Chemical Properties Of Graphene Research Articles

Smoothing effects of two-dimensional materials

Rippling in graphene, which is an out-of-plane corrugation induced by thermal fluctuations, plays a fundamental role in supporting the material’s stable existence. These ripples have also been instrumental in explaining various unconventional electronic and chemical properties of graphene. Previous experimental findings have indicated that graphene exhibits smoothing effects on underlying substrates in the high-spatial-frequency regime. To explain this phenomenon, we employed a force balance model that considered both van der Waals forces and strain forces. By utilizing traditional film-growth theory, our model successfully predicted experimental results.

A review of the types and properties of B and N co-doped graphene

This paper discusses the different types of B\N co-doped graphene, such as neighborhood, intercalation, para-doping on the carbon six-membered ring of monolayer graphene, and monolayer and stacked doping of h-BN with graphene. The structure and characterization of each type are examined. Additionally, the impacts of B\N co-doping on the optical properties, O2 adsorption, and chemical properties of graphene are explored. Finally, the future challenges in boron and nitrogen co-doped graphene research are outlined.

A-360 Reproducible Graphene Sensor with Desiccated Biology

Abstract Background Graphene, a two-dimensional material composed of carbon atoms, has garnered significant attention for its potential application in biosensors due to its unique electrical properties. Despite its promising attributes, however, the non-reproducible nature of graphene biosensors has hindered their widespread commercialization. This issue arises from the difficulty in obtaining a clean graphene layer due to: photoresist such as PMMA residues that effect the performance of graphene; etching process which affect the physical and chemical properties of graphene; variation in the coating of bio-receptors on to graphene. All these issues affect reliable and accurate sensor performance. These challenges have made it difficult for graphene biosensors to reach their full potential as commercial products and have limited their widespread adoption. Hememics has developed a unique process for synthesizing and fabricating graphene-based biosensors. This represents a major breakthrough in the commercialization of graphene-based biosensors and will likely lead to widespread adoption of these devices in the medical and biotechnology industries. Methods HemChip™ contains multiple sensor areas that are coated with ultra-sensitive graphene. Using Hememics’ unique proprietary process, the graphene layer is functionalized with bioreceptors such as aptamers and stabilized with HemSol™ to allow room temperature storage. The relative difficulty of stabilizing aptamers on a hydrophobic graphene substrate has been overcome by using HemSol™ to secure its structure during dry storage. Each sensor on the biochip allows independent functionalization with a bioreceptor. These sensors coated with bioreceptors are freeze-dried and stored in a sealed pouch at room temperature until use. Results We have tested over 2000 samples using our modified process. The functionality of the graphene-based biosensor is evaluated by measuring the distribution of Dirac points. The results show that the distribution follows a Gaussian distribution with a median of 80 mV and a very narrow spread of approximately 35 mV. This indicates that the majority of the Dirac points are tightly clustered around the median value of 80 mV. Furthermore, one standard deviation of the Dirac points fall within the range of 50 mV to 120 mV. In contrast, the standard published process of producing graphene-based biosensor shows a much wider distribution of Dirac points, ranging from 250–1500 mV. Conclusion Hememics has developed a production process for making graphene-based biosensors with desiccated detection biology that deliver repeatable performance data. The results of the Dirac point distribution demonstrate the high precision and accuracy for the functionalized biosensors. This combined with the ability to mass produce the biosensor, make graphene-based biosensors an attractive molecular and immuno-based detection tool. Additionally, the results suggest that the Hememics process can be adapted to produce functional graphene-based biosensors for wide ranging bio detection applications.

Prospects of Application and Global Significance of Graphene

The review article is an excursus into the world publications describing the properties of graphene, methods of synthesis of it and variety of its application fields. The paper describes in detail the structure of graphene as well as the methods for its fabrication: micromechanical cleavage, chemical stratification, epitaxial growth, and chemical gas-phase deposition, including their advantages and disadvantages. In addition, the review contains information on the electronic, mechanical, optical, and chemical properties of graphene, which lend its uniqueness. Due to its unique properties, graphene and its modified quasi-two-dimensional structures are the objects of increased scientific interest in various fields of science, such as energy, electronics, optoelectronics, medicine, bioengineering, aerospace, aviation, ecology, materials engineering, etc. In order to expand the journal readership among the physicists, chemists, and materials scientists, who are not deep specialists in graphene science, the style of the present review is somewhere close to popular science one.

