A. Lan

Detecting single-wall carbon nanotubes with surface-enhanced Raman scattering from metal-coated periodic structures

We report on surface-enhanced Raman scattering (SERS) from bundles of size-selected single-wall carbon nanotubes (SWCNTs) deposited on ordered arrays of silver- and gold-coated silica spheres. Selective enhancement of the Raman-active tangential and radial modes of SWCNTs is exhibited in backscattering at surface plasmon resonance conditions. Enhancement at plasmon wavelength and sub-wavelength is shown for various periodic pitches of the substrates used.

Growth of single-wall carbon nanotubes within an ordered array of nanosize silica spheres

Single-wall carbon nanotubes (SWCNTs), which were well-separated individuals or, small bundles of two to five tubes, were produced in a controllable manner by disproportionation of CO at 700 °C and 1 atm in the voids of an ordered array of silica spheres with embedded bimetallic Mo/Co catalytic particles. A combination of transmission electron microscopy, electron energy-loss spectroscopy, and Raman scattering excited with an Ar laser at λ=514.5 nm (2.41 eV), was used to characterize the nanotubes. The corresponding Raman spectra strongly indicate that these nanotubes are primarily chiral. This method offers a valid route for a high-quality single-step production of SWCNT composites for mechanical, electronic, and optoelectronic applications.

Linear and nonlinear optical properties of single-walled carbon nanotubes within an ordered array of nanosized silica spheres

The linear and nonlinear optical properties of well-separated, single-walled carbon nanotubes were measured. The tubes were grown into the voids of an ordered array of silica spheres. Transmission of light through these tubes increased with the incident laser intensity. The nonlinear decay time of a λ=800-nm probe was measured at 320 fs when the sample was pumped with 400-nm light. Current–voltage characteristics changed upon illumination with a laser beam. Raman scattering decreased as electrical biasing increased.

Optical and electronic characteristics of single walled carbon nanotubes and silicon nanoclusters by tetrahertz spectroscopy

We have conducted visible pump-THz (THz—terahertz) probe measurements on single wall carbon nanotubes deposited on quartz substrates. Our results suggest that the photoexcited nanotubes exhibit localized transport due to Lorentz-type photoinduced localized states from 0.2 to 0.7 THz. Upon modeling the THz transmission through the photoexcited layer with an effective dielectric constant given by Maxwell-Garnett theory we found that the data are best fit by a broad Lorentz state at 0.5 THz. These experiments were repeated for ion-implanted, 3–4 nm Si nanoclusters in quartz for which a similar behavior was observed.

Nonlinear optical properties of laser ablated silicon nanostructures

The role of crystallite symmetry on the nonlinear optical properties of laser ablated silicon films is discussed in this article. Laser ablated Si films exhibit a nonlinear refractive index change which may be as high as Δn=−0.5 at wavelength of λ=532 nm for films with an average thickness of 200 nm. However, the origin of this nonlinearity is not known. These films consist of large droplets comprised of hexagonal wurtzite symmetry crystallites and nanoclusters interspersed between them. Using Raman spectroscopy and linear and nonlinear optical measurements, we monitored the crystallographic symmetry of these droplets when annealed under various conditions. Based on the results we attribute the large nonlinear refraction coefficient to the hexagonal wurtzite symmetry of the crystallites, hence raising the possibility for developing very efficient nonlinear optical devices.

Detection of C60 using surface-enhanced Raman scattering from metal-coated periodic structures

Surface-enhanced Raman scattering from C60 deposited on ordered arrays of silver- and gold-coated silica spheres have been measured. Selective enhancement of the Raman-active modes was exhibited in backscattering at surface plasmon resonance conditions. The advantage of signal enhancement at excited (scattered) wavelengths for subwavelength surface plasmons was demonstrated for this photosensitive molecular solid.

Characteristics of nanoscale composites by terahertz spectroscopy

We have conducted visible pump-THz probe experiments on single wall carbon nanotubes (SWCNTs) on quartz substrates. Our results suggest an upper limit to the carrier-lifetime, which is on the order 1.5ps, limited only by the THz pulse duration. These experiments were repeated for ion-implanted, 3-4nm Si nanoclusters in quartz for which the carrier lifetime was also assessed at 1.5ps. THz time-domain spectroscopy (THz-TDS) of SWCNTs revealed that the THz pulse peak transmission changed under optical illumination.

Characteristics of nanoscale composites by THz spectroscopy

We have conducted visible pump-THz probe experiments on single wall carbon nanotubes (SWCNTs) deposited on quartz substrates. Our results suggest that the nanotubes exhibit localized transport due to Lorentz-type photo-induced localized states.

Femtosecond non-degenerate pump-probe measurements of single-wall carbon nanotubes (SWCNTs) within an ordered array of nanosize silica spheres

We present preliminary lifetime data of single-wall carbon nanotubes (SWCNTs) grown within the voids of an ordered array of silica spheres. Non-degenerate pump-probe measurements with /spl lambda//sub pump/ = 400 nm and /spl lambda//sub probe/ = 800 run indicate a decay of 319 /spl plusmn/ 25 fs.

Non-linear and linear optical properties of single wall carbon nanotubes within photonic crystals

We characterized Single Wall Carbon Nanotubes imbedded within an ordered array of nanosize silica spheres in the visible and THz spectral regions.