Structural transformation and room temperature ammonia sensing properties of TiS 2 nanostructures
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Structural transformation and room temperature ammonia sensing properties of TiS2 nanostructures Shivani Sharma1 · Sukhwinder Singh1 · Ravi Chand Singh1 · Sandeep Sharma1 Received: 17 January 2020 / Accepted: 30 March 2020 © Springer Nature Switzerland AG 2020
Abstract 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. Keywords 2-D material · TiS2 nanostructures · Room temperature NH3 gas sensor · Tmdcs · Liquid exfoliation · Sensitivity
1 Introduction In past few years transition metal dichalcogenides (TMDCs) have received significant attention due to their intriguing physical properties. This includes, the presence of intrinsic band gap, relatively larger electronic mobility, thermoelectric figure of merit and spin–orbit coupling strength. These features make them attractive for various electronic, spintronic, and thermoelectric applications [1, 2]. TMDCs have general formula M X2, where M is transition metal (Mo, W or Ti) and X is a chalcogen atom (S, Se or Te). Out of these TMDCs, MoS2, MoSe2 and WS2 have been studied extensively and studies on TiS2 are very rare. Titanium disulfide forms a layered structure in which neighboring layers are stacked via relatively weak van der Waals interactions. Each layer contains titanium atoms that are located in same plane, while sulfur atoms are located on top and below
the titanium planes. Therefore, a side view of one TiS2 layer consists of three planes containing S, Ti and S, respectively. As a result, each titanium atom co-ordinates with six neighbouring sulfur atoms and forms an octahedral geometry where each sulfur atom is connected with three neighbouring titanium atoms. Due to their technological importance as lubricants in petroleum industry, a catalyst, and use in high energy density batteries, they have been studied extensively in bulk form in last three decades [3–6]. But recent ad
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