Laser Annealing Nanoscale Carbons: Material Transformations

摘要

Laser processing of materials is not new, but using lasers to anneal, bond and otherwise transform carbons is. Fundamental understanding of the dependence upon carbon structure, morphology and chemistry is critical to implementing this technology into manufacturing and processing applications. Here initial results using pulsed laser annealing of nanocarbons are performed using a Nd:YAG laser operating at 1064 nm and laser fluence of 250 mJ/cm~2. A gated intensified CCD captured the spectra of the material incandescence, fitting the spectral profile yielded a temperature of 2800 K for this laser fluence. To resolve detailed morphological and nanostructural changes induced in the nanocarbons by the pulsed, high-intensity laser light, high-resolution transmission electron microscopy (HRTEM) is applied while electron energy loss spectroscopy (EELS) is applied to examine local sp~2/sp~3 chemistry. The annealing process accentuated the recognizable structural differences and led to graphitization of lamellae, but the spatial organization of lamellae was quite different across carbons tested. Initial nanostructure in conjunction with the chemistry of construction appears to govern the carbon transformation under pulsed laser annealing.