Tuning the electronic properties of hydrogen passivated C3N nanoribbons through van der Waals stacking

The two-dimensional (2D) C₃N has emerged as a material with promising applications in high performance device owing to its intrinsic bandgap and tunable electronic properties. Although there are several reports about the bandgap tuning of C₃N via stacking or forming nanoribbon, bandgap modulation of bilayer C₃N nanoribbons (C₃NNRs) with various edge structures is still far from well understood. Here, based on extensive first-principles calculations, we demonstrated the effective bandgap engineering of C₃N by cutting it into hydrogen passivated C₃NNRs and stacking them into bilayer heterostructures. It was found that armchair (AC) C₃NNRs with three types of edge structures are all semiconductors, while only zigzag (ZZ) C₃NNRs with edges composed of both C and N atoms (ZZCN/ CN) are semiconductors. The bandgaps of all semiconducting C₃NNRs are larger than that of C₃N nanosheet. More interestingly, AC-C₃NNRs with CN/CN edges (AC-CN/CN) possess direct bandgap while ZZ-CN/CN have indirect bandgap. Compared with the monolayer C₃NNR, the bandgaps of bilayer C₃NNRs can be greatly modulated via different stacking orders and edge structures, varying from 0.43 eV for ZZ-CN/CN with AB′-stacking to 0.04 eV for AC-CN/CN with AA-stacking. Particularly, transition from direct to indirect bandgap was observed in the bilayer AC-CN/CN heterostructure with AA′-stacking, and the indirect-to-direct transition was found in the bilayer ZZ-CN/CN with ABstacking. This work provides insights into the effective bandgap engineering of C₃N and offers a new opportunity for its applications in nano-electronics and optoelectronic devices.     

Light-induced interaction between graphene and magnetic film in a cavity

An interaction mechanism between graphene and magnetic film in cavity is presented in this work. The pseudospin in graphene can indirectly interact with the spins in magnetic film by the media of a circularly polarized photons under the conditions of high temperature and intense laser field. The interaction energy as well as the average values of pseudospin and spin components are calculated according to a generating functional approach. This interaction mechanism provides a scheme of detecting the pseudospin polarization effect.     

基于石墨烯/石墨烯卷轴复合薄膜高灵敏度柔性压力传感器

一维导电材料例如纳米线，大量应用于柔性压力传感器中. 但是一维材料和基底之间接触时相互作用力较弱，使得传感器灵敏度、响应时间、和循环寿命等性能指标有待进一步提高. 针对这些问题，设计了石墨烯/石墨烯卷轴多分子层复合薄膜作为传感器导电层. 石墨烯卷轴具有一维结构，而石墨烯的二维结构可以牢固地固定卷轴，以确保高导电性复合薄膜与基底之间的粘附性，同时整体结构的导电通道得到了增加. 由于一维和二维结构的协同效应，实现了应变灵敏度系数3.5 kPa^-1、 响应时间小于50 ms、能够稳定工作1000次以上的压阻传感器.     

Fabrication of high-performance nickel/graphene oxide composite coatings using ultrasonic-assisted electrodeposition

Ultrasonic-assisted electrodeposition was used to fabricate the nickel/graphene oxide composite coatings with high hardness, low friction coefficient, and high wear resistance. In the present study, the effects of ultrasonic power and concentration of graphene oxide on the mechanical and tribological properties of the electrodeposited nickel/graphene oxide composite coatings were systematically studied. X-ray diffraction (XRD) analyses showed that the crystallite size of the nickel decreased with an increase of ultrasonic power (0–50 W, 40 KHz, square wave) and concentration of graphene oxide (0.1–0.4 g/L). Morphologies of the surface and cross-section of the composite coatings observed by Scanning Electron Microscopy (SEM) confirmed the existence of graphene oxide particles in the nickel matrix. The results from microhardness measurement demonstrated that the hardness was increased by 1.8 times using 50 W ultrasonic-assisted electrodeposition with the fixed concentration of graphene oxide (0.1 g/L), compared to the pure nickel coating. The hardness was increased by 4.4 times for the 0.4 g/L graphene oxide with the optimized ultrasonic power of 50 W in comparison to the pure nickel coating. Meanwhile, the friction coefficient decreased gradually with an increase in ultrasonic power and concentration of graphene oxide, respectively, where the effect of the concentration of graphene oxide played a more important role.     

Graphene to graphite; a layer by layer experimental measurements and density function theory calculations of electric conductivity

ABSTRACT

We measured the electric conductivity of large (25?×?50?mm) graphene films as a function of number of layers in the range of 1–20 layers. We also calculated the energy gap for such samples using density function theory. Our results showed a conductivity slightly above that of ITO for monolayer graphene and an exponential decrease as the number of graphene layers increased. Both experimental and simulation results showed a convergence of graphene into graphite at as little as 18–20 layers.     

