大岩山의 植物相

閔雄基,張珍成,全正壹,金輝,崔道烈,鄭承洙 서울대학교 수목원 2000 서울大學校 樹木園 硏究報告 Vol.- No.20

This study was carried out to investigate the flora of Mts. Dae-am, Dae-woo, Baek-suk, and Sa-myung located on the east side of DMZ in province Yang-gu-gun, from July 1999 to August 2000. Although two hundred and fifty eight vascular plant taxa (70 families 167 genera) were recorded, this was only a part of representatives in this community because of the restrictin of collections within the military zone. The overall forest stand age of this area was 40 to 50 years, but occasionally ca 70 years old trees were found. We reported 11 taxa of the rare and endangered species proposed by the Ministry of Environment in this area. The Yong-neup, the only high altitude (alt. 1,200m) moore in south Korea, are located in the peak of Mt. Dae-am-san. Some species of this moore (Carex chordorrhiza Ehrh., Carex limosa L., and Gentiana jamesii Hemsl.) - were only found in south Korea. This moor would suffer vegetation change by natural moorland succession and human disturbances. The long-term monitoring of variation of annual vegetation, species distribution, numbers and distribution pattern of individuals of rare species are recommended for the wetland conservation.

雲達山의 植物相

閔雄基,張珍成,全正壹,金輝,崔道烈,金承昆 서울대학교 수목원 2001 서울大學校 樹木園 硏究報告 Vol.- No.21

This study was carried out to investigate the flora of Mt. Undal (alt. 1,097.2m) located on the northwestern side of province Gyeongsangbuk-do, near Myngyeong-si city, from April 2000 to Sept. 2000. Total number of vascular plants discovered in Mt. Undal were 70 families, 154 genera, and 243 taxa(including species, subspecies, varieties and forma). Major vegetation was Acer pictum var. mono - Quercus mongolica - Carpinus laxiflora community. The overall forest stand age of this area was 40 to 50 years, and occasionally ca 70 years old Abies holophylla trees were found. Although, there were no rare and endangered speices, we found two species of level IV by the Ministry of Environment - Anemone koraiensis Nakai, Anemone reflexa. Steph. et Willd.

Chirality-specific transport phenomena of isolated single-walled carbon nanotube

Jeong, Seung Yol,Perello, David,Kim, Sung Jin,Jang, Jin Ho,Kang, Bo Ram,Yu, Woo Jong,Bae, Dong Jae,Yun, Minhee,Lee, Young Hee WILEY-VCH Verlag 2007 Physica Status Solidi. B Vol.244 No.11

<P>Single-walled carbon nanotube-field effect transistors (SWCNT-FETs) have been fabricated using in-situ thermal chemical vapor deposition. For isolated devices, the resonant Raman spectra confirmed that the full width at half maximum (FWHM) of the radial breathing mode (RBM) peaks was about 4 cm<SUP>–1</SUP>, consistent with atomic force microscopy (AFM) images that clearly revealed the individually isolated SWCNTs on the patterned substrate with a diameter of 1.3 nm. Subsequent I –V measurements of the SWCNT-FET revealed a clear gating effect for samples with semiconducting SWCNTs. The transport phenomena of a device with mixed metallic and semiconducting SWCNTs network were governed by the metallic nanotube with severely suppressed gate modulation. Identification of the chirality of SWCNTs by resonant Raman spectroscopy prior to the I –V characteristics guarantees the validity of working FET devices. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)</P>

Highly Concentrated and Conductive Reduced Graphene Oxide Nanosheets by Monovalent Cation–<i>π</i> Interaction: Toward Printed Electronics

Jeong, Seung Yol,Kim, Sung Hun,Han, Joong Tark,Jeong, Hee Jin,Jeong, Soo Yeon,Lee, Geon‐,Woong WILEY‐VCH Verlag 2012 Advanced Functional Materials Vol.22 No.15

