Structural Effect on Formation of Alkylsilane Self-Assembled Monolayers on Indium Tin Oxide Surface

The effects of immersion time and the number of chlorine attached to silane atom on the formation of self-assembled monolayers (SAMs) on indium tin oxide (ITO) surface were examined by scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), and contact angle measurements. Among octadecyltrichlorosilane (OTS), octadecyldichloromethylsilane (ODDMS), and octadecyldimethylchlorosilane (ODMS), OTS SAMs on ITO surface formed after 1h deposition at room temperature have a high contact angle value of 86 compared to ODDMS and ODMS SAMs with 45 degrees and 31 degrees, reflecting that OTS on ITO surface would form a high-quality SAMs with a hydrophobic surface. STM imaging revealed that the surface structure of OTS SAMs on ITO surface was markedly different from that of bare ITO surface resulting from the the adsorption of OTS molecules. In addition, XPS measurements showed that the formation of OTS SAMs is strongly driven by the chemical reactions between the Si atoms and the hydroxyl group of ITO surface during self-assembly.