To gain further insights into the tube diameters, we performed an additional set of isothermal (750 and 850 ºC) and non-isothermal CVD growth experiments on thinner catalyst films (0.3 nm Co); this catalyst thickness produces sparse CNT growth (not vertically aligned arrays) containing a majority of single-walled CNTs, which makes it easier to distinguish between RBM peaks in the Raman spectra and enables statistical counting. Figure shows representative transmission electron microscopy (TEM) images from the nanotubes obtained in a typical growth experiment. Raman spectral mapping was performed on the substrates using three laser excitations -514.5, 633 and 785 nm. These three wavelengths cover a majority of CNTs with respect to helicities and therefore analysis of the RBM frequencies excited by these wavelengths provides a broad overview of the tube diameter distributions on the substrates. As done previously, the spacing between each point in the maps was set to 20 µm to avoid overcounting of tubes. Histograms of the RBM frequencies (bin width set to 5 cm -1 ) from the isothermal and non-isothermal growth experiments are shown in Figure . Between the two isothermal growths, the RBM frequencies are on average lower for 850 ºC, indicating larger diameter CNTs. Tube diameters (the top axis in Figure ) were calculated according to the formula dt = 248/wRBM, where dt and wRBM are the tube diameter and RBM frequency, respectively. The average diameter of the CNTs increased slightly from 1.3 to 1.41 nm as the temperature was increased from 750 to 850 ºC. This increase in diameter with temperature is expected due to catalyst particle coarsening. Interestingly, the CNT diameters in the non-isothermal growth (1.24 nm) were on average slightly smaller than the isothermal growth at 750 ºC (1.3 nm). As can be seen in the histogram in Figure , the non-isothermal growth has a higher density of RBMs above 220 cm -1 , which correspond to CNTs with diameters less than 1.1 nm.