Chu Changwoong, Na Jeong-Seok, Parsons Gregory N
Department of Chemical & Biomolecular Engineering, North Carolina State University, Raleigh, North Carolina 27695, USA.
J Am Chem Soc. 2007 Feb 28;129(8):2287-96. doi: 10.1021/ja064968s. Epub 2007 Feb 6.
Charge transport through alkane monolayers on gold is measured as a function of molecule length in a controlled ambient using a metal/molecule/nanoparticle bridge structure and compared for both thiol and amine molecular end groups. The current through molecules with an amine/gold junction is observed to be more than a factor of 10 larger than that measured in similar molecules with thiol/gold linkages. Conducting probe atomic force microscopy is also used to characterize the same monolayer systems, and the results are quantitatively consistent with those found in the nanoparticle bridge geometry. Scaling of the current with contact area is used to estimate that approximately 100 molecules are probed in the nanoparticle bridge geometry. For both molecular end groups, the room-temperature conductivity at low bias as a function of molecule length shows a reasonable fit to models of coherent nonresonant charge tunneling. The different conductivity is ascribed to differences in charge transfer and wave function mixing at the metal/molecule contact, including possible effects of amine group oxidation and molecular conformation. For the amine/Au contact, the nitrogen lone pair interaction with the gold results in a hybrid wave function directed along the molecule bond axis, whereas the thiol/Au contact leads to a more localized wave function.
利用金属/分子/纳米颗粒桥结构，在可控环境中测量了电荷通过金表面烷烃单分子层的传输，并将其作为分子长度的函数进行研究，同时对硫醇和胺类分子端基进行了比较。观察到具有胺/金结的分子中的电流比具有硫醇/金键的类似分子中测量的电流大10倍以上。导电探针原子力显微镜也用于表征相同的单分子层系统，结果与在纳米颗粒桥几何结构中发现的结果在数量上一致。利用电流与接触面积的比例关系估计，在纳米颗粒桥几何结构中大约探测了100个分子。对于这两种分子端基，低偏压下的室温电导率作为分子长度的函数，与相干非共振电荷隧穿模型有合理的拟合。不同的电导率归因于金属/分子接触处电荷转移和波函数混合的差异，包括胺基氧化和分子构象的可能影响。对于胺/金接触，氮孤对与金的相互作用导致沿着分子键轴方向的混合波函数，而硫醇/金接触导致更局域化的波函数。
