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 molecule/graphite interface. Moreover, we observe the existence of the negative differential resistance (NDR) regions on the I/V characteristics. We consider the resonant tunneling via modified electronic stares of the combined molecule/graphite system to explain observed phenomenon. (C) 1999 Elsevier Science B.V. All rights reserved.