Beyond van der Waals: next generation of covalent 2D-2D heterostructures

Interview to the authors

   How would you explain your work to someone who has no knowledge of the field?

Enrique Burzurí (EB): 2D materials are extremely (atomically) thin materials that present interesting properties for electronic applications. Depending on the nature of the material, these properties can be different (good electrical conductivity, sensitivity to light, etc). This is why scientists are trying to combine two or more of these materials into a new one. The most widespread method to do this is by manually stacking one material on top of the other one piece at a time. Instead, we use chemistry to bond the materials into strong structures where a small molecule is used as linker and as modulator of the electrical properties of the final material.

Emilio M. Pérez (EMP): Exactly! When trying to combine the best of two materials, most scientists have focused on simply piling them up together. What we do here is to actually design a molecular “Velcro” that is reactive towards one material on one end, and towards the other on the other end, so that we can put them together, easier, faster, many flakes at a time…Also, and this is important, the molecular linker actually affects the properties of the final assembly, so we add one more degree of control to the heterostructure.

   Why should an average person care about this research? What are some potential real-life applications?

EB: The approach we have followed has the potential to reduce costs and achieve a better control in the fabrication of new electronic devices based on 2D materials. These breakthroughs would bring the long-time sought implementation of 2D materials in real-life electronics closer.

EMP: This piece of work is best viewed as the development of a tool. We are providing a new means to make devices based on 2D-2D heterostructures. Besides possibly reducing costs of fabrication, as Enrique points out, this has potential implications in what the devices can do (for instance, enabling a new function), and on how well they do it (for example, improved performance of a sensor).

   Why did you choose to research this topic?

EMP: The chemistry of 2D materials is in itself very interesting, because it is very challenging. All atoms look the same, and are typically not very reactive, so it is difficult to do chemistry on them, and difficult means fun! Also, the privilege of chemistry is that we can transform matter, so that we can make it useful (or just more interesting). In this case, for instance, by sticking together two 2D materials easier and with better control. 

EB: For me, the combination of 2D materials into heterostructures is one of the most active fields in materials science. I find very interesting that this research field may lead not only to new technologies but also to new exciting physical phenomena.

   What is the most exciting thing about your results?

EB: I find very exciting that thanks to this chemical approach we can fabricate hundreds of these electronic devices in a single step. Moreover, this technique can be extended to other more exotic materials so we can create a new generation of electronic devices with properties that can complement electronics

EMP: I believe the simplicity of the method is what’s most exciting. Everything is done under mild conditions, at or close to room temperature, using common laboratory equipment and reagents… This also makes it very robust and reproducible: we’ve made literally hundreds of devices and the method just works!

   What is the novelty, the innovation beyond the state of the art of these results?

EMP: It’s always difficult to quantify these things…especially when it is your own research you are talking about. Perhaps the easiest way to gauge the novelty is that so far, the stacking of 2D materials on top of one another relied exclusively on van der Waals forces to the point that the whole field is often called “van der Waals heterostructures”. Van der Waals forces are great, you know? as a supramolecular chemist, I love noncovalent forces, but if you think of it, it is rather limiting to just have the one option…particularly considering that the properties of the final heterostructure depend crucially on how the nanomaterials are interfaced (I recently heard Prof. Luis Hueso state that “the interface is the device”). On the other hand synthetic chemistry is the paradigm of atomic-scale control. With this piece of work, we bring the huge toolbox of chemistry to the game of making 2D-2D heterostructures… I believe it is fair to say it is a noteworthy contribution.

EB: We have changed the way 2D heterostructures are made. For the first time we have used chemistry to covalently bond 2D materials and in-situ form several electronic devices at the same time.