Reduction of the divergence angle of an incident beam to enhance the demagnification factor of a two-stage acceleration lens in a gas ion nanobeam system of several tens of keVReduction of the divergence angle of an incident beam to enhance the demagnification factor of a two-stage acceleration lens in a gas ion nanobeam system of several tens of keV
The demagnification factor of a two-stage acceleration lens in a gas ion nanobeam system that produces ion beams with energies in the order of 10 keV was enhanced in this study so that a hydrogen ion beam with a diameter of 115 nm could be produced. The reduction of the divergence angle of the incident beam into the two-stage acceleration lens is the effective method for enhancing the demagnification factor. The divergence angle has been gradually reduced by firstly introducing the preacceleration electrodes to control the divergence angle, namely divergence-angle-control electrodes, and secondly replacing an anode with a modified anode that possesses a Pierce electrode, both of which were in an ion source directly connected to the lens. In this study, the divergence angle of less than 3.6 × 10−4 rad that was previously used to produce a 160-nm hydrogen ion beam with the energy of 46 keV by the above procedure was numerically determined using an ion beam extractionsimulation code. The determined minimum divergence angle of the incident ion beam was calculated to be 2.0 × 10−4 rad, which was about half of the previously obtained divergence angle; this was used to experimentally form a hydrogen beam with a diameter of 115 ± 10 nm and the energy of 47 keV. The demagnification factor was estimated to be 1,739 using the newly formed hydrogen beam, which was similar to the simulation result.