查看更多>>摘要：? 2022 Elsevier B.V.Nitrogen-vacancy (NV) centres in diamond are point-like defects that have attracted a lot of attention as promising candidates for quantum technologies particularly for sensing and imaging nanoscale magnetic fields. For this application, the use of a high NV density within a high-quality diamond layer is of prime interest. In previous works, it has been demonstrated that in situ doping with N2O rather than N2 during chemical vapour deposition (CVD), limits the formation of macroscopic defects and improves NV's photostability. In this work, we focus on the optimization of the CVD growth conditions to obtain a high NV density keeping a constant N2O concentration in the gas phase (100 ppm). For this purpose, freestanding CVD layers are prepared varying two main growth parameters: methane content and substrate temperature. High energy electron irradiation followed by annealing is finally carried out in order to increase the NV yield through partial conversion of N impurities. Defect concentrations and spin properties are investigated. We find that growth under lower methane concentrations and lower temperatures enhances NV doping. NV ensembles with a density of the order of 2 ppm are finally obtained with narrow spin resonance linewidth. In addition, higher annealing temperatures of 1200 °C following irradiation are found to efficiently remove defects thus improving spin properties.
Abraham O.F.Aigbodion V.S.Ejiogu E.C.Ogbuefi U.C....
7页
查看更多>>摘要：? 2022Due to the low toxicity, high theoretical capacity, abundant resources, low potential, of zinc oxide (ZnO), it is regarded as the next-generation lithium-ion battery anode material. However, because of the significant drawback in terms of volume expansion during the charge-discharge cycles, ZnO is easily pulverized and agglomerated. In this research work, we synthesize 0.5 g of rice husk-derived graphene (R0.5) and 1.0 g of ZnO (Z1.0) composite (R0.5Z1.0) to accommodate the volume expansion of ZnO during the charge-discharge process as a next-generation lithium-ion battery anode. Rice husk as a graphene source will support the future usage of bio-based materials for active material synthesis. The samples were characterized via SEM, XRD, and Fourier infrared spectroscopy, and with a discharge capacity of 895.2 mAhg?1 at a current density of 200 mAg?1 after 110 cycles, the composite material demonstrated remarkable Li storing characteristics and electrochemical performance as an anode for lithium-ion battery application.
查看更多>>摘要：? 2022 Elsevier B.V.In the present investigation, ZnO/rGO nanocomposites were prepared using conventional solid-state reaction method. Raman, XRD, FTIR, UV–Vis, PL and FESEM characterization tools were used to analyze the synthesized materials. Raman analysis reveals the formation of rGO with prominent D and G-band peaks. XRD patterns confirm the crystalline and hexagonal wurtzite structure with P63mc space group of all the samples. Rietveld refinement demonstrates the size variation (33 nm–56 nm) and strain profile. FESEM micrographs of ZnO/rGO composites have established the formation of densely packed hexagonal nano-pebbles. UV–Vis and room temperature PL measurements indicate that the optical properties of ZnO and ZnO/rGO nanocomposites are affected by the rGO concentration. It also confirms a band gap shrinkage during nanocomposite preparation compared to the pure ZnO structure. Urbach energy is found to increase with increase in rGO content and the strength of electron-phonon interaction enhances. It also affects the PL emission in the UV region. FTIR spectra confirm the presence of different functional groups. Present investigation shows that ZnO/rGO materials are potential candidates for design and development of sensors for detecting gases.
