Optimization of Electrochemical Etching Parameters in FIM/STM Tungsten Nanotip Fabrication

Field Ion Microscopy (FIM) and Scanning Tunneling Microscopy (STM) have found a wide application in nanotechnology. These microscopes use a metallic nanotip for image acquisition. Resolution of FIM and STM images depends largely on the radius of nanotip apex; the smaller the radius the higher the resolution. In this research, for tungsten nanotip fabrication, electrochemical etching of tungsten wire was used in which a 0.3 mm diameter tungsten wire, a graphite tube, and KOH solution in deionized water was applied as anode, cathode, and electrolyte respectively. The most important parameters that govern the nanotip fabrication process are the time delay in turning off the voltage at the end of tip fabrication process, electrolyte concentration, immersion length of the tungsten wire, inner diameter of the cathode tube, and the process voltage. In this research, the effects of these parameters on the radius of nanotip apex were investigated by using Taguchi method. It was found that the process parameters can be ranked in terms of their impact on the radius of nanotip apex as process voltage, electrolyte concentration, wire immersion length, and inner diameter of the cathode tube, respectively. By setting the process parameters on the optimum level, the radius of the nanotip apex was decreased by 5 times in comparison to the mean value of the experimental results. The radius of the nanotip apex was improved down to about 10 nm under the optimum conditions.