Identifying the Length Dependence of Orbital Alignment and Contact Coupling in Molecular Heterojunctions
Identifying the Length Dependence of Orbital Alignment and Contact Coupling in Molecular Heterojunctions
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DOI：
10.1021/nl803814f
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发表时间：
2009-03-01
期刊：
影响因子：
10.8
通讯作者：
Majumdar, Arun
中科院分区：
文献类型：
--
作者：
Malen, Jonathan A.;Doak, Peter;Majumdar, Arun
金属-分子-金属结中的输运是由分子轨道与金属接触中的连续电子态的排列和耦合定义的。通过测量和比较一系列具有不同结合基团的亚苯基和烷烃的热电势（S），探讨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，分子骨架决定了S的长度依赖性，而结合基团决定了零长度或接触S。亚苯基中的输运由最高占据分子轨道（HOMO）主导，其与接触的费米能更接近，类似于L-1，但与它们更解耦，类似于e（-L）。相比之下，链烷二硫醇的S的下降趋势表明，传输在很大程度上受到金-硫金属诱导的间隙状态之间的HOMO和最低未占分子轨道。
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 similar to L-1, but becomes more decoupled from them as similar to 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.