This work presents a systematic study of the ratio between the integrated intensities of the disorder-induced D and G Raman bands (ID∕IG) in nanographite samples with different crystallite sizes (La) and using different excitation laser energies. The crystallite size La of the nanographite samples was obtained both by x-ray diffraction using synchrotron radiation and directly from scanning tunneling microscopy images. A general equation for the determination of La using any laser energy in the visible range is obtained. Moreover, it is shown that ID∕IG is inversely proportional to the fourth power of the laser energy used in the experiment.

General equation for the determination of the crystallite size La of nanographite by Raman spectroscopy

We developed a hydrogen arc discharge exfoliation method for the synthesis of graphene sheets (GSs) with excellent electrical conductivity and good thermal stability from graphite oxide (GO), in combination with solution-phase dispersion and centrifugation techniques. It was found that efficient exfoliation and considerable deoxygenation of GO, and defect elimination and healing of exfoliated graphite can be simultaneously achieved during the hydrogen arc discharge exfoliation process. The GSs obtained by hydrogen arc discharge exfoliation exhibit a high electrical conductivity of210 3 S/cm and high thermal stability with oxidization resistance temperature of 601 °C, which are much better than those prepared by argon arc discharge exfoliation (2 10 2 S/cm, 525 °C) and by conventional thermal exfoliation (80 S/cm, 507 °C) with the same startingGO.Theseresultsdemonstratethatthishydrogenarcdischargeexfoliationmethodisagoodapproachfor the preparation of GSs with a good quality.

Synthesis of Graphene Sheets with High Electrical Conductivity and Good Thermal Stability by Hydrogen Arc Discharge Exfoliation

Measuring the degree of stacking order in graphite by Raman spectroscopy

Developing three-dimensional (3D) graphene assemblies with properties similar to those individual graphene sheets is a promising strategy for graphene-based electrodes. Typically, the synthesis of 3D graphene assemblies relies on van der Waals forces for holding the graphene sheets together, resulting in bulk properties that do not reflect those reported for individual graphene sheets. Here, we report the use of sol-gel chemistry to introduce chemical bonding between the graphene sheets and control the bulk properties of graphene-based aerogels. Adjusting synthetic parameters allows a wide range of control over surface area, pore volume, and pore size, as well as the nature of the chemical cross-links (sp(2) vs sp(3)). The bulk properties of the graphene-based aerogels represent a significant step toward realizing the properties of individual graphene sheets in a 3D assembly with surface areas approaching the theoretical value of an individual sheet.

High Surface Area, sp(2)-Cross-Linked Three-Dimensional Graphene Monoliths.

The transition from graphene to a fully disordered sp2 carbon material can be idealized by either cutting graphene into smaller and smaller pieces, or adding more and more point defects. In other words, from the dimensionality standpoint, defects in two-dimensional (2D) systems can be either one- (1D) or zero-dimensional (0D). From an application point of view, both in terms of bottom-up as well as top-down approaches, the discrimination between these two structural disorder in two-dimensional systems is urgently desired. In graphene, both types of defects produce changes in the Raman spectrum, but identifying separately the contribution from each defect-type has not yet been achieved. Here we show that a diagram can be built for disentangling contributions of point-like and line-like defects to the Raman spectra of graphene-related materials embracing, from the topology point of view, all possible structures from perfect to fully disordered sp2 bonded carbons. Two sets of graphene-related samples, produced by well-established protocols that generate either 0D or 1D defects in a controlled way, are analysed with our model and used to parameterize the limiting values of the phase space. We then discuss the limitations and apply our new methodology to analyse the structure of two-dimensional nanocarbons generated from renewable gas, used to produce inks and conducting coatings.

https://iopscience.iop.org/article/10.1088/2053-1583/aa5e77/pdf

Disentangling contributions of point and line defects in the Raman spectra of graphene-related materials

The heat-treatment effect on electronic properties is investigated in relation to structural change for pulsed-laser-deposited amorphous carbon thin films having ${\mathrm{sp}}^{2}{/sp}^{3}$ ratio $\ensuremath{\approx}9.$ The heat treatment at temperatures 200--400 $\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$ increases conductivity and modifies the hopping conduction mechanism at low temperatures, resulting in the generation of a Coulomb gap at ${E}_{\mathrm{F}}.$ This is attributed to the heat-treatment-induced modification of the disorder nature of the structure from atomic-scale ${\mathrm{sp}}^{2}{/sp}^{3}$ disorder to a disordered graphitic ${\mathrm{sp}}^{2}$-domain network by the migration of ${\mathrm{sp}}^{3}$ defects. In the heat-treatment temperature region above $600\ifmmode^\circ\else\textdegree\fi{}\mathrm{C},$ where the structure is featured with graphitic ${\mathrm{sp}}^{2}$ domains, considerably small positive thermoelectric power is suggestive of carrier compensation by the competition of hole and electron carriers that originate from the inhomogeneous charge distribution caused by the difference of Fermi levels among graphitic ${\mathrm{sp}}^{2}$ domains. In the high-heat-treatment-temperature region $800--1100\ifmmode^\circ\else\textdegree\fi{}\mathrm{C},$ the formation of an infinite percolation path network of the graphitic ${\mathrm{sp}}^{2}$ domains induces an insulator-to-metal transition, where the electron transport in the ${\mathrm{sp}}^{2}$-rich metallic state is featured by weakly temperature-dependent conductivity with majority hole and minority electron carriers.

Structure and electronic properties of a nongraphitic disordered carbon system and its heat-treatment effects

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Structure and electronic properties of a nongraphitic disordered carbon system and its heat-treatment effects