Morphology Of Graphene Research Articles

Unrecovered ion-irradiated damage after thermal annealing in graphene field effect transistors

Irradiation effects in graphene-based devices are crucial for applications of carbon-based devices utilized in aerospace and other radiation harsh environments. In this work, the deteriorated electrical properties of graphene field effect transistors (GFETs) induced by swift heavy ions (SHIs, 1.8 GeV Ta) and evolution of the defects in device materials after irradiation and thermal annealing have been investigated. The SHIs induced defects in graphene result in the increase of resistance and decrease in carrier mobilities. Thermal annealing at 110 °C could improve the carrier mobility at smaller scale that can be ascribed to the degassing effect. The defects in graphene were unrepairable after annealing at 110 °C. At higher temperature (e.g., 500 °C), the graphene structure was further damaged as a result of the compressive strain induced by thermal contraction of the SiO2 layer. The evolutions of graphene and SiO2 surface morphologies with increasing annealing temperature were studied by Atomic Force Microscopy investigations. After irradiation, the weakened lattice structure order of the Si layer and change of the SiO2/Si interface morphology were confirmed. It was also shown that the damage in SiO2/Si interface did not recover even after the high temperature (e.g., 1100 °C) annealing.

Guiding Graphene Derivatization for the On‐Chip Multisensor Arrays: From the Synthesis to the Theoretical Background

AbstractEngineering the physics and chemistry of 2D materials is a key to unlock the potential of the advanced e‐nose technologies limited by the current semiconductor technologies. Herein, the adjustment of the graphene's morphology, physics, and gas sensing properties upon its carboxylation via the developed photochemical method is demonstrated. Formation of matrices of nanoscale holes yet with the retention of the lamellar structure of the graphene layer is signified upon the introduction of up to 9.5 at% of carboxyl groups. The impact of the applied carboxylation on the conduction mechanism and electronic structure is demonstrated. The appearance of a set of the localized states in the valence band is revealed, originating from the molecular orbitals of carboxyls as is signified by the proposed approach for the identification of electronic states in graphene chemical derivatives. Given holey structure, predominance of highly affine carboxyls, and lateral inhomogeneity, the enhanced detection and discrimination of various alcohols, acetone, and ammonia vapors at room temperature is demonstrated. The opposite chemiresistive response toward ammonia in the humid air is also experimentally revealed and justified by the performed density functional theory modeling on the effect of ammonia, water, and their mix on electronic structure, and resistivity of the carboxylated graphene.

Morphology-Controllable Graphene-Modified Cu-Benzene-1,3,5 Tricarboxylic Acid Composites for Volatile Organic Compounds and CO2 Adsorption Property

Volatile organic compounds (VOCs) are the one kind of pollution, which lead to the severe atmospheric contamination problem. Metal organic frameworks (MOFs) and graphene are promising candidates to collect VOCs. In this study, composites which consist of graphene sheets and Cu-BTC (benzene-1,3,5 tricarboxylic acid) are prepared by the hydrothermal method to adsorb VOCs and CO. Moreover, the morphology of the resulting graphene material in the composites can be controlled by adjusting the pH value, reaction time and surfactant during the hydrothermal process, which further determines the adsorption ability for different gas molecules. According to the pore distribution features of various composites, the morphology of graphene exerts a fatal influence on the observed adsorption performances. Furthermore, the polarity of the as-prepared composites is another important determinant to selective adsorption for various VOCs. The stability of these composites under high temperature is also tested, and the results demonstrate that the adsorbents can be used in a wide temperature range. Moreover, the large BET areas and high stability of the composites in the water endow them a potential application in the sewage clarification field. After the corresponding optimization, the adsorption amounts of methanol and ethanol reach 13.6[Formula: see text]mmol[Formula: see text]g[Formula: see text] and 9.68[Formula: see text]mmol[Formula: see text]g[Formula: see text], respectively.

Morphology and electrical properties of high-speed flexography-printed graphene.

Printed graphene electrodes have been demonstrated as a versatile platform for electrochemical sensing, with numerous examples of rapid sensor prototyping using laboratory-scale printing techniques such as inkjet and aerosol jet printing. To leverage these materials in a scalable production framework, higher-throughput printing methods are required with complementary advances in ink formulation. Flexography printing couples the attractive benefits of liquid-phase graphene printing with large-scale manufacturing. Here, we investigate graphene flexography for the fabrication of electrodes by analyzing the impacts of ink and process parameters on print quality and electrical properties. Characterization of the printed patterns reveals anisotropic structure due to striations along the print direction, which is related to viscous fingering of the ink. However, high-resolution imaging reveals a dense graphene network even in regions of sparse coverage, contributing to robust electrical properties even for the thinnest films (< 100nm). Moreover, the mechanical and environmental sensitivity of the printed electrodes is characterized, with particular focus on atmospheric response and thermal hysteresis. Overall, this work reveals the conditions under which graphene inks can be employed for high-speed flexographic printing, which will facilitate the development of graphene-based sensors and related devices.

