Search Results (206)

Bilayer graphene has been a subject of intense study in recent years. Its most common structure is AB (Bernal) stacking, where one layer is shifted relative to the other, leading to distinct electronic behaviors compared to the less stable AA stacking or the fascinating twisted configurations. We extend a structural phase field crystal method to include an external potential based on the generalized stacking-fault energy that accounts for the effect from a bottom layer of graphene. Both of the favored stacking variants AB and BA are found with randomly generated initial phase fields. Using the width of the boundaries between different stacking variants as a function of the interactions between the two layers, we quantify the exact strength of the external potential by comparing the phase field crystal simulations with the results from atomistic simulation. Finally, we simulate a circular grain of one stacking phase enclosed by the other and find that, depending on the initial phase field, the center domain may shrink to form a uniform stacking phase, or may evolve to a relaxed state of a hexagon region or a triangular region that at each vertex the graphene structure is defected. Full article

Supercapacitors are limited by electrolyte cation desolvation, which directly impacts ion storage efficiency and capacitance. This study uses density functional tight-binding (DFTB+) first-principles calculations to investigate the desolvation of bispyrrolidinium cation complexes ([SBP(AN)]⁺, acetonitrile as solvent) in pristine (FP) and oxygen-functionalized (OFP: hydroxyl-HFP, carbonyl-CFP, aldehyde-AFP) bilayer graphene flat pores with AA/AB stacking. Critical desolvation diameters were determined: 5.0 Å (FP), 5.2 Å (HFP), 5.0 Å (AFP), and 4.6 Å (CFP). Hydroxyl functionalization expanded the critical diameter, reduced SBP⁺ intercalation energy, and increased relative capacitance by 1.02~1.03 times; carbonyl groups had the opposite effect, while aldehyde groups showed no significant impact. Density of States (DOS) analysis revealed enhanced conductivity for HFP and AFP after SBP⁺ embedding, but reduced conductivity for CFP. Charge density difference and Bader charge analysis confirmed electron transfer primarily between SBP⁺ (electron donor) and oxygen atoms in functional groups (electron acceptor), with SBP⁺ interacting mainly with functional groups rather than the carbon basal plane. This work provides theoretical guidance for optimizing graphene-based supercapacitor electrodes via pore structure and surface functionalization. Full article

Direct growth of high-quality, Bernal-stacked bilayer graphene (BLG) on dielectric substrates is crucial for electronic and optoelectronic devices, yet it remains hindered by poor film quality, uncontrollable thickness, and high-density grain boundaries. In this work, a facile, catalyst-assisted method to grow high-quality, single-crystalline BLG directly on dielectric substrates (SiO₂/Si, sapphire, and quartz) was demonstrated. A single-crystal monolayer graphene template was first employed as a seed layer to facilitate the homoepitaxial synthesis of single-crystalline BLG directly on insulating substrates. Nanostructure Cu powders were used as the remote catalysis to provide long-lasting catalytic activity during the graphene growth. Transmission electron microscopy confirms the single-crystalline nature of the resulting BLG domains, which validates the superiority of the homoepitaxial growth technique. Raman spectroscopy and electrical measurement results indicate that the quality of the as-grown BLG is comparable to that on metal substrate surfaces. Field-effect transistors fabricated directly on the as-grown BLG/SiO₂/Si showed a room temperature carrier mobility as high as 2297 ± 3 cm² V⁻¹ s⁻¹, which is comparable to BLG grown on Cu and much higher than that reported on in-sulators. Full article

Recent theoretical studies have shown that gapped Dirac materials (such as gapped monolayer graphene) optically pumped with circularly polarized light can host edge-localized plasmon modes with nonreciprocal dispersions driven by valley population imbalance. Here, we extend this framework to Bernal-stacked bilayer graphene. Using the Wiener–Hopf method, we compute the exact edge plasmon dispersion, confinement length, and electric potential. Our results show that bilayer graphene exhibits stronger nonreciprocity in edge plasmons, requiring approximately one order of magnitude lower pump amplitude to achieve splitting compared with monolayer Dirac systems. Furthermore, the gate-tunable energy gap of bilayer graphene provides an additional degree of control, positioning optically pumped bilayer graphene as a versatile platform for magnet-free nonreciprocal plasmonics. Full article

