Single Graphene Sheet Research Articles

Topological flat bands in a family of multilayer graphene moiré lattices

Moiré materials host a wealth of intertwined correlated and topological states of matter, all arising from flat electronic bands with nontrivial quantum geometry. A prominent example is the family of alternating-twist magic-angle graphene stacks, which exhibit symmetry-broken states at rational fillings of the moiré band and superconductivity close to half filling. Here, we introduce a second family of twisted graphene multilayers made up of twisted sheets of M- and N-layer Bernal-stacked graphene flakes. Calculations indicate that applying an electric displacement field isolates a flat and topological moiré conduction band that is primarily localized to a single graphene sheet below the moiré interface. Phenomenologically, the result is a striking similarity in the hierarchies of symmetry-broken phases across this family of twisted graphene multilayers. Our results show that this family of structures offers promising new opportunities for the discovery of exotic new correlated and topological phenomena, enabled by using the layer number to fine tune the flat moiré band and its screening environment.

All-optical quality control of indenene intercalation into graphene/SiC

Intercalating two-dimensional quantum materials beneath a sheet of graphene provides effective environmental protection and facilitates ex situ device fabrication. However, developing a functional device requires rapid, large-scale screening methods to evaluate the quality of the intercalant, which to date can be monitored only by slow, ultra-high vacuum-based surface science techniques. In this study, we utilize ex situ Raman micro-spectroscopy to optically and nondestructively identify the quantum spin Hall insulator indenene, a monolayer of indium sandwiched between a SiC(0001) substrate and a single sheet of graphene. Color modulation combined with indenene's distinctive low-frequency Raman fingerprint enables rapid assessment of its homogeneity and crystalline quality. Density functional perturbation theory indicates that this Raman signature originates mainly from indenene's shear and breathing modes, while additional higher order modes are tentatively attributed to defect-assisted and two-phonon Raman processes.

REFRACTIVE INDEX BASED DETECTION WITH A HIGH SENSITIVITY BIOSENSOR ENHANCED BY GRAPHENE

Over the past decade, optical sensors have made significant advances. An optical sensor examines the environmental impact through the change of an optical signal and offers advantages such as low cost and label-free detection. In this study, a sensor consisting of a single graphene layer and a slit positioned on the substrate is proposed. The strip gap made to improve the excitation of graphene plasmons allowed to achieve 96.2% high transmission resonance mode. This demonstrates the ability of the sensor surface to detect changing environmental conditions. The results show that the sensitivity of the sensor is 6282 nm/RIU when the sensor surface is exposed to analytes with different refractive indices. The use of a single graphene sheet eliminates the need for a metal resonator and achieves a higher sensitivity compared to some experiments recently published in the literature. Thus, the disadvantage of significant ohmic losses in metal resonators is avoided. Furthermore, a thorough discussion of various factors, including the modification of the strip gap width on the graphene layer and electrical tunability, led to the achievement of optimal sensitivity.

Surface area and porosity analysis in nanoporous carbons by atomistic pore domain model

We present a new atomistic model for evaluating the surface area and porosity of micro-mesoporous carbons. This method, referred to as the atomistic pore domain model (APDM), advances the adsorption porosity methodology by calculating textural properties of micro-mesoporous carbons without relying on assumptions about pore geometry. A thorough analysis of porosity across eleven porous carbons demonstrates a robust correlation between the surface area accessible to N2 molecules, as computed using APDM and the Brunauer-Emmett-Teller method with Rouquerol criterium. This correlation is observed across a spectrum of nanoporous carbons, ranging from ultramicroporous activated carbon fibers and nanoporous carbon beads to supermicro-mesoporous activated carbons and activated carbon fibers. APDM facilitates the extraction of the information regarding the N2 surface area accessibility and the intrinsic geometric surface area of micro-mesoporous carbons. The N2-to-He surface area accessibility ratio of the investigated porous carbons varies from approximately 57 %–94 %, indicating varying degrees of pore sieving among studied carbon samples. Except for ACF-25 micro-mesoporous activated carbon fiber, the intrinsic geometric surface areas of the studied micro-mesoporous carbons are smaller than the geometrical surface area of a single graphene sheet (2640 m2/g).

