# Multipolar Plasmonic Resonances of Aluminum Nanoantenna Tuned by Graphene
## 4 Conclusions  
In summary, we theoretically demonstrate the tunability of multipolar plasmonic resonances of Al nanoribbon structure in ultraviolet and visible regime controlled by utilizing monolayer graphene. Compared with the AlNIR structure, the absorbance at the plasmonic odd modes (\(l=1\) and \(l=3\)) of G-AlNR structure is enhanced while the absorption at the plasmonic even resonant mode (\(l=2\)) of G-AlNR structure is decreased due to the interactions of the monolayer graphene with the electric fields of the multipolar plasmonic resonances of the Al nanoribbon. The electric fields of the multipolar plasmonic resonances of the Al nanoribbon shows the same variation tendency. In particular, the plasmonic high-order mode (\(l=3\)) of G-AlNR with the full-width at half maximum of 8.5 nm and a high \(Q\)-factor of 27 is significantly enhanced. The sensitivity and figure of merit of the plasmonic high-order mode (\(l=3\)) of the proposed G-AlNR structure can reach 25 nm/RIU and 3, respectively, providing practical applications such as the ultraviolet refractive-index sensing.  
**Supplementary Materials:** The following are available online at [[https://www.mdpi.com/2079-499](https://www.mdpi.com/2079-499)]([https://www.mdpi.com/2079-499](https://www.mdpi.com/2079-499)) 1/11/1/185/s1, Figure S1: The Absorption spectrum of graphene embedded in the Al\({}_{2}\)O\({}_{3}\) substrate.  
**Author Contributions:** Z.Y., Writing--original draft and Writing--review and editing; Q.Z., Writing--original draft; X.L., Project administration; W.D., Project administration; X.P., Supervision; T.H., Supervision and Project administration; L.Y., Writing--review and editing; Z.H., Supervision; P.C., Supervision; and C.T., Supervision, Project administration, and Writing--review and editing. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This work was financially supported by the National Natural Science Foundation of China (NSFC) (11704184, 11704183, and 51701176), the Start-up Fund, Nanjing Forestry University and the Natural Science Foundation of Zhejiang Province (LY14A040004 and LQ1 YC100002).  
**Data Availability Statement:** Data available in a publicly accessible repository.  
**Conflicts of Interest:** The authors declare that we have no financial and personal relationships with other people or organizations that can inappropriately influence our work; there is no professional or other personal interest of any nature or kind in any product, service and/or company that could be construed as influencing the position presented in, or the review of, the manuscript entitled, \"Multipolar plasmonic resonances of aluminum nanoantenna tuned by graphene\".  
Figure 5: **(a)** Absorption spectra of the G–AlNR structure under TM polarization with inclined incidence angle (\(\theta\)) of 30\({}^{\circ}\), for different surrounding media with a refractive index changed from 1.00 to 1.15 with a step of 0.05. **(b)** Spectral shifts of the resonant positions of the plasmonic quadrupole mode (\(l=2\)) and the third-order plasmonic mode (\(l=3\)) with the surrounding refractive index changing from 1.000 to 1.040 with a step of 0.05. The geometrical parameters are the same as shown in Figure 1b.