Researches Of ITO-based Composite Films And Structures As Near-infrared Plasmonic Materials

As suggested in the past few years by researchers that noble metals,which have long been studied and are currently dominating the realm of plasmonics and metamaterials,suffer from large dissipative losses,chemical/mechanical instability and non-tunable optical properties.So,some of the new plasmonic materials,especially those operate at near-infrared(NIR)wavelengths region such as transparent conductive oxides(TCOs)and metal-nitrides,are proposed as metal-alternatives,holding the promise of applying in low-loss plasmonic,metamaterials and transformation optic(TO)structures.According to the numerical and analytical assessments in various work,metals,particularly silver holds the advantage over substitutional materials when it comes to comprehensive considerations of propagation length and the degree of confinement for plasmonics.Consequently,in order to find niche applications for TCOs,it is of interest to combine silver and TCOs in one single layer,thus improving the plasmonic properties of pure TCOs.The first topic presented in this thesis is about the introduction of silver as "dopings" in ITO films.Series of co-sputtered silver-indium tin oxide(ITO-Ag)films are systematically studied as optimized ITO-based composite films.By tuning the atomic ratio of silver,composite films are manifested to have different microstructures with limited silver amount(<3 at.%).The introduction of silver improves the preferred orientations of In2O3 component significantly.Remarkably,dielectric permittivity of ITO-Ag films exhibits high adjustability,which indicates more than 300 nm alteration in cross-over wavelength ?c through post rapid annealing,thus enabling tunable epsilon-near-zero and plasmonic properties in the NIR region.Angle-variable Krestchmann prism coupling is carried out to reveal the surface plasmon polariton(SPP)features of the films at telecommunication wavelength 1550 nm.Broad dips in reflectance curves around 52°-56° corresponds to the SPP existence on ITO-Ag films.Moreover,in order to further overcome the weakness of metals as shown above,metal-free plasmonic structures which have comparable performanc in plasmonics as metals are of importance.So the second topic discussed is about the introduction of titanium nitride(TiN)as the insertion of ITO films.Due to the gold-like properties of TiN and its unique plasmonic performance,ITO-based sandwich structures with ultrathin(<10 nm)TiN insertion are investigated as NIR plasmonic materials.The structural,electrical and optical properties reveal the improvement of the sandwich structures stemmed from TiN insertion.SPP of ITO-TiN-ITO sandwich at telecommunication wavelength is also activated by prism coupling.Compared with pure ITO films or sandwiches with metal insertion,the reflectivity dip for ITO-TiN-ITO is slightly deeper and wider,indicating the relatively enhanced coupling efficiency in the field of near-infrared plasmonics for this structures.The calculated SPP spatial profile based on the effective permittivies,penetration depth and degree of confinement,as well as the quality factors demonstrate the applicability of such sandwiches for NIR plasmonic materials in various devices.