Electrochemical preparation of STM probes for high aspect ratio nanometrology

The aspect ratio of the metallic tips near the apex regime rather than the whole probe tip play a more important role in high aspect ratio nanometrology. It is found that the etching rate is a key factor that executes main effect on the aspect ratio of probe tip near the apex. Through combination of different etching parameters, such as voltage, electrolyte concentration, immersion depth, cathode shape and size, tungsten nanotips with a controllable aspect ratio and sharpness can be obtained, tips with aspect ratio up to 450∶1, apex radius below 10nm and cone angle below 3°can also be obtained through applying the optimal parameters. The high aspect ratio tips also make it advantageous to measure micro structure with steep side wall using scanning tunneling microscopy.