NEW OPTOELECTRONIC TIP DESIGN FOR ULTRAFAST SCANNING-TUNNELING-MICROSCOPY

We have developed a scanning tunneling microscope using an optoelectro nic switch that gates the tunneling tip current, The switch is fabrica ted within 30 mu m from the tip by photolithography and an accurate cl eavage method. We demonstrate this approach by detecting picosecond el ectrical transients on a coplanar stripline. We have investigated the signal dependence on contact resistance and found significant differen ces when the tip is brought from low-ohmic contact into the tunneling regime. In this regime, the THz signal amplitude was found to depend l inearly on the tunnel conductance, and disappeared when the tip was re tracted. (C) 1996 American Vacuum Society.