AB INITIO STUDY OF OXYGEN DISSOCIATION MECHANISM ON STOICHIOMETRIC AND REDUCED ZnO(100) SURFACE FOR PRE-DETECTION STAGE OF GAS SENSOR

• Main Author: P. P. Setyagar, Nikita
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/43291
• Institution: Institut Teknologi Bandung

Gas sensors are needed in various aspects, from industry to the environment. Zinc oxide (ZnO) is one of the most popular semiconductor materials used as gas sensors with excellent performance, relatively inexpensive, and easily mass produced. There is still a lot of information about the mechanism of gas detection by ZnO that needs to be studied more deeply. To date, it is believed that the detection occurs because of the interaction between oxygen ions on the surface of ZnO and the target gas which gives rise to the phenomenon of chemiresitance. These oxygen ions are formed from dissociation of oxygen molecules (O2) which are bound to the surface of ZnO. However, O2 molecules are very difficult to adsorb on the stoichiometric ZnO surface, but it is easier to occur on ZnO surfaces that have vacant oxygen atom defects. However, the formation of oxygen vacancies on the surface of ZnO requires high formation energy so that it is difficult to be realized at low temperatures. Based on this, it is necessary to look for other ZnO configurations that are easily formed and can facilitate the adsorption of oxygen ions properly. In this research, an ab initio study was carried out to study the mechanism of adsorption and dissociation of O2 molecules on nonpolar ZnO (100) surfaces with vacancies of an O atom, a Zn atom, and a ZnO dimer, which were compared with a stoichiometric ZnO(100) surface. Computation was performed using DFT to calculate the energy and charge transfer in adsorption and dissociation of oxygen. As a result, it was found that adsorption and dissociation of oxygen can only occur on the surface of ZnO(100) with a vacancy of O atom or ZnO dimer. Obtained oxygen adsorption energy values of -1.61 eV and oxygen dissociation energy of 0.82 eV (atomic O vacancy), and adsorption energy of -0.08 eV and dissociation energy of 1.60 eV (ZnO dimer vacancy). Meanwhile, ZnO surface with a Zn vacancy and the stoichiometric one cannot facilitate the mechanism. It is also confirmed that there is a charge transfer between the adsorbed oxygen and the surface of ZnO(100) which indicates the existence of a chemiresistance mechanism.