Improved thermal stability of Au-capped antireflective substrates with organic adhesion layers for real-time...

Antireflective (AR) multilayer substrates have emerged as advanced platforms for surface-sensitive optical imaging. This study examines the thermal stability of AR substrates incorporating an ultrathin Au top layer, with a focus on the influence of the organic adhesion layer 3-mercaptopropyltrimethoxysilane (MPTMS). Au films (18 nm) deposited on MPTMS-modified SiO₂demonstrated considerably improved morphological and thermal robustness compared with films formed using conventional Cr adhesion layers or without any adhesion layer. Prior to annealing, the Au films on MPTMS-based AR substrates consisted of compact assemblies of fine grains (∼20 nm). After annealing, the films recrystallized with an enhanced (111) orientation within the face-centered cubic structure, yielding continuous, groove-free surfaces. The reflectance spectrum of the AR substrates remained largely unchanged even after annealing at 250 °C. However, annealing above 300 °C led to the formation of ∼300 nm polygonal nanoholes in the Au films. The internal angles of these nanoholes were often close to 120° and 240°, reflecting the high crystallinity and threefold symmetry of the Au(111) plane. As a proof of concept, real-time optical microscopy was used to monitor the thermal reduction of ultrathin patterned AuO_xlayers, highlighting the promise of MPTMS-based AR substrates for real-time imaging of thermally reactive nanomaterials in surface analysis, chemical sensing, and thin-film diagnostics.