High-repetition rate position sensitive atom probe

Abstract

Atom probe apparatus includes an emission tip from which atoms can be evaporated in atomic emission events, a position sensitive detector for detecting the position and timing of the charge cloud resulting from atomic emission events, and a pulse heating beam for heating the emission tip in short pulses to evaporate atoms essentially one at a time from the emission tip. The heating beam may be formed as an electron beam from an electron gun which is directed to the tip and scanned rapidly back and forth across the tip to be incident upon the tip for short periods of time as the beam is scanned back and forth. The beam may further be produced as a chopped beam of electrons by scanning the beam back and forth across a slit in an aperture plate so that only pulses of electrons pass through the plate as the beam passes across the slit. The electrons passing through the slit are then focused and directed to the tip. The tip may also be heated by light from a pulsed source such as a laser which is passed through a reflecting Schwarzschild objective and focused onto the tip in pulses to provide excitation by light photons. The position sensitive detector, which may include a microchannel plate backed by a position sensitive wedge and strip detector, determines both the time of arrival of a charge pulse from an atomic emission event and the relative position of the charge cloud at the point where it impacts upon the detector. The detector may also be formed as a three-level, trigonal array of pads which allows both one and two atomic events per heating pulse to be resolved.