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[.]
Trang 15
6
7 Sonik Bhatiaa,⇑, Neha Vermaa, R.K Bedib
Department of Physics, Kanya Maha Vidyalaya, Vidyalaya Marg, Jalandhar 144004, India
Satyam Institute of Engineering and Technology, Amritsar 143107, Punjab, India
10
1 2 a r t i c l e i n f o
13 Article history:
14 Received 29 December 2016
15 Received in revised form 6 February 2017
16 Accepted 6 February 2017
17 Available online xxxx
18 Keywords:
19 ZnO nanoparticles
20 Simple heat treatment
21 Thermal evaporation
22 Gas sensor
23
2 4
a b s t r a c t
25 Nowadays, applications of nanosized materials have been an important issue in basic and applied
26 sciences In this investigation, Zinc Oxide (ZnO) nanoparticles were prepared by two different techniques
27 (simple heat treatment, thermal evaporation-two zone furnaces) In order to control shape and size – ZnO
28 nanoparticles prepared from heat treatment were used as a source for thermal evaporation method by
29 using two zone split furnace by varying zone temperature (Zone 1–800°C and Zone 2–400 °C) For both
30 techniques 0.17 M of Zn acetate dihydrate is used as main precursor and film is deposited on glass
sub-31 strate Synthesized ZnO were characterized for XRD, FESEM, FTIR and UV–Vis spectrophotometer and LCR
32 meter XRD revealed hexagonal wurtzite structure with preferential orientation along (1 0 1) plane
33 FESEM observed that grain size in the range of range of50 ± 5 nm FTIR spectra showed that the peaks
34 between 400 and 500 cm1for ZnO stretching modes Optical properties has been studied and found that
35 the observed band gap lies in the range of 3.32–3.36 eV The higher value of capacitance is observed at
36 lower frequency Gas sensing properties showed the higher response in case of thermal evaporation as
37 compared to simple heat treatment at an operating temperature of 250°C
38
Ó 2017 Published by Elsevier B.V This is an open access article under the CC BY-NC-ND license (http://
39 creativecommons.org/licenses/by-nc-nd/4.0/)
40 41
42 Introduction
43 In the present scenario, semiconductor industry brings a new
44 invention in the field of science and technology ZnO is one of
45 the semiconducting material, it has hexagonal wurtzite structure
46 with space group P63mc having wide band gap 3.37 eV and large
47 exciton binding energy 60 meV at room temperature It is less
48 stable cubic zinc blende structure with space group F-43m These
49 properties make this material promising for potential
optoelec-50 tronic applications such as gas sensor, solar cell, liquid crystal
dis-51 plays [1–3] Moreover ZnO films are widely used for surface
52 acoustic wave devices[4] It is a transparent material absorptive
53 in UV region and transparent in visible range, it can be used as
54 UV detector Furthermore wide variety of morphology has been
55 developed including nanowires, nanobelts and nanoparticles From
56 the past few years, to control the shape and size various methods
57 paid attention for the synthesis of ZnO nanoparticles were
pre-58 pared by different techniques such as chemical vapour deposition,
59 rf magnetron sputtering, laser ablation, spray pyrolysis, sol gel
60 with spin and dip coating, simple heat treatment and thermal
61
evaporation method [5–12] Among these techniques, thermal
62
evaporation and simple heat treatment are such moderate
tech-63
niques which involve numerous advantages such as simplicity in
64
process control and cost effective
65
Recently, some research groups prepared ZnO nanoparticles by
66
different techniques and their effect has been studied which had
67
influence on different properties of synthesized nanoparticles In
68
order to consider practical applications, peoples always try to
pre-69
pare metal oxide based nanoparticles as soon as possible
There-70
fore, herein we studied the effect of different techniques for
71
same molar concentration on structural, morphological, optical
72
and electrical properties Synthesized ZnO (powder and film) are
73
finally used for fabrication of nanodevice to study the gas sensing
74
properties towards ethanol gas
75
Balouria et al [13] revealed that sensing behaviour of ZnO
76
nanoparticles was better for H2S as compared to CO, H2and Cl2
77
Dhawale et al.[14]reported that ZnO nanorods exhibits maximum
78
response of 80% upon exposure of LPG as compared to N2and CO2
79
Jai Singh et al.[15]studied the optical and field emission
proper-80
ties of ZnO by considering pure Zn in the presence of oxygen by
81
thermal evaporation Wang et al.[16]reported ZnO nanostructure
82
on multilayer graphene shows the response value reached to 35.8
83
under the exposure of 100 ppm of acetone On the basis of these
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/ ).
