Metamaterials typically consist of metallic and dielectric repeating structures. Electrodeposition of copper is the preferred approach to fabricating the metallic part of the metamaterials of interest in this study. The highly variant topography requires chemical additives, like chloride ions, 3-mercapto-1-propanesulfonic acid (MPSA), polyethylene glycol (PEG), and polyvinylpyrrolidone (PVP) to enhance bottom-up superfilling while maintaining terrace flatness. This study focuses on both experimental and computational investigations of the degradation potential of the additives and their adsorption mechanism in a highly acidic copper electrolyte in order to optimally parametrize the copper electrodeposition process. Results show Cl-MPSA-PEG-PVP additives perform well, but substitution of PVP with Janus Green B provides better terrace leveling. Additionally, NMR data show a quick and complete conversion of MPSA to bis(3-sulfopropyl) disulfide (SPS) in the acidic copper bath. Finally, FEM simulations further show that the accelerator species may initially accumulate and be transported vertically until overplating, whereby they are transported laterally.
An unconventional electrodynamic suspension system with transparent planar electrodes is described which stably levitates charged solid particles or liquid droplets without the need for feedback control. The system has been used with particles ranging from about 1 to 100 m diam, under vacuum and within stationary and flowing gases. Operation within low conductivity liquids is possible in principle. The suspension system consists of six transparent conducting electrodes arranged as faces of a hollow cube. Four of these electrodes are driven by a variable-frequency two-phase ac source operating in the low audio frequency range. Advantages of this type of trap for aerosol studies include relatively wide-angle optical access and a geometry naturally suited to the use of three-axis dc crossfields for particle manipulation. Conditions for stable levitation are reviewed as well as methods for determining the radius, mass, charge, and density of a spherical levitated object.
This work focuses on finite element modeling (FEM) of a three-dimensional metamaterial used as an absorber for terahertz energy harvesting. The metamaterial consists of patterned pillars of an SU-8 dielectric photoresist coupled to a copper metal overlayer. Our study shows that the electromagnetic performance of the metamaterial is dependent on the following characteristic design parameters of the SU-8 dielectric: pillar height, bottom side length, and spacing between adjacent pillars. Using FEM, the metamaterial geometry is successfully optimized and the surface plasmon can be tuned to a peak frequency of 1.2 THz and a maximum terahertz absorption amplitude of 30%.
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