Synthesis And Dip-pen Nanolithographical Patterning Of Ferrite Nanoparticles
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Magnetic nanoparticles are of great interest for researchers from a wide range of disciplines, including magnetic fluids, catalysis, biotechnology/biomedicine, magnetic resonance imaging, data storage, and environmental remediation. Ferrites, a class of ferrimagnetic ceramic compounds with the chemical formula of MFe₂O₄, where M represents any one of several metallic elements such as Mg, Fe, Co, Ni, Cu and so on, are commonly used magnetic materials for nanoparticles. Magnetite (Fe3O₄) is the prototype of ferrites. Magnetite nanoparticles have been prepared through the co-precipitation of Fe²⁺ and Fe³⁺ aqueous salt solutions by addition of base. They exhibit a size distribution from 4 nm to 16 nm, showing properties of superparamagnetism. Although co-precipitation is an easy and inexpensive method to prepare magnetite nanoparticles, the control of the particle size becomes the biggest experimental challenge. Centrifugation has been employed as a simple way for size selection. Dip-pen nanolithography (DPN) which was invented in 1999 by Mirkin's group in Northwestern University has been reported as a unique technique with a high resolution for transferring ink molecules on to substrate to create different kinds of micro- or nanostructures. In a typical lithographical experiment, an atomic force microscope (AFM) tip is coated with ink molecules. They are delivered to the surface of a substrate through or over a water meniscus that forms between the tip and the substrate. Water meniscus works as a medium for ink transportation. The self-assembly of ink molecules deposited using DPN can be modeled as a two dimensional diffusion with a source (AFM tip). Dot- and line- features of magnetite nanoparticles within micro- and nanoscale have been generated on 16-mercaptohexadecanoic acid (MHA) patterns created by DPN, giving a precise control of size and position. Dot diameter can be tuned by adjusting the writing time which has a t1/2 dependence (where t is the tipsubstrate contact time). Line width has a linear relationship with the scanning speed. The concentration of suspension of magnetite nanoparticles is crucial for the passivating effect of 1- Octadecanethiol (ODT). The optimum value of concentration of the magnetite nanoparticles suspension has been obtained.