INTELLIGENT PRE-SCAN IN SCANNING TRANSMISSION CHARGED PARTICLE MICROSCOPY

A method of imaging a specimen in a Scanning Transmission Charged Particle Microscope, comprising the following steps:- Providing the specimen on a specimen holder;- Providing a beam of charged particles that is directed from a source through an illuminator so as to irradiate the specimen;- Providing a segmented detector for detecting a flux of charged particles traversing the specimen;- Causing said beam to scan across a surface of the specimen, and combining signals from different segments of the detector so as to produce a vector output from the detector at each scan position, said vector output having components Dx, Dy along respective X, Y coordinate axes,specifically comprising:- Performing a relatively coarse pre-scan of the specimen, along a pre-scan trajectory;- At selected positionson said pre-scan trajectory, analyzing said components Dx, Dy and also a scalar intensity sensor value Ds;- Using said analysis of Dx, Dy and Ds to classify a specimen composition at each positioninto one of a group of composition classes;- For a selected composition class, performing a relatively fine scan at positionsassigned to that class.