A tri-layer approach to controlling nanopore formation in oxide supports

A novel tri-layer approach for immobilizing metal nanoparticles in SiO₂ supports is presented. In this work, we show that under rapid heating to temperatures of approximately 1,000 °C, metal nanoparticles less than 15 nm in size will entrench in the SiO₂ layer on a silicon wafer to create pores as deep as 250 nm. We studied and characterized this entrenching behavior and subsequent nanopore formation for a wide variety of metal nanoparticles, including Au, Ag, Pt, Pd, and Cu. We also demonstrate that an Al₂O₃ layer acts as a barrier to such pore formation. Thus, by creating a tri-layer architecture consisting of SiO₂ on Al₂O₃ on silicon wafers, we can control the depth to which nanoparticles entrench between 3–5 nm. This small range allows one to entrench particles for the purpose of immobilization but still present them above the surface. The two advances of moving into the sub-15 nm size regime and of controlled particle immobilization through entrenchment have important implications in studying site-isolated and stabilized metal nanoparticles for applications in sensing, separations, and catalysis.