Field-driven magnetic domain wall propagation in ferromagnetic nanostrips with trapezoidal cross section has been systematically investigated by means of micromagnetic simulation. Asymmetric dynamic behaviors of domai...Field-driven magnetic domain wall propagation in ferromagnetic nanostrips with trapezoidal cross section has been systematically investigated by means of micromagnetic simulation. Asymmetric dynamic behaviors of domain wall, depending on the propagation direction, were observed under an external magnetic field. When the domain walls propagate in the opposite direction along the long axis of the nanostrip, the Walker breakdown fields as well as the average velocities are different. The asymmetric landscape of demagnetization energies, which arises from the trapezoidal geometry, is the main origin of the asymmetric propagation behavior. Furthermore, a trapezoid-cross-section nanostrip will become a nanotube if it is rolled artificially along its long axis, and thus a two-dimensional transverse domain wall will become a three-dimensional one. Interestingly, it is found that the asymmetric behaviors observed in two-dimensional nanostrips with trapezoidal cross section are similar with some dynamic properties occurring in three-dimensional nanotubes.展开更多
WC-Co is used widely in die and mold industries due to its unique combination of hardness, strength and wear-resistance. For machining difficult-to-cut materials, such as tungsten carbide, micro-electrical discharge m...WC-Co is used widely in die and mold industries due to its unique combination of hardness, strength and wear-resistance. For machining difficult-to-cut materials, such as tungsten carbide, micro-electrical discharge machining(EDM) is one of the most effective methods for making holes because the hardness is not a dominant parameter in EDM. This paper describes the characteristics of the discharge conditions for micro-hole EDM of tungsten carbide with a WC grain size of 0.5 μm and Co content of 12%. The EDM process was conducted by varying the condenser and resistance values. A R-C discharge EDM device using arc erosion for micro-hole machining was suggested. Furthermore, the characteristics of the developed micro-EDM were analyzed in terms of the electro-optical observation using an oscilloscope and field emission scanning electron microscope.展开更多
We,for the first time,report the nanoscopic imaging study of anomalous infrared(IR)phonon enhancement of bilayer graphene,originated from the charge imbalance between the top and bottom layers,resulting in the enhance...We,for the first time,report the nanoscopic imaging study of anomalous infrared(IR)phonon enhancement of bilayer graphene,originated from the charge imbalance between the top and bottom layers,resulting in the enhancement of E1u mode of bilayer graphene near 0.2 eV.We modified the multifrequency atomic force microscope platform to combine photo-induced force microscope with electrostatic/Kelvin probe force microscope constituting a novel hybrid nanoscale optical-electrical force imaging system.This enables to observe a correlation between the IR response,doping level,and topographic information of the graphene layers.Through the nanoscale spectroscopic image measurements,we demonstrate that the charge imbalance at the graphene interface can be controlled by chemical(doping effect via Redox mechanism)and mechanical(triboelectric effect by the doped cantilever)approaches.Moreover,we can also diagnosis the subsurface cracks on the stacked few-layer graphene at nanoscale,by monitoring the strain-induced IR phonon shift.Our approach provides new insights into the development of graphene-based electronic and photonic devices and their potential applications.展开更多
A phase-pure NaTi2(PO4)3/reduced graphene oxide (rGO) nanocomposite was prepared using a microwave-assisted one-pot method and subsequent heat treatment. The well-crystallized NaTi2(PO4)3 nanoparticles (30-40 n...A phase-pure NaTi2(PO4)3/reduced graphene oxide (rGO) nanocomposite was prepared using a microwave-assisted one-pot method and subsequent heat treatment. The well-crystallized NaTi2(PO4)3 nanoparticles (30-40 nm) were uniformly precipitated on rGO templates through Ti-O-C bonds. The chemical interactions between the NaTi2(PO4)3 nanoparticles and rGO could immobilize the NaTi2(PO4)3 nanoparticles on the rGO sheets, which might be responsible for the excellent electrochemical performance of the nanocomposite. The NaTi2(PO4)B/rGO nanocomposite exhibited a specific capacity of 128.6 mA-h.g-1 approaching the theoretical value at a 0.1 C-rate with an excellent rate capability (72.9% capacity retention at 50 C-rate) and cycling performance (only 4.5% capacity loss after 1,000 cycles at a high rate of 10 C). These properties were maintained even when the electrodes were prepared without the use of an additional conducting agent. The excellent sodium storage properties of the NaTi2(PO4)B/rGO nanocomposite could be attributed to the nano-sized NaTi2(PO4)3 particles, which significantly reduced the transport lengths for Na+ ions, and an intimate contact between the NaTi2(PO4)3 particles and rGO due to chemical bonding.展开更多
基金Project supported by the National Key R&D Program of China(Grant Nos.2017YFB0903700 and 2017YFB0903702)Yichang Government Fund(Grant No.A19-402-a05)+1 种基金the Korea Research Foundation(NRF)(Grant No.2018R1A2B3009569)Korea Basic Science Institute(KBSI)(Grant No.D39614).
