Superhydrophobic Polysilicon Surface Induced by Stearic Acid-treated La(OH)3 Coating

The growth and surface functionalization of silicon (Si) thin films have attracted significant attention for applications in microelectronics, photovoltaics, sensors, and actuators. Among various surface functionalities, hydrophobicity is critical in environments where contact with water-based liquids must be minimized. In this study, a 50 μm-thick polycrystalline Si film was deposited on a SiO₂/Si substrate using plasma-enhanced chemical vapor deposition (PECVD). X-ray diffraction revealed a strong (220) preferential orientation with a naturally textured surface morphology. Surface modification with stearic-acid-treated lanthanum hydroxide [SA-La(OH)₃] converted the initially hydrophilic Si surface to a hydrophobic state. When the treatment duration exceeded 12 h, the surface exhibited superhydrophobic behavior, with a water contact angle exceeding 150°. Furthermore, when applied to PET substrates commonly used in flexible electronics and photovoltaic backsheets, the SA-La(OH)₃ coating significantly reduced water vapor permeation by effectively repelling moisture. These results highlight the potential of SA-La(OH)₃ as a robust moisture barrier and a functional coating for hydrophobic surface engineering on Si-based devices.