Loss of siloxane monolayers from GaN surfaces in water

Gallium nitride, with a thin passivating layer of Ga2O3, has been functionalized with octadecyltrichlorosilane (OTS) and aminopropyltriethoxysilane (APTES) self-assembled monolayers (SAMs). Water contact angles, atomic force microscopy, and X-ray photoelectron spectroscopy were used for characterization of the bare and functionalized surfaces. The SAMs are stable in acetonitrile, but both the hydrophobic OTS SAM and the hydrophilic APTES SAM completely desorb after 1-24 h of immersion in water and common buffers. The concentration of gallium in solution after a clean GaN chip is immersed in water is consistent with dissolution of roughly one monolayer of interfacial gallium oxide. Dissolution of this oxide layer could account for the loss of SAMs from GaN surfaces.