Defective Graphene Layers Research Articles

Study of the structure of graphene oxide obtained by oxidation of intercalated graphite compound by Raman light scattering method

This work shows the strategy of GO synthesis from intercalated graphite compound, rotation of the synthesis conditions was carried out, and the starting material and synthesis products were characterized in detail by a complex of physical and chemical methods: scanning electron microscopy, transmission electron microscopy, atomic force microscopy, Raman spectroscopy, and high-temperature catalytic oxidation. It was found by Raman spectroscopy that the initial IGC sample is a graphite structure with a low content of defects in graphene layers. Oxidation of this sample leads to a gradual increase in the measure of disordered carbon framework. One of the reasons for this is a decrease in the size of graphite-like crystallites with subsequent reorientation in the space of graphene layers. It has been established by a complex of physicochemical methods of research that the oxidation of IGC graphite with increasing oxidation time leads to an increase in the defectivity of the initial carbon framework due to a decrease in the linear size of carbon crystallites. When a certain reaction time is reached, the initial structure of the sample changes, and there is a partial reorientation of the crushed graphite-like fragments with a simultaneous increase in the number of defects.

Highly Durable and Efficient Seawater Electrolysis Enabled by Defective Graphene-Confined Nanoreactor.

Direct seawater electrolysis is a promising technology for massive green hydrogen production but is limited by the lack of durable and efficient electrocatalysts toward the oxygen evolution reaction (OER). Herein, we develop a core-shell nanoreactor as a high-performance OER catalyst consisting of NiFe alloys encapsulated within defective graphene layers (NiFe@DG) by a facile microwave shocking strategy. This catalyst needs overpotentials of merely 218 and 276 mV in alkalized seawater to deliver current densities of 10 and 100 mA cm-2, respectively, and operates continuously for 2000 h with negligible activity decay (1.0%), making it one of the best OER catalysts reported to date. Detailed experimental and theoretical analyses reveal that the excellent durability of NiFe@DG originates from the formation of the built-in electric field triggered by the defective graphene coating against chloride ions at the electrode/electrolyte interface, thus protecting the active NiFe alloys at the core from dissolution and aggregation under harsh operation conditions. Further, a highly stable and efficient seawater electrolyzer is assembled with the NiFe@DG anode and the Pt/C cathode to demonstrate the practicability of the catalysts.

Defective Graphene/Plasmonic Nanoparticle Hybrids for Surface-Enhanced Raman Scattering Sensors.

Two-dimensional-zero-dimensional plasmonic hybrids involving defective graphene and transition metals (DGR-TM) have drawn significant interest due to their near-field plasmonic effects in the wide range of the UV-vis-NIR spectrum. In the present work, we carried out extensive investigations on resonance Raman spectroscopy (RRS) and localized surface plasmon resonance (LSPR) from the various DGR-TM hybrids (Au, Ag, and Cu) using micro-Raman, spatial Raman mapping analysis, high-resolution transmission electron microscopy (HRTEM), and LSPR absorption measurements on defective CVD graphene layers. Further, electric field (E) mappings of samples were calculated using the finite domain time difference (FDTD) method to support the experimental findings. The spatial distribution of various in-plane and edge defects and defect-mediated interaction of plasmonic nanoparticles (NPs) with graphene were investigated on the basis of the RRS and LSPR and correlated with the quantitative analysis from HRTEM, excitation wavelength-dependent micro-Raman, and E-field enhancement features of defective graphene and defective graphene-Au hybrids before and after rapid thermal annealing (RTA). Excitation wavelength-dependent surface-enhanced Raman scattering (SERS) and LSPR-induced broadband absorption from DGR-Au plasmonic hybrids reveal the electron and phonon interaction on the graphene surface, which leads to the charge transfer from TM NPs to graphene. This is believed to be responsible for the reduction in the SERS signal, which was observed from the wavelength-dependent Raman spectroscopy/mappings. We implemented defective graphene and DGR-Au plasmonic hybrids as efficient SERS sensors to detect the Fluorescein and Rhodamine 6G molecules with a detection limit down to 10-9 M. Defective graphene and Au plasmonic hybrids showed an impressive Raman enhancement in the order of 108, which is significant for its practical application.

