Spectroscopic Infrared Photothermal Converters Using Uniaxially Oriented NiAl Superalloy Films with Metal‐Insulator‐Metal Strip Arrays

Abstract This study reports the fabrication of “ smooth and continuous ” nickel–aluminum (NiAl) superalloy films deposited via direct‐current sputtering using a two‐step deposition method. The process involves an initial film deposition with in situ heating, followed by a subsequent room‐temperature deposition and post‐annealing at 928 K. This two‐step deposition yields NiAl films with exceptionally smooth surface morphology, achieving a root mean squared roughness as low as ∼1.4 nm. To demonstrate the benefits of this approach, we fabricate a mid‐infrared device incorporating NiAl–Al 2 O 3– NiAl trilayers with an NiAl strip array on top. The NiAl films, self‐organized in the (110) orientation, are patterned using laser direct writing followed by reactive ion etching. As designed by our electromagnetic design, the fabricated infrared absorbers exhibit strong resonant absorption and tunability, which can be controlled by adjusting the periodicity, width, and thickness of the top NiAl strips. To assess the impact of our proposed deposition methods, we compare single‐step NiAl films deposited with in situ heating to the new two‐step NiAl films, both of which are used as the bottom and top layers in the trilayer devices. The latter method exhibits lower background noise in both absorption and thermal emission spectra, achieving excellent spectral selectivity.