Transmission of 30-keV He2+ ions through polycarbonate nanocapillaries: Dependence on the incident angle

Nanocapillaries in various materials have received considerable attention due to the rapid growth of the nanotechnology.Recent studies have focused on the transmission of ions through the nanocapillary.The pioneer work,the transmission of 3-keV Ne7+ through polyethylene terephthalate nanocapillaries based on guiding effect has been reported by Stolterfoht et al.(2002 Phys.Rev.Lett.88 133201),indicating that the selforganized charge patches on the capillary walls,which inhibits close contact between the ions and the inner capillary walls,deflecting the trajectories of ions,and thus the ions transmit along the direction of the capillary axis.For the high-energy region (E/Q > 1 MV),Hasegawa et al.(2011 J.Appl.Phys.110 044913) measured the outgoing angle and energy distribution of 2 MeV H+ ions transmitted through a tapered glass capillary.The results indicated that the main transport mechanism of the MeV ions in a tapered glass capillary is the multiple random inelastic collisions below the surface.In the medium-energy region (E/Q from dozens of kV to hundreds of kV),Zhou et al.(2016 Acta Phys.Sin.65 103401) measured the transmission features of the 100-keV protons transmitted through a polycarbonate (PC) membrane at a tilt angle of+1°,the transmitted particles were located around the direction along the incident beam,not along the capillary axis,the transport mechanism of the 100-keV protons in the nanocapillary is the charge-patch-assisted collective scatterings on the surface.With the nanocapillary membranes at different tilt angles,the transverse momentum of the incident ions are different.What is the transmission mechanism of the ions in nanocapillary membranes at different tilt angels? In the present study,we measure the time evolution of the angular distribution,charge state distribution and relatively transmission rate of 30-keV He2+ ions with 500 pA transmitting through a polycarbonate nanocapillary membrane at different incident angles (-0.5°,-1°,-1.5°,-2.5°).It is found that for the small tilt angles (-0.5°,-1°,-1.5°) the transmitted He2+ ions are located around the direction of incident beam,not along the capillary axis,and the directions of the transmitted H0 atoms change from the direction of capillary axis to the direction of incident beam gradually,during the experimental period,the charge exchange is observed.The charge patches in the capillaries overcome the transverse momentum of the incident ions,the ions are transmitted by specular scatterings on the inner surface of capillary,and the main transport mechanism of ions in the nanocapillary at the small tilt angles is the charge-patch-assisted collective scatterings on the surface.For a large tilt angle (-2.5°),the transmitted He2+ ions are located in the direction of the incident beam,and He0 atoms are always in the direction of capillary axis,the charge patches cannot overcome the transverse momentum of the incident ions,and the main transport mechanism of ions in the nanocapillary at the large tilt angles is the multiple random inelastic collisions below the surface.This finding increases the knowledge of charged ions through nanocapillary at different tilt angles within dozens of keV energies in many scientific fields.