Motivated by the seminal discoveries in graphene, the exploration of novel physical phenomena in alternative two-dimensional (2D) materials has attracted tremendous attention. In this work, through theoretical investigation using first-principles calculations, we reveal that Mo-intercalated ${\mathrm{CrI}}_3$ bilayer exhibits ferromagnetic semiconductor behavior with a small easy-plane magnetocrystalline anisotropy energy (MAE) of 0.618 meV/Cr(Mo) between (100) and (001) magnetizations. The spin–orbit coupling (SOC) opens a narrow band gap at the Fermi level for both magnetization orientations with nonzero Chern number for realizing the quantum anomalous Hall effect (QAHE) in the former and with trivial topology in the latter. The small MAE implies the efficient experimental manipulation of magnetization between distinct topologies through an external magnetic field. Our findings provide compelling evidence that the QAHE in this system originates from the quantum spin Hall effect (QSHE), driven by intrinsic magnetism under broken time-reversal symmetry. These unique properties position Mo-intercalated ${\mathrm{CrI}}_3$ as a promising candidate for tunable spintronic applications. Full article

As the scaling of silicon-based CMOS technology approaches its physical limits, two-dimensional (2D) materials have emerged as promising alternatives for future electronic devices. Among them, MoS₂ is a leading candidate due to its fascinating semiconducting nature and compatibility with CMOS processes. However, high contact resistance at the metal–MoS₂ interface remains a major bottleneck, limiting device performance. In this study, we report the fabrication and characterization of graphene–MoS₂ (Gr–MoS₂) lateral heterostructure FETs, where monolayer graphene, synthesized by inductively coupled plasma chemical vapor deposition (ICP-CVD), is directly used as the source and drain. Bilayer MoS₂ is selectively grown along graphene edges via edge-guided CVD, forming a chemically bonded in-plane junction without transfer steps. Electrical measurements reveal that the Gr–MoS₂ FETs exhibit a threefold increase in average field-effect mobility (3.9 vs. 1.1 cm² V⁻¹ s⁻¹) compared to conventional MoS₂ FETs. Y-function analysis shows that the contact resistance is significantly reduced from 85.8 kΩ to 20.5 kΩ at V_G = 40 V. These improvements are attributed to the replacement of the conventional metal–MoS₂ contact with a graphene–metal contact. Our results demonstrate that lateral heterostructure engineering with graphene provides an effective and scalable strategy for high-performance 2D electronics. Full article

In this study, the nonlinearity characteristics of bilayer graphene field-effect transistors (Bi-GFETs) are analyzed by using a small-signal equivalent circuit. The static nonlinearity is determined by applying mathematical operation on the drain current equation of Bi-GFETs. Furthermore, the closed expressions for the second- and third-order harmonic distortion (HD) and the intermodulation (IM) distortion of the second- and third-order for Bi-GFETs are analyzed graphically. Dynamic nonlinearity is studied and illustrated in the results by examining the input and output characteristics; i.e., the drain current versus the negative drain to the source voltage and the transfer characteristic curve at various gate voltages controlled by both the top gate as well as the back gate. The characteristic behavior of the gate voltage in Bi-GFETs at short channel lengths is observed and compared; that is, the characteristic curves exhibits strong nonlinearity, with a low power point with some kinks at high gate biasing and a constant linear region at low gate biasing. The quantitative values of the second-order harmonic distortion (HD) and intermodulation distortion (IM) of the proposed analytical model are −40 dB and −45 dB. Quantitative and qualitative outcomes of the characteristics of Bi-GFETs are compared with existing experimental data, which is available in the literature. Full article