⇑ Corresponding author.
E-mail address: sonikbhatiaphysics@gmail.com (S Bhatia).
Contents lists available atScienceDirect Results in Physics
j o u r n a l h o m e p a g e : w w w j o u r n a l s e l s e v i e r c o m / r e s u l t s - i n - p h y s i c s
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),
Trang 284 reports, it can be stated that gas sensing parameters had not only
85 influenced on surface to volume ratio, and particles size but also
86 on the interconnection present between ZnO nanoparticles
87 In this paper, novelty of the work is – ZnO nanoparticles was
88 prepared by two different techniques such as thermal evaporation
89 and simple heat treatment method Herein, ZnO nanoparticles
90 which were prepared by simple heat treatment method were used
91 as source for thermal evaporation technique Experimental
condi-92 tions were optimized by controlling the annealing temperature of
93 the prepared nanoparticles
94 Experimental
95 Methods of preparation
96 In this paper, ZnO thin films and powder has been prepared
97 using thermal evaporation technique (deposit on glass substrate)
98 and simple heat treatment method Here two different routes were
99 used for preparation of ZnO nanoparticles The mother solution for
100 samples was prepared by dissolving appropriate amount of Zn
101 acetate dihydrate The choice of this as source solution is due to
102 the fact that hydrolysis of acetate group gives the product which
103 is soluble in the solvent medium Fig 1 shows the systematic
104 scheme of ZnO nanoparticles prepared by simple heat treatment
105 and thermal evaporation method 0.17 M of Zn acetate dehydrate
106 (10 ml) mixed well with equi molar concentration of glucose at
107 room temperature under continuous stirring After stirring
pre-108 pared solution was filtered and transferred to a crucible which
109 was then placed into the furnace at 400°C The content results
110 the formation of spongy like material which was further annealed
111 at 500°C for an hour Finally white ZnO powder is obtained The
112 obtained samples were characterized in detail by using various
113 analytical techniques
114 Synthesized powder (simple heat treatment) in crucible was
115 annealed at 500°C for an hour This synthesized ZnO has been used
116 as source which was placed in molybdenum boat and glass as
sub-117 strate in case of thermal evaporation technique by using two zone
118 split furnace (zone 1–800°C and zone 2–400 °C) Variation in zone
119 temperature is considered so that synthesized ZnO from source
120 will deposit on the substrate Fig 1(b) shows the experimental
121 set up of ZnO films prepared by thermal evaporation technique
122 in two zone split furnace
123 Fabrication of ethanol gas sensor based ZnO nanoparticles
124 Annealed ZnO nanoparticles were used to obtain gas sensing
125 characteristics Synthesized nanoparticles by simple heat
126 treatment method were used as source for thermal evaporation
127
technique and glass as substrate To measure gas sensing
proper-128
ties as a function of temperature on exposure of host gas (ethanol)
129
a static gas sensing set up is used[17] The gas response (S = Ra/Rg)
130
of synthesized ZnO towards the host gas was measured Where Ra
131
is resistance in air and Rgis resistance in the presence of gas
132
Sensor is an electronic device which can sense the environment
133
changes, due to adsorption and desorption of test gas molecules
134
Adsorption is a surface defect; it can be increased by changing
var-135
ious operating conditions, various operating modes of sensor and
136
the use of different heating temperature which has strong chemical
137
affinity for specific gas molecules Before exposure to host gas,
oxy-138
gen atoms are adsorbed into ZnO surface; it takes electrons from
139
surface and become O(release oxygen) This Oion helps to
cre-140
ate the depletion layer on the host surface Variation in different
141
techniques help to completes the ZnO structure This allows more
142
oxygen to be adsorbed, which can enhance the response
143
Characterization of ZnO nanoparticles
144
Crystallinity of ZnO nanoparticles were analyzed by X Ray
145
Diffractometer (XRD) by use by use of analytical, Xpert Pro with
146
CuKa,Nickel metal is used asb filter, radiation source in the range
147
20–80° Surface morphology was observed from field emission
148
Scanning Electron Microscope (FESEM- JSM6100 (Jeol)) Fourier
149
Transformation Infrared Spectra (FTIR) was obtained from the
