| AVS 66th International Symposium & Exhibition | |
| Nanometer-scale Science and Technology Division | Wednesday Sessions |
| Session NS+2D+AS-WeA |
| Session: | Probing and Modifying Surface and Interfacial Chemistry at the Nanoscale |
| Presenter: | Arthur Baddorf, Oak Ridge National Laboratory |
| Authors: | C. Ma, Oak Ridge National Laboratory Z. Xiao, North Carolina State University A.A. Puretzky, Oak Ridge National Laboratory A.P. Baddorf, Oak Ridge National Laboratory W. Lu, North Carolina State University K. Hong, Oak Ridge National Laboratory J. Bernholc, North Carolina State University A.-P. Li, Oak Ridge National Laboratory |
| Correspondent: | Click to Email |
Highly controlled synthesis of graphene nanoribbons (GNRs) can be performed on a surface by polymerization of a selected precursor. Typically, this polymerization involves surface-assisted cyclodehydrogenations during thermal activation on catalytic metal surfaces. We have shown that armchair edge GNRs can be synthesized with 7, 14, and 21 carbon atom widths by absorbing 10,10’-dibromo-9,9’-bianthryl (DBBA) precursor molecules on Au(111).1 Synthesis follows a two-step process of which the first step is polymerization at 470 K. The second step, cyclodehydrogenation, can be promoted globally by annealing to 670 K, or locally following hole injection using a scanning tunneling microscope (STM) tip.2 Wider 14 or 21-aGNRs were formed when two or three 7-wide GNRs were conjugated side-by-side via inter-ribbon cyclodehydrogenation at the edge sites. Scanning Tunneling Spectroscopy (STS) reveals an electronic band gap dependent on the ribbon width. Bandgaps of ~2.6, ~0.3, and ~0.7 eV are measured for 7, 14, and 21 GNRs respectively, consistent with expectations of simple models.
For practical applications, understanding the stability of GNRs to oxidation is important. We have examined the thermal stability of 7-aGNRs after exposure to air.2 Combining STM, Raman spectroscopy, x-ray photoemission spectroscopy, and first-principles theory calculations, the armchair GNRs are found to oxidize first at the zigzag ends while the edges remain stable. Oxygen attaches to the zigzag ends at temperatures as low as 180°C. Armchair edges are stable up to 430°C and become oxidized only above 520°C. Two oxygen species are identified, one a hydroxyl (OH) and the second atomic oxygen bridging two carbons, both of which are common in oxidized graphitic lattices. The bandgap is significantly reduced from 2.6 eV to 2.3 eV in the vicinity of the hydroxyl and to 1.9 eV near bridging O. These results suggest that the oxidization will significantly affect the transport properties of GNRs and provide parameters useful for maintaining integrity of GNRs during processing for devices.
This research was conducted at the Center for Nanophase Materials Sciences, which is a DOE Office of Science User Facility.
1. C. Ma, et al., Nano Letters 17, 6241 (2017).
2. C. Ma, et al., Nature Communications 8, 14815 (2017).
3. C. Ma, et al., Physical Review Materials 2, 014006 (2018).