We investigate the thermal conductivity of graphene Moiré superlattices formed by twisting bilayer graphene (TBG) at small angles, employing approach-to-equilibrium molecular dynamics and lattice dynamics calculations based on the Boltzmann Transport Equation. Our simulations reveal a non-monotonic dependence of the thermal conductivity on the twisting angle, with a local minimum near the first magic angle ($\theta \sim$1.1°). This behavior is attributed to the evolution of local stacking configurations—AA, AB, and saddle-point (SP)—across the Moiré superlattice, which strongly affect phonon transport. A detailed analysis of phonon mean free paths (MFP) and mode-resolved thermal conductivity shows that AA stacking suppresses thermal transport, while AB and SP stackings exhibit enhanced conductivity owing to more efficient low-frequency phonon transport. Furthermore, we establish a direct correlation between the thermal conductivity of twisted structures and the relative abundance of stacking domains within the Moiré supercell. Our results demonstrate that even very small changes in twisting angle (<2°) can lead to thermal conductivity variations of over 30%, emphasizing the high tunability of thermal transport in TBG. Full article

In this paper, we conduct a detailed in silico study of the role of topological features in the electronic transport properties of all-carbon films. To create all-carbon film supercells, we used AA- and AB-stacked bilayer graphene, as well as (5,5), (6,0), (16,0), (12,6), and (8,4) single-walled carbon nanotubes (SWCNTs). For the first time, the simultaneous influence of several topological features on the quantum transport of electrons in graphene–nanotube films are considered. Topological features are understood as the topological type of nanotubes (chiral or achiral), the stacking order in bilayer graphene (AA or AB), and the mutual orientation of bilayer graphene and nanotubes. A characteristic feature of the studied all-carbon films is the presence of electrical conductivity anisotropy. Moreover, depending on the topological features of all-carbon films, the values of electrical resistance can differ by tens of times in different directions of electron transport. The patterns of formation of the profile of the electron transmission function of the studied structural configurations of all-carbon film are established. It is found that the mutual orientation of bilayer graphene and nanotubes plays an important role in the electronic transport properties of all-carbon films. The obtained results make a significant contribution to the understanding of the mechanisms controlling the electrical conductivity properties of all-carbon films at the atomic level. Full article

In this work, silicon oxide based coatings with embedded graphene nanoplatelets (content ranging from 1.8 wt.% to 7.2 wt.%) have been developed following the sol-gel route, using AISI430 stainless steel as substrate and dip and roll-to-roll as coating techniques. The tribological and corrosion behaviour of these coatings have been evaluated and compared to bare steel. Concerning tribological behaviour, the coefficient of friction and wear print were significantly reduced with increasing the graphene nanoplatelets content. Regarding corrosion, all coatings showed improved corrosion behaviour compared to bare steel. However, higher concentration of nanoplatelets revealed a negative effect on the corrosion resistance, probably due to aggregation. Taking into account these two counteracting effects, as final part of this work, a bilayer coating with different graphene content has been proposed and fabricated. A top layer, with high graphene nanoplatelets concentration has allowed enhanced tribological properties whereas bottom layer, with no graphene nanoplatelets assures corrosion inhibition under harsh environments. Full article

A novel bi-layered scaffold, obtained via 3D printing and electrospinning, was designed to improve osteochondral region reconstruction. The upper electrospun membrane will act as a barrier against unwanted tissue infiltration, while the lower 3D-printed layer will provide a porous structure for tissue ingrowth. Graphene was integrated into the scaffold for its antibacterial properties, and the drug Osteogenon^® (OST) was added to promote bone tissue regeneration. The composite scaffolds were subjected to comprehensive physical, thermal, and mechanical evaluations. Additionally, their biological functionality was assessed by means of NHAC-kn cells. The 0.5% graphene addition to PCL significantly increased strain at break, enhancing the material ductility. GNP also acted as an effective nucleating agent, raising crystallization temperatures and supporting mineralization. The high surface area of graphene facilitated rapid apatite formation by attracting calcium and phosphate ions. This was confirmed by FTIR, µCT and SEM analyses, which highlighted the positive impact of graphene on mineral deposition. The synergistic interaction between graphene nanoplatelets and Osteogenon^® created a bioactive environment that enhanced cell adhesion and proliferation, and promoted superior apatite formation. These findings highlight the scaffold’s potential as a promising biomaterial for osteochondral repair and regenerative medicine. Full article

