Interaction Of Graphene Research Articles

Dependence of high-harmonic generation in twisted bilayer graphene on laser pulse ellipticity

The ellipticity of a laser pulse offers a control knob to tune the efficiency and polarization of emitted higher-order harmonics. In this paper, we systematically investigate the ellipticity dependence of high-harmonic generation in various bilayer graphene systems, such as AA-stacked, AB-stacked, and twisted bilayer graphene. We demonstrate how the underlying symmetries and electronic band structures of different bilayer systems distinctly contribute to the characteristics of ellipticity dependence, such as elliptical enhancement and elliptical dichroism. Additionally, we showcase a unique applicability of high-harmonic spectroscopy as a tool for identifying stacking faults in bilayer graphene systems. Our findings offer valuable insights into the nonlinear optical interactions of twisted bilayer graphene with different twist angles. Published by the American Physical Society 2024

Spin-orbit coupling in monolayer graphene doped by Cd and Te atoms

Using the density functional theory, the electronic band structure of pure and doped by cadmium and tellurium atoms monolayer graphene has been studied. It is shown that doping by cadmium and tellurium leads to the appearance of an energy gap, as well as an enhancement of spin-orbit interaction in graphene. The maximum value of spin-orbit splitting in doped graphene obtained from energy spectra is 0.23 eV. The value of spin-orbit splitting for different doped atoms varies in the range of 0.08–0.23 eV. It should also be noted that the enhancement of spin-orbit interaction in graphene depends on the concentration of atoms doped into the lattice. At low concentrations, the energy states splitting caused by spin-orbit interaction is not observed.

Enhanced interfacial interaction of graphene nanoplatelets/cellulose nanofiber matrix driven by pyranine-based dispersant for efficient thermal managing materials

With the development of high-density electronics, polymer-based thermal conductive composites with excellent thermal and mechanical performance are receiving great attention. For the development of polymer-based thermal conductive composites with superior properties, it is essential to reduce the agglomeration of fillers and enhance the interfacial interactions between thermal conductive fillers and the polymer matrix. Among the several thermal conductive materials, graphene nanoplatelets (GNPs) and cellulose nanofiber (CNFs) are attracting attention. However, poor interfacial interaction between GNP and CNF leads to interfacial separation, which in turn, deteriorates its properties. Herein, we synthesized a pyranine-functionalized polyether dispersant (PyPE), which can significantly improve the interfacial interactions between GNPs and CNFs. The effect of PyPE on the dispersion behavior of GNPs and the thermomechanical properties of GNP-CNF composite were monitored. Furthermore, we also performed molecular dynamics (MD) simulations to investigate the impact of applying PyPE dispersant on the interfacial interactions between the GNPs and CNF matrix. The application of PyPE significantly enhanced the dispersibility of GNPs within the CNF matrix, resulting in a 15.5 % increase in-plane thermal diffusivity and a 24.5 % enhancement in tensile strength of the composite, demonstrating their potential applications in high power density electrical equipment and electronic devices.

Enhancing modulation performance by design of hybrid plasmonic optical modulator integrating multi-layer graphene and TiO2 on silicon waveguides

A novel way to enhance modulation performance is through the design of a hybrid plasmonic optical modulator that integrates multi-layer graphene and TiO2 on silicon waveguides. In this article, a design is presented of a proposed modulator based on the use of the two-dimensional finite difference eigenmode solver, the three-dimensional eigenmode expansion solver, and the CHARGE solver. Leveraging inherent graphene properties and utilizing the subwavelength confinement capabilities of hybrid plasmonic waveguides (HPWs), we achieved a modulator design that is both compact and highly efficient. The electrical bandwidth f 3dB is at 460.42 GHz and it reduces energy consumption to 12.17 fJ/bit with a modulator that functions at a wavelength of 1.55 μm. According to our simulation results, our innovation was the optimization of the third dielectric layer’s thickness, setting the stage to achieve greater modulation depths. This synergy between graphene and HPWs not only augments subwavelength confinement, but also optimizes light–graphene interaction, culminating in a markedly enhanced modulation efficiency. As a result, our modulator presents a high extinction ratio and minimized insertion loss. Furthermore, it exhibits polarization insensitivity and a greater bandwidth. Our work sets a new benchmark in optical communication systems, emphasizing the potential for the next generation of chip-scale with high-efficiency optical modulators that significantly outpace conventional graphene-based designs.

