1. Introduction
Polycrystalline titanium dioxide (TiO2) thinfilms are very important
in various applications, such as dye-sensitized solar cells [1–3],
photocatalysts [4–6], and transparent conducting films [7–9]. Physical
vapor deposition is widely used to grow polycrystalline TiO2 thin
films, where TiO2 crystallizes directly on a heated substrate during deposition or crystallizes from the amorphous precursor film by postdeposition annealing. However, the temperature required to crystallize
TiO2 is generally higher than temperatures tolerated by plastic substrates, preventing the fabrication of wide-area TiO2
films on flexible
plastic substrates using roll-to-roll techniques [10].
Recently, we reported the metal-induced crystallization (MIC) of an
amorphous TiO2 thin film. The crystallization temperature of TiO2
was
reduced by at least 30 °C when the amorphous TiO2 contacted a Ni or
Cu metal bottom layer [11]. In that work, we investigated Ni-induced
crystallization (Ni-MIC) in detail and proposed a reaction-assisted
crystallization model to interpret MIC of TiO2, wherein the formation
and decomposition of metastable metal-TiO2 compounds played
an important role [11]. However, to lower the cost of this process for
practical applications, cheaper metals must be used. Thus, in this
work we studied Cu-induced crystallization (Cu-MIC) of amorphous
TiO2 thin films.