Preparation of clean acid-terminated monolayers on silicon (111) surfaces

Acid-terminated (111) silicon surfaces have been prepared by molecular grafting of ω-functionalized alkenes on atomically flat hydrogenated surface and using two procedures: thermal hydrosilylation in ethyl ωalkenoates, followed by hydrolysis, and direct photochemical hydrosilylation in ω-alkenoic acids. In each case the chemical state of the surface was followed by FTIR spectroscopy in an extended spectral range and the surface cleanliness was assessed with Atomic Force Microscopy. It was found that organic contaminants may strongly physisorb on acid terminated surface, and are removed only by treatments with appropriate solvents. Clean ester-terminated surfaces can be fully converted into acid-terminated surfaces by hydrolysis in mild conditions. One-step photochemical modification in ω-alkenoic acids leads to surfaces free of Si-O bonds, which demonstrates the absence of Si oxidation and proves that the grafting occurs via a hydrosilylation process. The reaction kinetics appear faster for the acid than for the corresponding alkenes.