Wetting Transparency of Single-Layer Graphene on Liquid Substrates.

Graphene's wetting transparency offers promising avenues for creating multifunctional devices by allowing real-time wettability control on liquid substrates via the flow of different liquids beneath graphene. Despite its potential, direct measurement of floating graphene's wettability remains a challenge, hindering the exploration of these applications. The current study develops an experimental methodology to assess the wetting transparency of single-layer graphene (SLG) on liquid substrates. By employing contact angle measurements and Neumann's Triangle model, the challenge of evaluating the wettability of floating free-suspended single-layer graphene is addressed. The research reveals that for successful contact angle measurements, the testing and substrate liquids must be immiscible. Using diiodomethane as the testing liquid and ammonium persulfate solution as liquid substrate, the study demonstrates the near-complete wetting transparency of graphene. Furthermore, it successfully showcases the feasibility of real-time wettability control using graphene on liquid substrates. This work not only advances the understanding of graphene's interaction with liquid interfaces but also suggests a new avenue for the development of multifunctional materials and devices by exploiting the unique wetting transparency of graphene.

Superconductivity from spin fluctuations and long-range interactions in magic-angle twisted bilayer graphene

Superconductivity from spin fluctuations and long-range interactions in magic-angle twisted bilayer graphene

Decomposition of complex interactions in graphene oxide-superplasticizer-cement composites and proposed guidelines for sample preparation and assessment

Despite the recognized potential of graphene oxide (GO) in reinforcing and functionalizing cement composites, the commercialization of GO-incorporated cement composites still faces enormous challenges due to the huge variation on reported performance improvement among existing research. This phenomenon is largely attributed to the complex interactions in the GO-superplasticizer-cement system and the absence of standardized guidelines for sample preparation and performance assessment. To address these concerns, this study thoroughly designs a series of cement composites to decompose the ternary interaction with in-depth comparative analyses. Based on the results of workability and compressive strength, an interaction mechanism within the GO-superplasticizer-cement system is proposed and subsequently cross-validated. In addition, reinforcement efficiencies for each scenario are systemically assessed and summarized, effectively covering the majority of cases outlined in the prevailing literature. Accordingly, guidelines for sample preparation and evaluation in research related to GO-incorporated cement composites are developed.

Unraveling the Interactions between Lithium and Twisted Graphene.

Graphene is undoubtedly the carbon allotrope that has attracted the attention of a myriad of researchers in the last decades more than any other. The interaction of external or intercalated Li and Li+ with graphene layers has been the subject of particular attention for its importance in the applications of graphene layers in Lithium Batteries (LiBs). It is well known that lithium atoms and Li+ can be found inside and/or outside the double layer of graphene, and the graphene layers are often twisted around its parallel plane to obtain twisted graphene with tuneable properties. Thus, in this research, the interactions between Li and Li+ with bilayer graphene and twisted bilayer graphene were investigated by a first-principles density functional theory method, considering the lithium atom and the cation at different symmetry positions and with two different adsorption configurations. Binding energies and equilibrium interlayer distances of filled graphene layers were obtained from the computed potential energy profiles. This work shows that the twisting can regulate the interaction of bilayer graphene with Li and Li+. The binding energies of Li+ systematically increase from bilayer graphene to twisted graphene regardless of twisted angles, while for lithium atoms, the binding energies decrease or remain substantially unchanged depending on the twist angles. This suggests a higher adsorption capacity of twisted graphene towards Li+, which is important for designing twisted graphene-based material for LiB anode coating. Furthermore, when the Li or Li+ is intercalated between two graphene layers, the equilibrium interlayer distances in the twisted layers increase compared to the unrotated bilayer, and the relaxation is more significant for Li+ with respect to Li. This suggests that the twisted graphene can better accommodate the cation in agreement with the above result. The outcomes of this research pave the way for the study of the selective properties of twisted graphene.

