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

现代技术需要越来越多的新材料来适应特定应用的特定要求。在过去的十年里，对新材料，甚至更好的材料，可调谐材料的研究急剧加强。这里最好的策略是复合材料和异质结构，它允许最终调整材料参数，组合其他无法匹配的特性，并可以提供多种功能。然而，由于成本和组装/生产这种结构所需的复杂技术，通常这种材料不易获得。在这里，我们提出了一种创造这种复合材料的新范例：基于二维原子晶体的异质结构，可以通过大规模生产的方式组装。通过这种方式，我们可以将特定设备的性能与自然可用材料的特性解耦。最终目标是开发一种“按需材料”的新范例，其特性精确地为新颖复杂的建筑和结构量身定制。我们开创性的研究和大规模生产这种异质结构的技术的发展将对未来的技术产生巨大的影响。我们还将展示基于这种技术的多功能设备的原型。我们计划制造的设备的例子是温度、湿度、光、应变和许多其他传感器，这些传感器将是无电池的，通过吸收无线电波（RFID技术，也可以通过印刷电子设备实现）来提供动力，用于遥感应用。这种无线互联的可调谐传感器和执行器可以为快速增长的“物联网”范式创造一个平台。二维原子晶体是一种单原子厚度的材料。这种晶体家族非常庞大，包括过渡金属二硫族化合物、六方氮化硼、石墨烯等。总的来说，它们涵盖了很大范围的性能：从导电到绝缘，从透明到不透明，从机械硬度到柔顺性。此外，这种二维晶体的性质通常与它们的三维前体的性质非常不同。有趣的是，即使我们用这些材料制作悬浮液（2D墨水），2D晶体的许多独特性质也被保留了下来。这种油墨可用于将二维材料沉积到任何表面，从而产生低成本、保形功能涂层。尽管如此，该系列材料最重要的特性是可以将它们组装成3D堆叠，从而创造出新的异质结构。这种异质结构已经被证明具有新的功能（隧道晶体管，LED等），甚至是几种功能的组合。大量的二维晶体选择，确保了这种异质结构的参数可以在很宽的范围内调谐。在这个项目中，我们建议开发一种低成本的技术，能够从二维油墨中打印出这种异质结构。该联盟的几个成员已经证明，隧道二极管、隧道晶体管和光电探测器可以使用标准的批量生产技术进行印刷。我们将显著增加用这种方法生产的异质结构的范围，并将特别集中在产生主动响应的异质结构（热电、压电、光伏等）。这种异质结构可以在许多应用中充当传感器。然后，我们将把这项技术与已经开发的使用石墨烯油墨印刷RFID天线的技术结合起来。这将允许我们创建不需要电源的不同类型的RFID传感器。例如，我们可以记录产品的温度或该产品所经受的光照。这种技术自然可以实现多功能传感器（例如温度、应变和湿度可以同时记录）。

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).