SHARP TUNGSTEN TIPS FOR SCANNING TUNNELING MICROSCOPE PREPARED BY ELECTROCHEMICAL ETCHING PROCESS

Tips for scanning tunnelling microscope (STM) are now more frequently made by electrochemical etching of tungsten wire in an aqueous solutio n of an alkaline base. In this method it is observed that to get a sha rp tip the etching voltage has to be cut off as quickly as possible wh en there is a sudden drop in etch current. We have designed an electro nic circuit that can cut off the voltage within a time limit of 500 ns and employed it successfully to get very sharp tips with a radious of curvature of less than 1000 angstrom. Tips produced by this process h ave been characterized by scanning electron microscope (SEM) and are u sed successfully for STM applications. Atomic resolution image of (000 1) surface of graphite scanned with these tips is given as an example.