Thermal spike-induced cluster sublimation from carbon nanotubes

Abstract

We report and provide justification for the consistently observed four experimental facts of mass spectrometric data of carbon cluster emission from the Cs⁺-irradiated single-walled carbon nanotubes (SWCNTs). Firstly, the diatomic carbon C₂ is the most abundant sputtered species. Secondly, monatomic carbon C₁ yield is Cs⁺ energy dependent. Thirdly, at low caesium energies, only C₂, C₃ and C₄ are emitted. Lastly, the normalised yield of C₁ monotonically increases while C₂, C₃ and C₄ show gradual decrease leading to saturation. The experimental data for the normalised density of clusters and atoms follow the pattern  >  >  > . A statistical thermal model is developed to explain the experimentally observed sputtering of clusters. The probability of a cluster C_x to be emitted is proportional to that for the creation of an x-member vacancy with formation energy E_xv at temperature T_s as {exp(E_xv/kT_S) + 1}⁻¹. The energies of formation of vacancies from DFT calculations and the ratio of normalised experimental yields have been used to estimate T_S. Once T_s is evaluated, the formation energies of tri- and quarto-vacancies are obtained using the ratios of normalised densities and . We show that by invoking thermal spikes, cluster emission from, and the multiple vacancy generation in, the Cs⁺-irradiated SWCNTs can be explained.

Keywords:

• Carbon nanotubes
• ion irradiation
• clusters
• thermal spike
• Monte Carlo
• surface thermodynamics