• Proceedings of the Korean Vacuum Society Conference
• /
• 2012.08a
• /
• pp.385-385
• /
• 2012

Understanding the thermodynamics and structural transformation during the Metal-Insulator Transition (MIT) is critical to better understand the underlying physical origin of phase transition in the vanadiumdioxide ($VO_2$). Here, through the temperature-dependent in-situ high resolutiontransmission electron microscopy (HR-TEM), and systematic electrical transport study, we have shown that the tunable MIT transition of $VO_2$ nanowires is strongly affected by interplay between strain and domain nucleation by ion beam irradiation. Surprsingly, we have also observed that the $VO_2$ rutile (R) metallic phase could form directly in a strain-induced metastable monoclinic (M2) phase. These insights open the door toward more systematic approaches to synthesis for $VO_2$ nanostructures in desired phase and to use for applications including ultrafast optical switching, smart window, metamaterial, resistance RAM and synapse devices.

• Journal of Powder Materials
• /
• v.27 no.1
• /
• pp.58-62
• /
• 2020

Recently, electrochromic devices (ECDs) have gathered increasing attention owing to their high color contrast and memory effect, which make them highly applicable to smart windows, auto-dimming mirrors, sensors, etc. Traditional ECDs have a sandwich structure that contains an electrochromic layer between two ITO substrates. These sandwich-type devices are usually fabricated through the lamination of two electrodes and followed by the injection of a liquid electrolyte in the inner space. However, this process is sometimes complex and time consuming. In this study, we fabricated ECDs with a lateral electrode structure that uses only an ITO substrate and an all-in-one electrochromic gel, which is a mixture of electrolyte and electrochromic material. Furthermore, we investigated the EC properties of the lateral-type device by comparing it with a sandwich-type device. The lateral-type ECD shows strong blue absorption as the applied voltage increases and has a competitive coloration efficiency compared to the sandwich-type device.

• IEIE Transactions on Smart Processing and Computing
• /
• v.3 no.1
• /
• pp.28-34
• /
• 2014

Recently, ultrasound therapy has become a new and effective treatment for many brain diseases. Therefore, skull-mimicking phantoms have been developed to simulate the skull and brain tissue of a human and allow further research into ultrasound therapy. In this study, the suitability of various skull-mimicking materials(HDPE, POM C, Acrylic) for studies of brain-tumor treatments was evaluated using focused ultrasound. The acoustic properties of three synthetic resins were measured. The skull-mimicking materials were then combined with an egg white phantom to observe the differences in the ultrasound beam distortion according to the type of material. High-intensity polyethylene was found to be suitable as a skull-mimicking phantom because it had acoustic properties and a denatured-area shape that was close to those of the skull,. In this study, a skull-mimicking phantom with a multi-layer structure was produced after evaluating several skull-mimicking materials. This made it possible to predict the denaturation in a skull in relation to focused ultrasound. The development of a therapeutic protocol for a range of brain diseases will be useful in the future.

• Journal of the Korean Ceramic Society
• /
• v.54 no.4
• /
• pp.303-307
• /
• 2017

Pure $In_2O_3$, 0.5 and 1.0 wt% Mg doped $In_2O_3$ hollow spheres were synthesized by ultrasonic spray pyrolysis of a solution containing In-, Mg-nitrate and sucrose and their gas sensing characteristics to 5 ppm $C_2H_5OH$, p-xylene, toluene, and HCHO were measured at 250, 300 and $350^{\circ}C$. Although the addition of Mg decreases the specific surface area and the volume of meso-pores, the gas response (resistance ratio) of the 0.5 wt% Mg doped $In_2O_3$ hollow spheres to 5 ppm $C_2H_5OH$ at $350^{\circ}C$ (69.4) was significantly higher than that of the pure $In_2O_3$ hollow spheres (24.4). In addition, the Mg doped $In_2O_3$ hollow spheres showed the highest selectivity to $C_2H_5OH$. This was attributed to the dehydrogenation of $C_2H_5OH$ assisted by basic MgO into reactive $CH_3CHO$ and $H_2$.

• Journal of Sensor Science and Technology
• /
• v.25 no.3
• /
• pp.184-188
• /
• 2016

Highly ordered $SnO_2$ and NiO nanocolumns have been successfully achieved by glancing-angle deposition (GLAD) using an electron beam evaporator. Nanocolumnar $SnO_2$ and NiO sensors exhibited high performance owing to the porous nanostructural effect with the formation of a double Schottky junction and high surface-to-volume ratios. When all gas sensors were exposed to various gases such as $C_2H_5OH$, $C_6H_6$, and $CH_3COCH_3$, the response of the highly ordered $SnO_2$ nanocolumn were over 50 times higher than that of the $SnO_2$ thin film. This work will bring broad interest and create a strong impact in many different fields owing to its particularly simple and reliable fabrication process.

