In this study,we aim to contribute an understanding of the pathway of formation of Fe species during top-down synthesis of dispersed Fe on N-functionalized few layer graphene,widely used in electrocatalysis.We use X-r...In this study,we aim to contribute an understanding of the pathway of formation of Fe species during top-down synthesis of dispersed Fe on N-functionalized few layer graphene,widely used in electrocatalysis.We use X-ray absorption spectroscopy to determine the electronic structure and coordination geometry of the Fe species and in situ high angle annular dark field scanning transmission electron microscopy combined with atomic resolved electron energy loss spectroscopy to localize these,identify their chemical configuration and monitor their dynamics during thermal annealing.We show the high mobility of peripheral Fe atoms,first diffusing rapidly at the trims of the graphene layers and at temperatures as high as 573 K,diffusing from the edge planes towards in-plane locations of the graphene layers forming three-,four-coordinated metal sites and more complexes polynuclear Fe species.This process occurs via bond C-C breaking which partially reduces the extension of the graphene domains.However,the vast majority of Fe is segregated as a metal phase.This dynamic interconversion depends on the structural details of the surrounding graphitic environment in which these are formed as well as the Fe loading.N species appear stabilizing isolated and polynuclear Fe species even at temperatures as high as 873 K.The significance of our results lies on the fact that single Fe atoms in graphene are highly mobile and therefore a structural description of the electroactive sites as such is insufficient and more complex species might be more relevant,especially in the case of multielectron transfer reactions.Here we provide the experimental evidence of the formation of these polynuclear Fe-N sites and their structural characteristics.展开更多
Few-layer graphene grown on Ni thin films has been studied by scanning tunneling microscopy. In most areas on the surfaces, moir6 patterns resulted from rotational stacking faults were observed. At a bias lower than 2...Few-layer graphene grown on Ni thin films has been studied by scanning tunneling microscopy. In most areas on the surfaces, moir6 patterns resulted from rotational stacking faults were observed. At a bias lower than 200 mV, only one sublattice shows up in regions without moir6 patterns while both sublattices are seen in regions with moir6 pattens. This phenomenon can be used to identify AB stacked regions. The scattering characteristics at various types of step edges are different from those of monolayer graphene edges, either armchair or zigzag.展开更多
Assembly of the top-down graphene units mostly results in 3D porous structure with randomly organized pores.The direct bottom-up synthesis of macroscopic 2D graphene sheets with organized pores are long sought in mate...Assembly of the top-down graphene units mostly results in 3D porous structure with randomly organized pores.The direct bottom-up synthesis of macroscopic 2D graphene sheets with organized pores are long sought in materials chemistry field,but rarely achieved.Herein,we present a self-catalysisassisted bottom-up route usingL-glutamic acid and iron chloride as starting materials for the fabrication of the millimeter-sized few-layer graphene sheets with aligned porous channels parallel to the 2D direction.The amino-and carboxyl-functional groups inL-glutamic acid can coordinate with iron cations,thus allowing an atomic dispersion of iron cations.The pyrolysis thus initiated the growth of graphene catalyzed by in-situ generated iron nanoparticles,and a dynamic flow of iron nanoparticles eventually led to the formation of millimeter-sized few-layer graphene sheets with aligned channels(60-85 nm in diameter).Used as anodes in lithium-ion batteries,these graphene sheets showed a good rate capability(142 m A h g^(-1) at 2 A g^(-1))and high capacity retention of 93%at 2 A g^(-1) after 1200 cycles.Kinetic analysis revealed that lithium ions storage was dominated by diffusion behavior and capacitive behavior together,in that graphene sheets with aligned channels could accelerate electron transfer and shorten lithium ions transport pathway.This work provides a novel approach to prepare unique porous graphene materials with specific structure for energy storage.展开更多
To develop anode materials with superior volumetric storage is crucial for practical application of lithium/sodium-ion batteries.Here,we have developed a micro/nanostructured Sn S/few-layer graphene(Sn S/FLG)composite...To develop anode materials with superior volumetric storage is crucial for practical application of lithium/sodium-ion batteries.Here,we have developed a micro/nanostructured Sn S/few-layer graphene(Sn S/FLG)composite by facile scalable plasma milling.Inside the hybrid,SnS nanoparticles are tightly supported by FLG,forming nanosized primary particles as building blocks and assembling to microsized secondary granules.With this unique micro/nanostructure,the Sn S/FLG composite possesses a high tap density of 1.98 g cm^(-3)and thus ensures a high volumetric storage.The combination of Sn S nanoparticles and FLG nanosheets can not only enhance the overall electrical conductivity and facilitate the ion diffusion greatly,but alleviate the large volume expansion of Sn S effectively and maintain the electrode integrity during cycling.Thus,the densely compacted Sn S/FLG composite exhibits superior volumetric lithium and sodium storage,including high volumetric capacities of 1926.5/1051.4 m Ah cm^(-3)at 0.2 A g^(-1),and high retained capacities of 1754.3/760.3 m Ah cm^(-3)after 500cycles at 1.0 A g^(-1).With superior volumetric storage performance and facile scalable synthesis,the Sn S/FLG composite can be a promising anode for practical batteries application.展开更多
