The interlayer coupling can be used to engineer the electronic structure of van der Waals heterostructures (superlattices) to obtain properties that are not possible in a single material. So far research in heterostructures has been focused on commensurate superlattices with a long-ranged Moiré period. Incommensurate heterostructures with rotational symmetry but not translational symmetry (in analogy to quasicrystals) are not only rare in nature, but also the interlayer interaction has often been assumed to be negligible due to the lack of phase coherence. Here we report the successful growth of quasicrystalline 30° twisted bilayer graphene (30°-tBLG), which is stabilized by the Pt(111) substrate, and reveal its electronic structure. The 30°-tBLG is confirmed by low energy electron diffraction and the intervalley double-resonance Raman mode at 1383 cm Moreover, the emergence of mirrored Dirac cones inside the Brillouin zone of each graphene layer and a gap opening at the zone boundary suggest that these two graphene layers are coupled via a generalized Umklapp scattering mechanism-that is, scattering of a Dirac cone in one graphene layer by the reciprocal lattice vector of the other graphene layer. Our work highlights the important role of interlayer coupling in incommensurate quasicrystalline superlattices, thereby extending band structure engineering to incommensurate superstructures.

The moiré pattern is found to critically tune the electronic structure of the ErCu2 monolayer within the moiré pattern.

Cu 2 ZnSnS 4 (CZTS) is a promising thin-film solar-cell material consisted of earth abundant and nontoxic elements. Yet, there exists a fundamental bottle neck that hinders the performance of the device due to complexed intrinsic defects properties and detrimental secondary phases.Recently, it was proven experimentally that Na and K in co-evaporation growth of CZTS can enlarge the grain size and suppress formation of ZnS secondary phase near surface, but the reasons are not well understood. We used first principle calculations to investigate the kinetic processes on CZTS ( 112 ) surface involving Group I elements, including Na, K, and Cs, to demonstrate their surfactant effects. Both the structure of the reconstructed surfaces involving Group I elements and various diffusion paths of a Zn ad-atom in these reconstructed surfaces were explored. The advantages and concerns of the surfactant effects of Na, K, Cs, were systematically compared and discussed. Although Group I elements protect Cu sites on the subsurface layer, a disordered metastable configuration with a diffusion barrier of about 400meV was found. Therefore, a precise control of growth condition is essential to avoid the metastable phase. In addition, our studies provide a systematical design principle for surfactant effects during the growth.

Transition metal dichalcogenides, mainly focusing on MoS2, have attracted intensive studies in terms of their electronic and optical properties. Their lower-dimensional counterparts, such as nanoribbons and nanoclusters, gradually draw more research attention because of their potential applications in various electronic and spintronic devices. The edge states are essential to determine the intriguing electronic and magnetic properties of the nanocrystals. In this review, we mainly focus on the zigzag edges in the MoS2 system because they are more common in experiments. We first review the physical properties of the unreconstructed edges and then introduce the principles of edge reconstructions, the electron counting model (ECM). Then, based on the ECM, intrinsic edge reconstructions with different periodicities are discussed. The literature we reviewed suggests that the conductivities and magnetism of the edge states are highly related to the periodicities of the edges. Finally, the effects of the edge passivation with extrinsic atoms are reviewed. Edge passivation plays an important role in tuning the electronic and magnetic properties of the edge states and determining the morphology during the crystal growth. Furthermore, MoS2 zigzag edges could be an ideal platform to investigate the interplay between the edge states with different periodicities and magnetic dopants in the future.