Improving ethanol sensing characteristics of indium oxide thin films by nitrogen incorporation

Journal Pre-proof Improving ethanol sensing characteristics of indium oxide thin films by nitrogen incorporation P.K. Shihabudeen, Ayan Roy Chaudhuri

PII:

S0925-4005(19)31722-8

DOI:

https://doi.org/10.1016/j.snb.2019.127523

Reference:

SNB 127523

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Sensors and Actuators: B. Chemical

Received Date:

10 September 2019

Revised Date:

28 November 2019

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2 December 2019

Please cite this article as: Shihabudeen PK, Chaudhuri AR, Improving ethanol sensing characteristics of indium oxide thin films by nitrogen incorporation, Sensors and Actuators: B. Chemical (2019), doi: https://doi.org/10.1016/j.snb.2019.127523

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Improving ethanol sensing characteristics of indium oxide thin films by nitrogen incorporation P. K. Shihabudeen1 and Ayan Roy Chaudhuri1,2* 1. Materials Science Centre, Indian Institute of Technology Kharagpur, 721302 Kharagpur, West Bengal, India 2. Advanced Technology Development Centre, Indian Institute of Technology Kharagpur, 721302 Kharagpur, West Bengal, India

Corresponding author: Tel: +91-3222-283978

Electronic mail: [email protected] (Ayan Roy Chaudhuri)

Highlights

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In2O3 thin films with interstitial nitrogen doping has been prepared. N-In2O3 thin film has been investigated for potential ethanol sensing. Sensing response of N-In2O3 is superior to pure In2O3. N-In2O3 offers rapid response and stability against humidity.

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Abstract

Incorporation of suitable dopants in semiconducting metal oxide (SMO) based gas sensors

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have been one proficient approach employed to improve their sensing characteristics. Indium oxide (In2O3), which is a n-type SMO, has been widely investigated for its ethanol sensing

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characteristics. For doping of In2O3, typically various metal based dopants have been considered, whereas non-metallic dopants have drawn only limited attention. In this work we have examined the impact of nitrogen incorporation on the ethanol sensing properties of In2O3 thin film. Using urea as a source, nitrogen has been doped at the interstitial site of In2O3 synthesised using sol-gel technique. Ethanol sensing properties of the nitrogen doped In2O3 thin film has been compared with pure In2O3 sensor over a wide range of temperature. 1

Doping of nitrogen has been found to significantly enhance the ethanol sensing response of In2O3 (99.7% at 250 C), improves the stability of response under humid condition (change of response ~ 4.5% within relative humidity range 10-80%) and offers very fast response time (1 second for 300 ppm ethanol). We discuss that modification of the electronic properties of In2O3 due to interstitial nitrogen incorporation leads to its superior sensing properties on exposure to ethanol vapour.

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Keywords: Gas sensor, thin film, nitrogen doping, ethanol sensing

1. Introduction

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Detection of poisonous and combustible volatile organic compounds (VOCs) has received immense attention in recent time[1]. A large number of VOCs which have been found in

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human breath using gas chromatography are responsible for various diseases including

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alcoholism, lung cancer, breast cancer and diabetes[2]. In particular, ethanol, which is widely used in recreational beverages becomes a major cause of car accidents due to its adverse effect on human consciousness. Drunken driving has been prohibited by laws in many

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countries, which impose the permissible legal limit of ethanol concentration in blood for drivers of 0.05–0.08% corresponding to 130–208 ppm in human’s breath[3]. It is therefore

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pertinent to develop highly sensitive, highly selective, and low-cost portable sensors as

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ethanol breath analyser. One of the most promising types of such sensors is semiconducting metal oxide (SMO)-based chemiresistive gas sensors that offer high sensitivity, low fabrication costs, and compatibility with standard semiconductor technology[4–9]. Indium oxide (In2O3) which is a n-type semiconducting oxide (band-gap 3.5–3.7 eV), is a promising sensor material for breath analysis due to its excellent gas-sensing selectivity and sensitivity toward various VOCs particularly ethanol[10–12]. In2O3 thin film based gas 2

sensors have been widely investigated for ethanol sensing[8,13]. Similar to various other metal oxide gas sensors, characteristics of In2O3 thin film based VOC sensors are influenced by their crystal structure, structural morphology and film thickness. In order to improve the VOC sensing characteristics of In2O3 based sensors extensive research has been carried out that employ different strategies such as structure control, decoration with nanoparticle, and doping[14–16]. Incorporation of suitable dopants create controlled defects in metal oxides that can introduce the preferential adsorption sites to gas molecules. Therefore, doping stands

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as a simple, effective way to improve gas-sensing parameters such as sensitivity, reducing response time, increasing gas selectivity, and decreasing the optimal operating

temperature[14,17]. Researchers have focused on improving VOC sensing of indium oxide

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by forming composites and metal site doping[14,18,19]. However, the impact of anionic

dopant incorporation on the gas sensing properties of In2O3 thin films has not been explored

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widely for gas sensing application. Karla et al. reported enhanced photocatalytic properties of

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In2O3 thin films doped with substitutional and interstitial nitrogen. Later, Gai et al. reported enhanced ethanol sensing characteristics of In2O3 nanostructures doped with substitutional nitrogen[20]. However, to the best of our knowledge influence of nitrogen incorporation on

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the VOC sensing properties of In2O3 thin films have not been reported so far. In the present study we report about the synthesis of In2O3 thin film doped with nitrogen at the interstitial

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site and compare its ethanol sensing characteristics in comparison to pure In2O3 thin film. We

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demonstrate that nitrogen incorporated In2O3 thin film exhibits superior sensing response, rapid response time, and excellent stability of response over a wide range of relative humidity condition.

