Micromachined ultrasharp silicon and diamond-coated silicon tip as a stable field-emission electron source and a scanning probe microscopy sensor with atomic sharpness

Abstract

A novel combination of silicon micromachining and deposition on silicon whiskers on (111) oriented silicon substrates shows promise for stable field emission electron emitters and sensors for scanning probe microscopy. As a field emission electron emitters show promise for high-density and high-resolution electron beam applications owing to a small (within 3°) divergence half angle of emitted electrons. Due to the sharpening of the diamond coated Si tips the threshold voltage, which is necessary to create a stable emission current (nanoampers) is decreased from the initial 1300 V to about 150 V. The diamond coating stabilizes the field-emission current as large as about 100 μA from a single tip. Training of the emitter at a current of about 10−7 A for several hours results in an additional improvement of the current stability with an additional slight current increase. Second application of vapor–liquid–solid grown silicon whiskers described here is the recent progress toward high aspect ratio (>100) probes and relates a technique for preparation of cantilevers for atomic force microscopy with atomic resolution on the very end of the tip. The radii are less than 2 nm for silicon tips and the angles at the ends are less than 20°. In the case of diamond, the tip radius is 10 nm.