Hongqiang Zhang

Guiding of highly charged ions through insulating nanocapillaries

The guiding of highly charged ions through nanocapillaries in different insulating materials, such as polyethylene terephthalate, SiO2, and Al2O3 has been investigated by our group, using 7 keV Ne7 ...

Guiding of slow Ne7+-ions through insulating nano-capillaries of various geometrical cross-sections

We have studied guiding of slow highly charged ions through PET, SiO2, Al2O3, and now, for the first time, insulating nano-capillaries of non-circular cross-section. The guiding effect is been expl ...

Dynamics of slow electrons transmitting through straight glass capillary and tapered glass capillary

It has been found that the transmission rate of the electrons through insulating capillaries as a function of time/incident charge is not the same as that of the ions. The question arises that by using the electrons, if the negative charge patches can be formed to facilitate the transmission of the following electrons, thereby substantiating that the so-called guiding effect works also for electrons. This study aims to observe the time evolutions of the transmission of electrons through a straight glass tube and a tapered glass capillary. This will reveal the details of how and (or) if the negative charge patches can be formed when the electrons transport through them. In this work, a set of MCP/phosphor two-dimensional detection system based on Labview platform is developed to obtain the time evolution of the angular distribution of the transmitted electrons. The pulsed electron beams are obtained to test our detection system. The time evolution of the angular profile of 1.5 keV electrons transmitting through the glass tube/capillary is observed. The transmitted electrons are observed on the detector for a very short time and disappear for a time and then appear again for both the glass tube and tapered glass capillary, leading to an oscillation. The positive charge patches are formed in the insulating glass tube and tapered glass capillary since the secondary electron emission coefficient for the incident energy is larger than 1. It is due to the fact that fast discharge of the deposited charge leads to the increase of the transmission rate, while the fast blocking of the incident electrons due to the deposited positive charge leads to the decrease of the transmission rate. The geometrical configuration of the taper glass capillary tends to make the secondary electrons deposited at the exit part to form the negative patches that facilitate the transmission of electrons. This suggests that if the stable transmission needs to be reached for producing the electron micro-beam by using tapered glass capillaries, the steps must be taken to have the proper grounding and shielding of the glass capillaries and tubes. Our results show a difference in transmission through the insulating capillary between electrons and highly charged ions.

Transmission of highly charged ions through nanocapillaries of noncircular cross sections

We report on effects from the geometrical shape of the guiding channels on the ion transmission profile. We find that capillaries of rhombic cross section produce rectangular shaped ion transmission profiles and, vice versa, capillaries of rectangular geometry give a rhombic beam shape. Our trajectory simulations for the incidence of 14-keV Ne7+ ions give clear evidence that the observed effect is due to the image forces experienced by the transmitting ions. They gain transverse energy due the image charge attraction towards the inner surfaces of the capillary. This leads to a defocusing of the ions leaving the capillaries. Due to the blocking of large deflection angles at the exit of the capillary, the transmitted ion beam is tailored into certain geometrical patterns.

Transmission of slow highly charged ions through rectangular nanocapillaries

Transmission of slow highly charged ions through rectangular nanocapillaries in phlogopite mica is studied. The transmission profiles have rhombic pattern at tilt angles within the geometrical opening angle of the capillaries. The time evolution of ion transmission reveals certain features contributing to the tailored transmission profiles.