查看更多>>摘要：? 2022 Elsevier B.V.Lithium?sulfur (Li-S) batteries have been hindered by the difficulty of achieving satisfactory cycling stability of high sulfur loading owing to the structural instability and exaggerated shuttle problem. Here, we design and fabricate a “reinforced concrete” structure based on the carbon fibers (CFs) supporting graphene/carbon nanotubes (GC) matrix composites, followed by a slurry-casting process to produce the final CFs-S/GC cathode with 4.5– 5.5 mg cm?2 sulfur loading. The 3D architecture of the micro/nano-hybrid materials enhances the structural strength and builds an interconnected conductive network for efficient electrolyte infiltration and the rapid electric/ionic transport. Furthermore, carbon nanofibers (CNFs) are growth on the surface of CFs by chemical vapor deposition to formation of CFs@CNFs. The CFs@CNFs-S/GC cathode enables the effective confines of polysulfides on electrochemically active sites, leading to a much-improved cycling performance. The strategy reported in this paper provides a feasible way for the construction of CFs or modified CFs skeleton in nanostructured carbon materials for high energy density Li-S batteries.
查看更多>>摘要：? 2022 Elsevier B.V.Here two groups of experimental studies were performed to investigate the irradiation hardness and tribological performance of nanocrystalline diamond (NCD) films synthesized using hot-filament chemical vapor deposition. Extensive characterizations including the Raman, X-ray photoelectron spectroscopy, high-resolution transmission electron microscopy, and electron energy loss spectroscopy were applied, to explore the structural and property evolution of heavy-ion radiated films with a gradual increase of the displacement damage. Results indicated that films with different original structures possessed the same starting point of a quasi-saturation state at 2.0 dpa, above which films underwent a significant transformation from the sp3 to sp2 bonds within the depth of the projected range, forming an amorphous layer with an identical bonding structure among the different samples. The radiation-induced amorphization resulted in a change in the wear mechanism in dry sliding movements, i.e., from the abrasive wear in the pristine films to the adhesive wear in the radiated films. Furthermore, a formation of graphene nanocrystals was observed in the wear scars of radiated films, which favored the stability of friction coefficient curves. As the displacement damage further increased to 5.0 and 10.0 dpa, the bonding structure of the amorphous layer was well maintained, and in the meantime, the low-friction characteristics of the radiated films were also well maintained, even as the tribotests were continued for 5 × 105 laps and the wear depth had already exceeded the projected range of incident ions. Furthermore, the larger the irradiation damage, the greater the graphitization transformation occurring in the tribofilms, and the lower the film wear rates in an ambient air atmosphere. These results provide insights into what changes in the film nanostructures and sliding interfaces are responsible for the ultrahigh wear resistance of NCD films under nuclear irradiation conditions with large displacement damage.
查看更多>>摘要：? 2022Bi12TiO20/reduced graphene oxide (RGO) composites were successfully synthesized by combining sol-gel method with hydrothermal treatment. The TEM showed that Bi12TiO20 nanoparticles are well dispersed on the surface of graphene. The photocatalytic performance of Bi12TiO20/RGO composites was evaluated by degrading Rhodamine B (RhB) to innocuous substance under the visible light. The degradation rate of RhB over Bi12TiO20/RGO3 composites can reach 98%, which is much higher than Bi12TiO20. The introduction of graphene enhances the charge transfer ability and effectively inhibits the recombination of photogenerated electrons and holes. Bi12TiO20/RGO composites exhibit good stability in cycling experiments. The ?OH and h+ generated in the Bi12TiO20/RGO-photocatalyzed RhB degradation system are identified as active species by free radical and hole scavenging experiments and the photocatalytic degradation mechanism is proposed.
