Ethanol gas sensor based upon ZnO nanoparticles prepared by different techniques 1 3 4 5 6 7 8 9 10 1 2 13 14 15 16 17 18 19 20 21 22 23 2 4 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60[.]
RINP 571 No of Pages 6, Model 5G 10 February 2017 Results in Physics xxx (2017) xxx–xxx Contents lists available at ScienceDirect Results in Physics journal homepage: www.journals.elsevier.com/results-in-physics Ethanol gas sensor based upon ZnO nanoparticles prepared by different techniques Sonik Bhatia a,⇑, Neha Verma a, R.K Bedi b 10 2 13 14 15 16 17 18 19 20 21 22 23 a b Department of Physics, Kanya Maha Vidyalaya, Vidyalaya Marg, Jalandhar 144004, India Satyam Institute of Engineering and Technology, Amritsar 143107, Punjab, India a r t i c l e i n f o Article history: Received 29 December 2016 Received in revised form February 2017 Accepted February 2017 Available online xxxx Keywords: ZnO nanoparticles Simple heat treatment Thermal evaporation Gas sensor a b s t r a c t Nowadays, applications of nanosized materials have been an important issue in basic and applied sciences In this investigation, Zinc Oxide (ZnO) nanoparticles were prepared by two different techniques (simple heat treatment, thermal evaporation-two zone furnaces) In order to control shape and size – ZnO nanoparticles prepared from heat treatment were used as a source for thermal evaporation method by using two zone split furnace by varying zone temperature (Zone 1–800 °C and Zone 2–400 °C) For both techniques 0.17 M of Zn acetate dihydrate is used as main precursor and film is deposited on glass substrate Synthesized ZnO were characterized for XRD, FESEM, FTIR and UV–Vis spectrophotometer and LCR meter XRD revealed hexagonal wurtzite structure with preferential orientation along (1 1) plane FESEM observed that grain size in the range of range of 50 ± nm FTIR spectra showed that the peaks between 400 and 500 cm1 for ZnO stretching modes Optical properties has been studied and found that the observed band gap lies in the range of 3.32–3.36 eV The higher value of capacitance is observed at lower frequency Gas sensing properties showed the higher response in case of thermal evaporation as compared to simple heat treatment at an operating temperature of 250 °C Ó 2017 Published by Elsevier B.V This is an open access article under the CC BY-NC-ND license (http:// creativecommons.org/licenses/by-nc-nd/4.0/) 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 Introduction 43 In the present scenario, semiconductor industry brings a new invention in the field of science and technology ZnO is one of the semiconducting material, it has hexagonal wurtzite structure with space group P63mc having wide band gap 3.37 eV and large exciton binding energy 60 meV at room temperature It is less stable cubic zinc blende structure with space group F-43m These properties make this material promising for potential optoelectronic applications such as gas sensor, solar cell, liquid crystal displays [1–3] Moreover ZnO films are widely used for surface acoustic wave devices [4] It is a transparent material absorptive in UV region and transparent in visible range, it can be used as UV detector Furthermore wide variety of morphology has been developed including nanowires, nanobelts and nanoparticles From the past few years, to control the shape and size various methods paid attention for the synthesis of ZnO nanoparticles were prepared by different techniques such as chemical vapour deposition, rf magnetron sputtering, laser ablation, spray pyrolysis, sol gel with spin and dip coating, simple heat treatment and thermal 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 ⇑ Corresponding author evaporation method [5–12] Among these techniques, thermal evaporation and simple heat treatment are such moderate techniques which involve numerous advantages such as simplicity in process control and cost effective Recently, some research groups prepared ZnO nanoparticles by different techniques and their effect has been studied which had influence on different properties of synthesized nanoparticles In order to consider practical applications, peoples always try to prepare metal oxide based nanoparticles as soon as possible Therefore, herein we studied the effect of different techniques for same molar concentration on structural, morphological, optical and electrical properties Synthesized ZnO (powder and film) are finally used for fabrication of nanodevice to study the gas sensing properties towards ethanol gas Balouria et al [13] revealed that sensing behaviour of ZnO nanoparticles was better for H2S as compared to CO, H2 and Cl2 Dhawale et al [14] reported that ZnO nanorods exhibits maximum response of 80% upon exposure of LPG as compared to N2 and CO2 Jai Singh et al [15] studied the optical and field emission properties of ZnO by considering pure Zn in the presence of oxygen by thermal evaporation Wang et al [16] reported ZnO nanostructure on multilayer graphene shows the response value reached to 35.8 under the exposure of 100 ppm of acetone On the basis of these E-mail address: sonikbhatiaphysics@gmail.com (S Bhatia) http://dx.doi.org/10.1016/j.rinp.2017.02.008 2211-3797/Ó 2017 Published by Elsevier B.V This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/) Please cite this article in press as: Bhatia S et al Ethanol gas sensor based upon ZnO nanoparticles prepared by different techniques Results Phys (2017), http://dx.doi.org/10.1016/j.rinp.2017.02.008 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 RINP 571 No of Pages 6, Model 5G 10 February 2017 84 85 86 87 88 89 90 91 92 93 S Bhatia et al / Results in Physics xxx (2017) xxx–xxx reports, it can be stated that gas sensing parameters had not only influenced on surface to volume ratio, and particles size but also on the interconnection present between ZnO nanoparticles In this paper, novelty of the work is – ZnO nanoparticles was prepared by two different techniques such as thermal evaporation and simple heat treatment method Herein, ZnO nanoparticles which were prepared by simple heat treatment method were used as source for thermal evaporation technique Experimental conditions were optimized by controlling the annealing temperature of the prepared nanoparticles 94 Experimental 95 Methods of preparation 96 122 In this paper, ZnO thin films and powder has been prepared using thermal evaporation technique (deposit on glass substrate) and simple heat treatment method Here two different routes were used for preparation of ZnO nanoparticles The mother solution for samples was prepared by dissolving appropriate amount of Zn acetate dihydrate The choice of this as source solution is due to the fact that hydrolysis of acetate group gives the product which is soluble in the solvent medium Fig shows the systematic scheme of ZnO nanoparticles prepared by simple heat treatment and thermal evaporation method 0.17 M of Zn acetate dehydrate (10 ml) mixed well with equi molar concentration of glucose at room temperature under continuous stirring After stirring prepared solution was filtered and transferred to a crucible which was then placed into the furnace at 400 °C The content results the formation of spongy like material which was further annealed at 500 °C for an hour Finally white ZnO powder is obtained The obtained samples were characterized in detail by using various analytical techniques Synthesized powder (simple heat treatment) in crucible was annealed at 500 °C for an hour This synthesized ZnO has been used as source which was placed in molybdenum boat and glass as substrate in case of thermal evaporation technique by using two zone split furnace (zone 1–800 °C and zone 2–400 °C) Variation in zone temperature is considered so that synthesized ZnO from source will deposit on the substrate Fig 1(b) shows the experimental set up of ZnO films prepared by thermal evaporation technique in two zone split furnace 123 Fabrication of ethanol gas sensor based ZnO nanoparticles 124 Annealed ZnO nanoparticles were used to obtain gas sensing characteristics Synthesized nanoparticles by simple heat treatment method were used as source for thermal evaporation 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 125 126 technique and glass as substrate To measure gas sensing properties as a function of temperature on exposure of host gas (ethanol) a static gas sensing set up is used [17] The gas response (S = Ra/Rg) of synthesized ZnO towards the host gas was measured Where Ra is resistance in air and Rg is resistance in the presence of gas Sensor is an electronic device which can sense the environment changes, due to adsorption and desorption of test gas molecules Adsorption is a surface defect; it can be increased by changing various operating conditions, various operating modes of sensor and the use of different heating temperature which has strong chemical affinity for specific gas molecules Before exposure to host gas, oxygen atoms are adsorbed into ZnO surface; it takes electrons from surface and become O (release oxygen) This O ion helps to create the depletion layer on the host surface Variation in different techniques help to completes the ZnO structure This allows more oxygen to be adsorbed, which can enhance the response 127 Characterization of ZnO nanoparticles 143 Crystallinity of ZnO nanoparticles were analyzed by X Ray Diffractometer (XRD) by use by use of analytical, Xpert Pro with CuKa, Nickel metal is used as b filter, radiation source in the range 20–80° Surface morphology was observed from field emission Scanning Electron Microscope (FESEM- JSM6100 (Jeol)) Fourier Transformation Infrared Spectra (FTIR) was obtained from the KBr pellets using FTIR spectrometer (FTIR 8400S, IR Prestiage 21) obtained from Shimadzu, it gives the information about organic, inorganic compound and vibrational