Graphene Domains Research Articles

Optimizing Electrocatalysis and Domain Effects of Graphene on Li2S Cathodes for High-Efficient-Stable Li─S Batteries.

Reducing the initial activation barrier of Li2S is crucial for enhancing the coulomb efficiency and cycle life of Li─S batteries. Herein two Li2S-graphene cathode architectures are constructed and investigated the electrocatalytic and domain effects of two graphene on Li2S. Systematic studies reveal an unprecedented relevancy between Li2S activation and graphene electrocatalysis, as well as an intrinsic relationship between Li2S stability and the graphene domain. A dramatically reduced initial activation potential of 2.8V is achieved via the S─C bonding electrocatalysis of Li2S-graphene structure, much lower than the initial activation potential of 3.68V triggered by two-phase electrocatalysis of Li2S/graphene composite. Density functional theory calculations offer mechanism insights into the electrocatalytic effect of S─C bonding on reduced overpotential, and in situ NMR provides solid evidence for the confinement effect of core-shell structure on enhanced cyclability. Notably, a specially designed Li2S@graphene cathode with core-shell structure and S─C interactions exhibit both superior electrocatalytic activation and electrochemical reversibility, enabling Li─S battery promising electrochemical properties, including low charge-discharge overpotential, high specific capacity, and excellent cycling performance. More importantly, it demonstrates excellent chemical compatibility within various electrolytes. This study provides valuable theoretical insights for the development of high-performance Li2S-graphene cathode materials.

Ternary Boron Carbon Nitride nanosheets with improved and controllable linear and nonlinear optical response for efficient photocatalytic performance

This work reports the systematic variation of linear and nonlinear optical (NLO) properties of ternary boron carbon nitride (BCN) nanosheets with varying carbon concentrations. These nanosheets are synthesized by the thermal substitutional method to modulate the band-gap of BCN nanosheets by varying the hBN and graphene domain ratios which is confirmed through UV–Vis absorption spectroscopy. The third-order optical nonlinearity of nanosheets was explored through the Z-scan technique. With increases in both carbon content and laser power, samples' NLO properties have shifted from saturable absorption to reverse saturable absorption. The enhanced nonlinearity with carbon concentration in BCN samples was responsible for higher photoinduced charge separation time. In UV–Vis driven photoreduction of organic pollutants, BCN nanosheets with a decreased bandgap and an increased charge separation time show higher catalytic efficiency. Therefore, based on the combined effect of many processes, the results revealed that the BCN nanosheets displayed greater potential for photoinduced reduction.

Low temperature preparation of the monolayer-graphene/diamond heterostructure with superior mechanical properties

There is increasing interest in the preparation of graphene-on-diamond (GOD) hybrids since it is expected to reveal a new horizon of mechanical applications if the beneficial properties of diamond and graphene are effectively combined. Herein, we demonstrated the atomistic scale events leading to the growth of graphene domains on the diamond during the annealing of the nickel catalyst and diamond substrate by combining experiments and theoretical calculations, including the mechanism transition from high-to low-temperature. Concurrently, the high-quality heterostructure of monolayer graphene on diamond was prepared at a low temperature (760 °C) by rapid thermal annealing technique under the guidance of theoretical insights, and an extraordinarily low coefficient of friction (0.021) was exhibited, representing a 91.1 % reduction against the pristine diamond. The adhesion tests confirmed that such an excellent self-lubricity benefited from the adhesion shield effect of as-grown graphene and the consequent reduction in adhesion energy. Furthermore, the corresponding hardness and elastic modulus were also improved by 14.1 % and 32.5 %, respectively. This investigation presents a great potential of the preparation/integration and application of the GOD heterostructure.

