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

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 degrees) 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 mu A 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 degrees. In the case of diamond, the tip radius is 10 nm. (C) 1998 American Vacuum Society. [S0734-211X(98)18306-3].