We investigate the far-field and near-field properties of aluminum nanorods fabricated by electron beam lithography and exhibiting plasmonic resonance in the near-infrared region. First, we show that plasmonic modes within nanorod arrays can be tuned by geometrical parameters, allowing one to control the system transparency. Next, the light absorption in this structure is closely examined, and we demonstrate that aluminum has great potential due to its unique interband transition at 800 nm. The roles of the dielectric confinement and the coupling between plasmonic resonance and the interband transition are particularly emphasized, as their adjustment can be used to switch from highly scattering particles to absorbing particles without a significant modification of the plasmonic resonance position. Finally, we image the plasmon-generated local field distribution in the aluminum nanostructures and observe, for the first time, the effect of the interband transition on the near-field behavior. The effect of the dielectric confinement is also numerically investigated, as it is shown to play a significant role in near-field enhancement.O ver the past decade, metallic nanostructures have been extensively studied due to their plasmonic properties. Although the visible region has received the most attention, plasmonic systems working in the near-infrared (near-IR) region, wavelengths from 700 nm to a few micrometers, have received increasing interest due to their potential applications in various fields. The near-IR region corresponds to the transparent window of the majority of living tissues. 1 These structures are, thus, particularly well-adapted for noninvasive and nondestructive medical diagnosis 2,3 and treatment. 4,5 In the field of solar energy, the near-IR region is also very attractive, as 45% of the total solar intensity is located between 750 nm and 1.75 μm. 6 Plasmonic nanoparticles have been successfully employed to improve the light-harvesting efficiency in this spectral area using silicon-based solar cells. 7−9 Near-IR photocurrent generation 10 and water oxidation 11 have also been recently reported using gold (Au) nanorods.Au and silver (Ag) are the two most commonly used materials in plasmonics, as they show strong optical resonance and are easy to handle. However, these materials are expensive and are limited resources. Aluminum (Al) has recently been presented as a potential low-cost alternative to noble metals, as it can support localized surface plasmon resonance (LSPR) from deep UV to IR wavelengths. 12−18 Beyond its costeffectiveness, Al exhibits unique optical characteristics. First, its almost Drude-like behavior enables LSPR stability for shorter wavelengths (down to ∼150 nm) than Au (∼500 nm) and Ag (∼345 nm). Additionally, the light absorption efficiency is expected to be high in the near-IR region, as interband transitions (ITs) occur in that region. 19 As evidence of the growing interest in this material, Al nanoparticles 20 and disks 21,22 have recently been shown to increase the photocurr...
