Locally mapping conductance and potential energy of a donor-acceptor system

小分子可以用作半导体器件中的活性元件，因为填充和未填充轨道之间的能隙在大小上与硅基半导体的带隙相似。为了用表面科学技术研究这些体系，在金属表面沉积了亚分子到几个单分子层。通过共沉积两个分子物种，可以研究相之间的界面。关于这些难以探测的分子界面，有许多悬而未决的问题：某些部位的反应性是随着它们到界面的距离而增加还是减少？载流子对金属电极的电导是如何随界面距离的变化而变化的？在这个项目中，我们应用了两种技术来解决这些问题。第一种是非接触侧向力显微镜(LFM)，它是绘制短程相互作用势能图的自然候选者。其次，我们最近发现，通过同时测量隧道电流(STM)和力(AFM)，我们可以精确地测量块体的电导。这两项新技术超越了成像，使我们能够定量地表征分子界面。我们在低温和室温下应用这些技术，在那里我们可以在原子水平上控制尖端的尖端。这使我们能够确定针尖在室温下的特性以及温度对局部电导率的影响。分子界面附近导电性的表征将使我们能够为分子半导体器件提供更低的尺寸限制，而绘制局部势能图将指导器件制造。此外，该项目还将进一步推进两项新的扫描探头技术。

Small molecules can be used as active components in semiconductor devices because the energy gap between filled and unfilled orbitals is similar in magnitude to the bandgap of Si-based semiconductors. To investigate these systems with surface science techniques, sub- to few- monolayers of molecules are deposited on a metal surface. By co-depositing two molecular species, an interface between phases can be studied. There are many outstanding questions with respect to these hard-to-probe molecular interfaces: Are certain sites more or less reactive as a function of their distance to the interface? And how does conductance of charge carriers to the metal electrode change with distance to the interface? In this project, we apply two techniques to address these questions. The first is non-contact lateral force microscopy (LFM), which is a natural candidate for mapping the potential energy map of short-range interactions. Second, we have recently discovered that by simultaneously measuring the tunneling current (STM) and force (AFM) simultaneously, we can measure conductance to the bulk with atomic precision. These two novel techniques go beyond imaging and allow us to quantifiably characterize molecular interfaces. We apply these techniques at low temperature, where we can control the apex of the tip at the atomic level, and at room temperature. This allows us to determine the character of the tip at room temperature and the effect of temperature on local conductivity. Characterization of the conductivity near molecular interfaces will allow us to provide a lower size limit on molecular semiconductor devices and mapping the local potential energy will guide device manufacturing. Moreover, this project will further advance two novel scanning probe techniques.