Application of sculptured Mn conical (Spiral+helical) thin films for monitoring N2-CO and N2-CO2 gas mixtures: Gas ionization and field emission sensors

Abstract

This study deals with the design and fabrication of Mn sculptured conical (spiral + helical) thin films as electrodes for the detection of gas mixtures of different percentages (N2-CO and N2-CO2) in a gas ionization and field emission face to face sensor. The electrodes were produced using oblique angle deposition (OAD) technique. X-ray diffraction (XRD), atomic force microscopy (AFM) and field emission electron microscopy (FESEM) as well as energy dispersive x-ray spectroscopy (EDS) confirmed crystallography, morphology and elemental composition of materials of the designed samples. The sharp tip of the nano-helices were aimed to act as an electric field enhancer by applying voltage. The results indicated that Paschen's law is not applicable for inter-electrodes gaps less than 15 μm at pressures higher than 250 mbar where the field emission process becomes the dominant reaction. Enhanced selectivity and sensitivity were obtained for CO, CO2 and their mixtures with N2 gas at lower concentrations and shorter inter-electrodes gaps (<100 μm). The ionization energies of different ionization channel reactions of N2, CO and particularly CO2 in the gas mixtures were used to explain the behavior of Paschen's curves in different pressure ranges. Highest sensitivity of the sensor was obtained for inter-electrodes gaps of less than 100 μm. Comparison of the results with the published literature showed better performance of the present sensors relative to previously reported works.