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1701492 (1 of 8) © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

A Combined Experimental and Computational Study of Gas Sensing by Cu3SnS4 Nanoparticulate Film: High Selectivity, Stability, and Reversibility for Room Temperature H2S Sensing

Thripuranthaka M, Neha Sharma, Tilak Das, Swapnil Varhade, Satish S. Badadhe, Musthafa Ottakam Thotiyl, Mukul Kabir,* and Satishchandra Ogale*

DOI: 10.1002/admi.201701492

very important parameters in their perfor-mance evaluation.

Hydrogen sulfide H2S is a toxic gas that has hazardous effects on the respira-tory system leading to neurological disor-ders as well.[1] H2S, also called sewer gas, is released during the decay of organic materials, septic systems during bacterial breakdown, and petroleum drilling and refining. Hence, the demand to investigate new functional materials for the detection of traces of H2S is quite relevant.

Gas sensors have been fabricated using metal oxides,[6] polymers,[7,8] and organic–inorganic hybrid materials[9–11] for the sensing of a particular analyte. Metal oxide based sensors, for example, SnO2,[2,12,13] TiO2,[14] and CuO/ZnO[15] are the most investigated since they exhibit high sen-sitivity, fast response, and recovery. How-ever, they lack selectivity and possess safety and stability issues due to their

high-temperature operation,[16,13] and the signal drift[17,18] with time hinders the integration and miniaturization of the devices. As possible alternatives to metal oxides, nanostructured metal sulfides (i.e., SnS2 and CuxS)[4,19–21] and 2D layered transi-tion metal dichalcogenides such as MoS2,[22] WS2,[23,24] and MoSe2

[25,26] have been recently explored for NO2, NH3, and VOC sensing due to their tunable structural, electronic, and optical properties. Unfortunately, these materials are limited by their long response and recovery times and stability issues under ambient conditions. It has been reported that the decora-tion of noble metal nanoparticles (NPs) (Au, Ag, Pt) on metal oxides and metal sulfides enhances the performance of sensing materials in terms of their selectivity, stability, and recovery.[27] Nevertheless, this increases the cost and complexity of the syn-thesis and device fabrication.

On the other hand, studies on the physical and chemical properties of metal chalcogenides have shown the competence of these materials to operate as sensors at low powers leading to conservation of energy and also from the safety point of view as they could be operated at low temperatures.[18] The relatively lower band gap of metal chalcogenides is an added advantage for application as compared to wide band gap of semiconduc-tors. This motivates one to explore metal sulfides for sensing applications.[18]

Several binary sulfides are used for sensing of gases such as NH3, NO2, and H2, but not for H2S, especially at room temperature, because of the relative inactivity of metal sulfide surface bonds for this gas. The situation can be entirely different in the ternary case, however, due to the possible synergy of interactions involving dual cation surface chemistry. This is borne out by the present work wherein the Cu3SnS4 material, the Cu-rich ternary sulfide used for the first time in the gas sensing context, not only senses H2S at room temperature but also remarkably does so with high selectivity and stability. Thus, a combined experimental and computer modeling study on the use of nanocrystalline orthorhombic Cu3SnS4 phase is reported for H2S sensing. The material shows sensitivity for a wide range of H2S concentrations (from 10 to 2000 ppm). The performance of the sensing device fabricated on Kapton substrate remains intact even after several days and multiple bending cycles. Importantly, these experimental findings are consistent with the results of density functional theory calculations for binding energies for different gases, namely, H2S, NO2, NH3, and CO, on Cu3SnS4 surface.

T. M, Dr. T. Das, Dr. S. S Badadhe, Prof. M. Kabir, Prof. S. OgaleDepartment of Physics and Centre for Energy ScienceIndian Institute of Science Education and Research (IISER)Pune, Dr. Homi Bhabha Road, Pashan, Pune 411008, IndiaE-mail: [email protected]; [email protected]. Sharma, S. Varhade, Prof. M. O. ThotiylDepartment of Chemistry and Centre for Energy ScienceIndian Institute of Science Education and Research (IISER)Pune, Dr. Homi Bhabha Road, Pashan, Pune 411008, India

