David Goldhaber-Gordon Invited Talk

When two atomically-thin layers of a material are stacked one atop each other, with a relative twist angle between them, properties can emerge that bear little resemblance to the behavior of the individual layers. Electronic band structure is a strong, and remarkably-predictable, function of spatial structure in such stacks. Unfortunately, our control of that spatial structure remains imperfect.

I will introduce torsional force microscopy (TFM), a technique for mapping moirés midway through the stacking process. We extract from these maps highly-quantitative information on twist and even strain, which also has a strong influence on electronic properties. Our early efforts to compare such spatial structural information with subsequent electrical measurements have shown a close correspondence, but also evidence of intervening relaxation. Further work may elucidate whether this happens during the remainder of stacking, nanofabrication, and/or thermal cycling.

Finally, I'll describe work toward robotic stacking in vacuum and alternative stamp strategies, which combined with TFM mapping might help us get more repeatable control of structure and thus electronic properties in such twisted systems.