查看更多>>摘要：? 2021 Elsevier B.V.By placing a diamond in a H2 plasma and exposing it to air or overcoating it with Al2O3/SiO2, evaporated WO3, or other transition metal oxides a 2 dimensional, 2D, conductive hole gas forms on the diamond surface. Field effect transistors, FETs, made using this 2 D hole gas have the potential of replacing GaN FETs for use in high-power switching and high-frequency power applications. To achieve this goal, it is necessary to control the hole carrier density. When the carrier density is too high the device cannot be turned off and will have a low operational drain voltage due to electric-field break-down of diamond. On the other hand, too low a carrier density results in limited drain current, reduced power handling capability, and high on resistance. For diamond surface FETs using Al2O3/SiO2 as a gate oxide a carrier density between 1 × 1013 to 6 × 1013 cm?2 is the most desirable, depending on the intended operating voltage and the drain current density. This article discusses H-terminated procedure to controllably vary the carrier density from 1 × 1013 to 6 × 1013 cm?2. This is accomplished by varying the H-termination parameters; temperature, termination time, H2 pressure, and the microwave plasma power. During termination the diamond surface is etched and the density and type of crystal sets that form on the diamond surface is determined by these parameters. A model is presented of how the crystal step density and their character, single and double steps, can affect the carrier density.
查看更多>>摘要：? 2021This work provides an idea for the efficient and harmless utilization of lignin and further evaluates the textural properties of lignin-derived activated carbon/specific capacitance relationship. The yield of apricot shell lignin (ASL) was 30.42%. H3PO4/KOH was used to assist the preparation of ASL-derived activated carbons (AACs) for capacitors. The AAC prepared at a ratio of H3PO4 weight to ASL weight of 3 (AAC-P-3) had a specific surface area of 1475.16 m2/g. Similarly, the AAC obtained at a ratio of KOH weight to ASL weight of 2 (AAC-K-2) owned a specific surface area of 2136.56 m2/g. At 0.50 A/g, the specific capacitance of AAC-P-3 and AAC-K-2 was 169.14 F/g and 236.00 F/g, respectively. The average value of the correlation coefficients (AR2) between specific surface area and specific capacitance was highest, i.e., 0.983, followed by the AR2 (0.978) between Vmicro/Vmeso and specific capacitance, the AR2 (0.975) between pore-wall thickness and specific capacitance. Consequently, when using a current density range of 0.50–10.00 A/g and a three-electrode configuration with a 6 M KOH electrolyte, the specific capacitance of AACs depends not only on the specific surface area but also on the Vmicro/Vmeso, pore-wall thickness, and Vmicro.
查看更多>>摘要：? 2021We report mechanistic insights of the bottom-up synthesis of nanodiamonds (NDs) from adamantane derivatives as molecular precursors. Thermal cracking of tetracosane below the decomposition temperature of adamantane, 1-adamantylamine or 2-azaadamantane revealed the initial steps of seeded diamond growth mechanism based on pyrolysis studies.
查看更多>>摘要：? 2021 Elsevier B.V.In this paper, rGO-TiO2-MoO3, an active electrode material is synthesized by simple hydrothermal method and validated for high performance supercapacitor application. The anatase phase of TiO2 and orthorhombic phase of MoO3are distributed on the surface of the graphene sheet, which is confirmed by few characterization techniques, namely, X-ray diffraction technique (XRD), micro-Raman, Field Emission-Scanning Electron Microscope (FE-SEM) and High Resolution–Transmission Electron Microscope (HR-TEM). Further, the chemical composition of the prepared material is elucidated by X-ray Photoelectron Spectroscopy (XPS). The electrochemical performance of the active material is estimated by Cyclic Voltammetry (CV) and Galvanostatic Charge-Discharge (GCD) studies. The specific capacitance value of the prepared composite is calculated to be 472 F/gat current density 1 A/g in 2 M Na2SO4 electrolyte solution. The coulomb efficiency and the capacitance retention of the rGO-TiO2-MoO3 composite are estimated to be 98% and 98.6% at current density 7 A/g, respectively.
查看更多>>摘要：? 2021This work aims to deposit conductive and corrosion-resistant protective coatings for bipolar plates in proton exchange membrane fuel cells. The films' graphitization degree is regulated to obtain excellent conductivity and corrosion-resistance. A series of Cr-doped graphite-like carbon films with different substrate bias voltages and deposition times (600 V 2 h, 900 V, 2 h, 900 V, 3 h; and 1200 V, 2 h) were prepared on 304 stainless steels by plasma enhanced chemical vapour deposition method combined with magnetron sputtering technique. The results showed that an increase of substrate bias voltage increased substrate current density. The substrate current density was the highest when the substrate bias voltage was 1200 V at 400 °C. Subsequently high substrate bias voltage caused ID/IG to increase, indicating that the increase of energy contributes to graphitisation of the films. The particle size of the films decreased with increasing bias voltage, and the cross section showed that the prepared films were homogeneous and distinctive. The interface contact resistance (ICR) of the films at 1.4 MPa decreased with an increase of substrate bias voltage, showing that deeper graphitisation improves the conductivity of the films. The coated 304 stainless steels showed a considerable decrease in self-corrosion current density in comparison to the 304 stainless steel substrate. According to the VDI-3198 indentation test, the adhesion of the films and substrate belongs to the HF1 level. After long-term service, chromium oxides, iron oxides, and defects were formed on the surface, leading to an increase in ICR. The study revealed that the optimum technical parameters were 1200 V and 2 h.
