Question

Explain the SIMILARITIES and DIFFERENCES between Scanning Electron Microscope (SEM) and Scanning Tunneling Microscope?

Answer 1

They both use the interaction of electrons with a surface to produce an image. However, a scanning electron microscope uses a constantly rastered beam of electrons at moderately high accelerations to bombard the surface. Samples must be in low or high vacuum. The image is basically of topology, faster and with relatively low resolution. SEM generally handles rough surfaces very well. In contrast, a scanning tunneling microscope uses quantum tunneling to detect current variations between a rastered sharp conductive tip and a surface. The sample can be in normal atmosphere but best results occur for high vacuum. The image is of surface electronic states, frequently with atomic or sub atomic resolution. STM generally handles surface roughness very poorly.