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Colorless polyimide/organoclay nanocomposite substrates for flexible organic light-emitting devices.
Kim, Jin-Hoe,Choi, Myeon-Chon,Kim, Hwajeong,Kim, Youngkyoo,Chang, Jin-Hae,Han, Mijeong,Kim, Il,Ha, Chang-Sik American Scientific Publishers 2010 Journal of Nanoscience and Nanotechnology Vol.10 No.1
<P>We report the preparation and application of indium tin oxide (ITO) coated fluorine-containing polyimide/organoclay nanocomposite substrate. Fluorine-containing polyimide/organoclay nanocomposite films were prepared through thermal imidization of poly(amic acid)/organoclay mixture films, whilst on which ITO thin films were coated on the films using a radio-frequency planar magnetron sputtering by varying the substrate temperature and the ITO thickness. Finally the ITO coated fluorine-containing polyimide/organoclay nanocomposite substrate was employed to make flexible organic light-emitting devices (OLED). Results showed that the lower sheet resistance was achieved when the substrate temperature was high and the ITO film was thick even though the optical transmittance was slightly lowered as the thickness increased. approximately 10 nm width ITO nanorods were found for all samples but the size of clusters with the nanorods was generally increased with the substrate temperature and the thickness. The flexible OLED made using the present substrate was quite stable even when the device was extremely bended.</P>
Kim, Hwajeong,Kim, So Yeun,Nam, Sungho,Ronnett, Gabriele V.,Han, Hyung Soo,Moon, Cheil,Kim, Youngkyoo The Royal Society of Chemistry 2012 The Analyst Vol.137 No.9
<P>An artificial nose was developed to mimic aspects of sensory transduction of the peripheral mammalian olfactory system. We directly cultured and differentiated rat olfactory sensory neurons (OSNs) on indium-tin oxide electrodes of planar triode substrates without a coupling agent. Direct voltage (∼50 μV) and current (∼250 nA) signals were measured simultaneously when OSNs on the planar triode substrates were exposed to odorant mixtures. The response signals were sensitive to the concentration of the odorant mixture, with a typical lifetime, shape, and adaptation profile as seen in responses upon repeated stimulation <I>in vivo</I>. We found that the rising time to the peak current was ∼161 ms, while the signal back to baseline was in 1.8 s, which are in agreement with the natural intracellular electrophysiological responses. These results provide the first evidence that mature OSNs grown in a planar triode device are able to detect direct electrophysiological responses to odorants.</P> <P>Graphic Abstract</P><P>A planar triode-type artificial nose with olfactory sensory neurons (OSNs) generates direct voltage (~50 μV) and current (~250 nA) signals upon odorant stimulation. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c2an16205a'> </P>
Precursor Polymer Effect on Polyimide/Silica Hybrid Nanocomposite Films
Kim, Youngkyoo,Ha, Chang-Sik,Chang, Taehyun,Lee, Won-Ki,Goh, Wanhee,Kim, Hwajeong,Ha, Youri,Ree, Moonhor American Scientific Publishers 2009 Journal of Nanoscience and Nanotechnology Vol.9 No.8
<P>Here we report the influence of the polyimide precursor type on the surface morphology and properties of poly(p-phenylene biphenyltetracarboximide) (BPDA-PDA PI)/silica hybrid composite films. Two types of precursor polymer were employed: poly(p-phenylene biphenyltetracarboxamic acid) (BPDA-PDA PAA) and poly(p-phenylene biphenyltetracarboxamic diethyl ester) (BPDA-PDA PES). These precursor polymers were mixed with tetraethoxysilane in the presence of HCl and H2O, which led to the precursor mixture films that contain in-situ generated silica particles via sol-gel process. Then the precursor mixture films were subject to thermal imidization to make polyimide/silica hybrid composite films. Results showed that the PAA precursor has better compatibility with silica particles, which is mainly attributed to the early making of silyl ester bonds (as evidenced by X-ray photoelectron spectroscopy) between carboxylic acid groups in the PAA and hydroxyl groups in silanol molecules. Further evidences were provided by the measurement of surface nanomorphology, crystal nanostructure, thermal/mechanical properties, and optical birefringence.</P>
