Abstract
Ion Beam Aperture Array Lithography was applied to top-down fabrication of large dense (108–109 particles/cm2) arrays of uniform micron-scale particles at rates hundreds of times faster than electron beam lithography. In this process, a large array of helium ion beamlets is formed when a stencil mask containing an array of circular openings is illuminated by a broad beam of energetic (5–8 keV) ions, and is used to write arrays of specific repetitive patterns. A commercial 5-micrometer metal mesh was used as a stencil mask; the mesh size was adjusted by shrinking the stencil openings using conformal sputter-deposition of copper. Thermal evaporation from multiple sources was utilized to form magnetic particles of varied size and thickness, including alternating layers of gold and permalloy. Evaporation of permalloy layers in the presence of a magnetic field allowed creation of particles with uniform magnetic properties and pre-determined magnetization direction. The magnetic properties of the resulting particles were characterized by Vibrating Sample Magnetometry. Since the orientation of the particles on the substrate before release into suspension is known, the orientation-dependent magnetic properties of the particles could be determined.
Highlights
Nano- and micro-particles, especially spheres and nanoshells, play a growing role in medical diagnostic and therapeutic technologies
Magnetic particles have been manufactured in many different ways, including chemical synthesis [2], hydrothermal treatment [3], photochemical metal deposition [4], and sol-gel fabrication [5], but challenges remain in engineering particles with uniform size and composition, and resistance to corrosion in biological solutions
Using the Array Lithographic (AAL) technique, the particles are made with known pre-determined magnetic orientation, which allows characterization of their anisotropic magnetic properties using Vibrating Sample Magnetometer (VSM)
Summary
Nano- and micro-particles, especially spheres and nanoshells, play a growing role in medical diagnostic and therapeutic technologies. Magnetic particles have been manufactured in many different ways, including chemical synthesis [2], hydrothermal treatment [3], photochemical metal deposition [4], and sol-gel fabrication [5], but challenges remain in engineering particles with uniform size and composition, and resistance to corrosion in biological solutions. AAL was used to pattern large arrays of periodic structures in resist as a template for forming suspendable particles with engineered shape and composition. Particles with magnetic properties have customarily been manufactured by solution synthesis approaches [16]. Using the AAL technique, the particles are made with known pre-determined magnetic orientation, which allows characterization of their anisotropic magnetic properties using VSM
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