Two-dimensional van der Waals(2D vdW)material-based heterostructure devices have been widely studied for high-end electronic applications owing to their heterojunction properties.In this study,we demonstrate graphene(...Two-dimensional van der Waals(2D vdW)material-based heterostructure devices have been widely studied for high-end electronic applications owing to their heterojunction properties.In this study,we demonstrate graphene(Gr)-bridge heterostructure devices consisting of laterally series-connected ambipolar semiconductor/Gr-bridge/n-type molybdenum disulfide as a channel material for field-effect transistors(FET).Unlike conventional FET operation,our Gr-bridge devices exhibit nonclassical transfer characteristics(humped transfer curve),thus possessing a negative differential transconductance.These phenomena are interpreted as the operating behavior in two series-connected FETs,and they result from the gate-tunable contact capacity of the Gr-bridge layer.Multi-value logic inverters and frequency tripler circuits are successfully demonstrated using ambipolar semiconductors with narrow-and wide-bandgap materials as more advanced circuit applications based on non-classical transfer characteristics.Thus,we believe that our innovative and straightforward device structure engineering will be a promising technique for future multi-functional circuit applications of 2D nanoelectronics.展开更多
Herein,we report on the fabrication of a heterostructure diode adopting a p-Ni_(0.8)Cu_(0.2)WO_(4)oxide/n-Si junction and its demonstration toward a high-speed rectifier circuit up to 1 MHz operation.Novel p-type Cu-s...Herein,we report on the fabrication of a heterostructure diode adopting a p-Ni_(0.8)Cu_(0.2)WO_(4)oxide/n-Si junction and its demonstration toward a high-speed rectifier circuit up to 1 MHz operation.Novel p-type Cu-substituted NiWO_(4)was synthesized via a solid-state reaction,and its thin-film form was successfully deposited using an e-beam evaporation method.From X-ray diffraction and Raman spectroscopy results,it was confirmed that all the deposited Cu-substituted NiWO_(4)films exhibited amorphous phases,irrespective of the substrate heating temperature.UV-visible transmittance and electrical resistivity values decreased as substrate heating temperature was increased from 100 to 300℃,revealing that optical transparency and electrical conductivity were in a trade-off relation in the Cu-substituted NiWO_(4)film.Upon fabricating the p-Ni_(0.8)Cu_(0.2)WO_(4)/n-Si heterostructure diode,a highly rectifying behaviour was attained with an ideality factor of 1.23 and an on/off current ratio of∼104.When we configured an AC to DC converting half-wave rectifier circuit with the p-Ni_(0.8)Cu_(0.2)WO_(4)/n-Si diode,a high-speed operation up to 1 MHz was demonstrated,thereby strongly supporting that our newly developed p-type oxide can be utilized as a key component in practical oxide-based electronics such as radio frequency identification.展开更多
Tetrabutylammonium ions(TBA+)have commonly been used to exfoliate RuO_(2)into monolayers via ion exchange reactions.However,the low production yield of RuO_(2)exfoliation,which originates from the large molecular size...Tetrabutylammonium ions(TBA+)have commonly been used to exfoliate RuO_(2)into monolayers via ion exchange reactions.However,the low production yield of RuO_(2)exfoliation,which originates from the large molecular size of TBA^(+),limits wider utilisation of RuO_(2)monolayers in optoelectronic applications.We introduce a rapid and efficient dual-step exfoliation process beginning with intercalation of small organic molecules(tetramethylammonium ions)into RuO_(2),which is followed by the addition of TBA^(+)as a second intercalant to realize RuO_(2)monolayer production.Our dual-step intercalation process increases the RuO_(2)monolayer exfoliation yield from 9.9%to 60%after 14 days.Density functional theory calculations reveal that the activation energy of dual-step intercalation is much lower than that of direct intercalation of TBA^(+)ions into the RuO_(2)structure.The experimental and theoretical results of dual-step intercalation suggest that it is a facile and general approach for the production of metal oxide monolayers,and could widen the use of metal oxide monolayer nanosheets.展开更多