Few-layer graphenes were fabricated from expandable graphite by rapid microwave exfoliation. Expandable graphite was irradiated in a domestic microwave in full power for 3 min, then soaked in mixed strong hydrogen nit...Few-layer graphenes were fabricated from expandable graphite by rapid microwave exfoliation. Expandable graphite was irradiated in a domestic microwave in full power for 3 min, then soaked in mixed strong hydrogen nitrate and sulfuric acid with volume ratio of 1：1 for 24 h and re-irradiated, thus few-layer graphene sheets were obtained. Specimens gained from every step were selectively characterized by different techniques, such as SEM, XRD, Raman, AFM, XPS, FTIR and combustion elemental analysis. The results show that expandable graphite with loose, porous and worm-like morphology forms instantaneously in microwave irradiation with crackling sound and sparkles, which manifests physical exfoliation of graphene sheets. Few-layer graphene sheets with a dozen or more layers and average thickness of about 4.7 nm are obtained eventually after sequential treatment of microwave irradiation, mixed acid soaking and second microwave irradiation. The as-prepared few-layer graphenes still have high crystallinity and high purity with traces of oxide groups and without serious unrecoverable oxidation damage.展开更多
The performance of a lubricant largely depends on the additives it involves.However,currently used additives cause severe pollution if they are burned and exhausted.Therefore,it is necessary to develop a new generatio...The performance of a lubricant largely depends on the additives it involves.However,currently used additives cause severe pollution if they are burned and exhausted.Therefore,it is necessary to develop a new generation of green additives.Graphene oxide(GO)consists of only C,H and O and thus is considered to be environmentally friendly.So the tribological properties of the few-layer GO sheet as an additive in hydrocarbon base oil are investigated systematically.It is found that,with the addition of GO sheets,both the coefficient of friction(COF)and wear are decreased and the working temperature range of the lubricant is expanded in the positive direction.Moreover,GO sheets has better performance under higher sliding speed and the optimized concentration of GO sheets is determined to be 0.5wt%.After rubbing,GO is detected on the wear scars through Raman spectroscopy.And it is believed that,during the rubbing,GO sheets adhere to the sliding surfaces,behaving like protective films and preventing the sliding surfaces from contacting with each other directly.This paper proves that the GO sheet is an effective lubricant additive,illuminates the lubrication mechanism,and provides some critical parameters for the practical application of GO sheets in lubrication.展开更多
We have developed a dry transfer method that allows graphene to be transferred from polymer- thyl-methacrylate (PMMA)/Si (silicon) substrates on commercially available hexagonal boron ni- tride (hBN) crystals. With th...We have developed a dry transfer method that allows graphene to be transferred from polymer- thyl-methacrylate (PMMA)/Si (silicon) substrates on commercially available hexagonal boron ni- tride (hBN) crystals. With this method we are able to fabricate graphene devices with little wrin- kles and bubbles in graphene sheets, but that do not degrade the electronic quality more than the SiO2 substrate does. For hBN to perform the function described above substrate cleanliness is critical to get high quality graphene devices. Using hBN as a substrate, graphene exhibits enhanced mobility, reduced carrier inhomogeneity, and reduced intrinsic doping compared to graphene on SiO2 substrate.展开更多
We study graphene electrodes that can be used for contacting single molecules. The nanometer-scale gap is made by feedback controlled electroburning in few-layer graphene sheets. We analyze the time stability, and the...We study graphene electrodes that can be used for contacting single molecules. The nanometer-scale gap is made by feedback controlled electroburning in few-layer graphene sheets. We analyze the time stability, and the influence of the temperature and gate voltage on the current flowing through the empty gaps. The electrodes are stable at room temper- ature for long periods of time. We show statistics of the relation between the initial resistance of the few-layer graphe- ne flakes and the final size of the gaps. We find that thicker flakes are more suitable for the fabrication of the elec-trodes.展开更多
Twisted graphene possesses unique electronic properties and applications, which have been studied extensively. Recently, the phonon properties of twisted graphene have received a great deal of attention. To the best o...Twisted graphene possesses unique electronic properties and applications, which have been studied extensively. Recently, the phonon properties of twisted graphene have received a great deal of attention. To the best of our knowledge,thermal transports in twisted graphene have been investigated little to date. Here, we study perpendicular and parallel transports in twisted few-layer graphene（T-FLG）. It is found that perpendicular and parallel transports are both sensitive to the rotation angle θ between layers. When θ increases from 0° to 60°, perpendicular thermal conductivity κ（｜｜） first decreases and then increases, and the transition angle is θ = 30°. For the parallel transport, the relation between thermal conductivity κand θ is complicated, because intra-layer thermal transport is more sensitive to the edge of layer than their stacking forms. However, the dependence of interlayer scattering on θ is similar to that of κ⊥. In addition, the effect of layer number on the thermal transport is discussed. Our results may provide references for designing the devices of thermal insulation and thermal management based on graphene.展开更多
