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Kim Nahun,Jung Dawoon,Kim Yushin,Kim Sihoon,Hong Sung Ju,한강희,Bahk Young-Mi 한국물리학회 2023 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.82 No.1
We investigate simple chemical doping process and the optical characterization of large-area graphene. The large-area graphene is grown on copper foil by chemical vapor deposition method, where carrier density is varied by exposure duration within FeCl3 solution after complete etching of copper. Using terahertz time-domain spectroscopy, we obtain terahertz conductivity with diferent exposure duration. We confrm that the longer exposure time, the higher conductivity, which results from p-type doping due to copper etchant. The result implies that varying etching time during transfer process enables distinguished Fermi levels in graphene sheet, essential for simple fabrication of doping-level-controlled graphene sample.
Park Hajung,Kim Nahun,Yu Jaeyoung,Rhie Jiyeah,Choi Geunchang,Bahk Young-Mi 한국물리학회 2022 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.81 No.12
Drugs or foods in various forms, such as hydrate and anhydrous forms, can afect the diferent therapeutic efect, which is crucial to identify pseudo-polymorphic state. Cafeine, taken in various routes such as cofee, energy drinks, and drugs, has diferent characteristics in the form of cafeine hydrate or anhydrous cafeine. Here, we investigate a dehydration process of cafeine hydrate by monitoring temporal evolution of terahertz absorption spectra under various exposure times in ambient. It was observed that the main absorption peak of cafeine hydrate at 2.3 THz moves to 1.3 THz indicating anhydrous cafeine during the dehydration process. Moreover, we represent the dehydration process with a simple parameter by extracting the ratio between the absorption values at 2.3 THz and 1.3 THz corresponding to the main absorption resonances of cafeine hydrate and anhydrous cafeine, respectively. Our results demonstrate the feasibility of terahertz spectroscopy technique to monitor dehydration in real time during the manufacturing process in pharmaceutical or biological industries.