Graphene in gas separation membranes—State-of-the-art and potential spoors

Graphene and derivatives have been frequently used to form advanced nanocomposites. A very significant utilization of polymer/graphene nanocomposite was found in the membrane sector. The up-to-date overview essentially highpoints the design, features, and advanced functions of graphene nanocomposite membranes towards gas separations. In this concern, pristine thin layer graphene as well as graphene nanocomposites with poly(dimethyl siloxane), polysulfone, poly(methyl methacrylate), polyimide, and other matrices have been perceived as gas separation membranes. In these membranes, the graphene dispersion and interaction with polymers through applying the appropriate processing techniques have led to optimum porosity, pore sizes, and pore distribution, i.e., suitable for selective separation of gaseous molecules. Consequently, the graphene derived nanocomposites brought about numerous revolutions in high performance gas separation membranes. The structural diversity of polymer/graphene nanocomposites has facilitated the membrane selective separation, permeation, and barrier processes especially in the separation of desired gaseous molecules, ions, and contaminants. Future research on the innovative nanoporous graphene-based membrane can overcome design/performance related challenging factors for technical utilizations.

Interaction of industrial graphene and carbon nanotubes with human primary macrophages: Assessment of nanotoxicity and immune responses

The use of graphene and carbon nanotubes as part of commercial products has already been implemented in a wide variety of industrial sectors thanks to their outstanding physicochemical properties, opening the door to possible occupational and consumer exposure. Macrophages hold major importance in phagocytosis and immune activation against nanomaterials, so human primary macrophages are the most appropriate human models to obtain adequate information about health effects of nanomaterials. In this study, different types of industrially-employed graphene and carbon nanotubes were compared, to understand how their physicochemical properties affect cell behaviour using primary macrophages extracted from human blood donors. The phagocytic profiles were correlated with the toxicity effects provoked in the macrophages, looking to cell viability, membrane disruption and production of reactive oxygen species. To understand how these commercial nanomaterials could affect immune responses, this work was completed with a comprehensive study involving the activation of macrophages after interaction with the nanomaterials. This study provides conclusive results about the activated macrophage phenotypes and cytokine production profiles, including how the nanomaterials affect the communication of macrophages with the rest of immune cells and providing new insights about how the immune system is able to degrade these carbon-based nanomaterials.

High-efficiency light manipulation using a single layer of folded graphene microribbons

Since its one-atom thickness, it remains an open question to enhance light–matter interactions in graphene, which is usually implemented through external resonant structures such as Fabry–Perot cavity. Here, we propose an alternative scheme to enhance light–matter interactions in a single layer of folded graphene microribbons (FGMRs), and remarkably, for normal incidences rather than oblique incidences in most studies. By optimizing structural parameters (e.g., the location of folding axis and folding angle), three light manipulations such as perfect absorption, perfect reflection, and perfect transmission can be achieved independently. More interestingly, any one of the three functionalities can be actively switched to the other via changing material parameters (Fermi level and carrier mobility ), which is actually the most attractive feature of graphene plasmonics. Finally, we show FGMRs can also support triple functionalities, i.e., via changing material parameters, one of the three functionalities can be switched to the second one and then the third one. Our results will be of great interest to fundamental physics and pave the way for graphene plasmonic device applications.

Gold-Deposited Graphene Nanosheets for Self-Cleaning Graphene Surface-Enhanced Raman Spectroscopy with Superior Charge-Transfer Contribution.

