Article

Chiral index dependence of the G+ and G- Raman modes in semiconducting carbon nanotubes.

Center for Integrated Nanotechnologies, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA.
ACS Nano (Impact Factor: 12.03). 12/2011; 6(1):904-11. DOI: 10.1021/nn2044356
Source: PubMed

ABSTRACT Raman spectroscopy on the radial breathing mode is a common tool to determine the diameter d or chiral indices (n,m) of single-wall carbon nanotubes. In this work we present an alternative technique to determine d and (n,m) based on the high-energy G(-) mode. From resonant Raman scattering experiments on 14 highly purified single chirality (n,m) samples we obtain the diameter, chiral angle, and family dependence of the G(-) and G(+) peak position. Considering theoretical predictions we discuss the origin of these dependences with respect to rehybridization of the carbon orbitals, confinement, and electron-electron interactions. The relative Raman intensities of the two peaks have a systematic chiral angle dependence in agreement with theories considering the symmetry of nanotubes and the associated phonons.

1 Bookmark
 · 
163 Views
  • [Show abstract] [Hide abstract]
    ABSTRACT: Over the past two decades, single-walled carbon nanotubes (SWCNTs) have received much attention because their extraordinary properties are promising for numerous applications. Many of these properties depend sensitively on SWCNT structure, which is characterized by the chiral index (n,m) that denotes the length and orientation of the circumferential vector in the hexagonal carbon lattice. Electronic properties are particularly strongly affected, with subtle structural changes switching tubes from metallic to semiconducting with various bandgaps. Monodisperse 'single-chirality' (that is, with a single (n,m) index) SWCNTs are thus needed to fully exploit their technological potential. Controlled synthesis through catalyst engineering, end-cap engineering or cloning strategies, and also tube sorting based on chromatography, density-gradient centrifugation, electrophoresis and other techniques, have delivered SWCNT samples with narrow distributions of tube diameter and a large fraction of a predetermined tube type. But an effective pathway to truly monodisperse SWCNTs remains elusive. The use of template molecules to unambiguously dictate the diameter and chirality of the resulting nanotube holds great promise in this regard, but has hitherto had only limited practical success. Here we show that this bottom-up strategy can produce targeted nanotubes: we convert molecular precursors into ultrashort singly capped (6,6) 'armchair' nanotube seeds using surface-catalysed cyclodehydrogenation on a platinum (111) surface, and then elongate these during a subsequent growth phase to produce single-chirality and essentially defect-free SWCNTs with lengths up to a few hundred nanometres. We expect that our on-surface synthesis approach will provide a route to nanotube-based materials with highly optimized properties for applications such as light detectors, photovoltaics, field-effect transistors and sensors.
    Nature 08/2014; 512(7512):61-4. · 38.60 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The chiral structure of single-walled carbon nanotubes (SWNTs) and the edge structure of graphene nanoribbons (GNRs) play an important role in determining their electronic and phonon structures. Spectroscopic methods, which require simple sample preparation and cause minimal sample damage, are the most commonly utilized techniques for determining the structures of SWNTs and graphene. In this review the current status of various spectroscopic methods are presented in detail, including resonance Raman, photoluminescence (PL), and Rayleigh scattering spectroscopies, for determination of the chiral structure of individual SWNTs and the edge structure of isolated graphene, especially of graphene nanoribbons. The different photophysical processes involved in each spectroscopic method are reviewed to achieve a comprehensive understanding of the electronic and phonon properties of SWNTs and graphene. The advantages and limitations of each spectroscopic method as well as the challenges in this area are discussed.
    Small 03/2013; · 7.82 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The search for environmentally clean energy sources has spawned a wave of research into the use of carbon nanomaterials for photovoltaic applications. In particular, research using semiconducting single-walled carbon nanotubes has undergone dramatic transformations due to the availability of high quality samples through colloidal separation techniques. This has led to breakthrough discoveries on how energy and charge transport occurs in these materials and points to applications in energy harvesting. We present a review of the relevant photophysics of carbon nanotubes that dictate processes important for integration as active and passive material elements in thin film photovoltaics. Fundamental processes ranging from light absorption and internal conversion to exciton transport and dissociation are discussed in detail from both a spectroscopic and a device perspective. We also give a perspective on the future of these fascinating materials to be used as active and passive material elements in photovoltaics.
    Physical Chemistry Chemical Physics 08/2013; · 4.20 Impact Factor