Low-Temperature Sputtering and Polarity Determination of Vertically Aligned ZnO Nanocolumns

We report a scalable and low-thermal-budget growth of vertically aligned ZnO nanocolumns on Si(100) substrates by radio-frequency magnetron sputtering at temperatures of 80–100 °C. In this low-mobility growth regime, sputtering pressure controlled via the argon flow rate is the dominant parameter governing the morphological transition from dense columnar films to well-separated nanocolumns rather than the substrate temperature. High sputtering pressure enhances the self-shadowing effect, promoting the formation of well-separated nanocolumns under a limited adatom mobility regime. Conversely, low sputtering pressure facilitates void filling, yielding dense films with reduced surface roughness. Controlled preannealing of the Si substrate prior to deposition enables switching between O-polar and Zn-polar nanocolumns, plausibly attributed to modifications of the native SiO x surface chemistry. O-polar films and nanocolumns exhibit higher effective piezoelectric coefficients up to 20 pC/N. Their stable piezoelectric responses over 0.1–150 Hz correlate with higher differential resistance and reduced dielectric loss, suggesting the suppression of the carrier-induced screening effect. This work establishes a practical growth window compatible with thermally sensitive substrates, including those used in flexible and wearable electronics.