VARIABLE REFRACTIVE INDEX THIN FILMS
A method of forming a variable refractive index thin film includes forming a coating including a tin (II) halide precursor and a liquid solvent, where the composition and/or concentration of the liquid solvent may vary spatially over one or more lateral dimension(s) of the coating. Annealing at elevated temperature may induce densification of the coating and the formation of a thin film having a variable refractive index. Local variability in the refractive index may be correlated to the location oxidation state of tin within the thin film, which may be related to the conformation of the liquid solvent.
1 . An inorganic thin film comprising:
a tin oxyhalide phase comprising tin having a first valence within a first region of the thin film and tin having a second valence within a second region of the thin film.
2 . The inorganic thin film of claim 1 , wherein the tin oxyhalide phase within the first region comprises a first average valence of tin and the tin oxyhalide phase within the second region comprises a second average valence of tin.
3 . The inorganic thin film of claim 1 , wherein the tin oxyhalide phase is substantially amorphous.
4 . The inorganic thin film of claim 1 , wherein the thin film comprises a first refractive index within the first region and a second refractive index within the second region.
5 . The inorganic thin film of claim 1 , wherein the thin film comprises a first refractive index greater than approximately 1.7 within the first region, a second refractive index greater than approximately 1.7 within the second region, and a difference between the first refractive index and the second refractive index is at least approximately 0.1.
6 . The inorganic thin film of claim 1 , wherein the thin film comprises local refractive index variations of at least approximately 0.05.
7 . The inorganic thin film of claim 1 , wherein the thin film comprises an overall refractive index variability extending over a range of approximately 1.6 to approximately 2.1.
8 . The inorganic thin film of claim 1 , wherein the thin film comprises a visible light transmissivity of at least approximately 90%.
9 . The inorganic thin film of claim 1 , wherein the thin film comprises an optical absorption of less than approximately 0.1% per 100 nm thickness.
10 . The inorganic thin film of claim 1 , wherein the thin film comprise less than approximately 5% bulk haze.