Gas Sensors

1. Introduction

Gas sensors play a vital role in the detection and control of ana-lytes in several sectors such as environmental pollution, food quality control, safety, medical diagnostics, and many other situ-ations/conditions faced in our daily life.[1] Of particular interest are sensors for the detection of toxic gases such as CO, NH3, NOx, H2S, and volatile organic compounds (VOCs).[2–5] Impor-tantly, such sensors are required to be highly selective, robust, reversible, stable, and low cost. With the growing emphasis of the modern world on wearable devices, there is an increasing demand for flexible sensors as well. In addition to the sensi-tivity, the response and recovery times of the sensors are also

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Binary sulfides like SnS2[4,19] (for NO2 at 120 °C and for NH3

at 200 °C), CuxS[20,21] (H2S at 350 °C and H2 at room tempera-ture), and PbS[28,29] (H2S at 135 °C) have been tested for sensing of different gases. H2S sensitivity is observed in a few binary sulfides but at higher operating temperature. These binary metal sulfides already have metal sulfide bond; therefore, it is expected that they will have poor affinity for H2S. However, this need not be the case in ternary metal sulfides as the surface properties depend on the synergetic effect of both metals and therefore surface chemistry could be different as compared to binary metal sulfides. Zhu et al. were the first to show that Zn1−xCdxS ternary sulfide can serve as a gas sensor material for selective sensing of the ethanol vapors at 206 °C.[30] Another ter-nary sulfide Cu2SnS3/CdS was reported for the room tempera-ture sensing of the liquefied petroleum gas.[31] Recently, Zhang et al. studied CuInS2 quantum dots decorated ring-like NiO for the sensing of NO2 gas at room temperature although the material does not recover to its initial state.[32] Apart from these reports, to the best of our knowledge, no other ternary sulfides have been employed for the H2S sensing application. Various reports have proved that Cu has more affinity toward H2S among other transition elements;[33,34] thus, Cu-rich sulfides could be highly efficient for H2S sensing. Hence, a ternary metal sulfide Cu3SnS4 with a high Cu:Sn ratio of 3:1 was chosen in this study for selective H2S sensing at room temperature.

Cu3SnS4 is an interesting ternary sulfide that occurs in the orthorhombic, tetragonal, and cubic phases and is known to be p-type[35,36] in nature with the band gap varying from 1.22[37] to 1.75 eV[38] for different nanostructures as reported in the litera-ture. This material has been well explored for its application in photovoltaics and optoelectronics. Various nanostructures of Cu3SnS4 have been synthesized using different methods such as the colloidal method,[39] successive ionic layer adsorption and reaction method,[37] spray pyrolysis method,[38] microwave-refluxing method,[36] and co-sputtering of Cu and Sn metals fol-lowed by sulfurization.[40]

We have synthesized Cu3SnS4 NPs by a simple one pot solution processing route.[41] The Cu3SnS4 NPs are well characterized with X-ray diffraction (XRD), scanning electron micro scopy (SEM), transmission electron microscopy (TEM, diffuse reflec-tance spectroscopy (DRS), and inductively coupled plasma optical emission spectroscopy (ICP-OES). The gas sensor device

is fabricated using the material and investigated for the sensing of hazardous gases such as NH3, CO, NO2, and H2S.

The device shows selectivity toward H2S with a recovery time of nearly 30 min for concentrations lower than 100 ppm at room temperature. The device is highly stable and retains the sensitivity and selectivity with negligible changes in the response even after several days. We resorted to the first-principles calculations using the state-of-the-art density functional theory (DFT) for the evalua-tion of the binding energies and the electronic charge density of CO, NH3, NO2, and H2S gases. Our first-principles calculations predict that the thermodynamically stable [001] surface of Cu3SnS4 has more preference for H2S as compared to other gases.

