Dependence of plasmon polaritons on the thickness of indium tin oxide thin films

Abstract

The evolution of polariton features with increasing thickness in p-polarized (TM) reflectance spectra of indium tin oxide (ITO) thin films deposited on BK7 glass reveals the nature of plasmons in conducting thin films without interference from band-to-band transitions or the tendency of very thin films to form islands, both of which are complicating factors with the noble metals Au and Ag. Although the dependence on energy, film thickness, and angle of incidence is complex, these features are accurately described by the three-phase (substrate/overlayer/ambient) Fresnel model using only the Drude free-electron representation for the dielectric function of the ITO film. For film thicknesses less than 80nm the relevant excitation is a one-dimensional screened-bulk plasmon (SBP) that corresponds to charge transfer across the entire film. The associated SBP polariton (SBPP) occurs at the energy of the SBP and is relatively independent of the angle of incidence. For film thicknesses greater than 120nm, the relevant excitation is the surface plasmons (SP). The associated surface plasmon polariton (SPP) exhibits the usual strong dependence of energy on the angle of incidence. For larger thicknesses this structure gradually weakens, in agreement with theory. No other collective excitations are observed. The optimum thicknesses for the SPP in ITO is 160nm, whereas the SBPP is observed only when the film thickness is less than 70nm. The SBPP exhibits many of the features that make the SPP attractive for both science and technology, but has not been observed previously. Our results show that ITO films, in particular, and conducting-metal-oxide films in general provide new opportunities for investigating plasmons in conductors and obtaining new insights into plasmons, plasmon polaritons, and related optical phenomena.

Searching for better plasmonic materials

“…However, indium-tin-oxide (ITO) has been shown to be a potential plasmonic material in the NIR region [118][119][120][121][122][123]. ITO is a transparent, conducting oxide typically consisting of 90 %wt indium oxide (In 2 O 3 ) and 10 %wt tin oxide (SnO 2 ).…”

Indium tin oxide nanowires as hyperbolic metamaterials for near-field radiative heat transfer

“…The values of e 1 and C are 3.8 and 1.68 Â 10 14 rad/s, 25 respectively. The metallic nature of ITO results in a very small penetration depth for thermal radiation and therefore ITONWAs can be considered as semi-infinite in this study.…”

“…25 Note that, since the effect of spatial dispersion is considered, the extraordinary dielectric function is not only a function of angular frequency x like ordinary dielectric function. It is a function of wave vector component b as well.…”

“…Previous studies have looked into ITO thin films as plasmonic materials as well as transparent electrodes in solar cells and flat panel displays. [24][25][26][27] Basu and Wang demonstrated that the near-field heat flux between doped silicon nanowire arrays can exceed that between two bulk doped Si media. 11 Liu and Zhang have calculated the near-field heat flux between CNTs as HMMs with demonstrated higher heat transfer than that between graphite and silicon carbide.…”

Tailor-made surface plasmon polaritons above the bulk plasma frequency: a design strategy for indium tin oxide

“…For ITO we take the permittivity to be essentially of the form given by Rhodes et al [2] : Yao [11]) but in the infra-red regime considered in the present work we take that of SiO 2 to be 1.47 and use a value of 2.37 for TiO 2 .…”