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.