2.Experimental Nitrogen doped indium oxide thin film has been prepared through wet chemical sol-gel route using indium acetate (Alpha-aeser, 99.9 %) and urea (Alpha-aeser, 97 %) as the precursors. 3

For preparing the sol, 1.45 g of indium acetate was dissolved in 10 ml of ethanol (99.9%), to which ethanol amine (>98%) was added drop wise till a clear solution was obtained. In a separate beaker 1.2 g of urea was dissolved in 10 ml of ethanol. These two solutions were mixed together at 55 0C while stirring. The stirring was continued for 4 hours, till a stable solution (colour of the sol is stabilised) was obtained[21]. Pure In2O3 thin film was also prepared for using as with the same precursors without using urea. Thin films were deposited on thermally oxidised Si substrate. Prior to the deposition of films, the substrates were

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cleaned thoroughly by sonicating in methanol and DI water. After the substrate was dried, the precursor sol for N-In2O3 was spin coated at 3000 rpm. The film was synthesised by coating the sol 4 times. After each coating the sol was dried at 125 °C on a hot plate. Thus, prepared

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films were annealed at 500 0C for one hour in a muffle furnace to obtain crystalline N- In2O3 thin film. Simultaneously 4 times coated pure In2O3 thin film was prepared to use as the

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reference sample.

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2.2 Material Characterisation

The structural properties of the as-synthesized thin films were characterized by x-ray

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diffraction (XRD) analysis (X-pert PRO, PANalytical with a Cu-Kα radiation source (Kα = 1.54056 Å). Field emission scanning electron microscope (FESEM Merlin, Germany) was

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used to observe the surface morphologies and cross section of the thin films. Chemical composition of the samples was investigated by X-ray photoelectron spectroscopy (model

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PHI 5000 Versa Probe II, INC, Japan) measurement is done using A1-Kα x-ray of source (1486.6 eV) is used to study the chemical composition of compounds. In order to characterize the defects originated by nitrogen incorporation electron paramagnetic resonance (EPR) was studied at room temperature using X-band Bruker ELEXSYS 550 with flex line cavity at an operating frequency of 9.593 GHz with a field modulation frequency of 5 kHz. The magnetic field was scanned from 2500 to 4000 G and the microwave power of 15 mW. 4

2.3 Sensor measurements In this work, the N-In2O3 film have been tested for their suitability as VOC sensor. An in house developed quasi-static system has been used to characterise gas sensing behaviour. The setup is equipped with a humidity sensor (model SY-HS-220, Syhitech) to measure the relative humidity of the sensor ambient. A known load resistance is connected in series with the sensing element. A constant voltage (~5 V) is applied across the sensor and the output voltage across the load resistance is measured using Atmel ATMEGA 32 micro-controller

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based data acquisition circuit developed in house[22]. The data acquisition set up is

connected to a pc through RS232 interface for the data storage and further analyses. Figure 1(a) depicts the device structure. Inter digitated gold electrodes (electrode width and

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separation of 2 mm) has been deposited over the sensing layer. The equivalent circuit of thus

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obtained device is shown in figure 1(b). A 5 V power source is used to provide input voltage (Vc) to the sensing element. A variable load resistor (RL) is connected in series with the

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sensor (Rs). The voltage drop (Vout) across load resistance (RL) is related to the input voltage (VC) and sensor resistance (RS) in accordance with the following relation:

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𝑉𝑜𝑢𝑡 =

𝑅𝐿 𝑉 𝑅𝐿 + 𝑅𝑠 𝐶

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During sensing experiment, the temperature of thin film was maintained in the range of 150 °C to 300 °C. First the base resistance of the film has been stabilized at a constant operating

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temperature in atmospheric air. Thereafter, VOC of known concentration was injected into the gas sensing chamber by means of a micropipette. In the present work, the ethanol concentration was varied in the range of 35 to 300 ppm. Resistance of the samples were found to reduce on exposing to ethanol as expected as In2O3 is a ‘n’ type semiconductor. The resistance transient of the sensing elements has been recorded for response and recovery

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cycles. By measuring the output voltage and known values of the input voltage and load resistance. The gas sensor response (S) was calculated using the relations 𝑆 (%) =

(𝑅𝑎 −𝑅𝑔 ) 𝑅𝑎

× 100

(1)

Where 𝑅𝑎 and 𝑅𝑔 are the equilibrium resistances measured in presence of air and test gas respectively. The response (τres) and recovery (τrec) times (s) were estimated from the respective resistance transients where the base resistance is raised to 90% of the maximum

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resistance (τres) or fall to 90% of the equilibrium resistance in air (τrec). 4. Results and Discussion

Figure 2(a) compares the X-ray diffraction patterns of 4 times coated N- In2O3 and pure In2O3

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layers in the  -2 geometry. The diffraction peaks exhibited by the samples correspond to

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the cubic structure of In2O3 which have been indexed according to standard diffraction pattern for In2O3 (JCPDS 006-0416). The samples are found to be polycrystalline and are

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highly oriented along (222). The XRD peaks in case of N- In2O3 did not exhibit any obvious shift and no new peaks have been observed. This observation indicates the absence of any

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impurity or formation of secondary phase in the samples[23]. Further, only a small variation in intensity of the diffraction peaks indicate that the crystallinity and the film thickness are

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similar for the nitrogen incorporated and pure In2O3 films.

