Threshold Displacement Energy - Experimental Studies

Experimental Studies

The threshold displacement energies have been studied extensively with electron irradiation experiments. Electrons with kinetic energies of the order of hundreds of keVs or a few MeVs can to a very good approximation be considered to collide with a single lattice atom at a time. Since the initial energy for electrons coming from a particle accelerator is accurately known, one can thus at least in principle determine the lower minimum threshold displacement energy by irradiating a crystal with electrons of increasing energy until defect formation is observed. Using the equations given above one can then translate the electron energy E into the threshold energy T. If the irradiation is carried out on a single crystal in a known crystallographic directions one can determine also direction-specific thresholds .

There are several complications in interpreting the experimental results, however. To name a few, in thick samples the electron beam will spread, and hence the measurement on single crystals does not probe only a single well-defined crystal direction. Impurities may cause the threshold to appear lower than they would be in pure materials.