4. Conclusion

For many years, scanning electron microscopy saw few major upheavals, but the development over the last fifteen years of field emission guns (mainly Schottky emission) has changed the technique considerably. The development of new electronic column concepts and new detectors has extended the capabilities of these microscopes, particularly in terms of imaging resolution, but also in terms of observation capabilities at low and very low voltages. On the other hand, contrast interpretation has often become more complicated, as secondary and backscattered electronic emissions at low voltages no longer follow the same rules as at higher voltages (see [P 866]...