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Figure 3(a) and (b) represents the surface morphology of the N-In2O3 and pure In2O3 samples respectively. The scanning electron micrographs exhibit similar microstructure and uniform coagulated grain distribution in both the samples. Both pure and nitrogen doped In2O3 films have been found to be mesoporous in nature with grain size ranging between 8 to 12 nm. Thickness of the samples have been estimated to be ~ 250 nm from the crosssectional SEM investigation (supplementary information: Figure S1(a) and (b)).

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The presence of N in N-In2O3 and its nature of binding have been confirmed by high resolution XPS investigation. For this purpose, three areas of the XPS spectrum has been examined, e.g. the N 1s region (396-410 eV), the In 3d region (440-455 eV) and the O 1s region (526-535 eV). All the binding energies have been calibrated with reference to C 1s peak at 284.5 eV (not shown). Figure 4(a) compares the XPS spectrum of the N1s region for the pure and N incorporated In2O3 films. While the pure In2O3 sample did not exhibit any peak in this region, a clear peak corresponding to N has been observed for the N-In2O3

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sample that confirms the successful doping of nitrogen into In2O3 by the chosen synthesis method. Nitrogen atoms incorporated into In2O3 can occupy either the interstitial or

substitutional sites or both[20,23]. The N1s binding energy for substitutional N atoms lies in

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the range of 396.8-398 eV[20,23]. Thus, in reference to the previous study, presence of

substitutional nitrogen as a major doping component in our N-In2O3 sample can be ruled out.

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The single N 1s peak at 399.6 eV for N-In2O3 can be attributed to NO and/or NHx species at

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the interstitial site[23,24]. It is to be noted that existence of highly oxidized N species such as NO2 and NO3 (binding energies 405 and 408 eV, respectively) are improbable[25]. The nitrogen content in the thin film has been estimated to be 0.7 wt % with an N/In ratio of 0.05.

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Figure 4 (b) displays the In 3d peak for In2O3 and N-In2O3 thin film which clearly shows the doublet peaks corresponding to 3d5/2 and 3d3/2 . The In 3d5/2 peak appears at 443.8 eV, which

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corresponds to In-O bond formation[23,26]. As can be clearly seen from the In 3d peak

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position, N-incorporation doesn’t change its binding energy. Formation of In-N bonds can be ruled out due to the presence of the single In 3d5/2 (and In3d3/2) peak which further confirms absence of substitutional N doping. Nitrogen incorporation in In2O3 is known to create certain oxygen vacancies[27]. Figure 4.c demonstrates the O 1s peak for In2O3 and N-In2O3 films. In both the cases, the O 1s peak can be deconvoluted in to three peaks corresponding to In-O (~529.4 eV), non-stoichiometric oxygen (~530.3 eV - 530.5 eV) and surface hydroxyl groups

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(~532.2 eV - 532.4 eV)[28–30]. Analysis of the O 1s spectra clearly reveals that oxygen nonstoichiometry (oxygen vacancy) in In2O3 increases due to nitrogen incorporation. Room temperature electron paramagnetic resonance (EPR) spectroscopy has been measured to investigate the presence and nature of VOs in the samples. Figure 4 (d) depicts EPR spectra for pure and N-In2O3 thin films. While the pure In2O3 sample does not exhibit any EPR signal, a distinct broad EPR signal with g ~2.1 appears for the N-In2O3 sample. The EPR measurement suggests that N doping into In2O3 gives rise to singly ionized VOs[24].

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Incorporation of interstitial N has been observed to facilitate VO formation also in other metal oxides such as TiO2[31]. It is to be noted that in addition to VOs, the interstitial NO- species can also contribute to the EPR signal[32,33].

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In order to investigate the suitability of N-In2O3 as a VOC sensor, ethanol sensing

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characteristics of the films has been carried out in the temperature range of 150 °C to 300 °C. Figure 5(a) compares the response (%) of the pure and N-In2O3 thin films as a function of

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temperature for ethanol concentration fixed at 300 ppm. Clearly, the sensing response of the N-In2O3 thin film is much superior to that of the pure In2O3 film. Both the sensors exhibited

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maximum response at 250 °C which is selected as the optimum temperature for further investigation of their sensing characteristics. Figure 5 (b) displays one representative

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resistance transient characteristics of pure and N-In2O3 films for 300 ppm ethanol at 250 °C. The N-In2O3 sample exhibited very rapid response (one second) which is superior to the

