Synthesis of novel Al-doped SnO2 nanobelts with enhanced ammonia sensing characteristics

Abstract

Pure and Al-doped single-crystalline 1-D SnO2 based nanostructures were synthesized via a catalyst free simple chemical vapour transport and condensation process in Ar/O2 atmosphere. The crystalline structure, morphology and defect states of pure and Al-doped SnO2 nanostructures have been investigated in detail. Incorporation of Al in the interstitial voids of tetragonal SnO2 lattice is proved by investigating through various analytical techniques. Al doping in SnO2 significantly increases its defect concentration as demonstrated by photoluminescence spectra. The PL spectra for pure and Al-loaded SnO2 samples shows a less intense excitonic peak at ~384 nm in the UV region apart from the broad and intense yellow emission peak centred at around ~596 nm and a shallow peak at ~672 nm, respectively. For the development of stable and economically viable sensor modules for ammonia vapour detection, sensitivity at three different concentration of NH3 vapours (25ppm, 50 ppm and 100 ppm) were investigated by varying the operating temperature (250-400 °C). The minimum sensitivity for Al-doped SnO2 nanobelts was found to be 0.47 (at 25 ppm and 250 °C) and the maximum as 1.85 (at 100 ppm and 350 °C), which is 2-3 times higher than that for pure SnO2 nanowire assembles. Our results are found to be reproducible after cross examination by repeated observations. The response time (35-110 s), and recovery time (50-120 s) of our Al-doped SnO2 nanostructured sensors, for different concentrations of NH3 vapours, are equivalent or less if compared to those of available metal-oxide sensors in market.