2. Results and Discussion

2.1. Physical Characterization of Cu3SnS4 Nanoparticles

The crystal structure of the Cu3SnS4 NPs was examined by the powder X-ray diffraction (PXRD) method. Figure 1a shows the X-ray diffraction pattern with 2θ values of major diffraction peaks at 28.64, 47.82, and 56.48° representing the (0 0 1), (0 0 2), and (2 0 2) planes belonging to the orthorhombic phase of Cu3SnS4, which are in good agreement with the litera-ture.[38] The appearance of diffraction peak below 2θ = 28° is strong indication of the orthorhombic phase. In this system, NPs are faceted with preferred orientation along ⟨001⟩ direc-tion. The broadness (large full width at half maximum) of the peaks in the diffraction pattern could be attributed to the smaller size of NPs. The particles size calculated according to the Scherrer’s formula is ≈5–6 nm. Further, to confirm the phase of the NPs, Raman spectroscopy measurements were carried out. The Raman spectrum of NPs shown in Figure 1b exhibits two major peaks at 291 and 329 cm−1 that conclusively point to the orthorhombic structure as reported in previous experiments.[39] Indeed, the major phonon mode around 329 cm−1 is associated with the breathing-like vibration of the S atoms around the Sn atom (cf. Figure 1b, inset schematic), followed by a small hump at 346 cm−1, which is again a clear validation of the orthorhombic phase.[39] DRS was employed for the calculation of band gap. Figure 1c pre-sents the Tauc plot indicating the band gap of Cu3SnS4. The


Figure 1. Crystal structure and spectroscopic characterizations of the Cu3SnS4 nanoparticles: a) powder X-ray diffraction pattern of the Cu3SnS4 nano-particles; b) Raman spectrum of the nanoparticles excited with 532 nm from He-Ne laser; and c) diffuse reflectance spectrum of the nanoparticles.




band gap was calculated using the Kubelka–Munk function F(R) given in the equation[42]

( ) =−

F RR

R

(1 )

2

2

(1)

where R is the diffuse reflectance of the material. The band gap obtained from the Tauc plot is 1.76 eV that corroborates with the previous reports on DRS study of this material and depicts the semi-conducting nature of this orthorhombic phase of Cu3SnS4.[38] The corresponding UV reflectance spectrum of the material is given in the inset of Figure 1c. The composition of the material was also verified by ICP-OES with Sn to Cu ratio calculated about 1:3. Further the X-ray photoelectron spectros-copy of the materials is characterized and shown in Figure S1 of the Supporting Information.

The morphological investigation of the material was done using electron microscopy techniques. Figure 2a shows the SEM image of the NPs. High-resolution TEM (HRTEM) images of the NPs are shown in Figure 2b,c. The HRTEM micrographs present the irregular shape of the particles. The inset in Figure 2b is the selected area electron diffraction (SAED) pattern of the material and the diffused rings show the polycrystalline nature of the synthesized NPs. The preferred orientation of the Cu3SnS4 NPs as calculated from the lattice

fringe spacing (0.36 nm) is ⟨ 001⟩, which is in accordance with the PXRD result.

2.2. Theoretical Evaluation of the Cu3SnS4 Geometry

To corroborate the complex electronic interaction of gas mole-cules on the surface of the Cu3SnS4 films, we have performed extensive ab initio calculations within density functional theory as implemented in Vienna ab initio simulation package (Section S1(II), Supporting Information).[43,44] The lattice para-meters are calculated with perdew, burke and ernzerhof (PBE) formulation of the generalized gradient approximation (GGA) exchange-correlation energy functional.[45] The calculated lat-tice parameters of the bulk orthorhombic (Pmn21) Cu3SnS4 are (a = 7.59 Å, b = 6.57 Å, and c = 6.32 Å) in excellent agreement with the PXRD data (a = 7.53 Å, b = 6.60 Å, and c = 6.31 Å). In the bulk Cu3SnS4 crystal structure, each of the Cu and Sn atoms is tetrahedrally bonded to S atoms and such CuS4 and SnS4 tetra-hedrons are connected via corner sharing chain, in the ab plane. In the case of CuS4 tetrahedron, the apeak S atom is connected to one Sn and two Cu atoms, whereas the similar apeak S atom of SnS4 is connected to all the three Cu atoms belonging to the top in plane along the ⟨001⟩ direction (Figure 2d). The corner shared CuS4SnS4 and CuS4CuS4 chains along the a-axis and


Figure 2. a) SEM and b,c) TEM images of Cu3SnS4 nanoparticles; the inset in (b) is the SAED and the inset in (c) is the HRTEM image of the nano-particles. d) The periodic bulk crystal structure of the Cu3SnS4 with a two-formula unit (black solid line box) with top and side views in the panel. e) The PBE-GGA optimized 2 × 2 × 2 slab (001-Cu3SnS4) projected on the right side of the panel with a top view of the Sn-Cu-terminated face exposed to gas shown on the left of this panel (orange dashed box), whereas the other-half of the slab is kept fixed to substrate.




