2, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States
4, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States
5, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States
3, University of Nebraska-Lincoln, Lincoln, Nebraska, United States
6, Nebraska Center for Materials and Nanoscience, Lincoln, Nebraska, United States
Atomically precise graphene nanoribbons synthesized via wet chemical method opens opportunities for tailoring their structures as well as electronic properties and therefore have ignited enormous interest. Among different techniques for GNR characterization, scanning tunneling microscopy and spectroscopy (STM/STS) provide both morphological details and local electronic structure with atomic resolution. Here we applied a dry contact transfer technique  to deposit solution-synthesized doublewide GNRs (dGNRs) and extended-chevron GNRs (eGNRs)  onto clean InAs (110) and hydrogen-passivated Si(100) semiconducting surfaces under ultrahigh vacuum conditions. High-resolution STM images were collected to confirm their structures. By performing scanning tunneling spectroscopy, the band gap of the wGNRs and the eGNRs were determined to be 2eV and 2.6eV, respectively. For the wGNRs on InAs, we also carried out detailed analysis on mapping of the electronic density of states both spatially and energetically via STS and current imaging tunneling spectroscopy. We found that the electron orbital shapes at the GNR edges are different from those at the centers. Correspondent DFT simulations of isolated GNRs were also carried out and showed great consistency with our experimental results, indicating a very weak coupling between the GNR and the InAs at an equilibrium position. In addition, we demonstrated the tunable transparency effect of the GNRs with respect to the underlying substrate, creating tunable GNR-substrate interaction by pushing GNRs towards the surface.
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2. Mohammad Mehdi Pour, Andrey Lashkov, Adrian Radocea, Ximeng Liu, Tao Sun, Alexey Lipatov, Rafal A. Korlacki, Mikhail Shekhirev, Narayana R. Aluru, Joseph W. Lyding, Victor Sysoev & Alexander Sinitskii, Nature Communications 8, article 820, October 2017.