Chiral Graphene Research Articles

Flat bands in chiral multilayer graphene

Flat bands in chiral multilayer graphene

Chiral Nematic Graphene Films with a mesoporous Structure.

Ordering a crucial material like pure-graphene into the chiral nematic structure can potentially revolutionize the fields of photonics, chiral separation, and energy storage. However, the controlled fabrication of highly ordered graphene films with a long-range chiral nematic mesoporous structure is very challenging and as such, has not been achieved. Here, a chiral-template-directed chemical vapor deposition growth strategy is presented for the precise fabrication of mesoporous chiral nematic graphene films by using nanocrystalline cellulose as templates. It is evidenced that such graphene films possess the left-hand helical ordering, chiral nematic mesoporous structure with adjustable pore sizes (6.4-13.1nm), tailored pitch, excellent electrical conductivity (556 S cm-1), high specific surface area (1508 m2g-1) and mechanical flexibility. By coating Na anode with this film, uniform Na plating is achieved with no dendrite formation, resulting from its unique chiral nematic structure and tunable physicochemical properties. The films also achieved impressive thickness-dependent electromagnetic shielding, i.e., 35-63dB, demonstrating their potentially multi-disciplinary applications.

Multidimensional dynamic control of optical skyrmions in graphene–chiral–graphene multilayers

Abstract Optical skyrmions are topological quasiparticles with a complex vectorial field structure. Their associated characteristics of ultra-small, ultra-fast and topological protection have great application prospects in high density data storage, light matter interaction and optical communication. At present, the research of optical skyrmions is still in its infancy, where the construction and flexible regulation of different topological textures are current research hotspot. Here, we combine the twist degree of freedom of materials and optical skyrmions. Based on graphene–chiral–graphene multilayers structure, we demonstrate the field mode symmetry and hybridization to form Bloch-type graphene plasmons skyrmion lattice. At the same time, by changing chirality parameter, the Fermi energy of graphene and the phase of incident light, multidimensional control of Bloch-type optical skyrmions can be realized. Our work demonstrated that the properties of materials provide the additional dimensions to regulate the topological states, and the combination of different materials structures provides the possibility for dynamic construction and manipulation of multiple topological states, which is expected to find applications in integrated nanophotonics devices.

Dispersion Properties in Uniaxial Chiral–Graphene–Uniaxial Chiral Plasmonic Waveguides

Dispersion Properties in Uniaxial Chiral–Graphene–Uniaxial Chiral Plasmonic Waveguides

(Invited) Chiral Graphene Quantum Dot Enhanced Drug Loading into Exosomes

As nanoscale extracellular vesicles secreted by cells, exosomes have enormous potential as safe and effective vehicles to deliver drugs into lesion locations. Despite promising advances with exosome=based drug delivery systems, there are still challenges to drug loading into exosomes, which hinder the clinical applications of exosomes. Herein, we report an exogenous drug-agnostic chiral graphene quantum dots (GQDs) exosome-loading platform, based on chirality matching with the exosomal lipid bilayer. Both hydrophobic and hydrophilic chemical and biological drugs can be functionalized or adsorbed onto GQDs by π–π stacking and van der Waals interactions. By tuning the ligands and GQD size to optimize its chirality, we demonstrate drug loading efficiency of 66.3% and 64.1% for doxorubicin and siRNA, which is significantly higher than other reported sEV loading techniques. These drug/siRNA loaded exosomes can be applied to cancer treatment and immunotheraoy, which showed significant higher efficacy due to the efficient encapsulation of drugs or genetic materials.As nanoscale extracellular vesicles secreted by cells, exosomes have enormous potential as safe and effective vehicles to deliver drugs into lesion locations. Despite promising advances with exosome=based drug delivery systems, there are still challenges to drug loading into exosomes, which hinder the clinical applications of exosomes. Herein, we report an exogenous drug-agnostic chiral graphene quantum dots (GQDs) exosome-loading platform, based on chirality matching with the exosomal lipid bilayer. Both hydrophobic and hydrophilic chemical and biological drugs can be functionalized or adsorbed onto GQDs by π–π stacking and van der Waals interactions. By tuning the ligands and GQD size to optimize its chirality, we demonstrate drug loading efficiency of 66.3% and 64.1% for doxorubicin and siRNA, which is significantly higher than other reported sEV loading techniques. These drug/siRNA loaded exosomes can be applied to cancer treatment and immunotheraoy, which showed significant higher efficacy due to the efficient encapsulation of drugs or genetic materials.

