Samarasinghe, SR; (2008) Deposition of noble metals by electrohydrodynamic atomisation. Doctoral thesis , UCL (University College London).

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Abstract

There is an expanding interest in rapid prototyping capabilities of direct write technologies. Due to this, a number of candidate deposition systems have been used for fabricating microscale structures for electronics and biomedical applications such as fabricating conducting tracks for next generation electronic devices, bone replacement parts, flat screen displays and polymeric light emitting diodes...etc. In response to this growing interest in direct write technologies, an experimental investigation was carried out in order to find out whether electrohydrodynamic atomisation can be used as a competing direct write technology. In this research, initially, gold and silver alcosols were subjected to electrohydrodynamic atomisation. Different modes of atomisation and their parameters such as flow rate and voltage were recorded and a mode selection map was constructed for further studies. The main objective was to investigate the feasibility of electrohydrodynamic atomisation to fabricate films of thickness ranging between 100 nm - 1 urn to be used as substrates for e.g. in surface enhanced Raman spectroscopy, cell biology and bio-engineering. The gold alcosol was subjected to atomisation and the droplets resulting from jet break-up were collected on a substrate in order to produce dense gold films. Different flow rates and voltages were used and the optimum conditions such as flow rate, applied voltage and distance between the substrate and the capillary exit, for film fabrication were obtained. The deposition time was varied from 60 - 900 s and the variation of film thickness and surface morphology was observed with increasing deposition time. Dense film thicknesses ranging from -0.5 - -2 um were fabricated by electrohydrodynamic deposition technique. In order to pattern microscale structures on a substrate, gold and silver alcosols were subjected electrohydrodynamic atomisation printing. The main objective was to investigate whether using a low concentrated metal particle solution in conjunction with electrohydrodynamic atomisation printing technique can be utilised to produce conducting tracks in the range of 20 - 200 urns in diameter to be used in next generation electronic devices. Tracks containing metal particles were deposited at various flow rates. With increasing flow rate, the track width increased and the finest track width of -110 urn was achieved. Templates were used to fabricate finer tracks in conjunction with electrospraying and in this case gold tracks of -20 um were patterned on silicon wafer. Due to low metal particle concentration conductive tracks were not possible to produce by these methods. Layer-by-layer deposition method was used with electrohydrodynamic printing to fabricate conducting tracks. The electrical resistivity of the printed gold track in this study was measured to be 1.8 x 10" Qm. The gold hydrosol containing spherical shaped nanoparticles and a silver suspension containing micro size particles were subjected to co-axial electrohydrodynamic atomisation to study the encapsulation of these metals with polyethylene glycol (PEG) : polyethylene oxide (PEO) fibres. The main objective was to investigate feasibility of encapsulating metal particles in polymeric fibres. PEG and PEO was used as a model system to encapsulate silver and gold particles and this technique can be further developed to produce composite fibres to be used in optical, electrical and sensing devices. The relationships between the jet speed and particle arrangement in the encapsulation sheaths were also characterised using advance analytical techniques.

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