Development of Positron Annihilation Spectroscopy Techniques Applied to Damaged Polyimide Film

Abstract

Studying and understanding the internal structure of materials is important to development of device quality materials with well-defined electrical and mechanical properties. More and more, modern materials for highly optimised applications are manufactured material composites, or processed in some way. To understand macroscopic properties exhibited by these materials often atomic or nano scale changes need to be characterised and understood, as they can be the drivers for these effects.

Positron annihilation spectroscopy (PAS) is an established analytical technique used to investigate the internal structure of materials, as the different techniques are non-destructive and sensitive at the molecular (sub-nanometre) level. Developing high quality positron spectroscopy experiments can aid in the understanding of the evolution of materials over time in damaging environments, or precisely monitor material behaviour during fabrication and processing. The information obtained from PAS can identify the underlying causes of desirable macroscopic material properties and inform the design and manufacture of these materials for better performance.

At the Australian National University, the positron research group has developed positron annihilation lifetime spectroscopy (PALS) which relates the time taken for an implanted positron to annihilate inside a material to defect size and concentration. This thesis outlines the implementation of a complementary PAS technique added to the positron materials beamline, Doppler broadening of annihilation radiation (DBAR), which provides additional information on the chemical environment at positron annihilation sites.

The successful implementation of the DBAR experiment was used to characterise ion implanted and plasma exposed Kapton polyimide, in conjunction with existing positron techniques. The damage study explored the effects of damage similar to environmental exposure in long term space missions, where Kapton components from satellites or spacecraft interact with trapped ion plasmas inside the Earth's magnetic field, planetary atmospheres, and the solar wind. Show more