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0899-N04-03.1

Fabrication of Nanoparticles and Microspheres with Uniform Magnetic Half-Shells Brandon H. McNaughton1,2, Vladimir A. Stoica2, Jeffrey N. Anker1,2, Katherine M.Tyner3, Roy Clarke2 and Raoul Kopelman1,2,4 1 The University of Michigan, Department of Chemistry, Ann Arbor, MI 48109-1055 2 The University of Michigan, Applied Physics Program, Ann Arbor, MI 48109 3 The University of Michigan, Toxicology Program, Ann Arbor, MI 48109 4 Electronic mail: [email protected] ABSTRACT We report a method for fabricating, anisotropically designed, multiphasic nano-particles with uniform magnetic half-shells. Cobalt layers were deposited onto commercially made nonmagnetic polystyrene nanospheres and microspheres, using ultrahigh vacuum vapor deposition, which produced particles with a half-shell of uniform size, shape and magnetic content. Iron was also deposited onto commercially made silica nanospheres and microspheres and was characterized using transmission electron microscopy and scanning electron microscopy. The coercivity of the magnetic material layers, on the substrate-supported spheres, was enhanced compared to the bulk values of such films without spheres. The particles, once removed from the substrate, were amenable to being rotated in solution, which could allow for more accurate physical and chemical measurements in a variety of fluidic environments. Applications for imaging local mechanical, magnetic and electrical environments are also delineated. INTRODUCTION There are two principal approaches to fabrication of nanodevices: top-down, and bottomup. The top-down approach builds nanodevices by controlled deposition of materials onto substrates[1]. The bottom-up approach builds nanodevices by assembling monomers, dyes, and crystals into nanoparticles by wet-chemistry methods[2,3]. Both approaches have their advantages: the top-down approach allows fine and systematic control of the material and direct electrical interfacing; while the bottom-up approach allows rapid production[4], flexibility of design[2], and creation of devices for in situ control and measurement[5]. Combining bottom-up synthesis of nanospheres and microspheres with top-down methods of controlled deposition of magnetic and semiconductor materials, produces hybrid or multiphasic, anisotropically designed, particles with well controlled magnetic, optical, electronic, and chemical properties. Magnetic nanoparticles and microspheres have shown promise in a wide range of biomedical applications[6]. Generally, these magnetic particles are synthesized in bottom-up techniques[3-6]. However, limited uniformity often results from synthesis involving magnetic materials and this can affect the magnetic responsiveness of the particles[7]. Indeed Häfeli et al. demonstrated that many commercially produced magnetic particles have large variations (33%80% in a viscous solution) in their magnetophoretic mobility[7]. These variations reduce the reliability of magnetic probes, especially for single particle force and torque measurements on the viscoelastic