The interaction of graphene with metals initiates charge-transfer interaction-induced chemical enhancements, which critically depend on the doping effect from deposited metallic configurations. In this paper, we have explored the gold nanoparticle-decorated monolayer graphene nanosheets for the large graphene-induced Raman enhancement of adsorbed analytes, indicating the surface-enhanced Raman spectroscopy (SERS) capabilities of metal-doped graphene (G-SERS). Here, the systematically sputtered Au thickness optimization procedure revealed noticeable modifications in the graphene Raman spectra and photoluminescence (PL) background quenching, which indicated favorable charge transfer through n-type doping of chemical vapor deposition-grown graphene nanosheets. The highly consistent, individually distributed morphology of the gold nanoislands over graphene nanosheets depicted a reproducibly uniform G-SERS signal with excellent relative standard deviation values (<5%), resulting in the strongest Raman intensity enhancement factors of ∼108 (MB) (methylene blue) and 107 (DPA) (2,6-pyridinedicarboxylic acid) composed of the weakest PL background. The combined charge-transfer-induced chemical enhancement and electromagnetic enhancement from individual Au nanoislands result in a lowering of detectability down to 10-16 M (MB) and 10-11 M (DPA) concentrations with efficient time-dependent signal stability. Additionally, the GAu demonstrated its effective (∼94.4%) photocatalytic degradation capabilities by decomposing MB dye molecules from a concentration of 1 μM to 2.52 fM within 60 min. Therefore, the prominent charge-transfer contribution through controlled Au decoration over graphene nanosheets provides a potential strategy for fabricating superior SERS sensors and photocatalysts exhibiting adequate signal consistency, stability, and photodegradation efficiency through overcoming the limitations of the traditional sensing platforms.

Electromagnetic TE- and TM-waves propagation in a plane waveguide covered with graphene characterized by nonlinear conductivity

Background. Guiding properties of waveguiding structures with graphene are of great importance for various applications and have been studied in many papers. In all such studies, graphene was characterized, as a rule, by linear surface conductivity. However, if the intensity of an electromagnetic wave is large enough, the interaction of graphene with the electromagnetic wave becomes nonlinear; in this case, it is more correct to describe graphene by nonlinear conductivity.&#x0D; Aim. This work is aimed at studying the influence of cubic nonlinearity of graphene, corresponding to the so-called self-action effects (not affecting the frequency of the incident wave), on the propagation of TE- and TM-polarized waves in the structure, which is a plain dielectric layer covered on one side by graphene.&#x0D; Methods. In this study, the guiding properties of the waveguide are studied using primarily an analytical approach. Thus, from Maxwell's equations, material equations and boundary conditions, a couple of dispersion equations for TE-and TM-polarized waves is derived and then its solvability is studied. In addition, some numerical experiments are carried out in the study.&#x0D; Results. The dispersion equations of the studied waveguiding structure for TE- and TM-polarized waves are derived in explicit form. Studying analytically obtained equations, conditions for waveguide parameters are found, providing the existence of a given number of waveguide modes. In addition, some numerical results are obtained in the paper, which give an idea of the influence of nonlinear effects on the electromagnetic waves propagating in the structure.&#x0D; Conclusion. The results obtained in this paper reveal two effects related to the cubic nonlinearity of graphene. Firstly, in a plain dielectric layer with graphene coating in the strong nonlinear regime TE-waves with longer wavelength and TM-waves with shorter wavelength propagate compared to electromagnetic waves that propagate in the same structure in the linear regime. Secondly, the strong cubic nonlinearity leads to a greater localization of the electromagnetic wave within the waveguiding structure.

Intermolecular interactions in graphene and oxidized graphene nanocomposites

The spatial arrangement of graphene (G) or graphene oxide (GO) nanoplate agglomerations will significantly impact the material properties of graphene-based polymer nanocomposites. Therefore, we investigated the stability of G and GO agglomerates without the presence of a polymer network using molecular dynamics (MD) simulations, which was not considered in our previous work (Reil, 2022) [15]. G and GO nanoplates, often procured in powder forms, display a significant volume difference by visual observation. To this end, MD simulations were performed to model G or GO agglomerations in the powder form, including the effects of varied plate dimensions and localized surface oxidation. G plates on average released 231 kcal/mol upon agglomerating into aligned stacks, closely matching results in the literature. Simulations of GO resulted in agglomerations of clusters of plates rather than aligned stacks, releasing on average 16 % less energy than G. The clustered arrangement of GO plate agglomerates in simulations occupied a volume approximately 7x that of the aligned stack G plates, closely replicating the experimentally determined volume ratio of 10x. This research could yield further insight into the behavior of G and GO when in the presence of various polymer networks, which could be different than in isolation.

Interaction of graphene and WS2 with neutrophils and mesenchymal stem cells: implications for peripheral nerve regeneration.

