Correlation between density and hydrogen content in vertically aligned carbon nanotube forests by ion beam analysis

Interactions of vertically aligned multiwall carbon nanotubes (CNTs) with high energy He⁺ beams were studied using elastic recoil detection analysis and ion beam channeling. The relationship between the elastic recoil of hydrogen, the depth of He-H interactions, and the number of carbon atoms per volume (denoted as effective density) was calculated. Ion channeling was observed in CNT forests shorter than 40 μm. It was found that the effective density and hydrogen content were inversely correlated with the CNT height. In compliance with channeling and density calculations, the authors propose that this effect is due to the weakening of Van-der-Waals forces in taller CNT forests. The methodology suggested in this work may be extended to assessing densities of thin, highly porous materials.