Browsing by Author "Jia, Guobin"

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    Low Temperature Chemical Treatment of Graphene Films Made by Double Self-Assembly Process to Improve Sheet Resistance
    (Elsevier Science, 2021) ARAT, REFİK; Jia, Guobin; Plentz, Jonathan
    In this study, a low temperature hydro iodic acid (HI) vapor treatment of the self-assembled graphene films has been developed, and the electrical, optical, structural and morphological properties were investigated by four point probe, UV-Visible spectroscopy, Raman spectroscopy and scanning electron microscopy (SEM). Mono-, doubleand triple-layer of graphene flakes were deposited on glass substrates by using the Double Self-Assembly (DSA) process. The self-assembled graphene films were treated with HI vapors at 40 degrees C for different time intervals between 1 and 24 h. In addition, graphene deposition and HI-vapor treatment (at 40 degrees C for 1 h) was enforced three times to the same substrate. The optical transparency values of the self-assembled mono- (MGFs), double- (DGFs) and triple-layer graphene flakes (TGFs) were measured as 91, 85 and 80%, respectively (values at 550 nm). Due to the HI-vapor treatment, the sheet resistance of MGFs significantly reduced from 1.1 x 10(7) Omega omega square(-1) to 2.9 x 10(4) omega square(-1), the transparency of the graphene films slightly reduced by 2-5%, the I-D/I-G ratio of the DGFs decreased from 1.01 to 0.81, while the I-2D/I-G ratio increased from 0.43 to 0.48 in the Raman spectrum. Thanks to its impressive reducing effect on sheet resistance, HI-vapor treatment can be a suitable method to improve the conductivity of low-cost large area graphene films.
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    Solution Processed Transparent Conductive Hybrid Thin Films Based on Silver Nanowires, Zinc Oxide and Graphene
    (Elsevier, 2021) ARAT, REFİK; Jia, Guobin; Dellith, Jan; Dellith, Andrea; Plentz, Jonathan
    Transparent conductive hybrid thin films based on silver nanowires (AgNW), zinc oxide (ZnO) and graphene were prepared using solution processing methods. For this study, the hexagonal (wurtzite) ZnO particles with a flower-like structure were synthesized by sol-gel reaction using zinc acetate dihydrate as a precursor at room temperature and pH value of 10. Ethanol dispersions of ZnO and commercial AgNW were deposited by spincoating method on glass substrates with fixed parameters to obtain AgNW-ZnO and ZnO-AgNW films, then their surfaces were covered with monolayer graphene flakes (MGFs) using a double self-assembly (DSA) process. The hybrid ZnO-AgNW-MGFs and AgNW-ZnO-MGFs films were characterized by XRD, SEM, UV?vis, four-point probe conductivity measurement, thermal (85 degrees C for 120 h) and long-term (ambient condition for 120 days) stability analyzes. The transmittances of AgNW-ZnO and ZnO-AgNW films were identical at 550 nm (80 %) and their sheet resistances (R-s) values were measured as 20.6 and 21.6 Omega/sq, respectively. After the MGFs deposition, the transmittances of hybrid films reduced to 72.5 and 76.8 %, while their R-s values decreased to 17.6 and 21.4 Omega/sq, respectively. Graphene flakes coating both enhanced the conductivity of hybrid films by improving the connection between silver nanowires and increased the thermal and long-term ambient stability of the films due to its barrier property against oxidation of silver nanowires.