Fabrication of gold thin films on cooled glass substrates

Abstract

In this article, gold (Au) thin films were fabricated on glass substrates under vacuum conditions (4.5 x 10(-6) Torr) within a temperature range of 100-300 K, incrementing in steps of 50 K. Analyses through Field Emission Scanning Electron Microscopy (FESEM) revealed that at a substrate temperature of 230 K, the films featured spherical clusters of uniform size, e.g., 11-12 nm, suggesting that the soliton growth mechanism predominates at this temperature. Atomic Force Microscopy (AFM) further demonstrated that the average surface roughness (Ra) of the Au films varied with the substrate temperature, ranging from 1.2 to 4.7 nm, with the smoothest film observed at 230 K. X-ray diffraction (XRD) analysis confirmed that all films exhibited a cubic crystal structure oriented in the (111) plane. Optical analyses indicated that the films produced across the entire substrate temperature spectrum showed surface plasmon excitation within the 520-600 nm wavelength range. To excite surface plasmons at longer wavelengths, the Au film fabricated at 230 K was annealed at 773 K under vacuum conditions for an hour, enlarging the grain size to similar to 15 nm. Post-annealing, optical measurements revealed a 70-nm shift in the peak position of the plasmonic resonance to a longer wavelength of 650 nm, showcasing the tunable nature of the plasmonic effects through thermal processing.