Delamination and Photochemical Modification of a Novel Two-Dimensional Zr-Based Metal-Organic Frameworks.

In this contribution we present a novel two-dimensional Zr-based metal-organic framework (MOF) which offers the possibility for delamination and post-synthetic photochemical modification at the linker molecule derived from benzophenone-4,4'-dicarboxylic acid (H2 bzpdc). The new Zr-bzpdc-MOF crystallizes in the orthorhombic system as crystals with rhombic shape. The structure was determined from single-crystal diffraction data. The MOF is stable up to 300 °C in air and exhibits a moderate BET surface area of 650 m2 g-1 . The material can be obtained as thin sheets of a few nanometer thickness. Single crystals were modified post-synthetically, exploiting the intrinsic reactivity of the benzophenone group with C-H bond containing molecules. In this way, the surface properties of the MOF crystals (e.g., dispersibility in different solvents) can be changed drastically. Delamination and adaptation of the surface chemistry open up novel ways for shaping MOFs, for example, for the incorporation into polymer composites, and pave the way for various applications.

Superlattice structures in twisted bilayers of folded graphene.

The electronic properties of bilayer graphene strongly depend on relative orientation of the two atomic lattices. Whereas Bernal-stacked graphene is most commonly studied, a rotational mismatch between layers opens up a whole new field of rich physics, especially at small interlayer twist. Here we report on magnetotransport measurements on twisted graphene bilayers, prepared by folding of single layers. These reveal a strong dependence on the twist angle, which can be estimated by means of sample geometry. At small rotation, superlattices with a wavelength in the order of 10 nm arise and are observed by friction atomic force microscopy. Magnetotransport measurements in this small-angle regime show the formation of satellite Landau fans. These are attributed to additional Dirac singularities in the band structure and discussed with respect to the wide range of interlayer coupling models.