Diagnostics of laser-produced plume under carbon nanotube growth conditions

Abstract.

This paper presents diagnostic data obtained from the plume of a graphite composite target during carbon nanotube production by the double-pulse laser oven method. The in situ emission spectrum (300 to 650 nm) is recorded at different locations upstream of the target and at different delay times from the lasers (IR and green). Spectral features are identified as emissions from C₂ (Swan System: d³Π_g–a³Π_u) and C₃ (Comet Head System: A¹Π_u–X¹Σ_u ⁺). Experimental spectra are compared with computed spectra to estimate vibrational temperatures of excited state C₂ in the range of 2500 to 4000 K. The temporal evolution of the 510-nm band of C₂ is monitored for two target positions in various locations, which shows confinement of the plume in the inner tube and increase in plume velocity with temperature. The excitation spectra of C₂ are obtained by using a dye laser to pump the (0,1) transition of the Swan System and collecting the laser-induced fluorescence signal from C₂. These are used to obtain “ground-state” rotational and vibrational temperatures which are close to the oven temperature. Images of the plume are also collected and are compared with the spectral measurements.