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Park, Taejin,Leem, Mirine,Lee, Hyangsook,Ahn, Wonsik,Kim, Hoijoon,Kim, Jinbum,Lee, Eunha,Kim, Yong-Hoon,Kim, Hyoungsub American Chemical Society 2017 JOURNAL OF PHYSICAL CHEMISTRY C - Vol.121 No.49
<P>Vertical MoO<SUB>2</SUB>/MoS<SUB>2</SUB> core–shell structures were synthesized on an amorphous surface (SiO<SUB>2</SUB>) by chemical vapor deposition at a high heating rate using a configuration in which the vapor phase was confined. The confined reaction configuration was achieved by partially covering the MoO<SUB>3</SUB>-containing boat with a substrate, which allowed rapid buildup of the partially reduced MoO<SUB>3–<I>x</I></SUB> crystals in an early stage (below 680 °C). Rapid temperature ramping to 780 °C enabled spontaneous transition of the reaction environment from sulfur-poor to sulfur-rich, which induced a sequential phase transition from MoO<SUB>3–<I>x</I></SUB> to intermediate MoO<SUB>2</SUB> and finally to MoO<SUB>2</SUB>/MoS<SUB>2</SUB> core–shell structures. The orthorhombic crystal structure of MoO<SUB>3–<I>x</I></SUB> contributed to the formation of vertical crystals on the amorphous substrate, whereas the nonvolatility of the subsequently formed MoO<SUB>2</SUB> enabled layer-by-layer sulfurization to form MoS<SUB>2</SUB> on the oxide surface with minimal resublimation loss of MoO<SUB>2</SUB>. By adjustment of the sulfurization temperature and time, excellent control over the thickness of the MoS<SUB>2</SUB> shell was achieved through the proposed synthesis method.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jpccck/2017/jpccck.2017.121.issue-49/acs.jpcc.7b08171/production/images/medium/jp-2017-08171h_0005.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/jp7b08171'>ACS Electronic Supporting Info</A></P>
Wide dynamic range high-speed three-dimensional quantitative OCT angiography with a hybrid-beam scan
Park, Taejin,Jang, Sun-Joo,Han, Myounghee,Ryu, Sukyoung,Oh, Wang-Yuhl The Optical Society 2018 Optics letters Vol.43 No.10
<P>We demonstrate a novel hybrid-beam scanning-based quantitative optical coherence tomography angiography (OCTA) that provides high-speed wide dynamic range blood flow speed imaging. The hybrid-beam scanning scheme enables multiple OCTA image acquisitions with a wide range of multiple time intervals simultaneously providing wide dynamic range blood flow speed imaging independent of the blood vessel orientation, which was quantified over a speed range of 0.6 similar to 104 mm/s through the blood flow phantom experiments. A fully automated high-speed hybrid-beam scanning-based quantitative OCTA system demonstrates visualization of blood flow speeds in various vessels from the main arteries to capillaries in a 4 mm x 4 mm area (1024 A-lines x 512 B-scans) in vivo in 20 s, showing its potential as a useful imaging tool for various biomedical applications. (C) 2018 Optical Society of America</P>
Implementation of Neuromorphic System with Si-based Floating-body Synaptic Transistors
Park, Jungjin,Kim, Hyungjin,Kwon, Min-Woo,Hwang, Sungmin,Baek, Myung-Hyun,Lee, Jeong-Jun,Jang, Taejin,Park, Byung-Gook The Institute of Electronics and Information Engin 2017 Journal of semiconductor technology and science Vol.17 No.2
We have developed the neuromorphic system that can work with the four-terminal Si-based synaptic devices and verified the operation of the system using simulation tool and printed-circuit-board (PCB). The symmetrical current mirrors connected to the n-channel and p-channel synaptic devices constitute the synaptic integration part to express the excitation and the inhibition mechanism of neurons, respectively. The number and the weight of the synaptic devices affect the amount of the current reproduced from the current mirror. The double-stage inverters controlling delay time and the NMOS with large threshold voltage ($V_T$) constitute the action-potential generation part. The generated action-potential is transmitted to next neuron and simultaneously returned to the back gate of the synaptic device for changing its weight based on spike-timing-dependent-plasticity (STDP).
Noise Robust Automatic Speech Recognition Scheme with Histogram of Oriented Gradient Features
Park, Taejin,Beack, SeungKwan,Lee, Taejin The Institute of Electronics and Information Engin 2014 IEIE Transactions on Smart Processing & Computing Vol.3 No.5
In this paper, we propose a novel technique for noise robust automatic speech recognition (ASR). The development of ASR techniques has made it possible to recognize isolated words with a near perfect word recognition rate. However, in a highly noisy environment, a distinct mismatch between the trained speech and the test data results in a significantly degraded word recognition rate (WRA). Unlike conventional ASR systems employing Mel-frequency cepstral coefficients (MFCCs) and a hidden Markov model (HMM), this study employ histogram of oriented gradient (HOG) features and a Support Vector Machine (SVM) to ASR tasks to overcome this problem. Our proposed ASR system is less vulnerable to external interference noise, and achieves a higher WRA compared to a conventional ASR system equipped with MFCCs and an HMM. The performance of our proposed ASR system was evaluated using a phonetically balanced word (PBW) set mixed with artificially added noise.
Evenly transferred single-layered graphene membrane assisted by strong substrate adhesion
Park, Seongjae,Kim, Hoijoon,Seol, Daehee,Park, Taejin,Leem, Mirine,Ha, Hyunwoo,An, Hyesung,You Kim, Hyun,Jeong, Seong-Jun,Park, Seongjun,Kim, Hyoungsub,Kim, Yunseok IOP 2017 Nanotechnology Vol.28 No.14
<P>We explored the transfer of a single-layered graphene membrane assisted by substrate adhesion. A relatively larger adhesion force was measured on the SiO<SUB>2</SUB> substrate compared with its van der Waals contribution, which is expected to result from the additional contribution of the chemical bonding force. Density functional theory calculations verified that the strong adhesion force was indeed accompanied by chemical bonding. The transfer of single-layered graphene and subsequent deposition of the dielectric layer were best performed on the SiO<SUB>2</SUB> substrate exhibiting a larger adhesion force. This study suggests the selection and/or modification of the underlying substrate for proper transfer of graphene as well as other 2D materials similar to graphene.</P>