Structural, electronic, optical and vibrational properties of nanoscale carbons andnanowires: a colloquial review

Abstract

This review addresses the field of nanoscience as viewed through the lens of the scientificcareer of Peter Eklund, thus with a special focus on nanocarbons and nanowires. Peterbrought to his research an intense focus, imagination, tenacity, breadth and ingenuityrarely seen in modern science. His goal was to capture the essential physics of naturalphenomena. This attitude also guides our writing: we focus on basic principles, withoutsacrificing accuracy, while hoping to convey an enthusiasm for the science commensuratewith Peter’s. The term ‘colloquial review’ is intended to capture this style of presentation.The diverse phenomena of condensed matter physics involve electrons, phononsand the structures within which excitations reside. The ‘nano’ regimepresents particularly interesting and challenging science. Finite size effectsplay a key role, exemplified by the discrete electronic and phonon spectra ofC60 and other fullerenes. The beauty of such molecules (as well as nanotubes and graphene) isreflected by the theoretical principles that govern their behavior. As to the challenge,‘nano’ requires special care in materials preparation and treatment, since thesurface-to-volume ratio is so high; they also often present difficulties of acquiring anexperimental signal, since the samples can be quite small. All of the atoms participate inthe various phenomena, without any genuinely ‘bulk’ properties. Peter was a master ofovercoming such challenges.The primary activity of Eklund’s research was to measure and understand the vibrationsof atoms in carbon materials. Raman spectroscopy was very dear to Peter. Hepublished several papers on the theory of phonons (Eklund et al 1995a Carbon 33959–72, Eklund et al 1995b Thin Solid Films 257 211–32, Eklund et al 1992 J.Phys. Chem. Solids 53 1391–413, Dresselhaus and Eklund 2000 Adv. Phys. 49705–814) and many more papers on measuring phonons (Pimenta et al 1998bPhys. Rev. B 58 16016–9, Rao et al 1997a Nature 338 257–9, Rao et al 1997b Phys.Rev. B 55 4766–73, Rao et al 1997c Science 275 187–91, Rao et al 1998 Thin SolidFilms 331 141–7). His careful sample treatment and detailed Raman analysiscontributed greatly to the elucidation of photochemical polymerization of solidC60 (Rao et al 1993b Science 259 955–7). He developed Raman spectroscopy as a standard toolfor gauging the diameter of a single-walled carbon nanotube (Bandow et al 1998 Phys. Rev.Lett. 80 3779–82), distinguishing metallic versus semiconducting single-walled carbonnanotubes, (Pimenta et al 1998a J. Mater. Res. 13 2396–404) and measuring the number ofgraphene layers in a peeled flake of graphite (Gupta et al 2006 Nano Lett. 6 2667–73). Forthese and other ground breaking contributions to carbon science he received the GraffinLecture award from the American Carbon Society in 2005, and the Japan Carbon Prize in2008.As a material, graphite has come full circle. The 1970s renaissance in the science ofgraphite intercalation compounds paved the way for a later explosion in nanocarbonresearch by illuminating many beautiful fundamental phenomena, subsequentlyrediscovered in other forms of nanocarbon. In 1985, Smalley, Kroto, Curl, Heath andO’Brien discovered carbon cage molecules called fullerenes in the soot ablated from arotating graphite target (Kroto et al 1985 Nature 318 162–3). At that time, Peter’s researchwas focused mainly on the oxide-based high-temperature superconductors. He switched tofullerene research soon after the discovery that an electric arc can prepare fullerenes in bulkquantities (Haufler et al 1990 J. Phys. Chem. 94 8634–6). Later fullerene research spawnednanotubes, and nanotubes spawned a newly exploding research effort on single-layergraphene. Graphene has hence evolved from an oversimplified model of graphite (Wallace1947 Phys. Rev. 71 622–34) to a new member of the nanocarbon family exhibitingextraordinary electronic properties. Eklund’s career spans this 35-year odyssey.