ABSTRACT
Pure and dysprosium-loaded ZnO films were grown by radio-frequency magnetron sputtering. The films were characterized using a wide variety of morphological, compositional, optical, and electrical techniques. The crystalline structure, surface homogeneity, and bandgap energies were studied in detail for the developed nanocomposites. The properties of pure and dysprosium-doped ZnO thin films were investigated to detect nitrogen dioxide (NO2) at the ppb range. In particular, ZnO sensors doped with rare-earth materials have been demonstrated as a feasible strategy to improve the sensitivity in comparison to their pure ZnO counterparts. In addition, the sensing performance was studied and discussed under dry and humid environments, revealing noteworthy stability and reliability under different experimental conditions. In this perspective, additional gaseous compounds such as ammonia and ethanol were measured, resulting in extremely low sensing responses. Therefore, the gas-sensing mechanisms were discussed in detail to better understand the NO2 selectivity given by the Dy-doped ZnO layer.
ABSTRACT
We present a comparative investigation between thin films of graphene oxide (GO) and chemically reduced graphene oxide (rGO) deposited onto glass substrates via spray pyrolysis. Two reduction techniques are investigated: (1) the exposition of a sprayed layer of GO to vapors of hydrazine hydrate to produce rGOV and (2) the addition of liquid hydrazine hydrate to a suspended GO solution, which is then sprayed onto a substrate to produce rGOL. Three different spectroscopy techniques, Raman, Fourier transform infrared, and UV-Vis-NIR, show that the two reduced samples have less lattice disorder in comparison to GO, with rGOL having the highest degree of reduction. Interestingly, topography characterization by atomic force microscopy reveals a morphological change occurring during the exposure to hydrazine hydrate vapors, resulting in a thickness of 110 nm for the rGOV film, which is a factor of 16 larger than rGOL and GO. Finally, I-V measurements show a significant decrease of the GO's resistivity after the reduction process, where rGOL features a resistivity 90 times lower than rGOV, confirming that rGOL has the highest degree of reduction. Our results indicate that the reduction process for rGOV is susceptible to introducing intercalated water molecules in the material while the fabrication technique for rGOL is a suitable route to obtain a material with minimal lattice disorder and properties approaching those of graphene.
