Search Results (199)

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

The development of functional materials and the use of nanotechnology are ongoing projects. These fields are closely linked, but there is a need to combine them more actively. Nanoarchitectonics, a concept that comes after nanotechnology, is ready to do this. Among the related research efforts, research into creating functional materials through the formation of thin layers on surfaces, molecular membranes, and multilayer structures of these materials have a lot of implications. Layered structures are especially important as a key part of nanoarchitectonics. The diversity of the components and materials used in layer-by-layer (LbL) assemblies is a notable feature. Examples of LbL assemblies introduced in this review article include quantum dots, nanoparticles, nanocrystals, nanowires, nanotubes, g-C₃N₄, graphene oxide, MXene, nanosheets, zeolites, nanoporous materials, sol–gel materials, layered double hydroxides, metal–organic frameworks, covalent organic frameworks, conducting polymers, dyes, DNAs, polysaccharides, nanocelluloses, peptides, proteins, lipid bilayers, photosystems, viruses, living cells, and tissues. These examples of LbL assembly show how useful and versatile it is. Finally, this review will consider future challenges in layer-by-layer nanoarchitectonics. Full article

While billiard systems of various shapes have been used as paradigmatic model systems in the fields of nonlinear dynamics and quantum chaos, few studies have investigated anisotropic billiards. Motivated by the tremendous advances in using and controlling electronic and optical mesoscopic systems with bilayer graphene (BLG), representing an easily accessible anisotropic material for electrons when trigonal warping is present, we investigate billiards of various anisotropies and geometries using a trajectory-tracing approach founded on the concept of ray–wave correspondence. We find that the presence of anisotropy can change the billiards’ dynamics dramatically from its isotropic counterpart. It may induce chaotic and mixed dynamics in otherwise integrable systems and may stabilize originally unstable trajectories. We characterize the dynamics of anisotropic billiards in real and phase space using Lyapunov exponents and the Poincaré surface of section as phase space representation. Full article

Mesoscopic billiard systems for electrons and light, realized as quantum dots or optical microcavities, have enriched the fields of quantum chaos and nonlinear dynamics not only by enlarging the class of model systems, but also by providing access to their experimental realization. Here, we add yet another system class, two-dimensional billiards with anisotropies. One example is the anisotropic dispersion relation relevant in bilayer graphene known as trigonal warping, and another is the birefringent closed optical disk cavity. We demonstrate that the established concept of ray–wave correspondence also provides useful insight for anisotropic billiard systems. First, we approach the dynamics of the anisotropic disk from the ray-tracing side that takes the anisotropy in momentum space into account, based on the non-spherical index ellipsoid. Second, we use transformation optics to solve the wave problem and find the resonances to be those of the isotropic elliptical cavity. We illustrate ray–wave correspondence and mark differences in the description of optical and electronic anisotropic systems. Full article

Biofouling in membrane filtration systems poses significant operational challenges, leading to decreased permeate flux. The aim of this work was to study the anti-biofilm properties of new nanofiltration membranes produced via layer-by-layer, LBL, assembly by coating a polyvinylidene fluoride (PVDF) support with a polyethylenimine (PEI) and poly(acrylic acid)/graphene oxide (PAA-GO) mixture. The membranes were characterized according to contact angle, scanning electron microscopy (SEM), atomic force microscopy and their Z-potential. Biofilm quantification and characterization were carried out using crystal violet staining and SEM, while bacterial viability was assessed by using colony-forming units. The membrane with three bilayers ((PAA-PEI)₃/PVDF) showed a roughness of 77.78 nm. The incorporation of GO ((GO/PAA-PEI)₃/PVDF) produced a membrane with a smoother surface (roughness of 26.92 nm) and showed salt rejections of 16% and 68% for NaCl and Na₂SO₄, respectively. A significant reduction, ranging from 82.37 to 77.30%, in biofilm formation produced by S. aureus and E. coli were observed on modified membranes. Additionally, the bacterial viability on the modified membranes was markedly reduced (67.42–99.98%). Our results show that the modified membranes exhibited both antibiofilm and antimicrobial capacities, suggesting that these properties mainly depend on the properties of the modifying agents, as the initial adherence on the membrane surface was not totally suppressed, but the proliferation and formation of EPSs were prevented. Full article

In this study, we explore the substrate-mediated control of self-assembly behavior in diboron molecules (C₁₂H₈B₂O₄, B₂Cat₂) using scanning tunneling microscopy (STM). The structural transformation of B₂Cat₂ molecules from one-dimensional (1D) molecular chains to two-dimensional (2D) molecular arrays was achieved by changing the substrate from Au(111) to bilayer graphene (BLG), highlighting the key role of substrate interactions in determining the assembly structure. Notably, the B-B bond in the molecular arrays on BLG is distinctly pronounced, reflecting a more refined molecular resolution with distinct electronic states than that on Au(111). Density functional theory (DFT) calculations confirm the weak interaction between B₂Cat₂ molecules and the BLG substrate, which facilitates the formation of 2D molecular arrays on BLG. This work demonstrates how controlling substrate properties enables the formation of 1D chains and 2D arrays, providing valuable insights for the design of next-generation molecular electronics and catalysis systems. Full article

The Cooper-pair distribution function $D_{cp}(\omega ,T_c)$ of Untwisted-Misaligned Bilayer Graphene (UMBLG) in the presence of an external electric field is calculated and analysed within the framework of first-principle calculations. A bilayer graphene structure is proposed using a structural geometric approximation, enabling the simulation of a structure rotated at a small angle, avoiding a supercell calculation. The $D_{cp}(\omega ,T_c)$ function of UMBLG indicates the presence of the superconducting state for specific structural configurations, which is consistent with the superconductivity in Twisted Bilayer Graphene (TBLG) reported in the literature. The $D_{cp}(\omega ,T_c)$ function of UMBLG suggests that Cooper-pairs are possible in the low-frequency vibration region. Furthermore, the structural geometric approximation allowed the evaluation of the effect of the electric field on the superconducting state of UMBLG and its superconducting critical temperature through the $N_{cp}$ parameter. Full article

Ti matrix composites (TMCs) are promising structural materials that meet the increasing demands for light weight the automobile and aircraft industries. However, the room temperature brittleness in the traditionally homogeneous reinforcement distribution of TMCs limits their application in high-strain-rate impact environments. In the present study, novel bilayer TMCs with hierarchical microstructures were designed by the laminated combination of graphene nanoplatelet (GNPs) reinforced TC4 (Ti-6Al-4V) composites (GNPs/TC4) and a monolithic TC4. Meanwhile, the configuration of the microstructure, impact performance V₅₀, and deformation modes of the bilayered TC4-(GNPs/TC4) plate was investigated. The plates were fabricated via field-assisted sintering technology (FAST). It turned out that the TC4-(GNPs/TC4) plate with a 7.5 mm thickness against a 7.62 mm projectile exhibited greater impact performance (V₅₀~825 m/s) compared to the TC4 and GNPs/TC4 single-layer plates. The plate failure modes were dependent on the microstructure while the failure behaviors seemed to be influenced by the hierarchical configuration. This work provided a new strategy for utilizing TMCs in the field of high-strain-rate impact environments. Full article