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Tarsoly, Gergely,Pyo, Seungmoon Elsevier 2018 Optical materials Vol.80 No.-
<P><B>Abstract</B></P> <P>We report the opto-electrical response of organic field-effect transistors based on a thin-film of a semiconducting diketopyrrolopyrrole (DPP) core, a popular building block for molecular semiconductors, and a polymeric gate dielectric. The thin-film of the DPP core was thermally annealed at different temperatures under N<SUB>2</SUB> atmosphere to investigate the relationship between the annealing temperature and the electrical properties of the device. The results showed that the annealing process induces morphological changes in the thin film, and properly controlling the thermal annealing conditions can enhance the device performance. In addition, we also investigated in detail the photo-response behaviors by analyzing the responsivity (<I>R</I>) of the device with the optimally annealed DPP-core thin film under two light illumination conditions by considering the irradiance absorbed by the thin film instead of the total irradiance of the light source. We found that the proposed model could lead to a light-source-independent description of the photo-response behavior of the device, and which can be used for other applications.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Phototransistors were fabricated using a simple diketopyrrolopyrrole (DPP) and a polymer dielectric. </LI> <LI> Electrical and photoresponsive behavior of the devices were investigated. </LI> <LI> Mathematical model was constructed based on the irradiance absorbed by the DPP. </LI> <LI> Light source independent photoresponsivity was established. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>In this paper the photo-responsive behavior of a phototransistor based on thermally annealed DPP-R16 is discussed using two different polychromatic light sources, and a mathematical model is developed to evaluate light source independent responsivity.</P> <P>[DISPLAY OMISSION]</P>
Subcellular Neural Probes from Single-Crystal Gold Nanowires
Kang, Mijeong,Jung, Seungmoon,Zhang, Huanan,Kang, Taejoon,Kang, Hosuk,Yoo, Youngdong,Hong, Jin-Pyo,Ahn, Jae-Pyoung,Kwak, Juhyoun,Jeon, Daejong,Kotov, Nicholas A.,Kim, Bongsoo American Chemical Society 2014 ACS NANO Vol.8 No.8
<P/><P>Size reduction of neural electrodes is essential for improving the functionality of neuroprosthetic devices, developing potent therapies for neurological and neurodegenerative diseases, and long-term brain–computer interfaces. Typical neural electrodes are micromanufactured devices with dimensions ranging from tens to hundreds of micrometers. Their further miniaturization is necessary to reduce local tissue damage and chronic immunological reactions of the brain. Here we report the neural electrode with subcellular dimensions based on single-crystalline gold nanowires (NWs) with a diameter of ∼100 nm. Unique mechanical and electrical properties of defect-free gold NWs enabled their implantation and recording of single neuron-activities in a live mouse brain despite a ∼50× reduction of the size compared to the closest analogues. Reduction of electrode dimensions enabled recording of neural activity with improved spatial resolution and differentiation of brain activity in response to different social situations for mice. The successful localization of the epileptic seizure center was also achieved using a multielectrode probe as a demonstration of the diagnostics potential of NW electrodes. This study demonstrated the realism of single-neuron recording using subcellular-sized electrodes that may be considered a pivotal point for use in diverse studies of chronic brain diseases.</P>
Surface modified polymeric gate insulators for pentacene organic thin-film transistors
Kim, So Yeon,Ahn, Taek,Pyo, Seungmoon,Yi, Mihye Elsevier 2009 CURRENT APPLIED PHYSICS Vol.9 No.5
<P><B>Abstract</B></P><P>This paper demonstrates effects of a surface modification of polymeric gate insulators on a performance of organic thin-film transistor (OTFT). Pentacene OTFTs were fabricated with three types of polymer gate insulators—poly(4-vinylphenol) (PVP, <I>G1</I>) with comparably high dielectric constant, polyimide (PI, <I>G2</I>) with <I>n</I>-octadecyl (C<SUB>18</SUB>) side chain, which resulted in hydrophobicity and low dielectric constant, and surface modified PVP(<I>G3</I>). The <I>G3</I> was prepared by a spin-coating the solution of <I>G2</I> onto the <I>G1</I> film. We found that the <I>n</I>-octadecyl group of the <I>G3</I> protruded from the surface and made the PVP surface more hydrophobic. The less polar surface strongly improved the device performance. Subthreshold slope (s.s.) of the OTFT with <I>G3</I> as the gate insulator decreased significantly to 2.7V/dec, which was much smaller than that of OTFTs fabricated with <I>G1</I> (4.0V/dec). That is, thin layer with fewer C<SUB>18</SUB> group in contact with pentacene induced a good electrical property like lower s.s. Further the higher dielectric constant of the underlying layer resulted in higher mobility of the device. The mobility (0.50cm<SUP>2</SUP>V<SUP>−1</SUP>s<SUP>−1</SUP>) of the OTFT with <I>G3</I> as the gate insulator showed a higher value compared to that (0.25cm<SUP>2</SUP>V<SUP>−1</SUP>s<SUP>−1</SUP>) of the OTFT with <I>G2</I>.</P>
Lee, Yeon Ju,Jang, Yunseok,Cho, Kilwon,Pyo, Seungmoon,Hwang, Do-Hoon,Hong, Sung Chul American Scientific Publishers 2009 Journal of Nanoscience and Nanotechnology Vol.9 No.12
<P>Poly(4-hydroxystyrene) block copolymers containing maleic acid groups in one block were prepared through nitroxide mediated polymerization and their thin films with or without BaTiO3 nanoparticles were evaluated as a solution-processable dielectric materials. Poly(4-hydroxystyrene-co-maleic acid)-block-poly(4-hydroxystyrene) was successfully prepared through the hydrolysis of poly(4-acetoxystyrene-co-maleic anhydride)-block-poly(4-acetoxystyrene), as evidenced by GC, GPC, FT-IR and NMR. Through the incorporation of maleic acid group and BaTiO3 nanoparticles to poly(4-hydroxystyrene), higher dielectric constant was observed, suggesting that the dielectric constants of the composite films were strongly affected by the structural and compositional characteristics of polymers and nanocomposites.</P>