Epitaxial aluminum plasmonics covering full visible spectrum

Abstract

Aluminum has attracted a great deal of attention as an alternative plasmonic material to silver and gold because of its natural abundance on Earth, material stability, unique spectral capability in the ultraviolet spectral region, and complementary metal-oxide-semiconductor compatibility. Surprisingly, in some recent studies, aluminum has been reported to outperform silver in the visible range due to its superior surface and interface properties. Here, we demonstrate excellent structural and optical properties measured for aluminum epitaxial films grown on sapphire substrates by molecular-beam epitaxy under ultrahigh vacuum growth conditions. Using the epitaxial growth technique, distinct advantages can be achieved for plasmonic applications, including high-fidelity nanofabrication and wafer-scale system integration. Moreover, the aluminum film thickness is controllable down to a few atomic monolayers, allowing for plasmonic ultrathin layer devices. Two kinds of aluminum plasmonic applications are reported here, including precisely engineered plasmonic substrates for surface-enhanced Raman spectroscopy and high-quality-factor plasmonic surface lattices based on standing localized surface plasmons and propagating surface plasmon polaritons, respectively, in the entire visible spectrum (400–700 nm).

Tuning of Two-Dimensional Plasmon–Exciton Coupling in Full Parameter Space: A Polaritonic Non-Hermitian System

“…In the reflectance measurement, incident light at certain angle and frequency can be coupled into SPPs with the dispersion relation defined by the grating equation for a specific grating pitch and these SPPs can be out-coupled into the free space. The detailed analysis can be found in our recently published papers using all-metal plasmonic metasurface structures. − It is worth noting that strong coupling observed in ref is due to the interaction between localized LSPR and propagating SPP plasmon modes on metal surface lattices. At zero detuning, the reflectance dips of upper and lower plasmon–exciton polariton modes are symmetric in intensity and they are very sensitive to the detuning condition (see Supporting Information section S5).…”

Flexible Plasmonics Using Aluminum and Copper Epitaxial Films on Mica

“…Here, we highlight the results based on single-crystalline Al and Cu films grown on Mica substrates due to their importance for sustainable (natural abundance), scalable, and CMOScompatible plasmonic applications. Al has recently been demonstrated as a broad-band, low-cost alternative to noble metals owing to its chemical stability, high Q-factor resonances from Al nanostructrures, 16,17,41,49 and excellent optical properties (lowest optical loss) in the UV region. 16,17,25,39 As a result, Al has become the best choice for UV applications, and it is also suitable for the visible range with excellent performance.…”

“…16,17,25,39 As a result, Al has become the best choice for UV applications, and it is also suitable for the visible range with excellent performance. 16,41 In addition, Al remains very stable in the ambient environment due to the formation of surface native oxide (Al 2 O 3 ) with a thickness of 3−5 nm, 39 and it has been widely used as a plasmonic material for UV plasmonic lasers, 50,51 deep UV resonance, 17,52 UV photodetector, 25 surface-enhanced Raman spectroscopy, 16,17,53 and various visible-light applications, including CMOS-compatible color filters, 27−30 photocatalyst, 54 and nonlinear plasmonics. 55 Cu, however, is also a CMOS-compatible plasmonic material, widely used in microelectronic devices owing to its high electrical conductivity and natural abundance, and it can offer good plasmonic performance.…”

“…The most interesting observations in the SE measurements reside in the UV region (200−325 nm) for Al and in the visible and NIR regions (600−1500 nm) for Cu, where their optical losses (ε 2 ) outperform those of Ag and Au, respectively, making them good candidates to replace Au and Ag for plasmonic applications in these spectral regions. To illustrate the superior optical properties of Al/Mica and Cu/Mica films, we plot the quality factors for Q LSP and Q SPP , 41 as shown in Figure 2c,d. It is worth noting the Q factors of Cu/Mica film are better than that of Au/Mica film prepared by using the same deposition system.…”

“…To determine the SPP propagation length (L SPP ), we adopted a simple model that can provide the real and imaginary parts of the SPP wavenumber, that is, Re(k SPP ) and Im(k SPP ). 41 Then, the effective index can be extracted by using L SPP = 0.5 × Im(k SPP ). The SPP propagation lengths launching on the Al film can reach from 5 to 13 μm in the visible range (400−700 nm).…”