Metallic 1T‐WS₂ for Selective Impedimetric Vapor Sensing

Abstract

5611wileyonlinelibrary.com demonstrated only using pristine graphene transistor measuring low-frequency noise spectra [ 9 ] and with graphene/silicon heterojunction Schottky diode using electrochemical impedance spectroscopy measurements. [ 10 ] In the fi rst method a complex data processing was required while in the second one the relative impedance change was referred to the module spectrum measured in vacuum. Here, we developed a selective vapor sensor using metallic 1T-WS 2 nanosheets (obtained by exfoliation of natural WS 2 with tert -butyllithium ( t -Bu-Li) as intercalator) deposited onto interdigitated gold electrodes (see Figure 1 ) and recording impedance phase spectra. The resonance frequency (fr) is then used as distinctive parameter for a selective quantifi cation of methanol and water vapors in isolated samples and mixtures. One of the most common procedures to exfoliate layered TMD materials consists of a chemical intercalation of organolithium compounds in anhydrous solvents followed by a violent reaction with water which splits the sheets apart. [ 11 ] Different organolithium compounds (methyllithium, n -butyllithium, and tert -butyllithium) have been used and explored to produce single or few layer structures of different TMDs. It has been recently demonstrated that n -butyllithium and tert -butyllithium represent, with similar capabilities, the most effective intercalation agents. [ 12 ] Layered TMD materials generally exist with two possible polymorph structures: (i) 2H, most common for the naturally occurring materials, where the metal atom coordination is trigonal prismatic and (ii) 1T, where the metal atom coordination is octahedral. Beside structural differences the materials present signifi cantly different electronic properties depending on their polymorph structures. The 2H phase confers semiconducting properties to the material while the 1T phase presents a metallic character with a signifi cantly enhanced conductivity. [ 13 ] It has been demonstrated that Li intercalation followed by exfoliation induces a transition between the natural semiconducting 2H phase to the metallic 1T phase [ 14 ] although with different effi ciencies depending on the TMD material employed. [ 15 ] 2H → 1T phase transition is particularly favored with WS 2 using t -Bu-Li intercalation compound. [ 15 ] With the intention to employ impedance spectroscopy as transducer technique we recognized the fundamental importance of the material conductivity, where one may expect improved sensitivity using a more conductive material. As such we opted to employ WS 2 nanosheets having an enhanced Metallic 1T-WS 2 for Selective Impedimetric Vapor SensingCarmen C. Mayorga-Martinez , Adriano Ambrosi , Alex Yong Sheng Eng , Zdenȇk Sofer , and Martin Pumera * Selective gas sensing is of immense importance for industrial as well as safety purposes. Here it is shown that metallic 1T phase transition metal dichalcogenides, such as tungsten sulfi de (WS 2 ), provide sensitive and selective platform for gas sensing. Using impedance s...

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“…[1, 2] For this reason, they have been extensively explored for applications such as energy storagea nd conversion, [3,4] lubrication, [5] sensing, [6,7] and catalysis. In particular, the strategy of atomicd oping has garnereds ome success in tuning the electronic properties and harnessing the vast potentialt hat TMDs can offer in the catalysis of the hydrogen evolution reaction (HER).…”

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“…f) Schematic of 1T‐WS 2 nanosheets biosensor and their selectivity properties for methanol and water detection. Reproduced with permission . Copyright 2015, Wiley‐VCH.…”

“…Unlike graphene, TMDs such as MoS 2 , WS 2 , and their hybrids exhibit remarkable semiconducting properties with a tunable bandgap, which depends on their thickness and doping molecules. Thus, TMDs are promising materials for the fabrication of gas sensors.…”