Graphene and bidimensional (2D) materials have been widely used in nerve conduits to boost peripheral nerve regeneration. Nevertheless, the experimental and commercial variability in graphene-based materials generates graphene forms with different structures and properties that can trigger entirely diverse biological responses from all the players involved in nerve repair. Herein, we focus on the graphene and tungsten disulfide (WS2) interaction with non-neuronal cell types involved in nerve tissue regeneration. We synthesize highly crystalline graphene and WS2 with scalable techniques such as thermal decomposition and chemical vapor deposition. The materials were able to trigger the activation of a neutrophil human model promoting Neutrophil Extracellular Traps (NETs) production, particularly under basal conditions, although neutrophils were not able to degrade graphene. Of note is that pristine graphene acts as a repellent for the NET adhesion, a beneficial property for nerve conduit long-term applications. Mesenchymal stem cells (MSCs) have been proposed as a promising strategy for nerve regeneration in combination with a conduit. Thus, the interaction of graphene with MSCs was also investigated, and reduced viability was observed only on specific graphene substrates. Overall, the results confirm the possibility of regulating the cell response by varying graphene properties and selecting the most suitable graphene forms.

Interactions of graphene with oxidants in a mixed atmosphere: synergistic effects of O2/H2O and O2/CO2 on gasification reactivity and kinetics.

The gasification of carbon with O2, CO2, and H2O oxidants plays an important role in several energy-based applications. As most of the industrial gasification processes are conducted under mixed-atmosphere conditions, the oxidation of carbon in binary oxidant mixtures becomes crucially important. Using reactive force-field (ReaxFF) potentials, extensive MD simulations were carried out on the oxidation behavior of graphene in mixed O2/H2O and O2/CO2 environments for a range of gas compositions and temperatures. A graphene sheet with a line defect comprising of eight and four-membered rings was used as the starting carbon structure. In addition to enhanced carbon gasification with oxygen additions, MD simulations showed synergistic interactions between different oxidants and their net influence on the overall reactivities. The gasification levels achieved under the binary system were higher than the linear combination of contributions from individual oxidants. The addition of ∼40% O2 in the binary mix was identified as the region with the highest reactivity during the initial stages of gasification. The oxidation reactions with oxygen were found to start instantaneously in the presence of H2O or CO2 instead of the usual initial delay. A very fast reaction kinetics was also observed in the initial stages in the presence of oxygen. Our results show that the gasification reactions under H2O and CO2 started at lower temperatures than O2 thereby creating a partially oxidized structure. Due to the presence of a large number of activation sites, very high rates of gasification were achieved with oxygen. These findings could help identify optimal oxidant compositions towards maximizing carbon gasification and minimizing CO2 emissions.

Experimental observation and characterization of amorphous carbon generated in graphene on gold nanoparticles.

The interaction of graphene with gold nanoparticles is investigated using transmission electron microscopy. We observe gold-nanoparticle-mediated etching of graphene flakes, often leading to hole formation. Further, using a combination of high-angle annular dark field imaging and electron energy loss spectroscopy, we highlight that the catalytic effects of gold nanoparticles on graphene lead to the formation of amorphous carbon layers. From the extracted diffractograms, we observe regions with diffraction halos as well as some regions with a weak tetrahedral motif. Using independently performed Raman measurements, we confirm the presence of tetrahedral amorphous carbon as well as mixed graphitic-amorphous regions. For the amorphous carbon regions with mixed sp2-sp3 states, the Raman G peak is red-shifted to 1564 cm-1 and an I D/I G ratio of 0.63 indicates less than 20% sp3 content. For the tetrahedral amorphous carbon regions, we observe that the Raman G peak is at 1580 cm-1, close to that of monolayer graphene. However, there is no Raman D peak, i.e., I D/I G = 0, which indicates close to 100% sp3 content. The translation of the Raman G peak location and the I D/I G ratios is on par with the amorphization trajectory analysis of Ferrari and Robertson (Phys. Rev. B: Condens. Matter Mater. Phys., 2000, 61, 14095) and validates the conversion route of graphite to amorphous carbon to tetrahedral amorphous carbon. The presented method provides a promising pathway for creating defect-induced amorphous carbon at room temperature, which has a broader impact on the electronics and semiconductor industries.