Fluorescent Chiral Quantum Dots to Unveil Origin-Dependent Exosome Uptake and Cargo Release.

Exosomes are promising nanocarriers for drug delivery. Yet, it is challenging to apply exosomes in clinical use due to the limited understanding of their physiological functions. While cellular uptake of exosomes is generally known through endocytosis and/or membrane fusion, the mechanisms of origin-dependent cellular uptake and subsequent cargo release of exosomes into recipient cells are still unclear. Herein, we investigated the intricate mechanisms of exosome entry into recipient cells and intracellular cargo release. In this study, we utilized chiral graphene quantum dots (GQDs) as representatives of exosomal cargo, taking advantage of the superior permeability of chiral GQDs into lipid membranes as well as their excellent optical properties for tracking analysis. We observed that the preferential cellular uptake of exosomes derived from the same cell-of-origin (intraspecies exosomes) is higher than that of exosomes derived from different cell-of-origin (cross-species exosomes). This uptake enhancement was attributed to receptor-ligand interaction-mediated endocytosis, as we identified the expression of specific ligands on exosomes that favorably interact with their parental cells and confirmed the higher lysosomal entrapment of intraspecies exosomes (intraspecies endocytic uptake). On the other hand, we found that the uptake of cross-species exosomes primarily occurred through membrane fusion, followed by direct cargo release into the cytosol (cross-species direct fusion uptake). We revealed the underlying mechanisms involved in the cellular uptake and subsequent cargo release of exosomes depending on their cell-of-origin and recipient cell types. Overall, this study envisions valuable insights into further advancements in effective drug delivery using exosomes, as well as a comprehensive understanding of cellular communication, including disease pathogenesis.

Synthesis of chiral graphene structures and their comprehensive applications: a critical review.

From a molecular viewpoint, chirality is a crucial factor in biological processes. Enantiomers of a molecule have identical chemical and physical properties, but chiral molecules found in species exist in one enantiomer form throughout life, growth, and evolution. Chiral graphene materials have considerable potential for application in various domains because of their unique structural framework, properties, and controlled synthesis, including chiral creation, segregation, and transmission. This review article provides an in-depth analysis of the synthesis of chiral graphene materials reported over the past decade, including chiral nanoribbons, chiral tunneling, chiral dichroism, chiral recognition, and chiral transfer. The second segment focuses on the diverse applications of chiral graphene in biological engineering, electrochemical sensors, and photodetectors. Finally, we discuss research challenges and potential future uses, along with probable outcomes.

The effect of water on gold supported chiral graphene nanoribbons: rupture of conjugation by an alternating hydrogenation pattern.

In the last few years we have observed a breakpoint in the development of graphene-derived technologies, such as liquid phase filtering and their application to electronics. In most of these cases, they imply exposure of the material to solvents and ambient moisture, either in the fabrication of the material or the final device. The present study demonstrates the sensitivity of graphene nanoribbon (GNR) zigzag edges to water, even in extremely low concentrations. We have addressed the unique reactivity of (3,1)-chiral GNR with moisture on Au(111). Water shows a reductive behaviour, hydrogenating the central carbon of the zigzag segments. By combining scanning tunnelling microscopy (STM) with simulations, we demonstrate how their reactivity reaches a thermodynamic limit when half of the unit cells are reduced, resulting in an alternating pattern of hydrogenated and pristine unit cells starting from the terminal segments. Once a quasi-perfect alternation is reached, the reaction stops regardless of the water concentration. The hydrogenated segments limit the electronic conjugation of the GNR, but the reduction can be reversed both by tip manipulation and annealing. Selective tip-induced dehydrogenation allowed the stabilization of radical states at the edges of the ribbons, while the annealing of the sample completely recovered the original, pristine GNR.

Cove-Edged Chiral Graphene Nanoribbons with Chirality-Dependent Bandgap and Carrier Mobility.

