Electronically Connected Graphene Nanoribbons foresee High-Speed Electronics

Figure 1 shows interconnected graphene nanoribbons (GNRs). The interconnection points are observed as elbow structures. The inset of (a) shows the chemical structure of an elbow interconnection point of two chiral-edge GNRs. The top panel of (b) shows the scanning tunneling microscopy topograph, highlighting a single GNR and a pair of connected GNRs (elbow). The bottom panel of (b) shows the local density of states (LDOS) of these two structures share the same electronic architecture, including the elbow interconnection point. This indicates that electronic properties, such as electron and thermal conductivities, should be comparable between termini 1-2 and termini 3-4. Credit: Patrick Han

Chemical interconnection bridges electronic properties of graphene-nanoribbons with zigzag-edge features. The GNRs were interconnected exclusively end to end, forming elbow structures, identified as interconnection points. This configuration enabled researchers to demonstrate that the electronic architecture at the interconnection points between 2 GNRs is the same as that along single GNRs; evidence that GNR electronic properties, such as electron and thermal conductivities, are directly extended through the elbow structures upon chemical GNR interconnection. This work shows that future development of high-performance, low-power-consumption electronics based on GNRs is possible.

While current fabrication methods can control graphene’s electronic properties, eg high electron mobility, tailored band gaps and s pin-aligned zigzag edges, the connection aspect of graphene structures has never been directly explored. Eg, whether electrons traveling across the interconnection points of 2 GNRs would encounter higher electric resistance remains an open question. As the answers to this type of questions are crucial towards the realization of future high-speed, low-power-consumption electronics, we use molecular assembly to address this issue here.

“Current molecular assemblies either produce straight GNRs (i.e., without identifiable interconnection points), or randomly interconnected GNRs,” says Dr. Patrick Han, the project leader. “These growth modes have too many intrinsic unknowns for determining whether electrons travel across graphene interconnection points smoothly. The key is to design a molecular assembly that produces GNRs that are systematically interconnected with clearly distinguishable interconnection points.”

AIMR team used a Cu substrate, whose reactivity confines the GNR growth to 6 directions, and used scanning tunneling microscopy (STM) to visualize the GNR electronic structures. By controlling the precursor molecular coverage, it connects GNRs from different growth directions systematically end to end, producing elbow structures–identified as interconnection points. Using STM, they revealed delocalization of the interconnected GNR π-states extends the same way both across a single straight GNR, and across the interconnection point of two GNRs.

“The major finding of this work is that interconnected GNRs do not show electronic disruption (e.g., electron localization that increases resistance at the interconnection points),” says Han. “The electronically smooth interconnection demonstrates that GNR properties (including tailored band gaps, or even spin-aligned zigzag edges) can be connected to other graphene structures. These results show that finding a way to connect defect-free GNRs to desired electrodes may be the key strategy toward achieving high-performance, low-power-consumption electronics.” https://www.tohoku.ac.jp/en/news/research/graphene_nanoribbons_foresee_high_speed_electronics.html