Electroplating, electrospray emitter, phosphate sensor
In the electroplating process, dissolved metal cations are reduced by electrical current to a form a coherent metal coating on an electrode. Therefore, electroplating is primarily applied to modify the surface properties of an object (e.g. abrasion and wear resistance, corrosion protection, lubricity, aesthetic qualities, etc.), but also be applied to build up high aspect ratio structures on undersized parts or to form devices by electroforming. Compared with other common MEMS (microelectromechanical systems) metal device fabrication techniques, such as vapor depositions, electroplating has several outstanding advantages. First, the fabrication process is cost-efficient because electroplating process can be set up easily without complex and expensive facilities. Second, the fabrication condition of electroplating is less demanding and does not require high temperature or low pressure. Furthermore, the process is applicable to making various features consisting of nanometer to millimeter scale particles, wires, and films. Thus, in this thesis, based on the design requirements of electrospray emitters and environmental sensors, the electroplating method was chosen to fabricate micro- and nanoscale structures for such applications. Electrospray is an atomization technique by which an electrically conductive liquid through a small capillary is charged with high voltage (kV) and ejected to a ground electrode. To minimize the electric field edge effect of the emitter nozzles to get even electro-hydrodynamic pulling force on the liquid among the nozzles and minimize variation from one emitter to another, the device needs to have the viscous pressure drop across each nozzle dominant over the electro-hydrodynamic pulling force. Therefore, embedded structures that can create high flow impedance are desirable to achieve uniform feeding of low flow rate of liquid to each emitter. We designed and fabricated in-plane metallic electrospray devices with an embedded array of micropillars within a microchannel by photolithography and electroplating. The novelty of the proposed research lies in its embedded flow restriction structure, scalability, and ease of fabrication. The formation of jets as well as the flexing capability of the emitter was achieved. The other application of electroplating was demonstrated in the fabrication of environmental sensors. Utilizing a pulsed electroplating method, Co-Cu metal alloy films were prepared and Cu was selectively etched to fabricate nanoporous electrodes which could be used to measure both absolute levels and changes of phosphate concentration in aqueous environments. The formation of cobalt phosphate compound could be used for the detection. The increased surface area and relatively simple fabrication protocols make the proposed method attractive and promising for many environmental sensing applications.
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Cho, Hyoung Jin
Master of Science in Materials Science and Engineering (M.S.M.S.E.)
College of Engineering and Computer Science
Materials Science Engineering
Materials Science and Engineering
Length of Campus-only Access
Masters Thesis (Open Access)
Dissertations, Academic -- Engineering and Computer Science; Engineering and Computer Science -- Dissertations, Academic
Wang, Xiaochen, "Electroplated micro- and nanoscale structures for emitters and sensors" (2014). Electronic Theses and Dissertations, 2004-2019. 4617.