Ethanol sensing of V2O5 thin film prepared by spray pyrolysis technique: Effect of substrate to nozzle distance P. Immanuel, A. Arockia Prakash, and C. Raja Mohan
Citation: AIP Conference Proceedings 1832, 080022 (2017); doi: 10.1063/1.4980482 View online: http://dx.doi.org/10.1063/1.4980482 View Table of Contents: http://aip.scitation.org/toc/apc/1832/1 Published by the American Institute of Physics
Ethanol sensing of V2O5 Thin Film prepared by Spray Pyrolysis Technique: Effect of Substrate to Nozzle Distance P. Immanuel, A. Arockia Prakash and C. Raja Mohan* Nanostructure Lab, Department of Physics, Gandhigram Rural University, Gandhigram-624302, Tamilnadu, India *Email:
[email protected] Abstract. In the present investigation V2O5 thin films were prepared by spray pyrolysis by varying substrate to nozzle distance (SND) from 20 to 35 cm in steps of 5 cm. The structural studies by XRD results indicates that the crystallinity increases with increase in SND along (101), (201) orientation and for the film prepared at 30 cm gives a good crystallinity. The SEM image shows that the change in morphology, which strongly depends on the SND. Above 30 cm it slightly affects the surface morphology of the V2O5 thinfilm due to agglomeration. The presence of elemental constituents is confirmed from EDAX analysis. The band gap of the film prepared at 30 cm has a lowest value of 2.1 eV. The electrical studies like I-V, Hall Effect measurement and the conductivity is maximum for the film prepared at 30 cm. The ethanol sensing of the prepared film has been studied using Keithley source meter and the detailed results are presented and discussed. Keywords: Substrate to nozzle distance, Spray pyrolysis, thinfilm, Sensor, Vanadium Oxide. PACS: 81.15.RS, 81.15.-Z, 83.50.UV.
INTRODUCTION Recent research on thin film preparation increases due to the extensive applications in the diverse fields of electronics, optics, space science, aircrafts, defense and other industries. Vanadium pentoxide (V2O5) is one of the transition metal oxides with the band gap of 2.44 eV and having attractive properties like good chemical, thermal stability, and electro chromic properties [1]. Vanadium has various valance states and results in a number of oxide forms of vanadium oxide, such as VO, VO2, V2O3, V2O5, etc., among these V2O5 is the most stable one. V2O5 exhibits semiconductor to metal transition, which leads to abrupt change in the electrical properties[2]. V2O5 thin films have been prepared by various methods, such as electron-beam evaporation, Spray pyrolysis techniques (SPT)[3], Spray pyrolysis techniques (SPT) offers good quality and adherence of the material on large substance by controlling preparative parameters like substrate temperature, Substrate to Nozzle Distance (SND), precursor concentration, air flow rate and spray time. In the present work, V2O5 thin film has been prepared by spray pyrolysis technique (SPT) for different substrate to nozzle distance (SND) distance like 20, 25, 30, and 35 cm. Its structural, morphological, optical and electrical properties have been studied by using the X-ray diffraction (XRD), Scanning Electron
Microscopy (SEM), UV-visible spectrometer, Four probe setup, Hall measurement and Keithley source meter.
MATERIAL AND METHODS Vanadium chloride (99.99 % purchased from Sigma Aldrich) is used as a source material and Millipore water as a solvent. A precursor solution has been prepared by dissolving 0.03 M of VCl3 in 20 ml of Millipore water. Glass substrate was used to prepare the thin films. Before coating the film the substrate was immersed into chromic acid and heated for 30 minutes and annealed to cool till the room temperature is attained. After that, all the films are washed with running water. The treated substrates were put into ultrasonic cleaner filled with double distilled water for one hour. After the ultrasonic treatment, the substrates are put into hot air oven for one day. Now this cleaned glass substrate was used to prepare the thin films. The prepared vanadium chloride solution was sprayed on the glass substrate to form V2O5 thin film by varying the Nozzle distance of 20, 25, 30, and 35 cm. Temperature and concentration are maintained at Û& DQG 0 UHVSHFWLYHO\ $OO WKH VDPSOHV DUH prepared for the spray time of 3 minutes and for the pressure of 45 pascal.
DAE Solid State Physics Symposium 2016 AIP Conf. Proc. 1832, 080022-1–080022-3; doi: 10.1063/1.4980482 Published by AIP Publishing. 978-0-7354-1500-3/$30.00
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RESULTS AND DISCUSSION
Optical Studies The band gap of the prepared film has been REWDLQHG E\ SORWWLQJ ĮKȖ 2 versus energy (eV) for various SND and are presented in fig. 2. The band gap is found to be 2.4, 2.3, 2.1 and 2.5 eV for the film obtained at SND of 20, 25, 30 and 35 cm respectively. Optical studies reveals that for the film prepared at 30 cm distance has the lowest band gap of 2.1 eV.