alternate along the b direction (Figure 2d,e). Inclusion of on-site Coulomb interaction for Cu-d (UCu = 4 eV) and spin–orbit coup-ling does not alter the lattice parameters (Section S2, Table ST1, and Figure S2a,b, Supporting Information). On the metal ter-minated surface, which is exposed to gas, both the Cu and Sn sites loose one apeak S-bond and thus become threefold coordi-nated on the [001] surface, followed by the fully four coordinated S atoms just below these metal sites (Figure 2e). To understand the microscopic mechanism, we employed a 2 × 2 × 2 surface model, where the [001] surface is exposed to the gas mole-cules (Figure 2e). Calculated surface energies are 0.822 and 1.268 J m−2 for Sn-Cu and S-terminated surfaces, respectively, which indicate that the metal terminated [001] surface is ther-modynamically most stable. As the sulfur vacancy substan-tially increases the surface energy for both cases (>0.25 J m−2) (Section S3(I), Supporting Information), we have excluded vacancy induced surface calculations in the present study.

2.3. Sensing Results

The gas sensing device was fabricated by drop casting the dis-persion of Cu3SnS4 NPs in isopropyl alcohol (IPA) onto the electrodes patterned on the Kapton substrate. The details of the device fabrication process are given in the Experimental Sec-tion. Once the device was loaded into the sensing chamber, a constant flow of dry air (0.5 standard litre per minute) was

maintained throughout the experiment. To flush out the mois-ture present in the chamber, a constant flow of dry air was maintained through the chamber before the gas sensing measurements. All the sensing measurements were carried out with an applied bias of 2 V at room temperature (25 °C). Under the constant flow of dry air, a known concentration of the target gases NH3, NO2, CO, and H2S was flushed into the chamber for a fixed duration of 2 min and the change in the cur-rent of the device with respect to its current in the dry air flow was recorded. The response values were calculated using the formula

( )( ) =−

×RI I

I% 100

a g

a

(2)

where Ia is the current of the device in dry air and Ig is the cur-rent of the device in the presence of target gas. The plot of cal-culated response values of the sensor for 100 and 300 ppm concentrations of NH3, NO2, CO, and H2S is shown in Figure 3a. It is clear that the sensor has very good selectivity toward the H2S gas with a response value of 15.49% for 300 ppm and 6.54% for 100 ppm concentrations. For the concentration of 100 ppm the response value of the sensor for H2S is 13 times higher than the response for NH3, 6 times higher than the response for NO2, and 18 times higher than the response for CO. Whereas for the con-centration of 300 ppm H2S the sensor showed five times stronger response than NH3, 4.5 times than NO2, and seven times than


Figure 3. a) Selectivity plot of the sensor for 100 and 300 ppm concentrations of NH3, NO2, CO, and H2S. b) Sensing performance of the sensor for varying concentrations of H2S from 10 to 400 ppm at room temperature. c) Plot of response as a function of H2S concentration (ppm). d) Stability plot of the device.




CO. Based on these observations, we carried out further sensing experiments for the H2S gas to evaluate the response and recovery times and to investigate the lower limit of detection.

Figure 3b shows the response curves for the sensor for a wide range of H2S concentrations from 10 to 400 ppm. It is quite impressive that the device recovers almost completely even for higher concentrations of 400 ppm without the need of thermal activation. We tested the H2S sensing capability of the device for very high concentrations of 1000 and 2000 ppm as well. The device again showed almost complete recovery after sensing 2000 ppm of H2S (Figure S3, Supporting Information). Thus, the sensor device fabricated using Cu3SnS4 NPs demonstrates a robust sensing performance over a wide range of H2S concen-trations. From measurements we find that the recovery time is about 30 min for concentrations higher than 100 ppm, whereas the recovery time is less than 16 min for concentrations less than 100 ppm. These values are shown in Figure S4 of the Sup-porting Information. Figure 3c shows the plot of response as a function of the H2S gas concentration, which is quite linear showing that the response varies linearly with respect to the concentration of H2S. Figure 3d shows the stability plot of the device over a period of days. The device is quite stable with a reliable performance. A comparison table (Table ST2, Sup-porting Information) for room temperature H2S sensors with our results is provided in the Supporting Information.

