Sub‐40 nm resolution 1 keV scanning tunneling microscope field‐emission microcolumn

Recent advances in microcolumn design and fabrication have led to a significant improvement in the resolution obtained with a new 3.5 mm long microcolumn. At an electron energy of 1 keV and 2 mm working distance, the beam diameter, measured by the signal rise‐time while scanning over a sharp edge, is 40 nm and the resolution observed in scanning transmission electron microscope images is about 30 nm. These experimental results agree well with results of the electron‐optical modeling. All lenses and apertures in the column are made from silicon membranes and assembled using a novel ultrahigh vacuum compatible, multilayer anodic bonding technique. The scanning tunneling microscope aligned field‐emission source uses an oxygen processed, 50 nm radius, cold 〈111〉 W field‐emission tip. Good emission stability for scanning electron microscope operation has been achieved with a few percent of root‐mean‐square current fluctuation over about 30 min. With periodic tip flashes, the system has been operated reliably over several weeks. A novel in situ tip alignment technique with respect to the extractor electrode has been developed. This technique also provides information about the tip emission characteristics during column operation.