Patent ID: 7541580
Filing Date: 2009-06-02
Classification: G01N,H01J

Abstract:
1. A particle-optical apparatus, comprising: a sample holder arranged in a sample chamber for receiving a sample; a particle source arranged for producing a primary beam of first electrically charged particles along an optical axis for irradiating said sample; a pressure limiting aperture having a diameter, the pressure limiting aperture maintaining the pressure in the sample chamber at a higher pressure than the pressure in an electron optical column; a first electrode having an aperture and arranged for detecting electron signals originating from the sample due to said irradiation; a detection space formed above said sample holder and extending above the pressure limiting aperture; a magnetic lens for providing a magnetic field for focusing the primary beam in the vicinity of the sample holder; wherein the detector space includes an electric potential field that has a saddle point inside the detector space, the corresponding electric field causing electrons to oscillate about the saddle point, at least one of the electron oscillations bringing the electrons above the pressure limiting aperture to improve the detection efficiency.