Role of ripples in altering the electronic and chemical properties of graphene.

Ripples of graphene are known to manipulate electronic and hydrogenation properties of graphitic materials. More detailed work is needed to elucidate the structure-property relationship of these systems. In this work, the density functional theory is used to compute the energy and electronic structure of the graphene models with respect to variable curvatures and hydrogen adsorption sites. The magnitude of finite bandgap opening depends on the orientation of ripples, and the hydrogen adsorption energy depends on the local curvature of graphene. An adsorbed hydrogen alters the local curvature, resulting in relatively weakened adsorption on the neighboring three sites, which gives a rationale to experimentally observed dynamic equilibrium stoichiometry (H:C = 1:4) of hydrogenated graphene. The surface diffusion transition state energy of adsorbed hydrogen is computed, which suggests that the Eley-Rideal surface recombination mechanism may be important to establish the dynamic equilibrium, instead of the commonly assumed Langmuir-Hinshelwood mechanism.

Research Progress of Graphene Nano-Electromechanical Resonant Sensors-A Review.

Graphene nano-electromechanical resonant sensors have wide application in areas such as seawater desalination, new energy, biotechnology, and aerospace due to their small size, light weight, and high sensitivity and resolution. This review first introduces the physical and chemical properties of graphene and the research progress of four preparation processes of graphene. Next, the principle prototype of graphene resonators is analyzed, and three main methods for analyzing the vibration characteristics of a graphene resonant sheet are described: molecular structural mechanics, non-local elastic theory and molecular dynamics. Then, this paper reviews research on graphene resonator preparation, discussing the working mechanism and research status of the development of graphene resonant mass sensors, pressure sensors and inertial sensors. Finally, the difficulties in developing graphene nano-electromechanical resonant sensors are outlined and the future trend of these sensors is described.

Nitrogen-doped graphene as an efficient metal-free catalyst for ammonia and non-enzymatic glucose sensing

Theoretical studies reveal that the electronic and chemical properties of graphene can be significantly altered by chemical doping with a nitrogen atom. In the present work, a unique strategy has been applied for the manufacture of selective N-doped graphene (NG). A low cost, and facile one pot solvothermal approach has been adopted for the synthesis p-type nitrogen graphene. Moreover, the as-synthesized NG sheets exhibit a crossover from n-type to p-type behaviour. The presence of pyridinic-N in graphene planes is confirmed by high-resolution X-ray photoelectron spectroscopy. The as-synthesized NG presents excellent sensing properties towards ammonia, and fast electron transfer kinetics for glucose oxidase. The higher sensing activity is ascribed to synergistic effect of nitrogen, and oxygen-containing functional groups. The resultant NG is proven to act as a metal-free catalyst with much better performance for ammonia and glucose sensing at room temperature. This study will provide a promising potential for the development of NG type sensors in the real world and environmental applications.

Fluorinated graphene improving thermal reaction and combustion characteristics of nano-aluminum powder

Two-phase flow loss is an important factor to reduce the combustion performance of aluminum-based solid propellants, which can be decreased if aluminum particles burn more rapidly and produce more gaseous products to crack their agglomeration. To reduce aluminum agglomeration and improve the combustion performance, fluorine-containing organic substances (FCOS) is used as a modified material for aluminum powder. Fluorinated graphene (FG) is a promising FCOS with both the physical and chemical properties of graphene and polytetrafluoroethylene, so we studied the effects of FG on the combustion and agglomeration of nano-aluminum powder. Specifically, the ignition, combustion, and agglomeration characteristics of FG modified nano-aluminum with ammonium perchlorate were studied. Results show that FG can promote the decomposition of ammonium perchlorate. An appropriate amount of FG has a positive effect on the ignition delay time and flame propagation velocity of nano-aluminum powder. The increase of FG content can reduce the size of aluminum agglomerates. These results can be useful for the applications of FG in aluminum-based solid propellants.