Growth of centimeter-scale single-crystal graphene on polycrystalline copper foil for ultrahigh sensitive sweat sensors

The low-cost growth of wafer-scale single-crystal (SC) shows great potential in its practical application. Epitaxial growth of large-area SC graphene on pre-produced SC metal foil with a specific index surface has been reported, which requires a high cost and complexity of operational processes. Here, we demonstrate an easy and low-cost approach for the growth of wafer-scale SC graphene on polycrystalline copper foil, the growth kinetics and the lattice orientation for graphene growth controlled by induced surface steps. Despite graphene domains grown across the Cu grain boundary, the domains have a common crystal orientation at the macroscale induced by the surface steps. This work demonstrates the polycrystalline Cu foil can also grow graphene domains with unidirectional alignment and seamless stitching on the large area. The wearable 2D graphene array sensors have also been developed for the detection of interleukin-6 (IL-6) in sweat, which can locate and detect infection or disease in a non-invasive way. Our growth method and novel application put up a new way of production and utilization of SC two-dimensional (2D) materials.

Emergent Inhomogeneity and Nonlocality in a Graphene Field-Effect Transistor on a Near-Parallel Moiré Superlattice of Transition Metal Dichalcogenides.

At near-parallel orientation, twisted bilayers of transition metal dichalcogenides exhibit interlayer charge transfer-driven out-of-plane ferroelectricity. Here, we report detailed electrical transport in a dual-gated graphene field-effect transistor placed on a 2.1° twisted bilayer WSe2. We observe hysteretic transfer characteristics and an emergent charge inhomogeneity with multiple local Dirac points evolving with an increasing electric displacement field (D). Concomitantly, we also observe a strong nonlocal voltage signal at D ∼ 0 V/nm that decreases rapidly with increasing D. A linear scaling of the nonlocal signal with longitudinal resistance suggests edge mode transport, which we attribute to the breaking of valley symmetry of graphene due to the spatially fluctuating electric field from the underlying polarized moiré domains. A quantitative analysis suggests the emergence of finite-size domains in graphene that modulate the charge and the valley currents simultaneously. This work underlines the impact of interfacial ferroelectricity that can trigger a new generation of devices.

Cellular Impact and Biodegradability of S‐ and N‐Doped Graphene Quantum Dots on Human Monocytes and Macrophages

AbstractGraphene quantum dots (GQDs), small graphene domains with lateral dimensions lower than 10 nm, are increasingly used in electronics, composites, and biomedicine. Chemical doping of GQDs allows tuning their optical properties. Immune cells are among the first cells exposed to nanomaterials entering a living body, rapidly triggering a downstream immune response. However, the assessment of the impact of chemically‐doped GQDs on the immune system remains rather limited if not absent. In this context, the effects and the biodegradability of sulfur‐doped and nitrogen‐doped GQDs (S‐GQDs and N‐GQDs) on human monocytes and macrophages are evaluated. The metabolic activity, membrane integrity, apoptosis, and intracellular reactive oxygen species (ROS) generation are studied. In parallel, the degradation of GQDs using human myeloperoxidase and a peroxynitrite‐mediated system is investigated in test tube. Their degradation in macrophages is also pursued. High‐resolution transmission electron microscopy (HRTEM), fluorescence spectroscopy, Raman, and flow cytometry are used to confirm the degradation. Overall, both GQDs exert little activation on monocytes and macrophages although they decrease the metabolic viability in a dose‐dependent manner. The loss of native GQD structure and crystal lattice provide evidence of their biodegradability. Both the safety and biodegradability of S‐GQDs and N‐GQDs ensure their potential in biomedical applications.

Influence of Lattice Defects on Trans-Oligoene Substructure Formation in Graphene.

The photochemical reaction of iodine and graphene induces strong new Raman modes due to the formation of trans-oligoene substructures in graphene domains. This unique reactivity was demonstrated before on defect-free graphene, however leaving the influence of e. g. carbon vacancies, unexplored. Here, we investigate the photochemical reaction applied on graphene with varying average distances of lattice defects and statistically analyze the characteristic Raman modes which develop with the iodination reaction. We show that the iodination reaction does not lead to Raman-active defects and thus, the newly formed trans-oligoene substructures do not contribute to the D-mode of graphene. A statistical analysis reveals the correlation between the average distance of lattice defects and the intensity of the v1-mode. For defective graphene with average defect distances below ~1 nm no new Raman modes evolve, which is the lower limit of the substructure size probed at 532 nm and explains why this observation was not possible before using common graphene oxide as graphene source.

