Development of a high brightness gas field ion source

We have investigated the emission properties of gas field ionization emitters built up from electrochemically dc-etched W〈111〉 and W〈100〉 single crystal wires. A standard thermal field method was used to confine the ion emission to a single spot at the apex of the emitter. The angular current density obtained for these kinds of tips with a small end radius (100–200 nm) is in the range of 5 μA/sr. For H2 and Ne, maximum ion current was observed in the temperature range between 18 and 21 K. We have measured the ion current density for different gases (H2, He, and Ne) as a function of extraction voltage and gas pressure. The linear dependence of the angular current density on the gas pressure shows that current densities of 10 μA/sr and above can be expected with this type of emitter.