The device performance was also tested in the bent position approximately at an angle of 45° and the results are shown in Figure 4. The response values of the device recorded for 100 and 300 ppm of the H2S gas in the bent mode are shown in Figure 4a. From the figure we can see that the response values remain almost the same as in the unbent state while the recovery time is slightly reduced. Further, we also tested the device after it was brought back to the normal state, which is shown in Figure 4b. The results are closer to the original mode. These results clearly demonstrate the robustness of the flexible device and its ability to perform both in the flat and bent modes.

The selective physisorption of H2S on the [001] surface of Cu3SnS4 can be explained from the bonding analysis of H2S with metal atoms using Hard and Soft (Lewis) Acids and Bases theory proposed by Pearson in 1963. Although the exact nature of bonding of the physisorbed molecules is very difficult to pre-dict, the possible charge transfer mechanism between adsor-bent and adsorbate is provided below:

According to the hard soft acid base (HSAB) theory, both the Cu2+ and Sn2+ are at the borderline, whereas according to the Pauli’s scale of electronegativity, Cu (1.90) is slightly more electro-positive than the Sn (1.96) due to the larger size of the Sn as com-pared to Cu. Now, out of all the four gases, NO2 is highly oxi-dizing in nature; H2S, NH3, and CO gases are reducing in char-acter; CO is relatively weakly reducing in nature. In the case of H2S sensing, the two lone pairs of electrons in S atom play a cru-cial role.[46] Here, the lone pairs can be transferred to the surface Cu2+ and Sn2+ sites via infirm single bonding or edge sharing, as proposed below with four such schematics, (a) to Cu2+, (b) to Sn2+, (c) edge-sharing bidentate at Cu2+-Sn2+ sites, or (d) biden-tate at Cu2+-Cu2+ chain

Such electron transfer might lead to the formation of a weak metal sulfide bond, with strength neither equivalent to covalent nor the ionic bonding, which can be broken even with room temperature excitation. A similar mechanism can also be true, in principle, for the NH3 reducing gas, but such possibilities are less, as N in NH3 has only one such lone pair thus biden-tate-like bonds are forbidden, as shown below with the two schematics (a) and (b)

In the case of oxidizing NO2 gas, the available sites are the Sn2+ as both Sn2+ and NO2

− are on the border line of acid and


Figure 4. a) Response of the sensor device in the bent condition and b) the response of the device after its recovery to the normal state.




base scale, respectively, according to the HSAB principle. There will be three possible ways through which NO2 can bind with the Sn2+, as shown with the schematics (a), (b) and (c)

Thus, the poor sensing response seen for the NO2 gas is due to its attraction to the Sn2+ sites only, but unfavorable for the Cu2+ sites, as shown in Figure 5a, which favors relatively more H2S gas adsorption. Considering the chemical stoichiometry of Cu3SnS4, there is only one Sn site compared to three Cu sites on the surface [001]. Thus, larger number of the Cu sites indeed help for the physisorption of more H2S gas as compared to the NO2 gas on the less number of Sn sites.

The above-discussed mechanism is explained with the cal-culations of adsorption binding energies of these gases using first-principles calculations in DFT with inclusion of van der Waals dispersion energy corrections of gases on metal ter-minated [001] surface, as discussed in the next section of the manuscript.

2.4. Mechanism for H2S Selectivity Drawn from DFT Calculations

The gas molecules (H2S, NO2, NH3, and CO) can be adsorbed at different atomic sites on the [001] surface along with

different orientation (Figure 5a and Section S3(II), Sup-porting Information), and we have calculated the adsorp-tion energies, which is corrected by the zero-point energy,

= − − + ∆+E E E E ZPEb Cu SnS Gas Cu SnS Gas3 4 3 4 , where ΔZPE is the change in zero-point energy calculated using the vibrational fre-quencies. The weak van der Waals interaction was considered within DFT-D3 formulation.[47] The H2S and NH3 molecules prefer Cu-site over the hollow and Sn sites (Section S3(II), Sup-porting Information) for surface adsorption. While the adsorp-tion energy is least for H2S, the CO and NO2 do not show any adsorption. In contrast, we observe that NO2 may bind at the Sn site; however, the availability of such a site on the metal termi-nated [001]-Cu3SnS4 is scarce compared to Cu and hollow sites. To understand the trend in the adsorption we have further inves-tigated the electronic density of states shown in Figure 5a,b. While S-p orbital shows energy spread for Cu and hollow-site adsorption, it is atom-like for the Sn site. Further, the Fermi level EF is pushed 0.3 eV higher compared to the clean surface for H2S@Cu site, such movement of EF is much less (<0.1 eV) for hollow and Sn-site adsorption. These together with almost unperturbed valence band top and conduction band bottom indicate higher physisorption of H2S. The presence of more number of copper atoms on the Cu3SnS4 (001) surface thus results in the higher sensitivity of the sensor toward H2S. In contrast, considering the density of states of NH3, CO, and NO2 at the Cu site, we find the respective p-orbitals to be much local-ized, and the shift in EF is 0.15, −0.15, and −0.05 eV, respec-tively. These indicate higher binding energies of CO and NO2 binding at the Cu site (Section S3 and Figure S7c, Supporting Information) making adsorption of these gases unfavorable on the surface. Thus, in agreement with the present experimental results, these theoretical results corroborate higher sensitivity of Cu3SnS4 toward H2S molecule.