查看更多>>摘要：? 2021Well-sintered polycrystalline diamond composite (PDC) is a hard material obtained from WC–Co substrate and diamond using a high-temperature high-pressure (HPHT) process. PDC has immense potential in aerospace, automobile, oil and gas, and tool manufacturing industries. In this study, PDC was formed by sintering diamond powder (average crystal size = 10 μm) and WC–15 wt% Co substrates at HPHT and the diamond layer thickness is 1.2 mm. The thicknesses of the diamond layer on the PDC cutter were varied, and their effects on the PDC cutter wear were examined. Wear experiments and hardness tests were conducted on samples with varying diamond layer thicknesses. They were characterized using scanning electron microscopy, X-ray diffraction, and Hall effect, and these revealed that (1) hardness of the PDC slightly increased with an increase in the thickness of the diamond layer, and (2) the PDC tool's life could be improved by appropriately increasing the thickness of the diamond layer. The findings of this study provide insights for future studies on designing and optimizing the properties of the PDC.
查看更多>>摘要：? 2022 Elsevier B.V.As a potential metal-free semiconductor photocatalyst, h-BCN has a tunable band gap between h-BN and graphite. However, the chemical uniformity of the distribution of carbon atoms makes it the focus of the great controversy on whether the h-BCN is phase-separated or homogeneous structure. Herein, we investigated the structure and electronic properties of locally phase-separated and homogeneous BCN using Heyd-Scuseria-Ernzerhof (HSE) hybrid functional method. The valuable features such as, the band structure, density of states, effective mass and optical absorption were computed to explore the role of C concentration and distribution in BCN. The results indicated that the proposed models exhibit tunable band gaps from 4.69 eV to 1.50 eV at gradient C concentration from 8.33% to 58.33%. The suitable band edge potentials, smaller effective mass and more efficient carrier transfer channels make the homogeneous BCN with C concentration of 25.00% to 58.33% particularly suitable for water splitting and CO2 reduction.
查看更多>>摘要：? 2021In this research, a highly sensitive voltammetric sensor for hydrogen peroxide (H2O2) detection has been examined using a new hybrid material based polyaniline, dialdyhayed carboxmethyl cellouse and in the presence of ZnO nanoparticles abbreviated as (PANI/D-CMC/ZnO). Various approaches such as cyclic voltammetry (CV), and differential pulse voltammetry were used to investigate the electrocatalytic reduction of H2O2 (DPV). After preparation, (SEM) scanning electron microscopy, (XRD) X-ray diffraction, and (FTIR) Fourier transform infrared techniques were used to characterize and analyze the obtained PANI/D-CMC/ZnO material. Furthermore, as a suitable for determining hydrogen peroxide (H2O2), a high conductivity platform based on PANI/D-CMC/ZnO electrode modified nanocomposite was created. The modified PANI/D-CMC/ZnO, electrode indicated a good linear range and a low detection limit (LOD) of 0.45 M for hydrogen peroxide determination under optimal conditions (pH 5.7). The peak current of differential pulse voltammetry (DPV) method of hydrogen peroxide increased linearly with its concentration. The concentration has been linear from in the ranges of 0.50 to 5 μM and 10 to 50 μM. The sensor was successfully used to test for hydrogen peroxide in real samples like milk.
查看更多>>摘要：? 2022 Elsevier B.V.A simple hydrothermal approach was used to successfully fabricate NiO/G nanocomposites. Since the addition of nickel oxide nanoparticles (NiO) to graphene instead of conducting polymeric materials produces better capacitances and improved capacity retention. Graphene-based inorganic composites have been attracting more and more attention. The as prepared NiO/G nanocomposite is characterized by XRD, TEM, Raman, XPS and nitrogen adsorption/desorption. It is demonstrated that NiO nanoparticles adorn graphene sheets to generate hierarchical nanostructures with rich porosity (33.8 nm) and substantial specific surface area (51 m2 g?1). Electrochemical characterization demonstrate that the mesoporous graphene/NiO can deliver a specific capacitance of 632 F g?1 at a current density of 2 Ag?1 and have a capacitance retention of 99.7% at 2Ag?1 after 6000 continuous charge–discharge cycles. In addition, the ASC constructed from NiO/G shows excellent energy density (30.56 Whkg?1), excellent power density (2800 Wkg?1) and impressive cycle performance (capacitance retention after 6000 cycles is approximately 92.7%). This strategy aids in the fabrication and utilization of hybrid nanocomposite in high-geared reversible supercapacitors.
查看更多>>摘要：? 2022 Elsevier B.V.We developed an experimental setup and procedure to investigate improving the electron emission stability in the long-term operation of carbon nanotube (CNT)-based field emission cathodes (FECs) by using Xe plasma processing aging method. To find the optimum plasma processing conditions, we varied the FEC's exposure time, plasma environment, and bias voltage. Plasma processing increased the gate voltage required for a certain number of electron emissions, whereas we confirmed that the emission stability improved and the aging effect of plasma processing. A bias voltage of approximately ?15 V and a shorter exposure time were most suitable for plasma processing. Because the number of ion and electron collisions and the collision energies cause a moderate change in the CNT structure with minimal damage to the CNTs, we expect that the proposed plasma processing will improve the lifetime of CNT-based FECs, which is essential if they are to be used as electron emission sources for space propulsion systems.
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