Berlin 2012 – scientific programme

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O: Fachverband Oberflächenphysik

O 30: Focussed session: Functional molecules at surfaces I

O 30.1: Talk

Tuesday, March 27, 2012, 10:30–10:45, A 053

Activation of surface hydroxyl groups by modification of H-terminated Si(111) — •Peter Thissen¹, Tatiana Peixoto¹, Roberto Carlos Longo¹, Wolf Gero Schmidt², Kyeongjae Cho¹, and Yves Jean Chabal¹ — ¹Department of Materials Science and Engineering, University of Texas at Dallas, Richardson, USA — ²Lehrstuhl für Theoretische Physik, Universität Paderborn, Paderborn, Germany

Most approaches to self assembled monolayer grafting on silicon surfaces rely on chemical reactions with hydroxyl groups. To date, such groups have only been prepared on silicon oxide surfaces, leading to poor reactivity with only low number of important organic molecules. For instance, phosphonic acids are attractive because they can in principle attach to surfaces in different (mono-, bi- or tri-dentate) configurations that control their arrangement. However, all attempts to directly graft phosphonic acids on silicon has in the past decades not been possible, requiring a perturbating annealing step at 140° C. Here, we demonstrate, using a model surface prepared by functionalizing atomically flat, hydrogen terminated Si(111) with exactly 1/3 hydroxyl monolayer, that hydroxyl on oxide free silicon is more reactive than on oxides. With this model surface, we demonstrate that a perfectly ordered layer of phosphonic acid molecules can be directly grafted at room temperature, and explain why it can remain completely stable in aqueous environments in contrast to phosphonates grafted on oxides. This work opens new possibilities for surface functionalization needed for sensors, photovoltaic devices and fundamental studies.