modes For the optical measurements (Absorbance and optical band gap) a double beam spectrophotometer (UV–Vis 2600/2700) Shimadzu with the wavelength range 200–750 nm were employed, electrical properties were studied from LCR meter (Hioki 3532-50, LCR Hitester) 144 Results and discussion 157 Structural, morphological, compositional, optical and electrical properties of ZnO nanoparticles 158 To examine the crystal nature, prepared ZnO nanoparticles were characterized by XRD pattern Fig Shows the X-Ray diffraction pattern of ZnO nanoparticles were synthesized by different techniques All the observed XRD pattern exhibits well reflections at 2h = 31.78°, 34.26°, 36.31°, 47.53°, 56.62°, 62.91°, 66.40°, 68.05°, 69.19° and 77.02° corresponding to hexagonal phase of ZnO plane (1 0), (0 2), (1 1), (1 2), (1 0), (1 3), (2 0), (1 2), (2 1) and (2 2) respectively The presence of most prominent peak at (1 1) shows polycrystalline nature These observed diffraction planes are well matched with standard card number 160 Fig (a,b) Systematic scheme of ZnO nanoparticles prepared by simple heat treatment and thermal evaporation method Please cite this article in press as: Bhatia S et al Ethanol gas sensor based upon ZnO nanoparticles prepared by different techniques Results Phys (2017), http://dx.doi.org/10.1016/j.rinp.2017.02.008 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 145 146 147 148 149 150 151 152 153 154 155 156 159 161 162 163 164 165 166 167 168 169 RINP 571 No of Pages 6, Model 5G 10 February 2017 S Bhatia et al / Results in Physics xxx (2017) xxx–xxx Table Structural parameter for ZnO synthesized by different techniques Sample [P63mc] Lattice parameter (Å) Cell volume (Å)3 Density (g/ cm3) Simple heat treatment a = b = 3.25062 (Å) 47.652 11.35 47.674 11.34 c = 5.20740 (Å) Thermal evaporation a = b = 3.25107 (Å) c = 5.20847 (Å) q Fig XRD Spectra of ZnO nanoparticles prepared by (a) simple heat treatment (b) thermal Evaporation method 170 171 172 173 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 (JCPDS 36-1451) Which indicate hexagonal wurtzite crystalline phase with lattice parameters a = 3.248 nm and c = 5.205 nm The average crystal size can be calculated from Scherrer’s formula Kk D¼ b cosh where D is the crystalline size, K is constant i.e 0.92, k = 0.154 nm, mean wavelength of CuKa1 radiation, b is full width half maxima and h is Bragg’s angle in radians The average size is found to be in the range of 10–30 nm The increase in lattice spacing (‘a’ and ‘c’) w.r.t ZnO synthesis by simple combustion method was 0.014% and 0.020% respectively (Table 1) This shows the induced lattice defects by using different techniques, the atomic position of oxygen ions was found to be slightly shifted along z axis [18] X-ray diffraction pattern and density of ZnO nanoparticles in powder and thin film form can be justified by variation in density and volume in simple heat treatment and thermal evaporation technique were 11.35 and 11.34 g/cm3 and 47.652 and 47.674 respectively which can be calculated by using the relation D = (Molecular mass of ZnO)*(No of atoms in unit cell)/(Volume*NA) This clearly demonstrates the presence of defects in synthesized ZnO nanoparticles Fig shows the high resolution of FESEM image for the as synthesized ZnO nanoparticles Spherical, quardpole, flowers rods, leaves, pebbles and other morphologies can be clearly seen But mostly spherical shaped morphology is observed Fig shows the cross-sectional FESEM images of ZnO nanoparticles and thin film were synthesized by two different techniques The average width and length of ZnO nanoparticles are found to be 15.7 nm and 18.1 nm for simple heat treatment and 17.8 nm and 19.7 nm for film prepared by thermal evaporation technique The grain size of ZnO nanoparticles are in the range of 50 ± nm Different morphology shows best synthesized ZnO nanoparticles that has large surface to volume ratio which is responsible for optoelectronic applications [19,20] These results show that the synthesized nanoparticles by simple heat treatment have relatively rough surface and non uniform grains but in case of thermal evaporation method sol get more homogenous and stable Accordingly, the quality of prepared nanoparticles gets improved FTIR spectrum (FTIR 8400S, IR Prestiage 21) was used to detect phase transformation and functional groups of samples by using KBr pellets The use of KBr is because it is inert and it does not react with sample to be analyzed Fig shows the different peaks in FTIR spectra in the range of 400–4000 cm1 The FTIR spectra of ZnO by using different techniques showed different peaks with various functional group The band near the region 3000–4000 cm1 is only because of OH group The band is about 1650–1760 cm1 assigned to OH bond of water Band located near 400–500 cm1 indicates the stretching mode of ZnO This indicates the presence of ZnO [21] The absorbance spectra of ZnO nanostructure