In this project, reactive magnetron plasma technique has been employed with different operating conditions for the electric discharges of the argon and argon / oxygen gases mixtures at various mixing percentage to achieve the optimum conditions for the plasma parameters generated to prepare thin films of Vanadium pentoxide with the high-quality nanostructure and specific electrical conductivity used in the construction and study the laboratory prototype characteristics of a gas sensor for both nitrogen oxides and ammonia.
The DC electrical discharge properties in gases of argon and the mixture of argon /oxygen gases were studied, including the current-voltage, current-pressure and Paschen curve. The electrical plasma discharges properties were studied in different operating conditions (inter- electrodes spacing , gas pressure, discharge voltages). We found the optimum inter- electrodes spacing is (5cm). The left region of the Paschen curve was selected to study plasma characteristics and for the preparation of V2O5 thin films. It was found that the optimum condition of O2/Ar ratio mixture is 30%, discharge current of ) 40 mA( and working sputtering pressure of 0.08 mbar.
The spectral properties of plasma, which include electron temperature (Te), electron density, plasma frequency, and Debye length, were studied using optical emission spectroscopy with different gas pressure, applied voltages, inter electrodes spacing and gases mixture ratios. The electron temperature was decreased and electron density increased with increasing argon gas working pressure and oxygen gas percentage with oxygen /argon mixture .The obtained optimal conditions were employed as follows (distance between electrodes 5cm, discharge current 40mA, gas pressure 0.08 mbar, mixture ratio 30%, 680Volt voltage, and 120 min time) for the preparation of V2O5 thin films on glass substrates.
The structural properties of the prepared V2O5 thin films using DC reactive magnetron sputtering on glass substrates by X-ray diffraction were analyzed . The results showed that all films have polycrystalline structure in nature with Vanadium pentoxide phase in the direction of grow thing of (001) and (111). Optical measurements showed that the V2O5 thin films had a direct energy gap and increased from (2.4 - 2.6) eV with increase the percentage of oxygen in Ar/O2 mixture working pressure .
The surface topography and morphological factors of the V2O5 sputtered thin films were examined by using AFM and FESEM respectively. It was observed that the granular size of the prepared thin films depends on the discharge current, the discharge working pressure, and the variation of the mixing ratio of the oxygen gas in the Ar/O2 mixture. Sample of V2O5 thin films with highest discharge current and working sputtering pressure (40mA ,0.08 mbar) exhibits mostly large grains because at high deposition rate much more nuclei that provide growing sites for newly deposited material are present on the glass substrate. Also, we found that, the grain size values gradually reduced by the oxygen percentage increasing in Ar/O2 discharge sputtering. As the crystalline of V2O5 films increased with discharge current and sputtering working pressure the surface roughness increased.
A prototype gas sensor from V2O5 thin films was constructed and the sensitivity of prepared samples for NO2 and NH3 gases in different concentration in air at different operated temperature was studied. The optimum operation temperature of home - built gas sensor was found at 200Cᴼ and response time of (35sec) and recovery time of (17sec)
تاريخ النشر
25/09/2019
رقم المجلد
رقم العدد
الكلمات المفتاحية
Magnetron Sputtering Plasma, Electron Density, Electron Temperature
محمد شريف محمد | Mohammed Shareef Mohammed | 3254