SEM-EDX GUIDE FOR BUYERS

Chapter 4 - Electron Sources and High Voltage

Tungsten and CeB6 Filaments

Traditionally, CeB6 or tungsten filaments are used for beam generation for tabletop and compact laboratory devices. Both technologies provide comparable resolution. However, CeB6 filaments offer a 15-20 times longer service life and higher beam intensity, which is a significant advantage for the signal-to-noise ratio, especially when imaging with low voltage. A guideline value for the service life of a tungsten cathode is generally 100 operating hours and for the CeB6 cathode 1500-2000 operating hours. Furthermore, CeB6 filaments are subject to gradual wear, at which point the end of their service life is foreseeable and the cathode replacement can be planned. Tungsten filaments, on the other hand, burn out without warning, which in the worst case leads to the entire measurement being repeated during longer automatic analyses. Tungsten cathodes can be replaced independently by a trained user, whereas with CeB6 cathodes this is usually done by a service employee.

Low Voltages below 10 kV

For sensitive samples, setting the acceleration voltage below 10 kV is an essential parameter, as the sample is destroyed at high energies. Furthermore, fine structures can be overexposed and thus become blurred if the acceleration voltage is too high.

When choosing an SEM device, pay attention to how flexible the high voltage can be set and how much signal is still present at low voltages. Some benchtop devices offer setting options in 1 kV steps, while others only have preset levels for 5 kV, 10 kV and 15 kV.

low kV battery powder

Imaging at 5 kV shows smallest structures in the battery powder