A. L. Aguiar

Structural and Phonon Properties of Bundled Single- and Double-Wall Carbon Nanotubes Under Pressure

In this work, we report a theoretical coupled study of the structural and phonons properties of bundled single- and double-walled carbon nanotubes (DWNTs), under hydrostatic compression. Our results confirm drastic changes in volume of SWNTs in high-pressure regime as assigned by a phase transition from circular to collapsed phase which are strictly dependent on the tube diameter. For the DWNTs, those results show first a transformation to a polygonized shape of the outer tube and subsequently the simultaneous collapse of the outter and inner tube, at the onset of the inner tube ovalization. Before the DWNT collapse, phonon calculations reproduce the experimentally observed screening effect on the inner tube pressure induced blue shift both for RBM and tangential G

Raman evidence for pressure-induced formation of diamondene

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Pressure-induced phase transition and fracture in α-MoO 3 nanoribbons

modes . Furthermore, the collapse of CNTs bundles induces a sudden redshift of tangential component in agreement with experimental studies. The G

Carbon Nanotubes Under High Pressure Probed by Resonance Raman Scattering

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Pressure-Induced Collapse in Double-Walled Carbon Nanotubes: Chemical and Mechanical Screening Effects

band analysis of the SWNT collapsed tubes shows that the flattened regions of the tubes are at the origin of their G-band signal. This explains the observed graphite type pressure evolution of the G band in the collapsed phase and provides in addition a mean for the identification of collapsed tubes

Linear Carbon Chains under High-Pressure Conditions

Despite the advanced stage of diamond thin-film technology, with applications ranging from superconductivity to biosensing, the realization of a stable and atomically thick two-dimensional diamond material, named here as diamondene, is still forthcoming. Adding to the outstanding properties of its bulk and thin-film counterparts, diamondene is predicted to be a ferromagnetic semiconductor with spin polarized bands. Here, we provide spectroscopic evidence for the formation of diamondene by performing Raman spectroscopy of double-layer graphene under high pressure. The results are explained in terms of a breakdown in the Kohn anomaly associated with the finite size of the remaining graphene sites surrounded by the diamondene matrix. Ab initio calculations and molecular dynamics simulations are employed to clarify the mechanism of diamondene formation, which requires two or more layers of graphene subjected to high pressures in the presence of specific chemical groups such as hydroxyl groups or hydrogens.The synthesis of two-dimensional diamond is the ultimate goal of diamond thin-film technology. Here, the authors perform Raman spectroscopy of bilayer graphene under pressure, and obtain spectroscopic evidence of formation of diamondene, an atomically thin form of diamond.

Effects of intercalation and inhomogeneous filling on the collapse pressure of double-wall carbon nanotubes

MoO3 nanoribbons were studied under different pressure conditions ranging from 0 to 21GPa at room temperature. The effect of the applied pressure on the spectroscopic and morphologic properties of the MoO3 nanoribbons was investigated by means of Raman spectroscopy and scanning electron microscopy techniques. The pressure dependent Raman spectra of the MoO3 nanoribbons indicate that a structural phase transition occurs at 5GPa from the orthorhombic α-MoO3 phase (Pbnm) to the monoclinic MoO3-II phase (P21/m), which remains stable up to 21GPa. Such phase transformation occurs at considerably lower pressure than the critical pressure for α-MoO3 microcrystals (12GPa). We suggested that the applanate morphology combined with the presence of crystalline defects in the sample play an important role in the phase transition of the MoO3 nanoribbons. Frequencies and linewidths of the Raman bands as a function of pressure also suggest a pressure-induced morphological change and the decreasing of the nanocrystal size. The observed spectroscopic changes are supported by electron microscopy images, which clearly show a pressure-induced morphologic change in MoO3 nanoribbons.

Pressure-Induced Selectivity for Probing Inner Tubes in Double- and Triple-Walled Carbon Nanotubes: A Resonance Raman Study

The power of Raman spectroscopy for the study of the high-pressure evolution of carbon nanotubes is shown. After an introduction to carbon nanotubes and its resonance Raman scattering signal, we discuss the high-pressure Raman studies on single-wall carbon nanotubes with particular emphasis on the identification of pressure-induced structural and electronic transitions.