查看更多>>摘要：? 2022 Elsevier B.V.The magnetization of crystalline red diamond bulk samples were investigated in the temperature range between 2 K and 125 K and with the applied maximal magnetic field of ±7 T. The investigated diamond samples are of Type Ib with a nitrogen content less than 200 ppm. Diamonds without any treatment display a yellow color and were transformed to red color after irradiation with 10 MeV electrons at T=900°C, in vacuum, owing to the formation of nitrogen-vacancy centers. Field dependent magnetization m(H) measurements for temperatures T ? 10 K show unusual hysteresis loops, which we interpret as consequence of the superposition of coexisting superconducting and paramagnetic regions present in the sample. Temperature dependence of the magnetization m(T) measured in the zero field and field cooled modus shows a paramagnetic behavior accompanied with an irreversibility for T ? 13 K, while at higher temperatures shows a diamagnetic behavior which is similar to undoped diamond. Coexistence of superconductivity and paramagnetism is established because both phenomena exist in the same temperature range and fits done to the m(H) using an equation based upon Bean model, support our conclusion. Room temperature confocal photoluminescence measurements were done on both yellow and red diamond, showing that in the red diamond the amount of neutral NV° and negative charged nitrogen-vacancy centers NV? have been significantly created. The transformation process from yellow to red diamond has mainly caused the alteration of the superparamagnetic regions into paramagnetic, while the superconducting contribution of the sample was less affected, according to the parameters obtained after we fitted the field dependent magnetization results.
查看更多>>摘要：? 2022 Elsevier B.V.Modifying amorphous carbon (a-C) with rare-earth elements is a highly auspicious concept to synthetize functional films with unique characteristics. Among the rare earth elements, Er and Gd demonstrate abundant physicochemical properties and, hence, are of remarkable interest for the element modification of a-C films. Therefore, Er-containing a-C:Er and Gd-containing a-C:Gd films are prepared in a reactive-free magnetron sputtering process. The a-C:Er and a-C:Gd films have an amount of up to 5 at.-% Er and 4.8 at.-% Gd. High-resolution x-ray photoelectron spectroscopy analyses show the formation of Er[sbnd]C and Gd[sbnd]C components, which rise proportionally with increasing amount of the rare-earth element. The addition of Er and Gd lowers the sp3 content of C bonds. At the highest concentrations of the respective rare-earth elements, the a-C:Er and a-C:Gd films exhibit a reduced sp3 content of 8%. The number and size of sp2?carbon clusters in the amorphous network are enhanced with increasing amount of Er and Gd which is evaluated by Raman scattering measurements. X-ray diffraction analyses reveal Er and Gd carbide phases, indicating the formation of a nanocomposite structure consisting of carbidic nanocrystallites and an a-C network. In nanoindentation tests, the non-modified a-C demonstrates a hardness of (21.7 ± 1.6) GPa and an elastic modulus of (232 ± 10) GPa. With increasing Er and Gd contents, the hardness linearly decreases to (16.7 ± 0.9) GPa and (14.8 ± 0.9) GPa, respectively. An analogous behavior is also identified for the elastic modulus. The reduced hardness and elastic modulus are attributed to the lower sp3 content and the larger number and size of the sp2-hybridized carbon atoms. Additionally, the adhesion was slightly improved by the addition of Er and Gd in comparison to non-modified a-C.
查看更多>>摘要：? 2022 Elsevier B.V.Co@C core-shell particles with a uniform size of approximately 100 nm anchored on rGO nano sheets is synthesized by a one-pot hydrothermal process. The Co@C particle formation is realized with a self-assembly procedure of metal-organic framework (MOF), and with GO as the precursor of rGO, Co@C/rGO is achieved. After calcination, the synthesized Co@C/rGO with high crystallization is obtained. Fabricated as an electrode by electrophoretic deposition, the calcined Co@C/rGO is evaluated with a high specific capacity of 810 C g?1 at a current density of 1 A g?1. With the calcined Co@C/rGO served as positive electrode and with as-prepared 3D rGO aerogel as negative electrode, an assembled asymmetric supercapattery possesses a wide operating potential window of 1.2 V. The specific capacitance of the supercapattery can be as high as 120 F g?1 at 0.6 A g?1, while the energy density reaches 29.5 W h kg?1 at a power density of 720 W kg?1, and 11.2 W h kg?1 at 12,000 W kg?1. After 10,000 cycles of charge-discharge process at 5 A g?1, the asymmetric supercapattery device shows considerable cyclic stability with capacitance retention of 93.7%.
NSTL
Elsevier