Investigation into electronic interaction and work function tuning of phthalocyanine molecules and graphene interfaces.

Understanding the interfacial electronic structures of organic semiconductor phthalocyanines (MePc) and graphene is essential for their practical application in various fields. In this study, we investigated the electronic structure and the tuning of the work function of free metal phthalocyanine (Pc4), cobalt phthalocyanine (CoPc), and copper phthalocyanine (CuPc) molecules deposited on a graphene monolayer using X-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS). We found that the functionalization of MePc molecules induces p-doping to the graphene substrate due to the charge transfer mechanism with the MePc molecule. XPS analysis shows that the electronic interaction at the interface between Pc molecules and graphene substrate mainly occurs through the pyrrole species. Comparatively, it was observed that the electronic coupling between graphene and CuPc is relatively stronger than that between CoPc and graphene. The electronic interaction of the CuPc/Gr sample principally occurs through the Cu2+ 3d states of CuPc, the molecule, and the graphene 2p π states. This electronic interaction increases the work function of the graphene substrate to 5.75 eV, 6.05 eV, and 6.12 eV after depositing the Pc4, CoPc, and CuPc molecules, respectively. These results show that the MePc/Gr samples investigated in this study can be considered promising candidates for applications requiring a high work function to increase hole injection efficiency.

Structural Formation and Pore Control of Freeze-Cast Directional Graphene Aerogel (DGA).

Directional graphene aerogels (DGAs) are proposed as electrode materials to alleviate ionic and mass transport issues in organic redox flow batteries (ORFBs). DGAs with high pore directionality would provide low resistance channels for effective ionic charge and liquid electrolyte transport in these devices. DGAs' porous and directional characteristics can be controlled by the growth of ice crystals during freeze casting, which is influenced by the self-diffusivity of water, phase change driving forces, water-ice graphene interactions, and convection in the water-graphene media. It is found that mass transport-related properties of DGAs, including pore size and directionality, show a significant dependence on freezing temperature, graphene oxide (GO) loadings, and synthesis vessel diameter-to-height ratio (D/H). For the freezing temperature change from -20 to -115 °C, the average pore size progressively decreased from 120 to 20 μm, and the pore directionality transitioned from lamellar to ill-defined structures. When GO loadings were increased from 2 to 10 mg/mL at a fixed freezing temperature, pore size reduction was observed with less defined directionality. Furthermore, the pore directionality diminished with an increased width-to-height aspect ratio of DGA samples due to the buoyancy-driven convective circulation, which interfered with the directional ice/pore growth. Understanding the comprehensive effects of these mechanisms enables the controlled growth of ice crystals, leading to graphene aerogels with highly directional microstructures.

Enhancing Lithium-Sulfur Battery Performance by MXene, Graphene, and Ionic Liquids: A DFT Investigation.

The efficacy of lithium-sulfur (Li-S) batteries crucially hinges on the sulfur immobilization process, representing a pivotal avenue for bolstering their operational efficiency and durability. This dissertation primarily tackles the formidable challenge posed by the high solubility of polysulfides in electrolyte solutions. Quantum chemical computations were leveraged to scrutinize the interactions of MXene materials, graphene (Gr) oxide, and ionic liquids with polysulfides, yielding pivotal binding energy metrics. Comparative assessments were conducted with the objective of pinpointing MXene materials, with a specific focus on d-Ti3C2 materials, evincing augmented binding energies with polysulfides and ionic liquids demonstrating diminished binding energies. Moreover, a diverse array of Gr oxide materials was evaluated for their adsorption capabilities. Scrutiny of the computational outcomes unveiled an augmentation in the solubility of selectively screened d-Ti3C2 MXene and ionic liquids-vis à vis one or more of the five polysulfides. Therefore, the analysis encompasses an in-depth comparative assessment of the stability of polysulfide adsorption by d-Ti3C2 MXene materials, Gr oxide materials, and ionic liquids across diverse ranges.