<P><B>Abstract</B></P><P>A novel route to preparing highly concentrated and conductive reduced graphene oxide (RGO) in various solvents by monovalent cation–<I>π</I> interaction. Previously, the hydrophobic properties of high‐quality RGO containing few defects and oxygen moieties have precluded the formation of stable dispersion in various solvents. Cation–<I>π</I> interaction between monovalent cations, such as Na<SUP>+</SUP> or K<SUP>+</SUP>, and six‐membered sp<SUP>2</SUP> carbons on graphene were achieved by simple aging process of graphene oxide (GO) nanosheets dispersed in alkali solvent. The noncovalent binding forces introduced by the cation–<I>π</I> interactions were evident from the chemical shift of the sp<SUP>2</SUP> peak in the solid <SUP>13</SUP>C NMR spectra. Raman spectra and the <I>I</I>‐<I>V</I> characteristics demonstrated the interactions in terms of the presence of <I>n</I>‐type doping effect due to the adsorption of cations with high electron mobility (39 cm<SUP>2</SUP>/Vs). The RGO film prepared without a post‐annealing process displayed superior electrical conductivity of 97,500 S/m at a thickness of 1.7 μm. Moreover, mass production of GO paste with a concentration as high as 20 g/L was achieved by accelerating the cation–<I>π</I> interactions with densification process. This strategy can facilitate the development of large scalable production methods for preparing printed electronics made from high‐quality RGO nanosheets.</P>

Arrays of vertically aligned tubular-structured graphene for flexible field emitters

Jeong, Hee Jin,Kim, Ho Young,Jeong, Hae Deuk,Jeong, Seung Yol,Han, Joong Tark,Lee, Geon-Woong The Royal Society of Chemistry 2012 Journal of materials chemistry Vol.22 No.22

<P>Arrays of tubular-structured reduced graphene oxide (RGO) were fabricated by a simple method involving filtration of a solution containing highly dispersed RGO sheets. The length and alignment of the tubular-structured RGO arrays were controlled by the filtration rate and by tuning the interactions between the hydrophobic RGO sheets and the porous walls, rather than the top surfaces, of the polycarbonate filter membrane. As expected, the lengths of the RGO arrays increased with higher filtration rates; however, maximum field emission characteristics were obtained at an intermediate filtration rate because field screening reduced electron emission from the longer-length RGO arrays. ZnO-coated RGO arrays showed excellent emission stability without significant current degradation or fluctuations, even under O<SUB>2</SUB> exposure. The ZnO layer protected the emission site of the RGO arrays from the reactive ion bombardment of oxidative gas species. Moreover, the RGO arrays were highly flexible with preservation of the field emission properties, even at large bending angles. The excellent field emission characteristics of the tubular structured RGO arrays were attributed to the high crystallinity, abundant sharp edges, and the chemical stability of the RGO arrays, as well as the strong interactions between the RGO arrays and the substrate.</P> <P>Graphic Abstract</P><P>High-performance flexible field emission was demonstrated using tubular-structured reduced graphene oxide arrays by a simple method involving filtration of a solution containing highly dispersed RGO sheets. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c2jm31263h'> </P>

Autophagic flux induced by graphene oxide has a neuroprotective effect against human prion protein fragments

Jeong, Jae-Kyo,Lee, You-Jin,Jeong, Seung Yol,Jeong, Sooyeon,Lee, Geon-Woong,Park, Sang-Youel DOVE MEDICAL PRESS 2017 INTERNATIONAL JOURNAL OF NANOMEDICINE Vol.12 No.-

<P>Graphene oxide (GO) is a nanomaterial with newly developing biological applications. Autophagy is an intracellular degradation system that has been associated with the progression of neurodegenerative disorders. Although induction of autophagic flux by GO has been reported, the underlying signaling pathway in neurodegenerative disorders and how this is involved in neuroprotection remain obscure. We show that GO itself activates autophagic flux in neuronal cells and confers a neuroprotective effect against prion protein (PrP) (106–126)-mediated neurotoxicity. GO can be detected in SK-N-SH neuronal cells, where it triggers autophagic flux signaling. GO-induced autophagic flux prevented PrP (106–126)-induced neurotoxicity in SK-N-SH cells. Moreover, inactivation of autophagic flux blocked GO-induced neuroprotection against prion-mediated mitochondrial neurotoxicity. This is the first study to demonstrate that GO regulates autophagic flux in neuronal cells, and that activation of autophagic flux signals, induced by GO, plays a neuroprotective role against prion-mediated mitochondrial neurotoxicity. These results suggest that the nanomaterial GO may be used to activate autophagic flux and could be used in neuroprotective strategies for treatment of neurodegenerative disorders, including prion diseases.</P>

One-step transfer and integration of multifunctionality in CVD graphene by TiO2/graphene oxide hybrid layer.

