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2. Fabrication of a nanoporous template from a diblock copolymer film - solvent annealing
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An evaporation-induced flow in solvent cast block copolymer films can produce arrays of nanoscopic cylinders oriented normal to the surface and solvent annealing could markedly enhance the ordering of block copolymer microdomains in thin films. Without removing minor components, solvent-induced surface reconstruction can produce nanoporous structure in thin films. The porous film can be used as a template for deposition of quantum dots or as a mask for pattern transfer to the underneath substrates.

Contributors: T.P. Russell, S. Park, J.-Y. Wang, and B. Kim
Lab: NSF Center for Hierarchical Manufacturing

Manufactured Nanomaterial or Structure: Polystyrene-b-Poly(4-vinylpyridine) film with hexagonal array of nanopores
Chemical composition: Polystyrene/Poly(4-vinylpyridine)
Physical Form: Nanoporous thin film
Properties: 30 nm thick film containing a hexagonal array of 15-25 nm diameter pores with a period of 25-45 nm.

Process:

1.Clean a silicon wafer (or alternate substrate).
2.Synthesize or purchase diblock copolymer PS-b-P4VP, consisting of PS and P4VP, with a molecular weight of 68,500 or 32,000 daltons and a PS volume fraction of 0.70. These polymers will phase separate and self-assemble into hexagonally packed array of P4VP cylinders 15-25 nm in diameter
3.In a 0.6 wt% solution with toluene the PS-b-P4VP is spin cast onto a substrate into a film on order of 30 nm thick.
4.The films were exposed to toluene/THF mixture (20/80) vapor for 12 hrs to induce mobility and allow microphase separation to occur under N2. To control the solvent vapor treatment process, the samples were kept at a constant temperature (23 C) in a small vessel having solvent bubbling equipment.
5.Open the vessel, and then take out the sample.
6.To make nanoporous templates, the solvent annealed films are immersed into a preferential solvent, ethanol, for P4VP blocks for 20 minutes.
7.The highly oriented PS-b-P4VP nanoporous templates with 15-25 nm diameters and 25-45 nm spacing will be prepared. (See the schematic diagram in Figure 1)
Figure 1. Magnify
Figure 1.

Figure 1.

Notes: This nanoporous film can be prepared in any surface as was demonstrated in the original Adv. Mater. (2007) article. These thin nanoporous templates are useful for reactive ion etching.

Raw Materials:

  • Polystyrene denoted as PS
  • Poly(4-vinylpyridine) denoted as P4VP
  • Toluene and tetrahydrofuran (THF), solvent
  • Substrates (e.g. silicon, gold-coated silicon, germanium, polyimide, etc.)
  • Ethanol (solvent for surface reconstruction)
  • Metals (e.g. chromium, gold, etc.), evaporated on the nanoporous templates

Environmental Variables:

  • Cleanroom environment (recommended), room temperature, low humidity

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