查看更多>>摘要：? 2022The preparation of graphene by chemical vapor deposition (CVD) is often accompanied by the growth of some structural defects, one of which is crack. The understanding of crack formation is key to the preparation of high-quality graphene films. In this work, the crack defects of graphene grown on liquid copper substrates by chemical vapor deposition (CVD) were examined. Then, the effects of growth temperature, growth time and total pressure on kinetics of cracks were analyzed, respectively. It is found that (I) The crack appeared during the period of graphene growth, not the cooling process of graphene; (II) the crack preferred to propagate at the vertex angle of etched hexagonal holes; (III) the crack tended to orient along the same direction—the zigzag direction. Finally, a dynamic mechanism of crack growth was proposed. Our study provides significant insights into the tearing mechanism of defective graphene.
查看更多>>摘要：? 2022 Elsevier B.V.The behavior of characteristic centers in diamond crystals from the Mir pipe (Yakutia) was investigated upon electron irradiation. A series of diamond crystals of different types was chosen for experiments based on the nitrogen content and aggregation parameters. In electron-irradiated diamonds of the IaAB type, a new characteristic photoluminescence system was found with a zero-phonon line (ZPL) at 615 nm together with phonon replicas of 41 and 90 meV. The phonons' energies pointed to multiphonon interactions with a quasilocal vibration of a vacancy. According to our data, the nitrogen-related defect responsible for this phenomenon contains a vacancy and may be accompanied by some other impurity. Conversely, in an almost nitrogen-free crystal, a specific system with the ZPL at 558 nm was noted. The center in question is known to be vacancy-related and was formed in type IIa crystals from the Mir pipe not only by electron irradiation but also by high-pressure high-temperature annealing when vacancies were released as a result of motion or annihilation of dislocations. Regardless of the nitrogen impurity, specific systems with the ZPL at 454, 491, and 492 nm were registered in the irradiated diamond crystals from the Mir pipe. To examine the generated defects, the irradiated diamond crystals were subjected to low-temperature annealing at ≤600 °C. Although the 454 and 491 nm systems persisted, the annealing of the 492 nm system along with well-known 523.6, 489.0, and 503.4 nm (3H) centers indicated the interstitial-vacancy nature of the defect.
Johnson H.M.Brown J.M.Zaniewski A.M.Nemanich R.J....
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查看更多>>摘要：? 2022 Elsevier B.V.TiC at the diamond?titanium interface is known to be a stable and beneficial layer for diamond based electronic devices. However, certain cleaning steps can alter the chemical composition of this interface. One such process is oxygen plasma etching, which terminates the surface of the diamond with oxygen. Oxygen is highly reactive with titanium, forming titanium oxides. Theoretically the titanium-diamond interface can be improved through sufficient annealing after device fabrication. To test this, we investigated the interface of oxygen-terminated polycrystalline B-doped diamond and titanium via XPS in an effort to determine if oxygen would rearrange away from the diamond surface and TiC would be formed through post-deposition annealing. After annealing at temperatures up to 900 °C, it was found that TiC was not detected at any point in this experiment. Oxygen-termination, despite its de-scumming capabilities, likely inhibits the formation of TiC at the diamond surface.
查看更多>>摘要：? 2022Novel multi-functional materials with very high microwave (MW) absorbance in the X-band became demanding for varied high-sensitive electronic applications. To meet this goal, a new type of activated carbon sample containing fullerene-C70 was derived from coconut shells using the combined physical activation and milling process for the first time. The effects of various milling times (50, 75, and 100 min) on the structure, morphology, and MW reflection traits of these samples were examined. The crystalline phase of the activated fullerene-C70 was found to alter from cubic to rhombohedral structure at the milling time of 100, displaying a specific surface area of 946.499 m2/g and mean pore diameter of 3.42 nm. It was shown that by tuning the surface area and fullerene contents in the sample, the MW reflection loss of such activated carbon can be controlled. It is established that fullerene-C70 derived from the proposed activated carbon may be useful to produce low-cost and efficient MW absorption materials needed for diverse electronic devices with reduced electromagnetic interference.