Figure 5. a) The calculated total density of states (DOS) of the (001-Cu3SnS4 + H2S) model and S (p) DOS of the H2S within the model are shown, which become more atom-like going from the Cu site to the Sn site. The impact of H2S on the pristine slab of Cu3SnS4 is marginal with few tens of meV shift of the valence band top and conduction band bottom (indigo dashed line in the top panel of (a)) as seen in total DOS. b) The total DOS and cationic p-DOS for the other three gases CO, NO2, and NH3 are shown, with extreme atom-like nature of p-DOS for CO and NO2 than the NH3.




3. Conclusion

Cu3SnS4 NPs have been synthesized and evaluated for the room temperature gas sensing application. In contrast to binary sulfides, the NPs show selectivity toward H2S as com-pared to NO2, CO, and NH3 with good response and recovery time. The gas sensing mechanism is explained with the DFT modeling of adsorption binding energies of gases on the sur-face of the material and possible electronic hybridization from electronic density of states. Thermodynamically stable metal terminated surface with Sn-Cu along [001] gets more prefer-ence for the H2S gas to be physisorbed, as compared to the other gases. The device fabricated on flexible Kapton substrate is tested in the bent state as well and recovers almost to the original values when brought back to the normal state proving its flexibility. In addition to the desirable properties of selec-tivity and flexibility, this is the first report on Cu-rich Cu3SnS4 ternary metal sulfide for room temperature H2S sensing with complete recovery (>90%).

4. Experimental SectionMaterials and Methods—Synthesis of Cu3SnS4 Nanoparticles: The

Cu3SnS4 nanoparticles were synthesized following the reported protocol[41] with some modifications. Briefly, the metal precursors copper acetylacetonate and tin chloride were taken in certain molar ratio with excess of thioacetamide as sulfur precursor. The reagents were taken in a three-neck vessel with formamide as the solvent and were degassed under nitrogen for half an hour with constant stirring. Then, the mixture was heated to 170 °C at a rate of 10 °C min−1 and kept at that temperature for 1 h. After the completion, the reaction was quenched to room temperature. The nanoparticles were obtained by centrifuging and washing with ethanol several times. The NPs were dried at 80 °C overnight.

Material Characterization: The synthesized Cu3SnS4 nanoparticles were characterized using powder X-ray diffraction to investigate their crystal structure and the phase on a Bruker D8-Advance X-ray diffractometer (Germany) with CuKα radiation (λ = 1.54060 Å) at 40 kV and 30 mA. Raman spectroscopy measurements were done on a Renishaw InVia micro Raman spectrometer with an excitation wavelength of 532 nm from He-Ne laser. Transmission electron microscopy was done using JEOL, 2010F instrument at 200 kV. Diffused reflectance spectroscopy measurement was done on Shimadzu UV-3600plus UV–VIS–NIR spectrometer to find out the band gap of the synthesized material. ICP-OES analysis was done using SPECTRO ARCOS (Germany) with smart analyzer software.