Isotope Engineered Fluorinated Single and Bilayer Graphene: Insights into Fluorination Selectivity, Stability, and Defect Passivation.

Tailoring the physicochemical properties of graphene through functionalization remains a major interest for next-generation technological applications. However, defect formation due to functionalization greatly endangers the intrinsic properties of graphene, which remains a serious concern. Despite numerous attempts to address this issue, a comprehensive analysis has not been conducted. This work reports a two-step fluorination process to stabilize the fluorinated graphene and obtain control over the fluorination-induced defects in graphene layers. The structural, electronic and isotope-mass-sensitive spectroscopic characterization unveils several not-yet-resolved facts, such as fluorination sites and CF bond stability in partially-fluorinated graphene (F-SLG). The stability of fluorine has been correlated to fluorine co-shared between two graphene layers in fluorinated-bilayer-graphene (F-BLG). The desorption energy of co-shared fluorine is an order of magnitude higher than the CF bond energy in F-SLG due to the electrostatic interaction and the inhibition of defluorination in the F-BLG. Additionally, F-BLG exhibits enhanced light-matter interaction, which has been utilized to design a proof-of-concept field-effect phototransistor that produces high photocurrent response at a time <200 µs. Thus, the study paves a new avenue for the in-depth understanding and practical utilization of fluorinated graphenic carbon.

Oxidation evolutions of soot surface and pore properties with different O2-NO2 mixtures and temperatures

Soot oxidation evolutions at various oxidation degrees under different O2-NO2 mixtures and temperatures were performed. Results indicated that the internal burning-out process represented by shell-like particles at 500 °C independent on NO2 concentration, while the development of hollow shells for the soot was suppressed with increasing the temperature. A tendency with soot toward a less ordered arrangement with short and defective graphene layers after oxidizing at 500 °C was also observed, which was suppressed with added NO2 and increasing temperature. Many carbon oxygen functionalities produced at 40% oxidation and the intensity of the peak gradually increased as the increase of the oxidation degree, while the increase of the peak intensity became less sensitive with added NO2 and increasing temperature. Abundant micropores and mesopores formed inside the particles during the soot oxidation process depending on oxidizer and temperature, micropores (smaller than 2 nm) were extensively generated at the early stages of the oxidation while mesopores increased sharply after 20% oxidation. The trends were correspondent to the oxidation modes with different oxidizer and temperature. The correlationship observation suggested that soot oxidation behavior was dependent on competing rates of reaction kinetics versus mass transport of oxidizer according to the oxidation evolution of surface and pore.

Влияние обработки в He:O плазме на структуру многостенных углеродных нанотрубок

The functionalization of multi-walled carbon nanotubes in He:O plasma is investigated. It's shown that plasma treatment leads to the removal of defective outer graphene layers and their fragments due to oxidation. It is established that the surface of functionalized multi-walled carbon nanotubes contains numerous uncoordinated carbon atoms and oxygen-containing functional groups. The preservation of the structure of the internal graphene layers of nanotubes and the formation of broken chemical bonds ensures a decrease in electrical resistance. At the same time, there is a narrowing of the distribution of electrical resistance values of nanotube ensembles.

The effect of He : O plasma treatment on the structure of multi-walled carbon nanotubes

The functionalization of multi-walled carbon nanotubes in He : O plasma is investigated. It is shown that plasma treatment leads to the removal of defective outer graphene layers and their fragments due to oxidation. It is established that the surface of functionalized multi-walled carbon nanotubes contains numerous uncoordinated carbon atoms and oxygen-containing functional groups. The preservation of the structure of the internal graphene layers of nanotubes and the formation of broken chemical bonds ensure a decrease in electrical resistance. At the same time, there is a narrowing of the distribution of electrical resistance values of nanotube ensembles. Keywords: multi-walled carbon nanotubes, plasma treating, functionalization, transmission electron microscopy, X-ray photoelectron spectroscopy

Graphene–Iron(II) Phthalocyanine Hybrid Systems for Scalable Molecular Spintronics

