1. Fabrication of Nano-porous Templates Using Molecular Self-Assembly of Block Copolymers for the Synthesis of Nanostructures
Luke Soule, Jason Tresback
Center for Nanoscale Systems, Harvard University
Experimental Methods
Results
Introduction
Gold (left) and nickel (right) were electroplated in the microdomains to form nanodots arrays. Patchy area signifies overplating. Particles ~30nm
The 2:1 PS-b-PMMA, 82 kilodaltons block copolymer was used for synthesizing templates. Ag on Si, SiO2 on Si, ITO on glass and PET were the substrates used. A random brush copolymer was anchored to the surface to neutralize surface interactions.
Traditional methods for fabricating nano-scale devices often involves time consuming and expensive techniques, such as electron beam lithography. Di-block copolymers can be used to site-specifically synthesize nanostructures on various substrates much faster and cheaper. The PS-b-PMMA systems was used to develop nanoporous films on different substrates. Conductive ITO substrates were used to electrodeposit Ni, Au and functional oxides to form high density nanodot arrays. Electrochemistry has been used in the past to make nanodot and nanowire arrays using nanoporous alumina [1]. However, alumina is soluble in acid and base conditions, limiting its applications. Since polystyrene is not soluble in these conditions, the system allows for synthesis of complex oxides and other materials. Nanodot arrays of Ni, Au, and functional oxides were fabricated quickly, with low-cost processing techniques for catalyst, solar, and metamaterials applications. .
1 oh, Jaeho, Yongsug Tak, and Jaeyoung Lee. “electrodeposition of Cu2 O Nanowires using Nanoporous Alumina Tempalte.” N.p., N.d. Web 2016
The di-blocks were dissolved in toluene and spun cast on substrates at 4,000 RPM. Either 1 layer or 3 layers were spun based on desired thickness. Annealed for 48 hours. Si Ag
PS/PMMA
Brush
An oxide system was also electroplated, forming an island formation oppose to a dot conformation that occurred in the metals.
Post anneal, templates were developed using UV, mJ. This crosslinked PS and degraded PMMA. After a 5 minute acetic acid rinse, the templates were emptied and ready for electrodeposition.
Nickel and gold were electrodeposited in microdomains. Using an acetone liftoff, very dense arrays of nanodots and nanowires were synthesized.
Block Copolymer Self Assembly
Results
A Block copolymer is a long strand polymer that consists of groups of monomers “blocked” next to one another in a repeated fashion.
Where A is a polystyrene monomer and B is a methyl-methacrylate monomer.
Due to unfavorable segmental interactions, the two monomer blocks would like to repel each other. After annealing, the two strands self assemble into a variety of shapes and structures. The size of the structures is dictated by volume fraction and molecular weight.
AABBAABB
This AFM phase image shows close hexagonal packing. Pores are around 30nms in diameter and are spaced around 35nms apart. This is 3 layers of PS-b-PMMA on a SiO2 on Si substrate.
Conclusions and Future Work
Nanoporous templates were developed on Ag, SiO2, ITO, and flexible films. Nickel, gold, and an oxide system were plated to develop nano-dot arrays. Flexible films can be used for flexible solar cells and “internet of things” type applications. The gold and nickel systems can be used for catalyst and solar cell enhancement. The novel oxide will be used for catalyst applications due to its high surface area. S
Post development, an AFM height image was generated using a AC240BSA high aspect ratio tip. 1 layer ITO on glass
Acknowledgements
This work is funded by the NSF under the NNCI program. Fabrication and analysis was performed at the Center for Nanoscale Systems at Harvard University. Electroplating was done was performed in the Nocera Lab at Harvard University.