(201)
Intensity(a.u)
(101)
Structural Analysis (XRD)
35cm
12
30cm
10
20cm
10
20
2T q
30
40
FIGURE 1. XRD pattern for different of V2O5 Thin films at various SND
Fig.1. shows the XRD pattern of V2O5 thin films deposited for different SND like 20, 25, 30 and 35 cm. The observed peaks are in good agreement with the JCPDS Card no. 85-2422. It is observed that the film prepared at 20 cm has amorphous in nature, and the film prepared at 25, 30 and 35 cm has the orthorhombic structure along the plane (101) and (201). When the SND increases the intensity of the peaks also increases. Both (101) and (201) orientations are dominant only for the film prepared at 30 cm. The average Crystallite size was calculated using Scherrer’s formula. KO (1) D . ECosT where K= 0.9 (k is a constant depending on the SDUWLFOHVKDSH Ȝ c LVWKHZDYHOHQJWKRIWKH[ UD\UDGLDWLRQȕLVWKH )XOO:LGWKDQG+DOI0D[LPXP ):+0 DQG ș LV WKH DQJOH RI UHIOHFWLRQ 7KH PLFUR strain and dislocation density also calculated using eqn (2) and (3). Micro strain ECosT (2) P . 4
Dislocation density 1 G lines / m 2 . D2
(3)
TABLE 1. Calculated structural parameters of V2O5 thinfilms. SND 25 30 35
2ș
D (nm)
İ X10-3
12.20 12.19 12.71
18 20 40
1.27 1.70 0.85
8
DhJ)2 x10
12
25cm
į X1015 lines/m2 3.08 2.50 6.25
20cm 25cm 30cm 35cm
6 4 2 0
2.0
2.2
2.4
2.6 2.8 Energy(eV)
3.0
3.2
FIGURE 2. Band gap of V2O5 thin films (0.03 M) for various SND.
Scanning Electron Microscopy 20 cm
20cm
25cm
25cm
30cm
30cm
35cm
35cm
FIGURE 3. SEM and EDAX image of V2O5 thin films for various SND
The SEM images of the prepared samples for various SND are presented in the Fig.3. The morphology of the samples prepared at 20, 25 and 35 cm are almost smooth but the film prepared at 30 cm good grains. The presence of vanadium and oxide are confirmed by EDAX [4].
Electrical Studies The I-V Characterization of the V2O5 film prepared for SND has been measured using Keithley source meter. The anode voltage applied across V2O5 film is 5 to +5 V. All the measurements are carried out at the room temperature. The I-V studies suggest that the film prepared at 30 cm distance has the highest
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20 cm 25 cm 30 cm 35 cm
-5.0x10-6 -1.0x10-5 -1.5x10-5 -2.0x10-5 -2.5x10-5 -6
-4
0 5 Pl 10 Pl 15 Pl 20 Pl 25 Pl 30 Pl 35 Pl 40 Pl 45 Pl 50 Pl
-2
0
Voltage (v)
2
4
-4
1.2x10
I(mA)
3.0x10-5 2.5x10-5 2.0x10-5 1.5x10-5 1.0x10-5 5.0x10-6 0.0
1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0 -0.2 -0.4 -0.6 -0.8 -1.0 -1.2 -1.4 -1.6
Current (I)x 10-4
Current(I)
conductivity. This may be due to the lowest band gap of 2.1 eV.
8.0x10-5
0 5 Pl 10 Pl 15 Pl 20 Pl 25 Pl 30 Pl 35 Pl 40 Pl 45 Pl 50 Pl
4.0x10-5 4.8 voltage(v)
4.4
-4
-2
0
voltage(v)
2
80
Electron Mobility(cm2/volt-sec)
Carrier Concentraction(cm3)X 1018
Conductivity(:-1m-1)
Hall Effect measurements for the prepared V2O5 thin film were carried out at room temperature. From the measured value of carrier concentration and FRQGXFWLYLW\ ı +DOOFRHIILFLHQW 5H DQGPRELOLW\ ȝ were calculated from the following relation (4) V 1 (4) ;P RH ne ne where e is the electronic charge and n is the carrier concentration. Fig 5 shows that distance 30 cm have a highest carrier concentraction of the film. It may be due to the good conductivity. 120 100
4
80
3
60 2
40
1
20
0 25
30
Sunstrate to nozzle distance(cm)
60 50 40 30 20 10 0 -10
0
10
20
30
40
Volume of ethanol (Pl)
FIGURE 7. Variation of ethanol concentration.
50
electrical conductivity with
The conductivity of the V2O5 thinfilm exposed to various volumes of ethanol has been obtained from the I-V curve. The results shows that the conductivity increases with increase in ethanol concentration indicating that added ethanol act like shunt. After the ȝOFRQFHQWUDWLRQWKHFRQGXFWLYLW\LVDOPRVWVDPH
CONCLUSION
0 20
Error Conductivity
70
Hall Effect Measurements
carrier concentraction electron mobility
6
FIGURE 6. Ethanol sensor of V2O5 thin film.
6
FIGURE 4. I-V of V2O5 thin films for various SND
5
5.2
4
35
FIGURE 5. Carrier concentration and mobility of V2O5 thin films for various SND
Ethanol Sensor The film prepared at the SND of 30 cm has been used as sensing element due to good crystallinity, morphology, lowest band gap (2.1 eV) and highest conductivity, when compared to the film prepared at other SND. The film was exposed to various volume of ethanol in the chamber attached with the heater. The corresponding I-V characterization has been carried out without and with various volumes of ethanol and the results are presented in the fig.6.
The V2O5 thin films were prepared by spray pyrolysis by varying substrate to nozzle distance (SND) from 20 to 35 cm in steps of 5 cm. XRD and SEM result indicates that, for the film prepared at 30 cm gives a good crystallinity and morphology with grains. The band gap of the film prepared at 30 cm has a lowest value of 2.1 eV. The electrical studies like IV, Hall Effect measurement and the conductivity is maximum for the film prepared at 30 cm. The sensor setup revels that the V2O5 thin film can be used as a sensing element for ethanol.
REFERENCES 1. 2. 3. 4.
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A.Bouzidi, et. al. Mater.Sci.Engg. 95, 141-147, (2002). M.Mousavi. et.al. Adv.Manuf S. 1, 320-328, (2013). D.V Raj. et.al. Mat.Semicon. Proc. 16, 256-259, (2013). M.Abbsi. et.al. Mat Semicin.proc. 29, 132-135, (2015).