We study the thermal transport of few-layer graphene nanoribbons in the presence of the transversal pressure by using molecular dynamics simulations. It is reported that the pressure can improve the thermal conductivi...We study the thermal transport of few-layer graphene nanoribbons in the presence of the transversal pressure by using molecular dynamics simulations. It is reported that the pressure can improve the thermal conductivity of few-layer graphene nanoribbons. This improvement can reach 37.5% in the low temperature region. The pressure dependence of thermal conductivity is also investigated for different length, width and thickness of few-layer graphene. Our results provide an alternative option to tuning thermal conductivity of few-layer graphene nanoribbons, b-arthermore, it maybe indicate a so-called pressure-thermM effect in nanomaterials.展开更多
In this paper the anticorrosive properties of the few-layer graphene nanostructures were investigated. On the surface ofcopper and nickel plates the few-layer graphene nanostructures were formed using the CVD （chemic...In this paper the anticorrosive properties of the few-layer graphene nanostructures were investigated. On the surface ofcopper and nickel plates the few-layer graphene nanostructures were formed using the CVD （chemical vapor deposition） method.After that, these plates were exposed to the temperature in the air atmosphere. The results of elemental analysis, performed by theEDS （energy dispersive spectroscopy） method showed that the few-layer graphene coated metal plates proved to be more resistant tooxidation than bare metal plates. In addition, we presented computer models and theoretical calculations of the studied systems,performed by the DFT （density functional theory） and MD （molecular dynamics） methods. These results combined with experimentaldata show the high effectiveness of the protective action of the few-layer graphene against metal corrosion.展开更多
Large-area boron nanowire（BNW） films were fabricated on the Si（111） substrate by chemical vapor deposition（CVD）. The average diameter of the BNWs is about 20 nm, with lengths of 5–10 μm. Then, graphene-capped ...Large-area boron nanowire（BNW） films were fabricated on the Si（111） substrate by chemical vapor deposition（CVD）. The average diameter of the BNWs is about 20 nm, with lengths of 5–10 μm. Then, graphene-capped boron nanowires（GC-BNWs） were obtained by microwave plasma chemical vapor deposition（MPCVD）. Characterization by scanning electron microscopy indicates that few-layer graphene covers the surface of the boron nanowires. Field emission measurements of the BNWs and GC-BNW films show that the GC-BNW films have a lower turn-on electric field than the BNW films.展开更多
Graphene materials like turbostratic graphene exhibit remarkable promise for an array of applications,spanning from electronic devices to aerospace technologies.It is essential to develop a fabrication method that is ...Graphene materials like turbostratic graphene exhibit remarkable promise for an array of applications,spanning from electronic devices to aerospace technologies.It is essential to develop a fabrication method that is not only economical and efficient,but also environmentally sustainable.In this study,the molten salt-assisted magnesiothermic reduction(MSAMR)method is proposed for the synthesis of few-layer turbostratic graphene.K_(2)CO_(3)serves as both the carbon source and the catalyst for graphitization,facilitating the formation of the graphene structure,while in-situ generated MgO nanoparticles exert confinement and templating effects on the growth of graphene.The molten salts used effectively prevent the aggregation and the Bernal stacking of graphene sheets,ensuring the few-layer and turbostratic structure.The synergistic effects of K 2CO 3,in-situ generated MgO,and molten salts guarantee the formation of few-layer turbostratic graphene at a relatively low temperature,characterized with 4–8 stacking layers,a mesopore-dominated microstructure,and a high degree of graphitization.展开更多
The simultaneous modulation of electric and optical properties in graphene is essential for advancing high-performance applications in optoelectronics.However,achieving in-situ control of multiple electric and optical...The simultaneous modulation of electric and optical properties in graphene is essential for advancing high-performance applications in optoelectronics.However,achieving in-situ control of multiple electric and optical states in graphene devices remains a challenge.Here we demonstrate a versatile and reversible electric-field control of organic-ion intercalation from bilayer to pentalayer graphene.Through simultaneous optical imaging and electric measurements,we reveal multiple physical states controlled by the layer-by-layer intercalation processes,resulting in both high transparency and high electric conductance with an increase in the number of intercalated layers.Raman spectroscopy demonstrates that the intercalated graphene maintains a high carrier concentration without lattice degradation.Moreover,Hall effect measurements reveal that the carrier density can reach approximately 1.5×10^(14)cm^(-2)per layer.The ability to synchronously control the transparency and conductance states by adjusting the number of ion-intercalated layers highlights the potential of multistate modulation for the development of advanced optoelectronic devices in two-dimensional materials.展开更多