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response time of the pure In2O3 film (four seconds, inset, figure 5(b)). However, the recovery has been found to be slow. The recovery time is longer for the nitrogen incorporated sample (480 seconds) compared to pure In2O3 (350 seconds). It is to be noted that the gas sensing system employed in this study is a static setup. Therefore, the recovery starts already before sensor response can saturate. In general, for n-type semiconductor metal oxide sensors exposed to a reducing gas, the recovery time is often reported to be longer than response 8

time[34,35]. The impact of relative humidity (RH) on VOC sensing by the In2O3 based sensors has been investigated. Figure 6(c) shows the variation of ethanol sensing with the increase in RH% for both pure and N-In2O3 samples. While the pure In2O3 sensor suffers ~20% drop in the sensing response by changing the RH from 10-80%, the N-In2O3 exhibits significantly stable response (reduction of only 4.5%). Ethanol sensing response of the NIn2O3 film has been investigated over a longer time. As shown in figure 4(d) excellent base line recovery together with negligible change in the sensor response has been achieved over a

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duration of one month. In order to understand the superior gas sensing characteristics of N-In2O3 thin films let us first consider the mechanism of VOC sensing by In2O3. Figures 6(a-d) schematically

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represent the sensing mechanism for In2O3 (a,b) and N-In2O3 (c,d). Exposing In2O3 to air leads to the adsorption of aerial oxygen on its surface which captures electrons from the

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conduction band to form chemisorbed oxygen ions (figure 6(a)), such as O2−, O−and O− 2 [36].

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At the sensing temperature of 250 °C used in the present study, the oxygen species composed of O−and O− 2 are expected to dominate the redox reaction[36,37]. Ethanol molecules are

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oxidized by surface-adsorbed oxoanions, resulting in release of electrons into the conduction band of In2O3. As the chemisorbed oxygen leaves the sensor surface, free electrons carried by

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oxygen molecules are put back into the semiconductor, thereby increasing the surface

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conductivity (figure 6(b)). The sensing kinetics of ethanol can be described as follows: O2(gas)

O2(ads)

O2(ads) + e-

O2-(ads)

O2-(ads) + e-

2O-(ads)

2O-(ads) + e-

O2-(ads)

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C2H5OH + 6O2-(ads)

…(1)

2CO2 + 3H2O + 12e-

The improved ethanol sensing characteristics in case of N-In2O3 can be attributed to the effect of interstitial N on its electronic properties. Firstly, increase in VOs in N-In2O3 can lead to an enhancement in the dissociative adsorption of aerial oxygen on its surface. VOs have been argued to favour dissociative adsorption of oxygen also on ZnO surface[38]. Further, Sun et al. discussed that in case of N doping at the interstitial site of In2O3, the extra electron is shared between N and a lattice O atom creating a shoulder to shoulder  system of NO-

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species[33]. Similar to N-doped TiO2[31], interstitial N leads to impurity states in the band

gap of In2O3[33]. This lowers the resistivity of the N-In2O3 sample (not shown) and can aid

formation of the oxoanions[20], which leads to the superior sensing characteristics (figures 6(

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c) and (d)). In order to understand the slower recovery of N-In2O3 sample it is worth to

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mention that while response kinetics of SMO based gas sensor is related to the reaction of test gas with the chemisorbed oxygen on the sensor surface, recovery is related to the desorption

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of the reaction product. Dissociation of ethanol on SMO surfaces yields H2O and CO2 (eq. 1). N-sites on SMO surfaces has been reported to facilitate chemisorption of CO2 [39] which can

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retard the recovery process. The stable ethanol sensing response of N-In2O3 over a wide range of RH (10-80%) indicates preferential adsorption of oxygen molecules compared to the

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water molecules. This is possibly related to energetically favoured adsorption of O2 molecules on the N-sites which has been observed also in case of N-doped ZnO. Based on the

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SEM investigation (figure 2) we note that any predominant effect of thin film microstructure on the improved sensing response for N-In2O3 can be ruled out[39]. The sensors have been investigated for response and recovery resistance transients under different concentration of ethanol. Figure 7 (a) represents the concentration dependent (35 ppm -300 ppm) response-recovery characteristics of the N-In2O3 sensor operated at 250 °C. N-In2O3 exhibited significantly high response (~ 82.5 %) at lowest concentration of 35 ppm, 10

which is much superior to pure In2O3 sensor (~63 % at 35 ppm). The response, S, depends on concentration, C, according to the equation, S = βCn

(2)

Where n is the sensitivity and β is sensitivity coefficient which depends on activation energy for transduction process and operating temperature[34,40]. For In2O3 and N- In2O3 thin films n has been estimated to be ~0.08 and ~0.075 respectively (not shown), which indicates that

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higher response of N-In2O3 results from the facile transduction due to improved receptor function of the sensor as discussed before[41]. Figure 7(b) compares the sensing response of N- In2O3 sample towards ethanol, acetone and methanol at a fixed concentration of 300 ppm. The response % towards ethanol (~99.7%) is found to be superior as compared to acetone

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(~78%) and methanol (~66%) sensing, however, the sensing element is not selective to

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ethanol sensing. A detailed understanding of this phenomenon is lacking and further investigation is underway. We also report here the ethanol sensing characteristics of the N-

