twenty four thiol-functionalized ionic liquids based on imidazolium cation, 1-(12-mercaptododecyl)-3-alkylimidazolium salts, have been synthesized, and utilized to investigate the effects of alkyl-chain length and anion on the wettability of Au surfaces on the basis of self-assembled monolayers presenting [(CnSAMIM)X], where n = 1-6, X = Br, $BF_4$, $PF_4$ and $NTf_2$. Water wettabilities of the surfaces were measured as a water contact angle by contact angle goniometry. It was found that water wettability of the Au surfaces coated with imidazolium ions was largely dependent not only on counter anions but also on the length of alkyl chains. In the case of SAMs of N-alkylimidazolium ions having short length of N-alkyl chain (C1-$C_4$), anions played great role in determining water wettability of the surfaces.

• Proceedings of the KIEE Conference
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• 2007.07a
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• pp.2020-2021
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• 2007

Viologen derivative has been widely investigated because of their well-electrochemical behavior including the electron acceptor for the electric charge delivery mediation of the devices. The viologen exist in three main oxidation states, namely, $V^{2+}{\rightleftarrows}V^{{\cdot}+}{\rightleftarrows}V^0$. These redox reactions are highly reversible and can be cycled many times without significant side reaction. In this paper, we determined the time dependence to resonant frequency shift of QCM during self-assembly process and the electrochemical behavior of the self-assembled viologen monolayers by electrochemical QCM method. The redox reactions of viologen were highly reversible and the EQCM has been employed to monitor the electrochemically induced adsorption of SAMs during the redox reactions.

• Journal of the Korean Ceramic Society
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• v.39 no.7
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• pp.649-656
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• 2002

In situ patterned zinc oxide thin films were prepared by precipitation of Zn(NO$_3$)$_2$ aqueous solution containing urea and by microcontact printing using Self-Assembled Monolayers(SAMs) on A1/SiO$_2$/Si substrates. The visible precipitation of Zn(OH)$_2$ that was formed in the Zn(NO$_3$)$_2$ aqueous solution containing urea was enhanced with an increase of the reaction temperature and the amount of urea. As the reaction time of Zn(NO$_3$)$_2$ with urea was prolonged, the thickness and grain size of Zn(OH)$_2$ thin layers were increased, respectively. The optimum precipitation condition was at 80$\^{C}$ for 1 h for the solution with the ratio of Zn(NO$_3$)$_2$ to urea of 1 : 8. Homogeneous ZnO thin films were fabricated by the heat treatment of 600$\^{C}$ for 1 h of Zn(OH)$_2$ precipitation on Al/SiO$_2$/Si substrate. This was available to the in-situ patterned ZnO thin films with uniform grain size. Hydrophobic SAM, Octadecylphosphonic Acid(OPA) and hydrophilic SAM, 2-Carboxyethylphosphonic Acid(CPA) were applied on the Al/SiO$_2$/Si substrate by microcontact printing method. In situ patterned ZnO thin film was successfully prepared by the heat treatment of Zn(OH)$_2$ precipitated on the surface of hydrophilic SAM, CPA.

• Journal of Adhesion and Interface
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• v.24 no.2
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• pp.64-68
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• 2023

Organic field-effect transistors (OFETs) are attracting attention in the field of next-generation electronic devices, and they can be fabricated on a flexible substrate using an organic semiconductor as a channel layer. In particular, DPP-based semiconducting conjugated polymers are actively used because they have higher charge carrier mobility than other organic semiconductors, but they are still lower than inorganic semiconductors, so various studies are being conducted to improve the charge carrier mobility. In this study, the charge carrier mobility is improved by controlling the surface energy of the substrate by forming self-assembled monolayers (SAMs). As the surface energy of the substrate is controlled by the SAMs, the crystallinity increases, thereby improving the charge carrier mobility by 14 times from 3.57×10^-3 cm²V^-1s^-1 to 5.12×10^-2 cm²V^-1s^-1

• Journal of Environmental Health Sciences
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• v.48 no.6
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• pp.298-305
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• 2022