In this work,few-layer graphene oxide(GO)sheets are investigated as aqueous lubricant additives between ceramic surfaces.Three batches of GO sheets with various lateral sizes were selected,and the lateral sizes were m...In this work,few-layer graphene oxide(GO)sheets are investigated as aqueous lubricant additives between ceramic surfaces.Three batches of GO sheets with various lateral sizes were selected,and the lateral sizes were mainly within the ranges of 0.5±0.2,5.9±2.1,and 59.1±17.1μm.The weight concentration of the GO sheets in the aqueous lubricant ranged from 0.0005 to 0.8 wt%.The lubrication regime for the friction tests was kept at boundary lubrication.The GO sheets can enhance lubricity by entering the contact area and preventing the sliding surfaces from contacting each other directly,and lubricity is determined by the coverage of the contact area.For each batch of GO sheets,as the concentration increases,the coverage rate of the contact area increases;thus,the coefficient of friction(COF)and wear volume decrease.However,when the GO sheet concentration is very high,the COF approaches a stable value since the contact area is already fully covered by GO sheets,but the wear volume increases slightly due to the high acidity.Moreover,GO sheets with larger lateral sizes can lead to a smoother contact interface.Therefore,at the same concentration,GO sheets with larger lateral sizes can lead to lower COFs and wear volumes.These findings provide a general strategy for improving the performance of lubricants with two-dimensional(2D)material additives in a broad range of mechanical applications.展开更多
Optical modulation is significant and ubiquitous to telecommunication technologies,smart windows,and military devices.However,due to the limited tunability of traditional doping,achieving broadband optical property ch...Optical modulation is significant and ubiquitous to telecommunication technologies,smart windows,and military devices.However,due to the limited tunability of traditional doping,achieving broadband optical property change is a tough problem.Here,we demonstrate a remarkable transformation of optical transmittance in few-layer graphene(FLG)covering the electromagnetic spectra from the visible to the terahertz wave after lithium(Li)intercalation.It results in the transmittance being higher than 90%from the wavelengths of 480 to 1040 nm,and it increases most from 86.4%to 94.1%at 600 nm,reduces from∼80%to∼68%in the wavelength range from 2.5 to 11μm,has∼20%reduction over a wavelength range from 0.4 to 1.2 THz,and reduces from 97.2%to 68.2%at the wavelength of 1.2 THz.The optical modification of lithiated FLG is attributed to the increase of Fermi energy(E_(f))due to the charge transfer from Li to graphene layers.Our results may provide a new strategy for the design of broadband optical modulation devices.展开更多
With the miniaturization and high-frequency evolution of antennas in 5G/6G communications,aerospace,and transportation,polymer composite papers integrating superior wave-transparent performance and thermal conductivit...With the miniaturization and high-frequency evolution of antennas in 5G/6G communications,aerospace,and transportation,polymer composite papers integrating superior wave-transparent performance and thermal conductivity for radar antenna systems are urgently needed.Herein,a down-top strategy was employed to synthesize poly(p-phenylene benzobisoxazole)precursor nanofibers(prePNF).The prePNF was then uniformly mixed with fluorinated graphene(FG)to fabricate FG/PNF composite papers through consecutively suction filtration,hot-pressing,and thermal annealing.The hydroxyl and amino groups in prePNF enhanced the stability of FG/prePNF dispersion,while the increasedπ-πinteractions between PNF and FG after annealing improved their compatibility.The preparation time and cost of PNF paper was significantly reduced when applying this strategy,which enabled its large-scale production.Furthermore,the prepared FG/PNF composite papers exhibited excellent wave-transparent performance and thermal conductivity.When the mass fraction of FG was 40 wt%,the FG/PNF composite paper prepared via the down-top strategy achieved the wave-transparent coefficient(|T|2)of 96.3%under 10 GHz,in-plane thermal conductivity(λ_(∥))of 7.13 W m^(−1)K^(−1),and through-plane thermal conductivity(λ_(⊥))of 0.67 W m^(−1)K^(−1),outperforming FG/PNF composite paper prepared by the top-down strategy(|T|2=95.9%,λ_(∥)=5.52 W m^(−1)K^(−1),λ_(⊥)=0.52 W m^(−1)K^(−1))and pure PNF paper(|T|2=94.7%,λ_(∥)=3.04 W m^(−1)K^(−1),λ_(⊥)=0.24 W m^(−1)K^(−1)).Meanwhile,FG/PNF composite paper(with 40 wt%FG)through the down-top strategy also demonstrated outstanding mechanical properties with tensile strength and toughness reaching 197.4 MPa and 11.6 MJ m^(−3),respectively.展开更多
In this study,multilayer lamination welding was employed to prepare graphene/copper(Gr/Cu)composite billets from graphene-coated copper foils,followed by multi-pass cold drawing to produce Φ1 mm Gr/Cu composite wires...In this study,multilayer lamination welding was employed to prepare graphene/copper(Gr/Cu)composite billets from graphene-coated copper foils,followed by multi-pass cold drawing to produce Φ1 mm Gr/Cu composite wires.Microstructure and property analyses in both the cold-drawn and annealed states show that the incorporation of graphene significantly improves the ductility and electrical conductivity of the copper wire.After annealing at 350℃ for 30 minutes,the composite wire demonstrates a tensile strength of 270 MPa and an electrical conductivity of 102.74%IACS,both superior to those of pure copper wire under identical conditions.At 150℃,the electrical conductivity of the annealed composite wire reaches 72.60%IACS,notably higher than the 68.19%IACS of pure copper.The results suggest that graphene is uniformly distributed within the composite wire,with minimal impact on conductivity,while effectively refining the copper grain structure to enhance ductility.Moreover,graphene suppresses copper lattice vibrations at elevated temperatures,reducing the rate of conductivity degradation.展开更多
基金The UK Catalysis Hub for support provided via the membership of the UK Catalysis Hub Consortium and funded by EPSRC (portfolio grants EP/K014706/1, EP/K014668/1, EP/K014854/1, EP/K014714/1 and EP/I019693/1).
