Engineering quantum states and electronic landscapes through surface molecular nanoarchitectures

Abstract

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 twodimensional electron gas present at the ð111Þ-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.

Formation of an Extended Quantum Dot Array Driven and Autoprotected by an Atom-Thick h-BN Layer

“…The effective mass renormalization, necessary to optimize the agreement with the experiment (Figure S9), is tentatively attributed to the apparent surface corrugation induced by CuS structures. Such effective mass renormalization of the surface state has previously been reported to occur for surface alloys and due to the interaction of heteroatoms and/or molecular nanostructures with the substrate. ,, We find good agreement between the experimental d I /d V spectra and theoretical LDOS at the center, halfway, and corner positions of the pore; see Figure a.…”

“…Such effective mass renormalization of the surface state has previously been reported to occur for surface alloys 42 and due to the interaction of heteroatoms and/ or molecular nanostructures with the substrate. 3,43,44 We find good agreement between the experimental dI/dV spectra and theoretical LDOS at the center, halfway, and corner positions of the pore; see Figure 4a.…”

“…Common strategies to fabricate confining nanostructures on these surfaces, in ultrahigh vacuum (UHV), rely on atom-by-atom/molecule-by-molecule manipulation by the tip of a scanning tunneling microscope (STM) 1,2 at low temperature (<10 K) or on self-assembly protocols offered by, e.g., supramolecular chemistry principles. 3 Employing the former, quantum confinement in adatom corrals, 4,5 quantum mirage effects, 6 artificial lattices promoting exotic properties, 7,8 and pseudologic gates 9 could be realized and explored, expanding our fundamental understanding of quantum phenomena.…”

“…The most prominent target for this has been the Shockley surface state at coinage metal surfaces. Common strategies to fabricate confining nanostructures on these surfaces, in ultrahigh vacuum (UHV), rely on atom-by-atom/molecule-by-molecule manipulation by the tip of a scanning tunneling microscope (STM) , at low temperature (<10 K) or on self-assembly protocols offered by, e.g., supramolecular chemistry principles …”

High-Yield Production of Quantum Corrals in a Surface Reconstruction Pattern

“…On-surface chemical reactions , have recently developed into a promising way to prepare the otherwise inaccessible architectures with desired geometry as impressively exampled by the synthesis of graphene nanoribbons with atomically precise edges and well-defined width. , However, thermally activated on-surface reactions always lead to high defect density, small domain size, and limited regioselectivity. , For covalently linked organic nanopores and cycles, both entropy and in-plane strain effects coupled with competitive reaction pathways result in an ultralow yield and unwanted byproducts. , Long-range ordered two-dimensional (2D) nanoporous polymers in mesoscale lateral extension have been realized through topochemical photopolymerization, , but the number of known monomers with reactive packing is very limited. − Moreover, the realization of QCs in organic nanocavities on the noble metal surface requires that the pore size should be comparable to the Fermi wavelength of 2D electron gas. , These stringent requirements give rise to few experimental realizations of stable QCs in organic frameworks. − …”