Phosphonic Acid Surface Modification of Silicon

Surface modification using self-assembled monolayers (SAMs) offers a unique way to change the surface chemistry of a substrate.  SAMs have great potential with regard to organic electronics.  The surface of a silicon wafer is easily oxidized in air and becomes hydrophilic silica (silicon dioxide).  Since organic semiconductors are hydrophobic, delamination readily occurs at the interface from surface energy mismatching.  Polarity matching between the substrate and the organic semiconductor may aid in device stability as well as may potentially increase charge transfer. Several methods have been tested and detailed for chemically bonding phosphonic acids with nonpolar tails to the surface of native-oxide silicon.  A fluorinated phosphonic acid (FHOPA) was deposited from solution by the “T-BAG” method (tethering by aggregation and growth), by spin coating, and by an “in-house” method.  A combination of experimental design and reproduction of literature procedures was used discern the best method.  Samples were measured with X-ray Photoelectron Spectroscopy (XPS) and data was analyzed for both FHOPA coverage and uniformity. The end goal of this project is to determine the quickest, easiest, most effective way to modify the surface of silicon.  Now that a comparison has been done between available methods, the research can be expanded to optimize the protocol.  If an efficient method can be derived, future work may include polymerizing the semiconductor directly on the surface, which could further enhance transistor performance.