The Transmission Of Charged Particles Through Insulating Capillaries

The traditional equipment that deflects and focuses the charged particle beams by electronic and magnetic fields are expensive,huge and have complex structures.In contrast,the insulating capillaries can achieve the same effect but are cheap,tiny and have simple structures.The study of the transmission of charged particles through insulating capillaries is the foundation of using insulating capillaries as charged particle beam optics.The mechanisms of positive ions transmitting through the insulating capillaries are clear.The research topics of positive ions focus on the application research,such as,using capillaries make the microbeam of the highly charged ions to produce nanostructures on the selected surface area of materials.While the transmitting mechanisms of the particles with negative charge are unclear and unknown.For these reasons:the experimental and theoretical research on charged particles transmitting through insulating capillaries were performed;the shaping effect for electron beam by the square glass tube is measured by the first time;the evidence for the charge-up process of negative ions transmitting through the glass tube is found;the physical scenarios of the charging progresses induced by electrons and negative ions are proposed;the thermal spike model of highly charged ions is developed.The details are as follows:We studied the transmission process of electrons through the insulating capillaries.The transmission experiments of electrons through Al₂O₃ nanocapillaries were performed using 2-Dimensional(2-D)position sensitive detector.The dependence of transmission rate and angular distribution on the tilt angle,electron energy and the beam intensity are studied.It is found that the transmission is mainly limited by the geometrical opening angle of the capillary.The energy loss of transmitted electrons increases as the tilt angle increases.The characteristic charge for the exponential decrease is dependent on the secondary electron emitting rate in the experimental range.The transmission of electrons through the single glass capillary without/with the conductive-coated outer surface to the ground is reported.It is found that the charge-up process of electrons transmitting through the glass capillary with the conductive-coated outer surface to the ground shows a relatively simple and steady behavior.The conditions for stabilizing the transmission of the electrons through glass capillary are proposed.The charging-up process of the transmission of electrons through the glass capillary with the conductive-coated outer surface to the ground for various tilt angles is measured.The intensity of transmitted electrons for large tilt angle(i.e.,-1.15 deg)can be considered as first falling to zero,then keeping zero for a long time,finally rising to certain stable value.The energy losses are measured for various tilt angles.The more larger tilt angles,the more larger energy loss of transmitted electrons.The experimental results show that the transmission of electrons through insulating capillaries includes the charging-up process and the electron scattering process.The transmission processes of charged particles through the single square glass capillary are measured.It is found that the single square glass capillary can shape the electron beam in the charging process.The dependence of tilt angles and beam intensities is studied.The shaping effect does not work for positive and negative ions.The transmission experiments of N₂^-ions through single square glass capillary are performed.There are two kinds of particles in the transmitted particles:neutral particles and N₂^-ions.The intensity of neutrals is very weak.The N₂^-ions occupy the most of the transmitted particles.The transmitted N₂^-ions can be found when the glass tube is tilted by±1.6 deg,which is larger than the geometrical opening angle of 1 deg.The charging-up processes for various tilt angles are measured.The negative ions parts show double spots structures when the tilt angles are larger than 0.6 deg.One ion spot is near the 0 deg detection angle,and the other ion spot is close to the neutrals.All these two spots show intensity changing and position shifting in the charging-up process.The time dependence of the transmitted N₂^-intensity is similar to that of electrons,shows decreasing firstly and then increasing to steady-state.The experiments indicate the formation of the negative charge patches in the inner surface of capillary.The physical scenarios of the charging-up processes for electrons and negative ions transmitting in the insulating capillaries are proposed.All the experimental results can be explained well by these two physical scenarios.For electrons,the positive-negative double-decks charge distribution from surface to inside of the solid is proposed firstly.It is pointed out that the oscillations and recovery in the transmitted electron intensity come from the suddenly discharge of the double-decks charges.The reason why only the electrons are shaped by square glass capillary also be explained.For negative ions,the charging-up of the negative charge patches come from two kinds of physical processes:the charge-exchange process of the incident negative ions with the atoms on the inner surface,and the deposition of secondary electrons on the other side of the capillary.The thermal spike model of highly charged ions is developed.The contribution of potential energy is added in the equation of electronic system as heat source term.The calculations of nanostructure diameters and the thresholds of nanostructure formation agree well with the experimental data.The mechanism is discussed.