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Quantifying the Influence of Nanosheet Aspect Ratio on Network Morphology and Junction Resistance in Solution-Processed Nanosheet Networks

Eoin Caffrey,Jose M. Munuera,Cian Gabbett,Luke Doolan,Joseph Neilson,Rebekah A Wells,Mark McCrystall,A. McNamara,Tian Carey,Martin Gerlei,Paul Seifert,Georg S. Duesberg,Jonathan N. Coleman

Published 2025 in ACS Nano

ABSTRACT

Optimizing solution-processed nanosheet networks for electronic applications requires understanding the relationship between nanosheet dimensions, network morphology, and electrical properties. Here, we fabricate graphene nanosheets with both low- and high-aspect-ratios using liquid-phase exfoliation (LPE) and electrochemical exfoliation (EE), respectively. Spray-coated networks of both nanosheet types display distinct morphological and electrical properties. High-resolution 3D imaging shows that low-aspect-ratio LPE nanosheet networks display a disordered, porous structure with point-like junctions. Conversely, high-aspect-ratio EE graphene forms low-porosity networks with highly aligned nanosheets with large-area conformal junctions. Electrical measurements demonstrate that EE networks achieve lower resistivity and reduced percolation thicknesses due to reduced junction resistances and improved nanosheet alignment. We propose a theoretical model linking nanosheet bending rigidity, aspect ratio, and junction formation, highlighting the critical role of nanosheet flexibility in enabling conformal junctions. Furthermore, by size-selecting both nanosheet types, we measure the dependence of network resistivity on nanosheet thickness. LPE networks show increasing resistivity with thickness, whereas EE networks exhibit decreasing resistivity. We develop a simple model linking these behaviors to point-like and planar junctions respectively and quantify the size-dependence of both nanosheet and junction resistance for both cases. Unexpectedly, data analysis using this model predicts the EE nanosheets to be more conductive than the LPE ones, a fact confirmed by THz spectroscopy. This study establishes the importance of nanosheet aspect ratio and flexibility in governing network morphology and electrical performance. Our findings provide key insights for developing high-performance, solution-processed 2D material networks for future electronic devices.

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