Field Emission Studies of Heat Treated Mo Substrates

Molybdenum can be used as a substrate for bi-alkali antimonide photocathodes utilized for the generation of high brightness electron beams in superconducting radio frequency (SRF) photoinjector cavities. Operation at high field strength is required to obtain a low emittance beam, thus increasing the probability of field emission (FE) from the cathode surface. Usually, substrates are heated in situ before alkali deposition to remove oxide layers from the surface. FE onMo substrates was measured bymeans of a field emission scanning microscope (FESM). It turned out that in situ heat treatment (HT) of the Mo surface significantly changes the FE behaviour by activation of new emitters. For a better understanding of the mechanism for enhanced emission after in situ heating a witness Mo sample was investigated using x-ray photoelectron spectroscopy.