University College Cork Department of Chemistry
Tyndall National Institute, Cork, Ireland
Parvaneh Mokarian-Tabari
May 5, 2014 Polymer Engineering Academic Center
Aggarwal Lecture Hall Room 130 12:00 pm
An in-‐situ Study of Kine0cs of Rapid Self-‐ assembly in Block Copolymer Thin Films during “Solve-‐ microwave” annealing
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The University of Akron Department of Polymer Engineering
Special Lecture
Microwave annealing is an emerging technique for achieving ordered paFerns of block copolymer films in substrates, although liFle detailed understanding of how microwave annealing promotes the microphase separa0on of the blocks exists. Here, we use controlled power microwave irradia0on in the presence of a solvent tetrahydrofuran (THF), to achieve lateral microphase separa0on in high χ lamellar forming poly(styrene-‐b-‐lac0c acid) PS-‐b-‐PLA. A highly ordered line paFern was formed within seconds on a silicon substrate. In-‐situ temperature measurement of the silicon substrate coupled to condi0on changes during “solvo-‐microwave” annealing allowed understanding of the processes to be aFained. Our results suggest that the substrate has liFle effect on the ordering process and is essen0ally microwave transparent but rather, it is direct hea0ng of the polar THF molecules that causes microphase separa0on. It is postulated that the rapid interac0on of THF with microwaves and the resultant temperature increase to 55 ºC within seconds causes an increase of the vapor pressure of the solvent from19.8 kPa to 70 kPa. This enriched vapor environment increases the plas0city of both PS and PLA chains and leads to the fast self-‐assembly kine0cs. Comparing the paFerns 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 hea0ng during “solvo-‐microwave” annealing. Besides the short annealing 0me which has technological importance, the coherence length is on a micron scale and deweZng is not observed a[er annealing. The etched paFern (PLA was removed by an Ar/O2 reac0ve ion etch) was transferred to the underlying silicon substrate fabrica0ng sub-‐20 nm Si nanowires over large areas demonstra0ng that the morphology is consistent both across and through the film.
Dr. Mokarian-‐Tabari is a Research Fellow at the University College Cork and the Centre for Research on Adap0ve Nanostructures and Nanodevices (CRANN) and AMBER Centre, Trinity College Dublin, Dublin, Ireland. Dr. Mokarian-‐Tabari serves as a Conference Program CommiFee member for the 2014 SPIE Micro-‐and Nanotechnology Sensors, Systems and Applica0ons Conference, VI.
(a) AFM topography image of PS-‐b-‐PLA film a[er 60 seconds “solvo-‐microwave” annealing. (b) SEM cross sec0on of the film a[er paFern transfer to silicon.
