DC field emission scanning measurements on electropolished niobium samples

Electropolished (EP) Nb samples were investigated by a dc field emission scanning microscope, which has recently been modernized for the fast scans on large samples. Measurements on EP samples before and after high pressure rinsing (HPR) are compared. Reproducible voltage scans at various surface fields have been obtained partially down to μm resolution. The statistical overview of the density of emitting sites at 120 MV/m shows a reduction from about 30 before to 14 emitters/cm2 after HPR. Local measurements of selected emitters prove increased onset fields Eon at 1 nA and decreased values after HPR. High resolution SEM images and EDX measurements of the identified emitters will also be presented.