Gas Sensor Device Fabrication and Characterization: For fabricating the flexible gas sensor devices Kapton was chosen as substrate. Kapton sheets were cleaned first with de-ionised water by ultrasonicating for 30 min and then with isopropanol for another 30 min. After ultrasonication the substrates were dried at 80 °C. Thin films of titanium (Ti) and platinum (Pt) were successively deposited by a pulsed laser deposition method and laser scribed using a CO2 laser to form electrodes. The spacing between the electrodes was ≈100 µm. Finally, a dispersion of Cu3SnS4 nanoparticles in IPA was prepared by ultrasonication and drop casted onto the electrodes and dried in a hot oven at 75 °C for 4 h and used for characterizing its gas sensor performance. The sensor device was tested in the chemiresistive mode. The device was loaded into the home made sensor chamber made of glass and connected externally to the Keithley 2400-C source meter. The chamber was then continuously flushed with dry air while recording the current of the sensor as a function of time, till saturation in the I–t graph was seen. Mass flow controllers (Alicat Scientific, USA) were used to maintain a constant flow of both the dry air (as a carrier) and the target gases.

Supporting InformationSupporting Information is available from the Wiley Online Library or from the author.

AcknowledgementsT.M., N.S., and T.D. contributed equally to this work. The authors acknowledge funding support by the Board of Research in Nuclear Sciences (BRNS), Department of Atomic Energy (DAE), Government of India and the DST Nanomission (Thematic Unit). T.M. would like to thank the Council of Scientific & Industrial Research (CSIR) for support.

Conflict of InterestThe authors declare no conflict of interest.

KeywordsCu3SnS4, density functional theory, gas sensors, physisorption, ternary sulfides

Received: November 15, 2017Revised: January 15, 2018

Published online:

[1] E. Llobet, J. Brunet, A. Pauly, A. Ndiaye, C. Varenne, Sensors 2017, 17, 391.

[2] S. Bai, W. Guo, J. Sun, J. Li, Y. Tian, A. Chen, R. Luo, D. Li, Sens. Actuators, B 2016, 226, 96.

[3] Y. Chen, W. Zhang, Q. Wu, Sens. Actuators, B 2017, 242, 1216.[4] J. Z. Ou, W. Ge, B. Carey, T. Daeneke, A. Rotbart, W. Shan,

Y. Wang, Z. Fu, A. F. Chrimes, W. Wlodarski, S. P. Russo, Y. X. Li, K. Kalantar-zadeh, ACS Nano 2015, 9, 10313.

[5] S. Zhang, P. Zhang, Y. Wang, Y. Ma, J. Zhong, X. Sun, ACS Appl. Mater. Interfaces 2014, 6, 14975.

[6] G. Cui, P. Zhang, L. Chen, X. Wang, J. Li, C. shi, D. Wang, Sci. Rep. 2017, 7, 43887.

[7] M. Šetka, J. Drbohlavová, J. Hubálek, Sensors 2017, 17, 1.[8] L. Kumar, I. Rawal, A. Kaur, S. Annapoorni, Sens. Actuators, B 2017,

240, 408.[9] A. Kaushik, R. Kumar, S. K. Arya, M. Nair, B. D. Malhotra,

S. Bhansali, Chem. Rev. 2015, 115, 4571.[10] J. Shu, Z. Qiu, S. Lv, K. Zhang, D. Tang, Anal. Chem. 2017, 89,

11135.[11] D. Tang, Z. Gao, D. Tang, R. Niessner, D. Knopp, Anal. Chem. 2015,

87, 10153.[12] A. Mirzaei, S. G. Leonardi, G. Neri, Ceram. Int. 2016, 42,

15119.[13] D. R. Miller, S. A. Akbar, P. A. Morris, Sens. Actuators, B 2014, 204,

250.[14] N. Chen, D. Deng, Y. Li, X. Liu, X. Xing, X. Xiao, Y. Wang, Sci. Rep.

2017, 7, 1.[15] J. Kim, W. Kim, K. Yong, J. Phys. Chem. C 2012, 116, 15682.[16] E. Comini, Mater. Today 2016, 19, 559.[17] V. Guidi, B. Fabbri, A. Gaiardo, S. Gherardi, A. Giberti, C. Malagù,

G. Zonta, P. Bellutti, Procedia Eng. 2015, 120, 138.[18] A. Gaiardo, B. Fabbri, V. Guidi, P. Bellutti, A. Giberti, S. Gherardi,

L. Vanzetti, C. Malagù, G. Zonta, Sensors 2016, 16, 296.






[19] Y. Xiong, W. Xu, D. Ding, W. Lu, L. Zhu, Z. Zhu, Y. Wang, Q. Xue, J. Hazard. Mater. 2018, 341, 159.

