Figure 1: (a) An SEM image of the as-prepared Co/MgO catalyst and (b) the catalyst after CVD growth. Raman spectra of SWNTs acquired with different excitation wavelengths of (c) 633 nm and (d) 514 nm from different positions on the Co/MgO catalyst after CVD growth at 850°C. Top: laser center; middle: transition zone; and bottom: without laser irradiation.