This paper describes improved methods for both data acquisition and analysis that are pertinent to interpreting the structural composition of single-walled carbon nanotube (SWNT) mixtures and suspensions.
Rapid data acquisition of photoluminescence is made possible with a specially configured spectrofluorometer which uses a liquid nitrogen-cooled InGaAs array detector, imaging spectrograph, excitation reference photodiode and tunable xenon excitation source to collect seamless, instrument-corrected, excitation-emission quantum maps. The preferred instrument configuration with the InGaAs array can generate a quantum map with both high S/N levels and spectral resolution in only seconds to minutes; previous single-channel InGaAs photodiode and photomultiplier detector measurements took hours to days. The standard spectral range for excitation and emission is from 250 nm to 1700 nm with an option to extend to 2200 nm. Robust analysis of the quantum maps is facilitated by a custom global analysis program (US Patent Pending) which incorporates a powerful ‘double-convolution integral’ DCI algorithm to simultaneously model the excitation and emission spectral bands for each SWNT species. The patented DCI algorithm reduces the number of free fitting parameters for the spectral simulation by up to a factor of 1000 compared to conventional 2 D spectral simulators. The global analysis yields quantitative information on the chirality and diameter parameters of SWNT species in a given mixture. Together the acquisition hardware and analysis software constitute significant developments with respect to enhanced sensitivity and statistical significance for quantifying the components of complex SWNT mixtures.
Raman maps of SWNT's were collected from dispersions plated onto substrates such as silicon plates using multiple excitation wavelengths. Identification of the chirality of the tubes was made using the Kataura plot. In many instances single lines in the radial breathing mode region were recorded indicating the presence of a single tube. The implication for this observation is that there is more than adequate sensitivity to detect and identify single-walled tubes. More recently Raman excitation on an AFM using a gold-coated tip to induce surface enhancement has been achieved. In this configuration it will be possible to map the topology of the tubes using detailed information on their structural composition.