Final Report Summary - SURFPRO (Tuning electronic surface properties by molecular patterning)
Inspired by the possibility to create an artificial electronic surface structure through the interplay of a molecular nanoporous network with the surface electrons of a metallic substrate, the utilization of this concept for deliberately controlling the electronic surface properties of a material as well as establishing understanding of the underlying principles for the observed behavior was the overall aim of this project. Since the modification of the electronic surface properties also affects the material properties in general, this concept may have great potential for materials research and the development of new materials with adjustable electronic properties. Possible applications could be in e. g. (nano)electronic devices or sensors.
Based on supramolecular self-assembly, nanoporous networks were fabricated from specially designed molecular building blocks on either metallic substrates or graphene. Since both the metallic substrates and graphene feature a quasi-free 2D electron gas at their surfaces quantum confinement effects appear leading to confined states within the pores of the molecular network. Due to the coupling of these confined states, an artificial electronic surface structure can form.
The findings obtained are summarized below. The investigation of electron confinement effects in dependence of pore size, pore shape and even in partial confinement was examined for a porous 2D-sponge-like network. The network itself is made from two molecules which undergo covalent coupling reactions upon annealing at elevated temperatures on a Cu surface. Scanning tunneling spectroscopy measurements showed that the position of the confined states depend on the area of the pore size while the confinement itself is not perfect. Interestingly, even for open pores with a varying number of missing side walls, the confined state energy is identical to an intact pore. For two related rod-like molecules forming porous metal-organic coordination networks on Au surfaces we could directly relate the influence of the pore size to the energy positions of the confined states and to the newly formed electronic surface structure.
We could demonstrate that the electronic confined state as well as the coupling between neighboring confined states can be locally modified to a varying extent by a selective choice of adsorbates, here C60, interacting with the confining molecular barrier. In view of the wealth of differently interacting adsorbates trapped in the network pores, this approach allows for engineering quantum states in on-surface network architectures.
The condensation of individual Xe atoms could be mapped on a step by step basis upon restricting their freedom of movement by a porous molecular network which features a confined state in the pores. The Xe atoms always arranged according to a certain principle. For example, units of four atoms were only formed when there were at least seven atoms in the pore; and if there were twelve atoms in the pore (the maximum filling), this resulted in the creation of three highly stable four-atom units. The measurements allowed for the first time to draw key conclusions as to the nature of the physical bonds formed by Xe atoms.
We could successfully demonstrate that graphene can be grown by a single step CVD process onto copper oxide despite the - until then - prevailing belief that this would not be possible. The key advantage is that graphene is electronically decoupled from its substrate what results in zero doping and a band structure which is identical to the one of freestanding graphene.
The controlled opening of a band gap in graphene could be achieved by adsorbing monolayer coverages of two related carboxyl-functionalized molecules. This finding can be seen as a prerequisite for the potential implementation of graphene in future electronic devices.
Based on supramolecular self-assembly, nanoporous networks were fabricated from specially designed molecular building blocks on either metallic substrates or graphene. Since both the metallic substrates and graphene feature a quasi-free 2D electron gas at their surfaces quantum confinement effects appear leading to confined states within the pores of the molecular network. Due to the coupling of these confined states, an artificial electronic surface structure can form.
The findings obtained are summarized below. The investigation of electron confinement effects in dependence of pore size, pore shape and even in partial confinement was examined for a porous 2D-sponge-like network. The network itself is made from two molecules which undergo covalent coupling reactions upon annealing at elevated temperatures on a Cu surface. Scanning tunneling spectroscopy measurements showed that the position of the confined states depend on the area of the pore size while the confinement itself is not perfect. Interestingly, even for open pores with a varying number of missing side walls, the confined state energy is identical to an intact pore. For two related rod-like molecules forming porous metal-organic coordination networks on Au surfaces we could directly relate the influence of the pore size to the energy positions of the confined states and to the newly formed electronic surface structure.
We could demonstrate that the electronic confined state as well as the coupling between neighboring confined states can be locally modified to a varying extent by a selective choice of adsorbates, here C60, interacting with the confining molecular barrier. In view of the wealth of differently interacting adsorbates trapped in the network pores, this approach allows for engineering quantum states in on-surface network architectures.
The condensation of individual Xe atoms could be mapped on a step by step basis upon restricting their freedom of movement by a porous molecular network which features a confined state in the pores. The Xe atoms always arranged according to a certain principle. For example, units of four atoms were only formed when there were at least seven atoms in the pore; and if there were twelve atoms in the pore (the maximum filling), this resulted in the creation of three highly stable four-atom units. The measurements allowed for the first time to draw key conclusions as to the nature of the physical bonds formed by Xe atoms.
We could successfully demonstrate that graphene can be grown by a single step CVD process onto copper oxide despite the - until then - prevailing belief that this would not be possible. The key advantage is that graphene is electronically decoupled from its substrate what results in zero doping and a band structure which is identical to the one of freestanding graphene.
The controlled opening of a band gap in graphene could be achieved by adsorbing monolayer coverages of two related carboxyl-functionalized molecules. This finding can be seen as a prerequisite for the potential implementation of graphene in future electronic devices.