Spiral Growth of Adlayer Graphene.

The morphology of as-grown graphene in chemical vapor deposition (CVD) experiments is sensitive to the reaction environment. Understanding the mechanism of formation of different graphene morphologies is essential to achieve controlled graphene CVD growth. Here the growth and formation mechanism of adlayer graphene spirals are reported. An adlayer graphene spiral is formed by fast propagation of the tips of spiral arms along the edge of the first graphene layer. The driving force to form spirals is the limited availability of carbon diffusing from the Cu surface through the edge of the first graphene layer. In addition, it is found that graphene onions are formed by overlapping graphene spirals with clockwise and anticlockwise arms. Based on these features, a kinetic Monte Carlo (kMC) method is demonstrated using which all the observed graphene spiral structures are successfully reproduced at the atomic level. This study thus unravels the hither-to unresolved mechanism of graphene onion growth and paves the way to the controllable growth of few-layer graphene by increasing the carbon supply at the edge of the first layer graphene.

Atomic Structure Modification of Fe‒N‒C Catalysts via Morphology Engineering of Graphene for Enhanced Conversion Kinetics of Lithium–Sulfur Batteries

AbstractSingle‐atom M‒N‒C catalysts have attracted tremendous attention for their application to electrocatalysis. Nitrogen‐coordinated mononuclear metal moieties (MNx moities) are bio‐inspired active sites that are analogous to various metal‐porphyrin cofactors. Given that the functions of metal‐porphyrin cofactors are highly dependent on the local coordination environments around the mononuclear active site, engineering MNx active sites in heterogeneous M‒N‒C catalysts would provide an additional degree of freedom for boosting their electrocatalytic activity. This work presents a local coordination structure modification of FeN4 moieties via morphological engineering of graphene support. Introducing highly wrinkled structure in graphene matrix induces nonplanar distortion of FeN4 moieties, resulting in the modification of electronic structure of mononuclear Fe. Electrochemical analysis combined with first‐principles calculations reveal that enhanced electrocatalytic lithium polysulfide conversion, especially the Li2S redox step, is attributed to the local structure modified FeN4 active sites, while increased specific surface area also contributes to improved performance at low C‐rates. Owing to the synergistic combination of atomic‐level modified FeN4 active sites and morphological advantage of graphene support, Fe‒N‒C catalysts with wrinkled graphene morphology show superior lithium–sulfur battery performance at both low and high C‐rates (particularly 915.9 mAh g−1 at 5 C) with promising cycling stability.

Symmetric Supercapacitor Application of Electrochemically Exfoliated Graphene – Chitosan Hydrogel

In this work, electrochemically exfoliated graphene–chitosan hydrogel was prepared by a crosslinking reagent. Then, a symmetrical all-solid state supercapacitor was fabricated using graphene–chitosan hydrogel. Surface morphology of as-fabricated graphene was investigated using SEM and TEM. After constructing the symmetrical all-solid state supercapacitor, the device showed a specific capacitance (Cm) of 153.6 Fg-1 at 1 mAg-1 current density. A great capacitance retention after 1000 consecutive GCD cycles was observed with an over 97% of retention. The supercapacitor can carry a high energy density of 3.47 kWkg-1, as well as a high power density of 102.07 Wkg-1.

Insights into the lanthanum doping large-size graphene oxide effect on the polymer composites

Despite the significant progress made in polymer/graphene nanocomposites, the development of high-performance polymer/graphene nanocomposites, combined with excellent mechanical and electromagnetic shielding properties, remains a priority and a challenge. The lanthanum doping large-size graphene oxide (La-LsG) was obtained via static oxidation and thermal treatment. The effects of static oxidation and lanthanum doping on the property and morphologies of graphene and composites were investigated. The physicochemical property of considerable graphene oxide (GO), large-size graphene oxide (LsGO), lanthanum-doped graphene oxide (La-GO), La-LsG was analyzed by transmission electron microscopy (TEM), scanning electron microscopy (SEM), Raman spectroscopy, and X-ray energy spectroscopy (EDS). SEM and EDS characterized the microstructure of the composite material, and the mechanical properties and electromagnetic shielding performance of the composite material were studied. La-GO and La-LsG exhibited good dispersion and structural integrity, as well as enhancing the strength of the composites. The La-LsG/poly (methyl methacrylate) (PMMA) composites exhibited excellent mechanical properties (is ca. 73.6 MPa) and electromagnetic shielding effectiveness (is ca. 28 dB) in X-band frequencies (8.2–12.4 GHz), which may be assumed to be a promising integrated material of structure and function.

