Thermal activation and saturation of ion beam sculpting

Abstract

We report a material-dependent critical temperature for ion beam sculpting of nanopores in amorphous materials under keV ion irradiation. At temperatures below the critical temperature, irradiated pores open at a rate that soon saturates with decreasing temperature. At temperatures above the critical temperature, the pore closing rate rises rapidly and eventually saturates with increasing temperature. The observed behavior is well described by a model based on adatom diffusion, but is difficult to reconcile with an ion-stimulated viscous flow model.

Nanometer-thin solid-state nanopores by cold ion beam sculpting

“…At low temperatures, the surface diffusivity D can be reduced to the point that X m approaches zero and prefabricated SiN pores open instead of close under ion beam exposure. 1,4 In this work we show that in the low temperature limit, surface diffusion is almost completely suppressed and removal of material by sputtering dominates pore formation, allowing the fabrication of very thin nanopores. This cold ion beam sculpting (CIBS) method does not require preexisting pores and eliminates the "volcano phenomenon.…”

Superplastic nanoscale pore shaping by ion irradiation

“…It is worth pointing that some of the mentioned effects, such as sputtering and cavity swelling scale with temperature 26 – 28 . However, experiments performed at higher temperatures shows that the pore closure efficiency dramatically reduced by increasing the temperature, most probably due to the reduced mean-free path of the diffusive entities at higher temperatures 7 . Local temperature increase 29 at the interaction spot of the ion beam is not expected to be significant within the keV light-ion irradiation regime 3 , 7 .…”

“…However, experiments performed at higher temperatures shows that the pore closure efficiency dramatically reduced by increasing the temperature, most probably due to the reduced mean-free path of the diffusive entities at higher temperatures 7 . Local temperature increase 29 at the interaction spot of the ion beam is not expected to be significant within the keV light-ion irradiation regime 3 , 7 . This is also evident from our experiments, where pore closure rates reduced with increasing the beam-flux, or increasing the substrate temperature.…”

“…The concentration of the ion-induced 'adatoms' is proportional to irradiation flux 34 ; however, mobility of these entities depend on other parameters such as recombination rates 11 , electron’s mean-free path 10 , structural defects 12 , chemical bonds 10 , stress 34 , temperature 7 , and electrostatic forces 8 . Generally, enhancement in mobility/diffusion of these entities leads to improved mass-flow rates, and, therefore, efficiency in pore closure.…”

“…For instance, the size of a prefabricated pore (in a silicon nitride membrane) can be reduced to a sub-nanometer domain when irradiated with keV Ar + ions 1 , or the length of prefabricated nanowires (GaAs and InAs) can be increased by keV He + irradiation 4 . Various aspects of interaction of low-energy light ions with nanomaterials are being investigated 7 – 9 . However, the role of the chemical bonds and degree of disorder in bond breaking and diffusion of matter subjected to irradiation remains to be elucidated 10 – 12 .…”