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Parker, J, 2024. Dielectrophoresis - utilising a novel electrode geometry. PhD, Nottingham Trent University.
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Abstract
In this thesis, the phenomenon of dielectrophoresis (DEP) is explored by utilising a novel MOS capacitor-style geometry. Photolithography was used to pattern metal electrodes onto the polished surface of a doped p-type silicon wafer, which already had a 1-micron thick oxide layer thermally grown onto its surface. Due to the nature of the geometry only having one patterned electrode surface, it allowed for more complex patterns to be etched into the metal electrode than typical coplanar interdigitated electrodes (IDEs). An AC voltage was applied between the top metal electrode and the p-type silicon underside of the wafer, with the oxide layer forming an electrically insulating layer in the middle, therefore producing a MOS capacitor-type structure. By applying this voltage, highly localised non-uniform electric fields were produced along the edges of the top metal electrodes which were utilised to perform a variety of dielectrowetting and particle dielectrophoresis experiments.
Uni-directional dielectrowetting was achieved by etching long thin rectangular stripes into the metal electrode. A relationship of cos(θ) vs V2 was discovered for the contact angle vs voltage measurements. Axi-symmetric dielectrowetting was demonstrated in which the droplet of liquid mirrored the underlying patterns etched into the electrode as it spread, allowing the formation of hexagonal and square-shaped droplets before eventually spreading into a uniform thin film at larger voltages. Thin threads of liquid could be extracted from a parent droplet along the edge of the metal electrode. These threads were observed to follow a Lucas-Washburn type behaviour, as well as length, width and volume voltage dependence. The ability of the geometry to perform particle DEP was observed by placing a droplet suspension of polymer microspheres onto the top surface with a variety of striped and circular array patterns in the underlying electrode. In these experiments, the particles would arrange themselves depending on the voltage and frequency. The formation and evaporation of thousands of sub-picolitre microdroplets was also studied using this geometry. The microdroplets were observed to undergo diffusive evaporation and this was compared to Masoud’s theory of the evaporation of multiple droplets with some numerical simulations.
| Item Type: | Thesis |
|---|---|
| Description: | Abridged version |
| Creators: | Parker, J. |
| Contributors: | Name Role NTU ID ORCID |
| Date: | January 2024 |
| Rights: | The copyright in this work is held by the author. You may copy up to 5% of this work for private study, or personal, non-commercial research. Any re-use of the information contained within this document should be fully referenced, quoting the author, title, university, degree level and pagination. Queries or requests for any other use, or if a more substantial copy is required, should be directed to the author. |
| Divisions: | Schools > School of Science and Technology |
| Record created by: | Laura Borcherds |
| Date Added: | 10 Jun 2025 13:00 |
| Last Modified: | 10 Jun 2025 13:00 |
| URI: | https://irep.ntu.ac.uk/id/eprint/53717 |
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