Kim, Joonhyeon,Lee, Seungsoo,Nam, Sungho,Lee, Hyena,Kim, Hwajeong,Kim, Youngkyoo American Chemical Society 2012 ACS APPLIED MATERIALS & INTERFACES Vol.4 No.10
<P>We investigated the dispersion effect of crystalline silicon nanoparticles (SiNP) on the performance and stability of organic solar cells with the bulk heterojunction (BHJ) films of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C<SUB>61</SUB>-butyric acid methyl ester (PC<SUB>61</SUB>BM). To improve the dispersion of SiNP in the BHJ films, we attached octanoic acid (OA) to the SiNP surface via esterification reaction and characterized it with Raman spectroscopy and high-resolution transmission electron microscopy. The OA-attached SiNP (SiNP-OA) showed improved dispersion in chlorobenzene without change of optical absorption, ionization potential and crystal nanostructure of SiNP. The device performance was significantly deteriorated upon high loading of SiNP (10 wt %), whereas relatively good performance was maintained without large degradation in the case of SiNP-OA. Compared to the control device (P3HT:PC<SUB>61</SUB>BM), the device performance was improved by adding 2 wt % SiNP-OA, but it was degraded by adding 2 wt % SiNP. In particular, the device stability (lifetime under short time exposure to 1 sun condition) was improved by adding 2 wt % SiNP-OA even though it became significantly decreased by adding 2 wt % SiNP. This result suggests that the dispersion of nanoparticles greatly affects the device performance and stability (lifetime).</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/aamick/2012/aamick.2012.4.issue-10/am301250s/production/images/medium/am-2012-01250s_0011.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/am301250s'>ACS Electronic Supporting Info</A></P>
A FAMILY OF CHARACTERISTIC CONNECTIONS
Kim, Hwajeong Chungcheong Mathematical Society 2013 충청수학회지 Vol.26 No.4
The characteristic connection is a good substitute for Levi-Civita connection in studying non-integrable geometries. In this paper we consider the homogeneous space $U(3)/(U(1){\times}U(1){\times}U(1))$ with a one-parameter family of Hermitian structures. We prove that the one-parameter family of Hermtian structures admit a characteristic connection. We also compute the torsion of the characteristic connecitons.
Kim, Hwajeong,Nam, Sungho,Lee, Hyena,Woo, Sungho,Ha, Chang-Sik,Ree, Moonhor,Kim, Youngkyoo American Chemical Society 2011 The Journal of Physical Chemistry Part C Vol.115 No.27
<P>We report the influence of the controlled acidity of the hole-collecting buffer layer, poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), on the performance and lifetime of polymer:fullerene solar cells. The acidity was controlled by adding a strong base (NaOH) to the pristine PEDOT:PSS solutions. The NaOH-modified PEDOT:PSS layers were used for fabricating polymer:fullerene solar cells with active layers made from blend films of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C<SUB>61</SUB>-butyric acid methyl ester (PC<SUB>61</SUB>BM). The results showed that a small addition of NaOH (0.2 molar ratio) removed 23% of the sulfonic acid groups but did not change the device performance, even though further NaOH addition degraded the device performance owing to an increased sheet resistance and lowered work function, as well as a changed surface morphology. Storage lifetime tests showed that the device with the modified PEDOT:PSS layer (0.2 molar ratio NaOH) was almost not degraded, whereas the pristine PEDOT:PSS layer might affect the deterioration at the interface with the active layer (P3HT:PCBM). Under 1 sun illumination for 10 h, the modified PEDOT:PSS layer (0.2 molar ratio NaOH) resulted in ∼25% improved lifetime, which is in excellent agreement with the extent of reduction of the sulfonic acid groups (∼23%).</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jpccck/2011/jpccck.2011.115.issue-27/jp2028615/production/images/medium/jp-2011-028615_0001.gif'></P>
A NOTE ON THE JACOBI FIELDS ON MANIFOLDS
( Hwajeong Kim ) 호남수학회 2016 호남수학학술지 Vol.38 No.2
We consider Jacobi fields as the first derivatives for ε, the energy of harmonic extensions, in a given manifold. In this paper we see that the Jacobi field is bounded by the given boundary map. Here we give no restriction concerned with the curvature for the given manifold.