Sublimation Kinetics for Individual Graphite and Graphene Nano-particles (NPs): NP-to-NP Variations and Evolving Structure-Kinetics and Structure-Emissivity Relationships

A single nanoparticle (NP) mass spectrometry method was used to measure sublimation rates as a function of nanoparticle temperature (TNP) for a number of individual graphite and graphene NPs. Initially, the NP sublimation rates were ca. 400 times faster than that for bulk graphite, and there were large NP-to-NP variations. Over time, the rate slowed substantially, though remaining well above the bulk rate. The initial activation energies (Eas) were correspondingly low and doubled as a few monolayer's worth of material were sublimed from the surfaces. The high initial rates and low Eas are attributed to large numbers of edge and other low coordination sites on the NP surfaces, and the changes are attributed to atomic-scale "smoothing" of the surface by preferential sublimation of the less stable sites. The emissivity of the NPs also changed after heating, most frequently increasing. The emissivity and sublimation rates were anti-correlated, leading to the conclusion that high densities of low-coordination sites on the NP surfaces enhances sublimation but suppresses emissivity.