文摘In this study,we aim to contribute an understanding of the pathway of formation of Fe species during top-down synthesis of dispersed Fe on N-functionalized few layer graphene,widely used in electrocatalysis.We use X-ray absorption spectroscopy to determine the electronic structure and coordination geometry of the Fe species and in situ high angle annular dark field scanning transmission electron microscopy combined with atomic resolved electron energy loss spectroscopy to localize these,identify their chemical configuration and monitor their dynamics during thermal annealing.We show the high mobility of peripheral Fe atoms,first diffusing rapidly at the trims of the graphene layers and at temperatures as high as 573 K,diffusing from the edge planes towards in-plane locations of the graphene layers forming three-,four-coordinated metal sites and more complexes polynuclear Fe species.This process occurs via bond C-C breaking which partially reduces the extension of the graphene domains.However,the vast majority of Fe is segregated as a metal phase.This dynamic interconversion depends on the structural details of the surrounding graphitic environment in which these are formed as well as the Fe loading.N species appear stabilizing isolated and polynuclear Fe species even at temperatures as high as 873 K.The significance of our results lies on the fact that single Fe atoms in graphene are highly mobile and therefore a structural description of the electroactive sites as such is insufficient and more complex species might be more relevant,especially in the case of multielectron transfer reactions.Here we provide the experimental evidence of the formation of these polynuclear Fe-N sites and their structural characteristics.
基金supported by the National Basic Research Program of China(Grant No.2012CB921300)the National Natural Science Foundation of China(Grant Nos.11074005 and 91021007)the Chinese Ministry of Education
文摘Few-layer graphene grown on Ni thin films has been studied by scanning tunneling microscopy. In most areas on the surfaces, moir6 patterns resulted from rotational stacking faults were observed. At a bias lower than 200 mV, only one sublattice shows up in regions without moir6 patterns while both sublattices are seen in regions with moir6 pattens. This phenomenon can be used to identify AB stacked regions. The scattering characteristics at various types of step edges are different from those of monolayer graphene edges, either armchair or zigzag.
基金supported by the National Natural Science Foundation of China(No.21776041 and No.21875028)the Cheung Kong Scholars Programme of China(T2015036)。
文摘Assembly of the top-down graphene units mostly results in 3D porous structure with randomly organized pores.The direct bottom-up synthesis of macroscopic 2D graphene sheets with organized pores are long sought in materials chemistry field,but rarely achieved.Herein,we present a self-catalysisassisted bottom-up route usingL-glutamic acid and iron chloride as starting materials for the fabrication of the millimeter-sized few-layer graphene sheets with aligned porous channels parallel to the 2D direction.The amino-and carboxyl-functional groups inL-glutamic acid can coordinate with iron cations,thus allowing an atomic dispersion of iron cations.The pyrolysis thus initiated the growth of graphene catalyzed by in-situ generated iron nanoparticles,and a dynamic flow of iron nanoparticles eventually led to the formation of millimeter-sized few-layer graphene sheets with aligned channels(60-85 nm in diameter).Used as anodes in lithium-ion batteries,these graphene sheets showed a good rate capability(142 m A h g^(-1) at 2 A g^(-1))and high capacity retention of 93%at 2 A g^(-1) after 1200 cycles.Kinetic analysis revealed that lithium ions storage was dominated by diffusion behavior and capacitive behavior together,in that graphene sheets with aligned channels could accelerate electron transfer and shorten lithium ions transport pathway.This work provides a novel approach to prepare unique porous graphene materials with specific structure for energy storage.
基金the financial support from the Innovative Research Groups of the National Natural Science Foundation of China(No.51621001)National Natural Science Foundation of China(No.51671088,51671089)
文摘To develop anode materials with superior volumetric storage is crucial for practical application of lithium/sodium-ion batteries.Here,we have developed a micro/nanostructured Sn S/few-layer graphene(Sn S/FLG)composite by facile scalable plasma milling.Inside the hybrid,SnS nanoparticles are tightly supported by FLG,forming nanosized primary particles as building blocks and assembling to microsized secondary granules.With this unique micro/nanostructure,the Sn S/FLG composite possesses a high tap density of 1.98 g cm^(-3)and thus ensures a high volumetric storage.The combination of Sn S nanoparticles and FLG nanosheets can not only enhance the overall electrical conductivity and facilitate the ion diffusion greatly,but alleviate the large volume expansion of Sn S effectively and maintain the electrode integrity during cycling.Thus,the densely compacted Sn S/FLG composite exhibits superior volumetric lithium and sodium storage,including high volumetric capacities of 1926.5/1051.4 m Ah cm^(-3)at 0.2 A g^(-1),and high retained capacities of 1754.3/760.3 m Ah cm^(-3)after 500cycles at 1.0 A g^(-1).With superior volumetric storage performance and facile scalable synthesis,the Sn S/FLG composite can be a promising anode for practical batteries application.
