Graphene quantum dots （GQDs） are promising candidates for potential applications such as novel optoelectronic devices and bio-imaging. However, insufficient light absorption to exhibit their intriguing characteristi...Graphene quantum dots （GQDs） are promising candidates for potential applications such as novel optoelectronic devices and bio-imaging. However, insufficient light absorption to exhibit their intriguing characteristics. The strong confinement of light caused by the Au nanoparticles as an antenna can considerably boost the light absorption. With the assistance of ultraviolet irradiation, we prepared bluish-green luminescent nanospheres by the hybridiza- tion of GQD and Au nanoparticles （GQD/Au）. These nanospheres showed a photoluminescence quantum yield of up to 26.9%. The GQD/Au nanospheres were synthesized using a solution of GQDs and HAuC14 by a photochemical method with the reduction of GQDs and the formation of metallic Au. The GQDs and Au nanopartides self-assembled and aggregated into nanospheres via aurophilicity and hydrogen bonding interactions. The average size of the GQD/Au nanospheres was found to be in the range of 150-170 nm, which is much larger than that of the pristine GQDs （4-7 nm）. The GQD/Au nanospheres exhibited an absorption band at 541 nm, which indicates the presence of Au in the nanospheres. The typical absorbance features of GQDs were observed near 236 and 303 nrn. The photoluminescence characteristics were investigated using the excitation and emission spectra. The GQD/Au nanospheres exhibited two emission peaks at 468 and 529 nm in the visible range. The green fluorescent peak located at 529 nm was newly generated by the hybridization. The GQD/Au nanospheres showed an emission efficiency which was two times more than that of the intrinsic GQDs. The reason for this increase was the surface plasmon resonance from the Au particles, which improved the fluorescence property of the resulting nanospheres. These nanospheres can be perceived as outstanding candidates for applications such as displays, optoelectronic devices, and imaging of the biological samples with high emission intensity.展开更多
Owing to the tremendous demands for high-resolution pixel-scale thin lenses in displays,we developed a graphenebased ultrathin square subpixel lens(USSL)capable of electrically tuneable focusing(ETF)with a performance...Owing to the tremendous demands for high-resolution pixel-scale thin lenses in displays,we developed a graphenebased ultrathin square subpixel lens(USSL)capable of electrically tuneable focusing(ETF)with a performance competitive with that of a typical mechanical refractive lens.The fringe field due to a voltage bias in the graphene proves that our ETF-USSL can focus light onto a single point regardless of the wavelength of the visible light—by controlling the carriers at the Dirac point using radially patterned graphene layers,the focal length of the planar structure can be adjusted without changing the curvature or position of the lens.A high focusing efficiency of over 60% at a visible wavelength of 405 nm was achieved with a lens thickness of <13 nm,and a change of 19.42% in the focal length with a 9% increase in transmission was exhibited under a driving voltage.This design is first presented as an ETF-USSL that can be controlled in pixel units of flat panel displays for visible light.It can be easily applied as an add-on to high resolution,slim displays and provides a new direction for the application of multifunctional autostereoscopic displays.展开更多
Liquid-phase exfoliation （LPE） is an attractive method for the scaling-up of exfoliated MoS2 sheets compared to chemical vapor deposition and mechanical cleavage. However, the MoS2 nanosheet yield from LPE is too sm...Liquid-phase exfoliation （LPE） is an attractive method for the scaling-up of exfoliated MoS2 sheets compared to chemical vapor deposition and mechanical cleavage. However, the MoS2 nanosheet yield from LPE is too small for practical applications. We report a facile method for the scaling-up of exfoliated MoS2 nanosheets using freeze-dried silk fibroin powders. Compared to MoS2 dispersion in the absence of silk fibroin powder, sonicated MoS2 dispersions with silk fibroin powder （MoSJSilk dispersion） show noticeably higher exfoliated MoS2 nanosheet yields, with suspended MoS2 concentrations in MoS2/Silk dispersions sonicated for 2 and 5 h of 1.03 and 1.39 mg.mL-1, respectively. The MoS2 concentration in the MoS2/Silk dispersion after centrifugation above 10,000 rpm is more than four times that without the silk fibroin. The size of the dispersed silk fibroin is controlled by the change of centrifugation rate, showing the removal of silk fibroin above tens of micrometers in size after