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Bongsoo Lee,Kyoung Won Jang,Dong Hyun Cho,Wook Jae Yoo,Sang Hun Shin,Gye-Rae Tack,Soon-Cheol Chung,Sin Kim,Hyosung Cho,Byung Gi Park,Joo Hyun Moon,Siyong Kim IEEE 2008 IEEE transactions on nuclear science Vol.55 No.5
<P>In this study, a one-dimensional fiber-optic scintillating detector was developed for electron-beam therapy dosimetry. Each fiber-optic detector contains an organic scintillator as a sensitive volume and it is embedded and arrayed in a plastic phantom to measure one-dimensional high-energy electron-beam profiles of clinical linear accelerators. Plastic optical fibers guide the scintillating light which each detector probe generates to a photodiode array. The one-dimensional electron-beam profiles in the plastic phantom were measured in two different field sizes and for two electron-beam energies. Also, isodose and two-dimensional dose distributions in the plastic phantom were obtained using the one-dimensional scintillating detector array with two different electron beam energies.</P>
Lee, Myeongjae,Kim, Min Je,Ro, Suhee,Choi, Shinyoung,Jin, Seon-Mi,Nguyen, Hieu Dinh,Yang, Jeehye,Lee, Kyung-Koo,Lim, Dong Un,Lee, Eunji,Kang, Moon Sung,Choi, Jong-Ho,Cho, Jeong Ho,Kim, BongSoo American Chemical Society 2017 ACS APPLIED MATERIALS & INTERFACES Vol.9 No.34
<P>High carrier mobilities have recently been achieved in polymer field effect transistors (FETs). However, many of these polymer FET devices require the use of chlorinated solvents such as chloroform (CF), chlorobenzene (CB), and odichlorobenzene (DCB) during fabrication. The use of these solvents is highly restricted in industry because of health and environmental issues. Here, we report the synthesis of a low band gap (1.43 eV, 870 nm) semiconducting polymer (PDPP2DT-F2T2) having a planar geometry, which can be readily processable with nonchlorinated solvents such as toluene (TOL), o-xylene (XY), and 1,2,4-trimethylbenzene (TMB). We performed structural characterization of PDPP2DT-F2T2 films prepared from different solvents, and the electrical properties of the films were measured in the context of FETs. The devices exhibited an ambipolar behavior with hole dominant transport. Hole mobilities increased with increasing boiling point (bp) of the nonchloririated solvents: 0.03, 0.05, and 0.10 cm(2) V-1 s' for devices processed using TOL, XY, and TMB, respectively. Thermal annealing further improved the FET performance. TMB-based polymer FETs annealed at 200 degrees C yielded a maximum hole mobility of 1.28 cm(2) s(-1), which is far higher than the 0.43 cm(2) V-1 s(-1) obtained from the CF-based device. This enhancement was attributed to increased interchain interactions as well as improved long-range interconnection between fibrous domains. Moreover, all of the nonchlorinated solutions generated purely edge-on orientations of the polymer chains, which is highly beneficial for carrier transport in FET devices. Furthermore, we fabricated an array of flexible TMBprocessed PDPP2DT-F2T2 FETs on the plastic PEN substrates. These devices demonstrated excellent carrier mobilities and negligible degradation after 300 bending cycles. Overall, we demonstrated that the organized assembly of polymer chains can be achieved by slow drying using high bp nonchlorinated solvents and a post thermal treatment. Furthermore, we showed that polymer FETs processed using high bp nonhalogenated solvents may outperform those processed using halogenated solvents.</P>
Lee, Kee Doo,Seo, Se Won,Lee, Doh-Kwon,Kim, Honggon,Ko, Min Jae,Kim, BongSoo,Kim, Dong Hwan,Kim, Jin Young The Electrochemical Society 2013 ECS transactions Vol.50 No.51
