We report the direct and unambiguous evidence of the existenceof inner semiconducting tube (iSCT) photoluminescence (PL)from measurements performed on four individual free-standingindex-identified double-walled carbon nanotubes (DWNTs).Based on thorough Rayleigh scattering, Raman scattering andPL experiments, we are able to demonstrate that the iSCT PLis observed with a quantum yield estimated as a few 10−6 independentlyof the semiconducting or metallic nature of theouter tube. This result is mainly attributed to ultrafast excitontransfer from inner to outer tube. Furthermore, by carryingout PL excitation experiments on the (14,1)@(15,12) DWNT,we show that the iSCT PL can be detected through the opticalexcitation of the outer tube (Fig. 1) indicating that the excitontransfer can also occur in the opposite way.

We report the direct and unambiguous evidence of the existence of inner semiconducting tube (iSCT) photoluminescence (PL) from measurements performed on four individual free-standing index-identified double-walled carbon nanotubes (DWNTs). Based on thorough Rayleigh scattering, Raman scattering and PL experiments, we are able to demonstrate that the iSCT PL is observed with a quantum yield esti-mated as a few 10-6 independently of the semiconducting or metallic nature of the outer tube. This result is mainly attributed to ultrafast exciton transfer from inner to outer tube. Furthermore, by carrying out PL excitation experiments on the (14,1)@(15,12) DWNT, we show that the iSCT PL can be detected through the optical excitation of the outer tube (Figure 1) indicating that the exciton transfer can also occur in the opposite way.

Thermal decomposition of silicon carbide (SiC) provides transfer free and wafer-scale homogeneous graphene forming on a semi-insulating substrate. Large-area monolayer graphene growth was initially developed at the atmospheric pressure (around 900 mbar) in an argon ambient and at high temperature (>1650°C). However, it remains challenging to obtain films with different and controlled characteristics such as the number of graphene layers or the doping by tuning the growth parameters. In this work, we optimized the epitaxial growth of monolayer graphene (1LG) on 4H-SiC (0001) under a low argon pressure of 10 mbar. This intermediate pressure allows growing a continued 1LG in a short process time of ~1h30. Here, we discuss the initial growth stages from buffer layer to 1LG as a function of annealing temperature (same heating rate). The combined Raman spectroscopy and atomic force microscopy (AFM) analyses show that a buffer layer, fully covering the Si-face of SiC, forms as the first step of growth (1600°C). Subsequently, 1LG starts to grow at step edges (1700°C) and continue to cover the buffer layer with a step-flow growth mechanism, as shown in the literature. Eventually, continued large-scale graphene films were achieved at 1750°C with a reproducible process. These graphene films were characterised by Raman, STM and electrical measurement. The integrated intensity of G-band in Raman spectra normalized with respect to a HOPG reference, AG/AG-HOPG, of each spectrum in Raman map is very close to the experimental value reported for a 1LG. Atomically resolved scanning tunnelling microscopy evidences a (6x6) superstructure, indicative of 1LG covering a reconstructed interface layer. Moreover, quantum Hall plateau values observed in our graphene layers confirmed both continuity and thickness of the 1LG film. The carrier density of pHall~1010 - 1011 cm-2 in 1LG films can be achieved at 1.7K in helium atmosphere. Thus, our as-grown 1LG graphene films with low p-type carrier density provide perspectives for further studies and applications on graphene.

Double-walled carbon nanotubes (DWNT) are made of two concentric and weakly van der Waals coupled single-walled carbon nanotubes (SWNT). DWNTs are the simplest systems for studying the mechanical and electronic interactions between concentric carbon layers.In this paper we review recent results concerning the intrinsic features of phonons of DWNTs obtained from Raman experiments performed on index-identified DWNTs. The effect of the interlayer distance on the strength of the mechanical and electronic coupling between the layers, and thus on the frequencies of the Raman-active modes, namely the radial breathinglikemodes (RBLMs) and G-modes, are evidenced and discussed.

We present experimental measurements of the features of G band in individual index-identified free-standing double-walled carbon nanotubes. We examine Raman spectra of different electronic configurations of DWNTs, namely: SC@SC, SC@M, M@SC, M@M, and clearly establish that, as in SWNTs, the profile of LO G-mode of each layer is broad (narrow) when the layer is metallic (semiconducting). The dependence of G-modes on thediameter and inter-layer distance in several SC@SC, SC@M, M@SC, M@M index-identified DWNTs is reported. We find, that, independently of the metallic or semiconducting nature of the layers, the frequencies of LO and TO G-mode of the inner and outer layers shift significantly with respect to the frequencies of the same modes in the constituent SWNTs.

We report direct and unambiguous evidence of the existence of inner semiconducting tube (ISCT) photoluminescence (PL) from measurements performed on four individual freestanding index-identified double-walled carbon nanotubes (DWNTs). Based on thorough Rayleigh scattering, Raman scattering, and PL experiments, we are able to demonstrate that the ISCT PL is observed with a quantum yield estimated to be a few 10−6 independent of the semiconducting or metallic nature of the outer tube. This result is mainly attributed to ultrafast exciton transfer from the inner to outer tube. Furthermore, by carrying out PL excitation experiments on the (14,1)@(15,12) DWNT, we show that the ISCT PL can be detected through the optical excitation of the outer tube, indicating that the exciton transfer can also occur in the opposite way.