1. Transparent conducting oxides (TCOs) are often used in industrial applications. The utility of these semiconductors, as the name suggests, depends upon their conductivity and ability of light to pass through them. Zinc oxide (Zn0) has the potential to become a very good TCO, with further research. It is relatively cheap, compared with other TCO’s and isn’t toxic. Transparent Conducting Oxides The Goal Zinc oxide’s atomic structure, as a crystal, is regular and repeating. This rigid pattern binds all of the material’s electrons to the atoms. Atomic defects or irregularities in this atomic structure may increase the electron concentration, and hence the material's ability to conduct.. The goal of this project is to explore the defect structure of ZnO, analyzing influential factors and synthesis procedures. Side viewTop view represent O 2- represent Zn 2+ The Materials (ZnO) We used ZnO oxide powder from five different manufacturers, with each having different purity levels and grain size. Two, labeled N1 and N2, have spacing on the scale of nanometers, while the others, B1, B2, and B3, have larger spacing. The manufacturers also provided a purity level, in all cases above 99%. The purity level of each material determined their corresponding number, with 1 being the most pure. Since we sought to find the conductivity and thermopower of the materials, the powder had to be formed into a solid object. It was pressed into small pellets, of 6mm diameter and about 0.16 grams. All the synthesis and testing of electrical properties occurred in Byrne Hall at DePaul. Here the chamber where we kept the powders in a vacuum container is pictured. The Press: Used at just over 1000 pounds. The Scale: measuring grams accurate to 4 decimal places. The powders had to be macerated with acetone and then dried prior to pressing in order to break up any large chunks of ZnO. All five materials were pressed into pellets by the same procedure. A stainless steel die with an inner chamber of radius 3mm was used to hold the powder. Synthesis Removes oxygen to increase carrier concentration, which increases the conductivity Achieved up to 20% increase in conductivity Annealing Once the pellets were pressed, in order to increase the particle-particle contact, they were placed in a high temperature furnace. This process, called annealing, increases their durability, allowing us to test their properties without damaging the pellets. The pellets were baked in the furnace for a couple of days at 1200 degrees Celsius. The maximum temperature achievable by the furnace is 1500 degrees. Applications of TCO’s include LCD’s and solar cells. Testing the Electrical Properties Forming Gas Reduction Once annealed, about half of the pellets were chosen to be reduced in a forming gas chamber. Forming gas is a mixture of 4% hydrogen in nitrogen, and is commonly used to dissipate moisture and oxygen. We reduced these pellets in order to determine the effect forming gas reduction has on thermopower and conductivity. In theory, gas reduction will remove some oxygen molecules from ZnO, increasing the carrier concentration of electrons and thus conductivity. The reducing chamber in which our samples were placed. They were held at about 500 degrees under forming gas. Synthesis and Electrical Properties of Zinc Oxide Alexander Slawik Jared Hennen Tom McManus Advisor : Dr. Gonzalez Department of Physics After the pellets were annealed they were tested for their conductivity using a four-point probe. By applying different currents to the two outer probes and using a voltmeter to measure the voltage across the two inner probes we were able to determine the pellet’s conductivity. The four-point probe setup with the probe on the far left and the current source and voltmeter in the center and right, respectively. To test the thermopower we placed the pellet between two thermocouples. A temperature difference was created by placing the pellet on top of a metal block initially at room temperature and connecting a modified soldering iron to the top. This allows us to measure the carrier concentration of each pellet, which helped us determine the effect of the gas reduction process. Pellets were placed between the soldering iron and metal block with two thermocouple attachments. Conclusion Initial results indicated that forming gas reduction improved the conductivity by an average of 20%. The bulk sample B2 gave the most consistent results and improved significantly with gas reduction. More testing is needed but recent tests (conducted by Leonel Hernandez) have been promising and produced similar results.