First-Principles Study of Lithium and Sodium Atoms Intercalation in Fluorinated Graphite

The structure evolution of fluorinated graphite(CFx) upon the Li/Na intercalation has been studied by firstprinciples calculations. The Li/Na adsorption on single CF layer and intercalated into bulk CF have been calculated. The better cycling performance of Na intercalation into the CF cathode, comparing to that of Li intercalation, is attributed to the different strength and characteristics of the Li-F and Na-F interactions. The interactions between Li and F are stronger and more localized than those between Na and F. The strong and localized Coulomb attraction between Li and F atoms breaks the C—F bonds and pulls the F atoms away, and graphene sheets are formed upon Li intercalation.     

Josephson Current in a Gapped Graphene Superconductor/Barrier/Superconductor Junction: Case of Massive Electrons

The Josephson effect in a gapped graphene-based superconductor/barrier/superconductor junction is studied. The superconductivity in gapped graphene may be achieved by depositing conventional superconductor on the top of the gapped graphene such as graphene grown on SiC substrate. In gapped graphene system, the carriers exhibit massive Dirac fermions. We focus on the effect of pseudo-Dirac-like mass on the supercurrent. In contrast to that in the gapless graphene superconductor/barrier/superconductor junction, we find that the supercurrent exhibits dependency of the Fermi energy. Also, the massive supercurrent anomalously oscillates as a function of the gate potential. This novel behavior is due to the effect of electrons acquiring mass in gapped graphene.     

Defects in Graphene:Generation,Healing,and Their Effects on the Properties of Graphene:A Review

Graphene has attracted immense investigation since its discovery.Lattice imperfections are introduced into graphene unavoidably during graphene growth or processing.These structural defects are known to significantly affect electronic and chemical properties of graphene.A comprehensive understanding of graphene defect is thus of critical importance.Here we review the major progresses made in defectrelated engineering of graphene.Firstly,we give a brief introduction on the types of defects in graphene.Secondly,the generation and healing of the graphene defects are summarized.Then,the effects of defects on the chemical,electronic,magnetic,and mechanical properties of graphene are discussed.Finally,we address the associated challenges and prospects on the future study of defects in graphene and other nanocarbon materials.     

贵金属的结合能、体膨胀系数的研究

本文在郑伟涛等提出的贵金属位能函数理论基础上,从体系的自由能出发,并结合Midha状态方程,对贵金属Cu、Ag、Au多晶体的结合能、体膨胀系数进行了理论研究和计算,理论计算得到的结果与实验相当符合,其误差均在9％以内。     

Effect of Rough-Surfaced Diamond Content on the Microstructure,Tribological Behavior,and Corrosion Resistance of Ni/Diamond Composite Coatings

This study fabricates certain Ni/diamond composite coatings using a coelectrodeposition method and then evaluates the effect of diamond content on the morphology, phase structure, microhardness, wear, and corrosion resistance of such coatings, while exploring their tribological and anticorrosion mechanisms. It is demonstrated that the addition of diamond can change the preferred orientation of Ni from (200) to (111), and its texture coefficient value can be boosted from 23.3% to 64.4% with the increase of diamond content. In the experiment, at a diamond content of 3 g L⁻¹, the deposited diamond particles are more and evenly dispersed across the composite, with the microhardness of nickel-based coatings reaching an optimum value of 613 HV. In addition, the coefficient of friction is reduced to a minimum value of 0.627, while the wear rate is kept at only 1.79 × 10⁻⁵ mm³ Nm⁻¹, indicating a high wear resistance. Electrochemical test results demonstrate that the Ni/diamond composite coatings produced at 3 g L⁻¹ create the maximum charge transfer resistance (5429.3 Ω cm²) and the minimum corrosion current density (2.19 μA cm⁻²), features that can deliver the best corrosion resistance.     

Laser-Induced Graphene on a Polyimide Film: Observation of the Photon Drag Effect

Technical Physics Letters - Film structures of porous graphene have been produced by irradiating a polyimide film with focused radiation of a continuous CO2 laser. The generation of nanosecond...     

Effect of Intrinsic Defects on Electronic and Magnetic Properties in Tm-Doped GaN: First-Principles Calculations

Based on the density functional theory, we investigate the electronic and magnetic properties of various types of defect complexes formed by dopant Tm and Ga vacancies, N vacancies, or O interstitial in Tm-doped GaN. Formation energies are first calculated for all defect complexes to assess their stability. The single Tm dopant is found to introduce the local magnetic moment of about 2 μ_B/Tm in GaN. However, in the case of defect complexes, the magnetic moments of Tm can be suppressed by the existence of Ga vacancies around it, while the presence of N vacancies or O interstitial does not influence the magnetic moment of Tm. In addition, each Ga vacancy in the neutral charge state induces the local magnetic moment of about 2.1 μ_B and one octahedral O interstitial can lead to the local moment of about 1.6 μ_B.     

The Polar Optical Phonon Confinement Effect on the Binding Energy of a Hydrogenic Impurity in Quantum Wires Under Applied Electric and Magnetic Fields

The impurity bound polaron in a cylindrical quantum wire with a parabolic confining potential was studied by the variational approach. The polaron effects on the ground-state binding energy in electric and magnetic fields are investigated by means of Pekar-Landau variation technique by taking into account optical phonon confinement within the wire region and localization at its boundaries. It is shown that not only electron confinement, but also polar optical phonon confinement leads to a considerable enhancement of the polaron effect. The results for the binding energy as well as polaronic correction are obtained as a function of the applied fields.     

