Mass Resolution Enhancement in Local-Electrode Atom Probes : A Preliminary Study Using Field Emitter Arrays

Abstract

Abstract. The use of post-evaporation acceleration as a means to enhance mass resolution in localelectrode atom probes (LEAP) is experimentally investigated in this study. Gated silicon field emitter arrays which have an extraction electrode-tip structure similar to a LEAP are used to evaporate ions at low voltages which are then accelerated to higher voltages. The study confirms the expected improvement in mass resolution. The mass resolution achieved using this gated field emitter array is however quite poor owing to capacitive coupling between the extraction electrode and the tip which leads to a broadened evaporation pulse. An improved model to relate time-of-flight to ion mass-to-charge ratio is found to be necessary in this atom probe configuration. These findings suggest important design considerations for extraction electrodes for a LEAP.

First Data from a Commercial Local Electrode Atom Probe (LEAP)

“…proximity of the time-invariant field region inside the counter electrode,~b! post acceleration of the ions~Kelly et Bajikar et al, 1996!, and~c! a grounded second aperture~Kelly et al, 1995Cerezo et al, 2000;Deconihout et al, 2003!.…”

“…recognized the potential of this approach to solve the mass resolution needs of a wide field of view 3DAP~Kelly et al., 1995, 1996!. This then became the basis of the second scheme for improving mass resolution of 3DAPs. By extracting atoms at low voltages with a local electrode at the specimen and then accelerating them to higher energies, Kelly et al~Kelly et al, 1996;Bajikar et al, 1996! showed that the mass resolution of a 3DAP could be improved over its entire field of view.…”

Pulse shaping optimization for improving atom probe tomography

“…By accelerating the evaporated ions to a greater total potential after the local extraction electrode, the energy spread will be relatively small to the total energy leading to an improvement in the final mass resolution. Some preliminary experiments [16] show that a better mass resolution could be achieved. However, the required post-acceleration field is so high that it will affect the field on the tip.…”