Oxide Nanoskin Formed on Poly(methyl methacrylate)

Abstract

A silicon oxide (SiOx) layer of molecular-scale thickness, which we have named an “oxide nanoskin”, has been successfully formed on a poly(methyl methacrylate) (PMMA) substrate through the vapor-phase chemisorption of organosilane and subsequent photooxidation using 172-nm vacuum ultraviolet (VUV) light. First, a hydrophilized PMMA sample was exposed to the vapor of a precursor, that is, tetraethoxysilane (TEOS). As was confirmed by water contact-angle measurements and X-ray photoelectron spectroscopy (XPS), chemisorption of the TEOS molecules was accomplished after 3 h of vapor treatment. Next, VUV irradiation was conducted for more than 10 min, and the chemisorbed TEOS molecules were photochemically converted to SiOx, as was evidenced by XPS. The resulting oxide layer was confirmed by transmission electron microscopy to be continuous with a thickness of 3 nm or less. As a control experiment, a SiOx layer was deposited by the same procedure on a Si substrate covered with a native oxide. As was determined...