Abstract

ABSTRACT
Growth, Doping, and Characterization of ZnO Nanowires: Application in a Miniaturized Gas Ionization Sensor

Svetlana Spitsina, Ph. D.
Concordia University, 2013

Semiconductor ZnO has been the subject of research for many applications for the past several years, because the material is nontoxic, biosafe, chemically stable, and biocompatible. In this work we report studies on ZnO nanowires (NWs), its fabrication and applications. Techniques are developed to control the morphology and distribution of ZnO Nanowires (NWs). We have also investigated the conductivity of nanowires and its manipulation using various doping materials and their concentrations. Fabricated nanowires have potential applications such as integration in nano optoelectronics, solar cells, gas or humidity sensors, and many other devices. In this thesis we have explored its application to develop a gas sensor based on the ionization of gases, so-called Gas Ionization Sensor (GIS).
A GIS based on metallic nanowires (NWs) had been previously designed and developed in the Micro/Nano Laboratories in the ECE Department at Concordia University. However, the reported device suffered from very low durability. The high voltages induced at the NWs tips damage the apexes (due to their thin structure) and device loses its sensitivity after several episodes of usage.
High performance GIS sensors demand specific morphology of NWs, uniform distribution, low density, and demand that NWs be made of highly conductive and chemically stable materials. In this work we have introduced ZnO nanowires to replace the metallic nanowires in the GIS. It is the core of thesis to fabricate ZnO NWs having the characteristics to improve the functioning of the GIS.
In these investigations we have focused on the electrochemical synthesis of nanowires. We used this technique due to its advantages such as low cost, high throughput, repeatability, uniform and large area synthesis of NWs, strong adhesion of NWs to the substrate, ability to grow them with desired morphologies, as well as the possibility of effective doping during the growth. Effects of various growth parameters on the nanowire structures are investigated. Studies on doping the nanowires, p-type and n-type, were carried out. ZnO NWs with desired structures and conductivity were used to design and fabricate a GIS. The device was tested for various gases. Significantly improved performance of the GIS was demonstrated. GISs with p-type ZnO NWs illustrated high field enhancement factors because of the morphology, distribution, and conductivity of nanostructures. Also, the novel gas detectors illustrated superior sensitivity, reliability, and repeatability.