The authors have investigated the formation of block copolymer nanocavities on H-terminated conducting Si(111) surfaces as templates for the electrochemical growth of perpendicular metallic nanowire arrays. Poly(styrene)-block-poly(methyl methacrylate) block copolymers (PS-b-PMMA) of appropriate block length and PS to PMMA ratio were used to create a self-assembled array of perpendicular nanocavities in which the PS majority phase is continuous and surrounds cylinders of the minority PMMA phase. Here, we report that H-terminated conducting Si(111) surfaces are also capable of inducing a perpendicular orientation in block copolymers, which—in all likelihood—is a direct result of the H-termination (i.e., removal of the oxide layer). Atomic force microscopy reveals that an acetic acid wash of the annealed block copolymer causes the minority PMMA component to be rearranged, giving rise to cavities that are perpendicular to the conducting Si substrate. Subsequently, scanning electron microscopy reveals that electrodeposition into the nanocavities can be achieved, producing an array of metallic nanopillars, 20 nm in diameter.

Block copolymers that self-organize are of interest as templates for patterned media, as they potentially provide a low cost fabrication route. Poly(styrene)-Poly(methylmethacrylate) block co-polymers (PS-b-PMMA) of appropriate block length and PS to PMMA ratio self-assemble into a 2-D hexagonal phase in which the PS majority phase is continuous and surrounds cylinders of the minority, PMMA phase. For application of this phase to patterned media it is necessary that the cylinders of the minority phase be oriented perpendicular to the substrate surface. This can be achieved by a number of methods, including appropriate choice of substrate and use of a random co-polymer underlayer. We report here that indium tin oxide surfaces are also capable of inducing a perpendicular orientation in block co-polymers, likely due to the effect of surface roughness of the substrate. Use of an acetic acid wash causes the minority PMMA component can be induced to be rearranged, giving rise to pores perpendicular to the substrate. Using a conducting substrate such as Tantalum thin film on Silicon wafer, electrodeposition can be carried out into the open pores to produce arrays of magnetic nanopillars of 18 nm diameter.

Poly (Styrene)-Poly (Methylmethacrylate) block co-polymer (PS-b-PMMA) of 36000 g/mol molecular weight, with a composition of 67% PS and 33% PMMA, Polydispersity index of 1.09 were synthesized. Thin films of ca. 30 nm thickness were prepared by spin-coating from toluene solution onto a range of substrates including are carbon overcoated hard drive substrate and Indium Tin Oxide (ITO) glass. After annealing, AFM showed that the polymer had nanophase separated into cylinders of PMMA in a continuous film of PS, as expected from the composition of the polymer. On the carbon coated substrate annealing produced significant dewetting of the substrate to give micron scale holes where the substrate was not covered by the polymer. In the covered areas the orientation of the nanophase was PMMA cylinders perpendicular to the substrate. Films on ITO were predominantly oriented perpendicular to the ITO surface. Washing with glacial acetic acid resulted in rearrangement of the PMMA component to open pores in the film. Electrodeposition of nickel onto this substrate lead to nickel pillars of estimated 18 nm diameter.

Bit patterned media, including media fabricated with a gradient in composition, is being developed as a potential path to higher information storage density. The formation of metal nanopillars with 20-30 nm repeat spacing and precisely controlled magnetic properties presents a significant challenge to current fabrication methods. We have been developing cylinder forming block copolymer phases as a method to generate the desired patterns coupled with the processing steps necessary to transfer the pattern into magnetic material. This involves spin coating of the polymer on an appropriate orienting layer, annealing to allow the pattern to form by self-organization of the block copolymer, solvent processing to remove the minority domain, electrodeposition to form a hard mask, followed by ion-milling to transfer the pattern to the magnetic material. We have demonstrated each step in this process and report on the quality of the pattern achieved.

The development of patterned media for high density information storage requires the development of methods for cheaply creating patterns in the 20-40 nm range. Cylinderical phase block copolymers self-assemble on this length scale to give the desired patterns. However, use on noble metal capped magnetic phases of such cylinder forming phases needs a thin orienting layer to align the cylinders perpendicular to the substrate surface. Random copolymers of similar composition to the block copolymer provide an appropriate orienting layer. By attachment of a thiol group to the random co-polymer, the random copolymer will be covalently bound to a platinum or gold surface allowing the formation of a suitably thin orienting layer. Synthesis of such thiol-functionalized polystyrene-polymethylmethacrylate random co-polymers is reported. The synthesis uses a novel two-step route starting with commercially available polystyrene-polymethylmethacrylate random copolymer.