Ions transmitted through an anodic nanocapillary array

Abstract

The transmission of incident $10--20\phantom{\rule{0.3em}{0ex}}\mathrm{keV}∕q$ ${\mathrm{Ar}}^{+}$, ${\mathrm{Ar}}^{3+}$, ${\mathrm{Ne}}^{3+}$, and ${\mathrm{Ne}}^{7+}$ ions in an ${\mathrm{Al}}_{2}{\mathrm{O}}_{3}$ nanocapillary array was studied. The array consists of a dense distribution of pores typically $100\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ in diameter and $60\phantom{\rule{0.3em}{0ex}}\mathrm{\ensuremath{\mu}}\mathrm{m}$ in length. Emergent charge-state-selected angular distributions were studied at low energy using a two-dimensional (2D) position sensitive detector. The principal transmitted $q$ state is the incident $q$ state in all cases. The transmitted fraction of incident beam, $\ensuremath{\approx}2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}8}$, is many orders of magnitude smaller than the array's surface porosity $(\ensuremath{\approx}40%)$. No evidence of significant energy loss is observed for the transmitted ions. Yields in lower $q$ states and neutrals formed by electron capture are typically below 3% of the entrance $q$-state yield. Observed angular distributions consist of well resolved, 2D structures sitting on a continuum distribution. The angular distribution and sharp angular structures can be steered in the direction of the pores within about $\ifmmode\pm\else\textpm\fi{}0.5\ifmmode^\circ\else\textdegree\fi{}$ without a significant loss of transmitted intensity by rotating the sample with respect to the incident beam. All data suggest that the structure in the scattered ion angular distributions arises when ions bounce at ultralow grazing angles in very large impact parameter Coulomb collisions with electrically charged nanopore walls. Analysis of the observed structure has allowed the identification of single, double, and triple collisions inside the nanopores.