Bulk conductivities, chemical sensors

Chemical sensors for gas molecules may, in principle, monitor physisorp-tion, chemisorption, surface defects, grain boundaries or bulk defect reactions [40]. Several chemical sensors are available mass-sensitive sensors, conducting polymers and semiconductors. Mass-sensitive sensors include quartz resonators, piezoelectric sensors or surface acoustic wave sensors [41-43]. The basis is a quartz resonator coated with a sensing membrane which works as a chemical sensor. 

Functional polymers may be used for dihierent types of chemical sensors, including acoustic wave sensors (bulk acoustic wave, surface acoustic wave, and flexural plate wave sensors), electronic conductance sensors (semiconducting and capacitance sensors), and calorimetric sensors. ... 

Scherban E, Nowick AS (1989) Bulk protonic conduction in Yb-doped SrCe03. SoUd State Ionics 35 189-194 Schierbaum KD (1995) Engineering of oxide surfaces and metal/oxide interfaces for chemical sensors recent trends. 

This study also presents a possibility of designing PPy films with long-term electrical stability at elevated temperatures, although embrittlement and loss of mechanical properties might be anticipated. Furthermore, even if the inherent stability of the electrode side cannot be achieved in the bulk polymer, the observed anisotropy is of potential importance for applications at low temperature. The more sensitive growing side may be more responsive to environmental effects and thus more useful as a chemical sensor, while for applications which require long-term conductivity stability the growing side should preferentially protected. 

In recent years, nanotechnology has opened a new window on the physical-chemical properties of semiconductor materials nanostructuration. The development of nanostructured materials (nanowires, nanotubes, nanoparticles etc.) enables improvements in the response and recovery times of the sensor signal, due to the reduction of gas diffusion effects in the bulk of the material. Additionally, the sensitivity and the sensor response are also improved by the changes in the conduction mechanisms at the nanoscale and, finally, the reduction of the dimensions of the device allows the reduction of the power consumption by the system. 

Figure 14.6 Sensing ofHCI and NH3 using PPy/carbon nanofiber composites (a) SEM image of the nanofiber mat and (b) TEM of a single composite nanofibers (c) responses of the composite nanocables (a and b) and bulk PPy (c and d) to NHj (a and c) and HC (b and d) (Reprinted with permission from Sensors and Actuators B Chemical, CO gas sensing from ultrathin nano-composite conducting polymer film byM. K. Ram, O. Yavuz, f. Lahsangah and M. Aldissi, 106, 2, 750-757. Copyright (2005) Elsevier Ltd)...

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