基金Project(51274248)supported by the National Natural Science Foundation of China
文摘Few-layer graphenes were fabricated from expandable graphite by rapid microwave exfoliation. Expandable graphite was irradiated in a domestic microwave in full power for 3 min, then soaked in mixed strong hydrogen nitrate and sulfuric acid with volume ratio of 1：1 for 24 h and re-irradiated, thus few-layer graphene sheets were obtained. Specimens gained from every step were selectively characterized by different techniques, such as SEM, XRD, Raman, AFM, XPS, FTIR and combustion elemental analysis. The results show that expandable graphite with loose, porous and worm-like morphology forms instantaneously in microwave irradiation with crackling sound and sparkles, which manifests physical exfoliation of graphene sheets. Few-layer graphene sheets with a dozen or more layers and average thickness of about 4.7 nm are obtained eventually after sequential treatment of microwave irradiation, mixed acid soaking and second microwave irradiation. The as-prepared few-layer graphenes still have high crystallinity and high purity with traces of oxide groups and without serious unrecoverable oxidation damage.
基金Supported by National Natural Science Foundation of China(Grant Nos.51335005,51321092)National Key Basic Research Program of China(973 Program,Grant No.2013CB934200)the Foundation for the Supervisor of Beijing Excellent Doctoral Dissertation(Grant No.20111000305)
文摘The performance of a lubricant largely depends on the additives it involves.However,currently used additives cause severe pollution if they are burned and exhausted.Therefore,it is necessary to develop a new generation of green additives.Graphene oxide(GO)consists of only C,H and O and thus is considered to be environmentally friendly.So the tribological properties of the few-layer GO sheet as an additive in hydrocarbon base oil are investigated systematically.It is found that,with the addition of GO sheets,both the coefficient of friction(COF)and wear are decreased and the working temperature range of the lubricant is expanded in the positive direction.Moreover,GO sheets has better performance under higher sliding speed and the optimized concentration of GO sheets is determined to be 0.5wt%.After rubbing,GO is detected on the wear scars through Raman spectroscopy.And it is believed that,during the rubbing,GO sheets adhere to the sliding surfaces,behaving like protective films and preventing the sliding surfaces from contacting with each other directly.This paper proves that the GO sheet is an effective lubricant additive,illuminates the lubrication mechanism,and provides some critical parameters for the practical application of GO sheets in lubrication.
文摘We have developed a dry transfer method that allows graphene to be transferred from polymer- thyl-methacrylate (PMMA)/Si (silicon) substrates on commercially available hexagonal boron ni- tride (hBN) crystals. With this method we are able to fabricate graphene devices with little wrin- kles and bubbles in graphene sheets, but that do not degrade the electronic quality more than the SiO2 substrate does. For hBN to perform the function described above substrate cleanliness is critical to get high quality graphene devices. Using hBN as a substrate, graphene exhibits enhanced mobility, reduced carrier inhomogeneity, and reduced intrinsic doping compared to graphene on SiO2 substrate.
文摘We study graphene electrodes that can be used for contacting single molecules. The nanometer-scale gap is made by feedback controlled electroburning in few-layer graphene sheets. We analyze the time stability, and the influence of the temperature and gate voltage on the current flowing through the empty gaps. The electrodes are stable at room temper- ature for long periods of time. We show statistics of the relation between the initial resistance of the few-layer graphe- ne flakes and the final size of the gaps. We find that thicker flakes are more suitable for the fabrication of the elec-trodes.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.51376005 and 11474243)
文摘Twisted graphene possesses unique electronic properties and applications, which have been studied extensively. Recently, the phonon properties of twisted graphene have received a great deal of attention. To the best of our knowledge,thermal transports in twisted graphene have been investigated little to date. Here, we study perpendicular and parallel transports in twisted few-layer graphene（T-FLG）. It is found that perpendicular and parallel transports are both sensitive to the rotation angle θ between layers. When θ increases from 0° to 60°, perpendicular thermal conductivity κ（｜｜） first decreases and then increases, and the transition angle is θ = 30°. For the parallel transport, the relation between thermal conductivity κand θ is complicated, because intra-layer thermal transport is more sensitive to the edge of layer than their stacking forms. However, the dependence of interlayer scattering on θ is similar to that of κ⊥. In addition, the effect of layer number on the thermal transport is discussed. Our results may provide references for designing the devices of thermal insulation and thermal management based on graphene.
基金Supported in part by the National Natural Science Foundation of China under Grant Nos.11004082 and 11175067the Natural Science Foundation of Guangdong Province under Grant Nos.10451063201005249 and S201101000332the Fundamental Research Funds for the Central Universities,JNU under Grant Nos.21611437 and 50421288
文摘We study the thermal transport of few-layer graphene nanoribbons in the presence of the transversal pressure by using molecular dynamics simulations. It is reported that the pressure can improve the thermal conductivity of few-layer graphene nanoribbons. This improvement can reach 37.5% in the low temperature region. The pressure dependence of thermal conductivity is also investigated for different length, width and thickness of few-layer graphene. Our results provide an alternative option to tuning thermal conductivity of few-layer graphene nanoribbons, b-arthermore, it maybe indicate a so-called pressure-thermM effect in nanomaterials.