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In2O3 film under the interference of methanol and acetone. Figure 7.c shows the resistance transients of N- In2O3 thin film sensor in presence of 100 ppm acetone, 100 ppm ethanol and

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100 ppm methanol, 100 ppm ethanol and 100 ppm acetone mixture, 100 ppm ethanol and 100 ppm methanol mixture, 100 ppm acetone and 100 ppm methanol mixture and finally a

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mixture of 100 ppm ethanol, 100 ppm acetone and 100 ppm methanol measured at 250 °C. As shown in the figure pure acetone (∼57 %) and methanol (∼49 %) exhibits lower response

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as compared to pure ethanol (∼89 %). Although the sensor is not completely selective to ethanol, in mixed gas environment the sensor response was found to be intact as in case to pure ethanol ambience. This clearly indicates that N- In2O3 is capable of detecting ethanol under the interference of methanol and acetone. Table 1 compares ethanol sensing characteristics (e.g. response, operating temperature, response and recovery time, test gas concentration) of the present N-In2O3 sensor with those reported for different other SMO thin 11

film-based sensors reported earlier. Inspecting the table, it is clear that ethanol sensing characteristics of N-In2O3 thin film is superior compared to many of the routinely investigated conventional oxide based sensors. 5. Conclusion Pure and nitrogen incorporated In2O3 thin films have been fabricated on SiO2/Si substrates by spin coating of sols synthesized via wet chemical route. The phase formation and evolution of

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microstructure in the fabricated films have been investigated using x-ray diffraction pattern and scanning electron microscopy. The samples have been found to be crystalline and

mesoporous in nature. Nitrogen doping at the interstitial position was confirmed via detailed chemical analysis using x-ray photoelectron spectroscopy. Interstitial nitrogen incorporation

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in In2O3 gives rise enhanced oxygen vacancies and leads to the formation of gap states owing

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to NO- species which facilitate the formation of oxoanions on the surface of the oxide. Ethanol sensing response of the thin films was measured by varying their operating

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temperature (150°C to 300°C) and concentration of ethanol gas (35 to 500ppm). N-In2O3 exhibited superior response compared to pure In2O3. A significantly large response (~99.7%)

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and rapid sensing (~ 1 s) at a moderate operating temperature of ~250 °C could be realised. The sensor was able to efficiently detect ethanol over a large range of concentration between

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35-500 ppm. Ethanol sensing characteristics of N-In2O3 thin film have been found to be superior in comparison to different conventional oxide thin film based sensors reported in the

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recent past. The superior sensing characteristics of N-In2O3 has been attributed to the improved receptor function owing to nitrogen doping.

Declaration of interests

The authors declare no conflict of interest 12

Acknowledgement The authors acknowledge partial support from SERB, Govt. of India vide letter ECR/2017/000498 dated 20-03-2018 for executing this research. The authors acknowledge Prof. Subhasish Basu Majumder, Materials Science Centre, for extending experimental facilities pertinent to gas sensing measurements. The authors acknowledge SEM facility

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under DST-FIST program at Materials Science Centre, the pulsed EPR facility, CRF, IIT

Kharagpur. PKS acknowledges Mr. V. Ambardekar, and Ms T. Bhowmick for help with the

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sensing experiments.

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Reference [1]

A. Schütze, T. Baur, M. Leidinger, W. Reimringer, R. Jung, T. Conrad, T. Sauerwald, Highly Sensitive and Selective VOC Sensor Systems Based on Semiconductor Gas Sensors: How to?, Environments. 4 (2017) 20. doi:10.3390/environments4010020.

[2]

T. Arakawa, X. Wang, T. Kajiro, K. Miyajima, S. Takeuchi, H. Kudo, K. Yano, K. Mitsubayashi, A direct gaseous ethanol imaging system for analysis of alcohol

ro of

metabolism from exhaled breath, Sensors Actuators, B Chem. 186 (2013) 27–33. doi:10.1016/j.snb.2013.05.071. [3]

J. Park, H. Yee, K.S. Lee, W. Lee, M. Shin, T. Kim, S. Kim, Determination of breath

-p

alcohol using a differential-type amperometric biosensor based on alcohol dehydrogenase, 390 (1999) 83–91.

F. Qu, W. Shang, T. Thomas, S. Ruan, M. Yang, Sensors and Actuators B : Chemical

re

[4]

lP

Self-template derived ZnFe2O4 double-shell microspheres for chemresistive gas sensing, Sensors Actuators B. Chem. 265 (2018) 625–631.

[5]

na

doi:10.1016/j.snb.2018.03.108.

S. Zhang, M. Yang, K. Liang, A. Turak, B. Zhang, D. Meng, Sensors and Actuators

ur

B : Chemical An acetone gas sensor based on nanosized Pt-loaded Fe2O3 nanocubes, Sensors Actuators B. Chem. 290 (2019) 59–67. doi:10.1016/j.snb.2019.03.082. F. Qu, W. Shang, D. Wang, S. Du, T. Thomas, S. Ruan, M. Yang, Coordination

Jo

[6]

Polymer-Derived Multishelled Mixed Ni − Co Oxide Microspheres for Robust and Selective Detection of Xylene, (2018). doi:10.1021/acsami.8b03487.