Graphene nanoribbons (GNRs) have garnered significant interest due to their highly customizable physicochemical properties and potential utility in nanoelectronics. Besides controlling widths and edge structures, the inclusion of chirality in GNRs brings another dimension for fine-tuning their optoelectronic properties, but related studies remain elusive owing to the absence of feasible synthetic strategies. Here, we demonstrate a novel class of cove-edged chiral GNRs (CcGNRs) with a tunable chiral vector (n,m). Notably, the bandgap and effective mass of (n,2)-CcGNR show a distinct positive correlation with the increasing value of n, as indicated by theory. Within this GNR family, two representative members, namely, (4,2)-CcGNR and (6,2)-CcGNR, are successfully synthesized. Both CcGNRs exhibit prominently curved geometries arising from the incorporated [4]helicene motifs along their peripheries, as also evidenced by the single-crystal structures of the two respective model compounds (1 and 2). The chemical identities and optoelectronic properties of (4,2)- and (6,2)-CcGNRs are comprehensively investigated via a combination of IR, Raman, solid-state NMR, UV-vis, and THz spectroscopies as well as theoretical calculations. In line with theoretical expectation, the obtained (6,2)-CcGNR possesses a low optical bandgap of 1.37 eV along with charge carrier mobility of ∼8 cm2 V-1 s-1, whereas (4,2)-CcGNR exhibits a narrower bandgap of 1.26 eV with increased mobility of ∼14 cm2 V-1 s-1. This work opens up a new avenue to precisely engineer the bandgap and carrier mobility of GNRs by manipulating their chiral vector.

Electronic structure of conjugated oligomers that are building blocks for achiral and chiral graphene nanoribbons

The understanding of graphene π-electronic structure is further advanced by presenting the exact solution of the tight-binding eigenvalue problem for conjugated oligomers (polyparaphenylene (PPP) and polynaphthalene (PN) of different lengths), which can serve as building blocks for armchair and (2m,m) graphene nanoribbons. The problem is considered on the basis of the Su–Schrieffer–Heeger–Hückel-type Hamiltonian. We show that the π-electron spectrum of PN includes the local states unlike the spectrum of PPP consisting (as well as spectra of armchair graphene nanoribbons of arbitrary widths) only of extended states and present explicit analytic expressions for the wave functions of the conjugated oligomers.

Flat bands and high Chern numbers in twisted multilayer graphene

Motivated by recent Physical Review Letters of Wang and Liu [Phys. Rev. Lett. 128(17), 176403 (2022)] and Ledwith, Vishwanath, and Khalaf [Phys. Rev. Lett. 128(17), 176404 (2022)], we study [G. Tarnopolsky, A. Kruchkov, and A. Vishwanath, Phys. Rev. Lett. 122(10), 106405 (2019)] chiral model of two sheets of n-layer Bernal stacked graphene twisted by a small angle using the framework developed by Becker et al. [Probab. Math. Phys. 3(1), 69 (2022)]. We show that magic angles of this model are exactly the same as magic angles of chiral twisted bilayer graphene with multiplicity. For small inter-layer tunneling potentials, we compute the band separation at Dirac points as we turning on the tunneling parameter. Flat band eigenfunctions are also constructed using a new theta function argument and this yields a complex line bundle with the Chern number −n.

Detecting the spin-polarization of edge states in graphene nanoribbons

Low dimensional carbon-based materials can show intrinsic magnetism associated to p-electrons in open-shell π-conjugated systems. Chemical design provides atomically precise control of the π-electron cloud, which makes them promising for nanoscale magnetic devices. However, direct verification of their spatially resolved spin-moment remains elusive. Here, we report the spin-polarization of chiral graphene nanoribbons (one-dimensional strips of graphene with alternating zig-zag and arm-chair boundaries), obtained by means of spin-polarized scanning tunnelling microscopy. We extract the energy-dependent spin-moment distribution of spatially extended edge states with π-orbital character, thus beyond localized magnetic moments at radical or defective carbon sites. Guided by mean-field Hubbard calculations, we demonstrate that electron correlations are responsible for the spin-splitting of the electronic structure. Our versatile platform utilizes a ferromagnetic substrate that stabilizes the organic magnetic moments against thermal and quantum fluctuations, while being fully compatible with on-surface synthesis of the rapidly growing class of nanographenes.

