Stable transmission of low energy electrons in glass tube with outer surface grounded conductively shielding

Abstract

<sec>The electron microbeam is useful for modifying certain fragments of biomolecule. It is successful to apply the guiding effect to making the microbeam of positively charged particles by using single glass capillary. However, the mechanism for the electron transport through insulating capillaries is unclear. Meanwhile, previous researches show that there are oscillations of the transmission intensity of electrons with time in the glass capillaries with outer serface having no grounded conductive shielding, So, the application of glass capillary to making the microbeam of electrons is limited.</sec><sec>In this paper, the transmission of 1.5 and 0.9 keV electrons through the glass capillary without/with the grounded conductive-coated outer surface are investigated, respectively. This study aims to understand the mechanism for low energy electron transport in the glass capillaries, and find the conditions for the steady transport of the electrons. Two-dimensional angular distribution of the transported electrons and its time evolution are measured. It is found that the intensity of the transported electrons with the incident energy through the glass capillaries for the glass capillaries without and with the grounded conductive-coated outer surface show the typical geometrical transmission characteristics. The time evolution of the 1.5- keV electron transport presents an extremely complex variation for the glass capillary without the grounded conductive-coated outer surface. The intensity first falls, then rises and finally oscillates around a certain mean value. Correspondingly, the angular distribution center experiences moving towards positive-negative-settlement. In comparison, the charge-up process of the 0.9 keV electron transport through the glass capillary with the grounded conductive-coated outer surface shows a relatively simple behavior. At first, the intensity declines rapidly with time. Then, it slowly rises till a certain value and stays steady subsequently. The angular distribution of transported electrons follows the intensity distribution in general, but with some delay. It quickly moves to negative direction then comes back to positive direction. Finally, it regresses extremely slowly and ends up around the tilt angle. To better understand the physics behind the observed phenomena, the simulation for the interaction of the electrons with SiO₂ material is performed to obtain the possible deposited charge distribution by the CASINO code. Based on the analysis of the experimental results and the simulated charge deposition, the conditions for stabilizing the electron transport through glass capillary arepresented.</sec>