Production

production

We focus on engineering innovation through materials production and processing to device fabrication and integration where control over architecture, functionality and integration are central to their application. Scalable production of pristine 2d materials forms the basis of our ambitious research which not only targets laboratory demonstrations, but also prototypes that can be further refined by our industrial partners for commercial realisation. We also focus on other low dimensional nanomaterials, in particular, application of bandgap gradient semiconductor nanowires and various hierarchically porous oxide materials. We adopt solution processing strategy to exploit the properties of some of these nanomaterials to circumvent current limitations in large scale nanomaterial production of 'a well-defined structure and property at a well defined location.
In their bulk crystal forms, layered materials can be compared to a book with millions of individual sheets stacked on top of each other, bound by the weak van der Waals forces. In liquid environment, we employ shear forces generated by cavitation, typically through ultrasound and/or vortex/shear mixing to overcome these interlayer forces, resulting in exfoliation of nanometre-thin flakes from their bulk crystals. While graphene has attracted many of the headlines associated with layered materials science, technology and application, it is only one member of a much wider class of 2d materials which offer many complementary (opto)electronic, thermal and mechanical properties. In addition to graphene, our current portfolio of materials exhibit conducting, insulating and semiconducting properties, with varying bandgap. The library of materials we produce forms the core of the technology that can be used in the form of single, mixed or heterostructures, essentially engineering new materials that does not exist in nature.
In collaboration with our partners, we also work on production, processing and device fabrication of 0d hierarchically porous oxides, 1d nanotubes, nanowires and 2d layered materials and their heterostructures using alternative fabrication strategies.

Processing

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Layered materials produced via solution phase techniques require further processing and purification. We achieve this by employing various centrifugation, filtration and chemical techniques, all of which can be scaled up reliably through standard dimensional approach employed in the physical sciences and manufacturing industry. We explore a range of deposition strategies and substrates to realise our devices. In terms of deposition technology, our interest lies in a range of digital and analog printing techniques such as inkjet-, screen-printing, and web-, spray-coating. Each of these deposition methods offers different advantages and disadvantages for specific applications. They can also be extended to continuous roll-to-roll processing, allowing for high throughput and low cost production of flexible electrodes and devices. This requires us to consider tailoring the ink properties so as to achieve the best printing/coating conditions for specific device applications. Indeed, production of graphene and other 2d functional materials in a liquid environment allows the choice of solvent, dispersant, exfoliation parameters and materials post-processing strategies to produce dispersions with desired range of flake size and thickness, and material concentration.
The dispersions can then be formulated as printable inks through the use of additives to tune the viscosity and surface energy. Our strategy retains the unique functionalitities of the 2d flakes. We employ a wide range of substrates to develop our application platform, including plastic, various grades of paper, flexible glass, quartz, silicon etc. The substrates may require surface modification using self-assembled monolayers to allow uniform material deposition for device applications with an ultimate aim of achieving batch to batch reproducibility. Aside from printing, the dispersions can also be combined with polymer solutions to produce composite materials. These can either enhance the properties of the polymer (e.g. by introducing electrical conductivity, improving mechanical property), or allow easy handling of the functional nanomaterial (e.g. free-standing polymer films).
In collaboration with our industrial partner Novalia Ltd, and with funding from The Engineering and Physical Sciences Research Council, we have recently demonstrated high speed (> 100 metres/min) printing of highly conductive graphene ink using commercial flexographic printers. This technology has a great potential not only for flexible, stretchable and conformable electronic devices for wearable applications, but also in smart packaging, disposable sensors and RFID tags.

For more information, please see:
New graphene based inks for high-speed manufacturing of printed electronics.

Applications

application

The application part of our research involves device fabrication, through integrating different components to engineer complete devices such as smart windows, electroluminescent displays, transistors, photodetectors etc. In all these devices, the functional inks we develop either offer superior properties to existing materials or introduce completely new functionalities. Smart windows, for example, allows device flexibility while switching between transparent and scattering (blocking light) state, enabled by our ink systems. On the other hand, interfacing capabilities of our graphene printed inks with conventional electronics allow transparent piano or touchpad. The versatility of our materials systems is also highlighted in printed, flexible electroluminescent displays on paper using printed graphene electrodes.
On the other hand, composite materials, typically produced by mixing the 1d and 2d material dispersions with different host polymers, have a number of possible applications. They can act as a support structure for the exfoliated material, offering ease of handling while retaining the optical properties of the materials. Working very closely with our colleagues, we are using these type of composites to produce pulsed lasers for applications ranging from telecommunications to medical imaging. Like production and processing, we also have a strong interest is scaling up of 2d material based device manufacturability within acceptable statistical performance variations.
With our collaborators, we are also working towards high temperature growth of 2d materials and 0d oxides and their application in photodetection, sensing, Li ion batteries, supercapacitors, solar cells etc. All these devices can, in turn, be integrated with larger, semi-autonomous systems.