Chemical doping of atomically precise graphene nanoribbons

• Forschungsstelle: COST
• Projektnummer: C11.0123
• Projekttitel Englisch: Chemical doping of atomically precise graphene nanoribbons

Schlüsselwörter (Englisch)

graphene; graphene nanoribbons; bottom-up synthesis; electronic structure; chemical doping

Forschungsprogramme (Englisch)

COST-Action MP0901 - Designing novel materials for nanodevices: From Theory to Practise (NanoTP)

Kurzbeschreibung (Englisch)

The project aims at the fabrication of atomically precise graphene nanoribbons with specific electronic properties. Our recently presented surface-assisted bottom-up approach has proven to provide the needed atomic precision for the fabrication of graphene nanosturctures with specific and controlled electronic properties. Motivated by recent theretical predictions, we aim at extending our bottom-up approach by exploring three different ways of controlled chemical doping of graphene nanoribbons. More specifically, we aim at the atomically precise fabrication of graphene nanribbons with controlled chemical doping using i) edge functionalization, realized by designing precursor monomers including additional funcitonal groups, ii) substitutional doping of the aromatic board of the graphene nanoribbon, again by using specifically designed monomers and iii) after-growth doping by covalent attachment of specific funcitonal groups to the as-grown graphene nanoribbon. The three approaches differ with respect to their complexity and arising opportunities : Approach iii) directly builts on already proven fabrication schemes for the GNRs but allows only for a homogeneous doping. On the other hand, i) and ii) are experimentally more challenging but offer new opportunities for the succesful realization of heterostructures on single graphene nanoribbons by usings controlled sequence of the monomers during growth.

Weitere Hinweise und Angaben (Englisch)

Full name of research-institution/enterprise: Eidg. Materialprüfungs- und Forschungsanstalt EMPA Molecular nanostructures

Partner und Internationale Organisationen (Englisch)

BE; BG; HR; CY; CZ; DK; FI; FR; DE; EL; HU; IE; IT; NL; PL; PT; RO: SI; ES; SE; TR; UK; AM; RU; MX; AU; CA

Abstract (Englisch)

Graphene - a single atomic layer of carbon atoms arranged in a honeycomb lattice - has recently attracted considerable interest for its extraordinary electronic properties that are expected to quickly find ways into electronic and sensing applications. One of the major shortcomings of graphene, however, is the missing electronic band gap. This prevents graphene-based devices to be brought in a complete off state and thus inhibits the realization of efficient graphene-based electronic switching devices. Quantum confinement in graphene nanostructures, on the other hand, offers the possibility to introduce significant electronic band gaps that are of interest for a number of applications. For instance, graphene nanoribbons (GNRs), narrow stripes of graphene, have an electronic band gap that sensitively depends on their width and thus allows predefining the band gap by selecting the appropriate width of the GNRs. We have shown in an earlier study, that the needed atomic precision can be achieved by a bottom-up approach, which includes controlled colligation of specifically designed precursor monomers and their surface-assisted dehydrogenation. The present project aimed at exploiting the controlled chemical doping of GNRs in order to further refine the control over their electronic properties. Based on chemically modified precursor monomers we have shown that graphene nanostructure with controlled chemical substitutions can indeed be fabricated and allow to controllably modify their electronic properties. To this end we have grown Nitrogen-doped chevron-type GNRs by a bottom-up fabrication process involving precursor monomers where specific atomic sites are substituted with Nitrogen atoms. The electronic characterization of the Nitrogen-doped GNRs reveals a substantial down-shift of occupied and unoccupied electronic states while maintaining the electronic band gap of the undoped chevron GNRs. Since doped and Nitrogen-doped precursor monomers have compatible coupling motifs, this opens the opportunity to fabricate controlled heterostructures with covalently interlinked undoped and doped by combining undoped and doped GNR segments in the fabrication step. Experimentally, we find indeed a large band offset, which occurs over an extremely short distance and therefore results in large electric fields that are, for instance, interesting for efficient charge separation in photovoltaic applications. In order to further diversify control over the electronic structure of graphene nanomaterials we have been investigating on-surface synthesis routes allowing for the partial substitution of carbon rings by boron-nitride (B-N) rings. Our findings demonstrate that precursor monomers containing B-N rings can successfully be used for the controlled bottom-up fabrication of related heterostructures, thus proving for the first time that synthesis of atomically precise B-N-graphene heterostructures can indeed be achieved.

Datenbankreferenzen (Englisch)

Swiss Database: COST-DB of the State Secretariat for Education and Research Hallwylstrasse 4 CH-3003 Berne, Switzerland Tel. [phone] Swiss Project-Number: C11.0123