Patterned Langmuir-Blodgett Films of Monodisperse Nanoparticles of Iron Oxide Using Soft Lithography

Recently monodisperse magnetic nanoparticle systems such as FePt, Co, Fe, Fe₃O₄, and γ-Fe₂O₃ have been made through solutionphase syntheses.¹ It becomes increasingly important to develop strategies to fabricate these nanoparticles into patterned thin films to explore their collective properties and the potential applications, such as ultrahigh-density magnetic storage media and magnetooptical devices.^1-6 The unmediated self-assembly of monodisperse nanoparticles can only offer limited packing orders with almost no controls of the domain structure, packing density, and number of layers deposited. Among the techniques for the deposition of thin films of nanoparticles on solid substrates, layer-by-layer (LbL) deposition and Langmuir-Blodgett (LB, vertical lift) technique are some of the most promising methods because they enable fine control of the thickness and homogeneity of the monolayer, and ease for multilayer deposition.^3,6-8 Recently, Sun et al. have succeeded in making poly(ethylenimine)-PtFe nanoparticle thin films using ligand exchange and the LbL deposition method.³ Werts et al. have showed that it was possible to pattern LB films of gold nanoparticles using electron beam lithography.⁹ Although several methods have been explored in patterning, a predefined organic layer on a substrate is typically required to deposit nanoparticles in certain regions.^10,11 The approach is not ideally suitable for generating highly ordered and close-packed homogeneous patterns of nanoparticles, which is potentially important for applications.³