Post-transition-metal chalcogenides,such as SnSe,SnSe_(2),In_(4)Se_(3),and In_(2)Se_(3),have attracted renewed attention as promising thermoelectric materials mainly due to their inherent low lattice thermal conductiv...Post-transition-metal chalcogenides,such as SnSe,SnSe_(2),In_(4)Se_(3),and In_(2)Se_(3),have attracted renewed attention as promising thermoelectric materials mainly due to their inherent low lattice thermal conductivities,originating from the atomically layered structure.Herein,we demonstrate the enhanced thermoelectric transport properties of n-type InSe in an effort to search for new thermoelectric materials within post-transition-metal chalcogenide systems.By Si doping at the In site,significantly enhanced electrical conductivity is obtained,mainly due to the simultaneous increase in both carrier concentration and mobility.Meanwhile,the large Seebeck coefficient is maintained despite the increase of carrrier concentration with Si doping.Based on theoretical considerations for band structure change by Si doping,this unconventional trade-off between electrical conductivity and Seebeck coefficient is due to the generation of heavy flat energy levels near the conduction band minimum in the presence of Si at the In site.The doped Si also acts as an effective point defect phonon scattering center,resulting in reduced lattice thermal conductivity.Due to this synergetic effect,a 210%improved thermoelectric figure of merit(zT)of 0.14 at 795 K compared with pristine InSe was obtained by 7%Si doping.展开更多
The origin of the electrical and optical properties of Cu-substituted NiO(Cu:NiO)polycrystalline bulks synthesized via a solid-state reaction is reported.The partial substitution of Ni sites with Cu led to a drastic d...The origin of the electrical and optical properties of Cu-substituted NiO(Cu:NiO)polycrystalline bulks synthesized via a solid-state reaction is reported.The partial substitution of Ni sites with Cu led to a drastic decrease of the electrical resistivity from 7.73×10^(8)to 6.51×10^(4)Ω·cm and a reduction in the energy for the self-trapping barrier from 0.58 to 0.24 eV in accordance with small polaron hopping conduction.展开更多
基金Y.T.L.acknowledges the financial support from the National Research Foundation of Korea(NRF)(No.NRF-2021R1C1C1005235)D.K.H.acknowledges the financial support from the Korea Institute of Science and Technology(KIST)Institution Program(No.2E31532).
文摘Two-dimensional van der Waals(2D vdW)material-based heterostructure devices have been widely studied for high-end electronic applications owing to their heterojunction properties.In this study,we demonstrate graphene(Gr)-bridge heterostructure devices consisting of laterally series-connected ambipolar semiconductor/Gr-bridge/n-type molybdenum disulfide as a channel material for field-effect transistors(FET).Unlike conventional FET operation,our Gr-bridge devices exhibit nonclassical transfer characteristics(humped transfer curve),thus possessing a negative differential transconductance.These phenomena are interpreted as the operating behavior in two series-connected FETs,and they result from the gate-tunable contact capacity of the Gr-bridge layer.Multi-value logic inverters and frequency tripler circuits are successfully demonstrated using ambipolar semiconductors with narrow-and wide-bandgap materials as more advanced circuit applications based on non-classical transfer characteristics.Thus,we believe that our innovative and straightforward device structure engineering will be a promising technique for future multi-functional circuit applications of 2D nanoelectronics.
基金supported by the National Research Foundation of Korea(NRF)grant funded by the Korea government(MSIT)(No.RS-2024-00401881)“Regional Innovation Strategy(RIS)”through the National Research Foundation of Korea(NRF)funded by the Ministry of Education(MOE)(2023RIS-008)partly supported by research funds of Kunsan National University.
文摘Herein,we report on the fabrication of a heterostructure diode adopting a p-Ni_(0.8)Cu_(0.2)WO_(4)oxide/n-Si junction and its demonstration toward a high-speed rectifier circuit up to 1 MHz operation.Novel p-type Cu-substituted NiWO_(4)was synthesized via a solid-state reaction,and its thin-film form was successfully deposited using an e-beam evaporation method.From X-ray diffraction and Raman spectroscopy results,it was confirmed that all the deposited Cu-substituted NiWO_(4)films exhibited amorphous phases,irrespective of the substrate heating temperature.UV-visible transmittance and electrical resistivity values decreased as substrate heating temperature was increased from 100 to 300℃,revealing that optical transparency and electrical conductivity were in a trade-off relation in the Cu-substituted NiWO_(4)film.Upon fabricating the p-Ni_(0.8)Cu_(0.2)WO_(4)/n-Si heterostructure diode,a highly rectifying behaviour was attained with an ideality factor of 1.23 and an on/off current ratio of∼104.When we configured an AC to DC converting half-wave rectifier circuit with the p-Ni_(0.8)Cu_(0.2)WO_(4)/n-Si diode,a high-speed operation up to 1 MHz was demonstrated,thereby strongly supporting that our newly developed p-type oxide can be utilized as a key component in practical oxide-based electronics such as radio frequency identification.
