FORMATION OF ALKYLSILANE SELF-ASSEMBLED MONOLAYERS ON TITANIUM DIOXIDE AND INDIUM-TIN OXIDE SURFACES

Abstract

Indium-tin oxide (ITO) is transparent and conducting surface that is attractive to attach alkylsilanes for a variety of technical applications. However, it is difficult to get a high quality of self-assembled monolayer (SAM) on ITO due to a high roughness of substrate and low hydroxyl coverage. To overcome low surface reactivity, titanium dioxide (TiO2) is deposited on ITO surface by using atomic layer deposition (ALD) technique. We examined the effects of temperature, concentration, and the number of methyl group attached to silane atom in the formation of SAMs on TiO2-covered ITO and bare ITO surfaces. Alkylsilane SAMs were characterized by contact angle measurement, scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS). Contact angle measurements revealed that the adsorption of alkylsilane on both surfaces leads to hydrophobic surface, indicating the formation of SAMs. STM image in Figure 1 clearly shows the structural changes before and after the adsorption of octadecyltrichlorosilane (OTS), reflecting the formation of alkylsilane layers. In addition, XPS measurements revealed Si-O chemical bond formation during self-assembly. It was found that alkylsilanes can form a higher quality of SAMs on TiO2-covered ITO surface compared with bare ITO surface.