M.Sc Thesis


M.Sc StudentItai Kamienchick
SubjectNanostructured Sn02 Gas Sensors
DepartmentDepartment of Materials Science and Engineering
Supervisor Professor Rothschild Avner
Full Thesis text - in Hebrew Full thesis text - Hebrew Version


Abstract

In recent years, significant progress has been achieved in developing highly sensitive metal oxide gas sensors using novel quasi-1D nanostructured architectures. Among the different strategies for producing such sensors, electrospinning offers several advantages including ease of fabrication and versatility. Early results obtained with electrospun TiO2 layers demonstrated exceptionally high sensitivity to NO2 Based on these observations it was thought that the microstructure of the electrospun layers is ideally suited for gas sensing. Specifically, the combination of large (~1 mm) and small (~10 nm) pores, small grain size (~10 nm), and high surface area (~140 m2/g) enable efficient transport of gases into the layer and enhance the sensitivity to adsorbed gases.

This work aims at examining the factors that limit the sensitivity of nanostructured metal oxide gas sensors, comparing electrospun versus spun-coated layers of the same thickness and chemical composition. Sol-gel solutions of Tin-accetate were deposited on Si/SixNy substrates fitted with interdigitated Au electrodes by electrospinning and spin-coating methods. Following deposition the layers were hot-pressed and calcined. The layers thickness varied between 0.3 and 9 mm. Their microstructure was examined by HRSEM, TEM, and XRD. The layers received from both deposition methods were single phase SnO2 rutile with a grain size of less than 10 nm

The sensitivity of the electrospun and spin-coated layers to traces (25 ppb to 2.5 ppm) of NO2 and CO in dry air was examined at temperatures between 250 and 350°C. The effect of layer thickness and microstructure on the sensitivity to these gases can be explained based on the diffusion reaction model of metal oxide gas sensors.

To improve the sensitivity and selectivity to reducing gases (e.g., H2) Pd, a well known catalyst for H2 oxidation, was added to the feeding solution of the electrospinning process. The addition 30% Pd resulted in suppression of grain growth and in improved selectivity towards H2 over NO2 .