Near-surface-weighted non-equilibrium viscoelastic transitions during mist-CVD growth of amorphous TiO x revealed by dual-frequency quartz crystal microbalance

We demonstrate that the viscoelastic evolution during mist chemical vapor deposition (mist-CVD) of amorphous TiOx (a-TiOx) is governed by near-surface-weighted non-equilibrium transitions rather than spatially uniform processes. Using dual-frequency quartz crystal microbalance (QCM) measurements at 9 and 27 MHz, we show that higher-frequency data resolve discrete viscoelastic regimes that remain hidden in conventional depth-averaged measurements. To enhance analytical reliability, the characteristic relaxation time τ was extracted via a unified exponential fitting protocol with residual-based uncertainty estimation. Arrhenius analysis with error bars reveals a clear deviation from linearity, indicating that the relaxation cannot be described by a single activation energy. This non-Arrhenius behavior is further supported by the lognormal distribution of τ and its correlation with the viscoelastic slope parameter S, demonstrating the coexistence of multiple relaxation pathways. These findings establish multi-frequency QCM as a statistically robust, depth-selective probe for investigating near-surface-weighted non-equilibrium dynamics during solution-derived oxide growth.