<P>The effect of the heating rate during the sulfurization process on the properties of Cu<SUB>2</SUB>ZnSnS<SUB>4</SUB> (CZTS) thin film solar cells was investigated. A moderate heating rate of ~10 <SUP>o</SUP>C/min was found to result in a modest solar cell performance (2 %), whereas the higher heating rates resulted in worse performances. In the CZTS thin films annealed with the highest heating rate, the segregation of Cu atoms towards the outer surface of the films, which is believed to lead to shunting of the solar cells.</P>
Lee, Hyo Sang,Song, Hyeng Gun,Jung, Hyeseung,Kim, Myung Hwa,Cho, Changsoon,Lee, Jung-Yong,Park, Sungnam,Son, Hae Jung,Yun, Hui-Jun,Kwon, Soon-Ki,Kim, Yun-Hi,Kim, BongSoo American Chemical Society 2016 Macromolecules Vol.49 No.20
<P>The photostability of donor-acceptor (D-A) polymers remains a critical issue despite recent improvements in the power conversion efficiencies (PCEs) of organic photovoltaic (OPV) cells. We report the synthesis of three highly photostable polymers (PDTBDT-BZ, PDTBDT-BZF, and PDTBDT-BZF(2)) and their suitability for use in high-performance OPV cells. Under 1 sunlight of illumination in air for 10 h, these polymer films demonstrated remarkably high photostability compared to that of PTB7, a representative polymer in the OPV field. While the PDTBDT-BZ, PDTBDT-BZF, and PDTBDT-BZF2 polymer films maintained 97, 90, and 96% photostability, respectively, a PTB7 film exhibited only 38% photo stability under the same conditions. We ascribed the high photostability of the polymers to both the intrinsically photostable chemical moieties and the dense packing of alkyl side chains and planar backbone polymer chains, which prevents oxygen diffusion into the PDTBDT-BZ films. This work demonstrates the high photostability of planar PDTBDT-BZ series polymers composed of photostable DTBDT and BZ moieties and suggests a design rule to synthesize highly photostable photovoltaic materials.</P>
Measurements of Cerenkov Lights Using Optical Fibers
Bongsoo Lee,Kyoung Won Jang,Wook Jae Yoo,Sang Hun Shin,Jinsoo Moon,Ki-Tek Han,Dayeong Jeon IEEE 2013 IEEE transactions on nuclear science Vol.60 No.2
<P>Optical fibers can be a medium to produce Cerenkov light due to their dielectric components, and radiation-induced light signals can be obtained using optical fibers without any scintillating material. In this study, we measured and characterized gamma-ray induced Cerenkov light in silica optical fibers, a plastic optical fiber, and a plastic wavelength shifting fiber in order to select the adequate optical fiber for producing Cerenkov light. Also, we measured the intensity of Cerenkov light as functions of irradiated length, irradiation angle, and thickness of various scatterers using the chosen optical fiber.</P>
Lee, Sung-Sik,Kim, Bongsoo,Lee, Sungyul American Chemical Society 2014 The Journal of Physical Chemistry Part C Vol.118 No.36
<P>We present the structures, bonding characteristics, and infrared spectra of the gold surface (111)–Arg-Cys (Arg-Cys@Au(111)) complex calculated by a periodic plane wave DFT technique. We examine the detailed features of bonding between the gold surface and dipeptide. The dipeptide is revealed to form a covalent bond via the −SH group with 2–3 gold atoms, and also weak noncovalent interactions via the carboxyl and guanidine side chain lying more or less parallel to the gold surface. The S–H bond dissociates as a result of the S<SUP>–</SUP>–(Au)<SUB><I>n</I></SUB> bond formation, with the hydrogen atom binding to the guanidine moiety. The acidic proton stays at the carboxyl group in the most stable structure of Arg-Cys@Au(111). The calculated infrared spectra are compared with experimental observations reported by Petoral and Uvdal (<I>Colloids Surf., B</I> <B>2002</B>, <I>25</I>, 335).</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jpccck/2014/jpccck.2014.118.issue-36/jp412438f/production/images/medium/jp-2013-12438f_0008.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/jp412438f'>ACS Electronic Supporting Info</A></P>
Enhanced Deseleniumization of Selenophene Molecules Adsorbed on Si(100)-2 × 1 Surface
