Investigation of thermal emissivity and electrical resistivity of highly reflective nano-grained metal films

• A custom-built infrared thermography instrument enables accurate emissivity measurements for nano-grained Al, Ag, Pt, and Nb thin films under controlled conditions. • Substrate properties significantly affect grain size , surface roughness , and their impact on emissivity and resistivity. • A modified Hagen-Rubens relation models emissivity using electrical resistivity, accounting for thin-film deviations from bulk behavior. • A strong correlation between emissivity and resistivity is observed, influenced by nanostructural features like grain boundaries. • The findings guide the design of thin films with tailored emissivity and resistivity for use in thermal management and optoelectronics . This study investigates the effects of temperature and microstructure on the emissivity and its relationship with the electrical resistivity of nano-grained Al, Nb, Ag, and Pt films on the substrates of Si 3 N 4 /Si, Al 2 O 3 , and glass. An instrument was developed to precisely control the parameters affecting the emissivity of these highly reflective materials during measurements. Experimental results reveal that both the electrical resistivity and emissivity of the thin films increase with temperature and exhibit a strong correlation. Additionally, films with larger grain sizes exhibit lower emissivity and electrical resistivity, and vice versa. Within the temperature range of 70 °C to 145 °C, Al and Ag exhibit lower emissivity values (0.036–0.134), followed by Pt (0.078–0.168), while Nb shows the highest emissivity values (0.135–0.249). The temperature-dependent emissivity of the nanograined films has been successfully modeled based on the modified Hagen-Rubens relation.