Enhanced Radiation Tolerance of Ceramic Thin Films by Nano-structural Design
MetadataShow full item record
Thin films techniques are widely used in microelectronic devices, optical coatings, batteries and solar cells, which would be applied under harsh environment spanning from outer space to nuclear plant where defects are easily generated, accumulate and eventually degrade the materials properties. Oxide and nitride thin films are widely used and mostly studied in such applications. Moreover, MgO and ZrN have been considered as promising candidates of Inert Matrix materials to reduce hazardous nuclear waste. Therefore, studies on the defects development, and more importantly, the enhanced damage tolerance by microstructural design are of great importance. However, only limited study has been conducted up-to-date. In this dissertation, interface mitigation effects on radiation damage have been explored in TiN/MgO epitaxial thin films. After ion implantation with He+ ions, no hardness variation is observed in the epitaxial multilayers, and high resolution TEM indicates no obvious ion damage in the MgO layers within the epitaxial multilayer samples. However, single layer MgO film shows a significant hardness increase of ∼20% and high density point defect clusters are clearly identified. The results suggest that, in this system, epitaxial interfaces could act as effective point defect sinks in reducing the defect density and suppressing the ion-implantation induced hardening in MgO, and thus are responsible for the enhanced radiation tolerance properties. The grain size dependent response in nanocrystalline (nc) ZrN under high dose heavy ion implantation has been studied with Fe2+ ion, and it is found that the ZrN film with the average grain size of 9 nm shows prominently self-healing effects as evidenced by suppressed grain growth, alleviated radiation softening, as well as reduced variation in electrical resistivity. In contrast, ZrN with the larger average grain size of 31 nm shows prominent softening and resistivity increase after implantation, attributed to the high density of vacancy like defect clusters formed inside the grains. The distinct implantation effects on microstructure, residual stress, grain growth, and electric resistivity of thin films with different grain sizes were discussed, and the influence of grain boundaries on enhanced tolerance to implantation damage in nc-ZrN is demonstrated. In order to further study the real-time response of the designed microstructures, and their kinetic interactions with defects. In-situ irradiation on MgO/ZrN multilayer systems with non-epitaxial interfaces as well as grain boundaries has been conducted, which shows clearly the cyclic process of the defects removal by high angle grain boundaries and effectively absorbed by interfaces. Another In-situ study on the MgO/TiN epitaxial films has demonstrated that the implantation induced defects migrate to the interfaces, and annihilate there, that improve the MgO tolerance against amorphization. The comparison has shown that the non-epitaxial interfaces are more effective in absorbing defects manifested by the higher mobility of defects migration towards the MgO/ZrN interfaces. The research findings could provide guidance for microstructural design of functional ceramic thin films for advanced technological applications under extreme conditions from outer space exploration to nuclear energy generation.
Jiao, Liang (2015). Enhanced Radiation Tolerance of Ceramic Thin Films by Nano-structural Design. Doctoral dissertation, Texas A & M University. Available electronically from