Organic Modification of Solid Surfaces


I- Modification of conducting surfaces


The interfacial properties of solid surfaces can be tailored through modification with organic molecules. This can be achieved through self-assembly on a wide range of substrates including Au, Ag and Pt. Various precursors have successfully been used to form SAMs on solid surfaces, the archetypal example is that based on the affinity between sulfur containing precursors and gold surfaces. Thiols, sulfides and disulfides are the most used precursors in the reported studies. Thiosulfates, protected thiols and organic thiocyanates, have also been used as alternatives to overcome some of the observed limitations of the traditional precursors. Despite the extensive use of these precursors to obtain high quality aliphatic SAMs, their ability to form well-ordered aromatic SAMs is very limited. Long-range ordered aromatic SAMs, which are attracting increasing attention due to their electronic and optical properties, are indeed more difficult to obtain. Aromatic SAMs offer a wide range of potential applications especially in the emerging areas of molecular electronics, lithography and synthesis of nanocrystalline materials. This is, intrinsically related to the development of SAMs with lower defects and increased order.


We are particularly interested in discovering novel precursors for the rapid and efficient formation of long-range well-ordered aromatic SAMs. We already reported the use of arenesufenyl chlorides as precursors for the formation of highly ordered aromatic SAMs. We are presently investigating various series of novel precursors.


The investigated precursors are first synthesized and then used to modify conducting solid surfaces. The modified surfaces are characterized using a series of techniques including stripping cyclic voltammetry, X-ray photoelectron spectroscopy (XPS), IR spectroscopy, scanning tunnelling microscopy (STM), atomic force microscopy (AFM), etc.


Images resulting from scanning surfaces by methods such as STM and AFM


II- Modification of Si surfaces


Another attractive alternative substrate for biological microchip fabrication, in the field of biotechnology, is crystalline Si due to its high purity, its well-defined structure, and the available expertise in the existing microelectronic technology. However, development in this field is sample-preparation limited. We are working on developing new innovative approaches to overcome these limitations and provide new methodologies for the efficient organic modification of Si surfaces.


Different strategies have been developed to covalently bind organic molecules to Si surfaces in an attempt to form hybrid Si materials, ideally stable towards organic solvents, moisture and air. Thus organic molecules including alkenes, alkynes, alcohols, amines and alkyl halides have been successfully immobilized onto crystalline Si surfaces through thermal, photochemical, electrochemical and catalytic initiations. Nucleophilic reactions of Grignard and organolithium reagents with both chlorine and hydrogen terminated Si surfaces have also been reported. Radicalar processes are used when starting from H-terminated Si surfaces. Diazonuim salts have been shown to be excellent precursors for surface modification based on radical reactions. Their importance sterms from their facile reduction at potentials where the generated radicals are not further reduced to anions and are thus able to initiate surface modification.


We are particularly interested in discovering novel precursors for the efficient modification of Si surfaces. The modification can be done through thermal or electrochemical initiation. The modified surfaces are characterized using various techniques including. The involved mechanisms as well as factors controlling all aspects of the modifications are also investigated.


University of Guelph
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Guelph, Ontario, N1G 2W1