Structural transformation and room temperature ammonia sensing properties of TiS2 nanostructures

The nanostructures of TiS2 have been successfully synthesized in a single-step process using probe sonication in various liquid media. Initial visual inspection confirmed that the nanostructures prepared in de-ionized water and de-ionized water-ethanol mixture change color from black to white with time. Various structural, optical and vibrational measurements identified these changes due to structural transformation of TiS2 into TiO2 in presence of water molecules. However, this transformation was absent in TiS2 nanostructures prepared in media like di-methyle formamide and N-methyle pyrolidone. These nanostructures were used for making two terminal sensor devices and yielded entirely different results. The black colored TiS2 showed highly selective n-type behaviour towards ammonia (200 ppm) with nearly 72% relative response at room temperature. Corresponding rise time and recovery time were found to be 72 +/- 7 s and 165 +/- 10 s, respectively. Contrary to this, the other device made from white powder did not show a detectable change in base resistance of the sensor. These initial results indicate the potential use of stable TiS2 nanostructures as a highly selective and sensitive room temperature ammonia sensor.