Characterization of heterogeneity of CVD graphene on copper foil by scanning probe microscopy and Raman spectroscopy

The comparative analysis of the structural, morphological, and local electrical properties of CVD graphene films synthesized at atmospheric and low pressure CVD growth conditions was carried out. The use of electrical techniques of scanning probe microscopy, such as Kelvin probe force microscopy, scanning capacitance microscopy, electrostatic force microscopy, and conductive atomic-force microscopy for investigation of heterogeneous graphene coverage was discussed. A significant change in the surface potential values was observed indicating the formation of p-type multilayered graphene domains on single layer graphene at low pressure and n-type multilayered graphene films at atmospheric pressure CVD. The effect of Ar flow rate increasing during cooling stage in the temperature range of 700–200 °C causing graphite formation was described. The employment of surface potential spectroscopy allows to indicate the presence of nonlinear phenomena in heterogeneous graphene.

Metastable 2D amorphous Nb2O5 for aqueous supercapacitor energy storage

Nb2O5 is a promising electrode material of energy storage due to its high specific capacity and phase transition resistance. However, the facile generation of niobic acid poses a challenge, hindering controlled growth and impeding improvements in electrical conductivity and structural stability, especially in realizing two-dimensional (2D) Nb2O5. Herein, we have discerned that the addition of hexamethylenetetramine (HMTA) in ethanol solvent facilitates the controlled and restricted growth of metastable 2D amorphous Nb2O5 (a-Nb2O5) within graphene domains. Nitrogen atoms within HMTA, rich in lone pair electrons, strongly interact with niobium ions, promoting 2D amorphous growth on graphene interface. This unique 2D amorphous interface offers high surface area, enhanced electron mobility, rapid ion transport, and superior structural stability compared to crystalline counterparts. The prepared metastable 2D a-Nb2O5/rGO electrode exhibits unprecedented cycle life in aqueous asymmetric supercapacitor. This confined growth strategy offers a novel approach for the innovative design of metastable 2D materials.

Graphene films grown by chemical vapor deposition and their applications

In this article we provide the results of the synthesis of graphene films and discuss their potential applications in electronic structures. Graphene films were synthesized on copper foil using the CVD method at 1050 °C. During the initial stage of synthesis, graphene domains with hexagonal shapes and an average size of 10 μm were formed. The orientation and size of the graphene domains are based on the synthesis parameters and the copper foil. As the synthesis time increases, domain cross-linking occurs, resulting in polycrystalline continuous graphene film formation. Graphene films have areas up to 100 cm2 and thicknesses ~ 1 nm to 5 nm. To measure the Raman spectra, graphene films were transferred to SiO2/Si substrates. Graphene films exhibit an intense 2D peak that significantly exceeds the G peak of crystalline graphite. Flexible transparent conductive touch panels were created on the basis of the grown graphene films. A lamination method has been used to create graphene films that can be transferred from copper foil to polymer substrates. A laboratory touch screen with a graphene film acting as a capacitive touch sensor was constructed on the basis of the transferred film, and transparent electrodes for molybdenum disulfide-based photosensitive elements were also created. Resistive humidity sensors based on graphene films were developed and transferred to SiO2/Si and epoxy/Si substrates. The graphene humidity sensor has a low response, high temperature stability, and is highly reliable.