查看更多>>摘要：? 2022 Elsevier B.V.Carbon based composites derived from various biomasses have exhibited excellent application prospects in the field of supercapacitors. Herein, the Co3O4 nanoparticles supported on biomass eggfruit-derived porous carbon (EPC) was prepared via solvothermal method and subsequent calcination, in which the shells of eggfruit's kernel (SEK) were used as carbon source and cobalt phthalocyanine was employed as precursor of Co3O4. The resultant composite was denoted as Co3O4@EPC and its supercapacitive performances were checked in details. Scanning electron microscopy and transmission electron microscopy images of Co3O4@EPC show that EPC has a three-dimensional porous network structure, and Co3O4 nanoparticles with an average particle size of 7 nm are uniformly dispersed on the EPC carrier. In the three-electrode system with 6 mol L?1 KOH as electrolyte, the specific capacitance of Co3O4@EPC/Ni foam electrode is 781 F g?1 at the current density of 0.5 A g?1, which is much higher than that of p-Co3O4 electrode (429.69 F g?1 at 0.5 A g?1) or EPC (125.39 F g?1 at 0.5 A g?1) electrode under the same conditions. The energy density of a two-electrode device with Co3O4@EPC/Ni foam electrode as positive electrode and EPC/Ni foam electrode as negative electrode was 32.8 Wh K g?1 at the power density of 1333 W K g?1. In addition, the device has good cyclic stability with a capacitance retention rate of 96.7% after 20,000 cycles. These results indicate that the excellent properties of the Co3O4@EPC make it a potential electrode material for high-performance supercapacitors.
查看更多>>摘要：? 2022 Elsevier B.V.High-performance porous carbon materials have always received much interest for supercapacitors due to their excellent cycling stability, superior conductivity, etc. Herein, sulfur, phosphorous and chlorine tri-doped hierarchically porous carbon (SPC) were prepared by simply co-activating using KOH and Na2S with wheat bran as precursor. Na2S can not only improve the specific surface area (1310.3 m2 g?1 to 1585.5 m2 g?1) and pore volume (0.767 cm3 g?1 to 0.977 cm3 g?1), but also introduce sulfur atoms to contribute extra pseudocapacitance. Benefitting from the heteroatom doping and surface structure optimizing, the as-prepared SPC exhibits a large specific capacitance of 488 F g?1 (at 1 A g?1), superior to the porous carbon that was only activated by KOH (245 F g?1 at 1 A g?1), and still remains 51.6% of the initial specific capacitance at 20 A g?1.The supercapacitor assembled by SPC delivers a high energy density of 12.5 Wh kg?1 (at 250 W kg?1). After charge-discharge for 9000 cycles (at 10 A g?1), the capacitance can still remain 96% of the initial value, showing that SPC is a promising candidate for high-performance supercapacitor.
查看更多>>摘要：? 2022 Elsevier B.V.Using carbon nanomaterials to construct self-lubricating polymer materials with porous self-lubricating structures has become an effective way to improve the tribological performance of polymer composites. The synergistic effect between 1.0 wt% graphene oxide (GO) and lubricating oil resulted in excellent tribological properties of polyamide 6 (PA6) composites under different loads and speeds. It indicated that the introduction of GO in porous PA6 matrix (GO/PA6) would provide enhanced tribological performance with the friction coefficient reduction by 23.4% and wear resistance improvement by 36.2%. This was explained by the lubricating oil stored in the pores of PA6 material would be released to the surface of the matrix material under the dual effect of load and temperature during the friction process. The released lubricating oil would formed a solid-liquid double lubrication structure with the well-dispersed GO in the matrix, thus the porous oil-immersed GO/PA6 composite materials demonstrates excellent tribological performance. This work provides a solid-liquid double lubrication strategy for enhancing the tribological properties of self-lubricating polymers, which would promote the self-lubricating polymer composites more widely applied in the field of friction materials.
