Lu-Tao Weng oral presentation (OB2-Mon2-2-4)
Investigating the stability and structure of spin-coated polymer thin films using ToF-SIMS depth profiling
1 Hong Kong University of Science & Technology - Department of Chemical and Biomolecular Engineering, Clear Water Bay, Kowloon Hong Kong, China
2 Hong Kong University of Science & Technology - Materials Characterization and Preparation Facility, Clear Water Bay, Kowloon Hong Kong, China
3 Hong Kong University of Science & Technology - Division of Environment, Clear Water Bay, Kowloon Hong Kong, China
Spin coating is the most widely applied technique in the preparation of polymer thin films, due to its ability to produce films with excellent structural uniformity over large areas. However, polymer thin films prepared by spin-coating have also been observed to be unstable. Improving polymer thin film stability has thus been the focus of many research groups in polymer community. In the past, most of the research was focused only on the surface morphologies of the thin films because the analysis of the thin films in vertical direction (depth profile) is very challenging. The recent developments of cluster ion sources in SIMS have opened up new perspectives for the molecular depth profiling of organic materials and the depth analysis of the polymer thin films became possible. In this talk, the applications of ToF-SIMS depth profiling using cluster ion beam to the polymer thin films will be illustrated using some recent examples coming from our laboratory [1-4] or literature.
The first part of our talk will be focused on the stability of polymer thin films [1-3]. In general, the stability of polymer thin films is highly dependent on the interactions between polymer, solvent and substrate. Stable and unstable polymer thin films, prepared by changing different substrates and solvents, were systematically investigated using ToF-SIMS depth profiling. The results revealed that a high concentration of the polymer end groups was found at the polymer-substrate interface for stable thin films. In contrast, the end-groups were found to be more evenly distributed for the unstable thin films. The extent to which the end groups segregate to the interface depended on the competitive interactions between the polymer, the solvent and the substrate. Stronger polymer–solvent and solvent–substrate interactions prevented the segregation of the end groups to the interface, resulting in unstable polymer films.
The second part of our talk will be focused on the structure of polymer thin films . Polymer thin films with surface patterns were systematically investigated using ToF-SIMS 3D analysis. The results revealed that the surface patterns were hollow rather than solid, which were confirmed by optical microscopy analysis. Furthermore, the micro-area depth profiling analysis indicated that the hollow structure was sandwiched between two polymer layers rather than sitting on the substrate.
Acknowledgements: The work described in this paper was fully supported by the Research Grants Council of the Hong Kong Special Administrative Region, China (grant nos. 600513 and 16300314).
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 X.W. Ren, L.T. Weng, K.M.Ng, C.M. Chan; Surf. Interface Anal. 49, 2017, 210.
 X.W. Ren, L.T. Weng, C.M. Chan, K.M.Ng; Anal. Chem. 84, 2012, 8497.