Electronic Structures and Properties of Pd_n−C₆₀−Pd_n Nanocontacts: A Theoretical Investigation

Abstract

Theoretical study at the B3LYP/6-31G(d)∪LANL2DZ level was carried out to explore the structures and properties of nanocontacts in Pd n −C60−Pd n systems. Predicted interaction energies between the palladium clusters and the C60 were corrected for the basis set superposition error. It is revealed that palladium clusters interact more strongly with C60 than the analogous gold clusters. Further, generally in the case of C60−Pd complexes, electronic charges are transferred from metal clusters to C60 which is contrary to the direction of a charge transfer in C60−Au complexes. HOMO−LUMO energy gaps in Pd n −C60−Pd n system are found to be lower than C60 as well as the corresponding Au n −C60−Au n complexes. Charge transport properties in the Pd n −C60−Pd n system are discussed in terms of molecular orbitals and the Fermi energy level. Molecular electrostatic potential (MEP) mappings were performed for the qualitative visualization of the Schottky barrier at the C60−Pd interface. Similarity and differences between the Pd n −C60−Pd n and Au n −C60−Au n systems are also explored.

Density Functional Theory Investigation of Electronic Structures and Properties of Agn–C60–Agn Nanocontacts

“…The average of the HOMO and LUMO energies has been used as the Fermi level energy (E FL ) of some carbon clusters such as C 28 , C 60 , and C 70 25 and subsequently the E FL of Au n ÀC 60 ÀAu n and Pd n À C 60 ÀPd n nanocontact systems has also been computed using the similar approach. 6,7 At the B3LYP/6-31G(d) level the E FL value of C 60 is predicted to be about À4.6 eV and this was found to be in a good agreement with that obtained at the BLPY/cc-pVTZ level. 25 The computed E FL values of the Ag n ÀC 60 ÀAg n complexes taken as the average of the HOMO and LUMO energies of the corresponding system are shown in the Table 1.…”

“…Such increase in the CÀC bond is also revealed for the Au n ÀC 60 ÀAu n and Pd n ÀC 60 ÀPd n systems. 6,7 Here we would also like to point it out that a distinctive trend among the CÀC bond length with the size of The Journal of Physical Chemistry C ARTICLE the Ag cluster in the complexes studied here is not revealed (Table 1). On comparing the geometries of the Ag n ÀC 60 ÀAg n complexes with those of the corresponding Au n ÀC 60 ÀAu n species 6 one can see that Ag clusters involving three atoms form a triangular structure which was not revealed for the similar cluster involving the gold atoms (Figure 1).…”

Coordination chemistry on carbon surfaces

“…Leszczynski performed a series of theoretical studies to understand the coordination of several transition metal clusters to C 60 , where the fullerene is sandwiched between the clusters. The metal of the M n C 60 M n systems, where n = 2-8 and M = Au [510], Pd [511] and Ag [512], coordinate through one atom to the fullerene surface showing a 2(6 6) coordination. All the systems are stable, Pd being the most stable, followed by Au and Ag.…”

Transport properties of individual C60-molecules

“…Our second result is that C 60 has a slight tendency to charge negatively on Au with single adatom binding, though not as much as on Cu (or Ag). 31 This contrasts results on flat Au(111) where the charge transfer is negligible. 4,5 As a consequence, with Au-electrodes transport is more LUMO-dominated.…”