150
KBr pellets using FTIR spectrometer (FTIR 8400S, IR Prestiage 21)
151
obtained from Shimadzu, it gives the information about organic,
152
inorganic compound and vibrational modes For the optical
mea-153
surements (Absorbance and optical band gap) a double beam
spec-154
trophotometer (UV–Vis 2600/2700) Shimadzu with the
155
wavelength range 200–750 nm were employed, electrical
proper-156
ties were studied from LCR meter (Hioki 3532-50, LCR Hitester)
157
Results and discussion
158
Structural, morphological, compositional, optical and electrical
159
properties of ZnO nanoparticles
160
To examine the crystal nature, prepared ZnO nanoparticles
161
were characterized by XRD pattern.Fig 2Shows the X-Ray
diffrac-162
tion pattern of ZnO nanoparticles were synthesized by different
163
techniques All the observed XRD pattern exhibits well reflections
164
at 2h = 31.78°, 34.26°, 36.31°, 47.53°, 56.62°, 62.91°, 66.40°,
165
68.05°, 69.19° and 77.02° corresponding to hexagonal phase of
166
ZnO plane (1 0 0), (0 0 2), (1 0 1), (1 0 2), (1 1 0), (1 0 3), (2 0 0),
167
(1 1 2), (2 0 1) and (2 0 2) respectively The presence of most
promi-168
nent peak at (1 0 1) shows polycrystalline nature These observed
169
diffraction planes are well matched with standard card number
Fig 1 (a,b) Systematic scheme of ZnO nanoparticles prepared by simple heat treatment and thermal evaporation method.
2 S Bhatia et al / Results in Physics xxx (2017) xxx–xxx
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),
Trang 3170 (JCPDS 36-1451) Which indicate hexagonal wurtzite crystalline
171 phase with lattice parameters a = 3.248 nm and c = 5.205 nm The
172 average crystal size can be calculated from Scherrer’s formula
173
b cosh
175
176 where D is the crystalline size, K is constant i.e 0.92,k = 0.154 nm,
177 mean wavelength of CuKa1radiation,b is full width half maxima
178 andh is Bragg’s angle in radians The average size is found to be
179 in the range of 10–30 nm
180 The increase in lattice spacing (‘a’ and ‘c’) w.r.t ZnO synthesis by
181 simple combustion method was 0.014% and 0.020% respectively
182 (Table 1) This shows the induced lattice defects by using different
183 techniques, the atomic position of oxygen ions was found to be
184 slightly shifted along z axis[18] X-ray diffraction pattern and
den-185 sity of ZnO nanoparticles in powder and thin film form can be
jus-186 tified by variation in density and volume in simple heat treatment
187 and thermal evaporation technique were 11.35 and 11.34 g/cm3
188 and 47.652 and 47.674 respectively which can be calculated by
189 using the relation D = (Molecular mass of ZnO)*(No of atoms in
190 unit cell)/(Volume*NA) This clearly demonstrates the presence of
191 defects in synthesized ZnO nanoparticles
192 Fig 3shows the high resolution of FESEM image for the as
syn-193 thesized ZnO nanoparticles Spherical, quardpole, flowers rods,
194 leaves, pebbles and other morphologies can be clearly seen But
195 mostly spherical shaped morphology is observed Fig 3 shows
196 the cross-sectional FESEM images of ZnO nanoparticles and thin
197 film were synthesized by two different techniques The average
198 width and length of ZnO nanoparticles are found to be 15.7 nm
199 and 18.1 nm for simple heat treatment and 17.8 nm and 19.7 nm
200 for film prepared by thermal evaporation technique The grain size
201 of ZnO nanoparticles are in the range of50 ± 5 nm Different
mor-202 phology shows best synthesized ZnO nanoparticles that has large
203 surface to volume ratio which is responsible for optoelectronic
204 applications [19,20] These results show that the synthesized
205 nanoparticles by simple heat treatment have relatively rough
sur-206 face and non uniform grains but in case of thermal evaporation
207 method sol get more homogenous and stable Accordingly, the
208 quality of prepared nanoparticles gets improved
209 FTIR spectrum (FTIR 8400S, IR Prestiage 21) was used to detect
210 phase transformation and functional groups of samples by using
211 KBr pellets The use of KBr is because it is inert and it does not react
212 with sample to be analyzed.Fig 4shows the different peaks in FTIR
213 spectra in the range of 400–4000 cm1 The FTIR spectra of ZnO by
214
using different techniques showed different peaks with various
215
functional group The band near the region 3000–4000 cm1 is
216
only because of OH group The band is about 1650–1760 cm1
217
assigned to OH bond of water Band located near 400–500 cm1
218