Low-Loss Organic Hyperbolic Materials in the Visible Spectral Range: A Joint Experimental and First-Principles Study

Hyperbolic media strengthen numerous attractive applications in optics such as super-resolution imaging, enhanced spontaneous emission, and nanoscale waveguiding. Natural hyperbolic materials exist at visible frequencies; however, implementations of these materials suffer substantial compromises resulting from the high loss in the currently available candidates. Here, the first experimental and theoretical investigation of regioregular poly(3-alkylthiophenes) (rr-P3ATs), a naturally low-loss organic hyperbolic material (OHM) in the visible frequency range, is shown. These hyperbolic properties arise from a highly ordered structure of layered electron-rich conjugated thiophene ring backbones separated by insulating alkyl side chains. The optical and electronic properties of the rr-P3AT can be tuned by controlling the degree of crystallinity and alkyl side chain length. First-principles calculations support the experimental observations, which result from the rr-P3AT's structural and optical anisotropy. Conveniently, rr-P3AT-based OHMs are facile to fabricate, flexible, and biocompatible, which may lead to tremendous new opportunities in a wide range of applications.     

First-Principles Study on the Structural, Electronic, Magnetic and?Optical Properties of UFe2 and PuFe2 Compounds

The structural, electronic and magnetic properties of UFe₂ and PuFe₂ have been calculated in the presence and absence of spin?Corbit interaction using density-functional theory by the WIEN2K package. The total energy calculations indicate that at zero pressure the ferromagnetic phase is the most stable phase. Both the energy band calculation and the density of states curves indicate that spin?Corbit interaction has a considerable effect and cannot be ignored. The magnetic moment calculation within local density approximation (LDA) and generalized gradient approximation (GGA) approaches show that LDA and GGA are not good approaches for this compound. To improve the result, we have calculated the magnetic moment using the GGA+U and LDA+U approaches. The calculation of the magnetic moment as a function of pressure has been investigated.     

Powder,Paper and Foam of Few‐Layer Graphene Prepared in High Yield by Electrochemical Intercalation Exfoliation of Expanded Graphite

A facile and high‐yield approach to the preparation of few‐layer graphene (FLG) by electrochemical intercalation exfoliation (EIE) of expanded graphite in sulfuric acid electrolyte is reported. Stage‐1 H₂SO₄‐graphite intercalation compound is used as a key intermediate in EIE to realize the efficient exfoliation. The yield of the FLG sheets (<7 layers) with large lateral sizes (tens of microns) is more than 75% relative to the total amount of starting expanded graphite. A low degree of oxygen functionalization existing in the prepared FLG flakes enables them to disperse effectively, which contributes to the film‐forming characteristics of the FLG flakes. These electrochemically exfoliated FLG flakes are integrated into several kinds of macroscopic graphene structures. Flexible and freestanding graphene papers made of the FLG flakes retain excellent conductivity (≈24 500 S m^?1). Three‐dimensional (3D) graphene foams with light weight are fabricated from the FLG flakes by the use of Ni foams as self‐sacrifice templates. Furthermore, 3D graphene/Ni foams without any binders, which are used as supercapacitor electrodes in aqueous electrolyte, provide the specific capacitance of 113.2 F g^?1 at a current density of 0.5 A g^?1, retaining 90% capacitance after 1000 cycles.     

Effect of Mechanical Activation on the Packed-Bed, High-Temperature Behavior of Hematite and Graphite Mixture in Air

The present study reports the effect of mechanical activation on the reaction behavior of the Fe₂O₃/C powder mixture at high temperature under air atmosphere. Hematite and graphite were ground up to 150 hours using a ball mill with an alumina vial. The mixture was heated isothermally in the temperature range of 1173-1373°K using an electric furnace. The degree of reaction was determined by weight-loss measurement using a high accurate balance. It was found that low-energy mechanical milling at room temperature increases (the degree and) the rate of reaction at constant temperature. However, this effect was more significant at temperatures above 1273°K. At temperatures below 1273°K, the main reaction is oxidation of graphite and the total reaction process is controlled by diffusion of gases, whereas above 1273°K both chemical reaction (gasification reaction) and diffusion were controlling mechanisms. However, increasing milling time would shift the controlling mechanism from diffusion toward pure chemical reaction above 1273°K. It was observed that the mechanical milling might cause the mechanism to be changed at lower temperatures. This could be attributed to the increase of the rate of reaction due to mechanical milling. It was also observed that milling of powder mixture would decrease the difference in the average reaction rates at various degrees of reaction.     

Atmosphere-Induced Effect in Microhardness, Dislocation Mobility and Plasticity of C60 and Graphite Crystals

Formation of hard, brittle and toluene-insoluble near-surface layer (∼0.3 μm) of C₆₀ crystals under atmospheric exposure was observed. Similar atmosphere-induced effect was found for graphite crystals and might also be expected for other molecular solids. Data on ageing kinetics of C₆₀ and graphite crystals are presented. Variation of hardness with indentation depth can be described by the microhardness model for bilayer medium with different mechanical properties. Specific feature of C₆₀ and graphite crystals is that no size effect appears in the intrinsic microhardness and dislocation mobility characteristics in the indentation depth range of 0.6-4μm.     

Strain,Bubbles, Dirt,and Folds: A Study of Graphene Polymer‐Assisted Transfer

For many applications, in particular in electronics, where chemical vapor deposited (CVD) graphene is used, it needs to be transferred from the growth substrate to the device substrate, generally employing a polymer film as a support layer. This process step is crucial for the overall integrity and electronic performance of the graphene. In this work we will investigate the effects of the transfer using various polymers with atomic force, Raman spectroscopy and X‐ray photoelectron spectroscopy combined with field dependent transport measurements to build up a complete picture regarding the morphology, structural integrity and electrical performance of CVD graphene. Further, we introduce nitrocellulose based polymer alternatives to the most commonly used poly(methyl methacrylate) resist, outperforming the latter in most respects.