Manufacturing-Enabled Tunability of Linear and Nonlinear Epsilon-Near-Zero Properties in Indium Tin Oxide Nanofilms

Epsilon-near-zero (ENZ) materialshave attracted great interestdue to their exotic linear and nonlinear responses, which makes itsignificant to tune ENZ wavelengths for wavelength-dependent applications.However, studies to achieve tunability in a wide spectral range andlink the fabrication parameters with linear and nonlinear ENZ propertieshave been uncovered. ENZ indium tin oxide (ITO) nanofilms are fabricatedby magnetron sputtering, through which the control of ENZ propertiesis demonstrated. Factors in the sputtering process, such as the gasratio and annealing, have a great impact on the ITO samples. TunableENZ parameters are listed to provide a beneficial database for ENZITO, mainly attributed to the change of carrier concentration. Theinfluence of ENZ parameters on optical characteristics via annealingtreatment is further explored. The ENZ wavelength is blue-shiftedby 609 nm, and the intrinsic loss is reduced by 63.2%, while the ITOsamples exhibit better linear scattering properties and stronger fieldintensity enhancement. Additionally, the laser testing system illustratesthe change from reverse saturable absorption to saturable absorptionwith an absolute modulation depth of 21.9%, improved by 222.1%, andthe nonlinear refractive index n (2) andnonlinear absorption coefficient & beta; are 2.07 x 10(-16) m(2) W-1 and -3.16 x 10(-10) m W-1 for post-annealed ITO samples,respectively. The proposed sputtering protocol offers a feasible techniqueto control the linear and nonlinear ENZ performance, which has greatpotential in laser technology and nanophotonics.