Graphene - transition metal phthalocyanine (G-MPc) hybrid systems constitute promising platforms for densely-packed single-molecule magnets (SMMs). Here, we selected iron(II) phthalocyanine (FePc) and investigated its interaction with pristine and defective graphene layers employing density functional theory. Our calculations indicate that thorough proper dehydrogenation of the benzol rings in the FePc molecule its adsorption to graphene is thermodynamically favorable. In general, the presence of anchoring sites on the graphene layer, i.e. point defects, additionally facilitates the adsorption of FePc, allowing one to achieve high density of SMMs per unit area. Using the combination of group theory, ligand field splitting, and the calculated PBE0 Kohn-Sham eigenvalue spectrum, we resolved the electronic structure and predicted the spin states of both, the isolated FePc and G-FePc hybrid systems. Regardless of adsorption site and the number of removed hydrogen atoms from the benzol rings of FePc, the magnetic moment of the SMM remains unchanged with respect to free FePc. These results should mediate a successful synthesis of densely-packed G-MPc systems and may open up new avenue in designing scalable graphene - SMMs systems for spintronics applications.

The role of activated carbon in boosting the activity of clitoria ternatea powder photocatalyst for hydrogen production

This research observes hydrogen production from water using biophotocatalyst from activated carbon (AC) and Clitoria ternatea powder (CTP). AC is assembled by defective graphene layers and CTP by aromatic ring with hydroxyl groups. AC and CTP have been tested individually and in combination at irradiation light wave length from 600 to 400 nm. The results show that the same wave length of the absorbance peak of AC and CTP is due to their aromatic ring. The very low absorbance intensity in AC is due to its very low effective surface contact and the negative charges around the pores of AC attract hydrogen proton that hinders hydrogen production. The hydroxyl groups in CTP energize delocalized electron in aromatic ring by attracting the electron to transit them, therefore, absorb high light intensity. When they are combined, the photo catalyst performance in hydrogen production increase almost four fold. This is due to attracted force from the charge in the pores of AC to hydroxyl groups in CTP that further energizes delocalized electron in aromatic ring of CTP, thereby boosts the photocatalyst activity. When the wave length of irradiation light is the same as the catalyst light absorbance wave length, the hydrogen production is the highest.

Platinum carbonyl clusters decomposition on defective graphene surface

Having single atoms or small clusters docked onto a single layer graphene represents a charming feature for energy-storage and catalysis. Unfortunately, the large cohesion energy of transition metals often prevents the isolation of nanoscopic clusters, which invariably tend to aggregate. The decoration of defective graphene layers with single Pt atoms and sub-nanometric clusters is herein achieved by exploiting metal carbonyl clusters, as precursor, and investigated by means of transmission electron microscopy and X-ray photoemission spectroscopy. Unexpectedly, the process of aggregation of Pt into larger clusters is inhibited onto the surface of defective graphene, where the Pt-clusters are found to fragment even into single metal atoms.

Mechanical properties of a G/h-BN heterobilayer nanosheets coupled by interlayer sp3 bonds and defects

The mechanical properties of graphene/hexagonal boron nitride (G/h-BN) heterobilayer nanosheets coupled by interlayer sp3 bonds and defects have been investigated by using the molecular dynamics (MD) simulation. For this purpose, interlayer sp3 bonds and two kinds of geometric imperfection (including rhombus and square nanopore) are formed in the G/h-BN heterobilayer nanosheets. The effects of adding the nanopore diameter, interlayer sp3 bonds fraction, and the influence of different position of geometric imperfection in heterobilayer nanostructure on mechanical properties have been investigated. The result shows that when sp3 bonds and nanopore coexist, the mechanical properties of defective graphene layer are higher than that of defective hexagonal boron nitride (h-BN) layer. Meanwhile, the negative effect of rhomboid nanohole on mechanical properties of heterostructure is weaker than that of square nanohole. It is observed that that interlayer sp3 bonds have greatest influence on the fracture strain of G/h-BN heterobilayer nanostructure, followed by fracture stress, and finally Young’s modulus. Another important point is that interlayer sp3 bonds can be regarded as a special defect, and its value seems to outweigh the intrinsic defects.

