Guided transmission of 3 keV Ar~(7+) ions through dense polycarbonate nanocapillary arrays: Blocking effect and time dependence of the transmitted neutrals

摘要

In the present work dynamic properties of 3 keV Ar ions guided through polycarbonate (PC) nanocap-illaries at different tilt angles ranging from 1° to 7° are studied together with the transmitted neutrals. Two-dimensional transmission profiles were measured with a position sensitive detector. The guided ions and the transmitted neutrals were separated by an electrostatic deflector. The measured quantities are plotted as function of deposited charge in the surface of the sample, which is regarded as a measure of time. We found weak oscillations in the position of transmission profiles. Depending on the tilt angle the intensity of ions started from zero or from a small value and increased fast at the beginning. After reaching a maximum, it strongly decreased in time, similarly as in previous measurements with PC capillaries. This phenomenon is called as blocking effect. The time dependence of the intensity of neutrals was similar except that it started from a non-negligible value and final values are relatively larger than in the case of ions. This indicates that neutrals come from multiple sources. It seems there is a nearly steady contribution from the entrance region, where ions are impinging and neutralized on the surface of capillary wall, in accordance with the picture that was used earlier to explain the non-zero starting value for the intensity of neutrals for polyethylene terephthalate capillaries. Neutrals can also be created from the guided ions later at the exit region, which explains the similarities in the time dependences. The decreasing part of the curves was fitted by exponential functions giving a characteristic deposited charge value for blocking effects. It was higher for larger tilt angles showing the blocking effect is faster for smaller angles. Our results support the scenario presented in a previous work that the blocking is caused by the repulsive field of charges accumulated inside the capillaries.