Measuring the kinetic energy of multicharged ions for nanofabrication

Devices like mass spectrometers, ion implanters, and particle accelerators require ion sources to form singly charged ions (SCIs) for operation. More recently, multicharged ions (MCIs) — atoms or molecules with an excess or deficit of more than one electron — have been explored as a tool for nanoprocessing and nanofabrication.

Compared to SCIs, MCIs have the advantage of greater potential energy released through localized charge exchange when interacting with a solid,resulting in irreversible structural changes within a few-nanometer depth. In Review of Scientific Instruments, a team of physicists from Clemson University report on their investigation of the properties of MCIs produced by an electron beam ion source (EBIS). The experiment was conducted at the Clemson University Electron Beam Ion Trap (CUEBIT) facility, which produces MCIs from a neutral gas with a high-current, high-energy, and highly-compressed electron beam.

The authors state that maximizing interaction time between the MCIs and solid for localized coupling is achieved by using precise ion beams of low kinetic energies. However, in an EBIS, an offset is induced in the kinetic energy of the extracted ions that ensues from the ionizing electron beam-trapping region interaction. Using a retarding field analyzer, the team measured these kinetic energy offsets for argon MCIs as a function of the current and energy of the electron beam.

The Clemson researchers observed significant offsets that depended on the space charge of the electron beam. An effective size of the electron beam inside the trapping region was inferred from these offsets. According to coauthors Dhruva Kulkarni and Joan P. Marler, these findings have implications for MCI-surface experiments and also offer a significant technique to experimentally infer the size of the electron beam in an EBIS.

Source: “Kinetic energy offsets for multicharged ions from an electron beam ion source,” by D. D. Kulkarni, C. D. Ahl, A. M. Shore, A. J. Miller, J. E. Harriss, C. E. Sosolik, and J. P. Marler, Review of Scientific Instruments (2017). The article can be accessed at https://doi.org/10.1063/1.4997962 .