The effect of two ferromagnetic metal stripes on valley polarization of electrons in a graphene

As the key factor for designing the valleytronic devices is to well understand the valley-dependent transport mechanism in graphene, we investigate, in this work, the effect of two ferromagnetic (FM) metal stripes on the valley polarization in a graphene nanostructure with a strain. The nearly 100% valley polarization is observed at certain energy windows and it can be easily controlled through changing the width and the position of the FM stripe as well as the strength of the magnetic field induced by the FM stripe. Our interesting findings reveal the valley-dependent transport mechanism of electrons and promote the realization of the new types of valleytronic devices modulated by the FM stripe and the strain.     

Tunable magnetism through edge functionalization in zigzag green phosphorene nanoribbons

Ab initio density-functional theory calculations with spin polarization are performed to explore magnetic properties in zigzag green phosphorene nanoribbons (ZGPNRs) with no passivation or edge-saturated by H, OH and O chemical species. It is found that antiferromagnetic order at intra-edges is the most energetically favorable for the pristine and oxygen passivated ribbons, while H- or OH-saturated ZGPNRs show nonmagnetic order. It indicates that edge states arising from the unsaturated bonds are vital for the formation of the magnetic moment in the ZGPNRs. The magnitude of the edge magnetism in the pristine and O-saturated ZGPNRs is comparable to that in zigzag black phosphorene nanoribbons. Electronic band structures, spin densities and spd-orbital projected density of states for the studied pristine and O-passivated ZGPNRs are further analyzed to study their electronic properties. The magnetic and electronic properties discovered in the ZGPNRs may suggest potential applications in future spintronics and electronics.     

Computational study of the formation of aluminum-graphene nanocrystallites

The molecular dynamics method is used to study the formation of the Al/graphene nanocomposite in the structural grains of different size under the action of internal stresses. The behavior of graphene sheets inside an individual structural grain as well as in the process of two Al grains containing graphene are joined is investigated. The motion of graphene films, starting from the middle of the aluminum matrix, ends with their location at the crystallite boundaries. Graphene moves in the Al matrix along closely packed planes. In this case, graphene sheets acquire curvature. An intergrowth of graphene sheets is also observed. A contact between two Al-C nanocrystallites through a graphene interlayer is created. The self-diffusion coefficients of atoms and the partial potential energies increased with decreasing nanocrystallite size. The angular distribution of the nearest geometric neighbors and the distribution of distances to the nearest neighbors are determined using the construction of Voronoi polyhedra.     

Mechanisms of graphene influence on cell differentiation

The graphene family of nanomaterials (GFN) have a common carbon lattice base structure but represent a diverse range of materials with distinct chemical and physical characteristics. These characteristics are determined by the fabrication method and impart each material with specific chemical properties which govern interaction with cells and biomolecules, and physical properties that give unique nanotopography, stiffness, and electrical properties. Remarkably, members of the GFN have been shown to promote tissue formation and influence cell differentiation in a variety of tissue types, including neural, bone, and cardiac muscle, making them of high interest to the biomedical field. The diverse range of materials and experimental setups in the literature make uncovering the mechanism of action challenging. Nevertheless, it is becoming clear that the ability of GFN to form non-covalent interactions (π-π, hydrogen bonding, electrostatic) with biomolecules may increase their bioavailability via sequestering/concentration/conformation protection to induce cell differentiation. In addition to the chemical properties, the stimulation of mechanosensing pathways, cytoskeletal rearrangement, and enhanced electrical activity of cells on GFN substrates demonstrates the importance of the physical properties in directing cell differentiation. The understanding of the mechanism behind the ability of GFN to enhance cell differentiation will allow the design and selection of materials with the desired properties for tissue repair and regeneration.     

In-situ growth of hybrid NaTi8O13/NaTiO2 nanoribbons on layered MXene Ti3C2 as a competitive anode for high-performance sodium-ion batteries

In the work, we successfully explore a two-step hydrothermal method for scalable synthesis of the hybrid sodium titanate (NaTi₈O₁₃/NaTiO₂) nanoribbons well in-situ formed on the multi-layered MXene Ti₃C₂ (designed as NTO/Ti₃C₂). Benefiting from the inherent structural and componential superiorities, the resulted NTO/Ti₃C₂ composite exhibits long-duration cycling stability and superior rate behaviors when evaluated as a hybrid anode for advanced SIBs, which delivers a reversible and stable capacity of ∼82 mAh/g even after 1900 cycles at 2000 mA/g for SIBs.