Tuning the epsilon near zero wavelength of ITO in the near-IR spectral region via post-process free sputtering

Abstract Indium tin oxide (ITO) has become an important material in photonics due to its transparency, high electrical conductivity, and, more recently, its epsilon-near-zero (ENZ) properties for nonlinear optics. In this work, we present a single-step RF magnetron sputtering protocol optimised for hybrid-ENZ metasurfaces, enabling precise tuning of the ENZ wavelength ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mi>λ</mml:mi> <mml:mrow> <mml:mi>ENZ</mml:mi> </mml:mrow> </mml:msub> </mml:mrow> </mml:math> ) across 1130–1700+ nm without post-deposition annealing. Through deposition runs across two RF sputtering systems, we systematically explore the effects of film thickness, substrate temperature, and background gas composition on the optical properties of ITO, offering an ITO recipe development protocol for fabricating ENZ-tuned films suitable for advanced nonlinear optical and metasurface devices.