[7]

S. Choi, F. Fuchs, R. Demadrille, B. Gre, B. Jang, S. Lee, J. Lee, H.L. Tuller, I. Kim, Fast Responding Exhaled-Breath Sensors Using WO3 Hemitubes Functionalized by

14

Graphene-Based Electronic Sensitizers for Diagnosis of Diseases, (2014). doi:10.1021/am501394r. [8]

K. Inyawilert, A. Wisitsora-At, A. Tuantranont, P. Singjai, S. Phanichphant, C. Liewhiran, Ultra-rapid VOCs sensors based on sparked-In2O3 sensing films, Sensors Actuators, B Chem. 192 (2014) 745–754. doi:10.1016/j.snb.2013.11.064.

[9]

A. Jayalatha, V. Elavalagan, P. Shankar, Nanostructured Cerium-doped ZnO thin fi lm

doi:10.1016/j.ceramint.2016.08.156.

ro of

– A breath sensor, Ceram. Int. 42 (2016) 18289–18295.

[10] A. Gurlo, M. Ivanovskaya, N. Ba, Grain size control in nanocrystalline In2O3

-p

semiconductor gas sensors, 44 (1997) 327–333.

[11] M. Seetha, S. Bharathi, D. Mangalaraj, D. Nataraj, Reducing gas response kinetics of

lP

doi:10.1016/j.tsf.2010.03.105.

re

nanostructured indium oxide thin films, Thin Solid Films. 518 (2010) e125–e128.

[12] Z. Zhan, J. Lu, W. Song, D. Jiang, J. Xu, Highly selective ethanol In2O3 -based gas

na

sensor, 42 (2007) 228–235. doi:10.1016/j.materresbull.2006.06.006. [13] K.K. Makhija, A. Ray, R.M. Patel, U.B. Trivedi, H.N. Kapse, Indium oxide thin film

ur

based ammonia gas and ethanol vapour sensor, Bull. Mater. Sci. 28 (2005) 9–17.

Jo

doi:10.1007/BF02711165. [14] H. Yang, S. Wang, Y. Yang, Zn-doped In2O3 nanostructures: preparation, structure and gas-sensing properties, CrystEngComm. 14 (2012) 1135–1142. doi:10.1039/C1CE06143G. [15] S. Park, S. Kim, G. Sun, C. Lee, Synthesis , Structure , and Ethanol Gas Sensing Properties of In2O3 Nanorods Decorated with Bi2O3 Nanoparticles, (2015). 15

doi:10.1021/acsami.5b00972. [16] J.M. Chem, High-aspect-ratio single-crystalline porous In2O3 nanobelts with enhanced gas sensing properties, (2011) 12852–12857. doi:10.1039/c1jm11356a. [17] B.A. Prim, E. Pellicer, E. Rossinyol, F. Peiró, A. Cornet, J.R. Morante, A Novel Mesoporous CaO-Loaded In2O3 Material for CO2 Sensing , (2007) 2957–2963. doi:10.1002/adfm.200601072.

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[18] M. Gholami, A.A. Khodadadi, A. Anaraki Firooz, Y. Mortazavi, In2O3-ZnO nanocomposites: High sensor response and selectivity to ethanol, Sensors Actuators, B Chem. 212 (2015) 395–403. doi:10.1016/j.snb.2015.02.030.

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[19] X. Liu, L. Jiang, X. Jiang, X. Tian, X. Sun, Y. Wang, W. He, P. Hou, X. Deng, X. Xu, Applied Surface Science Synthesis of Ce-doped In2O3 nanostructure for gas sensor

re

applications, Appl. Surf. Sci. 428 (2018) 478–484. doi:10.1016/j.apsusc.2017.09.177.

lP

[20] L. Gai, L. Ma, H. Jiang, Y. Ma, Y. Tian, H. Liu, Nitrogen-doped In2O3 nanocrystals constituting hierarchical structures with enhanced gas-sensing properties,

na

CrystEngComm. 14 (2012) 7479–7486. doi:10.1039/c2ce25789k. [21] L. Ma, H. Fan, H. Tian, J. Fang, X. Qian, The n-ZnO/n- In2O3 heterojunction formed

ur

by a surface-modification and their potential barrier-control in methanal gas sensing,

Jo

Sensors Actuators, B Chem. 222 (2016) 508–516. doi:10.1016/j.snb.2015.08.085. [22] A. Ghosh, A. Maity, R. Banerjee, S.B. Majumder, Volatile organic compound sensing using copper oxide thin films: Addressing the cross sensitivity issue, J. Alloys Compd. 692 (2017) 108–118. doi:10.1016/j.jallcom.2016.09.001. [23] K.R. Reyes-Gil, E.A. Reyes-García, D. Raftery, Nitrogen-Doped In2O3 Thin Film Electrodes for Photocatalytic Water Splitting, J. Phys. Chem. C. 111 (2007) 14579– 16

14588. doi:10.1021/jp072831y. [24] K.R. Reyes-Gil, Y. Sun, E. Reyes-Garća, D. Raftery, Characterization of photoactive centers in n-doped In2O3 visible photocatalysts for water oxidation, J. Phys. Chem. C. 113 (2009) 12558–12570. doi:10.1021/jp902454b. [25]

Reaction of NO2 with Zn and ZnO Photoemission, XANES, and Density Functional Studies on the Formation of NO3, J. Phys. Chem. B. 104 (2000) 319-328. Characterization of Indium−Tin Oxide Interfaces Using X-ray Photoelectron

ro of

[26]

Spectroscopy and Redox Processes of a Chemisorbed Probe Molecule Effect of Surface pretreatment conditions, Langmuir.18 (2002) 450-457.

