Particle-optical apparatus involving detection of Auger electronics

A method for separating electrically charged particles in a particle-optical apparatus according to direction of travel, in which apparatus

• providing a primary beam of electrically charged particles from an electron source which travel along on an optical axis (4) of the apparatus,
• arranging a Wien filter (36) and a focusing device (8) in the optical axis of the primary beam,
• the focusing device (8) forming an end focus of the primary beam in the vicinity of a sample holder (20) for a sample (14) to be irradiated by the primary beam, wherein electrically charged particles are released from the sample (14) in response to the incidence of the primary beam on the sample, said released particles travel in the direction opposing the direction of travel of the primary beam,
• wherein said released particles are deflected away from the primary beam in the Wien filter (36), and wherein
• an intermediate focus (40) of the primary beam is formed substantially at the center of the Wien filter (36), generating a quadrupole field at an area of the Wien filter, at least part of which coincides with a field of the Wien filter.