17 research outputs found
Encoding Velocity in a Photograph
Author Institution: Los Alamos National LaboratorySlides presented at the 2018 Photonic Doppler Velocimetry (PDV) Users Workshop, Drury Plaza Hotel, Santa Fe, New Mexico, May 16-18, 2018
The Unique Origin of Colors of Armchair Carbon Nanotubes
The colors of suspended metallic colloidal particles are determined by their
size-dependent plasma resonance, while those of semiconducting colloidal
particles are determined by their size-dependent band gap. Here, we present a
novel case for armchair carbon nanotubes, suspended in aqueous medium, for
which the color depends on their size-dependent excitonic resonance, even
though the individual particles are metallic. We observe distinct colors of a
series of armchair-enriched nanotube suspensions, highlighting the unique
coloration mechanism of these one-dimensional metals.Comment: 4 pages, 3 figure
Fundamental optical processes in armchair carbon nanotubes
Single-wall carbon nanotubes provide ideal model one-dimensional (1-D) condensed matter systems in
which to address fundamental questions in many-body physics, while, at the same time, they are
leading candidates for building blocks in nanoscale optoelectronic circuits. Much attention has been
recently paid to their optical properties, arising from 1-D excitons and phonons, which have been
revealed via photoluminescence, Raman scattering, and ultrafast optical spectroscopy of semiconducting
carbon nanotubes. On the other hand, dynamical properties of metallic nanotubes have been poorly
explored, although they are expected to provide a novel setting for the study of electronヨhole pairs in
the presence of degenerate 1-D electrons. In particular, (n,n)-chirality, or armchair, metallic nanotubes
are truly gapless with massless carriers, ideally suited for dynamical studies of TomonagaヨLuttinger
liquids. Unfortunately, progress towards such studies has been slowed by the inherent problem of
nanotube synthesis whereby both semiconducting and metallic nanotubes are produced. Here, we use
post-synthesis separation methods based on density gradient ultracentrifugation and DNA-based ion-exchange chromatography to produce aqueous suspensions strongly enriched in armchair nanotubes.
Through resonant Raman spectroscopy of the radial breathing mode phonons, we provide macroscopic
and unambiguous evidence that density gradient ultracentrifugation can enrich ensemble samples in
armchair nanotubes. Furthermore, using conventional, optical absorption spectroscopy in the nearinfrared
and visible range, we show that interband absorption in armchair nanotubes is strongly
excitonic. Lastly, by examining the G-band mode in Raman spectra, we determine that observation of
the broad, lower frequency (G!) feature is a result of resonance with non-armchair “metallic”
nanotubes. These !ndings regarding the fundamental optical absorption and scattering processes in
metallic carbon nanotubes lay the foundation for further spectroscopic studies to probe many-body
physical phenomena in one dimension
Coherent Lattice Vibrations in Single-Walled Carbon Nanotubes
We have generated and detected coherent lattice vibrations in single-walled carbon nanotubes corresponding to the radial breathing mode (RBM) using ultrashort laser pulses. Because the band gap is a function of diameter, these RBM-induced diameter oscillations cause ultrafast band gap oscillations, thereby modulating the interband excitonic resonances at the phonon frequencies (3−9 THz). Excitation spectra show a large number of pronounced peaks, allowing the determination of the chiralities present in particular samples and relative population differences of particular chiralities between samples