Response and recovery times

Comparing the two optical transduction techniques (absorption or SPR) used in this work, we can conclude that SPR technique appears to be more suitable for gas sensing even if it presents some limitation regarding the suitable film thickness for SPR excitation. Moreover, the response and recovery times during the anal5fle/sensing layer interaction appears shortest in the case of optical absorption measurements. Further investigations are in... 

Response and recovery times of NO sensors are extremely important for their use in vivo. Theoretically, since the rate of mass transport at a microelectrode is very... 

Response and Recovery Times. Figure 11A gives AVpg for a Pd/Si02/... 

As may be seen from Table I, the response times in hydrogen exposures of capacitor structures tend to be comparable to those of diode structures however, the capacitor structures can be susceptible to the HID phenomenon (16) especially at elevated temperatures. In general, the presence of water vapor or oxygen reduces the response and recovery times of both device classes. There are differences in gas sensing ability between the two structures. For example,. the Pd/TiOx/Si and Pd/SiOx/Si diodes do not respond to CO in... 

The response and recovery time of the sensor are < 30 s. Mixed films containing BDN and stearyl alcohol are electrically conducting and derived chemiresistor sensors were fabricated by depositing layers of this material onto interdigital electrodes. When exposed to NH3 or ppb levels of hydrazine,... 

Improvement of the geometric structure of the working electrode by a well-controlled PEVD process benefits the performance of a CO sensor in many ways. To optimize kinetic behavior, the response and recovery times of CO potentiometric sensors were studied at various auxiliary phase coverages. This was realized by a unique experimental arrangement to deposit the Na COj auxiliary phase in-situ at the working electrode of type III potentiometric CO sensors by PEVD in a step-wise fashion. Since the current and flux of solid-state transported material in a series of PEVD processes can be easily moiutoredto control the amount of deposit... 

For sample 1, a stable EMF response from the sensor was obtained after passing about 0.468 C of Na ions. According to the previous discussion, this corresponds to the point where the PEVD auxiliary phase just covers the entire Pt thick film surface. The response times and recovery times of the sensor after each PEVD process step are recorded. Both response and recovery times are plotted against the Na ion flux through the solid electrolyte during the PEVD process in Figure 23. Curve (1) is the response time and curve (2) is the recovery time. 

The response and recovery times of both samples at each PEVD step are compared at a working electrode flow rate of 40 seem in Figures 25a and b, respectively. Because of the inability to fabricate a consistent Pt thick film at the working electrode of both sensors, the response and recovery curves do not exactly match. However, the curves from both samples follow the same trends. Taking into account the geometric factor for both samples, the results from this study can be considered to be fairly consistent. 

Both the response and recovery times first drop dramatically with increasing auxiliary phase thickness, reach a minimum point, and then increase steadily with increasing auxiliary... 

The results indicate that sensor response behavior is not only related to the thickness of the auxiliary phase, but is also controlled by other working electrode geometric factors - most likely the aspect ratio of the working electrode surface. Because of the high aspect ratio, the response and recovery times of the sensor are... 

Fig. 26 Response and recovery times vs. the thickness of the auxiliary phase.

Another advantage of ultrathin organic films is their fast response and recovery times because so little material is present. 

The sensitivity of these sensors was defined as a signal change upon exposure to the known concentrations of vapors. Sensitivity of the 2.8-nm CdSe nanocrystals was 0.8 PL counts/Torr of methanol with almost no detectable sensitivity to toluene. The sensitivity of the 5.6-nm CdSe nanocrystals was 2.9 PL counts/Torr of methanol and 8.8PL counts/Torr of toluene. Although this environmental sensitivity was compatible with earlier reported sensors based on polished or etched bulk CdSe semiconductor crystals3940 and polymer-nanocrystals composites,16 the sensor reported here had a more selective response to polar and nonpolar vapors due to the multiwavelength PL from different-size nanocrystals incorporated into the polymer film. The response and recovery kinetics of PL from the 2.8-nm nanocrystals in PMM A upon exposure to methanol were very fast (<0.5 min). However, 5.6-nm nanocrystals in the same sensor film exhibited a much longer response and recovery times upon interactions with methanol, 4 and 20min, respectively. The 5.6-nm nanocrystals had 4-min response and 0.5-min recovery times upon interactions with toluene. 

Knowing the most influential parameters of a specific biosensor architecture is the basis to understand and fine tune the performance of these devices in a rational manner. Figure 1.8 summarizes the key features of typical biosensors and lists several that are of additional importance for commercial devices. Among these, selectivity, sensitivity, accuracy, response, and recovery time as well as operating lifetime are some of the most important key factors. Keeping in mind the needs of the specific analytical task of interest, it seems to be necessary to characterize at least the key parameters mentioned in Figure 1.8 in order to specify the analytical performance of a biosensor design. 

Gas flows through the SE will be different ( ventilation effect) and will depend on how the oxide SE was applied on the surface of YSZ and how it was heat-treated and sintered afterwards. The vast majority of the modem technologies will allow creating a uniform thickness of SEs (REs). However, the stmctural orientation of an oxide SE and, especially, its surface and bulk porosity will change from one technology to another and from one sintering temperature to another [9]. This fact, in turn, will influence characteristics of the YSZ-based sensor, such as sensitivity, reproducibility of measurements, response and recovery time, and so on. Let s indicate both necessary and sufficient conditions of existence of such a ventilation effect within the SE. 

The addition of K2CO3 to a-Fe203 has a beneficial effect on the humidity sensing characteristics as shown in Figure 20-7. The resistance of this sensor decreased with an increase in operation temperature and the sensor became sensitive below 50% r.h. The response and recovery times of this sensor are about 10 and 20 s, respectively [14]. 

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