Building Organic Monolayers Based on Fluorinated Amines on the Si(111) Surface

Functionalized silicon surfaces can serve as starting points for a wide variety of structures. Controlled introduction of fluorine-containing monolayers on silicon may affect a number of chemical and physical properties of silicon substrates. This approach becomes especially interesting when these monolayers are built based on the interaction of amino-functionalized fluoroorganics with chlorinated silicon single crystals. In this work, a carefully prepared H-terminated Si(111) surface is converted into ClSi(111) by mild chlorination with PCl5 and then reacted with trifluoroethylamine (TFEA) and p-fluoroaniline (pFA) using a wet-chemistry procedure in an oxygen-free environment. The surface species formed and the efficiency of the reactions are monitored by infrared spectroscopy and X-ray photoelectron spectroscopy, and complemented with density functional theory (DFT) studies. Although the reaction of TFEA can be optimized to form a nearly complete monolayer, the similar procedure with pFA results primarily in surface oxidation, despite similar reaction energy landscapes predicted by DFT. This difference is discussed based on the differences of adsorption geometries of the two amines on Cl-terminated Si(111) surfaces.