Fabrication and characterization of Au/Cr and Cr/Au Multilayered plasmonic nanofilms for sensing applications

A highly sensitive/selective heavy metals and C2H2 gas-sensing structures utilizing plasmonic nanostructured films, mainly Au and Cr-based are fabricated using radio frequency magnetron sputtering. The chemical composition, morphological, and optical properties of the designed sensors are studied with various techniques. Scanning electron microscopy (SEM) images reveal the growth of winkle network Au and Cr nanostructured thin layers on glass substrates. To confirm the chemical compositions of the prepared Au and Cr nanostructures, Raman and energy-dispersive X-ray (EDX) spectra have been investigated. From 200 to 2500 nm, the optical transmission/reflection/absorption spectra have been studied. The spectra showed absorption band tuned from visible to infrared region with tuned optical band gap (Egop) from 1.94 eV for Au(4)/Cr(4) to 1.49 eV for Au(2)/Cr(2) versus 1.5 and 2.25 eV for Cr(4)/Au(4). The 4-layered Cr/Au/glass and Au/Cr/glass films are tested as Hg2+ sensors and C2H2 gas sensors. Heavy metals sensing property utilizing surface-enhanced fluorescence reveals high sensitivity upon the addition of Hg2+ ions (0.1–10 μM) and high selectivity against Cd2+ and Pb2+ (10 μM). The gas sensing sensitivity, detection limit, recovery time, and response time are estimated and presented at different gas concentrations. The sensitivity of the sensors reached 96.0% and 97.9% @100 sccm for Au/Cr/glass and Cr/Au/glass sensors, respectively. The Cr/Au/glass sensor (tres = 42 s, trecov = 58 s @20 sccm) showed smaller response and recovery times than the Au/Cr/glass sensor (tres = 52 s, trecov = 77.7 s @20sccm).