-p

[27] N. Lu, C. Shao, X. Li, F. Miao, K. Wang, Y. Liu, A facile fabrication of nitrogen-

doped electrospun In2O3 nanofibers with improved visible-light photocatalytic activity,

re

Appl. Surf. Sci. 391 (2017) 668–676. doi:10.1016/j.apsusc.2016.07.057.

lP

[28] J.H. Kim, Y.J. Jang, J.H. Kim, J. Jang, S.H. Choi, J.S. Lee, Nanoscale for photoelectrochemical water splitting †, (2015) 19144–19151. doi:10.1039/c5nr05812k.

na

[29] X. Wang, X. Wang, Q. Di, H. Zhao, B. Liang, J. Yang, Mutual Effects of Fluorine Dopant and Oxygen Vacancies on Structural and Luminescence Characteristics of F

ur

Doped SnO2 Nanoparticles, (2017). doi:10.3390/ma10121398.

Jo

[30] L.B. Hoch, T.E. Wood, P.G.O. Brien, K. Liao, L.M. Reyes, C.A. Mims, G.A. Ozin, The Rational Design of a Single-Component Photocatalyst for Gas-Phase CO2 Reduction Using Both UV and Visible Light, 2 (2014) 1–10. doi:10.1002/advs.201400013. [31] C.W. Dunnill, I.P. Parkin, I. Parkin, Nitrogen-doped TiO2 thin films : photocatalytic applications for healthcare environments, (2011) 1635–1640. doi:10.1039/c0dt00494d. 17

[32] C. Di Valentin, G. Pacchioni, A. Selloni, S. Livraghi, V.R. Cozzi, Characterization of Paramagnetic Species in N-Doped TiO2 Powders by EPR Spectroscopy and DFT Calculations, (2005) 11414–11419. doi:10.1021/jp051756t. [33] H. Sun, W. Fan, Y. Li, X. Cheng, P. Li, X. Zhao, Origin of the Visible Photocatalytic Activity of N-Doped In2O3 :A Quantum Mechanical Study, J. phy chem. 114 (2010) 3026–3036.

ro of

[34] V. Ambardekar, P.P. Bandyopadhyay, S.B. Majumder, Atmospheric plasma sprayed SnO2 coating for ethanol detection, J. Alloys Compd. 752 (2018) 440–447. doi:10.1016/j.jallcom.2018.04.151.

-p

[35] I. Hwang, E. Lee, S. Kim, J. Choi, J. Cha, H. Lee, B. Ju, J. Lee, Sensors and Actuators

re

B : Chemical Gas sensing properties of SnO2 nanowires on micro-heater, Sensors Actuators B. Chem. 154 (2011) 295–300. doi:10.1016/j.snb.2009.11.012.

lP

[36] H. Dong, Y. Liu, G. Li, X. Wang, D. Xu, Z. Chen, T. Zhang, J. Wang, L. Zhang, Sensors and Actuators B : Chemical Hierarchically rosette-like In2O3 microspheres for

na

volatile organic compounds gas sensors, Sensors Actuators B. Chem. 178 (2013) 302– 309. doi:10.1016/j.snb.2012.12.103.

ur

[37] K. Inyawilert, A. Wisitsora-at, A. Tuantranont, P. Singjai, Sensors and Actuators B :

Jo

Chemical Ultra-rapid VOCs sensors based on sparked- In2O3 sensing films, Sensors Actuators B. Chem. 192 (2014) 745–754. doi:10.1016/j.snb.2013.11.064.

[38] Y. Yan, S. Wei, Oxygen-vacancy mediated adsorption and reactions of molecular oxygen on the ZnO „ 101, (2005) 1–4. doi:10.1103/PhysRevB.72.161307. [39] N. Tit, W. Othman, A. Shaheen, M. Ali, Sensors and Actuators B : Chemical High selectivity of N-doped ZnO nano-ribbons in detecting H2 , O2 and CO2 molecules : 18

Effect of negative-differential resistance on, 270 (2018) 167–178. [40] A. Ghosh, S.B. Majumder, Modeling the sensing characteristics of chemi-resistive thin film semi-conducting gas sensors, Phys. Chem. Chem. Phys. 19 (2017) 23431–23443. doi:10.1039/c7cp04241h. [41] G. Korotcenkov, B.K. Cho, Metal oxide composites in conductometric gas sensors: Achievements and challenges, Sensors Actuators, B Chem. 244 (2017) 182–210.

ro of

doi:10.1016/j.snb.2016.12.117. [42] W. Wen, J.M. Wu, Y. De Wang, Gas-sensing property of a nitrogen-doped zinc oxide fabricated by combustion synthesis, Sensors Actuators, B Chem. 184 (2013) 78–84.

