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.

Graphene is a two-dimensional network in which sp2-hybridized carbon atoms are arranged in two different triangular sub-lattices (A and B). By incorporating nitrogen atoms into graphene, its physico-chemical properties could be significantly altered depending on the doping configuration within the sub-lattices. Here, we describe the synthesis of large-area, highly-crystalline monolayer N-doped graphene (NG) sheets via atmospheric-pressure chemical vapor deposition, yielding a unique N-doping site composed of two quasi-adjacent substitutional nitrogen atoms within the same graphene sub-lattice (N2AA). Scanning tunneling microscopy and spectroscopy (STM and STS) of NG revealed the presence of localized states in the conduction band induced by N2AA-doping, which was confirmed by ab initio calculations. Furthermore, we demonstrated for the first time that NG could be used to efficiently probe organic molecules via a highly improved graphene enhanced Raman scattering.

The isolation of few-layered transition metal dichalcogenides has mainly been performed by mechanical and chemical exfoliation with very low yields. In this account, a controlled thermal reduction-sulfurization method is used to synthesize large-area (~1 cm(2)) WS2 sheets with thicknesses ranging from monolayers to a few layers. During synthesis, WOx thin films are first deposited on Si/SiO2 substrates, which are then sulfurized (under vacuum) at high temperatures (750-950 °C). An efficient route to transfer the synthesized WS2 films onto different substrates such as quartz and transmission electron microscopy (TEM) grids has been satisfactorily developed using concentrated HF. Samples with different thicknesses have been analyzed by Raman spectroscopy and TEM, and their photoluminescence properties have been evaluated. We demonstrated the presence of single-, bi-, and few-layered WS2 on as-grown samples. It is well known that the electronic structure of these materials is very sensitive to the number of layers, ranging from indirect band gap semiconductor in the bulk phase to direct band gap semiconductor in monolayers. This method has also proved successful in the synthesis of heterogeneous systems of MoS2 and WS2 layers, thus shedding light on the controlled production of heterolayered devices from transition metal chalcogenides.

Novel Physical Phenomena may arise from co-axial nanotube structuresHighly crystalline and pure double-walled carbon nanotubes (DWNTs) are needed in order to probe electronic properties, thermal transport and mechanical behavior of individual DWNTs.Here we report the fabrication of a new type of a paper-like material consisting of high-purity DWNTs in high yields using a catalytic chemical vapor deposition (CVD) method in conjunction with an optimized purification treatment. These tubes are hexagonally packed in bundles and show a narrow diameter distribution.DWNTs, which consist of two concentric graphene cylinders, have attracted the attention of numerous scientists because these hybrid structures [lying between single-walled carbon nanotubes (SWNTs) and multi-walled carbon nanotubes (MWNTs)], may exhibit intriguing electronic and mechanical properties that have not been reported hitherto. Therefore, various attempts to produce high purity DWNTs have been published [1][2][3][4][5][6][7] . Unfortunately, these reports usually generate mixtures of DWNTs and SWNTs, in addition to metal particles, amorphous carbon and multi-layer carbon nanotubes. The CCVD method is considered to be most efficient in dealing with the large-scale production of nanotubes 8, 9 . Arc-discharge methods and thermal treatments of C 60 peapods result in DWNTs as well as unwanted carbon nanomaterials 1, 4 , and the cross-sections of the DWNTs (using high resolution transmission electron microscope (HRTEM)) were never shown because the uniformity and purity of the DWNT material has not yet reached that of SWNTs [1][2][3][4][5][6][7] .The synthesis of DWNTs was carried out using a conditioning catalyst (Mo/Al 2 O 3 ) on one end of the furnace, and the nanotube catalyst (Fe/MgO) in the middle part of the furnace (see supplemental information). Subsequently, a CH 4 +Ar gas mixture (1:1) was fed into the reactor for 10 minutes at 875°C. When using the conditioning catalyst 10 , preferential growth of DWNTs over SWNTs occurred, possibly due to an increased portion of active carbon species. In order to obtain a pure DWNT paper (Fig. 1a), a two-step purification process was applied to the synthesized products. In particular, HCl treatments (18wt%HCl, 373K, 10hrs) were carried out in order to remove iron catalyst and the supporting material, followed by air oxidation at 500 o C for 30 minutes. The latter process is used to remove amorphous carbon and chemically active SWNTs. After a filtering process, we obtained a dark and stable paper-like sheet, which is very flexible and mechanically stable (tough) (Fig. 1a). Careful HRTEM (JEOL JEM-2010FEF) observations revealed an extremely high-yield of DWNTs (more than 95%) arranged in bundles (Fig. 1c).The DWNT paper (see Fig. 1b and 1c) contains nanotubes with a narrow diameter distribution, exhibiting a hexagonal packing (Fig. 1d). Raman studies were carried out in order to determine the radial breathing mode (RBM) frequency, which is inversely related to the tube diameter.Raman peaks appear above 25...

A carbon nanofiber‐based electrode, exhibiting a large accessible surface area (derived from the nanometer‐sized fiber diameter), high carbon purity (without binder), relatively high electrical conductivity, structural integrity, thin web macromorphology, a large reversible capacity (ca. 450 mA h g–1), and a relatively linearly inclined voltage profile, is fabricated by nanofiber formation via electrospinning of a polymer solution and its subsequent thermal treatment. It is envisaged that these characteristics of this novel carbon material will make it an ideal candidate for the anode material of high‐power lithium‐ion batteries (where a high current is critically needed), owing to the highly reduced lithium‐ion diffusion path within the active material.