Strain sensitivity and microscopic deformation mechanism of graphene foam containing active nanoparticles under magnetic fields

Magnetic aerogels have attracted many practical applications in recent years, which requisites a comprehensive understanding on basic mechanics of this hybrid composite system. In this paper, the microscopic deformation mechanism and strain variation (εΔ) of such a hybrid material under external magnetic field (Ef) is systematically studied by the coarse-grained molecular dynamics simulation method. The major factors like layer thickness, magnitude of external magnetic field and crosslinks effects are mainly considered. The recovery behavior is also studied under cyclic Ef. Interestingly, the εΔ of such a hybrid material is much affected by the graphene sheet thickness, magnitude of applied Ef and crosslinks, due to their direct influences on the microstructural evolution. The εΔ of non-bonded hybrid composite with single layer thick graphene sheet (εΔ⁓0.19) is four times higher relative to eight layers thick system (εΔ⁓0.045). With the increase of graphene sheet thickness, the microstructural evolution of nanoparticles will change from wrapping of single layer sheets around them to flow and jump from one thick sheet to other. We also found the critical value of Ef, i.e., 200 nN for single layer thick graphene sheet hybrid systems beyond which the εΔ tend to decrease, however, εΔ for eight layers system continue to increase as a function of Ef magnitude. The addition of crosslinks remarkably enhances the εΔ (⁓0.74) and recovery (⁓90%) of hybrid composite system. The bonded nanoparticles initiate the folding and unfolding mechanism of graphene sheets during cyclic Ef. The results clarify the micro mechanism and basic mechanics of magnetic aerogels that will be helpful to the design the future devices and advanced sensors.

On the Highly Ordered Graphene Structure of Non-Graphitic Carbons (NGCs)—A Wide-Angle Neutron Scattering (WANS) Study

Non-graphitic carbons (NGCs), such as glass-like carbons, pitch cokes, and activated carbon consist of small graphene layer building stacks arranged in a turbostratic order. Both structure features, including the single graphene sheets as well as the stacks, possess structural disorder, which can be determined using wide-angle X-ray or neutron scattering (WAXS/WANS). Even if WANS data of NGCs have already been extensively reported and evaluated in different studies, there are still open questions with regard to their validation with WAXS, which is usually used for routine characterization. In particular, using WAXS for the damping of the atomic form factor and the limited measured range prevent the analysis of higher-ordered reflections, which are crucial for determining the stack/layer size (La, Lc) and disorder (σ1, σ3) based on the reflection widths. Therefore, in this study, powder WANS was performed on three types of carbon materials (glass-like carbon made out of a phenol-formaldehyde resin (PF-R), a mesophase pitch (MP), and a low softening-point pitch (LSPP)) using a beamline at ILL in Grenoble, providing a small wavelength and thus generating WANS data covering a large range of scattering vectors (0.052 Å−1 < s < 3.76 Å−1). Merging these WANS data with WANS data from previous studies, possessing high resolution in the small s range, on the same materials allowed us to determine both the interlayer and the interlayer structure as accurately as possible. As a main conclusion, we found that the structural disorder of the graphene layers themselves was significantly smaller than previously assumed.

Low temperature electrical transport in microwave plasma fabricated free-standing graphene and N-graphene sheets

In this paper, the electrical transport in free-standing graphene and N-graphene sheets fabricated by a microwave plasma-based method is addressed. Temperature–dependent resistivity/conductivity measurements are performed on the graphene/N-graphene sheets compressed in pellets. Different measurement configurations reveal directional dependence of current flow—the room-temperature conductivity longitudinal to the pellet’s plane is an order of magnitude higher than the transversal one, due to the preferential orientation of graphene sheets in the pellets. SEM imaging confirms that the graphene sheets are mostly oriented parallel to the pellet’s plane and stacked in agglomerates. The high longitudinal electrical conductivity with values on the order of 103 S/m should be noted. Further, the current flow mechanism revealed from resistivity-temperature dependences from 300K down to 10K shows non-metallic behavior manifested with an increasing resistivity with decreasing the temperature usually observed for insulating or localized systems. The observed charge transport shows variable range hopping at lower temperatures and thermally activated behaviour at higher temperatures. This allows us to attribute the charge transport mechanism to a partially disordered system in which single graphene sheets are placed predominantly parallel to each other and stacked together.