基金supported by the Basic Science Research Program through the National Research Foundation of Korea(NRF)funded by the Ministry of Education(NRF-2019R1A6A1A11055660,NRF-2019R1C1C1005632,and NRF-2017R1D1A1B03034322).
文摘Tetrabutylammonium ions(TBA+)have commonly been used to exfoliate RuO_(2)into monolayers via ion exchange reactions.However,the low production yield of RuO_(2)exfoliation,which originates from the large molecular size of TBA^(+),limits wider utilisation of RuO_(2)monolayers in optoelectronic applications.We introduce a rapid and efficient dual-step exfoliation process beginning with intercalation of small organic molecules(tetramethylammonium ions)into RuO_(2),which is followed by the addition of TBA^(+)as a second intercalant to realize RuO_(2)monolayer production.Our dual-step intercalation process increases the RuO_(2)monolayer exfoliation yield from 9.9%to 60%after 14 days.Density functional theory calculations reveal that the activation energy of dual-step intercalation is much lower than that of direct intercalation of TBA^(+)ions into the RuO_(2)structure.The experimental and theoretical results of dual-step intercalation suggest that it is a facile and general approach for the production of metal oxide monolayers,and could widen the use of metal oxide monolayer nanosheets.
基金supported by a grant from the Korean National Research Funds(NRF-2017R1D1A1B03034257&NRF-2018R1D1A1B07042573)This research was also supported by Low-dimensional Materials Genome Development by Korea Research Institute of Standards and Science(KRISS-2018-18011084).
文摘Post-transition-metal chalcogenides,such as SnSe,SnSe_(2),In_(4)Se_(3),and In_(2)Se_(3),have attracted renewed attention as promising thermoelectric materials mainly due to their inherent low lattice thermal conductivities,originating from the atomically layered structure.Herein,we demonstrate the enhanced thermoelectric transport properties of n-type InSe in an effort to search for new thermoelectric materials within post-transition-metal chalcogenide systems.By Si doping at the In site,significantly enhanced electrical conductivity is obtained,mainly due to the simultaneous increase in both carrier concentration and mobility.Meanwhile,the large Seebeck coefficient is maintained despite the increase of carrrier concentration with Si doping.Based on theoretical considerations for band structure change by Si doping,this unconventional trade-off between electrical conductivity and Seebeck coefficient is due to the generation of heavy flat energy levels near the conduction band minimum in the presence of Si at the In site.The doped Si also acts as an effective point defect phonon scattering center,resulting in reduced lattice thermal conductivity.Due to this synergetic effect,a 210%improved thermoelectric figure of merit(zT)of 0.14 at 795 K compared with pristine InSe was obtained by 7%Si doping.
基金supported by Basic Science Research Program through the National Research Foundation of Korea(NRF)funded by the Ministry of Education(NRF-2019R1A6A1A11055660)It was also partly supported by the MEXT,Element Strategy Initiative to form a research core.M.S.O.acknowledges the National Research Foundation of Korea(NRF)Grant funded by the Ministry of Science and ICT for the First-Mover Program for Accelerating Disruptive Technology Development(NRF-2018M3C1B9088458)S.L.was supported by the National Research Foundation of Korea through NRF-2019M3F3A1A02072175.We also thank Prof.H.Lei for valuable discussions.
文摘The origin of the electrical and optical properties of Cu-substituted NiO(Cu:NiO)polycrystalline bulks synthesized via a solid-state reaction is reported.The partial substitution of Ni sites with Cu led to a drastic decrease of the electrical resistivity from 7.73×10^(8)to 6.51×10^(4)Ω·cm and a reduction in the energy for the self-trapping barrier from 0.58 to 0.24 eV in accordance with small polaron hopping conduction.
