Electrical Characterization of Metal-Coated Carbon Nanotube Tips

Electrical characteristics of bare and metal-coated carbon nanotube (CNT) tips were investigated with an independently driven four-tip scanning tunneling microscope (STM). The CNT was glued on a W tip apex and wholly coated ex situ by metal thin layers. The resistance between the CNT-tip end and the W supporting tip scattered very widely from ca. 50k Omega to infinity for the bare tips, while coating the tip with a 6-nm-thick PtIr film stably reduced the resistance to less than approximately 10 k Omega. The W coating was also effective for stabilizing the resistance, although they showed slightly larger resistance (ca. 50k Omega). The metal-coated tips kept their low resistance and flexibility even after 100 repeated contacts to an object for conductivity measurements. They are expected to be useful for nanometer-scale transport measurements with multiprobe STM as well as for conventional single-tip STM.