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.

Monolayer Doping via Phosphonic Acid Grafting on Silicon: Microscopic Insight from Infrared Spectroscopy and Density Functional Theory Calculations

“…Figure (bottom line) shows all of the typical spectral features of a monodentate phosphonic acid:11, 26–28 the stretch mode of the (P = O) at 1227 cm −1 , the asymmetric and symmetric stretch modes of the (P–O) at 1078 and 1004 cm −1 , and the deformation mode of the (P–O–H) feature clearly present at 956 cm −1 29. In the aliphatic region, the spectral positions of the strong asymmetric and symmetric stretch modes of the (CH 2 ) at 2918 and 2850 cm −1 , respectively, indicate an ordered arrangement on the surface.…”

Ozone oxidation methods for aluminum oxide formation: Application to low-voltage organic transistors

“…The AlÀOÀH deformation mode is also present near 850 cm À1 . This mode was observed at 840 cm À1 for the condensation reaction of octadecylphosphonic acid onto aluminum oxide/hydroxide surface [26] and measured near 840-847 cm À1 in kaolinites [27]. However, the associated AlÀOÀH stretching modes are expected between 3200 and 3700 cm À1 [28] where they overlap with the HÀOÀH stretching mode of water.…”

Surface modification of alumina-coated silica nanoparticles in aqueous sols with phosphonic acids and impact on nanoparticle interactions

“…1 The degree of aggregation can be controlled by playing with the pH or salt content in order to tune electrostatic repulsions. 15,16 Actually, very few studies have been reported on the surface modification of aqueous colloidal silica by organotrialkoxysilanes. 12,13 Functionalization of silica is usually done by grafting organotrialkoxysilanes, see, e.g., ref.…”