ADVANCES IN ULTRAFAST SCANNING-TUNNELING-MICROSCOPY

Time resolved tunnel current was measured over 4 orders of magnitude i n separation between tip and sample using an ultrafast scanning tunnel ing microscope (USTM). These measurements reveal two distinct regimes for tip height dependence of the signal. In addition, we report 900 fe mtosecond temporal resolution with a sensitivity of 20 mV/root Hz in U STM measurements of voltage pulses on a coplanar transmission line, an d we show that the microscope operates as a high impedance probe. (C) 1996 American Institute of Physics.