Evidence of the Key Role of Metal-Molecule Bonding in Metal-Molecule-Metal Transport Experiments

Abstract

The transport properties of two oligothiophene derivatives, that differ only by the chemical group coupling to gold, are compared. It is shown that the role of the coupling group in the transport properties can be decoupled from that of the conjugated body of the molecules and that Se is a better electronic coupling group than S. These results are accounted for semiquantitatively within the frame of the scattering theory of transport, using results from ultraviolet photoemission spectroscopy experiments as inputs for the position in energy of the molecular orbitals with respect to the Fermi level of the electrodes.

First-principles calculation of the transport properties of molecular wires between Au clusters under equilibrium

“…Because we calculate the electrodes and extended molecule separately, we have to face the difficulty that how to unify the zero As what we have shown in Table 1, after considering the UPS data of E F − E HOMO 0.6eV [18] [17], which has a comparable electronic structure with the incorporation of phenyl and carbon-chain group like BDMT, can give us useful enlightenments. Unlike the small value (0.5 ∼ 0.6eV ) in pure π-bonded molecules [16,18] and the large value (> 5eV ) in saturated carbon-chain molecules [15,19], the above mixed electronic structure has a 1.9eV gap of E F − E HOMO [17]. It provides the prompt on estimating the E F − E HOMO value of BDMT.…”

“…As what Patrone has pointed out [16], UPS experiments can give direct information about E F − E HOMO , which is an important energy reference in the molecular transport calculation. Because we calculate the electrodes and extended molecule separately, we have to face the difficulty that how to unify the zero As what we have shown in Table 1, after considering the UPS data of E F − E HOMO 0.6eV [18] [17], which has a comparable electronic structure with the incorporation of phenyl and carbon-chain group like BDMT, can give us useful enlightenments.…”

“…Ultraviolet photoelectron spectroscopy (UPS) was referenced for the purpose of determining "line up" about the Fermi level [15][16][17][18][19]. UPS experiments can provide direct spectroscopic information about the gap between HOMO and E F , which is one of the key points in the transport calculation of molecule-metal sandwichtype structures.…”

Electronic Transport and Thermopower in Aperiodic Dna Sequences

“…(17) and (19) at room temperature taking ε A = 8.24 eV, ε T = 9.14 eV, ε C = 8.87 eV, and ε G = 7.75 eV [45,46]. For the moleculemetal electronic coupling we consider values within the range τ = 0.1−0.5 eV, corresponding to the μ − E HOMO shift recently reported for oligothiophene derivatives adsorbed on gold [47]. The spectral window is given by the graphite π bandwidth [−6.8, 0] eV, corresponding to the tight-binding parameters t m = 1.7 eV, and ε m = −3.4 eV [48].…”

Computational Tools to Study and Predict the Long-Term Stability of Nanowires.

“…Without discussion the most widely used anchoring group is thiol Haiss et al, 2008;Haiss et al, 2009;Huang et al, 2006;Huang et al, 2007a;Huang et al, 2007b;Li et al, 2007b;Li et al, 2006a;Ulrich et al, 2006;Xu et al, 2003a;Xu et al, 2005;Xu & Tao, 2003), although pyridine (Xu et al, 2003a;Xu & Tao, 2003), isocyanide (Beebe et al, 2002;Kiguchi et al, 2007;Kim et al, 2006a), selenium (Patrone et al, 2003a;Patrone et al, 2003b;Yasuda et al, 2006), amine Hybertsen et al, 2008;Kamenetska et al, 2009;Kiguchi et al, 2008;Park et al, 2007;Park et al, 2009;Quek et al, 2007;Quek et al, 2009;Quinn et al, 2007;Venkataraman et al, 2006a;Venkataraman et al, 2007;Venkataraman et al, 2006b), phosphines Park et al, 2007) and carboxylate Martín et al, 2008) have proved to provide enough binding strength to yield a stable contact. In most of these works, the metallic electrodes that the molecule bridges are made of gold, but some recent reports showed the utility of platinum electrodes for those purposes (Kiguchi et al, 2007;Kiguchi et al, 2008).…”