Surface-enhanced Raman scattering effect in binary systems formed by graphene on aluminum plasmonic nanostructures

Binary systems (BS) formed by graphene (GR) deposited on top of aluminum (Al) nanoconcaves (Al-NC) and Al nanodomes (Al-ND) were synthesized by electrochemical anodization of Al. Using the plasmonic response of Al-NC and Al-ND and the distinctive physical and chemical properties of GR, these BS are proposed as Surface-Enhanced Raman Scattering (SERS) sensors using rhodamine 6G (R6G) as a proof molecule. As expected, the BS significantly enhances Raman signals of R6G molecules in comparison with substrates used as references, also suppressing the fluorescence background of R6G molecules.

Production of thin graphite films on a dielectric substrate by heteroepitaxial synthesis

Problem statement. Development of methods for producing large-area isolated graphene under controlled conditions is an important task, which is primarily interested in the unique physical and chemical properties of graphene: high electrical and thermal conductivity, dependence of electronic characteristics on the presence of attached different radicals on the graphene surface, adjustable band gap, and high carrier mobility. Goal. It is necessary to develop regimes for producing thin graphite films on a dielectric substrate by annealing the structure (0001)Al2O3/(111)Ni/ta-C with a minimum density of defects in the crystal structure by the heteroepitaxial synthesis method. Results. The method of obtaining thin graphite films on a dielectric substrate by annealing the structure (0001)Al2O3/(111)Ni/ta-C has been tested. The method is based on the catalytic decomposition of hydrocarbons on the single crystal surface of a metal catalyst, diffusion and crystallization of carbon on the reverse side of the metal film. The surface of the obtained carbon films with a thickness significantly exceeding one atomic layer is uniform within the 5x5 mm samples. Varying the annealing temperature and time, as well as the initial amount of carbon, will further allow to control the amount of carbon involved in the formation of atomic layers. Practical significance. The described method is promising for developing a scalable technological process for obtaining largearea graphene on a dielectric substrate.

Highly Effective Methods of Obtaining N-Doped Graphene by Gamma Irradiation.

The design and fabrication of a new effective manufacturing method of heteroatom-doped carbon materials is still ongoing. In this paper, we present alternative and facile methods to obtain N-rich graphene with the use of low energy gamma radiation. This method was used as a pure and facile method for altering the physical and chemical properties of graphene. The obtained materials have an exceptionally high N content—up to 4 wt %. (dry method) and up to 2 wt %. (wet method). High-resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectra and X-ray photoelectron spectroscopy (XPS) studies allowed us to evaluate the quality of the obtained materials. The presented results will provide new insights in designing and optimizing N-doped carbon materials potentially for the development of anode or cathode materials for electrochemical device applications, especially supercapacitors, metal–air batteries and fuel cells. Nitrogen atoms are exclusively bonded as quaternary groups. The method is expandable to the chemical insertion of other heteroatoms to graphene, especially such as sulfur, boron or phosphorus.

Effect of graphene grain boundaries on MoS2/graphene heterostructures**Project supported by the National Natural Science Foundation of China (Grant No. 11874423).

The grain boundaries of graphene are disordered topological defects, which would strongly affect the physical and chemical properties of graphene. In this paper, the spectral characteristics and photoresponse of MoS2/graphene heterostructures are studied. It is found that the blueshift of the G and 2D peaks of graphene in Raman spectrum is due to doping. The lattice mismatch at the graphene boundaries results in a blueshift of MoS2 features in the photoluminescence spectra, comparing to the MoS2 grown on SiO2. In addition, the photocurrent signal in MoS2/hexagonal single-crystal graphene heterostructures is successfully captured without bias, but not in MoS2/polycrystalline graphene heterostructures. The electron scattering at graphene grain boundaries affects the optical response of MoS2/graphene heterostructures. The photoresponse of the device is attributed to the optical absorption and response of MoS2 and the high carrier mobility of graphene. These findings offer a new approach to develop optoelectronic devices based on two-dimensional material heterostructures.