Investigation of the Morphology and Electrical Properties of Graphene Used in the Development of Biosensors for Detection of Influenza Viruses.

In this study, we discuss the mechanisms behind changes in the conductivity, low-frequency noise, and surface morphology of biosensor chips based on graphene films on SiC substrates during the main stages of the creation of biosensors for detecting influenza viruses. The formation of phenylamine groups and a change in graphene nano-arrangement during functionalization causes an increase in defectiveness and conductivity. Functionalization leads to the formation of large hexagonal honeycomb-like defects up to 500 nm, the concentration of which is affected by the number of bilayer or multilayer inclusions in graphene. The chips fabricated allowed us to detect the influenza viruses in a concentration range of 10−16 g/mL to 10−10 g/mL in PBS (phosphate buffered saline). Atomic force microscopy (AFM) and scanning electron microscopy (SEM) revealed that these defects are responsible for the inhomogeneous aggregation of antibodies and influenza viruses over the functionalized graphene surface. Non-uniform aggregation is responsible for a weak non-linear logarithmic dependence of the biosensor response versus the virus concentration in PBS. This feature of graphene nano-arrangement affects the reliability of detection of extremely low virus concentrations at the early stages of disease.

Phenomenological description of the thermal reduction kinetics in graphene oxide films

This study introduces a straightforward and cost-effective route to elaborate a thermally reduced graphene oxide film (R-GOF) at 350 °C under ambient atmosphere, followed by the investigation of the kinetic triplet of the related thermal reduction mechanism by a model-free approach. The structural, the morphological, and the electrical properties of the as-prepared films are scrutinized via a series of characterization techniques. The results demonstrate the successful reduction of the graphene oxide film (GOF), leading to a prominent electrical conductivity (3275 S m−1). Moreover, a model-free approach is applied to a differential scanning calorimetry (DSC) data to evaluate the kinetic triplet of the reduction mechanism. The activation energy (Ea) is assessed according to the most accurate isoconversional methods including Friedman (FRI), Vyazovkin (VYA), convincingly suggesting that the thermal reduction process of GOF can be treated as a one step process, giving values of 88 ± 8 and 79 ± 6 kJ mol−1, respectively. The pre-exponential factor and the kinetic model of the reaction are determined by the combination of isoconversional model with a compensation effect. Conclusively, the estimated activation energy values indicate that the graphene oxide structure, morphology and reduction conditions are the main factors to be considered when modeling and predicting its thermal reduction mechanism.

Effects of the Heating-up Atmosphere on the Nucleation of Graphene on Copper Foils

Heated up in H2 and N2 respectively at the heating-up stage, the copper foils were used as the substrates to fabricate graphene by low pressure chemical vapor deposition. The fabricated graphene presented different characteristics. Heated up in H2, on the substrate appeared polycrystalline films with small domains of poor quality; while in N2, the size of the graphene domain was up to 500 μm with good quality. The results indicated that the heating-up atmosphere caused the differences in graphene morphology by changing the surface microstructure of the substrate. In N2, the copper surface tended to become smoother, leading to difficult nucleation; while in H2, plenty of terraced steps appeared on the surface of the substrate, providing much more favorable sites for active carbon atoms to cluster and nucleate.

Chemical Vapor Deposition Mechanism of Graphene-Encapsulated Au Nanoparticle Heterostructures and Their Plasmonics.

Direct encapsulation of graphene shells on noble metal nanoparticles via chemical vapor deposition (CVD) has been recently reported as a unique way to design and fabricate new plasmonic heterostructures. But currently, the fundamental nature of the growth mechanism of graphene layers on metal nanostructures is still unknown. Herein, we report a systematic investigation on the CVD growth of graphene-encapsulated Au nanoparticles (Au@G) by combining an experimental parameter study and theoretical modeling. We studied the effect of growth temperature, duration, hydrocarbon precursor concentration, and extent of reducing (H2) environment on the morphology of the products. In addition, the influence of plasma oxidation conditions for the surface oxidation of gold nanoparticles on the graphene shell growth is evaluated in combination with thermodynamic calculations. We find that these parameters critically aid in the evolution of graphene shells around gold nanoparticles and allow for controlling shell thickness, graphene shell quality and morphology, and hybrid nanoparticle diameter. An optimized condition including the growth temperature of ∼675 °C, duration of 30 min, and xylene feed rate of ∼10 mL/h with 10% H2/Ar carrier gas was finally obtained for the best morphology evolution. We further performed finite-element analysis (FEA) simulations to understand the equivalent von Mises stress distribution and discrete dipolar approximation (DDA) calculation to reveal the optical properties of such new core-shell heterostructures. This study brings new insight to the nature of CVD mechanism of Au@G and might help guiding their controlled growth and future design and application in plasmonic applications.