lies in the range of 200–750 nm were observed from UV–Vis spectrophotometer at room temperature UV–Vis spectra give the information about the excitonic and inter transition of nanomaterials The transmittance of the sample is defined as the ratio of photons that pass through the sample over the incident number of photons [22] Fig shows absorbance spectra of ZnO nanoparticles in the strongest absorption range from 350–380 nm It has been found that more absorbance is observed in case of thermal evaporation technique than simple heat treatment The absorbance spectra can be found from the transmittance spectra by using the relation Absorbance ẳ log10 %Tị In absorbance spectra red shift in peak was observed from 369– 372 nm which may be due the size difference of synthesized ZnO nanoparticles [22] Absorbance intensity of UV peak in case of simple heat treatment method is less than the thermal heat treatment method Optical band gap of synthesized ZnO can be found by using following relation Eg ¼ hc 1240 ¼ eV kmaxi kmaxi Optical band gap lies in the range of 3.10–3.22 eV and more band gap was observed in case simple heat treatment method than thermal evaporation technique (two zone split furnace) This is assumed to have better conductivity in case of thermal evaporation technique Reported band gap was lies in the range of 3.32– 3.36 eV, which matched with our observations [23,24] The refractive index of ZnO nanoparicles can be calculated from the formula 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 233 234 235 236 237 238 239 240 241 243 244 245 246 247 248 249 250 251 p Eg n2 1ị ẳ p n2 ỵ 1ị 20 252 From this formula it has found that the refractive index lies in the range of 1.90–2.00 This is approximately matched with the exact value of refractive index of ZnO which is approximately 2.4 To study the semiconductor in the field of electronics various methods has been proposed by different researchers Fig shows the variation in capacitance and applied frequency (0.2 MHz– 3.6 MHz) Low value of capacitance was observed at high frequency This is due to the fact that more value of capacitance resulting from interface states in equilibrium with ZnO nanoparticles can follow the ac signal [25] It has also observed that the more value of capacitance has been observed in case of thermal evaporation technique in comparison with simple heat treatment method 255 Please cite this article in press as: Bhatia S et al Ethanol gas sensor based upon ZnO nanoparticles prepared by different techniques Results Phys (2017), http://dx.doi.org/10.1016/j.rinp.2017.02.008 254 256 257 258 259 260 261 262 263 264 265 266 RINP 571 No of Pages 6, Model 5G 10 February 2017 S Bhatia et al / Results in Physics xxx (2017) xxx–xxx Fig FESEM images of ZnO nanoparticles prepared by different techniques (a) simple heat treatment (b) thermal evaporation technique Fig FTIR spectra of ZnO nanoparticles and films prepared by heat treatment and thermal evaporation Fig Absorbance spectra of ZnO nanoparticles prepared by different techniques (heat treatment, thermal evaporation) respectively 267 268 270 271 272 273 274 275 276 277 278 279 The value of dielectric constant can be found from the formula charge carriers does not fallow the external field which results decrease in dielectric constant 280 Gas response measurements 282 To find the operating temperature, the sensor is exposed to 450 ppm of ethanol at different operating temperature Fig shows the responses of the sensor was found to increase by increasing the operating temperature The maximum response value was observed at 250 °C Approximate same behaviour is observed for the ZnO nanoparticles synthesized by simple combustion method but a very slow increase to reach the maximum value of 22 at the same operating temperature This high response of ZnO 283 281 C ¼ ð€0 €r AÞ=d where C is capacitance, €0 is dielectric constant, A is the area of circular pellets and d is its thickness It was observed from the Fig that the dielectric constant decreases with frequency This variation with frequency is due to charge transport relaxation time [26,27] Fig demonstrates the observed dielectric constant is high at low frequency which can be explained by Mawell-Wanger model [28] This model studies dielectric medium is made of conducting grains Under an external field these free charge carrier accumulate which is high at low frequency whereas at higher frequency, Please cite this article in press as: Bhatia S et al Ethanol gas sensor based upon ZnO nanoparticles prepared by different techniques Results Phys (2017), http://dx.doi.org/10.1016/j.rinp.2017.02.008 284 285 286 287 288 289 290 RINP 571 No of Pages 6, Model 5G 10 February 2017 S Bhatia et al / Results in Physics xxx (2017) xxx–xxx Fig Capacitance vs frequency of ZnO nanoparticles prepared by Simple heat treatment and Thermal evaporation method respectively Fig Dielectric constant vs