PERFORMANCE OF THE TRIAL SCANNING ATOM-PROBE - NEW APPROACH TO EVALUATE THE MICROTIP APEX

In order to examine the feasibility of realizing the scanning atom pro be, a trial instrument was constructed by modifying a low-temperature ultrahigh vacuum scanning tunneling microscope (STM). A scanning elect ron microscope was mounted on the trial instrument to inspect the rela tive position of both the open hole at the end of the funnel-shaped ex traction electrode and a cusp apex on a specimen surface. In the preli minary experiment, a single sharp W tip of the STM and two extraction electrodes with respective open hole diameters of 10 and 20 mu m were employed. The tip was brought near the electrode by employing a micros crew and a piezoactuator as with a conventional STM. The variation of the field emission current with the position of the center of the hole relative to the cusp apex was found to be significant enough to bring the apex precisely to the center of the hole. An interesting finding was that the field emission was observed from a tip with a radius of m ore than 2 mu m at a relatively low voltage, indicating that the field confined to a narrow space between the electrode and the tip apex was high enough to induce field emission. (C) 1996 American Vacuum Societ y.