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We studied blocking effects on ion guiding through nanocapillaries in highly insulating polyethylene terephthalate (PET). The experiments were initiated in view of a previous study with capillaries in polycarbonate (PC) for which strong blocking effects were observed, whereas for PET these effects could not be detected. The aim was to find out whether the different results are caused by differences in the PET and PC materials or by differences in the areal densities of the capillaries. Transmission experiments of 3-keV Ne7+ ions were performed for a variety of PET samples with an areal capillary density ranging from 3 to 60 x 10(6) cm (2). The tilt angles were close to zero degree because previous blocking effects were found to be largest at small angles. Our results clearly show that blocking effects also exist for PET and that they are sensitively dependent on the areal capillary density, i.e., the mean capillary distance. The potential produced by the charges accumulated in neighboring capillaries is calculated showing that it plays an important role in the ion blocking. In addition, model calculations are performed providing expressions to determine the direct ion transmission for small tilt angles and divergent ion beams.

We studied the dynamic properties of ion guiding through nanocapillaries etched in insulating polycarbonate (PC). Capillaries with diameters of 95 and 165 nm and a length of 10 mu m were used. In a further sample, the capillaries had a diameter of 175 nm and a length of 30 mu m. A few additional measurements were made using capillaries in polyethylene terephthalate (PET). The temporal evolution of the intensity and the angular distribution of the transmitted ions were studied by measuring transmission profiles as a function of the charge deposited on the sample surface. The tilt angle of the capillary axis was varied from 0 degrees to 5 degrees. The mean emission angle of the transmission profiles exhibit pronounced oscillations, similarly as in previous measurements using PET. However, for PC, nearly an order of magnitude more charge needs to be inserted into the capillaries to accomplish the oscillations. In contrast to PET, with PC, we observed a strong decrease of the profile intensities with irradiation time. This observation provides evidence of blocking effects on the ions, which are likely to be due to a repulsive field produced by significant charge deposition inside the PC capillaries.

The semiclassical approximation is applied in second order to describe time ordering of two-step processes in energetic ion-atom collisions. Emphasis is given to the conditions for interferences between first- and second-order terms. In systems with two active electrons, time ordering gives rise to a pair of associated paths involving a second-order process and its time-inverted process. Combining these paths within the independent-particle frozen orbital model, time ordering is lost. It is shown that the loss of time ordering modifies the second-order amplitude so that its ability to interfere with the first-order amplitude is essentially reduced. Time ordering and the capability for interference is regained, as one path is blocked by means of the Pauli exclusion principle. The time-ordering formalism is prepared for papers dealing with collision experiments of single excitation [Stolterfoht et al., following paper, Phys. Rev. A 48, 2986 (1993)] and double excitation [Stolterfoht et al. (unpublished)].