Study of the kinetics and mechanism of rapid self-assembly in block copolymer thin films during solvo-microwave annealing

Mokarian-Tabari, Parvaneh; Cummins, Cian; Rasappa, Sozaraj; Simao, Claudia; Sotomayor Torres, Clivia M.; Holmes, Justin D.; Morris, Michael A.

Study of the kinetics and mechanism of rapid self-assembly in block copolymer thin films during solvo-microwave annealing

Files

PMT_StudySV2014.pdf(1.69 MB)

Submitted Version

Date

2014-08-19

Authors

Mokarian-Tabari, Parvaneh

Cummins, Cian

Rasappa, Sozaraj

Simao, Claudia

Sotomayor Torres, Clivia M.

Holmes, Justin D.

Morris, Michael A.

Publisher

American Chemical Society

Published Version

10.1021/la503137q

Abstract

Microwave annealing is an emerging technique for achieving ordered patterns of block copolymer films on substrates. Little is understood about the mechanisms of microphase separation during the microwave annealing process and how it promotes the microphase separation of the blocks. Here, we use controlled power microwave irradiation in the presence of tetrahydrofuran (THF) solvent, to achieve lateral microphase separation in high- lamellar-forming poly(styrene-b-lactic acid) PS-b-PLA. A highly ordered line pattern was formed within seconds on silicon, germanium and silicon on insulator (SOI) substrates. In-situ temperature measurement of the silicon substrate coupled to condition changes during "solvo-microwave" annealing allowed understanding of the processes to be attained. Our results suggest that the substrate has little effect on the ordering process and is essentially microwave transparent but rather, it is direct heating of the polar THF molecules that causes microphase separation. It is postulated that the rapid interaction of THF with microwaves and the resultant temperature increase to 55 degrees C within seconds causes an increase of the vapor pressure of the solvent from 19.8 to 70 kPa. This enriched vapor environment increases the plasticity of both PS and PLA chains and leads to the fast self-assembly kinetics. Comparing the patterns formed on silicon, germanium and silicon on insulator (SOI) and also an in situ temperature measurement of silicon in the oven confirms the significance of the solvent over the role of substrate heating during "solvo-microwave" annealing. Besides the short annealing time which has technological importance, the coherence length is on a micron scale and dewetting is not observed after annealing. The etched pattern (PLA was removed by an Ar/O-2 reactive ion etch) was transferred to the underlying silicon substrate fabricating sub-20 nm silicon nanowires over large areas demonstrating that the morphology is consistent both across and through the film.

Keywords

PS-b-PMMA , Diblock copolymers , Low temperatures , Polystyrene , Orientation , Polylactide , Diffusion , Silicon , Arrays

Citation

MOKARIAN-TABARI, P., CUMMINS, C., RASAPPA, S., SIMAO, C., SOTOMAYOR TORRES, C. M., HOLMES, J. D. & MORRIS, M. A. 2014. Study of the Kinetics and Mechanism of Rapid Self-Assembly in Block Copolymer Thin Films during Solvo-Microwave Annealing. Langmuir, 30, 10728-10739. http://dx.doi.org/10.1021/la503137q

Copyright

© 2014 American Chemical Society. This document is the Submitted Manuscript version of a Published Work that appeared in final form in Langmuir, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see http://pubs.acs.org/doi/pdf/10.1021/la503137q

Full item page