Aminosilane densities on nanotextured silicon

Aminosilanization of hydroxylated surfaces is used for attachment of biomolecules which have various applications. The density of the surface amine group is of importance as it determines the density of the subsequent immobilized or self-assembled molecules over the aminosilylated layer; hence there is a need to understand the processes and the phenomena that control the surface aminosilane density. Crystalline silicon surfaces, nanotextured using the HF/HNO₃/H₂O chemistry, were silanized using aminosilanes (APTES and APTMS). Masks were not used to obtain the surface topography; rather the surface textures (< 100 nm RMS roughness) were controlled by process conditions such as temperature, etchant composition and etch time. The aminosilane densities were dependent on the surface texture and composition. Our results showed that oxidation of the surface resulted in lower silane densities. While increased surface area enhanced the densities, processes like the HNO₃-rich chemistries while increasing the surface area were also associated with surface oxidation resulting in lower densities compared to surfaces textured with HF-rich compositions.