Controlled, Low-Coverage Metal Oxide Activation of Silicon for Organic Functionalization: Unraveling the Phosphonate Bond

Abstract

Deposition of thin films and grafting of organic molecules on semiconductor surfaces, particularly oxide surfaces, are widely studied as means of passivation and functionalization for a variety of applications. However, organic functionalization of silicon oxide is challenging, as the currently used molecules (silanes and phosphonates) do not form layers that are stable in aqueous environments and present challenges during the grafting process. For instance, the chemical grafting of phosphonates requires high temperature (140 °C) to perform. Modification of SiO(2) surfaces with metal oxides is an attractive alternative since strong bonds can be established between metal oxides and relevant molecules (silanes, phosphonates). While such modification is possible using vapor-phase methods, such as atomic layer deposition and physical vapor-phase deposition, wet chemical processing is inexpensive and technologically very attractive. We describe here a simple wet chemical method to deposit an ultrathin layer of metal oxide/hydroxide groups. Further, using a model surface with exactly one-third monolayer OH groups on oxide-free Si surfaces, the precise adsorption geometry on single Al(OH)(3) groups is shown to be bidentate, and the distance between the Al and P atoms is determined to be the main influencing parameter for a thermodynamically stable formation of the Al-O-P bond.