Back-Surface Gold Mirrors for Vibrationally Resonant Sum-Frequency (VR-SFG) Spectroscopy Using 3-Mercaptopropyltrimethoxysilane as an Adhesion Promoter

Back-surface mirrors are needed as reference materials for vibrationally resonant sum-frequency generation (VR-SFG) probing of liquid-solid interfaces. Conventional noble metal mirrors are not suitable for back-surface applications due to the presence of a metal adhesion layer (chromium or titanium) between the window substrate and the reflective metal surface. Using vapor deposited 3-mercaptopropyltrimethoxysilane (MPTMS) as a bi-functional adhesion promoter, gold mirrors were fabricated on fused silica substrates. These mirrors exhibit excellent gold adhesion as determined by the Scotch® tape test. They also produce minimal spectroscopic interference in the C–H stretching region (2800–3000 cm⁻¹), as characterized by VR-SFG. These mirrors are thus robust and can be used as back-surface mirrors for a variety of applications, including reference mirrors for VR-SFG.