• Korean Chemical Engineering Research
• /
• v.45 no.5
• /
• pp.415-423
• /
• 2007

Photocatalytic water splitting (PWS) is the most promising technology to produce $H_2$ energy directly from renewable water and solar light. In spite of the remarkable progress made in the last decade, there are still many technical challenges remaining particularly in finding new photocatalytic materials with high efficiency and durability. This article discusses the application of nanocomposite materials in search of new photocatalytic materials for solar hydrogen production from water. It has been demonstrated that smart combination and modification of known materials and functions could be fruitful approach for the purpose.

• Smart Structures and Systems
• /
• v.6 no.3
• /
• pp.263-275
• /
• 2010

In the last decade, wireless sensor networks have emerged as a promising technology that could accelerate progress in the field of structural monitoring. The main advantages of wireless sensor networks compared to conventional monitoring technologies are fast deployment, small interference with the surroundings, self-organization, flexibility and scalability. These features could enable mass application of monitoring systems, even on smaller structures. However, since wireless sensor network nodes are battery powered and data communication is the most energy consuming task, transferring all the acquired raw data through the network would dramatically limit system lifetime. Hence, data reduction has to be achieved at the node level in order to meet the system lifetime requirements of real life applications. The objective of this paper is to discuss some general aspects of data processing and management in monitoring systems based on wireless sensor networks, to present a prototype monitoring system for civil engineering structures, and to illustrate long-term field test results.

• Restorative Dentistry and Endodontics
• /
• v.44 no.3
• /
• pp.23.1-23.9
• /
• 2019

Objectives: The aim of this study was to investigate the microshear bond strength (${\mu}SBS$) of different universal adhesive systems applied to hybrid computer-aided design/computer-aided manufacturing (CAD-CAM) restorative materials repaired with a composite resin. Materials and Methods: Four types of CAD-CAM hybrid block materials-Lava Ultimate (LA), Vita Enamic (VE), CeraSmart (CS), and Shofu Block HC (SH)-were used in this study, in combination with the following four adhesive protocols: 1) control: porcelain primer + total etch adhesive (CO), 2) Single Bond Universal (SB), 3) All Bond Universal (AB), and 4) Clearfil Universal Bond (CU). The ${\mu}SBS$ of the composite resin (Clearfil Majesty Esthetic) was measured and the data were analyzed using two-way analysis of variance and the Tukey test, with the level of significance set at p < 0.05. Results: The CAD-CAM block type and block-adhesive combination had significant effects on the bond strength values (p < 0.05). Significant differences were found between the following pairs of groups: VE/CO and VE/AB, CS/CO and CS/AB, VE/CU and CS/CU, and VE/AB and CS/AB (p < 0.05). Conclusions: The ${\mu}SBS$ values were affected by hybrid block type. All tested universal adhesive treatments can be used as an alternative to the control treatment for repair, except the AB system on VE blocks (the VE/AB group). The ${\mu}SBS$ values showed variation across different adhesive treatments on different hybrid CAD-CAM block types.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.36 no.1
• /
• pp.1-9
• /
• 2023

According to the recent global warming, it is necessary to use energy efficiently together with eco-friendly energy. The development of alternative technologies is requisite for managing the current energy and climate crises. In this regard, "smart windows," which can control solar radiation, can be used to mitigate energy demands. Electrochromic devices (ECDs) effectively control the amount of solar energy reaching commercial and other living areas and maintain climate conditions via color modulation in response to small external stimuli, such as temperature and light irradiation. However, the performance and the stability of ECDs depend on the state of the electrolyte and sealing of the device. To resolve the aforementioned issues, an ECD was manufactured by using a poly (methyl methacrylate) (PMMA)-based gel polymer electrolyte (GPE), and a laminating method was used to adequately seal the ECD. The concentrations of PMMA, acetonitrile (ACN), and ferrocene (Fc) were controlled to optimize the composition of the GPE to achieve an enhanced electrochromic performance. The fabricated GPE-based ECD afforded high optical contrast (~81.92%), with high electrochromic stability up to 10,000 cycles. Moreover, the lamination method employing the GPE could be used to fabricate large-area ECDs.

• Journal of Sensor Science and Technology
• /
• v.23 no.1
• /
• pp.15-18
• /
• 2014

We present gas sensing performance based on $2{\times}2$ sensor array with four different elements ($TiO_2$, $SnO_2$, $WO_3$ and $In_2O_3$ thin films) fabricated by rf sputter. Each thin film was deposited onto the selected $SiO_2$/Si substrate with Pt interdigitated electrodes (IDEs) of $5{\mu}m$ spacing which were fabricated on a $SiO_2$/Si substrate using photolithography and dry etching. For 5 ppm $NO_2$ and 50 ppm CO, each thin film sensor has a different response to offers the distinguishable response pattern for different gas molecules. Compared with the conventional micro-fabrication technology, $2{\times}2$ sensor array with such remarkable response pattern will be open a new foundation for monolithic integration of high-performance chemoresistive sensors with simplicity in fabrication, low cost, high reliablity, and multifunctional smart sensors for environmental monitoring.