Formation and stability of self-assembled monolayers on thin films of lead zirconate titanate (PZT)

Self-assembled monolayers (SAMs) of alkylsiloxanes were formed from hexyltrichlorosilane (HTS) and octadecyltrichlorosilane (OTS) on surfaces of thin films of a complex oxide, lead zirconate titanate (PZT). X-ray photoelectron spectroscopy (XPS) and contact angle measurements confirmed the formation of a thin, uniform organic layer on the surface of the PZT, consistent with the hypothesis that a densely packed organic monolayer is formed on the PZT. Angle-resolved high-resolution XPS suggested that the surface of the PZT thin film includes a top layer deficient in titanium and consisting mainly of oxides of lead and zirconium, along with hydroxylated zirconium that may react with alkyltrichlorosilanes to form the SAMs. The effect on these SAMs of exposure to acidic media was probed by wettability measurements, XPS, and scanning electron microscopy(SEM). Contact angle measurements with water and hexadecane indicated that the SAMs formed from the longer alkylsilane, OTS, were stable in HCl over long periods of time (at least 3 days), while the SAMs formed from the short-chain alkylsilane, HTS, degraded after 12 h. The XPS spectra of SAMs formed from OTS and exposed to HCl solution were similar to those obtained for similar SAMs not exposed to HCl. SEM also confirmed that the SAMs formed from OTS can act as protective barriers for PZT against etching by HCl.