Micropatterned Strain Domain in Graphene on Cu Substrates: Correlation with Facet Structures

Metallic catalysts have emerged as prominent materials for graphene growth because the choice of the substrate significantly influences the properties of graphene. Among metallic catalysts, Cu is a highly promising catalytic substrate because it facilitates the growth of monolayer graphene. However, the growth process often induces strain and structural deformations that affect the electronic properties and device performance of graphene. In this study, we present the first observation of micropatterned strain domains in graphene grown on Cu substrates using chemical vapor deposition. Distinct strain‐induced shifts and broadening in the Raman peaks by employing Raman spectroscopy and atomic force microscopy are revealed, demonstrating the unique structural characteristics within the patterned domains. Furthermore, a strong correlation between the strain patterns in graphene and the facet structures of the underlying Cu surface is established. Our findings reveal intriguing variations in strain within the patterned domains and along the line boundaries, offering valuable insights into the intricate interactions between graphene and the Cu surface. These observed strain patterns and their spatial correlations with the Cu facet structures provide crucial guidance for designing graphene‐based devices with tailored strain engineering.

Visualizing the Local Twist Angle Variation within and between Domains of Twisted Bilayer Graphene

Moiré superlattices in twisted two-dimensional materials have emerged as ideal platforms for engineering quantum phenomena, which are highly sensitive to twist angles, including both the global value and the spatial inhomogeneity. However, only a few methods provide spatial-resolved information for characterizing local twist angle distribution. Here we directly visualize the variations of local twist angles and angle-dependent evolutions of the quantum states in twisted bilayer graphene by scanning microwave impedance microscopy (sMIM). Spatially resolved sMIM measurements reveal a pronounced alteration in the local twist angle, approximately 0.3° over several micrometers in some cases. The variation occurs not only when crossing domain boundaries but also occasionally within individual domains. Additionally, the full-filling density of the flat band experiences a change of over 2 × 1011 cm−2 when crossing domain boundaries, aligning consistently with the twist angle inhomogeneity. Moreover, the correlated Chern insulators undergo variations in accordance with the twist angle, gradually weakening and eventually disappearing as the deviation from the magic angle increases. Our findings signify the crucial role of twist angles in shaping the distribution and existence of quantum states, establishing a foundational cornerstone for advancing the study of twisted two-dimensional materials.

Centimeter-sized diamond composites with high electrical conductivity and hardness

Achieving high-performance materials with superior mechanical properties and electrical conductivity, especially in large-sized bulk forms, has always been the goal. However, it remains a grand challenge due to the inherent trade-off between these properties. Herein, by employing nanodiamonds as precursors, centimeter-sized diamond/graphene composites were synthesized under moderate pressure and temperature conditions (12 GPa and 1,300 to 1,500 °C), and the composites consisted of ultrafine diamond grains and few-layer graphene domains interconnected through covalently bonded interfaces. The composites exhibit a remarkable electrical conductivity of 2.0 × 104 S m-1 at room temperature, a Vickers hardness of up to ~55.8 GPa, and a toughness of 10.8 to 19.8 MPa m1/2. Theoretical calculations indicate that the transformation energy barrier for the graphitization of diamond surface is lower than that for diamond growth directly from conventional sp2 carbon materials, allowing the synthesis of such diamond composites under mild conditions. The above results pave the way for realizing large-sized diamond-based materials with ultrahigh electrical conductivity and superior mechanical properties simultaneously under moderate synthesis conditions, which will facilitate their large-scale applications in a variety of fields.

Suppression of Nucleation Density in Twisted Graphene Domains Grown on Graphene/SiC Template by Sequential Thermal Process

Suppression of Nucleation Density in Twisted Graphene Domains Grown on Graphene/SiC Template by Sequential Thermal Process

Controlled Growth of Single-Crystal Graphene Wafers on Twin-Boundary-Free Cu(111) Substrates.

