Jaehyun Park EE235 Student presentation / Mar 09, 2009

Motivation Among NGL methods : use molds for imprinting features into thin polymer films Evaluation of resolution limits : most effectively done by using molds Difficult to fabricate structures of sub 5nm using conventional methods : resolution limit and non- uniformities

Their solution Use SWNTs as templates –Features of SWNT (single-walled nanotube) Cylindrical cross-sections Atomic scale uniformity Chemical inertness Ability to grow or deposit them in large quantities over large areas : 0.5~5nm dia.,1~10 tubes/μm 2 Research on polymer characteristics with SWNT molds

Fabrication process Master mold : –Grow SWNT using CVD on SiO 2 /Si Replicated mold : –Spin h-PDMS on cured PDMS –Casting & curing: Platinum catalyst used to form 3D crosslinking Imprinting : –Spin low viscosity PU –Lightly press mold & cure under UV –Peel off

Experiments : AFM AFM Shows heights of features Accurately reproduces nanoscale features over multiple cycles Some distortions : surface roughness of molded PU

Experiments : TEM TEM shows widths of features PAA used instead of PU Imprinted structures similar to master features For widths below 3nm : difficult to determine due to grain size of Pt/C (~1nm) TEM : mold TEM : master

Experiments : AFM at sub 2nm scale featurecapability > 2nmReliable 1~2nmPartial capability, still possible to identify heights < 1nmLittle to no capability, significant loss of height defects appeared

Polymer limits resolution Clues 1.Beaks in molded feature occurs at the same position 2.Imprinted features with dissimilar polymers have similar surface roughness 3.SiO 2 /Si has 0.19nm surface roughness 4.Distance between crosslinks of polymer (1nm for h-PDMS)

Density of crosslinks Crosslink density : affects capability of defining small feature and retaining shape Attempts to increase in h-PDMS : failed due to stiction to mater mold

Surface roughness Got 0.26nm RMS at 9k rpm of polymer spin Processing conditions : extremely important in achieving high-fidelity nanoimprint lithography in the 1-10nm regime. F. Hua, et. al., “Processing Dependent Behavior of Soft Imprint Lithography on the 1-10 nm Scale”, IEEE Trans. on Nanotechnology, 5, 301 (2006)

Conclusion Simple method for evaluating resolution limits on imprinting polymers, as small as 2nm Resolution is determined by both polymer chemistry and process condition To enhance the resolution –Polymer having high crosslink density –Process to make smaller roughness

Supplements : TEM TEM analysis for lateral dimension Sample prepared by metal shadowing technique PAA can replicate fine feature and is dissolvable by water Pt/C has fine grain Carbon mechamically support the thin film

Supplements : Pt catalyst