Magnetic Iron Oxide Nanocubes - The Effect of Substrate Modification, and Post Assembly Manipulation on the Formation of a Monolayer
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Over the last decade, nanoparticles have become particles of great research interest because of their inherent chemical compositions such as size, shape, ability to be coated by other molecules, and control over their magnetic properties. The Assembly of these particles into a monolayer allows their unique properties to be harnessed and applied in various fields of study. The goal of this study was to use various surface modification techniques to assemble magnetic iron oxide (Fe3O4) nanocubes suspended in a 3:1 chloroform: methanol dispersing agent, into a monolayer. By exploring literature on how changing different factors such as plasma cleaning, Langmuir-Blodgett (LB) technique, and annealing, the conditions optimal for the monolayer formation were characterized and verified using transmission electron microscopy (TEM) imaging and subsequent analysis. For the primary objective of nanoparticle assembly into monolayer films, the techniques of spin coating onto a carbon TEM substrate was used. The role of TEM grid modification using plasma cleaning and LB technique was explored to see the effect on the even distribution of the nanoparticles. Post-modification annealing on spin-coated nanoparticles was also explored and was projected to play a vital role in morphological stability and even particle distribution on the carbon TEM substrate. After annealing, the grids are imaged under TEM at different magnifications. Using the Java-based program, Image J, it was found that the nanocubes maintained their shape and the mean cubic length of 15.50 nm at temperatures ranging from 100 – 150 oC. The TEM grids with no surface modification, annealed at 100 oC showed the highest area coverage of 80%. The results so far indicate that plasma cleaning of TEM grids can hinder the formation of a uniform monolayer. This could be due to the unfavorable interaction between the hydrophobic decanoic acid coating of nanocubes and the hydrophilic TEM grid. The TEM grids coated with heptadecanoic acid (HDA) had a more evenly dispersed layer of nanocubes. This could be due to the favorable hydrophobic interactions between hydrocarbon chains of HDA and decanoic acid. The study reveals how different surface modification techniques affect the assembly of nanocubes into a monolayer formation. Further investigation is needed to confirm if the annealing of nanocubes at 100 ̊ C on a hydrophobic substrate is the best modification to promote the formation of a uniform monolayer.