Multidimensional tunable graphene chiral metasurface based on coherent control.

The deep application of chiral metasurfaces requires higher flexibility. Herein, we propose a multidimensional tunable chiral graphene metasurface, which uses coherent control to obtain more than 0.8 circular conversion dichroism (CCD) at 2.4 THz as a transmission structure. Its operating frequency can be changed in the 1.3-2.4 THz range, while the amplitude has almost perfect modulation depth in the range of 0-0.8. The mechanism of differential absorption was analyzed through numerical simulation. The device designed is easy to obtain reverse CCD, which is used for unit layout and proves its advantages in near-field imaging. Our work has broadened the path for the development of chiral metasurfaces towards higher degrees of freedom.

Chirality-Induced Spin Selectivity in Supramolecular Chirally Functionalized Graphene.

Chiral graphene hybrid materials have attracted significant attention in recent years due to their various applications in the areas of chiral catalysis, chiral separation and recognition, enantioselective sensing, etc. On the other hand, chiral materials are also known to exhibit chirality-dependent spin transmission, commonly dubbed "chirality induced spin selectivity" or CISS. However, CISS properties of chiral graphene materials are largely unexplored. As such, it is not clear whether graphene is even a promising material for the CISS effect given its weak spin-orbit interaction. Here, we report the CISS effect in chiral graphene sheets, in which a graphene derivative (reduced graphene oxide or rGO) is noncovalently functionalized with chiral Fmoc-FF (Fmoc-diphenylalanine) supramolecular fibers. The graphene flakes acquire a "conformational chirality" postfunctionalization, which, combined with other factors, is presumably responsible for the CISS signal. The CISS signal correlates with the supramolecular chirality of the medium, which depends on the thickness of graphene used. Quite interestingly, the noncovalent supramolecular chiral functionalization of conductive materials offers a simple and straightforward methodology to induce chirality and CISS properties in a multitude of easily accessible advanced conductive materials.

(Invited) Stereoselective Synthesis of Molecular Nanographenes

The precise control of stereogenic elements in chemical structures has always been a higly demanding synthetic task.1 In this regard, most of the currently available asymmetric methods require the presence of a heteroatom in the starting substrates that serves as an anchoring point for the successful transfer of chiral information. This eventually emerges, typically, in the form of a new stereogenic centre while the heteroatom remains in the product. This general procedure could account for the lack of stereoselective protocols in all-carbon atom compounds.2,3 Actually, optically active nanographenes have so far been obtained only by either top-down or bottom-up racemic syntheses, followed by time consuming chiral chromatographic separations.4-6 In this presentation, we will introduce a general overview on the efforts carried out in our group in the search for stereoselectivity to introduce and extend stereogenic elements into polyaromatic sp2 carbon-based molecular nanographenes. Acknowledgements The author acknowledge support from the MICIN of Spain (project: PID2020-114653RB-I00) and the European Research Council (ERC) Synergy Grant “TOMATTO” (Project 951224). References H. Kuang, C. Xu, Z. Tang, “Emerging Chiral Materials”, Adv. Mater. 2020, 32, e2005110.M. Rickhaus, M. Mayor, M. Juricek, “Strain-induced helical chirality in polyaromatic systems”, Chem. Soc. Rev. 2016, 45, 1542-1556.J. M. Fernández-García, P. Izquierdo-Garcia, M. Buendia, S. Filippone, N. Martín, “Synthetic chiral molecular nanographenes: the key figure of the racemization barrier”, Chem. Commun. 2022, 58, 2634-2645.P. J. Evans, J. Ouyang, L. Favereau, J. Crassous, I. Fernández, J. Perles-Hernáez, N. Martín "Synthesis of a Helical Bilayer Nanographene" Angew. Chem. Int. Ed. 2018, 57, 6774 –6779.P. Izquierdo-García, J. M. Fernández-García, I. Fernández, J. Perles, N. Martín, “Helically Arranged Chiral Molecular Nanographenes", J. Am. Chem. Soc., 2021, 143, 11864−11870.M. Vázquez-Nakagawa, L. Rodríguez-Pérez, N. Martín, M. A. Herránz, “Supramolecular Assembly of Edge Functionalized Top-Down Chiral Graphene Quantum Dots”, Angew. Chem. Int. Ed. 2022, 61, e202211365.