Figure of Merit Enhancement of Surface Plasmon Resonance Biosensor Using Ga-Doped Zinc Oxide in Near Infrared Range

This work presents a surface plasmon resonance biosensor for the figure of merit enhancement by using Ga-doped zinc oxide (GZO), i.e., nanostructured transparent conducting oxide as plasmonic material in place of metal at the telecommunication wavelength. Two-dimentional graphene is used here as a biorecognition element (BRE) layer for stable and robust adsorption of biomolecules. This is possible due to stronger van der Waals forces between graphene's hexagonal cells and carbon-like ring arrangement present in biomolecules. The proposed sensor shows improved biosensing due to fascinating electronic, optical, physical, and chemical properties of graphene. This work analyses the sensitivity, detection accuracy, and figure of merit for the GZO/graphene SPR sensor on using the dielectric layer in between the prism and GZO. The highest figure of merit of 366.7 RIU−1 is achieved for the proposed SPR biosensor on using the nanostructured GZO at the 3000 nm dielectric thickness. The proposed SPR biosensor can be used practically for sensing of larger size biomolecules with due availability of advanced techniques for the fabrication of the nanostructured GZO and graphene.

Electronic Structure of Nitrogen- and Phosphorus-Doped Graphenes Grown by Chemical Vapor Deposition Method.

Heteroatom doping is a widely used method for the modification of the electronic and chemical properties of graphene. A low-pressure chemical vapor deposition technique (CVD) is used here to grow pure, nitrogen-doped and phosphorous-doped few-layer graphene films from methane, acetonitrile and methane-phosphine mixture, respectively. The electronic structure of the films transferred onto SiO2/Si wafers by wet etching of copper substrates is studied by X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy using a synchrotron radiation source. Annealing in an ultra-high vacuum at ca. 773 K allows for the removal of impurities formed on the surface of films during the synthesis and transfer procedure and changes the chemical state of nitrogen in nitrogen-doped graphene. Core level XPS spectra detect a low n-type doping of graphene film when nitrogen or phosphorous atoms are incorporated in the lattice. The electrical sheet resistance increases in the order: graphene < P-graphene < N-graphene. This tendency is related to the density of defects evaluated from the ratio of intensities of Raman peaks, valence band XPS and NEXAFS spectroscopy data.

Electrical and Chemical Properties of Graphene over Composite Materials: A Technical Review

Graphene is a material that has superior mechanical, electrical, and thermal properties. It has drawn the attention of many scientific researchers for this purpose. In this paper, three different types of fillers, GNPs, MWCNTs and EG reinforced epoxy nanocomposites were mainly studied. Different shear mixing speeds and shear mixing times were considered during the study of the nanocomposites with 0.1 wt% loading of the fillers. The effects of various types of fillers and different shear mixing speeds and durations on mechanical and electrical properties of the final composites were examined. The GNPs-reinforced epoxy nanocomposite was the only one that showed a 13% improvement in elastic modulus as compared to pure epoxy when the shear mixing conditions were 3000 rpm for 2 hours. The research also studied the effects of different loadings of GNPs and the addition of acetone as a solvent on the final mechanical, electrical and thermal properties of the composites (with the fixed shear mixing speed and time). The tensile strength of the composites reduced drastically when the loading of GNPs increased while the elastic modulus shows some increase with the growth in GNP loading. The study found that GNPs reinforced composites did not show the percolation threshold even with 5 wt% (with the ratio to the weight of epoxy) loading of the GNPs. The GNPs-reinforced epoxy composites showed an 116% improvement in the thermal conductivity as compared to the pure epoxy samples when the GNPs loading was 5 wt%. The results from the studied literatures also showed that the samples prepared with the addition of acetone had higher thermal diffusivity than the samples prepared without acetone.

Three-Dimensional-Structured Boron- and Nitrogen-Doped Graphene Hydrogel Enabling High-Sensitivity NO2 Detection at Room Temperature.

Heteroatom-doping has been proved as an effective method to modulate the electronic, physical, and chemical properties of graphene (Gr). Developing a new strategy of heteroatom-doping for high-performance gas sensing is a pivotal issue. Here, we demonstrate novel Gr-based gas sensors through three-dimensional (3D)-structured B-/N-doping nanomaterials for high-performance NO2 sensing. The 3D porous B- and N-doped reduced graphene oxide hydrogels (RGOH) are synthesized via one-step hydrothermal self-assembly and employed as transducing materials to fabricate room-temperature high-performance chemiresistors. The systematic characterizations of the as-synthesized B- and N-RGOH clearly show the uniform doping of the B and N heteroatoms and the formation of B and N components with C/O. In comparison with the pristine RGOH counterpart, the 3D B- and N-RGOH sensors exhibit 38.9 and 18.0 times enhanced responses toward 800 ppb NO2, respectively, suggesting the remarkable doping effect of the heteroatoms in improving the sensitivity. Significantly, B- and N-RGOH display the exceptionally low limit of detection of 9 and 14 ppb NO2, respectively, which are much lower than the threshold limit recommended by the U.S. Environmental Protection Agency. In addition, the developed NO2 sensors show good linearity, reversibility, fast recovery, and impressive selectivity. This work opens up a new avenue to fabricate room-temperature and high-performance NO2 sensors by incorporating B and N heteroatoms into 3D RGOH via a convenient hydrothermal self-assembly approach.

