Invited Paper SS+EM-WeA9
2012 AVS Medard Welch Award Lecture: Chemical Functionalization of H-terminated Silicon Surfaces

Wednesday, October 31, 2012, 4:40 pm, Room 22

Silicon is best known for its oxide because of its propensity to oxidize and the remarkable properties of the Si/SiO₂ interface. Yet, oxidation is ill-defined and hard to control. Moreover, modification of chemically stable oxide surfaces mostly involves silanization, typically characterized by disorder and poor chemical stability in solution. The ability to functionalize oxide-free Si surfaces opens new opportunities for a broader range of applications. Precise modification of clean Si surfaces in an ultra-high vacuum environment leads to interesting chemistry but is not widely applicable. In contrast, wet chemical preparation of well-defined H-terminated Si surfaces provides a platform for both fundamental science and further applications. Much work has been done to functionalize H/Si using well known chemical procedures, such as UV- or catalyst-induced hydrosilylation with alkene molecules or halogens followed by Grignard chemistry. Relatively little attention has been placed on the role of structure in H-terminated surfaces for selective modification. Yet, just as structure is important in etching, it also plays a role during chemical modification of surfaces, as illustrated by the reaction of ammonia on stepped Si(111) surfaces.¹ Understanding the role of structure during HF etching is also critical to devise new methods for expanding the functionality of H-terminated surfaces. This talk illustrates this concept and shows that thermal chemistry is well suited to explore such effects. It discusses, for instance, the use of methoxylation of H-terminated Si(111) surfaces to provide a well-defined template for interesting surface chemistry and a broader range of functionalization,² such as the grafting of phosphonates, amines, and metal complexes.

¹ Dai, M., Y. Wang, J. Kwon, M.D. Halls, and Y.J. Chabal, Nitrogen interaction with hydrogen-terminated silicon surfaces at the atomic scale. Nature Materials 8, 825 (2009).