Hydrothermal Synthesis of TiO2 Nanorods and Their Application for Sensor Devices

Abstract

This thesis aims at the synthesis and analysis of sensor applications based on TiO2 nanorods Rutile phase TiO2 nanorods were chosen as sensing material due to its quit stable property With different hydrothermal temperatures and acidities the influences on the TiO2 nanorod morphologies and crystalline qualities to photodetector humidity sensor and gas sensor were studied First of all we reported the growth of TiO2 nanorods on seed layer TiO2/SiO2/Si substrate through hydrothermal treatment It was found that the length width and crystalline quality of TiO2 nanorods were all increased by increasing the hydrothermal temperature Under high acidity hydrothermal conditions the greater crystalline quality of nanorods was obtained but the formation of nanorods was inhibited In order to find out the optimization growth parameters for our TiO2 nanorod sensor devices the hydrothermally treated TiO2 nanorod sensors under different acidities and untreated TiO2 seed layer film-type sensor were then fabricated followed by a comparison of their sensor response In the application of UV photodetector the TiO2 nanorod sensors with various acidities showed larger response to UV light as compared to the TiO2 film-type sensor The largest response of nanorod sensor was 6 times larger than film sensor The nanorod sensors outperform the film sensor mainly for the larger surface area Besides the best crystalline quality sensor was found to have the shortest response time due to the reduction of the recombination induced by the defects The shortest response time was 4 seconds In the application of humidity sensor the hydrothermally treated TiO2 nanorod sensors with different acidities tended to give higher response than that of untreated TiO2 seed film sensor Also it was found that the humidity response of the sensors significantly depended on the surface area The optimum TiO2 nanorod humidity sensor response is about 11 24 during RH40%~ RH90% In the application of gas sensor the sensing performance of TiO2 nanorod and TiO2 film sensor has also been investigated at different temperatures for various volatile organic compounds (VOCs) such as methanol ethanol and acetone The measuring results showed that the larger response was mainly attributed to the larger surface area The optimum TiO2 nanorod gas sensor response is around 5 42 measured at 300 oC in 200 ppm ethanol Since our gas sensor performance was much more competitive than other sensors we further improved its sensing ability by Au nanoparticles The result showed that the gas sensing performances of Au nanoparticles/TiO2 nanorod were all promoted The response of 200 ppm ethanol was four times larger than pristine TiO2 sensor the rise and decay time was halved All the sensor applications were performed by the same MSM structure with Ti interdigital electrodes indicated that we successfully fabricated a multifunctional TiO2 nanorod sensor with stability and good response The sensing mechanisms under various conditions were also investigated

Date of Award	2015 Jul 8
Original language	English
Supervisor	Shoou-Jinn Chang (Supervisor)