Creation of high-refractive-index amorphous titanium oxide thin films from low-fractal-dimension polymeric precursors synthesized by a sol-gel technique with a hydrazine monohydrochloride catalyst.

Amorphous titanium dioxide (TiO2) thin films exhibiting high refractive indices (n ≈ 2.1) and high transparency were fabricated by spin-coating titanium oxide liquid precursors having a weakly branched polymeric structure. The precursor solution was prepared from titanium tetra-n-butoxide (TTBO) via the catalytic sol–gel process with hydrazine monohydrochloride used as a salt catalyst, which serves as a conjugate acid–base pair catalyst. Our unique catalytic sol–gel technique accelerated the overall polycondensation reaction of partially hydrolyzed alkoxides, which facilitated the formation of liner polymer-like titanium oxide aggregates having a low fractal dimension of ca. 5/3, known as a characteristic of the so-called “expanded polymer chain”. Such linear polymeric features are essential to the production of highly dense amorphous TiO2 thin films; mutual interpenetration of the linear polymeric aggregates avoided the creation of void space that is often generated by the densification of high-fractal-d...