Ion transmission through nanochannels: Energy dependent acceptance angle and transmission probability

Abstract

The transmission of energetic (0.1–2 MeV) light ions through an array of parallel nanochannels was measured as a function of incident angle with respect to the channel axis. The angular transmission can be viewed macroscopically, similar to an ion passing through a collection of parallel slits which then determine the beam profile or similar to ion channeling in crystals. In the first case, the number of transmitted ions as a function of incident angle would be determined simply by the line-of-sight geometry (length over diameter) of the nanotube resulting in a critical angle of about 0.2° whereas in the second case, the acceptance angle would be much larger, nearly 0.8°, and analogous to the acceptance angle typically encountered in ion channeling in crystals. The measured critical angle varies between 0.4° and 0.8° depending on the incident ion energy, but with increasing energy the critical angle becomes larger rather than smaller. The transmittance at the optimal angle increases with energy and shows a strong linear correlation with it. This can be understood as a consequence of repeated interactions with the channel walls as the channeled ions travel along the channel.