Jeong, Hee Jin,Kim, Ho Young,Jeong, Hyun,Han, Joong Tark,Jeong, Seung Yol,Baeg, Kang-Jun,Jeong, Mun Seok,Lee, Geon-Woong Wiley-VCH 2014 Small Vol.10 No.10

<P>We present a straightforward method for simultaneously enhancing the electrical conductivity, environmental stability, and photocatalytic properties of graphene films through one-step transfer of CVD graphene and integration by introducing TiO2/graphene oxide layer. A highly durable and flexible TiO2 layer is successfully used as a supporting layer for graphene transfer instead of the commonly used PMMA. Transferred graphene/TiO2 film is directly used for measuring the carrier transport and optoelectronic properties without an extra TiO2 removal and following deposition steps for multifunctional integration into devices because the thin TiO2 layer is optically transparent and electrically semiconducting. Moreover, the TiO2 layer induces charge screening by electrostatically interacting with the residual oxygen moieties on graphene, which are charge scattering centers, resulting in a reduced current hysteresis. Adsorption of water and other chemical molecules onto the graphene surface is also prevented by the passivating TiO2 layer, resulting in the long term environmental stability of the graphene under high temperature and humidity. In addition, the graphene/TiO2 film shows effectively enhanced photocatalytic properties because of the increase in the transport efficiency of the photogenerated electrons due to the decrease in the injection barrier formed at the interface between the F-doped tin oxide and TiO2 layers.</P>

All‐Carbon Nanotube‐Based Flexible Field‐Emission Devices: From Cathode to Anode

Jeong, Hee Jin,Jeong, Hae Deuk,Kim, Ho Young,Kim, Jun Suk,Jeong, Seung Yol,Han, Joong Tark,Bang, Dae Suk,Lee, Geon‐,Woong WILEY‐VCH Verlag 2011 Advanced functional materials Vol.21 No.8

<P><B>Abstract</B></P><P>The fabrication of a flexible field‐emission device (FED) using single‐walled carbon nanotube (SWNT) network films as the conducting electrodes (anode and cathode) and thin multi‐walled CNT/TEOS hybrid films as the emitters is reported. P‐type doping with gold ions and passivation with tetraethylorthosilicate (TEOS) made the SWNT network film highly conductive and environmentally stable, and hence a good alternative to conventional indium tin oxide electrodes. CNT/TEOS hybrid emitters showed high current density, low turn‐on field, and long‐term emission stability, compared with CNT emitters; these characteristics can be attributed to the TEOS sol, acting both as a protective layer surrounding the nanotube tip, and as an adhesive layer enhancing the nanotube adhesion to the substrate. All‐CNT‐based flexible FEDs fabricated by this approach showed high flexibility in field emission characteristics and extremely bright electron emission patterns.</P>

ROOM TEMPERATURE DEPOSITION OF SINGLE-WALLED CARBON NANOTUBE THIN FILMS

SEUNG YOL JEONG,BHARVIN PAREKH,VARUN GUPTA,GIOVANNI FANCHINI,MANISH CHHOWALLA 성균관대학교(자연과학캠퍼스) 성균나노과학기술원 2010 NANO Vol.5 No.5

A simple method for direct deposition of single-walled carbon nanotube (SWNT) networks on flexible substrates at room temperature is reported. Deposition of thin films was carried out using a two-zone tube furnace where the nucleation and growth of SWNTs occur in vapor phase in the hot zone and condense onto substrates in the cold zone. Raman spectroscopy and scanning electron microscopy reveal individual, uniformly distributed SWNTs over large areas (several cm2). The coverage density of the SWNTs on flexible substrates can be controlled by the location of the substrates within the cold zone. The opto-electronic properties of the thin films indicated that they can be transparent and conducting with sheet resistances ranging from 4 to 21 kΩ/sq at corresponding transparencies of 51 to 87%, respectively.

High Performance GaN-Based Light-Emitting Diodes by Increased Hole Concentration Via Graphene Oxide Sheets

Hyun Jeong,Seung Yol Jeong,Hyun Joon Jeong,Doo Jae Park,Yong Hwan Kim,HyoJung Kim,Geon-Woong Lee,Mun Seok Jeong 한국진공학회 2013 한국진공학회 학술발표회초록집 Vol.2013 No.8