Photomask-driven selective oxidation and optical imaging of ultrathin gold oxide films on antireflective substrates

Abstract Ultrathin gold oxide (AuO x ) films were patterned on gold surfaces using UV/O 3 treatment applied through quartz photomasks with Cr patterns. The formation of AuO x films was confirmed through reflective spectroscopy and X-ray photoelectron spectroscopy. Reflective spectroscopy conducted on antireflective (AR) multilayer substrates demonstrated a minimum reflectance at 535 nm, which shifted by 3.0 nm toward longer wavelengths upon AuO x formation. This shift enabled the imaging of the AuO x patterns by the camera. The maximum contrast of the AuO x patterns reached 9.3% in the images obtained under 530 nm light. Fine patterns, including a 12.7 μm wide line pattern and numerical designs, were successfully fabricated. This method enabled the real-time imaging of AuO x patterns using standard optical setups and cameras, with AR substrates enhancing the optical sensitivity. These results demonstrate a scalable and precise approach for analyzing ultrathin films and advancing nanofabrication applications.