SHIELDING OF A SCANNING ELECTRON-MICROSCOPE AGAINST EXTERNAL ELECTROMAGNETIC-FIELDS

We use a box made of 8 mm thick 99.5% aluminium plates for the shieldi ng of a scanning electron microscope against electromagnetic fields th at cause distortion in image geometries. The pill-box construction req uires a ceiling crane to fit the microscope column into the lower box and to move the upper box (about 150 kg) vertically (inspection, sampl e change). A knife edge contact provides closure between the boxes and excludes electric field migration into the box. For stability the upp er box is mounted on a wall on two vertical rails. The box is about an order of magnitude less expensive than whole room shielding, The meas ured shielding factors (frequency dependant) demonstrate the effective ness of the device.