Plasmons, light-induced collective excitations of electrons, are the pivotal strategy to integrate electronics and optics at the nanoscale enabling single-molecule detection, improved photovoltaics, nanoscale photometry, cancer therapy, or nonlinear optics. Plasmon properties offer sub-wavelength optical confinement for enhanced imaging resolution and huge optical enhancements by strong light-matter interaction at nanostructures for colour generation. More interestingly, two dimensional (2D) graphene-plasmons are electrically tunable by electrostatic doping, enabling order-unity changes in absorption and tunable excitation plasmon energies. Additionally, the graphene’s high mobility extends its application to ultrafast light modulation up to 100s GHz commutation rates. However, graphene plasmons have been observed at mid-infrared wavelengths, which are far from the near-infrared (NIR) telecom range. To further tune graphene-plasmons to higher frequencies is necessary to open a bandgap by confining the lateral size (D), since the frequency scales as square root of (E_Fermi/D). Therefore, reaching the telecommunication frequency regime (E_fermi approximately 1 eV) requires a lateral size D reduction below 5 nm, which is beyond the state-of-art of top-down lithography.
Interestingly, covalent self-assembly of graphene-like building blocks such as polycyclic aromatic hydrocarbons render atomically precise 1-3 nm-wide graphene nanoribbons (GNR) by controlling sequential reactions on catalytic substrates. The GNR quantum confinement shifts graphene plasmons to the visible and near-infrared (vis-NIR). However, GNRs are rather short (~30 nm) and randomly distributed on the surface. To date, little effort has been directed to control their size and the overall morphology of the ensemble, setting a barrier for the implementation of GNRs on actual devices. As a solution, we propose two-dimensional (2D) nanoporous graphene (NPG) consisting in covalently bonded parallel arrays of ultra-long GNRs (>200 nm) featuring nanopores of 0.4-0.9 nm. Indeed, the theoretical optical response of NPG reveals a remarkable change in absorption at vis-NIR peaks by increasing the doping level to 1 eV, just at the telecom range. Therefore, the overall objective is to explore the feasibility of fabricating gate-modulated optoelectronic devices based on atomically precise graphene nanostructures, as a new venue to expand graphene into the vis-NIR region.
