TUNNELING CURRENT OSCILLATIONS EXCITED BY DC-VOLTAGE

Investigating a polycrystalline gold laver on glass bq a scanning tunn eling microscope in air, tunneling current oscillations were found. wh ich are excited by the DC voltage across the gap. The oscillation ampl itude is dependent on the place on the surface of the sample and corre lates with its topography. The frequency spectra of these oscillations are influenced by resonances of the mechanical system (z-piezo/sample holder/transducer/sample). A piezoelectric transducer is able to dete ct alternating forces originating from the tunnel junction. The resona nces in the spectrum of the AC tunneling current and the mechanical re sonances of the STM system seem to be related. Trapping and subsequent delayed desorption of charge carriers at localized surface states cou ld play a role in generating the observed time-dependent forces across the gap and thereby creating tunneling current oscillations.