Conductance of individualC60molecules measured with controllable gold electrodes

Abstract

We investigated the conductance of C 60 molecules using mechanically controllable break-junction electrodes at 10 K in UHV. The molecules are evaporated in situ. With this method, we obtain clean and low-resistance contacts. From the analysis of conductance histograms and differential-conductance ͑dI / dV͒ traces, we deduce the preferred conductance value of a single C 60 molecule between gold electrodes to be close to 0.1 G 0 . The presence of C 60 is evidenced by features in the derivative of the dI / dV at energies close to the molecular vibration energies. The characteristics of the molecules disappear upon cold working of the junctions. DOI: 10.1103/PhysRevB.76.125432 Over the last years, much progress has been achieved in the understanding of the electronic transport through single molecules. Since the seminal experiment by Joachim et al. 1 in which a C 60 molecule was contacted by a scanningtunneling microscope tip, the fullerenes have become benchmark systems for the development of new measurement schemes for molecular electronics applications. Much theoretical work has been performed on different metal-C 60 systems including the noble metals 2 and aluminum. 3 It has been measured that C 60 between gold electrodes would form ionic contacts, giving rise to high conductances. 4,5 Due to its high symmetry, only a few different contact geometries have to be explored although the molecule bears manifold possible functionality including the possibility of endodoping by magnetic 6,7 or other ions. 8 Most of the single-molecule transport experiments performed so far can be categorized into two groups: The first set of experiments is characterized by rather high resistance contacts allowing for the investigation of Coulomb blockade ͑CB͒ and molecular level spectroscopy by inelastic electron tunneling spectroscopy. These devices can be fabricated by different techniques including scanningtunneling microscopy ͑STM͒ and spectroscopy, 1 electromigrated electrode structures, 9,10 and mechanically controllable break junctions ͑MCBJs͒.11 Among those, STM provides the largest variability in the combination of metals and molecules, to tune the contact after its formation, to reestablish a new contact after it has been broken, and to image the configuration of the environment. With electromigrated electrodes, very stable devices are achieved but without any possibility to tune the coupling after the contact has been established and with usually very low yield. The MCBJ technique interpolates between these two extremes. It combines tunability of the contacts with high mechanical stability, enabling measurements over several hours on the same contact configuration at low temperatures and the application of external fields.For the study of CB, oxide or other contamination layers between electrodes and molecules might be helpful for ensuring the weak coupling which is necessary for considering the molecular systems as independent from the metal electrodes. However, for the application of single-molecule contacts in ele...

Thermal conductance and thermoelectric figure of merit of C60 -based single-molecule junctions: Electrons, phonons, and photons

“…This kind of symmetric geometry is more likely to be realized in a break-junction configuration like that of Ref. 17. The results for the different transport properties G, S, κ el and κ pn are qualitatively similar to those of the bluntsharp geometries discussed above.…”

“…The fullerene C 60 is a test-bed molecule for molecular electronics and its electrical transport properties have been extensively investigated both experimentally [14][15][16][17][18][19][20][21][22] and theoretically [18,[20][21][22][23][24][25][26][27][28][29][30][31][32]. Also in the context of thermoelectricity, C 60 -based single-molecule junctions have been analyzed and several groups have reported room-temperature thermopower measurements [33][34][35].…”

Numerically exact, time-dependent treatment of vibrationally coupled electron transport in single-molecule junctions

“…The signature of nuclear motion has been observed in conduction measurements of a variety of molecular junctions, 11,14,16,18,19,[25][26][27][35][36][37][38][39][40][41][42][43][44][45][46] e.g., H 2 between platinum electrodes, 14 C 60 molecules between gold electrodes, 11 and copper phthalocyanine 19 on aluminum oxide film. Vibrational signatures of molecular bridges have also been observed in inelastic electron tunneling spectroscopy.…”

Communication: Electrical rectification of C59N: The role of anchoring and doping sites

“…The transport behavior of the individual C 60 molecule was studied experimentally 10 and theoretically. 11,12 While an individual C 60 molecule does not display appreciable rectification behavior, 11,9 the C 59 N molecule deposited on the alkanethiol self-assembled monolayer (SAM) surfaces displays strong rectification behavior when compared with C 60 (cf.…”