Emerging Trends and Future Direction of Graphene Family of Materials as Potential Antimicrobials: A Critical Review

Graphene research has progressed at an unprecedented rate since 2004 when Novoselov and Geim isolated and described a single sheet of graphene. In fact, the relentless progress in graphene literature over the past decades makes it challenging to diversify research efforts in varied directions. The superior optical, electrical, thermal, and mechanical properties of graphene usher in a broad spectrum of applications that attracts the interest of various scientific domains, including material scientists, physicists, chemists, and biologists. These exceptional properties of the graphene family of materials (Gfam) have inspired researchers to explore a cornucopia of potential applications surrounding graphene and its derivatives in the realm of bacterial, fungal, and viral cells. Herein, we provide an exhaustive discussion of the antimicrobial mechanism of Gfam against different pathogen types: bacteria, fungi, and viruses. In addition, we present the physicochemical differences among members of Gfam and the correlation of their germicidal activities to material properties. A comparative analysis of Gfam’s activities pertaining to bare metals and the enhanced broad-spectrum antimicrobial action of graphene family-based nanocomposites as well as surface coatings are also described. The review analyzes and discusses the present constraints and anticipated future directions that would enable graphene-based nanomaterials to advance as high-performance antimicrobial structures. Thus, Gfam as a robust biocidal material of interest can effectively bridge the gap between academia and industry.

Cholesterol-Induced Nanoscale Variations in the Thickness of Phospholipid Membranes.

Graphene-induced energy transfer (GIET) is a recently developed fluorescence-spectroscopic technique that achieves subnanometric optical localization of fluorophores along the optical axis of a microscope. GIET is based on the near-field energy transfer from an optically excited fluorescent molecule to a single sheet of graphene. It has been successfully used for estimating interleaflet distances of single lipid bilayers and for investigating the membrane organization of living mitochondria. In this study, we use GIET to measure the cholesterol-induced subtle changes of membrane thickness at the nanoscale. We quantify membrane thickness variations in supported lipid bilayers (SLBs) as a function of lipid composition and increasing cholesterol content. Our findings demonstrate that GIET is an extremely sensitive tool for investigating nanometric structural changes in biomembranes.

Commercial Screen-Printed Electrode Decorated with Carbonaceous Binary Sulfides for Direct Glucose Detection in Human Fluid Samples

