Simultaneous measurement of force and tunneling current at room temperature

We have performed simultaneous scanning tunneling microscopy and atomic force microscopy measurements in the dynamic mode using metal-coated Si cantilevers at room temperature. Frequency shift (Delta f) and time-average tunneling current (< I(t)>) images are obtained by tip scanning on the Si(111)-(7x7) surface at constant height mode. By measuring site-specific Delta f(< I(t)>) versus tip-surface distance curves, we derive the force (tunneling current) at the closest separation between the sample surface and the oscillating tip. We observe the drop in the tunneling current due to the chemical interaction between the tip apex atom and the surface adatom, which was found recently, and estimate the value of the chemical bonding force. Scanning tunneling spectroscopy using the same tip shows that the tip is metallic enough to measure local density of states of electrons on the surface.