Magnetotransport properties of graphene layers decorated with colloid quantum dots**Project supported by the National Key Research and Development Program of China (Grant Nos. 2016YFA0300601 and 2017YFA0303304) and the National Natural Science Foundation of China (Grant Nos. 11774005, 11874071, 91221202, and 91421303).

The hybrid graphene-quantum dot devices can potentially be used to tailor the electronic, optical, and chemical properties of graphene. Here, the low temperature electronic transport properties of bilayer graphene decorated with PbS colloid quantum dots (CQDs) have been investigated in the weak or strong magnetic fields. The presence of the CQDs introduces additional scattering potentials that alter the magnetotransport properties of the graphene layers, leading to the observation of a new set of magnetoconductance oscillations near zero magnetic field as well as the high-field quantum Hall regime. The results bring about a new strategy for exploring the quantum interference effects in two-dimensional materials which are sensitive to the surrounding electrostatic environment, and open up a new gateway for exploring the graphene sensing with quantum interference effects.

Bismuth mediated defect engineering of epitaxial graphene on SiC(0001)

Structural defects are commonly undesirable in materials, however, atomic-level defect engineering is promising to improve the electronic, mechanical and chemical properties of graphene, if the density and types of defects could be well controlled. Herein, bismuth-mediated defect engineering method for epitaxial graphene (EG) grown on SiC(0001) is demonstrated. It is found that single defects and defect clusters could be facilitated by evaporating Bi atoms on SiC(0001) substrate before the standard EG preparation and, Bi atoms could be thoroughly cleaned away from the EG and the unwanted doping effects of Bi will be avoided by post-annealing at higher temperature. Scanning tunneling microscopy/spectroscopy characterization reveals the atomic structures, the electronic states and the Fermi level shift of flower-like, tube-like and point defects. This study sheds light on the metal-mediated formation of defects in graphene, and provides a practical defect engineering method.

Laser-Structured Graphene/Reduced Graphene Oxide Films towards Bio-Inspired Superhydrophobic Surfaces

Abstract Fine-tuning the physical and chemical properties of graphene and its derivatives is crucial for developing novel multi-functional graphene-based devices. Natural bio-surfaces with rich micro-nanostructures are inspirational for such schemes since they possess unique properties such as superhydrophobicity. In order to effectively acquire these bio-functions, graphene-related materials need to be structured into regularly arranged biomimetic structures. Laser-processing techniques, such as two beam laser interference lithography and femtosecond laser direct-writing, are powerful prototype techniques for their outstanding patterning ability. Herein, we briefly reviewed laser-structuring on graphene or graphene oxide to realize highly functional biomimetic surfaces.

Ultrasensitive Heterojunctions of Graphene and 2D Perovskites Reveal Spontaneous Iodide Loss

Summary Despite the demonstrated high efficiency of perovskite solar cells and light-emitting devices, the understanding of the intrinsic stability of perovskites is far from complete. In this work, using an ultrasensitive, exfoliated 2D perovskite single-crystal sheet/graphene heterostructure device, we reveal spontaneous iodide loss as an important degradation pathway of 2D perovskite single crystals, which n-dopes the perovskite semiconductor by generating positively charged iodide vacancies. Furthermore, we show that covering perovskites with graphene can suppress the iodide loss, significantly improving perovskite stability. A perovskite phototransistor is demonstrated with a graphene/2D perovskite/graphene structure, which shows no degradation after 75 days. Our work not only provides important insights for future stable perovskite optoelectronic device development, but also demonstrates the potential of graphene as a promising sensitive diagnostic tool for device and material degradation studies.