We hereby demonstrate a highly controllable, green, and rapid synthesis strategy for the production of binary metal sulfides on carbon nano-horns (CNHs) for the fabrication of non-enzymatic glucose sensor using commercial graphite screen-printed electrodes (GSPEs). CNHs were synthesized using the submerged arc discharge method as described elsewhere. In the next step, one droplet (50 µL) of the well-dispersed CNHs was carefully cast on the surface of the GCE (and GSPE). In the final step of preparing the modified electrodes, CNH/GCEs were covered by a thin layer of nickel cobalt sulfide by a simple electrochemical deposition procedure.Following the structural examination of the prepared electrocatalyst were examined. In this regard, several microscopic methods like FE-SEM or TEM were used to know more regard the morphology of the material. The FE-SEM images confirmed the successful formation of sponge like nanosheets of NiCo-S on carbonaceous material. Since CNHs are prepared from graphene sheets with open ends in horn-like shapes, they can be considered as being formed from the origami-like or crushing contortion of a single graphene sheet. According to the FE-SEM images, the agglomeration of CNHs establishes discrete nano-sphere structures with diameters in the range of 50 to 150 nm. The TEM images also confirm this nano-sphere strictures.Following detailed structural characterization, the electrocatalytic activity of the fabricated NiCo-S/CNH electrodes toward electro-oxidation of glucose is examined in detail. The cyclic voltammetry was also used for glucose electro-oxidation mechanism investigation. In addition, parameter optimization was also done by utilizing cyclic voltammetry technique. These include medium pH, deposition cycles, and metals mole ration. Moreover, the effect of the presence and absence of CNH on the electrochemical performance of glucose oxidation were also examined. It shows that in the presence of CNH the peak current density for glucose oxidation is higher that is perfect for analytical purposes and increase the analytical sensitivity. The structural properties and electrochemical response of the fabricated electrodes were also compared to their corresponding mono-metallic counterparts.The amperometric method was utilized as one of the most prevalent and momentous techniques for the quantitative determination of glucose. The applied potential in amperometric tests was optimized to be +0.5 V (vs. Ag/AgCl). The proposed electrodes were operated within two distinct linear dynamic ranges of 0.001- 0.330 mM and 0.330 - 4.53 mM of standard glucose with sensitivities of 1842 µA.mM-1.cm-2, and 854 µA.mM-1.cm-2, respectively. On the other hand, an analytical sensitivity of 467 µA.mM-1.cm-2, within the linear dynamic range of 0.5 - 6 mM was obtained for the static chronoamperometric measurements for modified commercial screen-printed electrode (GSPE). The proposed sensor showed outstanding selectivity against iso-structures and co-existing interferences, long-term durability, rapid response (1.7 s), excellent poisoning resistance against chloride ions, good repeatability, and reproducibility. The tested interferences were 0.1 mM solutions of fructose, galactose, sucrose, lactose, ascorbic acid, uric acid, dopamine hydrochloride, and NaCl. In order to demonstrate the capability of the fabricated electrodes and to evaluate their potential for glucose measurements in real physiological specimens, the glucose level was successfully measured in human blood serum, urine, and saliva samples, without any sample pre-treatment. All in all, the encouraging results make NiCo-S/CNH electrodes immensely promising for clinical and physiological glucose-level measurements.Figure 1. (a) FE-SEM image of CNH. (b) FE-SEM image of NiCo-S/CNH. (c) TEM image of CNHs. (d) Cyclic voltammogarm of NiCo-S/CNH in the absence and presence of various concentration of glucose. (e) The amperometric responses of the NiCo-S/CNH/GCEs after addition of 1 mM glucose followed by successive injection of 0.1 mM fructose, galactose, sucrose, lactose, AA, UA, DA, and NaCl. (f) Chrono amperograms of the NiCo-S/CNH/GSPEs in the presence of the different glucose concentration ranging from 0.5 ~ 10.0 mM under applying +0.5 V. Amperogram of the NiCo-S/GCEs current response obtained from the addition of (g) 50 µL human blood serum, (h) 200 µL urine, and (i) 100 µL saliva followed by injection of 400 µM standard glucose solutions under the optimum potential of +0.5 V, the amperograms of five successive glucose addition. Figure 1

Engineering Graphene Grain Boundaries for Plasmonic Multi-Excitation and Hotspots.

Surface plasmons, merging photonics and electronics in nanoscale dimensions, have been the cornerstones in integrated informatics, precision detection, high-resolution imaging, and energy conversion. Arising from the exceptional Fermi-Dirac tunability, ultrafast carrier mobility, and high-field confinement, graphene offers excellent advantages for plasmon technologies and enables a variety of state-of-the-art optoelectronic applications ranging from tight-field-enhanced light sources, modulators, and photodetectors to biochemical sensors. However, it is challenging to co-excite multiple graphene plasmons on one single graphene sheet with high density, a key step toward plasmonic wavelength-division multiplexing and next-generation dynamical optoelectronics. Here, we report the heteroepitaxial growth of a polycrystalline graphene monolayer with patterned gradient grain boundary density, which is synthesized by creating diverse nanosized local growth environments on a centimeter-scale substrate with a polycrystalline graphene ring seed in chemical vapor deposition. Such geometry enables plasmonic co-excitation with varied wavelength diversification in the nanoscale. Via using high-resolution scanning near-field optical microscopy, we demonstrate rich plasmon standing waves, even bright plasmonic hotspots with a size up to 3 μm. Moreover, by changing the grain boundary density and annealing, we find the local plasmonic wavelengths are widely tunable, from 70 to 300 nm. Theoretical modeling supports that such plasmonic versatility is due to the grain boundary-induced plasmon-phonon interactions through random phase approximation. The seed-induced heteroepitaxial growth provides a promising way for the grain boundary engineering of two-dimensional materials, and the controllable grain boundary-based plasmon co-generation and manipulation in one single graphene monolayer will facilitate the applications of graphene for plasmonics and nanophotonics.

