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Kwon, Sun Sang,Yi, Jaeseok,Lee, Won Woo,Shin, Jae Hyeok,Kim, Su Han,Cho, Seunghee H.,Nam, SungWoo,Park, Won Il American Chemical Society 2016 ACS APPLIED MATERIALS & INTERFACES Vol.8 No.1
<P>We have studied the role of defects in electrolyte-gated graphene mesh (GM) field-effect transistors (FETs) by introducing engineered edge defects in graphene (Gr) channels. Compared with Gr-FETs, GM-FETs were characterized as having large increments of Dirac point shift (similar to 30-100 mV/pH) that even sometimes exceeded the Nernst limit (59 mV/pH) by means of electrostatic gating of H+ ions. This feature was attributed to the defect-mediated chemisorptions of H+ ions to the graphene edge, as supported by Raman measurements and observed cycling characteristics of the GM FETs. Although the H+ ion binding to the defects increased the device response to pH change, this binding was found to be irreversible. However, the irreversible component showed relatively fast decay, almost disappearing after 5 cycles of exposure to solutions of decreasing pH value from 8.25 to 6.55. Similar behavior could be found in the Gr-FET, but the irreversible component of the response was much smaller. Finally, after complete passivation of the defects, both Gr-FETs and GM-FETs exhibited only reversible response to pH change, with similar magnitude in the range of 68 mV/pH.</P>
Chemical and biological sensors based on defect-engineered graphene mesh field-effect transistors
Cho Seunghee H.,Kwon Sun Sang,Yi Jaeseok,Park Won Il 나노기술연구협의회 2016 Nano Convergence Vol.3 No.14
Graphene has been intensively studied for applications to high-performance sensors, but the sensing characteristics of graphene devices have varied from case to case, and the sensing mechanism has not been satisfactorily determined thus far. In this review, we describe recent progress in engineering of the defects in graphene grown by a silica-assisted chemical vapor deposition technique and elucidate the effect of the defects upon the electrical response of graphene sensors. This review provides guidelines for engineering and/or passivating defects to improve sensor performance and reliability.
Baek, Kwang Min,Kim, Jaehoon,Kim, Shinho,Cho, Seunghee H.,Jang, Min Seok,Oh, Jihun,Jung, Yeon Sik American Chemical Society 2018 Chemistry of materials Vol.30 No.17
<P>To realize a more rapid and accurate detection technique for diverse trace molecules, surface-enhanced Raman scattering (SERS) analysis has been extensively investigated in recent decades. However, a practical fabrication method to scalably and reproducibly produce SERS substrates with highly effective SERS-active sites and extensive optical tunability still remains an important research target. Here, we present an electrochemical pathway to generate a high-performance SERS substrate. This method provides not only ultrahigh-density hot spots as a form of nanogaps for strong and uniform SERS signal enhancement but also tunable plasmonic properties for capability of matching the plasmonic resonance wavelength with that of the Raman excitation laser. The unique Au nanopillar array decorated with ultrafine Au nanoparticles records a high SERS signal enhancement effect, which enables trace-molecule detection on the entire measured area with highly reproducible signal intensity. Also, via aptamer-functionalization on this substrate, an extremely sensitive and highly selective SERS-based Hg<SUP>2+</SUP> ions detection sensor is demonstrated. Trace-amount (10 ppb) Hg<SUP>2+</SUP> ions can be selectively identified in a mixture solution containing six different metallic ion species as well as in a beverage containing numerous other components.</P> [FIG OMISSION]</BR>