The metallisation onto non conductive surfaces using chlorophyll: where nature meets electronics Prof. Marc Desmulliez Heriot-Watt University, Edinburgh Scotland, United Kingdom m.desmulliez@hw.ac.uk
Outline Taxonomy (or roadmap) of additive metallisation technologies. Established light-directed additive metallisation process from Heriot-Watt University. Bio-inspired process. Conclusion.
Deposition and patterning of metals The industry standard: photolithography. (i) Blanket evaporate / sputtering metals. (ii) Photo-patternable polymer. (iii) Selective plating through the patterned polymer coating. 30µm diametre 60µm pitch
Additive metallisation examples Laser thermal decomposition. Slow scan speed 200µm/s. Fine line width: 6µm. Credit: Aminuzzaman et al., 2010, (Tohoku University, Japan)
Additive metallisation examples Inkjet printing. Ink formulation, droplet size, spreading, sintering.
Super-fine droplets: <1µm diameter, printed on polyimide. Credit: NanoPaste (Harima Chemical Inc., Japan)
Metals by reduction Reduce metal ions by electrons donated via: Thermal Chemical Photo in hydrogen atmosphere. with (usually toxic) reducing agents. with (usually mild) photo-reducing agents.
Advantages of light-directed processes Contact-less, high resolution patterning.
Old Heriot-Watt process Photo-activated mild reducing agent. MPEG - methoxy poly(ethylene glycol). Apply on metal ion-exchanged polyimide.
Old Heriot-Watt process Photoreducing agent coating, donates electrons to the region of the substrate exposed to light. Metal nanoparticles produced only on the sites exposed to light. Ng et al., IEEE Trans Nano 2012 vol. 11 (1) pp. 139-147 Ng et al., Micro Nano Lett 2008 vol. 3 (3) pp. 82-89
hoto-reducing agent coating Nanocomposite layer Bulk polyimide Metal particles are shaped by the surrounding polymer chains, and grow during light exposure. Coating washed away after exposure Bulk polyimide Thus the metal nanoparticles are mechanically interlocked within the modified polymer matrix.
40µm line & space
Issues Mild photo-reducing agent MPEG takes several hours of processing time. UV attack on polymer substrate.
Why bio-inspired process? Faster. Process efficiency in nature is often optimised. Cleaner. Environmentally friendly alternative to synthetic agents. Easier. Less steps, less labour intensive, less man-made materials required.
Photosystems I and II Consist of several light-absorbing proteins + >200 cofactors.
How far do electrons travel? PS I and II 2.5µm Chloroplast length = 5µm Electron transport chain in the thylakoid membrane.
New Heriot-Watt process
Excited electron transfer: 1 nanometre in a few picoseconds. Light absorbing antenna -> electron acceptor chains Strong reducing agents in PS II.
(1) Efficient electron transfer within the PS I & II complex. - Rapid charge separation (10-30picoseconds) upon light exposure. - Iron-sulfur receptors (Fa) pick up the electrons in an energy cascade. - Electrons shuttled away from Fa at almost perfect quantum yield. 470 nm illumination PS I & II Ag + Ag + Ag Ag + Ag + + Ag + Ag + Ag + Ag + Ag + Ag + Ag + Ag +
(2) Plasmon enhancement of photon fields. - PS I & II proteins confined in nano-cavities amongst Ag-NPs. - Ag-NPs act as artificial antennas can enhance the light absorption of the proteins (broadband?, narrow spectra?). 470 nm illumination PS I & II Ag-NP Ag + Ag + - - - - - - - -- - - - - -- - - - - - - -- - - Ag-NP Nanocavities Ag-NP Ag-NP Ag + Ag + Ag + Ag + Ag + Ag + Ag + Ag + Ag + Plasmon field
(3) Ag-NPs as large surface area nanostructured electrodes. - Excited electrons stored on the surfaces of Ag-NPs. 470 nm illumination PS I & II - - - - - - - -- - - - Ag-NP Ag + Ag + - Ag-NP - - Ag-NP Ag-NP Ag + -- - - - - - -- - - Ag + Ag + Ag + Ag + Ag + Ag + Ag + Ag + Ag +
Exposure times: (a) 0s, (b) 30s, (c) 60s, (d) 180s, (e) 600s.
1W/cm 2 1W/cm 2 1W/cm 2
Broadband ion beam (BIB) dissected cross-section.
Next manufacturing phase
Conclusions Shorter exposure times by the use of bio-materials. Sustainable manufacturing. Further work to understand how the physical phenomena affect the manufacturing of the metal features. Proper DOE of this new process and use in Additive manufacturing. Theme for Manufacturing with Light proposal.