Experiments of keV negative ions transmitted through straight and tapered glass capillaries: tilt angle dependence

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THE EUROPEAN PHYSICAL JOURNAL D

Regular Article

Experiments of keV negative ions transmitted through straight and tapered glass capillaries: tilt angle dependence Hanyu Song, Zhisui Yang, Loufei Yu, Daijie Zhou, Dianwei Zhou, Jianxiong Shao, and Aixiang Yanga School of Nuclear Science and Technology, Lanzhou University, Lanzhou 730000, P.R. China Received 5 December 2019 / Received in final form 9 April 2020 / Accepted 26 August 2020 Published online 8 October 2020 c EDP Sciences / Societ`

a Italiana di Fisica / Springer-Verlag GmbH Germany, part of Springer Nature, 2020 Abstract. In this study, experiments are performed to study the transmission of 15 keV C− ions through straight and tapered borosilicate glass capillaries. The tilt angle is varied from 0◦ to 0.8◦ . In a straight capillary, the transmitted ions produced only one spot on the detector, and its intensity declined with increasing tilt angle. In this case, almost 98% of the transmitted particles maintained their initial charge. However, in the tapered capillary, the transmitted particles formed a different pattern composed of a core and a halo. The negative ion fractions of the core and the halo were 97.5% and 42.5% at a 0◦ tilt angle, respectively. Therefore, the particles formed the halo by scattering after colliding with the inner surface of the capillary, and most of them were neutralized. As the tilt angle increased, the intensity and negative ion fraction of the transmitted particles declined, and the halo gradually became quite asymmetric. These results indicate that the scattering process plays a role in the transmission.

1 Introduction Tapered glass capillaries have attracted attention because they can function as a tool to create a focused ion beam (FIB). One advantage of this scheme is that the initial beam qualities, such as energy spread and angular divergence, are not crucial in FIB fabrication, differing from the traditional electrostatic and magnetic lens focusing schemes [1]. Moreover, it is an effective scheme in some surface modification experiments [2,3] because it reserves sufficient space for additional installations before the focusing micro point region. In 2002, a guiding effect was observed by Stolterfort et al. in the experiment of slow highly charged ions (3 keV Ne7+ ) transmitted through insulating polyethylene terephthalate (PET) nanocapillaries (with a diameter of 100 nm and a length of 100 µm) [4]. The experimental results showed that the majority of transmitted ions maintained their initial charge and kinetic energy when the capillary was tilted relative to the incident HCI beam [5]. The guiding effect was attributed to self-organized charge patches deposited on the wall of the insulting capillaries. These patches establish an electrostatic field that repel subsequent ions flowing along the capillary axis [6–8]. Consequently, it was believed that a tapered glass capillary could form an ideal tool for focusing an ion beam [9]. Nebiki et al. [10] performed an experiment to investigate the transmission of MeV ions throu