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Bottom-up fabrication of graphene nanoribbons: From molecules to devices

Borin Barin, Gabriela (EMPA, Dübendorf, CHE); Fairbrother, Andrew (EMPA, Dubendorf, CHE); Sanchez-Valencia, Juan Ramon (EMPA, Dubendorf, CHE); Llinás, Juan Pablo (UC Berkeley, California, USA); Feng, Xinliang (TU Dresden, Dresden, GER); Mullen, Klaus (Max Planck Institute for Polymer Research, Mainz, GER); Ruffieux, Pascal (EMPA, Dubendorf, CHE); Paillet, Matthieu (Université de Montpellier, Montpellier, FRA); Bokor, Jeffrey (UC Berkeley, California, USA); Fasel, Roman (EMPA, Dubendorf, CHE)

Atomically precise graphene nanoribbons (GNRs) exhibit a sizeable bandgap, and thus potentially overcome many of the limitations of graphene in electronic device applications. However, in spite of their exceptional properties, significant challenges remain for GNR fabrication, processing and characterization1. Bottom-up synthesis of graphene nanoribbons2 is most commonly performed under ultra-high vacuum conditions, which are difficult to maintain in an industrial setting. Additionally, little is known about the stability of ultra-narrow GNRs under ambient conditions or during device processing. This contribution addresses some of these challenges, in particular regarding GNR fabrication scalability, characterization, and device fabrication. On-surface synthesis from molecular precursors was focused on 7-and 9- AGNRs (7 and 9 carbon atoms wide GNRs with armchair edges, respectively) on 200nm Au(111)/mica substrates, under high to ultrahigh vacuum conditions. 7- AGNRs were found to be stable for several months under ambient conditions, with minor alterations to the Raman characteristics of the ribbons. The most notable changes were an increase in the full-width-at-half-max of all peaks and a blue-shift of the G-peak, which we ascribe to intercalation of water between the GNRs and the metal substrate. Detailed studies including polarized and multi-wavelength Raman characterization of 7-and 9-AGNRs will be discussed. Concerning device application, field effect transistors (FET) fabricated with 7-AGNRs have shown low drive current of 1 nA for 1 V drain bias due to large Schottky barriers at the contacts caused by the large band gap of 7-AGNRs (>3eV)3. Due to their significantly lower band gap (~2.1eV), 9-AGNRs demonstrate a two orders of magnitude improvement with 100 nA of on-current and on-off ratios >103 which can potentially improve the on-state performance of GNR-FETs4.

[1] L.Talirz et al., Adv. Mater.( 2016)

[2] J. Cai et al., Nature (2010)

[3] P.B. Bennet et al., Appl. Phys. Lett. (2013)

[4] J.P. Llinás et al., Field effect transistors with 9-atom and 13-atom wide graphene nanoribbons, in preparation 

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