Lee, Han-Koo,Park, Jinwoo,Kim, Ki-jeong,Kim, Hyeong-Do,Lee, Ik-Jae,Shin, Hyun-Joon,Kim, Bongsoo,Yu, B. D.,Hong, Suklyun,Chung, J. W. American Chemical Society 2011 The Journal of Physical Chemistry Part C Vol.115 No.36
<P>We report the bonding structure of the selenophene molecules adsorbed on the Si(100)-2 × 1 surface at 300 K, and its evolution upon annealing investigated by adopting core-level photoemission spectroscopy, near-edge X-ray absorption fine structure (NEXAFS), and ab initio calculations. The Si 2p, C 1s, Se 3d core-level spectra measured at two temperatures, 300 and 350 K, are consistently interpreted in terms of the two major structures suggested by theory, a twisted (<I>T</I>) 2,5-dihydroselenophene (<I>T</I>-DHS) and a <I>T</I>-deseleniumization where the selenium atom is dissociated from the selenophene ring. We find a significantly enhanced deseleniumization of selenophene molecules by mild thermal annealing indicating that these two equally abundant structures at 300 K become a single uniform phase of the <I>T</I>-deseleniumization structures at 350 K by overcoming a relatively low dissociation energy barrier between the two structures. In addition, we obtain an average tilt angle of a selenophene ring at 300 K from our NEXAFS spectra α∼53 ± 3°, which represents an ensemble average of the tilt angles, α = 15° of the <I>T</I>-DHS and 75° of the <I>T</I>-deseleniumization.</P><P>High-resolution photoemission spectroscopy data combined with ab initio calculation suggest a significantly enhanced thermally activated deseleniumization of selenophene molecules on the Si(100) surface revealing the <I>T</I>-deseleniumization as the most stable structure at 350 K over the <I>T</I>-DHS equally abundant at 300 K.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jpccck/2011/jpccck.2011.115.issue-36/jp203894v/production/images/medium/jp-2011-03894v_0008.gif'></P>
Lee, JoongSuk,Son, Seon Kyoung,Song, Sanghoon,Kim, Hyunjung,Lee, Dong Ryoul,Kim, Kyungkon,Ko, Min Jae,Choi, Dong Hoon,Kim, BongSoo,Cho, Jeong Ho American ChemicalSociety 2012 Chemistry of materials Vol.24 No.7
<P>We investigated the performance of ambipolar field-effecttransistors based on a seriesof alternating low band gap polymers of oligothiophene and diketopyrrolopyrrole(DPP). The polymers contain oligothiophene units of terthiophene [T3]and thiophene-thienothiophene-thiophene [T2TT] and DPP units carryingbranched alkyl chains of 2-hexyldecyl [HD] or 2-octyldodecyl [OD].The structural variation allows us to do a systematic study on therelationship between the interchain stacking/ordering of semiconductingpolymers and their resulting device performance. On the basis of synchrotronX-ray diffraction and atomic force microscopy measurements on polymerfilms, we found that longer branched alkyl side chains, i.e., OD,and longer and more planar oligothiophene, i.e., T2TT, generate themore crystalline structures. Upon thermal annealing, the crystallinityof the polymers was largely improved, and polymers containing a longerbranched alkyl chain responded faster because longer alkyl chainshave larger cohesive forces than shorter chains. For all the polymers,excellent ambipolar behavior was observed with a maximum hole andelectron mobility of 2.2 and 0.2 cm<SUP>2</SUP> V<SUP>–1</SUP> s<SUP>–1</SUP>, respectively.</P><P>We investigated the performance of ambipolarfield-effecttransistors based on a series of alternating low band gap polymersof oligothiophene and diketopyrrolopyrrole (pDPPT3-HD, pDPPT3-OD,pDPPT2TT-HD, and pDPPT2TT-OD). Herein, we report the high carriermobilities and the good correlation between the interchain stackingof polymers and their device performance.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/cmatex/2012/cmatex.2012.24.issue-7/cm2037487/production/images/medium/cm-2011-037487_0008.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/cm2037487'>ACS Electronic Supporting Info</A></P>