Enhanced Photo-Electrocatalytic Hydrogen Generation in Graphene/hBN van der Waals Structures

Development of atomic layers and their heterostructures opened new avenues in developing novel photocatalysts for enhanced light–matter interaction. Graphene–hexagonal boron nitride (G/hBN) van der Waals structures were recently predicted for interfacial exciton generation upon visible light excitation, and also, the authors have shown their van der Waals stacking-induced electrocatalytic activity. Here, an enhanced photo-electrocatalytic hydrogen evolution reaction (HER) is demonstrated upon white light illumination on samples where graphene and hBN are stacked via van der Waals interaction. The individual layers of graphene and hBN-modified electrodes have no light-induced effects along with a “poor” electrocatalytic HER activity. The origin of such light-induced activity is probed via density-functional-theory-based calculations. The catalytic activity of such heterostructures is found to be further enhanced by nanostructuring, where the coupling between individual defective graphene layers is ensured via direct carbon–carbon coupling through the Suzuki reaction. With band-engineering-induced inherent activity enhancement and nanostructuring-enabled enhanced active sites, we were able to develop a G/hBN structure that has an exceptional photo-electrocatalytic activity.

Single‐Walled Carbon Nanotubes Shock‐Compressed to 0.5 Mbar (Phys. Status Solidi B 11/2017)

Single-walled carbon nanotubes (SWCNTs) have been dynamically (shock) compressed to 0.5 Mbar, above the limit of their structural integrity. Two distinct types of material are identified by high-resolution transmission electron microscopy (HRTEM) and multi-wavelength Raman spectroscopy in the sample recovered after shock: multi-layer graphene (MLG) and a two-phase material composed of nano-clustered graphene and amorphous carbon whereas no diamond-like carbon or carbon nano-onions are found. Peak decomposition of the Raman spectra was used to estimate the coherent scatterers (clusters) size in MLG at 36 nm from the D- to G-band intensity ratio dependence on the photon excitation energy. Botella et al. (article no. 1700315) propose the peak fitting model for decomposition of the Raman spectra of highly disordered carbon material containing graphene nano-clusters and stress the importance of accounting for heptagonal- and pentagonal-ring defects in graphene layers for the analysis of such spectra. The cover image shows HRTEM images and the correspondent Raman spectra of the two types of material along with peak decomposition of the two-phase material with the peaks assigned to heptagons (a) and pentagons (b). Particulars of the SWCNTs transformation to other structural forms of carbon at high pressure/temperature are discussed.

Cluster-Type Structure of Amorphous Smooth Hydrocarbon CD x Films (x ~ 0.5) from T-10 Tokamak

Structure of smooth hydrocarbon CD x films with a high deuterium ratio x ~ 0.5 redeposited from T-10 tokamak D-plasma discharges (NRC Kurchatov Institute, Moscow) has been studied. For the first time, small and wide angle X-ray scattering technique using synchrotron radiation and neutron diffraction have been employed. A fractal structure of CD x films is found to consist of mass-fractals with rough border, surface fractals (with rough surface), plane scatterers and linear chains forming a branched and highly cross-linked 3D carbon network. The found fractals, including sp2 clusters, are of typical size ~1.60 nm. They include a C13 fragment consisting of three interconnected aromatic rings forming a minimal fractal sp2 aggregate 9 × C13. These graphene-like sp2 clusters are interconnected and form a 3D lattice which can be alternatively interpreted as a highly defective graphene layer with a large concentration of vacancies. The unsaturated chemical bonds are filled with D, H atoms, linear sp2 C=C, C=O, and sp3 structural elements like C-C, C-H(D), C-D2,3, C-O, O-H, COOH, C x D(H) y found earlier from the infrared spectra of CD x films, which are binding linear elements of a carbon network. The amorphous structure of CD x films has been confirmed by the results of earlier fractal structure modeling, as well as by researches with X-ray photoelectron spectroscopy which allow finding a definite similarity with the electron structure of their model analogues — polymeric a-C:H and a-C:D films with a disordered carbon network consisting of atoms in sp3 + sp2 states.

Mass Transport through Defects in Graphene Layers

The paper reports an experimental study of ZnTe and CuI transport through graphene wall of SWNTs by high resolution transmission electron microscopy. It is shown that encapsulated material evacuates the tube through the defects in the nanotube walls, while in-tube diffusion appears high enough to provide matter intake from the nanotube volume. Diffusion kinetics was studied by “atoms count” resulting in ZnTe and CuI diffusivities of 7.67 × 10–21 and 1.99 × 10–20 m2/s through single defects in SWNT wall. Semiempirical and DFT modeling of potential energy profiles for different types of defects was utilized to propose minimal structural disturbances in a graphene layer to make possible cross-plane transport of matter. The comparison of experimentally observed diffusivities with calculated activation barrier heights was carried out taking into account an effective temperature of substance under electron beam. Neither of the defects including framework disturbance with 5–7 defects or sp3-bound carbon atomic p...