文摘In this paper the anticorrosive properties of the few-layer graphene nanostructures were investigated. On the surface ofcopper and nickel plates the few-layer graphene nanostructures were formed using the CVD （chemical vapor deposition） method.After that, these plates were exposed to the temperature in the air atmosphere. The results of elemental analysis, performed by theEDS （energy dispersive spectroscopy） method showed that the few-layer graphene coated metal plates proved to be more resistant tooxidation than bare metal plates. In addition, we presented computer models and theoretical calculations of the studied systems,performed by the DFT （density functional theory） and MD （molecular dynamics） methods. These results combined with experimentaldata show the high effectiveness of the protective action of the few-layer graphene against metal corrosion.
基金Project supported by the National Basic Research Program of China(Grant No.2013CB933604)the National Natural Science Foundation of China(Grant No.51572290)the Chinese Academy of Sciences(Grant Nos.1731300500015 and XDB07030100)
文摘Large-area boron nanowire（BNW） films were fabricated on the Si（111） substrate by chemical vapor deposition（CVD）. The average diameter of the BNWs is about 20 nm, with lengths of 5–10 μm. Then, graphene-capped boron nanowires（GC-BNWs） were obtained by microwave plasma chemical vapor deposition（MPCVD）. Characterization by scanning electron microscopy indicates that few-layer graphene covers the surface of the boron nanowires. Field emission measurements of the BNWs and GC-BNW films show that the GC-BNW films have a lower turn-on electric field than the BNW films.
基金the funding support from the National Natural Science Foundation of China(Grant No.22278404).
文摘Graphene materials like turbostratic graphene exhibit remarkable promise for an array of applications,spanning from electronic devices to aerospace technologies.It is essential to develop a fabrication method that is not only economical and efficient,but also environmentally sustainable.In this study,the molten salt-assisted magnesiothermic reduction(MSAMR)method is proposed for the synthesis of few-layer turbostratic graphene.K_(2)CO_(3)serves as both the carbon source and the catalyst for graphitization,facilitating the formation of the graphene structure,while in-situ generated MgO nanoparticles exert confinement and templating effects on the growth of graphene.The molten salts used effectively prevent the aggregation and the Bernal stacking of graphene sheets,ensuring the few-layer and turbostratic structure.The synergistic effects of K 2CO 3,in-situ generated MgO,and molten salts guarantee the formation of few-layer turbostratic graphene at a relatively low temperature,characterized with 4–8 stacking layers,a mesopore-dominated microstructure,and a high degree of graphitization.
基金supported by the National Natural Science Foundation of China(Grant Nos.12274252,and 12350404)the Basic Science Center Project of NSFC(Grant No.52388201)the Innovation Program for Quantum Science and Technology(Grant No.2021ZD0302502)。
文摘The simultaneous modulation of electric and optical properties in graphene is essential for advancing high-performance applications in optoelectronics.However,achieving in-situ control of multiple electric and optical states in graphene devices remains a challenge.Here we demonstrate a versatile and reversible electric-field control of organic-ion intercalation from bilayer to pentalayer graphene.Through simultaneous optical imaging and electric measurements,we reveal multiple physical states controlled by the layer-by-layer intercalation processes,resulting in both high transparency and high electric conductance with an increase in the number of intercalated layers.Raman spectroscopy demonstrates that the intercalated graphene maintains a high carrier concentration without lattice degradation.Moreover,Hall effect measurements reveal that the carrier density can reach approximately 1.5×10^(14)cm^(-2)per layer.The ability to synchronously control the transparency and conductance states by adjusting the number of ion-intercalated layers highlights the potential of multistate modulation for the development of advanced optoelectronic devices in two-dimensional materials.
基金supported by the Zhejiang Provincial Natural Science Foundation of Chinat(No.LR24E050001)the National Natural Science Foundation of China(NSFC)(No.52475223)the NSFC Excellent Young Scientists Fund Program(Overseas).
文摘In this work,few-layer graphene oxide(GO)sheets are investigated as aqueous lubricant additives between ceramic surfaces.Three batches of GO sheets with various lateral sizes were selected,and the lateral sizes were mainly within the ranges of 0.5±0.2,5.9±2.1,and 59.1±17.1μm.The weight concentration of the GO sheets in the aqueous lubricant ranged from 0.0005 to 0.8 wt%.The lubrication regime for the friction tests was kept at boundary lubrication.The GO sheets can enhance lubricity by entering the contact area and preventing the sliding surfaces from contacting each other directly,and lubricity is determined by the coverage of the contact area.For each batch of GO sheets,as the concentration increases,the coverage rate of the contact area increases;thus,the coefficient of friction(COF)and wear volume decrease.However,when the GO sheet concentration is very high,the COF approaches a stable value since the contact area is already fully covered by GO sheets,but the wear volume increases slightly due to the high acidity.Moreover,GO sheets with larger lateral sizes can lead to a smoother contact interface.Therefore,at the same concentration,GO sheets with larger lateral sizes can lead to lower COFs and wear volumes.These findings provide a general strategy for improving the performance of lubricants with two-dimensional(2D)material additives in a broad range of mechanical applications.