[20] A. A. Sagade, R. Sharma, Sens. Actuators, B 2008, 133, 135.[21] X. L. Yu, Y. Wang, H. L. W. Chan, C. B. Cao, Microporous Mesoporous

Mater. 2009, 118, 423.[22] D. J. Late, Y. K. Huang, B. Liu, J. Acharya, S. N. Shirodkar, J. Luo,

A. Yan, D. Charles, U. V. Waghmare, V. P. Dravid, C. N. R. Rao, ACS Nano 2013, 7, 4879.

[23] C. C. Mayorga-Martinez, A. Ambrosi, A. Y. S. Eng, Z. Sofer, M. Pumera, Adv. Funct. Mater. 2015, 25, 5611.

[24] N. Huo, S. Yang, Z. Wei, S.-S. Li, J.-B. Xia, J. Li, Sci. Rep. 2014, 4, 5209.

[25] W. Yang, L. Gan, H. Li, T. Zhai, Inorg. Chem. Front. 2016, 3, 433.[26] S. Y. Choi, Y. Kim, H. S. Chung, A. R. Kim, J. D. Kwon, J. Park,

Y. L. Kim, S. H. Kwon, M. G. Hahm, B. Cho, ACS Appl. Mater. Interfaces 2017, 9, 3817.

[27] J. Lu, J. H. Lu, H. Liu, B. Liu, L. Gong, E. S. Tok, K. P. Loh, C. H. Sow, Small 2015, 11, 1792.

[28] H. Liu, M. Li, G. Shao, W. Zhang, W. Wang, H. Song, H. Cao, W. Ma, J. Tang, Sens. Actuators, B 2015, 212, 434.

[29] M. Li, D. Zhou, J. Zhao, Z. Zheng, J. He, L. Hu, Z. Xia, J. Tang, H. Liu, Sens. Actuators, B 2015, 217, 198.

[30] L. Zhu, Y. Wang, D. Zhang, C. Li, D. Sun, S. Wen, Y. Chen, S. Ruan, ACS Appl. Mater. Interfaces 2015, 7, 20793.

[31] A. C. Lokhande, A. A. Yadav, J. Lee, M. He, S. J. Patil, V. C. Lokhande, C. D. Lokhande, J. H. Kim, J. Alloys Compd. 2017, 709, 92.

[32] J. Zhang, D. Hu, S. Tian, Z. Qin, D. Zeng, C. Xie, Sens. Actuators, B 2018, 256, 1001.

[33] X. Xue, L. Xing, Y. Chen, S. Shi, Y. Wang, T. Wang, Energy 2008, 4, 12157.

[34] G. Cui, M. Zhang, G. Zou, Sci. Rep. 2013, 3, 1.[35] Y. Li, W. Ling, Q. Han, T. W. Kim, W. Shi, J. Alloys Compd. 2015, 633,

347.[36] N. Tipcompor, S. Thongtem, T. Thongtem, Jpn. J. Appl. Phys. 2013,

52, 4.[37] H. Guan, H. Shen, C. Gao, X. He, J. Mater. Sci. Mater. Electron.

2013, 24, 1490.[38] U. Chalapathi, Y. B. K. Kumar, S. Uthanna, V. S. Raja, Thin Solid

Films 2014, 556, 61.[39] V. M. Dzhagan, A. P. Litvinchuk, M. Kruszynska, J. Kolny-olesiak,

M. Y. Valakh, D. R. T. Zahn, J. Phys. Chem. C 2014, 118, 27554.[40] P. A. Fernandes, P. M. P. Salomé, A. F. Da Cunha, J. Phys. D: Appl.

Phys. 2010, 43, 215403.[41] Y. Park, H. Jin, J. Park, S. Kim, CrystEngComm 2014, 16, 8642.[42] B. Sawicki, E. Tomaszewicz, M. Piatkowska, T. Gron, H. Duda,

K. Górny, Acta Phys. Pol., A 2016, 129, A94.[43] G. Kresse, J. Hafner, Phys. Rev. B 1993, 47, 558.[44] G. Kresse, J. Furthmüller, Phys. Rev. B 1996, 54, 11169.[45] J. P. Perdew, K. Burke, M. Ernzerhof, Phys. Rev. Lett. 1996, 77,

3865.[46] T. Fu, Electrochim. Acta 2013, 112, 230.[47] S. Grimme, J. Comput. Chem. 2004, 25, 1463.

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