indicates the stretching mode of ZnO This indicates the presence
219
of ZnO[21]
220
The absorbance spectra of ZnO nanostructure lies in the range of
221
200–750 nm were observed from UV–Vis spectrophotometer at
222
room temperature UV–Vis spectra give the information about
223
the excitonic and inter transition of nanomaterials The
transmit-224
tance of the sample is defined as the ratio of photons that pass
225
through the sample over the incident number of photons [22]
226
Fig 5 shows absorbance spectra of ZnO nanoparticles in the
stron-227
gest absorption range from 350–380 nm It has been found that
228
more absorbance is observed in case of thermal evaporation
tech-229
nique than simple heat treatment The absorbance spectra can be
230
found from the transmittance spectra by using the relation
231
234
In absorbance spectra red shift in peak was observed from 369–
235
372 nm which may be due the size difference of synthesized ZnO
236
nanoparticles[22] Absorbance intensity of UV peak in case of
sim-237
ple heat treatment method is less than the thermal heat treatment
238
method
239
Optical band gap of synthesized ZnO can be found by using
fol-240
lowing relation
241
Eg¼ hc
kmaxi
kmaxi
eV
243 244
Optical band gap lies in the range of 3.10–3.22 eV and more
245
band gap was observed in case simple heat treatment method than
246
thermal evaporation technique (two zone split furnace) This is
247
assumed to have better conductivity in case of thermal evaporation
248
technique Reported band gap was lies in the range of 3.32–
249
3.36 eV, which matched with our observations[23,24]
250
The refractive index of ZnO nanoparicles can be calculated from
251
the formula
252
ðn2 1Þ
ðn2þ 1Þ¼ 1
ffiffiffiffiffiffi Eg
p ffiffiffiffiffiffi 20
p
254 255
From this formula it has found that the refractive index lies in
256
the range of 1.90–2.00 This is approximately matched with the
257
exact value of refractive index of ZnO which is approximately 2.4
258
To study the semiconductor in the field of electronics various
259
methods has been proposed by different researchers.Fig 6shows
260
the variation in capacitance and applied frequency (0.2 MHz–
261
3.6 MHz) Low value of capacitance was observed at high
fre-262
quency This is due to the fact that more value of capacitance
263
resulting from interface states in equilibrium with ZnO
nanoparti-264
cles can follow the ac signal[25] It has also observed that the more
265
value of capacitance has been observed in case of thermal
evapora-266
tion technique in comparison with simple heat treatment method
Table 1 Structural parameter for ZnO synthesized by different techniques.
Sample [P6 3 mc] Lattice parameter
(Å)
Cell volume (Å) 3
Density (g/
cm 3 ) Simple heat
treatment
a = b = 3.25062 (Å) 47.652 11.35
c = 5.20740 (Å) Thermal
evaporation
a = b = 3.25107 (Å) 47.674 11.34
c = 5.20847 (Å)
q
Fig 2 XRD Spectra of ZnO nanoparticles prepared by (a) simple heat treatment (b)
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),
Trang 4267 The value of dielectric constant can be found from the formula
268
C¼ ð€0€rAÞ=d
270
271 where C is capacitance,€0is dielectric constant, A is the area of
cir-272 cular pellets and d is its thickness It was observed from theFig 7
273 that the dielectric constant decreases with frequency This variation
274 with frequency is due to charge transport relaxation time[26,27]
275 Fig 7demonstrates the observed dielectric constant is high at
276 low frequency which can be explained by Mawell-Wanger model
277 [28] This model studies dielectric medium is made of conducting
278 grains Under an external field these free charge carrier accumulate
279 which is high at low frequency whereas at higher frequency,
280
charge carriers does not fallow the external field which results
281
decrease in dielectric constant
282
Gas response measurements
283
To find the operating temperature, the sensor is exposed to
284
450 ppm of ethanol at different operating temperature Fig 8
285
shows the responses of the sensor was found to increase by
286
increasing the operating temperature The maximum response
287
value was observed at 250°C Approximate same behaviour is
288
observed for the ZnO nanoparticles synthesized by simple
combus-289
tion method but a very slow increase to reach the maximum value
290
of 22 at the same operating temperature This high response of ZnO
Fig 3 FESEM images of ZnO nanoparticles prepared by different techniques (a) simple heat treatment (b) thermal evaporation technique.