Single-crystal graphene (SCG) wafers are needed to enable mass-electronics and optoelectronics owing to their excellent properties and compatibility with silicon-based technology. Controlled synthesis of high-quality SCG wafers can be done exploiting single-crystal Cu(111) substrates as epitaxial growth substrates recently. However, current Cu(111) films prepared by magnetron sputtering on single-crystal sapphire wafers still suffer from in-plane twin boundaries, which degrade the SCG chemical vapor deposition. Here, it is shown how to eliminate twin boundaries on Cu and achieve 4 in. Cu(111) wafers with ≈95% crystallinity. The introduction of a temperature gradient on Cu films with designed texture during annealing drives abnormal grain growth across the whole Cu wafer. In-plane twin boundaries are eliminated via migration of out-of-plane grain boundaries. SCG wafers grown on the resulting single-crystal Cu(111) substrates exhibit improved crystallinity with >97% aligned graphene domains. As-synthesized SCG wafers exhibit an average carrier mobility up to 7284 cm2 V-1 s-1 at room temperature from 103 devices and a uniform sheet resistance with only 5% deviation in 4 in. region.

Assessing the quality of large-area monolayer graphene grown on liquid copper for size-selective ionic/molecular membrane separations

Monolayer graphene growth on liquid copper (Cu) has attracted attention due to advantages of a flat/smooth catalytic growth surface, high synthesis temperature (>1080 °C) as well as the possibility of forming graphene domains that are mobile on the liquid Cu with potential to minimize grain boundary defects and self-assemble into a continuous monolayer film. However, the quality of monolayer graphene grown on liquid copper and its suitability for size-selective ionic/molecular membrane separations has not been evaluated/studied. Here, we probe the quality of monolayer graphene grown on liquid Cu (via a metallurgical process, HSMG®) using Scanning Electron Microscope (SEM), High-resolution transmission electron microscope (HR-TEM), Raman spectroscopy and report on a facile approach to assess intrinsic sub-nanometer to nanometer-scale defects over centimeter-scale areas. We demonstrate high transfer yields of monolayer graphene (>93% coverage) from the growth substrate to polyimide track etched membrane (PITEM, pore diameter ∼200 nm) supports to form centimeter-scale atomically thin membranes. Next, we use pressure-driven transport of ethanol to probe defects > 60 nm and diffusion-driven transport of analytes (KCl ∼0.66 nm, L-Tryptophan ∼0.7–0.9 nm, Vitamin B12 ∼1–1.5 nm and Lysozyme ∼3.8–4 nm) to probe nanoscale and sub-nanometer scale defects. Diffusive transport confirms the presence of intrinsic sub-nanometer to nanometer scale defects in monolayer graphene grown on liquid Cu are no less than that in high-quality graphene synthesized via chemical vapor deposition (CVD) on solid Cu. Our work not only benchmarks quality of graphene grown on liquid copper for membrane applications but also provides fundamental insights into the origin of intrinsic defects in large-area graphene synthesized via bottom-up processes for membrane applications.

Неотерический взгляд на sp2 аморфный углерод

Presented is a concentrated synopsis of facilities of empirical and virtual analytics that, once applied, have provided a fully new vision of sp2 amorphous carbons. This study proved that the solids are multilevel structures, started with the first-level basic structural units (BSUs) and accomplished as macroscopic agglomerates of globular structures, consisting, in its turn, of stacked BSUs. BSUs present necklaced graphene molecules, size, and shape of which are governed by the relevant graphene domains while chemical composition in addition to basic carbon is controlled with heteroatoms of the necklaces. This study shows that BSUs and stacks of BSUs determine the short-range order of the solids and are the main subject of the applied analytics. The synopsis consists of two parts related to empirical and virtual analytics. The former is composed of sections related to structural determination, total and atomic chemical content evaluation and elicitation of the covalent bond composition. The second presents new analytic approaches based on the Digital Twins concept and virtual vibrational spectrometry. The synopsis is configured as an atlas composed of generalized pictures accompanied with necessary explanations to be discussed in detail in the extended references.

Controllable Synthesis and Growth Mechanism of Interlayer-Coupled Multilayer Graphene.

