Size and space controlled hexagonal arrays of superparamagnetic iron oxide nanodots: magnetic studies and application

Tandra Ghoshal,Saibal Roy,Justin D Holmes,Patrick Carolan,Michael A Morris,Ramsankar Senthamaraikannan,Tuhin Maity,Matthew T Shaw

doi:10.1038/srep02772

Abstract

Highly dense hexagonally arranged iron oxide nanodots array were fabricated using PS-b-PEO self-assembled patterns. The copolymer molecular weight, composition and choice of annealing solvent/s allows dimensional and structural control of the nanopatterns at large scale. A mechanism is proposed to create scaffolds through degradation and/or modification of cylindrical domains. A methodology based on selective metal ion inclusion and subsequent processing was used to create iron oxide nanodots array. The nanodots have uniform size and shape and their placement mimics the original self-assembled nanopatterns. For the first time these precisely defined and size selective systems of ordered nanodots allow careful investigation of magnetic properties in dimensions from 50 nm to 10 nm, which delineate the nanodots are superparamagnetic, well-isolated and size monodispersed. This diameter/spacing controlled iron oxide nanodots systems were demonstrated as a resistant mask over silicon to fabricate densely packed, identical ordered, high aspect ratio silicon nanopillars and nanowire features.

Highlights

Dense hexagonally arranged iron oxide nanodots array were fabricated using PS-b-PEO self-assembled patterns
The dimensional control over the self-assembled block copolymer nanopatterns was achieved by different molecular weight PS-PEO systems and the corresponding compositions of the constituent blocks represented as S1 (102 k–34 k), S2 (42 k–11.5 k), S3 (32 k–11 k) and S4 (16 k–5 k)
The solvent/s chosen for solvent annealing depending on the molecular weight and weight fraction of PS of the systems

Summary

Introduction

Dense hexagonally arranged iron oxide nanodots array were fabricated using PS-b-PEO self-assembled patterns. As an alternative to conventional photolithographic processing, self-assembly has been often explored as a potential technique to create patterned magnetic substrates[8,9] These have been limited in application because attaining the required size and shape uniformity providing required mechanical robustness of samples has proved difficult[10,11]. In this work we combine emerging methods in block copolymer lithography with solution based nanoparticle preparation to fabricate nanodots arrays of controlled size and separation. In this way it is shown that the particles demonstrate superparamagnetism and the variation in magnetic properties with size and spacing in the nanoscale can be described precisely. By combining a dry etch technique and using the oxide nanodots as a hard mask, the high density nanopillars/ wires can be generated with controlled distance and topography ensuring complete separation

Methods

Results

Conclusion