Mr. Evarestus Enuka Profile

Evarestus Enuka

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Proceedings Article | 31 January 2020 Presentation + Paper

3D inkjet printing of ferrite nanomaterial thin films for magneto-optical devices

Evarestus Enuka, Mahmuda Akter Monne, Xing Lan, Vincent Gambin, Rachel Koltun, Maggie Yihong Chen

Proceedings Volume 11288, 112881K (2020) https://doi.org/10.1117/12.2542181

KEYWORDS: Thin films, Magnetism, Inkjet technology, Printing, Particles, Manganese, 3D printing, Thin film devices

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A novel method of preparing magnetic ink belonging to the class of ferrofluids which contains magnetic particles with a polar surface-active agent is disclosed. The magnetic material belongs to the group known as magnetite (Fe₃O₄), typically to those with γ-Fe₂O₃ and their likes. Ni-Zn ferrite and Mn ferrite inks were prepared using this method. The inks have a PH value and total dissolved solute of about 6.3, 3.78 mS and 5.9, 4.2 mS respectively, and a viscosity of about 7 cPa, 7.4 cPa respectively. The saturation magnetization of Mn ferrite ink at 300K was 62 emu/cm³. This lower value of the saturation magnetization of Mn ferrite compared to the bulk is because of the shell-core structure of the surfactant coated ferrite particles. The inks were used to prepare various thicknesses ranging from 0.5um to 20um of both Ni-Zn ferrite and Mn ferrite thin films. The surface morphology of the thin film was observed using Atomic Force Microscopy (AFM), showing a compact, dense and relatively smooth film. The microstrip transmission line permeameter approach was used to extract the permittivity and permeability of the thin film samples within the frequency range of 10MHz-1GHz. A relative permeability of 2 was measured. The developed ink and thin film are promising for future magneto-optical applications.

Proceedings Article | 25 August 2017 Presentation + Paper

Inkjet printed graphene-based field-effect transistors on flexible substrate

Mahmuda Akter Monne, Evarestus Enuka, Zhuo Wang, Maggie Yihong Chen

Proceedings Volume 10349, 1034905 (2017) https://doi.org/10.1117/12.2280039

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This paper presents the design and fabrication of inkjet printed graphene field-effect transistors (GFETs). The inkjet printed GFET is fabricated on a DuPont Kapton FPC Polyimide film with a thickness of 5 mill and dielectric constant of 3.9 by using a Fujifilm Dimatix DMP-2831 materials deposition system. A layer by layer 3D printing technique is deployed with an initial printing of source and drain by silver nanoparticle ink. Then graphene active layer doped with molybdenum disulfide (MoS₂) monolayer/multilayer dispersion, is printed onto the surface of substrate covering the source and drain electrodes. High capacitance ion gel is adopted as the dielectric material due to the high dielectric constant. Then the dielectric layer is then covered with silver nanoparticle gate electrode. Characterization of GFET has been done at room temperature (25°C) using HP-4145B semiconductor parameter analyzer (Hewlett-Packard). The characterization result shows for a voltage sweep from -2 volts to 2 volts, the drain current changes from 949 nA to 32.3 μA and the GFET achieved an on/off ratio of 38:1, which is a milestone for inkjet printed flexible graphene transistor.

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