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Structural Stability and Performance of Noble Metal-Free SnO2-Based Gas Sensors.

Tricoli A - Biosensors (Basel) (2012)

Bottom Line: The effect of crystal growth during operation (TO = 320 °C) on the sensor response to ethanol has been reported, revealing possible long-term destabilization mechanisms.In particular, crystal growth and sintering-neck formation were discussed with respect to their potential to change the sensor response and calibration.Furthermore, the effect of SiO2 cosynthesis on the cross-sensitivity to humidity of these noble metal-free SnO2-based gas sensors was assessed.

View Article: PubMed Central - PubMed

Affiliation: Department of Mechanical and Process Engineering, ETH Zurich, CH-8092 Zurich, Switzerland. atricoli@ethz.ch.

ABSTRACT
The structural stability of pure SnO2 nanoparticles and highly sensitive SnO2-SiO2 nanocomposites (0-15 SiO2 wt%) has been investigated for conditions relevant to their utilization as chemoresistive gas sensors. Thermal stabilization by SiO2 co-synthesis has been investigated at up to 600 °C determining regimes of crystal size stability as a function of SiO2-content. For operation up to 400 °C, thermally stable crystal sizes of ca. 24 and 11 nm were identified for SnO2 nanoparticles and 1.4 wt% SnO2-SiO2 nanocomposites, respectively. The effect of crystal growth during operation (TO = 320 °C) on the sensor response to ethanol has been reported, revealing possible long-term destabilization mechanisms. In particular, crystal growth and sintering-neck formation were discussed with respect to their potential to change the sensor response and calibration. Furthermore, the effect of SiO2 cosynthesis on the cross-sensitivity to humidity of these noble metal-free SnO2-based gas sensors was assessed.

No MeSH data available.


Response of a gas sensor made of small SnO2 nanocrystals to ethanol after a 12 h sintering step at 600 °C.
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biosensors-02-00221-f006: Response of a gas sensor made of small SnO2 nanocrystals to ethanol after a 12 h sintering step at 600 °C.

Mentions: Figure 6 shows the response to increasing EtOH concentrations of a SnO2 sensor made of small nanoparticles that was sintered at 600 °C for 12 h prior to gas sensing. The sensor shows (Figure 6) similar response and recovery time to that having an as prepared SnO2 nanoparticle film (Figure 5). This is in agreement with the identical surface composition and film thickness of the as prepared and sintered SnO2 films. However, the magnitude of the sensor response was drastically increased with respect to the latter. In particular, the sintered sensor (Figure 6) had a response of nearly 17 to 10 ppm of EtOH while the as prepared barely reached 8. This is surprising as high temperature sintering is expected to increase crystal size leading to lower sensitivity [3,5]. Here, it is suggested that the enhancement of the sensor response arise from the formation of sintering necks with size below that of the main grains between the SnO2 particles. Formation of partially or fully depleted sintering necks can increase the sensitivity of metal-oxide gas sensors and can hardly be measured by XRD or nitrogen adsorption [7]. As a result, two instability mechanisms are suggested for the pure SnO2 nanoparticles. A first, where the average crystal (and grain) size is increased (Figure 4) resulting in a drop of the sensor response, and a second, where partially depleted sintering necks are formed increasing the sensitivity. Similar effects were observed for size selected SnO2 agglomerates [21]. There, very small changes in the sintering properties of the agglomerates that could hardly be tracked by XRD analysis led to drastic variations in their sensing response to EtOH. Both dynamics can be accelerated by a pre-sintering step leading to (Figure 6) higher response and more stable sensing properties.


Structural Stability and Performance of Noble Metal-Free SnO2-Based Gas Sensors.

Tricoli A - Biosensors (Basel) (2012)

Response of a gas sensor made of small SnO2 nanocrystals to ethanol after a 12 h sintering step at 600 °C.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4263576&req=5

biosensors-02-00221-f006: Response of a gas sensor made of small SnO2 nanocrystals to ethanol after a 12 h sintering step at 600 °C.
Mentions: Figure 6 shows the response to increasing EtOH concentrations of a SnO2 sensor made of small nanoparticles that was sintered at 600 °C for 12 h prior to gas sensing. The sensor shows (Figure 6) similar response and recovery time to that having an as prepared SnO2 nanoparticle film (Figure 5). This is in agreement with the identical surface composition and film thickness of the as prepared and sintered SnO2 films. However, the magnitude of the sensor response was drastically increased with respect to the latter. In particular, the sintered sensor (Figure 6) had a response of nearly 17 to 10 ppm of EtOH while the as prepared barely reached 8. This is surprising as high temperature sintering is expected to increase crystal size leading to lower sensitivity [3,5]. Here, it is suggested that the enhancement of the sensor response arise from the formation of sintering necks with size below that of the main grains between the SnO2 particles. Formation of partially or fully depleted sintering necks can increase the sensitivity of metal-oxide gas sensors and can hardly be measured by XRD or nitrogen adsorption [7]. As a result, two instability mechanisms are suggested for the pure SnO2 nanoparticles. A first, where the average crystal (and grain) size is increased (Figure 4) resulting in a drop of the sensor response, and a second, where partially depleted sintering necks are formed increasing the sensitivity. Similar effects were observed for size selected SnO2 agglomerates [21]. There, very small changes in the sintering properties of the agglomerates that could hardly be tracked by XRD analysis led to drastic variations in their sensing response to EtOH. Both dynamics can be accelerated by a pre-sintering step leading to (Figure 6) higher response and more stable sensing properties.

Bottom Line: The effect of crystal growth during operation (TO = 320 °C) on the sensor response to ethanol has been reported, revealing possible long-term destabilization mechanisms.In particular, crystal growth and sintering-neck formation were discussed with respect to their potential to change the sensor response and calibration.Furthermore, the effect of SiO2 cosynthesis on the cross-sensitivity to humidity of these noble metal-free SnO2-based gas sensors was assessed.

View Article: PubMed Central - PubMed

Affiliation: Department of Mechanical and Process Engineering, ETH Zurich, CH-8092 Zurich, Switzerland. atricoli@ethz.ch.

ABSTRACT
The structural stability of pure SnO2 nanoparticles and highly sensitive SnO2-SiO2 nanocomposites (0-15 SiO2 wt%) has been investigated for conditions relevant to their utilization as chemoresistive gas sensors. Thermal stabilization by SiO2 co-synthesis has been investigated at up to 600 °C determining regimes of crystal size stability as a function of SiO2-content. For operation up to 400 °C, thermally stable crystal sizes of ca. 24 and 11 nm were identified for SnO2 nanoparticles and 1.4 wt% SnO2-SiO2 nanocomposites, respectively. The effect of crystal growth during operation (TO = 320 °C) on the sensor response to ethanol has been reported, revealing possible long-term destabilization mechanisms. In particular, crystal growth and sintering-neck formation were discussed with respect to their potential to change the sensor response and calibration. Furthermore, the effect of SiO2 cosynthesis on the cross-sensitivity to humidity of these noble metal-free SnO2-based gas sensors was assessed.

No MeSH data available.