High mass resolution local-electrode atom probe

Abstract

An atom probe provides rapidly pulsed field evaporation/desorption of ions from a tip utilizing a local extraction electrode positioned closely adjacent to the tip. A bias potential is applied between the tip and the local extraction electrode which provides an electric field at the tip which is less than but near the field intensity required for field evaporation of ions. Additional potential is applied between the tip and the extraction electrode in relatively low over-voltage pulses to obtain field evaporation of ions without substantially accelerating the ions. The ions extracted from the tip by the sharply defined pulses pass through an aperture in the extraction electrode and are accelerated by a large potential difference between the tip and a detector spaced from the tip and the local extraction electrode. An intermediate acceleration electrode may be positioned between the extraction electrode and the detector, with the acceleration electrode having an aperture therein to pass ions therethrough to the detector. The acceleration electrode is maintained at a higher potential with respect to the tip than the extraction electrode, and may be maintained at the same potential as the detector so that ions passed through the acceleration electrode coast to the detector. The use of relatively low voltage pulses to obtain evaporation of ions permits rapid repetition of the pulses, on the order of hundreds of thousands of pulses per second, to allow rapid accumulation of atom probe data.