centrifugation at 2,000 rpm. Size-controlled silk fibroin biomolecules combined with MoS2 nanosheets are expected to increase the practical use of such materials in fields related to tissue engineering, biosensors and electrochemical electrodes. Atomic force microscopy and Raman spectroscopy provide the height of the MoS2 nanosheets spin-cast from MoS2/Silk dispersions, showing thicknesses of 3--6 nm. X-ray photoelectron spectroscopy and X-ray diffraction indicate that the outermost surface layer of the hydrophobic MoS2 crystals interact with oxygen-containing functional groups that exist in the hydrophobic part of silk fibroins. The amphiphilic properties of silk fibroin combined with the MoS2 nanosheets stabilize dispersions by enhancing solvent-material interactions. The large quantities of exfoliated MoS2 nanosheets suspended in the as-synthesized dispersions can be utilized for the fabrication of vapor and electrochemical devices requiring high MoS2 nanosheets contents.展开更多
We demonstrate the dipole-assisted carrier transport properties of bis(trifluoromethane)sulfonamide(TFSI)-treated O-ReS_(2) field-effect transistors.Pristine ReS_(2) was compared with defect-mediated ReS_(2) to confir...We demonstrate the dipole-assisted carrier transport properties of bis(trifluoromethane)sulfonamide(TFSI)-treated O-ReS_(2) field-effect transistors.Pristine ReS_(2) was compared with defect-mediated ReS_(2) to confirm whether the presence of defects on the interface enhances the interaction between O-ReS_(2) and TFSI molecules.Prior to the experiment,density functional theory(DFT)calculation was performed,and the result indicated that the charge transfer between TFSI and O-ReS_(2) is more sensitive to external electric fields than that between TFSI and pristine ReS_(2).After TFSI treatment,the drain current of O-ReS_(2) FET was significantly increased up to 1,113.4 times except in the range of−0.32–0.76 V owing to Schottky barrier modulation from dipole polarization of TFSI molecules,contrary to a significant degradation in device performance in pristine ReS_(2) FET.Moreover,in the treated O-ReS_(2) device,the dipole direction was highly influenced by the voltage sweep direction,generating a significant area of hysteresis in I–V and transfer characteristics,which was further verified by the surface potential result.Furthermore,the dipole state was enhanced according to the wavelength of the light source and photocurrent.These results indicate that TFSI-treated ReS_(2) FET has large potential for use as next-generation memristor,memory,and photodetector.展开更多
文摘Graphene quantum dots （GQDs） are promising candidates for potential applications such as novel optoelectronic devices and bio-imaging. However, insufficient light absorption to exhibit their intriguing characteristics. The strong confinement of light caused by the Au nanoparticles as an antenna can considerably boost the light absorption. With the assistance of ultraviolet irradiation, we prepared bluish-green luminescent nanospheres by the hybridiza- tion of GQD and Au nanoparticles （GQD/Au）. These nanospheres showed a photoluminescence quantum yield of up to 26.9%. The GQD/Au nanospheres were synthesized using a solution of GQDs and HAuC14 by a photochemical method with the reduction of GQDs and the formation of metallic Au. The GQDs and Au nanopartides self-assembled and aggregated into nanospheres via aurophilicity and hydrogen bonding interactions. The average size of the GQD/Au nanospheres was found to be in the range of 150-170 nm, which is much larger than that of the pristine GQDs （4-7 nm）. The GQD/Au nanospheres exhibited an absorption band at 541 nm, which indicates the presence of Au in the nanospheres. The typical absorbance features of GQDs were observed near 236 and 303 nrn. The photoluminescence characteristics were investigated using the excitation and emission spectra. The GQD/Au nanospheres exhibited two emission peaks at 468 and 529 nm in the visible range. The green fluorescent peak located at 529 nm was newly generated by the hybridization. The GQD/Au nanospheres showed an emission efficiency which was two times more than that of the intrinsic GQDs. The reason for this increase was the surface plasmon resonance from the Au particles, which improved the fluorescence property of the resulting nanospheres. These nanospheres can be perceived as outstanding candidates for applications such as displays, optoelectronic devices, and imaging of the biological samples with high emission intensity.
基金supported by Nano·Material Technology Development Program(NRF-2017M3A7B4041987)the Korean Government(MSIP-2015R1A5A1037668)through the National Research Foundation of Korea(NRF)funded by the Ministry of Science,ICT,and Future Planning.