Fig 4 FTIR spectra of ZnO nanoparticles and films prepared by heat treatment and thermal evaporation.
Fig 5 Absorbance spectra of ZnO nanoparticles prepared by different techniques (heat treatment, thermal evaporation) respectively.
4 S Bhatia et al / Results in Physics xxx (2017) xxx–xxx
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),
Trang 5291 films prepared by thermal evaporation technique is attributed to
292 high surface to volume ratio[27,28]
293 Fig 9shows the response of synthesized ZnO based sensors by
294 exposed to different concentrations of ethanol at 250°C.Table 2
295 shows the response of ZnO based sensors by different techniques
296 and it has been found that more response is observed in case of
297 thermal evaporation technique in comparison to simple heat
treat-298 ment method which increased the sensitivity This mechanism is
299 based upon adsorption and desorption of test gas molecules It
300 forms the ionic species on sample surface It clearly shows that
301 thermal evaporation technique yields the best sensing response
302 at 250°C As response and recovery time are an important
param-303 eters for evaluating the sensor potential applications[29,30]
Fig 9 Response of the ZnO to ethanol of various concentrations at 250 °C (a) simple heat treatment (b) thermal evaporation technique.
Table 2
Ethanol conc (ppm) Response
Simple heat treatment Thermal evaporation method
Fig 6 Capacitance vs frequency of ZnO nanoparticles prepared by Simple heat treatment and Thermal evaporation method respectively.
Fig 7 Dielectric constant vs frequency of ZnO nanoparticles prepared by simple heat treatment and thermal evaporation method respectively.
Fig 8 Response of synthesized ZnO by (a) simple combustion method (b) thermal
evaporation technique at different temperatures, respectively.
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),
Trang 6304 Mechanism of gas sensing performance
305 The ethanol sensing mechanism of the sample is explained as
306 follows Adsorption is a surface defect It forms the ionic species
307 (O2 and O) on sample surface Kinetic reaction before and after
308 the ethanol exposure is described in Eqs.(1)–(3)
309
311
312
O2ðadsÞ þ e$ O
314
315
317
318 Before exposure to organic gas, oxygen atoms are adsorbed into
319 ZnO surface, it takes electrons from surface and become O
320 (release oxygen) This Oion helps to create the depletion layer
321 on the host surface Addition of double doping element help to
322 completes the ZnO structure This allows more oxygen to be
323 adsorbed and increased the surface area which can enhance the
324 response
325 Conclusions
326 To conclude, ZnO nanoparticles were synthesized by using two
327 different techniques (simple combustion and thermal
evapora-328 tion) Herein, nanoparticles which were prepared by simple
com-329 bustion have been used as source in case of thermal evaporation
330 technique on glass substrate Synthesized ZnO by using different
331 techniques were used for the fabrication of nanodevice (gas senor)
332 towards ethanol gas On the basis of this response towards ethanol
333 gas for different concentrations has been studied and higher
334 response was found in case of thermal evaporation for 50 ppm as
335 compared to simple combustion method In our investigation, high
336 sensitivity of fast response and recovery are found to be at an
oper-337 ating temperature of 250°C This fact confirms that thermal
evap-338 oration technique for 50 ppm ethanol is an effective method for gas
339 sensing applications
340 Acknowledgments
341 Authors are grateful to UGC, New Delhi for providing financial
342 assistance for carrying out project (F.No 42-770/2013) Thanks
343
due to the IKGPTU Kapurthala, Director, R.S.I.C, Panjab University
344
Chandigarh, for providing SEM and XRD facility
345
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6 S Bhatia et al / Results in Physics xxx (2017) xxx–xxx
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),