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Influence of Thickness on Ethanol Sensing Characteristics of Doctor-bladed Thick Film from Flame-made ZnO Nanoparticles

View Article: PubMed Central

ABSTRACT

ZnO nanoparticles were produced by flame spray pyrolysis (FSP) using zinc naphthenate as a precursor dissolved in toluene/acetonitrile (80/20 vol%). The particle properties were analyzed by XRD, BET, and HR-TEM. The sensing films were produced by mixing the particles into an organic paste composed of terpineol and ethyl cellulose as a vehicle binder and were fabricated by doctor-blade technique with various thicknesses (5, 10, 15 μm). The morphology of the sensing films was analyzed by SEM and EDS analyses. The gas sensing characteristics to ethanol (25-250 ppm) were evaluated as a function of film thickness at 400°C in dry air. The relationship between thickness and ethanol sensing characteristics of ZnO thick film on Al2O3 substrate interdigitated with Au electrodes were investigated. The effects of film thickness, as well as the cracking phenomenon, though, many cracks were observed for thicker sensing films. Crack widths increased with increasing film thickness. The film thickness, cracking and ethanol concentration have significant effect on the sensing characteristics. The sensing characteristics with various thicknesses were compared, showing the tendency of the sensitivity to ethanol decreased with increasing film thickness and response time. The relationship between gas sensing properties and film thickness was discussed on the basis of diffusively and reactivity of the gases inside the oxide films. The thinnest sensing film (5 μm) showed the highest sensitivity and the fastest response time (within seconds).

No MeSH data available.


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Schematic of the sensing mechanism of semiconducting material doctor-bladed on Al2O3 substrate interdigitated with Au electrodes with the analyte gas exposure
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f3-sensors-07-00185: Schematic of the sensing mechanism of semiconducting material doctor-bladed on Al2O3 substrate interdigitated with Au electrodes with the analyte gas exposure

Mentions: The sensor samples to be measure were placed in the center of quartz tube (3 cm diameter and 60 cm length). The tube was put in a tubular oven (Nabertherm Controller P320, Germany). Gold wires were soldered to the sensor Au electrodes externally connected with a digital multimeter (KEITHLEY model 2700 DMM, Germany) to record the sensor resistance. The sensors were tested for ethanol vapor at the operating temperature of 400°C. The sensors were certainly exposed to ethanol vapor at various concentrations ranging from 25-250 ppm. A total gas flow rate of 2 l/min was passed through the quartz tube and controlled by mass flow controllers (Bronkhorst HITEC, Germany). By monitoring the output voltage across the sensor, as the operating temperature increased up to 400°C, the resistances of the sensor in dry air and in test gas were alternately increased and decreased, which can be measured. The sensing mechanism of material was shown in Fig. 3. The analyte ethanol gas adsorbs on the ZnO sensing layer and causes a change in resistance depending on the gas concentration. This is monitored by a digital multimeter connected to the sensor substrate with Au wires. The corresponding resistance and time showed the sensing characteristics in terms of sensitivity, response, and recovery time. The sensitivity, S is defined as the ratio Ra/Rg, where Ra is the resistance in dry air, and Rg is the resistance in test gas. The response time, Tres is defined as the time required until 90 % of the response signal is reached. The recovery times, Trec denotes the time needed until 90 % of the original baseline signal is recovered. After annealing and sensing test of sensor fabricated using samples P0 with controlled a various film thicknesses of 5, 10, and 15 μm, they were designated as S1, S2, and S3, respectively. Finally, the film thickness sensing layers were analyzed by SEM and EDS analyses.


Influence of Thickness on Ethanol Sensing Characteristics of Doctor-bladed Thick Film from Flame-made ZnO Nanoparticles
Schematic of the sensing mechanism of semiconducting material doctor-bladed on Al2O3 substrate interdigitated with Au electrodes with the analyte gas exposure
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3756700&req=5

f3-sensors-07-00185: Schematic of the sensing mechanism of semiconducting material doctor-bladed on Al2O3 substrate interdigitated with Au electrodes with the analyte gas exposure
Mentions: The sensor samples to be measure were placed in the center of quartz tube (3 cm diameter and 60 cm length). The tube was put in a tubular oven (Nabertherm Controller P320, Germany). Gold wires were soldered to the sensor Au electrodes externally connected with a digital multimeter (KEITHLEY model 2700 DMM, Germany) to record the sensor resistance. The sensors were tested for ethanol vapor at the operating temperature of 400°C. The sensors were certainly exposed to ethanol vapor at various concentrations ranging from 25-250 ppm. A total gas flow rate of 2 l/min was passed through the quartz tube and controlled by mass flow controllers (Bronkhorst HITEC, Germany). By monitoring the output voltage across the sensor, as the operating temperature increased up to 400°C, the resistances of the sensor in dry air and in test gas were alternately increased and decreased, which can be measured. The sensing mechanism of material was shown in Fig. 3. The analyte ethanol gas adsorbs on the ZnO sensing layer and causes a change in resistance depending on the gas concentration. This is monitored by a digital multimeter connected to the sensor substrate with Au wires. The corresponding resistance and time showed the sensing characteristics in terms of sensitivity, response, and recovery time. The sensitivity, S is defined as the ratio Ra/Rg, where Ra is the resistance in dry air, and Rg is the resistance in test gas. The response time, Tres is defined as the time required until 90 % of the response signal is reached. The recovery times, Trec denotes the time needed until 90 % of the original baseline signal is recovered. After annealing and sensing test of sensor fabricated using samples P0 with controlled a various film thicknesses of 5, 10, and 15 μm, they were designated as S1, S2, and S3, respectively. Finally, the film thickness sensing layers were analyzed by SEM and EDS analyses.

View Article: PubMed Central

ABSTRACT

ZnO nanoparticles were produced by flame spray pyrolysis (FSP) using zinc naphthenate as a precursor dissolved in toluene/acetonitrile (80/20 vol%). The particle properties were analyzed by XRD, BET, and HR-TEM. The sensing films were produced by mixing the particles into an organic paste composed of terpineol and ethyl cellulose as a vehicle binder and were fabricated by doctor-blade technique with various thicknesses (5, 10, 15 μm). The morphology of the sensing films was analyzed by SEM and EDS analyses. The gas sensing characteristics to ethanol (25-250 ppm) were evaluated as a function of film thickness at 400°C in dry air. The relationship between thickness and ethanol sensing characteristics of ZnO thick film on Al2O3 substrate interdigitated with Au electrodes were investigated. The effects of film thickness, as well as the cracking phenomenon, though, many cracks were observed for thicker sensing films. Crack widths increased with increasing film thickness. The film thickness, cracking and ethanol concentration have significant effect on the sensing characteristics. The sensing characteristics with various thicknesses were compared, showing the tendency of the sensitivity to ethanol decreased with increasing film thickness and response time. The relationship between gas sensing properties and film thickness was discussed on the basis of diffusively and reactivity of the gases inside the oxide films. The thinnest sensing film (5 μm) showed the highest sensitivity and the fastest response time (within seconds).

No MeSH data available.


Related in: MedlinePlus