Engineering van der Waals heterostructures: from atomic level layer-by-layer assembly to printable innovative devices

Modern technology demands increasingly larger number of new materials to suit the specific requirement of the particular applications. The search for new materials, or even better, for materials with tuneable properties, has dramatically intensified over the last decade. The best strategy here are the composite materials and heterostructures, which allow ultimate tuning of material parameters, combinations of otherwise unmatchable properties and can provide multiple functionalities. However, usually such materials are not readily accessible due to cost and the complex technology required for assembly/production of such structures. Here we propose a new paradigm in creating such composite materials: heterostructures based on 2D atomic crystals, which can be assembled by mass-production means. This way we will decouple the performance of particular devices from the properties of naturally available materials. The ultimate goal is to develop a new paradigm of "materials on demand" with properties precisely tailored for novel complex architectures and structures. The ground-breaking nature of our research and the development of the mass-production technique of the production of such heterostructures will have huge impact on future technology. We will also demonstrate prototypes of multifunctional devices which are based on such a technology. Examples of devices we are planning to create are temperature, humidity, light, strain and many other sensors which will be battery-free and powered by absorbing radio waves (RFID technology, also enabled by printed electronics) for remote sensing applications. Such wirelessly interconnected tuneable sensors and actuators can create a platform for the fast-growing "Internet of Things" paradigm.

2D atomic crystals are one atom thick materials. The family of such crystals is very large and includes transition metal dichalcogenides, hexagonal boron nitride, graphene among many others. Collectively, they cover a large range of properties: from conductive to insulating, from transparent to opaque, from mechanically stiff to compliant. Also, very often the properties of such 2D crystals are very different from the properties of their 3D precursors. Interestingly, many of the unique properties of the 2D crystals are preserved even when we create suspensions (2D inks) out of these materials. Such inks can be used for deposition of the 2D materials to any surfaces, creating low-cost, conformal functional coating.

Still, the most important property of materials in this family is the possibility to assemble them into 3D stacks, creating novel heterostructures. Such heterostructures have proven to have new functionalities (tunnelling transistors, LED, etc) or even combinations of several functionalities. The large selection of 2D crystals, ensures that the parameters of such heterostructures can be tuned in a wide range.

In this project we propose to develop a low-cost technique to be able to print such heterostructures from 2D inks. Several members of the consortium have already demonstrated that tunnelling diodes, tunnelling transistors and photodetectors can be printed using standard mass-production technologies. We will significantly increase the range of heterostructures produced by such methods, and will specifically concentrate on heterostructures which produce active response (thermo-power, piezoelectric, photovoltaic, etc). Such heterostructures can act as sensors in a number of applications. We will then combine this technology with already developed technique of printing RFID antenna by using graphene inks. This would allow us to create RFID sensors of different types which do not require power source. For instance, we can record temperature of a product or illumination this product has been subjected to. Multifunctional sensors can naturally be achieved with such technique (for instance temperature, strain and humidity could be recorded at the same time).

This project has a broad range of ambitious objectives: from identifying new 2D materials to developing mass-production methods of producing heterostructures based on such materials. Consequently, we expect a broad impact on industrial, research and academic communities:
* Materials Library and engagement with broader academic and engineering communities: We will initiate an active intelligent search (with the help of DFT calculations) for novel 2D materials and create heterostructures based on such materials. As we expect to accumulate a significant database on such crystals we will publish a catalogue (in a form of a research paper) which will provide structured information on the properties of all known 2D materials and the way they interact when assembled in heterostructures. We expect such a catalogue to be widely used by researchers in academia and industry. We also will create a web version of the catalogue.
* Paradigm Shift: We expect the very concept of "materials on demand" will have a significant resonance in the academic and industrial community. The possibility to design the materials for any specific application is new and very attractive. We will work with various industrial partners (including those outside of the project) with the aim of demonstrating the capabilities of our platform for various applications. We expect this to create a significant impact on the manufacturing community worldwide.
* Materials supply: We will initiate the creation of a spin-off company which will supply monolayer flakes as well as inks of various materials for academic and research purposes. Having a wide variety of well-characterised 2D materials (both in flake and ink form) on offer will benefit a large spread of researchers as well as industries.
* Equipment design: We are planning to use standard printing equipment at the beginning of the project. As we develop a more mature recipe for the inks, we will inevitably implement certain modifications to the equipment. We expect that such modifications will be of interest for equipment manufacturers as 2D inks become increasingly more used in industry.
* Software design: The use of printing technology relies on a very precise tuning of the properties of the inks. We are planning to design software which will allow one to design the inks with specific properties and simulate the printing results. Such software will be of interest to a large community of researchers and engineers working in the area of printing technology.
* Business engagement: We have a number of project partners within the consortium. We are planning to transfer the technology developed within the project to those partners. In particular, Merck is interested in development of stable inks of 2D materials. BGT Materials will be most interested in the technology of printed heterostructures. Such technology transfer will contribute to job creation and technology development.
* Training of Workforce for Industry : The project will generate a large amount of know-how along with papers and patents. We expect that the postdocs involved in the project will be of high value for the commercial companies involved in materials research (both those involved in the project and those outside of the project). Thus, this project will provide training for future staff for the advanced materials industry.
* Engaging community, allowing other materials and heterostructures (developed in other groups) to enter industrial applications: The pool of researchers studying various 2D materials and their heterostructures is increasing daily. Arguably, it is the most dynamically developing direction of research in modern condensed matter physics. Our project will create a pathway for novel materials and heterostructures to be implemented in applications. We will offer to apply our expertise and the technology developed within the project to materials and heterostructures from other research groups to bring those to application.