Abstract: In an atom probe having a vacuum chamber containing a specimen mount and a detector for receiving ions emitted from the specimen, a high vacuum subchamber is provided about the specimen mount, with an aperture in the subchamber allowing passage of emitted ions to the detector. The high vacuum subchamber may be pumped to higher vacuum (lower pressure) than the vacuum chamber, and so long as the pressure in the vacuum chamber is below about 10?1 Pa, very little gas diffusion takes place through the aperture, allowing higher vacuum to be maintained in the subchamber despite the aperture opening to the chamber. The higher vacuum in the subchamber about the specimen assists in reducing noise in atom probe image data. The aperture may conveniently be provided by the aperture in a counter electrode, such as a local electrode, as commonly used in atom probes.

Abstract: In an atom probe having a vacuum chamber containing a specimen mount and a detector for receiving ions emitted from the specimen, a high vacuum subchamber is provided about the specimen mount, with an aperture in the subchamber allowing passage of emitted ions to the detector. The high vacuum subchamber may be pumped to higher vacuum (lower pressure) than the vacuum chamber, and so long as the pressure in the vacuum chamber is below about 10?1 Pa, very little gas diffusion takes place through the aperture, allowing higher vacuum to be maintained in the subchamber despite the aperture opening to the chamber. The higher vacuum in the subchamber about the specimen assists in reducing noise in atom probe image data. The aperture may conveniently be provided by the aperture in a counter electrode, such as a local electrode, as commonly used in atom probes.