Density functional theory study of adsorption and diffusion of potassium atoms on zigzag graphene nanoribbons with different terminal groups

Despite the extensive use of graphene-based materials in K-ion batteries, the effects of various edge morphologies of graphene on K atom adsorption and diffusion are unclear. In this study, the effects of K atom adsorption and diffusion on zigzag graphene nanoribbons (ZGNRs) with hydrogen (−H), ketone (=O), hydroxyl (−OH), and carboxyl (−COOH) terminal groups were investigated by density functional theory calculations. ZGNRs terminating with −H, =O and −COOH promote K atom adsorption, whereas those terminating with −OH suppress it. The −H, =O, −OH and −COOH terminations have a negligible effect on K atom diffusion in the inner region of ZGNRs. In the edge region, the diffusion barriers are nearly unchanged for −H and −OH terminations; however, they are increased for =O and −COOH terminations in the edge region compared to those in the inner region. All the terminal groups hinder K atom diffusion from the edge region toward the inner region. Our results suggest that −H termination enhances K atom adsorption and has a negligible effect on the diffusion barrier of K atom in the edge region. Therefore, the ZGNR with −H termination could be a promising candidate for K-ion batteries.

A novel synthesis of three-dimensional graphene by carburization and powder metallurgy from nickel nanoparticles

The unique structure and excellent performance of three-dimensional graphene make it widely applicable in various fields like electronics, catalytic electrodes and sensors. However, it remains a challenge to produce low-cost, large-size and shape-controllable three-dimensional graphene. It is thus proposed in this study to prepare three-dimensional graphene by carburizing and powder metallurgy with triethylene glycol as the carbon source and nickel nanoparticles as a template. The morphology and microstructure of three-dimensional graphene were characterized by scanning electron microscopy, transmission electron microscopy, Raman spectroscopy and X-ray diffraction. The three-dimensional graphene consisting of multilayer graphene nanosheets is obtained that demonstrated not only large specific surface area but also high mechanical strength, which is conducive to increasing the area of contact with electrolyte and providing a conductive path for the active materials loaded on it. As a result, the electrochemical performance of supercapacitor can be improved effectively.

Green, fast and scalable preparation of few-layers graphene

Few-layers graphene is prepared by one-step liquid-phase exfoliation with carbon quantum dots (CQDs) as exfoliating agents, which is prepared by a novel electrochemical interface technology. The morphology, structure and composition of CQDs and graphene, as well as the mechanism for the realization of large-scale preparation of CQDs and graphene was proposed. The results showed that CQDs with D50 size of 55.12 nm has excellent dispersion and exfoliation properties for graphite, and the graphene yield is as high as 97.25% (D50 size of 3.651 μm and 1–5 layers). Further, we successfully prepared graphene film, which has high electrical conductivity (3100.45 S/cm) and thermal conductivity (950.31 W/(m·K)) after graphitization.

Strain control in graphene on GaN nanowires: Towards pseudomagnetic field engineering

Gallium nitride nanowire and nanorod substrates are prospective platforms allowing to control the local strain distribution in graphene films on top of them, resulting in an induction of pseudomagnetic fields. AFM measurements performed in a HybriD mode complemented by SEM allow for a detailed visualization of the strain distribution on graphene surface. Graphene in direct contact with supporting regions is tensile strained, while graphene located in-between is characterized by lower strain. Characteristic tensile strained wrinkles also appear in the areas between the supporting regions. A positive correlation between strain gradient and distances between borders of supporting regions is observed. These results are confirmed by analysis of the Raman D’ band intensity, which is affected by an enhancement of intravalley scattering. Furthermore, scanning tunneling spectroscopy shows a local modification of the density of states near the graphene wrinkle and weak localization measurements indicate the enhancement of pseudomagnetic field-induced scattering. Therefore, we show that nanowire and nanorod substrates provide strain engineering and induction of pseudomagnetic fields in graphene. The control of graphene morphology by modification of distances between supporting regions is promising for both further fundamental research and the exploration of innovative ways to fabricate pseudomagnetic field-based devices like sensors or filters.

Defect-Dependent Corrugation in Graphene.

