Abstract
Alternative designs of plasmonic metamaterials for applications in solar energy-harvesting devices are necessary due to pure noble metal-based nanostructures’ incompatibility with CMOS technology, limited thermal and chemical stability, and high losses in the visible spectrum. In the present study, we demonstrate the design of a material based on a multilayer architecture with systematically varying dielectric interlayer thicknesses that result in a continuous shift of surface plasmon energy. Plasmon resonance characteristics of metal/semiconductor TiN/(Al,Sc)N multilayer thin films with constant TiN and increasing (Al,Sc)N interlayer thicknesses were analyzed using aberration-corrected and monochromated scanning transmission electron microscopy-based electron energy loss spectroscopy (EELS). EEL spectrum images and line scans were systematically taken across layer interfaces and compared to spectra from the centers of the respective adjacent TiN layer. While a constant value for the TiN bulk plasmon resonance of about 2.50 eV was found, the surface plasmon resonance energy was detected to continuously decrease with increasing (Al,Sc)N interlayer thickness until 2.16 eV is reached. This effect can be understood to be the result of resonant coupling between the TiN bulk and surface plasmons across the dielectric interlayers at very low (Al,Sc)N thicknesses. That energy interval between bulk and decreasing surface plasmon resonances corresponds to wavelengths in the visible spectrum. This shows the potential of tailoring the material’s plasmonic response by controlling the (Al,Sc)N interlayer thickness, making TiN-based multilayers good prospects for plasmonic metamaterials in energy devices.
Highlights
Plasmonic resonances are collective, coherent excitations of a metal’s conduction electrons stimulated by incident electromagnetic waves [1]
We demonstrate the design of a material based on a multilayer architecture with systematically varying dielectric interlayer thicknesses that result in a continuous shift of surface plasmon energy
While a constant value for the TiN bulk plasmon resonance of about 2.50 eV was found, the surface plasmon resonance energy was detected to continuously decrease with increasing (Al,Sc)N interlayer thickness until 2.16 eV is reached. This effect can be understood to be the result of resonant coupling between the TiN bulk and surface plasmons across the dielectric interlayers at very low (Al,Sc)N thicknesses
Summary
Coherent excitations of a metal’s conduction electrons stimulated by incident electromagnetic waves [1]. Surface plasmons of metallic nanostructures localize light below the diffraction limit and can generate intense electric near fields with well-defined resonances within the optical window [2, 3]. Applications exploiting this unique effect include single-molecule spectroscopy, molecular sensors, photothermal cancer therapy, photocatalytics, and photovoltaics, the latter due to the enhancement of efficiency in hot-electron-based solar energy-harvesting devices [4,5,6,7,8,9]. Noble metals limit the efficiency in applications due to characteristic losses from interband transitions in the optical range [10, 11]. Designs for plasmon induced hot-electron photovoltaics have been most recently demonstrated [18,19,20], including theoretical reports that shown that metal/semiconductor layered structured could demonstrate higher performances in such photovoltaic devices in comparison with a bilayer metal/semiconductor structure [21]
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