Energy loss of H+ and H2+ beams in carbon nanotubes: a joint experimental and simulation study

Abstract

Carbon nanotube properties can be modified by ion irradiation; therefore it is important to know the manner in which ions deposit energy (how much and where) in the nanotubes. In this work, we have studied, experimentally and with a simulation code, the irradiation of multi-walled carbon nanotubes (MWCNT), supported on a holey amorphous carbon (a-C) substrate, with low energy (2−10 keV/u) H + and H2 + molecular beams, impinging perpendicularly to the MWCNT axis. The energy distribution of protons traversing the nanotubes (either from the H + beam or dissociated from the H2 + beam) was measured by the transmission technique in the forward direction. Two well-differentiated peaks appear in the experimental energy-loss distribution of the fragments dissociated from the molecular H2 + beam, in correspondence to the ones detected with the proton beam. One is the low-energy loss peak (LELP), which has a symmetric width; the other is the high-energy loss peak (HELP), which shows an asymmetric broadening towards larger energy loss than the corresponding proton energy distribution. A semi-classical simulation, accounting for the main interaction processes (both elastic and inelastic), of the proton trajectories through the nanotube and the supporting substrate has been done, in order to elucidate the origin of these structures in the energy spectra. Tregarding the H + energy spectrum, the LELP corresponds to projectiles that travel in quasi-channelling motion through the most outer walls of the nanotubes and then pass thorugh the substrate holes, whereas the HELP results mostly from projectiles traversing only the a-C substrate, with the asymmetry broadening being due to a minor contribution of those protons that cross the a-C substrate after exiting the nanotube. The broadening of the peaks corresponding to dissociated fragments, with respect to that of the isolated protons, is the result of vicinage effects between the fragments, when travelling in quasi-channelling conditions through the outer layers of the nanotube, and Coulomb explosion just after exiting the target. The excellent agreement between the measured and the simulated energy spectra of the H + beam validates our simulation code in order to predict the energy deposited by ion beams in carbon nanotubes.

Special issue: Dynamics of systems on the nanoscale (2018). Editorial

“…These software packages have been designed to become powerful and universal instruments of computational research in the field of MBN Science, which should play a role of a "virtual microscope" and a "camera" capable to explore, simulate, record and visualize both structure and dynamics of the MBN-world with an atomistic level of accuracy, in order to both reproduce its known features and predict the new ones. In this Topical Issue, many contributions [12][13][14][15][16][17][18][19][20][21][22][24][25][26][27][28][29][30][31][32][33][34][35] provide case studies conducted with these packages and demonstrate their application to a broad variety of topical areas in MBN science as listed at the beginning of this Editorial. To be noted that these universal and powerful software packages are fully applicable to a broad variety of the topical areas of the MBN Science listed above in the introductory part of the Editorial.…”

“…Irradiation of nanosystems affects their structure and dynamics resulting in transformations and damage. A study by Valdes et al [22] reports experimental and computational results of irradiation of multi-walled carbon nanotubes (MWCNT) deposited on a holey amorphous carbon (a-C) substrate with low energy (2-10 keV/u) H + and H + 2 molecular beams, impinging perpendicularly to the MWCNT axis. The energy distribution of protons traversing the nanotubes (either from the H + beam or dissociated from the H + 2 beam) was measured by the transmission technique in the forward direction.…”