This Materials Interdisciplinary Research Team (MIRT) proposal examines the assembly and physical properties of new composite materials created by 'nano-laminating' atomic sheets of different van der Waals (vdW) materials. These vdW building blocks are materials in which the atomic bonds are strong in two directions, but weak in the third. This gives them a layered structure, like a stack of paper, and makes it easy to separate ('exfoliate') the layers. Common vdW materials include graphite, which can be exfoliated to form single sheets (graphene); many high-T superconductors; and layered chalcogenides such as MoS2. Many of these systems already display interesting behavior due to the low dimensionality of their electronic structure. The team pioneered a technique for re-stacking dissimilar vdW materials in a controlled fashion ('nano-lamination'). Using this technique, it is possible to create heterostructures that are essentially designer materials, with control at the level of the individual atomic layer. The aim of the MIRT is to create materials that provide unique functionality that is of interest to fundamental science and engineering applications.
The MIRT proposal includes a central synthesis effort that seeks to broaden the set of materials under study from the first examples (graphene and hexagonal boron nitride) to include layered chalcogenides, 2D oxides, topological insulators, and low-dimensional organic systems. The synthesis effort combines nano-lamination with single-crystal growth, molecular beam epitaxy, templated materials growth, and intercalation. Fundamental issues to be addressed include the nature of interfaces between dissimilar layers, how interlayer alignment changes properties, and 'design rules' for growth on vdW surfaces. The MIRT includes extensive characterization of the new materials by multiple techniques. These techniques include structural characterization, electronic transport, optical and Raman spectroscopy, scanned probe microscopy, and chemical methods.
Using the techniques and materials developed under the MIRT program, the team seeks to address a number of fundamental issues regarding behavior of materials in low dimensions. For instance, it will be possible to study the 3D-to-2D evolution of correlated electronic behavior such as superconductivity and charge density wave states as the host materials approach the limit of single atomic sheets. Likewise, nano-lamination will allow materials such as topological insulators and superconductors to be brought into proximity in order to probe exotic phases predicted to exist at these interfaces.
The MIRT team seeks to broaden the impact of its activities through REU and RET programs, as well as a school visitation program. In addition, a central goal of the MIRT is to strengthen interaction between Columbia and CCNY through better coordination of research and use of shared facilities, as well as joint student advising and recruiting.