Insights into the Mechanism by Which Vacancy Defects Influence the Electrical and Piezoresistive Properties of Graphene.

Owing to its exceptional mechanical and electrical properties, graphene is regarded as an ideal sensing material for piezoresistive pressure sensors. However, vacancy defects inevitably introduced during graphene preparation and transfer significantly alter its electrical characteristics and piezoresistive performance. Based on first-principles calculations, this work systematically investigates the influence of mono-, di-, and tri-vacancy defects on the electrical and piezoresistive properties of graphene. The results indicate that di- and tri-vacancy defects reconstruct into 5-8-5 and 5-10-5 configurations during relaxation. Mono-, di-, and tri-vacancy defects effectively open bandgaps in graphene, yielding values of 0.62, 0.48, and 0.72 eV, respectively. The mono-vacancy introduces localized defect states near the Fermi level, the di-vacancy shifts the Dirac point from K to M, and the tri-vacancy moves it along the K-Γ path, eventually placing it between K and Γ. The application of strain not only widens the bandgap of defective graphene but also induces the movement of defect energy levels toward the band edges in the mono-vacancy system. All three defect types enhance the piezoresistive effect, with the tri-vacancy defect showing the most pronounced enhancement-boosting the gauge factor by a factor of 5.58. These findings provide a theoretical foundation for optimizing graphene-based pressure sensors.