Sh. Seyyedin, S. M. Hosseini-Golgoo, M. H. Ghezel Ayagh, F. Agend,
Volume 33, Issue 2 (3-2015)
Abstract
In this paper, manufacturing and evaluation of ethanol gas sensors based on thin films of nanostructure tin oxide have been investigated. SnO2 thin films were prepared by both thermal evaporation (type I) and sputtering (type II) methods and heat treated on silicon wafer substrates. Scanning electron microscope (SEM), atomic force microscope (AFM), X-ray diffraction (XRD) and energy dispersive spectra (EDS) are employed to study the morphology and chemical composition of the semiconductor samples. Nano-scale grain size with homogenous distribution showed in SEM images of both types. Sensors resistance in air and its variation-transient response toward ethanol vapours (3000 ppm) was determinated. The response of the stable sensors was obtained 3 and 1.18 for type I and type II, respectively. That showes thin film of nanostructure tin oxide by thermal evaporation (type I) has better sensitivity than the other. More effective surface, adsorption sites and base-line resistance due to the more fine grain size in type I nanostructure, are its important reasons. however, it is slow due extensive rise time and fall time.
A. Karimian, Kalantar,
Volume 39, Issue 1 (5-2020)
Abstract
In this research, barium calcium hexaferrite (Ba1-xCaxFe12O19 , 0≤x£1) nanoparticles were synthesized through a sol-gel combustion method. The dried gel samples were then calcined at 950ºC for 4:30h. The phase and microstructural evolution of calcined samples were investigated by X-ray powder diffraction (XRD) and scanning electron microscopy (SEM), respectively. The results revealed formation of calcium -barium hexaferrite phase with a small amount of hematite as a secondary phase. The average particle size is between 60-100 nm and the particle morphology is hexagonal or plate like structure. Results of a vibrating sample magnetometer (VSM) showed that the sample with x=0.4, exhibited the lowest value of saturation magnetization in comparison with others. This could be due to structural heterogeneity and presence of higher amounts of non- magnetic phases (BaFe2O4 and Fe2O3) in this sample compared to others. The results of sensory testing in acetone gas showed that the barium-calcium hexaferrite sample with x=0.2 had the highest sensitivity (0.28) and shortest response (15s) at a concentration of 900 ppm and a temperature of 200 °C despite of the long recovery time.
