| 摘要 |
A signal detector for detecting electrically charges particles in a gaseous medium has an electrode (21) a tip region of which gathers the particles. The electrode is connected to a voltage source for applying a voltage that generates an electro-static field around the electrode so as to attract the particles thereto. An output from the electrode provides an output representative of the number of particles detected. At least part of the tip region of the electrode has a radius of curvature which is sufficiently small (or in the case of a pointed tip or edge of a pointed tip or edge infinitesimal) to create, in use, a localised high intensity electro-static field which defines a detection zone in which, in use, charge particles are accelerated by the electric field to an extent sufficient to ionise gas molecules in the zone and thus amplify the signal received by the detector. The detector is suitably suitable for detecting secondary electrons in a scanning electron microscope since only electrons which have collisions in the detection zone will give rise tot he amplified signal, and backscattered electrons will generally tend to travel through the zone without having any such collision. |