基金supported by the National Key R&D Program of China(No.2022YFA1404201)the National Natural Science Foundation of China(Nos.62305200,U22A2091,62127817,and 62075240)the Fundamental Research Program of Shanxi Province(No.202203021222001).
文摘Optical modulation is significant and ubiquitous to telecommunication technologies,smart windows,and military devices.However,due to the limited tunability of traditional doping,achieving broadband optical property change is a tough problem.Here,we demonstrate a remarkable transformation of optical transmittance in few-layer graphene(FLG)covering the electromagnetic spectra from the visible to the terahertz wave after lithium(Li)intercalation.It results in the transmittance being higher than 90%from the wavelengths of 480 to 1040 nm,and it increases most from 86.4%to 94.1%at 600 nm,reduces from∼80%to∼68%in the wavelength range from 2.5 to 11μm,has∼20%reduction over a wavelength range from 0.4 to 1.2 THz,and reduces from 97.2%to 68.2%at the wavelength of 1.2 THz.The optical modification of lithiated FLG is attributed to the increase of Fermi energy(E_(f))due to the charge transfer from Li to graphene layers.Our results may provide a new strategy for the design of broadband optical modulation devices.
基金the support from the National Natural Science Foundation of China(52473083,52373089,52403085)Natural Science Basic Research Program of Shaanxi(2024JC-TBZC-04)+2 种基金the Innovation Capability Support Program of Shaanxi(2024RS-CXTD-57)Natural Science Basic Research Plan in Shaanxi Province of China(2024JC-YBMS-279)Natural Science Foundation of Chongqing,China(2023NSCQMSX2547)
文摘With the miniaturization and high-frequency evolution of antennas in 5G/6G communications,aerospace,and transportation,polymer composite papers integrating superior wave-transparent performance and thermal conductivity for radar antenna systems are urgently needed.Herein,a down-top strategy was employed to synthesize poly(p-phenylene benzobisoxazole)precursor nanofibers(prePNF).The prePNF was then uniformly mixed with fluorinated graphene(FG)to fabricate FG/PNF composite papers through consecutively suction filtration,hot-pressing,and thermal annealing.The hydroxyl and amino groups in prePNF enhanced the stability of FG/prePNF dispersion,while the increasedπ-πinteractions between PNF and FG after annealing improved their compatibility.The preparation time and cost of PNF paper was significantly reduced when applying this strategy,which enabled its large-scale production.Furthermore,the prepared FG/PNF composite papers exhibited excellent wave-transparent performance and thermal conductivity.When the mass fraction of FG was 40 wt%,the FG/PNF composite paper prepared via the down-top strategy achieved the wave-transparent coefficient(|T|2)of 96.3%under 10 GHz,in-plane thermal conductivity(λ_(∥))of 7.13 W m^(−1)K^(−1),and through-plane thermal conductivity(λ_(⊥))of 0.67 W m^(−1)K^(−1),outperforming FG/PNF composite paper prepared by the top-down strategy(|T|2=95.9%,λ_(∥)=5.52 W m^(−1)K^(−1),λ_(⊥)=0.52 W m^(−1)K^(−1))and pure PNF paper(|T|2=94.7%,λ_(∥)=3.04 W m^(−1)K^(−1),λ_(⊥)=0.24 W m^(−1)K^(−1)).Meanwhile,FG/PNF composite paper(with 40 wt%FG)through the down-top strategy also demonstrated outstanding mechanical properties with tensile strength and toughness reaching 197.4 MPa and 11.6 MJ m^(−3),respectively.
基金Funded by Hunan Provincial Natural Science Foundation(No.2023JJ40074)Hunan Provincial Education Department Excellent Youth Project(No.21B0757)Hunan Provincial Engineering Technology Center(No.2022TP2036)。
文摘In this study,multilayer lamination welding was employed to prepare graphene/copper(Gr/Cu)composite billets from graphene-coated copper foils,followed by multi-pass cold drawing to produce Φ1 mm Gr/Cu composite wires.Microstructure and property analyses in both the cold-drawn and annealed states show that the incorporation of graphene significantly improves the ductility and electrical conductivity of the copper wire.After annealing at 350℃ for 30 minutes,the composite wire demonstrates a tensile strength of 270 MPa and an electrical conductivity of 102.74%IACS,both superior to those of pure copper wire under identical conditions.At 150℃,the electrical conductivity of the annealed composite wire reaches 72.60%IACS,notably higher than the 68.19%IACS of pure copper.The results suggest that graphene is uniformly distributed within the composite wire,with minimal impact on conductivity,while effectively refining the copper grain structure to enhance ductility.Moreover,graphene suppresses copper lattice vibrations at elevated temperatures,reducing the rate of conductivity degradation.
