The following describes our method for quantifying the relative metallic and semiconducting enrichment of our nanotube products. In short, we determine the metallic/semiconducting transition-energy peaks of the CNT species in our material using simple tight-binding calculations. We then measure these peaks via optical absorbance, and scale them by empirically determined extinction coefficients. Read on for more information. Starting Material and Predictions We start with electric-arc discharge SWNTs having a fairly narrow diameter distribution. Manufacturer claims: tight diameter distribution between 1.2-1.7 nm (with majority between 1.25-1.55 nm), peaked at 1.4nm Using a cc ~ 0.143 nm, γo ~ 2.9 eV and d ~ 1.2-1.7 nm, we can obtain rough estimates for E ii ranges: - SE22 transitions should lie between ~ 900-1270 nm - ME11 transitions should lie between ~ 600-850 nm - SE33 transitions should lie between ~ 450-630 nm - ME22 transitions should lie between ~ 300-420 nm We estimate our purities based on ratios of the M11 and S22 peak areas after linear background subtraction - The individual peak areas are scaled by empirically-determined values for the M11 and S22 extinction coefficients to determine metal-semiconductor purities
