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Self-Assembly of Pentacene on Sub-nm Scale Surface Roughness- Controlled Gate Dielectrics
Mingyuan Pei,고중세,신환호,조민상,백지민,김규동,육지호,양회창 한국고분자학회 2018 Macromolecular Research Vol.26 No.10
Surface roughness (R q) of dielectric materials plays an important role in the ordering and charge-carrier transport of organic semiconductors, and is directly involved in the development of nuclei and crystal grains on a surface. To investigate the effect of R q-controlled dielectrics with similar surface energy (γ) on the development of nuclei and crystal grain, a series of triethoxysilane-terminated polystyrene (PSTES) polymers with different molecular weights (MW) values is synthesized using reversible addition-fragmentation chain transfer polymerization. The different MW PS-TES films are spun-cast on a hydroxyl (-OH)-rich SiO2 dielectric surface, and chemically coupled with -OH moieties at 110 °C. Some films are also rinsed with an excess of toluene to remove unreacted polymer residue, increasing the average R q values of the treated SiO2 surfaces. The resulting polymer-treated dielectrics show similar surface energy values of 41.6-42.5 mJ m-2 but different R q values ranging from 0.29 to 1.07 nm. On the nanoscale roughness-controlled dielectric surfaces, 40-nm-thick pentacene films show discernible types of crystal grains with different phases, shapes, sizes, and ordering, all of which significantly affect charge-carrier transport along π-conjugated semiconductors in organic field-effect transistors (OFETs). Pentacene OFETs show large variations in fieldeffect mobility (μFET) from 0.89 to 0.19 cm2 V-1 s-1. Specifically, at R q=0.40 nm the μFET value suddenly decreases to 0.30 cm2 V-1 s-1. On polymer treated SiO2 dielectrics with an R q value greater than 0.40 nm, polymorphic, less-ordered, and smaller grains of pentacene containing large number of charge trap sites developed, resulting in significantly degraded charge-carrier transport along the intra- and inter-grains in OFETs, in comparison to the well-ordered grains on smooth polymer-treated surfaces (R q< 0.40 nm).
Water Repellency of Large-Scale Imprinting-Assisted Polymer Films
최하림,이슬이,박상희,고중세,양회창 한국고분자학회 2017 Macromolecular Research Vol.25 No.6
We report that the water repellency of polymeric film surfaces can be simply tuned by pressing softened polymer films into porous anodized aluminum oxide (AAO) templates. Highly-dense nano-pillars and nano-hairs on the polymer surfaces are reproduced via physically or chemically separating the AAO templates from the impressed polymer films. The resulting polymeric nano-textures show various aspect ratios (ARs) between height and cross-sectional diameter (from 2 to 130), depending on the viscoelastic response of the polymer chains during hot AAO pressing and the subsequent separation procedures. The water contact angle values on the nano-textured polymer films considerably changed from 91° to 160° with an increase in AR. Using hot pressing and physical detachment of a porous AAO-covered Al cylinder roller, we successfully demonstrated the potential for large-area fabrication of superhydrophobic polymer films with characteristics that are similar to lotus leaves.