Past exam of the MPhil in micro- and nanotechnology enterprise course of the University of Cambridge / 2017 / Paper 1 / Section A(i) / 1 / i / Solution

The electron-optical column contains an electron gun, an accelerating supply, a condenser lens system, an objective aperture, an electron objective lens, scan coils and alignment/stigmation controls. The electron gun may use thermionic emission or field emission. The condenser lens system sets the incident probe current and source demagnification; the electron objective lens focuses the probe on the specimen. A movable specimen stage controls position, tilt and working distance. The column and specimen chamber need a vacuum system, appropriate pumps and specimen-transfer hardware. Detectors collect secondary electrons, backscattered electrons or characteristic X-rays; amplification and synchronized raster acquisition assign a measured signal to each image pixel. The first two signals provide different imaging information, while characteristic X-rays allow elemental analysis. A source, probe-forming optics, raster scan, specimen stage, detectors, acquisition electronics and vacuum system form the essential chain.^[ref]