Aromatic structure degradation of single layer graphene on an amorphous silicon substrate in the presence of water, hydrogen and Extreme Ultraviolet light

Abstract In this paper we study the reaction of water and graphene under Extreme Ultraviolet (EUV) irradiation and in the presence of hydrogen. In this work, single layer graphene (SLG) on amorphous Si as an underlying substrate was dosed with water (0.75 mL) and exposed to EUV ( λ = 13.5 nm, 92 eV) with partial pressures of H 2 in the background. The results show that the aromatic structure of graphene, when exposed to EUV and H 2 , breaks down into aryl ketones and enols of 1,3 di-ketone. Infrared (IR) spectroscopy shows that SLG oxidizes, with increasing H 2 pressure leading to the grain boundary edges of graphene forming ketones and carboxylic acids. In situ and post exposure analyses also reveal that EUV exposure reduces the sp 2 content of the graphene layer, with the sp 3 content increasing, resulting in a more defective graphene layer.

First-principles study of the mechanism of wettability transition of defective graphene

Hydrophobicity of graphene limits its application potential in polar media, therefore modifications of graphene wettability have been in an area of active research for many years. Recently, a reversible wettability transition of graphene has been reported (Xu et al 2014 Sci. Rep. 4 6450). The presence of undercoordinated carbon atoms in otherwise hydrophobic graphene is believed to trigger the hydrophobic to hydrophilic transition, but the underlying mechanism, especially of the reverse process, remained unclear. Using density functional theory with range-separated hybrid functional HSE06, we investigate the dissociative adsorption of up to two water molecules on the defective graphene layer containing odd number of missing lattice atoms. We show, that depending on the defect type either a full dissociation of the water molecule or a partial splitting of H2O to OH and H takes place leading to the saturation of graphene dangling bonds due to the formation of oxiranes or by hydroxyls, respectively. The dissociation barriers are significantly lower for the water dimer than for the single molecule. Our findings providing detailed insights into the remarkable differences between the reactivity of vacancy defects with water shed new light on the wettability-transition mechanism of defective graphene.

Fermi-level pinning of bilayer graphene with defects under an external electric field

The electronic structure of bilayer graphene, where one of the layers possesses monovacancies, is studied under an external electric field using density functional theory. Our calculations show that Fermi-level pinning occurs in the bilayer graphene with defects under hole doping. However, under electron doping, the Fermi level rapidly increases at the critical gate voltage with an increasing electron concentration. In addition to the carrier species, the relative arrangement of the gate electrode to the defective graphene layer affects the Fermi energy position with respect to the carrier concentration. Because the distribution of the accumulated carrier depends on the electrode position, the quantum capacitance of bilayer graphene with defects depends on the electrode position.

Effect on hydrogen adsorption due to a lonely or a pair of carbon vacancies on the graphene layer.

The influence on the hydrogen molecule adsorption on a pristine and a defective graphene layer is compared. The different lengths for the C-C bonds on the graphene layer with one vacancy are visualized and compared respect to pristine graphene. The energy of formation of one vacancy is calculated and a comparison of the binding energy for the hydrogen molecule is presented when the molecule is adsorbed on pristine graphene or on the defective graphene layer. The adsorption is studied for a single vacancy and at least for two different pairs of carbon vacancies. The qualitative general result, and contrary to the expected effect of the carbon vacancies on the hydrogen adsorption is that the rearrangement of the carbon atoms on the defective graphene layer allows only a relatively small increase in the magnitude of the binding energy for the hydrogen molecule.

Density of states of adsorbed sulphur atoms on pristine and defective graphene layers.

The density of states for adsorbed sulphur atom on a graphene layer system is discussed for pristine graphene layer and for mono and divacancies on the graphene layer. To our knowledge this is the first time that an entire adsorption of the sulphur atom is reported at the plane of the carbon atoms, when there is a pair of closer vacancies at the graphene layer.