Single-electron tunneling force spectroscopy of electronic states in nonconducting surfaces*

Typically, the scanning tunneling microscope (STM) cannot directly perform current-voltage spectroscopy on any electronic state with a lifetime greater than $\sim $10$^{-6}$ seconds---the state cannot empty fast enough to supply the necessary $\sim $0.1 pA ($\sim $10$^{6}$ e/s) imaging current. Recently, we reported a scanning probe technique that detects, by electrostatic force, single-electron tunneling events between a probe and states in a nonconducting surface. Here we determine the energy level of such a state by a single-electron tunneling spectroscopy, implemented by tuning the probe Fermi level with respect to the state by a dc voltage. A random telegraph signal (RTS), due to an electron tunneling back-and-forth between the probe and state, is observed when the Fermi level is near the state energy. We present spectroscopic data and extract the energy of a state in a thermal silicon dioxide film. The origin of the RTS is discussed. Additionally, we find evidence for energy relaxation and charge movement in these states. This new nanometer-scale approach provides the means to characterize electronic states in nonconducting surfaces, opening for exploration materials not accessible to the STM. \newline [1] E. Bussmann, D. J. Kim {\&} C.C. Williams, \textit{Appl. Phys. Lett.} \textbf{85}, 2538 (2004)