Light activated gas nanosensors

Identificador:  TDX:2899

Handle: https://hdl.handle.net/20.500.11797/TDX2899

Autors:  González León, Oriol

Resum:
This thesis is focused on exploring the potential of ultraviolet light to activate metal oxide gas sensors (MOX), and to compare the results obtained against those when only temperature activation is used. MOXs need to be heated in order to show their properties as semiconductors and also react, on their surface, with the target gases, where we measure conductivity variations as a response towards those gases. In this thesis we have obtained promising results applying pulses of UV light. First of all, we have reduced the temperature for gas detection, then we have noticed that other kind of interactions appeared when the material is at low temperatures under UV excitation, which allows us to discriminate better between gases. We have also improved the response time at room temperature with pulsed UV in contrast to temperature alone. The proposed methodology consists of irradiating the sensitive material with on and off cycles of UV light, creating transients ( a ripple) in sensor resistance. What we have observed is that these transients are related to the concentration of the pollutant gases. This allows to design strategies to improve selectivity. During this thesis, we have studied In2O3 (octahedra) and WO3 (nanoneedles) as sensing layers for the detection of NO2, NH3, acetone, and ethanol, also under humid conditions. In conclusion we can say that with this methodology we can improve response time, reduce consumption (operation temperature can be lowered significantly) and improve sensitivity and selectivity, both for reducing and oxidizing gases.