Electromechanical coupling at the nanoscale: The ubiquitous case of flexoelectricity

I will discuss a recent experimental observation focused on self-assembled graphene NWs formed on flat MoS2 substrates. The mismatch in elastic properties between these materials creates strain gradients, which we mapped using sub- micro Raman spectroscopy. Conductive atomic force microscopy (c-AFM) measurements revealed consistent, reproducible flexoelectric currents under appropriate bias potential across extensive networks of dense NWs This research establishes graphene NWs as an ideal system for investigating strong flexoelectric effects. The findings highlight significant potential applications in strain-engineered nanoscale electronic and electromechanical devices, opening new avenues for harnessing this phenomenon in future technologies. This work bridges theoretical predictions with experimental validation, advancing our understanding of how nanoscale structural deformations in 2D materials can be leveraged for novel electronic properties and functionalities.

Abstract: 
Electromechanical coupling at the nanoscale involves the direct conversion between mechanical and electrical energy in structures with dimensions of 1-100 nanometers. This phenomenon enables critical functionality in nanotechnology applications such as energy harvesters, nanoresonators, and nanoscale sensors where piezoelectric, electrostrictive, and flexoelectric effects become particularly significant due to increased surface-to-volume ratios. 

Flexoelectricity—the polarization induced by strain gradients—manifests with remarkable intensity in two-dimensional materials due to their extraordinary mechanical flexibility and structural sensitivity. This phenomenon reaches peak expression in highly curved nanostructures, where extreme charge redistribution creates measurable electrostatic effects.

My presentation will begin with an introduction to flexoelectricity's fundamental principles in 2D materials. [1] I will then explore its microscopic origins in graphene nanowrinkles (NW) through density functional theory (DFT), demonstrating how intense curvature at the top of the NWs generates significant local Gaussian curvature values, producing observable macroscopic effects.   
 

Bio:

Vincent Meunier serves as P. B. Breneman Chair, department head, and professor of engineering science and mechanics. Before joining Penn State in 2022, he was an endowed chair and department head of the physics, applied physics, and astronomy department at Rensselaer Polytechnic Institute. Meunier is a fellow of the American Association for the Advancement of Science (AAAS), the American Physical Society (APS), and the Institute of Physics (IOP).

His research group develops and employs large-scale computational methods to examine the properties and functionalities of materials from an atomic level perspective. His approach focuses on examining the fundamental principles of condensed matter physics and the expression of quantum mechanics at the nanoscale. Of particular interest to Meunier are low-dimensional materials, including those with intriguing electronic transport properties.

The research proceeds synergistically with engineers and experimentalists to optimize these materials, starting at the atomic level and targeting functionality. Meunier is also the editor-in-chief of the open access journal Carbon Trends.