Invited Paper GR+AS+NS+SS-ThM9
Graphene Nanostructures: Top-down vs. Bottom-up Approaches

Thursday, October 31, 2013, 10:40 am, Room 104 B

Graphene, a two-dimensional carbon allotrope, is often considered as a complement or even replacement for silicon in many electronics applications. However, the absence of an electronic bandgap in graphene prevents its use in logic devices. According to the theoretical studies, a bandgap compared to that in silicon (1.1 eV) could be found in narrow graphene nanoribbons (GNRs) that have atomically precise armchair edges and widths less than 2 nm. Different top-down approaches, such as a combination of electron-beam lithography and dry etching, sonochemical method, nanowire lithography, and unzipping of carbon nanotubes, typically yield ribbons with widths > 10 nm and have a limited control over the edge structure in GNRs. Several recent studies have also focused on the development of bottom-up chemical approaches for narrow GNRs. Most of these methods are based on a polymerization of pre-synthesized molecular precursors followed by a cyclodehydrogenation. The reported bottom-up techniques could yield narrow atomically-engineered GNRs that are currently unachievable by any top-down approach, stimulating further research and development of new synthetic methods for GNRs. However, several problems still need to be solved, such as a limited length of synthetic GNRs, their poor solubility, difficulties with their precise placement on dielectric substrates for device fabrication, etc.

In this talk I will review recent efforts to synthesize GNRs with an emphasis on a comparative analysis of top-down and bottom-up approaches. I will also discuss a recently developed bottom-up approach for gram quantities of narrow GNRs that are less than 2 nm wide and have atomically precise armchair edges. These GNRs could be conveniently deposited from solution on any substrate, such as Si/SiO2, mica and Au(111), for further studies. The GNRs were characterized by different techniques, including NMR, UV-vis-NIR and Raman spectroscopy, XPS, EDX, PES/IPS, SEM, AFM and STM. These data suggest that GNRs obtained by this novel synthetic approach could be promising for applications in field-effect transistors with high on-off ratios. Also, since these GNRs could be synthesized in gram quantities and at a very high yield, they could be used for bulk applications, including coatings, composites and photovoltaic devices.