Nanocarbon materials: probing the curvature and topology effects using phonon spectra

Abstract

Much has been learned from the use of resonance Raman spectroscopy and high-resolution transmission electron microscopy techniques about the micro-/nanoscopic structure of various nanostructured carbons. However, they still possess some features that are not entirely understood particularly in terms of topological characteristics, which go beyond making a distinction with just the geometrical structure at nanoscale. To effectively utilize the potential of these materials for technological needs, understanding both the geometrical and topological structure and perhaps relating these attributes to physical (optical/electronic, lattice vibrational) properties become indispensable. Here, we make an attempt to describe the differences between various nanostructures and provide geometrical and topological property assessment semiquantitatively by monitoring the phonon spectra using resonance Raman spectroscopy thereby also capturing the electronic spectra. We elucidate the notion of global topology and curvature for a range of technologically important nanoscale carbons including tubular (single-, double-and multiwalled nanotubes, peapod), spherical (hypo-and hyperfullerenes, onion-like carbon) and complex (nanocones, nanohorns, nanodisks and nanorings) geometries. To demonstrate the proof-of-concept, we determined the variation in the prominent Raman bands of the respective materials, represented as D, G and D * (the overtone of D) bands, as a possible topological or curvature trend due to their sensitivity toward structural modification. The latter arises from local topological defects such as pentagons giving rise to curved nanocarbons. In this study, we provide systematics of their variation with respect to their geometric forms and compare with highly oriented pyrolytic graphite and monolayer graphene since the nanocarbons discussed are their derivatives. Once established, this knowledge will provide a powerful machinery to understand newer nanocarbons and indeed point to an unprecedented emergent paradigm of global topology/curvature → property → functionality relationship. We emphasize that these concepts are applicable to other topologically distinct nanomaterials, which include boron-nitride (BN) nanotubes and nanotori, helical gold nanotubes and Möbius conjugated organics. Copyright

Nanostructuration of carbonaceous dust as seen through the positions of the 6.2 and 7.7μm AIBs

“…When curvature increases with no defects, R Tor increases because curvature enhances the 2*D1 band intensity compared to that for mostly planar graphene layers (Larouche & Stansfield 2010;Gupta & Saxena 2009). If the number of defects is increasing, R Tor decreases.…”

“…It was shown that, depending on the flame conditions, flat to strongly curved native nanoparticles may be produced (Violi 2004). Curvature due to the presence of defects, such as pentagonal rings, within the polyaromatic unit leads to spherical structures, while perfectly hexagonal graphene sheet can form only tubular-type curvature (Gupta & Saxena 2009). Tortuosity A40, page 10 of 14 is associated with reticulation due to small aliphatic bridges that link different polyaromatic units.…”

Functionalized Graphene–Polyoxometalate Nanodots Assembly as “Organic–Inorganic” Hybrid Supercapacitors and Insights into Electrode/Electrolyte Interfacial Processes

“…In general, all absorption spectral bands arising in UV-Vis range of the electronic spectra of heteropoly compounds containing Keggin polyanion [ [55,56]. Raman spectroscopy is widely used non-destructive technique for the characterization of carbon-based materials [57] and POMs [58][59][60], M = Mo and W since it is highly sensitive to local structure and lattice vibrational bonding configurations within molecules and their interactions with graphene. Keggin-type HPAs are formed by assembling three MO 6 octahedra by edge-sharing oxygen atoms (M-O c -M) to form M 3 O 13 sets, which further condense by sharing corner oxygen atoms (M-O b -M) around a central atom (P or Si) to form a cage.…”

Evaluation of crystalline perfection degree of multi‐walled carbon nanotubes: correlations between thermal kinetic analysis and micro‐Raman spectroscopy

“…[5,13] As a result, only the E 2g symmetry in-plane optical mode (G line at 1582 cm −1 ), associated with the stretching of all C C pairs, is detected in its first-order Raman spectrum (spectrum (a) in Fig. 1).…”

“…In recent years, attention, initially focused on nanostructures with simple geometries (planar: graphene; [3] tubular: single-, double-and multi-walled CNTs; [2] spherical/spheroidal: fullerenes, onion-like carbon, nanocages [4] ) has been extended to C sp 2 allotropic forms with complex geometries (nanorings, nanocones, nanohorns, nanodisks, Y, T and X junctions, twisted ribbons). [5] However, in spite of the great proliferation of novel and attractive nanocarbons, CNTs still play a leading role in nanotechnologies, involving the most disparate application fields, from nanoelectronics [6] to medicine. [7] Single-and multi-walled carbon nanotubes (SWCNTs and MWCNTs) are successfully synthesised by a number of methods.…”