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Yu, Hojeong,Bao, Zhenan,Oh, Joon Hak WILEY‐VCH Verlag 2013 Advanced functional materials Vol.23 No.5
<P>On page 629, Hojeong Yu, Zhenan Bao, and Joon Hak Oh report single‐crystalline nanowire organic phototransistors (NW‐OPTs) fabricated using an n‐channel organic semiconductor, <I>N</I>,<I>N</I>′‐bis(2‐phenylethyl)‐perylene‐3,4:9,10‐tetracarboxylic diimide. Highly sensitive and reproducible photoresponses are observed from the NW‐OPTs and photogenerated charge carrier behavior is quantitatively investigated. The findings highlight single‐crystalline NW‐OPTs as an alternative to conventional thin‐film‐type photodiodes and could pave the way for optoelectronic device miniaturization. </P>
Yu, Hojeong,Oh, Youngjin,Kim, Soowon,Song, Seok Ho,Kim, Donghyun Optical Society of America 2012 Optics letters Vol.37 No.18
<P>Metallic wires can discriminate light polarization due to strong absorption of electric fields oscillating in parallel to wires. Here, we explore polarization-based biosensing of DNA hybridization in situ by employing metal target-conjugated nanoparticles to form a wire-grid polarizer (WGP) as complementary DNA strands hybridize. Experimental results using gold nanoparticles of 15 nm diameter to form a WGP of 400 nm period suggest that polarization extinction can detect DNA hybridization with a limit of detection in the range of 1 nM concentration. The sensitivity may be improved by more than an order of magnitude if larger nanoparticles are employed to define WGPs at a period between 400 and 500 nm.</P>
Yu, Hojeong,Park, Kwang Hun,Song, Inho,Kim, Myeong-Jong,Kim, Yun-Hi,Oh, Joon Hak The Royal Society of Chemistry 2015 Journal of Materials Chemistry C Vol.3 No.44
<▼1><P>Systematic side-chain engineering through adjustment of spacer groups in diketopyrrolopyrrole-thiophene vinylene thiophene (DPP-TVT) polymers reveals odd–even dependence of device performance.</P></▼1><▼2><P>For systematic investigation of the structure–property relationship, a series of diketopyrrolopyrrole-thiophene vinylene thiophene (DPP-TVT) polymers, ranging from 25-DPP-TVT to 32-DPP-TVT, with branched alkyl groups containing linear spacer groups from C2 to C9, has been synthesized. The electrical performance of these polymers is clearly dependent on the length of the spacer group and shows the odd–even alterations in chemical and electronic properties induced by the different alkyl chain spacers. Spacer groups with even numbers of carbon atoms exhibit higher charge-carrier mobilities than those with odd numbers of carbon atoms for the linear spacer groups from C2 to C7. Furthermore, the optimal side chain geometry in the DPP-TVT system for the most efficient charge transport contains the C6 spacer between the branching point and the backbone, showing the maximum hole mobility of 8.74 cm<SUP>2</SUP> V<SUP>−1</SUP> s<SUP>−1</SUP> (at <I>V</I>GS, <I>V</I>DS = −100 V). The results obtained herein demonstrate the intriguing odd–even effects induced by the length of the side chain alkyl spacers for DPP-TVT polymers, and provide insight into the side chain engineering for the most efficient charge transport in DPP-based polymer semiconductors.</P></▼2>
Yu, Hojeong,Cho, Han-Hee,Cho, Chul-Hee,Kim, Ki-Hyun,Kim, Dong Yeong,Kim, Bumjoon J.,Oh, Joon Hak American Chemical Society 2013 ACS APPLIED MATERIALS & INTERFACES Vol.5 No.11
<P>A series of <I>o</I>-xylene and indene fullerene derivatives with varying frontier molecular orbital energy levels were utilized for assessing the impact of the number of solubilizing groups on the electrical performance of fullerene-based organic-field-effect transistors (OFETs). The charge-carrier polarity was found to be strongly dependent upon the energy levels of fullerene derivatives. The <I>o</I>-xylene C<SUB>60</SUB> monoadduct (OXCMA) and indene C<SUB>60</SUB> monoadduct (ICMA) exhibited unipolar <I>n</I>-channel behaviors with high electron mobilities, whereas the bis- and trisadducts of indene and <I>o</I>-xylene C<SUB>60</SUB> derivatives showed ambipolar charge transport. The OXCMA OFETs fabricated by solution shearing and molecular <I>n</I>-type doping showed an electron mobility of up to 2.28 cm<SUP>2</SUP> V<SUP>–1</SUP> s<SUP>–1</SUP>, which is one of the highest electron mobilities obtained from solution-processed fullerene thin-film devices. Our findings systematically demonstrate the relationship between the energy level and charge-carrier polarity and provide insight into molecular design and processing strategies toward high-performance fullerene-based OFETs.