NOVEL METHODS FOR PREPARING EC STM TIPS

We present a dynamic electrochemical etching technique for preparing s canning tunneling microscope (STM) tips. Current vs, potential measure ments have led to the development of a dynamic technique which provide s atomic resolution and which is faster and more reliable, reproducibl e and productive than conventional static methods. Tungsten tips are p repared in a 2M NaOH film while the electrolyte is flowing through the film, keeping concentrations and etching rate constant. In order to a pply the STM in liquids, an appropriate tip insulating technique is de veloped so as to prevent Faradaic current. A molten thermoplastic wax film is used for reproducible insulation. The STM tips and insulated t ips were characterized by optical microscopy, scanning electron micros copy, STM, and electrochemical STM. Imaging with atomic resolution was demonstrated on HOPG.