frequency of ZnO nanoparticles prepared by simple heat treatment and thermal evaporation method respectively Fig Response of synthesized ZnO by (a) simple combustion method (b) thermal evaporation technique at different temperatures, respectively 291 292 293 294 295 296 297 298 299 300 301 302 303 films prepared by thermal evaporation technique is attributed to high surface to volume ratio [27,28] Fig shows the response of synthesized ZnO based sensors by exposed to different concentrations of ethanol at 250 °C Table shows the response of ZnO based sensors by different techniques and it has been found that more response is observed in case of thermal evaporation technique in comparison to simple heat treatment method which increased the sensitivity This mechanism is based upon adsorption and desorption of test gas molecules It forms the ionic species on sample surface It clearly shows that thermal evaporation technique yields the best sensing response at 250 °C As response and recovery time are an important parameters for evaluating the sensor potential applications [29,30] Fig Response of the ZnO to ethanol of various concentrations at 250 °C (a) simple heat treatment (b) thermal evaporation technique Table Ethanol conc (ppm) 10 20 50 Response Simple heat treatment Thermal evaporation method 2.3 2.8 3.2 4.2 4.4 6.5 7.6 14.4 Please cite this article in press as: Bhatia S et al Ethanol gas sensor based upon ZnO nanoparticles prepared by different techniques Results Phys (2017), http://dx.doi.org/10.1016/j.rinp.2017.02.008 RINP 571 No of Pages 6, Model 5G 10 February 2017 S Bhatia et al / Results in Physics xxx (2017) xxx–xxx 304 Mechanism of gas sensing performance 305 The ethanol sensing mechanism of the sample is explained as follows Adsorption is a surface defect It forms the ionic species (O and O ) on sample surface Kinetic reaction before and after the ethanol exposure is described in Eqs (1)–(3) 306 307 308 309 311 O2 ðgasÞ $ O2 adsị 1ị 312 314 O2 adsị ỵ e $ O2 adsị 2ị 315 317 O2 adsị ỵ e $ 2O ðadsÞ ð3Þ 324 Before exposure to organic gas, oxygen atoms are adsorbed into ZnO surface, it takes electrons from surface and become O (release oxygen) This O ion helps to create the depletion layer on the host surface Addition of double doping element help to completes the ZnO structure This allows more oxygen to be adsorbed and increased the surface area which can enhance the response 325 Conclusions 326 339 To conclude, ZnO nanoparticles were synthesized by using two different techniques (simple combustion and thermal evaporation) Herein, nanoparticles which were prepared by simple combustion have been used as source in case of thermal evaporation technique on glass substrate Synthesized ZnO by using different techniques were used for the fabrication of nanodevice (gas senor) towards ethanol gas On the basis of this response towards ethanol gas for different concentrations has been studied and higher response was found in case of thermal evaporation for 50 ppm as compared to simple combustion method In our investigation, high sensitivity of fast response and recovery are found to be at an operating temperature of 250 °C This fact confirms that thermal evaporation technique for 50 ppm ethanol is an effective method for gas sensing applications 340 Acknowledgments 341 Authors are grateful to UGC, New Delhi for providing financial assistance for carrying out project (F.No 42-770/2013) Thanks 318 319 320 321 322 323 327 328 329 330 331 332 333 334 335 336 337 338 342 due to the IKGPTU Kapurthala, Director, R.S.I.C, Panjab University Chandigarh, for providing SEM and XRD facility 343 References 345 [1] Lucas Gonỗalves Dias Mendonỗa NIM, Torikai Delson, Ibrahim Ricardo Cury, Simoes Eliphas Wagner ABCM Symp Ser Mechatron 2008;3:580 [2] Ito S, Murakami TN, Comte P, Liska P, Grätzel C, Nazeeruddin MK, et al Thin Solid Films 2008;516:4613 [3] Hsu K, Hsiao C, Lee Y, Chen, Liu D, 2015; 7745 [4] Nath RK, Nath SS, Sunar K J Anal Sci Technol 2012;3:85 [5] Shakti N Appl Phys Res 2010;2:19 [6] Srinatha N, No YS, Kamble VB, Chakravarty S, Suriyamurthy N, 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Bhatia S et al Ethanol gas sensor based upon ZnO nanoparticles prepared by different techniques Results Phys (2017), http://dx.doi.org/10.1016/j.rinp.2017.02.008 344 388 ... of ZnO nanoparticles prepared by simple heat treatment and thermal evaporation method Please cite this article in press as: Bhatia S et al Ethanol gas sensor based upon ZnO nanoparticles prepared. .. the response of synthesized ZnO based sensors by exposed to different concentrations of ethanol at 250 °C Table shows the response of ZnO based sensors by different techniques and it has been... frequency, Please cite this article in press as: Bhatia S et al Ethanol gas sensor based upon ZnO nanoparticles prepared by different techniques Results Phys (2017), http://dx.doi.org/10.1016/j.rinp.2017.02.008