The potential applications of multilayer graphene in many fields, such as superconductivity and thermal conductivity, continue to emerge. However, there are still many problems in the growth mechanism of multilayer graphene. In this paper, a simple control strategy for the preparation of interlayer-coupled multilayer graphene on a liquid Cu substrate was developed. By adjusting the flow rate of a carrier gas in the CVD system, the effect for finely controlling the carbon source supply was achieved. Therefore, the carbon could diffuse from the edge of the single-layer graphene to underneath the layer of graphene and then interlayer-coupled multilayer graphene with different shapes were prepared. Through a variety of characterization methods, it was determined that the stacked mode of interlayer-coupled multilayer graphene conformed to AB-stacking structure. The small multilayer graphene domains stacked under single-layer graphene was first found, and the growth process and growth mechanism of interlayer-coupled multilayer graphene with winged and umbrella shapes were studied, respectively. This study reveals the growth mechanism of multilayer graphene grown by using a carbon source through edge diffusion, paving the way for the controllable preparation of multilayer graphene on a liquid Cu surface.

Surface-Enhanced Raman Spectroscopy (SERS) Investigation of a 3D Plasmonic Architecture Utilizing Ag Nanoparticles-Embedded Functionalized Carbon Nanowall.

Surface-enhanced Raman scattering (SERS) is a highly sensitive technique for detecting DNA, proteins, and single molecules. The design of SERS substrates plays a crucial role, with the density of hotspots being a key factor in enhancing Raman spectra. In this study, we employed carbon nanowall (CNW) as the nanostructure and embedded plasmonic nanoparticles (PNPs) to increase hotspot density, resulting in robust Raman signals. To enhance the CNW's performance, we functionalized it via oxygen plasma and embedded silver nanoparticles (Ag NPs). The authors evaluated the substrate using rhodamine 6G (R6G) as a model target molecule, ranging in concentration from 10-6 M to 10-10 M for a 4 min exposure. Our analysis confirmed a proportional increase in Raman signal intensity with an increase in concentration. The CNW's large specific surface area and graphene domains provide dense hotspots and high charge mobility, respectively, contributing to both the electromagnetic mechanism (EM) and the chemical mechanism (CM) of SERS.

(Digital Presentation) Deconstructing Proton Transport through Atomically Thin Monolayer CVD Graphene Membranes

Selective proton (H+) permeation through the atomically thin lattice of graphene and other 2D materials offers new opportunities for energy conversion/storage and novel separations. Practical applications necessitate scalable synthesis via approaches such as chemical vapor deposition (CVD) that inevitably introduce sub-nanometer defects, grain boundaries and wrinkles, and understanding their influence on H+ transport and selectivity for large-area membranes is imperative but remains elusive. Using electrically driven transport of H+ and potassium ions (K+) we probe the influence of intrinsic sub-nanometer defects in monolayer CVD graphene across length-scales for the first time. At the micron scale, the areal H+ conductance of CVD graphene (∼4.5–6 mS cm−2) is comparable to that of mechanically exfoliated graphene indicating similarly high crystalline quality within a domain, albeit with K+ transport (∼1.7 mS cm−2). However, centimeter-scale Nafion|graphene|Nafion devices with several graphene domains show areal H+ conductance of ∼339 mS cm−2 and K+ conductance of ∼23.8 mS cm−2 (graphene conductance for H+ is ∼1735 mS cm−2 and for K+ it is ∼47.6 mS cm−2). Using a mathematical-transport-model and Nafion filled polycarbonate track etched supports, we systematically deconstruct the observed orders of magnitude increase in H+ conductance for centimeter-scale CVD graphene. The mitigation of defects (>1.6 nm), wrinkles and tears via interfacial polymerization results in a conductance of ∼1848 mS cm−2 for H+ and ∼75.3 mS cm−2 for K+ (H+/K+ selectivity of ∼24.5) via intrinsic sub-nanometer proton selective defects in CVD graphene. We demonstrate atomically thin membranes with significantly higher ionic selectivity than state-of-the-art proton exchange membranes while maintaining comparable H+ conductance. Our work provides a new framework to assess H+ conductance and selectivity of large-area 2D membranes and highlights the role of intrinsic sub-nanometer proton selective defects for practical applications.