Swt Sensor Lab

The sensor was kept in oven at 70ºC for few/ 3 hours prior to each experiment session for the purpose of gas molecule desorption. The SWCNT sensor was then placed inside the gas cell in the flow of N2 gas until the equilibrium condition was obtained, i.e. the resistance measurement stabilized. The response of sensor resistance to two different explosive chemical: (i) Dinitrotoluene – DNT, (ii) Ammonium Nitrate, NH4NO3; both oxidizing agent, at different parameters and various concentrations was monitored.
Typical baseline resistance for the SWCNT sensor ranged from 10 to 15 Ω. Multiple cycled testing was also performed for each sample during which the ambient inside the test setup was alternated between pure N2 (%)and the target explosive vapors

DNT being nitro-aromatic compound, contains two NO2 group/molecule attached to its toluene ring and so behave as an oxidizing agent. The possible adsorption sites available for these molecules are the surface of the SWCNTs and the grooves formed in between two outer tubes of the adjacent bundles. When the CNT film gets exposed to DNT, the NO2 molecules of DNT interact with the p-type of SWNT and charge transfer takes place. NO2 being strong oxidizing agent, withdraws electrons from the SWCNT thus increasing its hole concentration and decreasing the resistance of film. As can be seen in fig. 5.2 – 5.6, the conductance of the sensor increases at every exposure of DNT thus depicting its oxidizing

Same method of vapor generation and transfer had been followed with ammonium nitrate too as in the case of DNT detection. The experiment has been conducted at a constant flow rate of 0.5 LPM. Fig. 5.7 shows the response to 0.005 ppm concentration of ammonium nitrate for 1 minute in the flow of N2 which acts as a carrier and then recovered in pure N2 flow for 5 minutes. The graph shows a prompt increase of conductance by about 0.7% in a duration of 1 minute. The data of fig. 5.7 also shows that the conductance starts to decrease immediately upon the removal of chemical vapor, however the rate of recovery in this case is very