Study on electrochemical effects of carbon nanotube material defects

The study and implementation of clean, efficient, and long-lasting forms of new energy are currently the focal point of scientific inquiry all over the globe. Carbon nanotubes are excellent hydrogen storage materials, catalyst carriers, and electronic device components due to their outstanding electrochemical properties and near-ideal one-dimensional nanospace. The periodic structure of the crystal and the surrounding charge distribution can be effectively altered by constructing defects in electrode materials or electrocatalysts, as has been demonstrated in a large number of recent studies. This paper provides a summary of the interaction of carbon-carbon double bonds, an analysis of the electrochemical properties of single-wall carbon nanotubes with various chiral graphene defects, and an investigation of the electrochemical properties of double-walled carbon nanotubes with blade dislocation, spiral dislocation, and their composite structures, all based on molecular dynamics simulation.

Enhanced Goos–Hänchen shifts for cross-polarization in the metamaterials containing chiral media and graphene

The cross-polarization Goos–Hänchen (GH) shifts of reflected wave from the symmetric layered metamaterials consisting of isotropic chiral media and graphene have been investigated. The influences of the physical parameters of chiral layers and graphene on the cross-polarization GH shifts for p polarized wave are discussed in detail. It is found that by adding graphene in the metamaterials, and only monolayer graphene needed, the cross-polarization GH shifts will be greatly enhanced. Meanwhile, extremely large cross-polarization GH shifts close to the Brewster angles will be obtained as a reasonable smaller chemical potential of the graphene is selected. Additionally, by adjusting the thickness and the chirality of the chiral material, the cross-polarization GH shifts can be enhanced with positive and negative peaks at different Brewster angles.

Importance of kink energy in calculating the formation energy of a graphene edge

The formation energy of an arbitrary graphene edge or that of other 2D materials has been estimated as a summation of the armchair (AC) and zigzag (ZZ) edge sites. Such an estimation assumes that each site is independent from its neighboring sites, which is unlikely due to the overlap of electron densities. Here, we show that to accurately calculate the formation energy of graphene edges with various functional groups the energy of the junction between AC and ZZ sites, the ``kink energy,'' is essential. It is significant that the kink energies of graphene edges with different functional groups are all negative, namely, kink formation stabilizes the chiral graphene edges.

Chiral Graphene Quantum Dots Enhanced Drug Loading into Small Extracellular Vesicles.

As nanoscale extracellular vesicles secreted by cells, small extracellular vesicles (sEVs) have enormous potential as safe and effective vehicles to deliver drugs into lesion locations. Despite promising advances with sEV-based drug delivery systems, there are still challenges to drug loading into sEVs, which hinder the clinical applications of sEVs. Herein, we report an exogenous drug-agnostic chiral graphene quantum dots (GQDs) sEV-loading platform, based on chirality matching with the sEV lipid bilayer. Both hydrophobic and hydrophilic chemical and biological drugs can be functionalized or adsorbed onto GQDs by π-π stacking and van der Waals interactions. By tuning the ligands and GQD size to optimize its chirality, we demonstrate drug loading efficiency of 66.3% and 64.1% for doxorubicin and siRNA, which is significantly higher than other reported sEV loading techniques.

Molecular dynamics simulation of reinforcement mechanism of graphene/aluminum composites and microstructure evolution

Graphene/Aluminum (Gr/Al) composites with different graphene chirality and distribution patterns were established. The contribution of graphene interfaces to the mechanical properties of composites was investigated by using molecular dynamics methods. The composites strengthen about 10% of Young's modulus and 5% of tensile yield strength compared with aluminum. Influenced by the chiral structures of graphene, the fracture strain of zigzag composite is larger, and the yield stress of armchair composite is higher. Folding deformation of graphene promotes the yielding of the composites under compressive loading. Even if the graphene breaks, the graphene interface can effectively limit the dislocation motion, and the twins can only expand around the graphene. The results of both tensile and compressive tests showed that the uniform distribution of graphene was beneficial to enhance the mechanical properties of the composites. Graphene hinders the motion of pre-dislocations more than pinning dislocations. Therefore, the Bauschinger effect of composite is lower than that of pure aluminum under tension-compression loading.