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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>
Beam Emittance Measurement and Simulation of the PEFP Front End Accelerator
Hyeok-Jung Kwon,Han-Sung Kim,Dae-Il Kim,Ji-Ho Jang,조용섭 한국물리학회 2010 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.56 No.61
A 20-MeV proton accelerator has been developed and tested at the Korea Atomic Energy Institute (KAERI) by the Proton Engineering Frontier Project (PEFP). It consists of a 50-keV proton injector, a 3-MeV radio frequency quadrupole (RFQ), and a 20-MeV drift tube linac (DTL). The beam emttance was measured at the middle point between two solenoids of the proton injector. Based on the measured data, the beam properties through the proton injector were simulated using the T-step code for various operating conditions. Also, the transmission ratio through the RFQ was calculated using the output data obtained from the T-step code. In this paper, the emittance measurement results are presented, and the simulation results based on the measurement data are discussed.
Nanotube-on-graphene heterostructures for three-dimensional nano/bio-interface
Kwon, Sun Sang,Shin, Jae Hyeok,Choi, Jonghyun,Nam, SungWoo,Park, Won Il Elsevier 2018 Sensors and actuators. B Chemical Vol.254 No.-
<P><B>Abstract</B></P> <P>We report the synthesis, fabrication, and characterization of a nanotube-on-graphene (NT-on-Gr) field-effect sensor array for electrical detection of the biological activity of living cells. In order to form vertical nanotubes on a graphene surface, Ge/Si core-shell nanowires were vertically grown on graphene, followed by cap opening and Ge core-etching processes. Source-drain current versus water-gate potential measurements in electrolyte solutions with various pH values showed typical gate-dependent ambipolar characteristics with a decrease in pH sensitivity versus that of a flat graphene field-effect sensor. This is associated with limited solution gating of Si nanotubes that form nanoscale fluidic channels and thus interconnect the solution with the graphene field-effect sensor. The Si nanotubes also bridged interconnections between cells and the graphene field effect sensors, which were then able to record electrical spike peaks caused by cell networks.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The nanotube-on-graphene heterostructure devices were fabricated for sensor application. </LI> <LI> Investigate the ability to record cellular electrical activity using nanotube-on-graphene heterostructure devices. </LI> <LI> Demonstrate the potential of the multiplexed electrical recording capabilities of biological sensor arrays based on vertical nanotubes and planar graphene FETs. </LI> </UL> </P>
Dependence of the RFQ Output Beam Current on the Proton Injector Operation Parameters
Hyeok-Jung Kwon,Han-Sung Kim,Dae-Il Kim,Ji-Ho Jang,Yong-Sub Cho 한국물리학회 2009 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.54 No.5
A 20-MeV proton accelerator has been developed by the Proton Engineering Frontier Project (PEFP). It consists of a 50-keV proton injector, a 3-MeV radio-frequency quadrupole (RFQ) and a 20-MeV drift tube linac (DTL). An ion source and a low-energy beam transport (LEBT) system constitute the proton injector. The main roles of the proton injector are to generate the proton beams and to transport and match the beam from the ion source into the RFQ. The output beam current and the transmission of the RFQ are directly influenced by the operation parameters of the proton injector, especially the two solenoid magnets. The output beam current of the RFQ was measured for various values of the solenoid magnet current and the results were compared with that of the simulation.
Defect-Mediated Molecular Interaction and Charge Transfer in Graphene Mesh–Glucose Sensors
Kwon, Sun Sang,Shin, Jae Hyeok,Choi, Jonghyun,Nam, SungWoo,Park, Won Il American Chemical Society 2017 ACS APPLIED MATERIALS & INTERFACES Vol.9 No.16
<P>We report the role of defects in enzymatic graphene field-effect transistor sensors by introducing engineered defects in graphene channels. Compared with conventional graphene sensors (Gr sensors), graphene mesh sensors (GM sensors), with an array of circular holes, initially exhibited a higher irreversible response to glucose, involving strong chemisorption to edge defects. However, after immobilization of glucose oxidase, the irreversibility of the responses was substantially diminished, without any reduction in the sensitivity of the GM sensors (i.e., -0.53 mV/mM for the GM sensor vs -0.37 mV/mM for Gr sensor). Furthermore, multiple cycle operation led to rapid sensing and improved the reversibility of GM sensors. In addition, control tests with sensors containing a linker showed that sensitivity was increased in Gr sensors but decreased in GM sensors. Our findings indicate that edge defects can be used to replace linkers for immobilization of glucose oxidase and improve charge transfer across glucose oxidase graphene interfaces.</P>