Simulations and analytic models of ion guiding through a nanocapillary in insulating polymers

Simulations of ion guiding through an insulating cylindrical nanocapillary are performed in continuation of a recent theoretical work [N. Stolterfoht, Phys. Rev. A 87, 012902 (2013)]. The ions are assumed to move on classical trajectories affected by the electric field primarily produced by the charge patch deposited near the capillary entrance. The deposited charges are transported along the capillary wall using a nonlinear conductivity law. Calculations for different capillary tilt angles from 0 degrees to 8 degrees are performed and compared with previous experimental results. The main focus of the analysis is to reveal unknown guiding mechanisms by a detailed investigation of the calculated results. Surprisingly, after reaching a maximum, the field component perpendicular to the capillary axis is found to decrease with increasing charge inserted into the capillary. At equilibrium, this field is nearly constant in all directions of the capillary along the entrance charge patch. The extension of this charge patch increases with increasing tilt angle although a simple picture of undeflected ions predicts the opposite behavior. These unexpected results simplify the theoretical treatment so that analytical expressions could be derived describing essential properties of the ion guiding. In particular, unknown parameters previously introduced in semiempirical models are interpreted. DOI:10.1103/PhysRevA.87.032901