Vibration analysis of single and multi-walled circular graphene sheets in thermal environment using GDQM

The present study researches the free vibration of single and multi-walled circular graphene sheets in a thermal environment. To this aim, the graphene sheet is assumed to be single-layer and two-layer. In order to reach the governing equation, the nonlocal strain gradient theory is used along with the theories of higher-order shear deformation of the plate. Further, the effect of the heat field on the vibration behavior of the graphene sheet is investigated. Also, it is assumed that the graphene sheet is set on the viscoelastic medium to consider the foundation effect. Hamilton’s principle is utilized to obtain the governing equations and is solved analytically using the generalized differential quadrature method. Results of the current research indicate that in all boundary conditions and for any value of the nonlocal parameter, the dimensionless natural frequency decreases with increasing temperature.

The Effect of Single-Walled Carbon Nanotubes on UDP-Glucuronosyltransferase 1A Activity in Human Liver

Single-walled carbon nanotubes (SWCNTs) are made from rolled single graphene sheets with a diameter in the nanometer range and are potential carriers for drug delivery systems. However, their effects on uridine 5'-diphosphate-glucuronosyltransferase (UGT) 1A activities remain unclear. The present study aimed to investigate the effect of two kinds of SWCNTs (EC1.5-P- and FH-P-SWCNTs) and other nanocarbons on human UGT1A activity due to the proposed application of SWCNTs in drug and gene delivery. β-Estradiol 3-glucuronidation, which is catalyzed mainly by UGT1A1, was inhibited by 99 and 76% in the presence of 0.1 mg/mL EC1.5-P- and FH-P-SWCNTs in human liver microsomes, respectively. The observed decrease of free UGT1A1 protein in the enzyme reaction mixture suggests a higher interaction with SWCNTs, and indicates the inhibition of β-estradiol 3-glucuronidation. Imipramine N-glucuronidation, which is formed mainly by UGT1A4, was also decreased by SWCNTs. Serotonin glucuronidation, which is mainly responsible for UGT1A6, was only influenced by specific nanocarbons in human liver microsomes. The attenuation of free UGT1A6 protein was observed with SWCNTs and carbon black, indicating that UGT1A6 activity was not influenced by the direct interaction of SWCNTs. We also observed a 127% increase by FH-P-SWCNTs for propofol glucuronidation in human liver microsomes, which is catalyzed mainly by UGT1A9. The values of maximum velocity and intrinsic clearance for propofol glucuronidation in the presence of FH-P-SWCNT were 1.8- and 2.0-fold higher than those of the control in human liver microsomes. These results suggest that the effects of SWCNTs on UGT1A are different among isoforms.

Buckling analysis of single and double-layer annular graphene sheets in thermal environment

Buckling analysis of single and double-layer annular graphene sheets in thermal environment

Coexistence of Canted Antiferromagnetism and Bond Order in ν=0 Graphene

Motivated by experimental studies of graphene in the quantum Hall regime, we revisit the phase diagram of a single sheet of graphene at charge neutrality. Because of spin and valley degeneracies, interactions play a crucial role in determining the nature of the ground state. We show that, generically within the Hartree-Fock approximation, in the regime of interest there is a region of coexistence between magnetic and bond orders in the phase diagram. We demonstrate this result both in continuum and lattice models, and argue that the coexistence phase naturally provides a possible explanation for unreconciled experimental observations on the quantum Hall effect in graphene.

Plasmonic imaging the catalysis of single graphene sheets – The edge effect

Oxygen evolution reaction on a graphene sheet at negative potential is observed using surface plasmon resonance microscopy (SPRM). It is found that oxygen nanobubbles are evolved at negative potential due to the disproportion reaction of superoxide originated from the reduced dissolved oxygen, suggesting that graphene acts as a superoxide dismutase (SOD) mimic. SPRM reveals that the catalytic sites distribute at the edge and the bulk of graphene. Atomic force microscopy suggests that the active sites for bubble evolution in the bulk of graphene are located at internal edge originated from the holes in the graphene rather than the metal oxide residues remained on the graphene sheet. The metal oxide nanoparticles on the graphene sheet are not the direct active sites but also play important roles in promoting the catalysis by increasing the superoxide concentration through an electrocatalyzed Fenton reaction. This work also presents the first experimental evidence that the catalysis of graphene is generated from the edge effect in an in operando manner. The SPRM represents a universal tool to reveal the catalytic mechanism at microscale, and it is hoped to discover more exciting reactions on nanomaterials due to its label free feature, high sensitivity, and versatility to most of materials.

