title: Molecular bandgap engineering of bottom-up synthesized graphene nanoribbon heterojunctions.
abstract: Bandgap engineering is used to create semiconductor heterostructure devices that perform processes such as resonant tunnelling and solar energy conversion. However, the performance of such devices degrades as their size is reduced. Graphene-based molecular electronics has emerged as a candidate to enable high performance down to the single-molecule scale. Graphene nanoribbons, for example, can have widths of less than 2 nm and bandgaps that are tunable via their width and symmetry. It has been predicted that bandgap engineering within a single graphene nanoribbon may be achieved by varying the width of covalently bonded segments within the nanoribbon. Here, we demonstrate the bottom-up synthesis of such width-modulated armchair graphene nanoribbon heterostructures, obtained by fusing segments made from two different molecular building blocks. We study these heterojunctions at subnanometre length scales with scanning tunnelling microscopy and spectroscopy, and identify their spatially modulated electronic structure, demonstrating molecular-scale bandgap engineering, including type I heterojunction behaviour. First-principles calculations support these findings and provide insight into the microscopic electronic structure of bandgap-engineered graphene nanoribbon heterojunctions.
authors.affiliation: 1] Department of Physics, University of California at Berkeley, Berkeley, California 94720, USA [2] Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.
authors.forename: Yen-Chia
authors.initials: YC
authors.lastname: Chen
authors.affiliation: 1] Department of Physics, University of California at Berkeley, Berkeley, California 94720, USA [2] Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.
authors.forename: Ting
authors.initials: T
authors.lastname: Cao
authors.affiliation: Department of Chemistry, University of California at Berkeley, Berkeley, California 94720, USA.
authors.forename: Chen
authors.initials: C
authors.lastname: Chen
authors.affiliation: Department of Physics, University of California at Berkeley, Berkeley, California 94720, USA.
authors.forename: Zahra
authors.initials: Z
authors.lastname: Pedramrazi
authors.affiliation: Department of Physics, University of California at Berkeley, Berkeley, California 94720, USA.
authors.forename: Danny
authors.initials: D
authors.lastname: Haberer
authors.affiliation: 1] Department of Physics, University of California at Berkeley, Berkeley, California 94720, USA [2] Centro de Física de Materiales CSIC/UPV-EHU-Materials Physics Center, San Sebastián, E-20018, Spain.
authors.forename: Dimas G
authors.initials: DG
authors.lastname: de Oteyza
authors.affiliation: 1] Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA [2] Department of Chemistry, University of California at Berkeley, Berkeley, California 94720, USA [3] Kavli Energy NanoSciences Institute at the University of California and Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.
authors.forename: Felix R
authors.initials: FR
authors.lastname: Fischer
authors.affiliation: 1] Department of Physics, University of California at Berkeley, Berkeley, California 94720, USA [2] Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.
authors.forename: Steven G
authors.initials: SG
authors.lastname: Louie
authors.affiliation: 1] Department of Physics, University of California at Berkeley, Berkeley, California 94720, USA [2] Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA [3] Kavli Energy NanoSciences Institute at the University of California and Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.
authors.forename: Michael F
authors.initials: MF
authors.lastname: Crommie