文摘Field-driven magnetic domain wall propagation in ferromagnetic nanostrips with trapezoidal cross section has been systematically investigated by means of micromagnetic simulation. Asymmetric dynamic behaviors of domain wall, depending on the propagation direction, were observed under an external magnetic field. When the domain walls propagate in the opposite direction along the long axis of the nanostrip, the Walker breakdown fields as well as the average velocities are different. The asymmetric landscape of demagnetization energies, which arises from the trapezoidal geometry, is the main origin of the asymmetric propagation behavior. Furthermore, a trapezoid-cross-section nanostrip will become a nanotube if it is rolled artificially along its long axis, and thus a two-dimensional transverse domain wall will become a three-dimensional one. Interestingly, it is found that the asymmetric behaviors observed in two-dimensional nanostrips with trapezoidal cross section are similar with some dynamic properties occurring in three-dimensional nanotubes.
基金supported by a Grant-in-aid for the National Core Research Center Program from MOST and KOSEF, Korea (No.R15-2006-022-01001-0)partly supported by Pusan National University Research Grand,2008
文摘WC-Co is used widely in die and mold industries due to its unique combination of hardness, strength and wear-resistance. For machining difficult-to-cut materials, such as tungsten carbide, micro-electrical discharge machining(EDM) is one of the most effective methods for making holes because the hardness is not a dominant parameter in EDM. This paper describes the characteristics of the discharge conditions for micro-hole EDM of tungsten carbide with a WC grain size of 0.5 μm and Co content of 12%. The EDM process was conducted by varying the condenser and resistance values. A R-C discharge EDM device using arc erosion for micro-hole machining was suggested. Furthermore, the characteristics of the developed micro-EDM were analyzed in terms of the electro-optical observation using an oscilloscope and field emission scanning electron microscope.
基金support of the KPFM calibration.J.J.,S.L.and E.S.L.acknowledge the supports from the National Research Foundation of Korea(NRF)grant(MSITGrant No.2022R1C1C1008766)+3 种基金the Nano Material Technology Development Program(Grant No.2016M3A7B6908929)funded by the Korea government.S.G.M.M.S.J.acknowledge the Basic Science Research Program through the NRF funded by the Ministry of Education(Grant No.2021R1I1A1A01057510)the support of the NRF grant funded by MSIT(2022R1A2C2092095).D.K.J.S.acknowledged to the National Research Council of Science&Technology(NST)grant by the Korea government(MSIT)(No.CRC-20-01-NFRI)and the KIST Institutional program(2E32634).
文摘We,for the first time,report the nanoscopic imaging study of anomalous infrared(IR)phonon enhancement of bilayer graphene,originated from the charge imbalance between the top and bottom layers,resulting in the enhancement of E1u mode of bilayer graphene near 0.2 eV.We modified the multifrequency atomic force microscope platform to combine photo-induced force microscope with electrostatic/Kelvin probe force microscope constituting a novel hybrid nanoscale optical-electrical force imaging system.This enables to observe a correlation between the IR response,doping level,and topographic information of the graphene layers.Through the nanoscale spectroscopic image measurements,we demonstrate that the charge imbalance at the graphene interface can be controlled by chemical(doping effect via Redox mechanism)and mechanical(triboelectric effect by the doped cantilever)approaches.Moreover,we can also diagnosis the subsurface cracks on the stacked few-layer graphene at nanoscale,by monitoring the strain-induced IR phonon shift.Our approach provides new insights into the development of graphene-based electronic and photonic devices and their potential applications.
文摘A phase-pure NaTi2(PO4)3/reduced graphene oxide (rGO) nanocomposite was prepared using a microwave-assisted one-pot method and subsequent heat treatment. The well-crystallized NaTi2(PO4)3 nanoparticles (30-40 nm) were uniformly precipitated on rGO templates through Ti-O-C bonds. The chemical interactions between the NaTi2(PO4)3 nanoparticles and rGO could immobilize the NaTi2(PO4)3 nanoparticles on the rGO sheets, which might be responsible for the excellent electrochemical performance of the nanocomposite. The NaTi2(PO4)B/rGO nanocomposite exhibited a specific capacity of 128.6 mA-h.g-1 approaching the theoretical value at a 0.1 C-rate with an excellent rate capability (72.9% capacity retention at 50 C-rate) and cycling performance (only 4.5% capacity loss after 1,000 cycles at a high rate of 10 C). These properties were maintained even when the electrodes were prepared without the use of an additional conducting agent. The excellent sodium storage properties of the NaTi2(PO4)B/rGO nanocomposite could be attributed to the nano-sized NaTi2(PO4)3 particles, which significantly reduced the transport lengths for Na+ ions, and an intimate contact between the NaTi2(PO4)3 particles and rGO due to chemical bonding.