Surfaces are at the frontier of every known solid. They provide versatile supports for functional nanostructures and mediate essential physicochemical processes. Intimately related to two-dimensional materials, interfaces and atomically thin films often feature distinct electronic states with respect to the bulk, which is key to many relevant properties, such as catalytic activity, interfacial charge-transfer, and crystal growth mechanisms. To induce novel quantum properties via lateral scattering and confinement, reducing the surface electrons’ dimensionality and spread with atomic precision is of particular interest. Both atomic manipulation and supramolecular principles provide access to custom-designed molecular assemblies and superlattices, which tailor the surface electronic landscape and influence fundamental chemical and physical properties at the nanoscale. Here the confinement of surface-state electrons is reviewed, with a focus on their interaction with molecular scaffolds created by molecular manipulation and self-assembly protocols under ultrahigh vacuum conditions. Starting with the quasifree two-dimensional electron gas present at the $(111)$-oriented surface planes of noble metals, the intriguing molecule-based structural complexity and versatility is illustrated. Surveyed are low-dimensional confining structures in the form of artificial lattices, molecular nanogratings, or quantum dot arrays, which are constructed upon an appropriate choice of their building constituents. Whenever the realized (metal-)organic networks exhibit long-range order, modified surface band structures with characteristic features emerge, inducing noteworthy physical phenomena such as discretization, quantum coupling or energy, and effective mass renormalization. Such collective electronic states can be additionally modified by positioning guest species at the voids of open nanoarchitectures. The designed scattering potential landscapes can be described with semiempirical models, bringing thus the prospect of total control over surface electron confinement and novel quantum states within reach.

中文翻译：

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通过表面分子纳米结构设计量子态和电子景观

曲面处于所有已知固体的前沿。它们为功能性纳米结构提供多功能支持并介导必要的物理化学过程。与二维材料密切相关，界面和原子薄膜通常具有相对于体积不同的电子态，这是许多相关特性的关键，例如催化活性、界面电荷转移和晶体生长机制。为了通过横向散射和限制来诱导新的量子特性，以原子精度降低表面电子的维数和扩散是特别令人感兴趣的。原子操纵和超分子原理都提供了定制设计的分子组装和超晶格的途径，这些组装和超晶格可以定制表面电子景观并影响纳米尺度的基本化学和物理性质。这里回顾了表面态电子的限制，重点是它们与超高真空条件下分子操纵和自组装协议创建的分子支架的相互作用。从存在于的准自由二维电子气开始$（111）$贵金属的定向表面平面，说明了基于分子的有趣的结构复杂性和多功能性。调查的是人工晶格、分子纳米光栅或量子点阵列形式的低维限制结构，这些结构是根据适当选择的建筑成分而构建的。每当实现的（金属）有机网络表现出长程有序时，就会出现具有特征特征的改性表面能带结构，从而引发值得注意的物理现象，例如离散化、量子耦合或能量以及有效质量重正化。这种集体电子态可以通过将客体物种放置在开放纳米结构的空隙中来额外修改。设计的散射势景观可以用半经验模型来描述，从而使表面电子限制和新型量子态的完全控制的前景成为可能。