Tearing Graphene Sheets From Adhesive Substrates Produces Tapered Nanoribbons

Abstract: Graphene is a truly two-dimensional atomic crystal with exceptional electronic and mechanical properties. Whereas conventional bulk and thin-film materials have been studied extensively, the key mechanical properties of graphene, such as tearing and cracking, remain unknown, partly due to its two-dimensional nature and ultimate single-atom-layer thickness, which result in the breakdown of conventional material models. By combining first-principles ReaxFF molecular dynamics and experimental studies, a bottom-up investigation of the tearing of graphene sheets from adhesive substrates is reported, including the observation of the formation of tapered graphene nanoribbons. Through a careful analysis of the underlying molecular rupture mechanisms, it is shown that the resulting nanoribbon geometry is controlled by both the graphene-substrate adhesion energy and by the number of torn graphene layers. By considering graphene as a model material for a broader class of two-dimensional atomic crystals, these results provide fundamental insights into the tearing and cracking mechanisms of highly confined nanomaterials.

Tearing Graphene Sheets From Adhesive Substrates Produces Tapered Nanoribbons: A Technical Analysis

The paper titled "Tearing Graphene Sheets From Adhesive Substrates Produces Tapered Nanoribbons" addresses the mechanical behavior of graphene, a two-dimensional (2D) material of exceptional electronic and mechanical properties. This study is an in-depth exploration into the fracture mechanics of graphene, specifically focusing on the tearing process to produce tapered nanoribbons. Through a combination of experimental observations and atomistic ReaxFF molecular dynamics simulations, the authors offer insights into the formation process of these tapered structures.

Key Findings and Methodology:

The research utilizes experimental methods alongside computational modeling to observe the tearing behavior when graphene sheets are detached from adhesive substrates. The authors highlight the ability to form graphene nanoribbons with tapered geometries that are directly influenced by the substrate adhesion energy and the number of graphene layers torn. The findings suggest that conventional models, typically applicable to bulk or thin-film materials, are inadequate in explaining graphene's mechanical properties due to its ultimate single-atom-layer thickness.

Two distinct regimes are identified based on adhesion strength:

1. At low adhesion strengths, tearing is primarily dictated by bending energy, following a linear relation of the sine of half the tearing angle with the square root of adhesion energy.
2. At high adhesion strengths, the tearing process involves significant stretching energy, deviating from conventional macroscopic theories and exhibiting a scaling where the sine of half the tearing angle is proportional to the square of adhesion energy.

The simulations are corroborated by experimental data, displaying consistent results in tearing angles for both monolayer and bilayer graphene when subjected to substrates of varying adhesive characteristics.

Implications and Future Work:

This paper provides substantial insights into the mechanical behavior of graphene when undergoing tear loading, contributing to the fundamental understanding of 2D atomic crystals. The research posits that the results have implications for developing manufacturing techniques to create graphene nanostructures with precise geometries and edge characteristics.

The interplay between atomic lattice geometry and mechanical tearing introduces significant avenues for future research, especially concerning molecular electronics applications where band gap variations may be pivotal. Further investigations could delve into the electronic consequences of the observed 5–7 defects at tear edges, contributing to the material's potential utility in nanotechnology and electronic industries.

Conclusion:

The paper effectively illustrates an intricate understanding of graphene's tearing mechanics, offering detailed computational and experimental analysis. Its contributions lie in the nuanced distinction between bending and stretching regimes dictated by adhesion strength, alongside implications for tailoring graphene nanostructures. As the field progresses, the insights offered by this research could drive developments in the application of graphene and other 2D materials in cutting-edge technological domains.