Fabrication of STM Tungsten Nanotip by Electrochemical Etching Method

With developments in nanoscience and nanotechnology, Scanning Tunneling Microscope (STM) has found a wide application in imaging the atoms, molecules, and nanostructures. This microscope uses an ultra sharp metallic tip for scanning sample surface to produce surface topographic image with atomic resolution. Reliability and resolution of STM images depend largely on the sharpness of the tip apex and repeatability of images depends on mechanical strength of tip material. During last decades, a variety of techniques and processes have been developed for fabrication of different metallic tips made from tungsten, platinum, platinum–iridium, gold, and silver. Electrochemical etching process is the most popular method for fabrication of nanotips with desired quality, reliability, and reproducibility and tungsten is normally the first choice for fabrication of STM tips as it has a high mechanical strength as well as a good electrical conductivity. Fabrication of STM tungsten tip by using electrochemical etching method and tip characterization has been the subject of several researches. Nevertheless, to our knowledge, effect of voltage type (AC/DC), time delay in turning off the voltage, tungsten wire diameter, environmental vibrations, electrolyte type, cathode material, and perpendicularity of tungsten wire (toward electrolyte surface) on the tip sharpness have not been studied so far. In this paper, effects of these parameters on the tip shape and sharpness are investigated. A proper set-up for STM tungsten nanotip fabrication by using electrochemical etching method is presented.