Peridynamic Model for Single-Layer Graphene Obtained from Coarse-Grained Bond Forces

An ordinary state-based peridynamic material model is proposed for single-sheet graphene. The model is calibrated using coarse-grained molecular dynamics simulations. The coarse-graining method allows the dependence of bond force on bond length to be determined, including the horizon. The peridynamic model allows the horizon to be rescaled, providing a multiscale capability and allowing for substantial reductions in computational cost compared with molecular dynamics. The calibrated peridynamic model is compared to experimental data on the deflection and perforation of a graphene sheet by an atomic force microscope probe.

Periodic Nanoarray of Graphene pn‐Junctions on Silicon Carbide Obtained by Hydrogen Intercalation

AbstractGraphene pn‐junctions offer a rich portfolio of intriguing physical phenomena. They stand as the potential building blocks for a broad spectrum of future technologies, ranging from electronic lenses analogous to metamaterials in optics, to high‐performance photodetectors important for a variety of optoelectronic applications. The production of graphene pn‐junctions and their precise structuring at the nanoscale remains to be a challenge. In this work, a scalable method for fabricating periodic nanoarrays of graphene pn‐junctions on a technologically viable semiconducting SiC substrate is introduced. Via H‐intercalation, 1D confined armchair graphene nanoribbons are transformed into a single 2D graphene sheet rolling over 6H‐SiC mesa structures. Due to the different surface terminations of the basal and vicinal SiC planes constituting the mesa structures, different types of charge carriers are locally induced into the graphene layer. Using angle‐resolved photoelectron spectroscopy, the electronic band structure of the two graphene regions are selectively measured, finding two symmetrically doped phases with p‐type being located on the basal planes and n‐type on the facets. The results demonstrate that through a careful structuring of the substrate, combined with H‐intercalation, integrated networks of graphene pn‐junctions could be engineered at the nanoscale, paving the way for the realization of novel optoelectronic device concepts.

Understanding the steric effect of graphene in graphene wrapped silicon suboxides anodes for Li-ion batteries

Due to high electrical conductivity and excellent mechanical properties, graphene has attracted extensive attention for Li-ion batteries, but generally as a functional additive with the content ≤1 wt%. Unfortunately, single graphene sheets and orderly stacked graphene films are likely to impede Li-ion transportation as a physical barrier. Herein, we compare pure graphene anodes with different stacking manners and SiO anodes wrapped with variant mass of graphene to unveil the steric hindrance. The rapidly fading capacity indicates a serious steric effect on lithium-ion diffusion once graphene mass loading goes beyond the critical value of ∼0.3 mg cm−2. When graphene stacked to parallel Li-ion diffusion direction, it delivers near-theoretical specific capacity, even for thick electrode up to 5.5 mg cm−2. Furthermore, no remarkably adverse impact from graphene is shown in graphene wrapped SiO anodes even with 19 wt% graphene and at 4C in the half cells. Importantly, polarization associated voltage leap and average voltage demonstrate a significant steric effect when the graphene mass loading exceeds 0.33 mg cm−2 in the commercial level pouch cells. In conclusion, the steric effect on electrochemical performances can be eliminated once the critical value of graphene mass loading in the electrode is below ∼0.3 mg cm−2.

A highly durable graphene monolayer electrode under long-term hydrogen evolution cycling.

Achieving long term stability of single graphene sheets towards repeated electrochemical hydrogen evolution reaction (HER) cycling has been challenging. Here, we show through appropriate electrode preparation that it is possible to obtain highly durable isolated graphene electrodes, which can survive several hundreds of HER cycles with virtually no damage to the sp2-carbon framework and persistently good electron transfer characteristics.