Simulation of ion guiding through nanocapillaries

Complete text of publication follows. The ion guiding capability of nanocapillaries etched in polymer foils has recently been discovered. According to our recent knowledge, the guiding effect may be a result of charge deposition on the capillary walls. The accumulated charges on the inner surfaces of the capillary repel the latter arriving ions, thereby close collisions with the walls can be avoided. Theoretical description of these processes is difficult and the existing models fail to reproduce all experimental observations. To understand the phenomenon better, a microscopic model was developed. In our model the individual local events of charge deposition and migration are traced. The electric potential of the deposited charges is numerically calculated. The calculation is performed for a single capillary, but the effects of the other capillaries in the foil are included by setting up periodic boundary conditions in the x, y directions. In this way the simulation describes the case, where all the capillaries charge up in the same manner. The ion trajectories in the electric filed are calculated numerically. When an ion trajectory crosses the capillary surface the trajectory calculation is stopped. Than the charge of the ion is deposited at the surface. The potential of the corresponding charge is calculated and added to the previous potential. Until the next ion is coming (roughly a few tenth of second) the charges are migrating, which is driven by the electric field. If a charge reaches the conductive layers, it is neutralized instantly. As an example, Fig. 1 shows typical trajectories for 3 keV Ne7+ ions passing through a polyethylene terephthalate nanocapillary with a diameter of 100 nm and length of 6.5 μm. Both sides of the capillary are covered by conductive layers. (author)