Spectroscopic Fingerprints of Few-Layer Graphene on PET: Toward Intelligent Food Packaging Systems

This work explores the optical behavior of monolayer, bilayer, and trilayer graphene films synthesized via chemical vapor deposition (CVD) and transferred onto polyethylene terephthalate (PET) substrates, with the aim of assessing their suitability for integration into smart labels for food packaging. Graphene is selected for this application because it uniquely combines optical transparency, mechanical flexibility, and high electrical conductivity, enabling the realization of labels that are unobtrusive yet multifunctional. The increasing demand for sustainable and intelligent packaging solutions has driven interest in flexible and transparent materials capable of incorporating sensing or data-storage functions. Spectroscopic ellipsometry analysis demonstrates that the dielectric response of few-layer graphene on PET can be accurately modeled using two Lorentz oscillators. A strong absorption feature at 4.6 eV is attributed to the van Hove singularity in the graphene density of states. Unlike what has been observed for bilayer graphene on SiO₂/Si substrates, this peak does not show a red shift on PET, suggesting reduced exciton–substrate interactions and supporting turbostratic stacking. A second oscillator, centered around 4.0 eV, is assigned to π–π* transitions typical of graphitic structures. The absence of significant spectral shifts highlights the substrate-dependent nature of excitonic features in graphene. These results provide a spectroscopic fingerprint for few-layer CVD graphene on flexible PET, which is essential for non-destructive quality control in industrial settings. Ultimately, this study contributes to the fundamental knowledge required to enable the development of transparent, flexible, and functional smart packaging technologies, where the ability to verify film quality via rapid, non-destructive inspection supports scalable production. The main advantages for packaging are the reliable integration of intelligent functions, the preservation of transparency and recyclability, and the possibility of adding sensing, traceability, and anti-counterfeiting capabilities without compromising the sustainability of PET-based food packaging.