Ultraviolet Irradiated ZnO-Nanorod Sensor for High Performance Oxygen Detection under Low Working Temperatures

• Main Authors: Chen-Shiun Chou, 周辰勳
• Other Authors: Lin, Che-Hsin
• Format: Others
• Language: zh-TW
• Published: 2013
• Online Access: http://ndltd.ncl.edu.tw/handle/00034463447166283321

碩士 === 國立中山大學 === 機械與機電工程學系研究所 === 101 === This work presents a novel ultraviolet irradiation assisted nanostructured ZnO film for high performance oxygen sensing under a low working temperature. Nanorod ZnO structures are synthesized on a glass substrate with interdigital sensing electrodes utilizing the developed two-stage sol-gel and hydrothermal processes. An 80 mW LED with the emission wavelength of 370 nm is then used to enhance the sensing performance of the nanostructured ZnO film. Results indicate that the sensing performance of the nano ZnO oxygen sensor is greatly improved. The oxygen sensor can work at a low temperature of 50˚C with the assist of UV exposure, which is much lower than the working temperature of typical solid state metal oxide sensors of around 350˚C. The response of the UV-assisted ZnO film shows 4.66 times larger than the same film without UV exposure. The method developed in the present study provides a simple yet high performance method for oxygen sensing under low operation temperature. ZnO has been used as the sensing material for oxygen or volatile organic compound (VOC) sensing. Typical solid state gas sensors rely on an operation temperature of 300 - 350˚C to enhance the carrier mobility of the metal oxide for sensing purpose. This approach usually consumes more energy for heating the sensing element and also significantly reduces the lifetime of the sensor. Alternatively, zinc oxide is II-VI group semiconductor with a wide band gap of 3.3 eV. UV exposure is an efficient way to produce hole-electron pairs in ZnO surface to enhance the sensing performance of ZnO-based gas sensor. With this approach, high operation temperature can be excluded for gas sensing. Adsorbed oxygen molecules will attract the UV induced electrons and form O2¯ due to the large electronegativity, resulting in the resistance incensement of the sensing layer due to the decease of electron carriers. A simplified process is used for producing the ZnO-based oxygen sensor. The sensing area for the nanostructured ZnO is 8.0 mm x 8.0 mm. The XRD patterns of the ZnO nanorods presents strong diffraction peak of (002) illustrates that the high tendency of ZnO nanorods growing along the c-axis. The SEM image shows the synthesized ZnO seed layer prior to the growth of nanorods. Ultra-fine ZnO nanospheres are about 15 nm on the substrate. The growth of the nanorods is preferred in the direction perpendicular to the substrate. The length of ZnO nanorods is about 600 nm. The measured response for sensing 97% oxygen is used various ZnO sensing layers with and without UV exposure at a low temperature of 50˚C. Results show that the nanorod ZnO film with the assist of UV exposure exhibits higher response. The response of UV-assisted ZnO nanorods was significantly higher than the same film without UV irradiation at all operation temperatures. The measured result of the 97% oxygen for three repeating tests evaluates the sensing repeatability of the developed sensor. The calculated variation for these three measurements was only 3.3%. The nice linearity (R2=0.9952) from 5 to 1000 mTorr confirms the good sensing performance of the developed sensor. Result also indicates that the detection limit of the sensor can be as low as 5 mTorr. The developed oxygen sensor utilizing UV-assisted ZnO nanorods has shown its potential to be a high performance oxygen sensor which can work at a low temperature.