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/aamick/2013/aamick.2013.5.issue-11/am400618r/production/images/medium/am-2013-00618r_0007.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/am400618r'>ACS Electronic Supporting Info</A></P>
Yu, Hojeong,Bao, Zhenan,Oh, Joon Hak WILEY‐VCH Verlag 2013 Advanced functional materials Vol.23 No.5
<P><B>Abstract</B></P><P>The photoelectronic characteristics of single‐crystalline nanowire organic phototransistors (NW‐OPTs) are studied using a high‐performance n‐channel organic semiconductor, <I>N</I>,<I>N′</I>‐bis(2‐phenylethyl)‐perylene‐3,4:9,10‐tetracarboxylic diimide (BPE‐PTCDI), as the photoactive layer. The optoelectronic performances of the NW‐OPTs are analyzed by way of their current–voltage (<I>I</I>–<I>V</I>) characteristics on irradiation at different wavelengths, and comparison with corresponding thin‐film organic phototransistors (OPTs). Significant enhancement in the charge‐carrier mobility of NW‐OPTs is observed upon light irradiation as compared with when performed in the dark. A mobility enhancement is observed when the incident optical power density increases and the wavelength of the light source matches the light‐absorption range of the photoactive material. The photoswitching ratio is strongly dependent upon the incident optical power density, whereas the photoresponsivity is more dependent on matching the light‐source wavelength with the maximum absorption range of the photoactive material. BPE‐PTCDI NW‐OPTs exhibit much higher external quantum efficiency (EQE) values (≈7900 times larger) than thin‐film OPTs, with a maximum EQE of 263 000%. This is attributed to the intrinsically defect‐free single‐crystalline nature of the BPE‐PTCDI NWs. In addition, an approach is devised to analyze the charge‐transport behaviors using charge accumulation/release rates from deep traps under on/off switching of external light sources.</P>
Jaeho Park,Yu-Chan Kim,Myoung-Ryul Ok,Wonryung Lee,Hyung-Seop Han,Jeong-Yun Sun,Hojeong, Jeon 대한기계학회 2021 대한기계학회 춘추학술대회 Vol.2021 No.11
As the increasing demand for semiconductor, it has been studied for high integration, and miniaturization. Therefore, a more sophisticated process is essential such as plasma etching within high vacuum system. However, the inner wall of the etching equipment can be easily damaged since the surface is exposed to highly reactive atmosphere, so the surface should be coated with high corrosion resistant property. Currently, yttrium-based ceramic materials with excellent corrosion resistance (e.g, Y2O3, YOF) are synthesized and widely used as coating materials. The materials are used to apply in high-temperature and pressure system. However, residual stress, cracks, pores, and low coating strength of the coating layer inevitably exist. In this study, it is not only does not require pretreatment, but also coat simultaneously a plasma-resistant material on substrate via a pulsed laser heat source. The surface was selectively coated with Y2O3 or YOF by modifying the solution concentration used as a precursor. The coating process in this study is simple compared to the existing method. In addition, it can form a high-density layer that minimizes cracks and pores with improved process efficiency and plasma resistance. It is expected that the ceramic material of the desired composition can be selectively applied to various products by utilizing the highly integrated energy of the laser beam.