Tunneling spectroscopy of isolatedC60molecules in the presence of charging effects

Abstract

The discrete molecular-level spectrum of an isolated C 60 molecule is resolved and its interplay with singleelectron charging effects is studied using room-temperature and cryogenic scanning tunneling spectroscopy. The tunneling current-voltage spectra of these molecules exhibit rich structures resulting from both resonant tunneling through the discrete levels and charging effects. In particular, we observe degeneracy lifting within the molecular orbitals, probably due to the Jahn-Teller effect and local electric fields. Theoretical fits account well for our experimental data.

Electronic structure of single DNA molecules resolved by transverse scanning tunnelling spectroscopy

“…The contribution of single-electron tunnelling effects 8,33 to the fluctuation in the I-V gaps and peaks is believed to be small in comparison with the observed voltage gaps. When the capacitance of the tip-molecule junction is much smaller than that of the molecule-substrate junction, as it is believed to be in this case (checked by current-distance measurements), the latter junction is the fast one and the incoming charge rapidly tunnels out and charging effects are not observed 10 .…”

“…This change in the STS spectra by altering the composition and structure of the DNA is further proof that our measurements probe the deposited molecules and are sensitive to their electronic structure. To support our assumption that the measured conductance curves approximately reflect the sample DOS according to expression (2), although the measurement is collected at finite temperature, it is desirable to assign the peaks to molecular electron states 7,8 . Simulations of I-V and (dI /dV )-V curves were so far done by empirical models, namely by using tight-binding hamiltonians with parameters either fixed through experimental fitting 29 or taken from ab initio calculations.…”

“…When the capacitance of the tip-molecule junction is much smaller than that of the molecule-substrate junction, as it is believed to be in this case (checked by current-distance measurements), the latter junction is the fast one and the incoming charge rapidly tunnels out and charging effects are not observed 10 . Moreover, small changes in I set during STS measurements on particles would change their residual charge, Q 0 , and cause a variation in the Coulomb blockade voltage gap 8,33 . Typically, in our measurements, these variations are negligible with respect to the range of the observed gap widths (2.0-2.9 eV), ruling them out as a possible source of the observed conductance fluctuations, and leaving structural fluctuations or changes of the molecule-substrate contact as the most likely origin.…”

“…Hence, it is desirable to get this knowledge for DNA to understand its suitability to support electrical currents and the viable transport mechanisms. Scanning tunnelling spectroscopy (STS) is the technique of choice for measuring the electronic density of states (DOS) of a single molecule 6 , as was demonstrated through the years for various carbon nanostructures 7,8 , molecular objects 9 and inorganic nanoparticles 10 deposited on substrates.…”

Theory of an all-carbon molecular switch

“…3 One of the most intensively studied molecules in the field is the fullerene C 60 , whose electronic transport properties were measured and manipulated by scanning tunneling microscopy ͑STM͒ techniques. 5 Several examples of fullerenebased devices have been investigated both experimentally [6][7][8][9] and theoretically. [10][11][12][13] Suggested mechanisms to control the conductance at a single C 60 molecular junction are either of electromechanical nature ͑utilizing an STM tip to compress the molecule 5,10 ͒ or based on charge transfer ͑controlled by a gate potential in a three-terminal geometry 12 ͒.…”