Study on transport process of 16 keV C<sup>– </sup>ions in tapered glass capillary: Role of capillary tilt angles

Abstract

<sec>The tapered glass capillaries have been widely used in physics, biology, materials. The features of ions transmitted through the insulating tapered glass capillary manifest themselves mainly in the interaction between positive ions and tapered glass capillary, However, the transmission process of negative ions in tapered glass capillary has been studied scarcely so far.</sec><sec>In the present study, we measure the properties of 16 keV C<sup>–</sup> ions transmitted through the tapered glass capillary, such as the two-dimensional spectral distribution, the relative transmission rate, the centroid angle, the charge state purity and the full width at half maximum of the transmitted particles. As the tapered glass capillary tilt angle is equal to 0°, the transmitted particles are composed of three components, i.e. the core, the C<sup>–</sup> of halo and the C<sup>0</sup> of halo. As the tilt angle is 1°, the transmitted particles are composed of two components, i.e. C<sup>–</sup> and C<sup>0</sup>. As the tilt angle is >1°, there is no core region, the transmitted particles are composed of two components, i.e. C<sup>–</sup> and C<sup>0</sup>. No matter how the tilt angle changes, the centroid angles of core are always along the direction of the incident ions, independent of the tilt angels. And the centroid angles of transmitted C<sup>–</sup> and C<sup>0</sup> are always along the direction of the capillary axis. The transmission processes of 16 keV C<sup>–</sup> ions in tapered glass capillary with different tilting angles are analyzed qualitatively. When the tilting angle is small (0°–1°), the C<sup>–</sup> ions are directly traveling straight through the back cone hole of tapered glass capillary, which are mainly composed of C<sup>–</sup> ions. When the tilt angle is large (>1°), the C<sup>–</sup> ions cannot directly travel straight through the back cone hole of the tapered glass capillary, and the core region does not appear. Due to the guiding effect of the negative charges deposited on inner wall of tapered glass capillary, the transmitted C<sup>–</sup> ions are located around the direction of the capillary axis. The tapered glass capillary has a focusing effect on the incident ions. This experiment covers the lack of the studies of low-energy negative ions transmitted through tapered capillary and helps to strengthen the understanding of the transmission process of low-energy ions transmitted through tapered capillary.</sec>