Scanning tunneling spectroscopy observations of the Coulomb staircase at room temperature from the dioctyldithiophosphate sodium salt molecules deposited on the 0001/graphite surface

In our contribution, we discuss the growth of the NaDDP dioctyldithiophosphate sodium salt.molecules on the 0001. graphite substrate from solution. We observe rod-like structures and smooth terraces. The scanning tunneling spectroscopy STS.measurements on narrow rods show a distinct Coulomb gap and step-like structures, where steps are more pronounced at the occupied part of the spectra. To explain the observed phenomenon, we consider a double junction model, in which electrons tunnel through two barriers. One is formed between the scanning tunneling microscopy STM.tip and the molecule. The other one is the space interval at the moleculergraphite interface. Moreover, we observe the existence of the negative differential resistance NDR.regions on the IrV characteristics. We consider the resonant tunneling via modified electronic states of the combined moleculergraphite system to explain observed phenomenon. q1999 Elsevier Science B.V. All rights reserved.