-p

doi:10.1016/j.snb.2013.04.052.

[43] Z. Wang, Z. Tian, D. Han, F. Gu, Highly Sensitive and Selective Ethanol Sensor

lP

5474. doi:10.1021/acsami.6b00339.

re

Fabricated with In-Doped 3DOM ZnO, ACS Appl. Mater. Interfaces. 8 (2016) 5466–

[44] Q. Wang, X. Kou, C. Liu, L. Zhao, T. Lin, F. Liu, X. Yang, J. Lin, G. Lu,

na

Hydrothermal synthesis of hierarchical CoO/SnO2 nanostructures for ethanol gas sensor, J. Colloid Interface Sci. 513 (2018) 760–766. doi:10.1016/j.jcis.2017.11.073.

ur

[45] K. Inyawilert, A. Wisitsoraat, C. Sriprachaubwong, A. Tuantranont, S. Phanichphant, C. Liewhiran, Rapid ethanol sensor based on electrolytically-exfoliated graphene-

Jo

loaded flame-made In-doped SnO2 composite film, Sensors Actuators, B Chem. 209 (2015) 40–55. doi:10.1016/j.snb.2014.11.086.

[46] G. Singh, N. Kohli, R.C. Singh, Sensitive and selective ethanol sensor based on Zndoped SnO2 nanostructures, J. Mater. Sci. Mater. Electron. 28 (2017) 13013–13023. doi:10.1007/s10854-017-7133-x.

19

[47] L. Yu, F. Guo, Z. Liu, S. Liu, B. Yang, M. Yin, X. Fan, Materials Characterization Facile synthesis of three dimensional porous ZnO films with mesoporous walls and gas sensing properties, Mater. Charact. 112 (2016) 224–228. doi:10.1016/j.matchar.2015.12.029. [48] C. Feng, X. Kou, B. Chen, G. Qian, Y. Sun, G. Lu, Sensors and Actuators B : Chemical One-pot synthesis of In doped NiO nanofibers and their gas sensing properties, Sensors Actuators B. Chem. 253 (2017) 584–591.

Jo

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doi:10.1016/j.snb.2017.06.115.

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P K Shihabudeen received his master degree (MTech) in nanoscience and technology from National Institute of Technology Calicut, India in 2014. Currently, He is pursuing Ph.D. in the Materials Science Centre, Indian Institute of Technology, Kharagpur, India.. His research interests are related to the semiconducting metal oxide based sensors.

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Ayan Roy Chaudhuri obtained Ph. D degree in materials science from Indian Institute of Science, Bangalore, India. He is an Assistant Professor at the Materials Science Centre, Indian Institute of Technology, Kharagpur, India. His current research interests include fabrication and investigation of structure property correlation in heterostructures of functional materials for nanoelectronic, optoelectronic, sensing and energy applications.

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List of Figures

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1. Figure 1.a) device structure and b) equivalent circuit of sensor device.

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2. Figure 2. X-ray diffractogram of pure and N-In2O3 thin films.

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3. Figure 3. Surface morphology of a) N-In2O3 thin film and b) pure In2O3 thin film.

4. Figure 4. High resolution XPS spectrum of a) N 1s, b) In 3d c) O 1s and d) EPR

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spectrum of In2O3 and N-In2O3 thin films.

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5. Figure 5.a) Ethanol sensing response of pure and nitrogen doped In2O3 thin films at 300 ppm concentration and various temperature b) Response transient of In2O3 and NIn2O3 thin films, c) humidity dependent response of the thin films and d) long term

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stability transient of N- In2O3 thin film. Lines are to guide the eyes.

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6. Figure 6. gas sensing mechanism of a) & b) In2O3 and c) & d) N- In2O3 thin film.

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7. Figure 7. a) Concentration variation profile of N-In2O3 thin film at 250 °C b) response of N-In2O3 thin film for various VOCs with concentration of 300 ppm and c) Sensing

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characteristics of N-In2O3 thin film in mixed VOC conditions with concentration of 100 ppm at 250 °C.

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Table 1. Comparison of ethanol sensing characteristics of different metal oxide semiconductors. Sensing Material

No

1

Nitrogen doped

Working

Concent-

Response

Response

Recovery

Temperature

ration

(%)

Ra/Rg

time(s)

time(s)

Ref

(°C)

(ppm)

485

300

-

90

N/A

N/A

[42]

250

100

-

88

250

100

-

140

300

1000

ZnO 2

In-doped 3DOM

N/A

N/A

[43]

2-3

N/A

[44]

80

1.8

N/A

[45]

CoO/SnO2

4

In-doped SnO2

5

RuO2/NaBi(MoO4)4

340

285

7

In-doped NiO

300

nanofibers

SnO2 film coating

300

WO3-SnO2 9

composite film

10

N-In2O3 thin film

96

-

10

10

[46]

200

-

36.6

N/A

N/A

[47]

6

273

26

[48]

200

-

300

82

-

8

340

[34]

250

300

72

-

10

312

[42]

250

300

99.7

313

1

480

This

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8

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Porous ZnO films

100

na

nanosheets 6

-

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composite film

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nanostructures

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ZnO 3

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work

30

31

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