Low Acceleration Scanning Electron Microscope
A low acceleration scanning electron microscope ( LASEM ) offers several advantages: no charging effects low radiation damage high yield for secondary electron emission high sensitivity for surface topography The application of a low acceleration microscope, however, has been limited to special purposes because of its poor resolution. A high resolution LASEM has been developed and is shown in Fig.1. The microscope uses a new electron gun with a field emission cathode. The gun 1,000 times brighter than a conventional thermionic cathode. The relation between brightness and resolution of a SEM for 1 kV acceleration voltage is shown in Fig.2. The three regions in the figure correspond to tungsten thermionic, LaB6 thermionic and field emission guns. Resolution is approximately 1 μm in the case of the tungsten thermionic gun at 1 kV, while resolution is 200 A in the new microscope equipped with a field emission gun.