In situ HVTEM observation of the tip shape of tin liquid metal Ion sources

Tin liquid metal ion sources (LMISs) were mounted to a special specimen holder for in situ observation in a 1 MeV TEM revealing the formation of the field-stabilized tin liquid cone, the change in the tip shape as a function of the ion emission current, spatial shifts of the liquid cone, and microdroplet emission from a tin liquid metal ion source. This has facilitated the better understanding of the ion and microdroplet emission process from tin LMISs in a large range of ion current. Below the onset voltage the shape of the tip covered with the liquid tin is spherical. In a small voltage range above the onset value (similar to 20 V) oscillations of the Taylor cone between two well defined positions appear (with and without cone). At a slightly higher voltage the cone appears stable. A jet at the cone vertex may or may not exist. At higher ion emission currents there was a jet-like protrusion at the Taylor cone vertex. A linear dependence was observed of the decrease of the cone half-angle cu and of the increase of the length 1 of the jet-like protrusion on the increased ion emission current. Emission of microdroplets was observed at the surroundings of the Taylor cone. The radius of microdroplets varied between 30 and 900 nm. These microdroplets are emitted in time intervals of about 0.1 s and more.