Graphene's intrinsically corrugated and wrinkled topology fundamentally influences its electronic, mechanical, and chemical properties. Experimental techniques allow the manipulation of pristine graphene and the controlled production of defects which allows one to control the atomic out-of-plane fluctuations and thus tune graphene's properties. Here, we perform large scale machine learning-driven molecular dynamics simulations to understand the impact of defects on the structure of graphene. We find that defects cause significantly higher corrugation leading to a strongly wrinkled surface. The magnitude of this structural transformation strongly depends on the defect concentration and specific type of defect. Analyzing the atomic neighborhood of the defects reveals that the extent of these morphological changes depends on the preferred geometrical orientation and the interactions between defects. While our work highlights that defects can strongly affect graphene's morphology, it also emphasizes the differences between distinct types by linking the global structure to the local environment of the defects.

Tailoring the graphene oxide chemical structure and morphology as a key to polypropylene nanocomposite performance

AbstractIn this work, we designed and studied two synthetic routes, based on modified Hummers method, to obtain graphene oxide (GO), and investigated their influence on the performance of polypropylene (PP)/GO nanocomposites. The two synthetic routes differed in the application condition of the oxidizing agent, potassium permanganate (KMnO4), which was added either as a powder (GO‐P) or as a water solution (GO‐S). This apparently subtle synthetic change yielded GOs with different degrees of oxidation and particle sizes, where GO‐P presented a higher oxidation degree and smaller particles. The different GOs were then melt‐blended with PP and the correlation between their different chemical/morphological structures and the nanocomposites' thermomechanical/rheological properties were evaluated. The milder oxidation process suffered by GO‐S, and consequent less hydrophilic character, yielded a PP/GO‐S nanocomposite with improved performance as the consequence of a better matrix/filler chemical affinity, mainly in compositions with lower GO‐S contents. The thermal stability was increased by more than 10°C when 0.1 wt% GO‐S was inserted into PP. When compared to the composition with 0.1 wt% GO‐P, the increase was 13°C. Reinforcing effects were also observed in that sample (with 0.1 wt% GO‐S), which exhibited the highest storage modulus and complex viscosity. These results suggest that tailoring the GO's oxidation degree and morphology is a key point to obtain an ideal interfacial interaction between phases.

Enhanced bifunctional catalytic activities of N-doped graphene by Ni in a 3D trimodal nanoporous nanotubular network and its ultralong cycling performance in Zn-air batteries

Free-standing and flexible air electrodes with long-lasting bifunctional activities for both the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) are crucial to the development of wearable Zn-air rechargeable batteries. In this work, we synthesize a flexible air electrode consisting of 3D nanoporous N-doped graphene with trimodal shells and Ni particles through repeated chemical vapor deposition (CVD) and acidic etching processes. Our results indicate that such trimodal graphene morphology significantly enhances the active N-dopant sites and graphene-coated Ni surface, which consequentially boosts both the ORR and OER activities, as well as catalytic durability. First-principles density functional theory (DFT) calculations reveal the synergetic effects between the Ni and the N-doped graphene; namely, the Ni nanoparticles boost the bifunctional activities of the coated N-doped graphene, and in turn the graphene-covering layers enhance the stability of Ni. Thanks to the better protection from the triple graphene shells, our trimodal N-doped graphene/Ni-based Zn-air battery can be stably discharged/recharged beyond 2500 h with low overpotentials. It is reasonable to expect that such free-standing trimodal graphene/Ni would be promising in many flexible energy conversion/storage devices.

Tuning Mechanical and Electrical Properties of Elastomer Composites with Hybrid Filler Network Containing Graphene for Stretchable Strain Sensors

Conductive elastomer composites (CECs) with segregated filler networks display a combination of good mechanical properties and electrical conductivity, enabling potential applications in flexible and stretchable electronics. However, it is challenging to achieve high strain sensitivity and to retain good elasticity. Here, hybrid fillers of carbon nanostructures (CNS, also known as branched carbon nanotubes) and graphene are used to achieve high strain sensitivity of thermoplastic polyurethane (TPU)‐based CECs without decreasing elasticity and electrical conductivity. By changing the graphene type, namely, single layer graphene nanosheet (GNS) and graphene nanoplatelets (GNP), mechanical properties and strain–sensing performances of the CECs can be modulated effectively at proper hybrid filler compositions. Due to the effect of graphene morphology, the TPU/CNS–GNP system has higher strain sensitivity by comparison with the TPU/CNS–GNS system. These CECs demonstrate potential applications as flexible/wearable electronics in body joint bending and flexible switches and resistors for current regulation.