Optical detection of CO gas by the surface-plasmon resonance of Ag nanoparticles and nanoclusters synthesized on a hydrogenated amorphous carbon (a-C:H) film

Ag nanoparticles were deposited on a hydrogenate amorphous carbon (a-C:H) thin film as a host by radio frequency plasma enhanced chemical vapor deposition (RF-PECVD) for various deposition times. We observed that as the sputtering time increases, the particle shape of the deposited nanostructures changes to a cluster shape. AFM images show that the accumulation of the nanoparticles on each other leads to the vertical growth of the nanoclusters. According to X-ray diffraction patterns, the crystalline structure is formed for the nanocluster shape. The Fourier-transform infrared (FTIR) spectroscopy showed that bonds are formed between Ag ions and free hands of carbons on the surface of the a-C:H film. The peak related to carbide structures is seen around 2100cm^-1. UV-Vis spectroscopy demonstrates that the formation of Ag nanoclusters leads to the appearance of a sharp plasmonic peak, shifted towards longer wavelengths. The plasmonic peak of Ag was used for detecting CO gas in the ambient air. The adhesion of CO molecules to the Ag particles makes a significant change in the plasmonic peak. In the presence of CO gas flow, the localized surface plasmon resonance (LSPR) of Ag nanoclusters moves to a longer wavelength (red-shift) and the LSPR intensity increases. The sample with a nanocluster structure is a better adsorber for CO molecules due to its larger specific surface area.