An electric field applied to the Bernal-stacked bilayer graphene opens an energy gap; its reversal in some regions creates domain walls and leads to the appearance of one-dimensional chiral gapless states localized at the walls. Here, we investigate the energy structure of bilayer graphene with superlattice potential defined by an external electric field. The calculations are performed within an atomistic π-electron tight-binding approximation. We study one-dimensional and two-dimensional superlattices formed by arrays of electric-field walls in the zigzag and armchair directions and investigate different field polarizations. Chiral gapless states discretize due to the superlattice potential and transform into minibands in the energy gap. As the main result, we show that the minibands can cross at the Fermi level for some field polarizations. This leads to a new kind of two-dimensional gapless states of topological character that form Dirac-like cones at the crossing points. This also has application potential: changing the field polarization can close the energy gap and change the character of the superlattice from semiconducting to metallic. Full article

Bilayer graphene exhibits intriguing physical and mechanical properties that are suitable for advanced electronic device applications. By introducing a new degree of freedom through interlayer twisting, exotic phenomena such as superconductivity can arise. However, in practical experiments, manual manipulation is often required to fabricate such a configuration and therefore, scaled production of magic angle bilayer graphene is challenging. In this work, we propose utilizing the grain boundaries and accompanying localized out-of-plane deformation in graphene to facilitate twisted bi-layer graphene formation. Based on molecular dynamics simulations, the structure folding process along the boundary line is examined where a lower energetic cost is found. Once stabilized, the folded bilayer structure shows twist angles that differ visibly from the conventional AA or AB stacking modes and can achieve twist angles close to the 1.1° magic angle. This observation suggests a potential novel strategy for synthesizing stable twisted bilayer graphene or other two dimensional van der Waals heterostructures with greater efficiency. Full article

Hexagonal BCN (h-BCN), an isoelectronic counterpart to graphene, exhibits chirality and offers the distinct advantage of optical activity in the vacuum ultraviolet (VUV) region, characterized by significantly higher wavelengths compared to graphene nanoflakes. h-BCN possesses a wide bandgap and demonstrates desirable semiconducting properties. In this study, we employ Density Functional Theory (DFT) calculations to investigate the proximity effects of adsorbed h-BCN flakes on two-dimensional (2D) substrates. The chosen substrates encompass monolayers of 3D transition metals and WSe₂, as well as a bilayer consisting of WSe₂/Ni. Notably, the hydrogen-terminated h-BCN nanoflakes retain their planar configuration following adsorption. We observe a strong interaction between h-BCN and fcc-based monolayers such as Ni(111), resulting in the closure of the optical bandgap, while the adsorption energy on WSe₂ is significantly weaker, preserving an approximate 1.1 eV bandgap. Furthermore, we demonstrate the magnetism induced by the proximity of adsorbed chiral h-BCN molecules, and the chiral-induced spin selectivity within the proposed systems. Full article

We theoretically investigate the comprehensive modulation effect of interlayer twisting and external electric field to the two-photon absorption (TPA) in twisted graphene/hexagonal boron nitride (tG/hBN) heterojunction with small twist angles (2° < θ < 10°) starting from an effective continuum model. It is found that the TPA of tG/hBN is extended to the visible light band from infrared light band of that in twisted bilayer graphene (tBLG) due to the increase in energy band gap caused by twisting and the potential energy of the boron nitride atomic layer. And the TPA coefficient is enhanced several times via an external electric field, which increases the density of states, leading to an increase transition probability for two-photon absorption. Full article