文摘Owing to the tremendous demands for high-resolution pixel-scale thin lenses in displays,we developed a graphenebased ultrathin square subpixel lens(USSL)capable of electrically tuneable focusing(ETF)with a performance competitive with that of a typical mechanical refractive lens.The fringe field due to a voltage bias in the graphene proves that our ETF-USSL can focus light onto a single point regardless of the wavelength of the visible light—by controlling the carriers at the Dirac point using radially patterned graphene layers,the focal length of the planar structure can be adjusted without changing the curvature or position of the lens.A high focusing efficiency of over 60% at a visible wavelength of 405 nm was achieved with a lens thickness of <13 nm,and a change of 19.42% in the focal length with a 9% increase in transmission was exhibited under a driving voltage.This design is first presented as an ETF-USSL that can be controlled in pixel units of flat panel displays for visible light.It can be easily applied as an add-on to high resolution,slim displays and provides a new direction for the application of multifunctional autostereoscopic displays.
文摘Liquid-phase exfoliation （LPE） is an attractive method for the scaling-up of exfoliated MoS2 sheets compared to chemical vapor deposition and mechanical cleavage. However, the MoS2 nanosheet yield from LPE is too small for practical applications. We report a facile method for the scaling-up of exfoliated MoS2 nanosheets using freeze-dried silk fibroin powders. Compared to MoS2 dispersion in the absence of silk fibroin powder, sonicated MoS2 dispersions with silk fibroin powder （MoSJSilk dispersion） show noticeably higher exfoliated MoS2 nanosheet yields, with suspended MoS2 concentrations in MoS2/Silk dispersions sonicated for 2 and 5 h of 1.03 and 1.39 mg.mL-1, respectively. The MoS2 concentration in the MoS2/Silk dispersion after centrifugation above 10,000 rpm is more than four times that without the silk fibroin. The size of the dispersed silk fibroin is controlled by the change of centrifugation rate, showing the removal of silk fibroin above tens of micrometers in size after centrifugation at 2,000 rpm. Size-controlled silk fibroin biomolecules combined with MoS2 nanosheets are expected to increase the practical use of such materials in fields related to tissue engineering, biosensors and electrochemical electrodes. Atomic force microscopy and Raman spectroscopy provide the height of the MoS2 nanosheets spin-cast from MoS2/Silk dispersions, showing thicknesses of 3--6 nm. X-ray photoelectron spectroscopy and X-ray diffraction indicate that the outermost surface layer of the hydrophobic MoS2 crystals interact with oxygen-containing functional groups that exist in the hydrophobic part of silk fibroins. The amphiphilic properties of silk fibroin combined with the MoS2 nanosheets stabilize dispersions by enhancing solvent-material interactions. The large quantities of exfoliated MoS2 nanosheets suspended in the as-synthesized dispersions can be utilized for the fabrication of vapor and electrochemical devices requiring high MoS2 nanosheets contents.
基金This work was supported by the national research foundation of Korea(NRF)grant funded by the Korea government(MIST)(Nos.NRF-2019R1A2C2090443,NRF-2017M3A7B4041987,NRF-2020M3F6A1081009,and NRF-2017M1A3A3A02015033)Korea Electric Power Corporation.(Grant No.R19XO01-23).
文摘We demonstrate the dipole-assisted carrier transport properties of bis(trifluoromethane)sulfonamide(TFSI)-treated O-ReS_(2) field-effect transistors.Pristine ReS_(2) was compared with defect-mediated ReS_(2) to confirm whether the presence of defects on the interface enhances the interaction between O-ReS_(2) and TFSI molecules.Prior to the experiment,density functional theory(DFT)calculation was performed,and the result indicated that the charge transfer between TFSI and O-ReS_(2) is more sensitive to external electric fields than that between TFSI and pristine ReS_(2).After TFSI treatment,the drain current of O-ReS_(2) FET was significantly increased up to 1,113.4 times except in the range of−0.32–0.76 V owing to Schottky barrier modulation from dipole polarization of TFSI molecules,contrary to a significant degradation in device performance in pristine ReS_(2) FET.Moreover,in the treated O-ReS_(2) device,the dipole direction was highly influenced by the voltage sweep direction,generating a significant area of hysteresis in I–V and transfer characteristics,which was further verified by the surface potential result.Furthermore,the dipole state was enhanced according to the wavelength of the light source and photocurrent.These results indicate that TFSI-treated ReS_(2) FET has large potential for use as next-generation memristor,memory,and photodetector.