查看更多>>摘要：? 2022 Elsevier B.V.In this paper, we found that the presence of sodium chloride (NaCl) can effectively inhibit the diffusion of graphene oxide (GO) in water. Based on this discovery, we reported a simple preparation method of GO paper regulated by Na ions. By adjusting the drying temperature and the mass fraction of NaCl solution, the preparation and complete stripping of GO paper can be easily completed, thereby obtaining free-standing GO paper. Further, we also found that the introduction of sodium ions would cause changes in the microwave irradiation spectrum of GO paper, and the change was related to the mass fraction of NaCl solution used, which could be used to detect sodium ions and the concentration of NaCl solution. Besides, our study also showed that MWRGO paper with NaCl solution treatment can more effectively remove methylene blue in water, compared with MWRGO paper without NaCl solution treatment. This study provides the possibility of the preparation of GO paper based on seawater and also provides a new method for the detection of sodium ions and determination of sodium chloride solution concentration. It has important application prospects in the preparation of GO paper, sensor and water treatment.
查看更多>>摘要：? 2022 Elsevier B.V.Herein, the attractive N-doped porous carbon nanosheets (NPCs-4, mass ratio = 4/1) were synthesized by a simple one-step carbonization approach using the mixtures of melamine cyanurate and xylitol (mass ratio = 4/1), which formed the interconnected carbon framework with abundant pore structure. The NPCs-4 electrode displayed a large specific surface area of 703.2 m2/g with hierarchical pore sizes (2–4 nm) and expanded interlayer spacing of ~0.39 nm. The abundant pore structure and N-doping of the NPCs-4 facilitated high Na-ion storage capacity, fast transfer kinetics and stable cycling. As a result of these improvements, the as-prepared NPCs-4 electrode delivered an advanced rate performance (191.1 mA h/g at 20 A/g), and an outstanding ultra-long cycling performance with a specific capacity of 171 mA h/g at 10 A/g after 10,000 cycles (0.0017% loss per cycle), which was the one of the optimal long-cycle properties at high current density reported for carbon-based anode for SIBs to date. Moreover, the kinetic analysis revealed a capacitance-dominated sodium storage mechanism in the NPCs-4 electrode, and possessed a superior Na+ ion diffusion coefficient (1.92 ? 10?12 cm2/s), on account of synergistic interaction of rational nanopore structure and appropriate N-doping in NPCs-4. This work provided a facial route to synthesize controlled N-doping porous carbon nanosheets with enlarged interplanar spacing and high specific area, meeting the various requirements unitized as anodes in rechargeable Na+ ions batteries.
查看更多>>摘要：? 2022 Elsevier B.V.Two orthorhombic novel superhard sp3-sp2 carbon phases Hcc-C14 and DHcc-C20 are considered theoretically in this study, based on density functional theory. Hcc-C14 and DHcc-C20 allotropes exhibit distinct structural geometries, including C4, C6, and two kinds of C8 carbon rings, containing 14 and 20 carbon atoms in the unit cell, respectively. The electronic band structure calculations of Hcc-C14 and DHcc-C20 show that both allotropes are semiconductors with an indirect bandgap of 2.235 eV and 2.863 eV, respectively. The phonon dispersion under 0 and 100 GPa and calculated elastic constants at 0 GPa prove that these two structures are mechanically and dynamically stable. Also, the hardness of Hcc-C14 and DHcc-C20 is predicted to be 83.7 GPa and 80.9 GPa, which shows the ultra-hardness of these structures. The combination of these outstanding and significant properties indicates these two carbon structures are potential materials for high-frequency electronics, high-temperature, high elastic constants, and for use in aviation and military industry.
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