Background: The concentration of air pollutants as measured by the Air Quality Monitoring System (AQMS) is not an accurate population exposure level since actual human activities and temporal and spatial variability need to be considered. Therefore, to increase the accuracy of exposure assessment, the population should be considered. However, it is difficult to obtain population data due to limitations such as personal information. Objectives: The existing population defined in this study is the number of people in each region's grid. The purpose is to provide a methodology for evaluating exposure to PM_2.5 through existing population data provided by the National Geographic Information Institute. Methods: The selected study period was from October 26 to October 28, 2021. Using PM_2.5 concentration data measured at the Sensor-based Air Monitoring Station (SAMS) installed in Guro-gu and Wonju-si, the concentration for each grid was estimated by applying inverse distance weights through QGIS version 3.22. Considering the existing population, population-weighted average concentration (PWAC) was calculated and the exposure level of the population was compared by region. Results: The outdoor PM_2.5 concentration as measured through the SAMS was high in Wonju-si on all three days. Wonju-si showed an average 22% higher PWAC than Guro-gu. As a result of comparing the PWAC and outdoor PM_2.5 concentration by region, the PWAC in Guro-gu was 1~2% higher than the observed value, but it was almost the same. Conversely, observations of Wonju-si were 10.1%, 11.3%, and 8.2% higher than PWAC. Conclusions: It is expected that the Geographic Information System (GIS) method and the existing population will be used to evaluate the exposure level of a population with a narrow activity radius in further research. In addition, based on this study, it is judged that research on exposure to environmental pollutants and risk assessment methods should be expanded.

• Proceedings of the KIEE Conference
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• 2004.07c
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• pp.1715-1717
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• 2004

We attempt to investigate morphology of self-assembled dipyridinium dithioacetate on Au(111) substrate by Scanning Tunneling Microscopy(STM). Also, we measured electrical properties using Scanning Tunneling Spectroscopy(STS). Sample that use this experiment acquires thiol function beside quantity by dipyridinium dithioacetate, is structure that can be self-assembled easily to Au(111) substrate. The same self-assembly procedure was used for two different concentrations, 0.5mmol/ml and 1mmol/ml. Dilute density of sample by 0.5mmol/ml, 1mmol/ml and observed dipyridinium dithioacetate's image by STM after self-assembled on Au(111) substrate. The structure of Tip/SAMs/Au(111) has been used measurement for electrical properties(i-v) using STM. The current-voltage measurement result, observed negative differential resistance(NDR) properties.

• Bulletin of the Korean Chemical Society
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• v.33 no.10
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• pp.3269-3273
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• 2012

In this study, we report a new method for the high contrast imaging of biomolecular interactions at roller printed protein surfaces using thermotropic liquid crystals (LCs). Avidin was roller printed and covalently immobilized onto the obliquely deposited gold surface that was decorated with carboxylic acid-terminated self-assembled monolayers (SAMs). The optical response of LCs on the roller printed film of avidin contrasted sharply with that on the obliquely deposited gold surface. The binding of biotin-peroxidase to the roller printed avidin was then investigated on the obliquely deposited gold substrate. LCs exhibited a non-uniform and random orientation on the roller printed area decorated with the complex of avidin and biotin-peroxidase, while LCs displayed a uniform and planar orientation on the area without roller printed proteins. The orientational transition of LCs from uniform to non-uniform state was triggered by the erasion of nanometer-scale topographies on the roller printed surface after the binding of biotin-peroxidase to the surface-immobilized avidin. The specific binding events of protein-receptor interactions were also confirmed by atomic force microscopy and ellipsometry. These results demonstrate that the roller printing of proteins on obliquely deposited gold substrates could provide a high contrast signal for imaging biomolecular interactions using LC-based sensors.

• Proceedings of the Materials Research Society of Korea Conference
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• 2009.11a
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• pp.33.2-33.2
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• 2009

Block copolymer lithography has attracted great attention for emerging nanolithography since nanoscaleperiodic patterns can be easily obtained through self-assembly process without conventional top-down patterning process. Since the morphologies of self-assembled block copolymer patterns are strongly dependent on surface energy of a substrate, suitable surface modification is required. Until now, the surface modification has been studied by using random copolymer or self-assembled mono layers (SAMs). However, the research on surface modifications has been limited within several substrates such as Si-based materials. In present study, we investigated the formation of block copolymer on Au substrate by $O_2$ plasma treatment with the SAM of 3-(p-methoxy-phenyl)propyltrichloro-silane [MPTS, $CH_3OPh(CH_2)_3SiCl_3$]. After $O_2$ plasma treatment, the chemical bonding states of the surface were analyzed by X-ray photoelectron spectroscopy (XPS). The static contact angle measurement was performed to study the effects of $O_2$ plasma treatment on the formation of MPTS monolayer. The block copolymer nanotemplates formed on Au surface were analyzed by scanning electron microscopy. The results showed that the ordering of self-assembled block copolymer pattern and the formation of cylindrical nano hole arrays were enhanced dramatically by oxygen plasma treatment. Thus, the oxidation of gold surface by $O_2$ plasma treatment enables the MPTS to form the monolayer assembly leading to surface neutralization of gold substrates.