PLEASE MAKE SURE YOU HAVE PRIOR EXPERIENCE ON PHYSICS/MATHEMATICS AND MATERIALS (SENSORS)
Resistive sensors have been laboratory, called S4 and S8. Both sensors have been fabricated using the Vapour-Liquid-Solid Method, consisting in the deposition of Au on the surface of the sensor and, introducing a precursor gas that diffuses into the Au droplet, supersaturates and precipitates to form nanowires. In these samples the nanowires are SnO2. The difference between both sensors is that on S4 the Au covers the whole surface and the decomposition occurs everywhere, while sensor S8 the Au is only deposited in a line of 10 micrometres width between 2 metal stripes. So, the active surface (the area where the sensing is taking place) is different in both sensors. The data files supplied contain the response of these sensors to different concentrations of CO (reducing gas) and NO2 (oxidising gas). The 4 columns of data are: time (in s), resistance (in Ohm), concentration of NO2 (in part per million – ppm) and concentration of CO (in ppm). All the data of these files was made as follows: i) An initial 2 hour stabilisation time to get more or less a constant and stable baseline (not always possible). ii) After this, 4 times 1 hour pulses of a fixed CO concentration followed by 2 hours of recovery. (you can read the CO concentration in the 4th column). iii) 5 times 1 hour pulses of a fixed NO2 concentration followed by 2 hours of recovery. (you can read the NO2 concentration in the 3rd column). iv) After this, the temperature is changed by applying a power to the heater of the sensor and after 2 hours stabilisation, the process is repeated in steps ii) and iii). This gives rise to measurements at 5 different temperatures, which nominally are 200, 250, 300, 350 and 400ºC. The task is to take these data files and analyse them to get the following information: a) The response to the different concentrations of a specific gas at different temperatures. b) The response time (variation of the resistance from 10 to 90% of the span between the base resistance and the steady state resistance at this gas concentration and temperature) and the recovery time (calculated the opposite way: from 90% to 10%). c) Comparison of the differences between both sensors. which is faster or more sensitive of both and why? So, you will have to fit your data to obtain the required data and you have to take into account that there might be a drift of the sensor as a result of the temperature variation during the experiment. For this, you will have to figure out which is the drift of the base resistance and calculate the variations occurring on top of this. A three page report needs to be made showing the fitting method you have used, how you have calculated the different values, and which are your conclusions about the difference between the sensors.