Malen Jonathan A, Doak Peter, Baheti Kanhayalal, Tilley T Don, Segalman Rachel A, Majumdar Arun
Department of Mechanical Engineering, University of California, Berkeley, Berkeley, California 94720, USA.
Nano Lett. 2009 Mar;9(3):1164-9. doi: 10.1021/nl803814f.
Transport in metal-molecule-metal junctions is defined by the alignment and coupling of molecular orbitals with continuum electronic states in the metal contacts. Length-dependent changes in molecular orbital alignment and coupling with contact states were probed via measurements and comparisons of thermopower (S) of a series of phenylenes and alkanes with varying binding groups. S increases linearly with length for phenylenediames and phenylenedithiols while it decreases linearly in alkanedithiols. Comparison of these data suggests that the molecular backbone determines the length dependence of S, while the binding group determines the zero length or contact S. Transport in phenylenes was dominated by the highest occupied molecular orbital (HOMO), which aligns closer to the Fermi energy of the contacts as approximately L(-1), but becomes more decoupled from them as approximately e(-L). In contrast, the decreasing trend in S for alkanedithiols suggests that transmission is largely affected by gold-sulfur metal induced gap states residing between the HOMO and lowest unoccupied molecular orbital.
金属-分子-金属结中的输运由分子轨道与金属接触中的连续电子态的排列和耦合决定。通过对一系列具有不同结合基团的亚苯基和烷烃的热电势（S）进行测量和比较，探究了分子轨道排列和与接触态耦合的长度依赖性变化。对于苯二胺和苯二硫醇，S随长度线性增加，而对于烷二硫醇，S随长度线性减小。这些数据的比较表明，分子主链决定了S的长度依赖性，而结合基团决定了零长度或接触时的S。亚苯基中的输运主要由最高占据分子轨道（HOMO）主导，该轨道与接触的费米能的排列接近程度约为L(-1)，但随着约为e(-L)而与它们的耦合减弱。相比之下，烷二硫醇的S下降趋势表明，传输在很大程度上受位于HOMO和最低未占据分子轨道之间的金-硫金属诱导能隙态的影响。
