光吸收和光电流谱研究分子电子学中重要长度尺度
Optical Absorption and Photocurrent Spectroscopy for Investigating Important Length Scales in Molecular Electronics
摘要：
本文报道了不同分子结构和厚度的大面积分子结的光吸收特性和光电流谱。通过实验评估的光学吸收的分子在溶液中和化学吸附到透明的，导电的碳膜，作为厚度的函数的各种分子层的吸收的能量范围和强度被确定。我们的研究结果表明，光吸收是红移的化学吸附的分子层相对于在溶液中的分子，表明分子和表面之间的电子耦合。然而，我们也发现，从2-22 nm的厚度，吸收特性遵循比尔定律，没有进一步的移动，在最大吸收或低能量吸收开始的波长。对于没有发生吸收的能量，发生内部光电发射过程，导致可以在有限范围内维持的光电流。对于分子组分吸收光的能量，光电流可以在更长的距离上进行，并且光电流产率相对于厚度的趋势显示出有趣的趋势，其可能与载流子可以与导电触点通信的距离尺度有关。这种方法是特别相关的强耦合系统，依赖于分子特性介导的电荷传输，因为激发直接发生在分子层内，并提供了一个直接的探针的能量系统，显示批量有限的运输。
英文摘要：
We report the optical absorption characteristics and the photocurrent spectra for large-area molecular junctions containing different molecular structures and thicknesses. Through experimental assessment of the optical absorption of molecules in solution and chemisorbed onto transparent, conductive carbon films, the energy ranges and intensity of absorption for a variety of molecular layers as a function of thickness were determined. Our findings show that optical absorption is red-shifted for a chemisorbed molecular layer relative to the molecule in solution, indicating electronic coupling between the molecule and the surface. However, we also find that from 2-22 nm in thickness, the absorption characteristics follow Beers law, with no further shifts in the wavelength of maximum absorption or low-energy absorption onset. For energies where no absorption occurs, an internal photoemission process takes place resulting in photocurrent that can be sustained over a limited range. For energies at which the molecular component absorbs light, photocurrent can proceed over longer distances, and the trends in photocurrent yield versus thickness shows interesting trends that may be related to the distance scale over which charge carriers can communicate with the conductive contacts. This method is particularly relevant for strongly coupled systems that rely on molecular properties to mediate charge transport, since excitation takes place directly within the molecular layer, and provides a direct probe of energetics in systems that show bulk-limited transport.
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