Dislocations represent one of the most fascinating and fundamental concepts in materials science. Most importantly, dislocations are the main carriers of plastic deformation in crystalline materials. Furthermore, they can strongly affect the local electronic and optical properties of semiconductors and ionic crystals. In materials with small dimensions, they experience extensive image forces, which attract them to the surface to release strain energy. However, in layered crystals such as graphite, dislocation movement is mainly restricted to the basal plane. Thus, the dislocations cannot escape, enabling their confinement in crystals as thin as only two monolayers. To explore the nature of dislocations under such extreme boundary conditions, the material of choice is bilayer graphene, the thinnest possible quasi-two-dimensional crystal in which such linear defects can be confined. Homogeneous and robust graphene membranes derived from high-quality epitaxial graphene on silicon carbide provide an ideal platform for their investigation. Here we report the direct observation of basal-plane dislocations in freestanding bilayer graphene using transmission electron microscopy and their detailed investigation by diffraction contrast analysis and atomistic simulations. Our investigation reveals two striking size effects. First, the absence of stacking-fault energy, a unique property of bilayer graphene, leads to a characteristic dislocation pattern that corresponds to an alternating AB B[Symbol: see text]AC change of the stacking order. Second, our experiments in combination with atomistic simulations reveal a pronounced buckling of the bilayer graphene membrane that results directly from accommodation of strain. In fact, the buckling changes the strain state of the bilayer graphene and is of key importance for its electronic properties. Our findings will contribute to the understanding of dislocations and of their role in the structural, mechanical and electronic properties of bilayer and few-layer graphene.

Covalently functionalizing mechanical exfoliated mono- and bilayer graphenides with λ-iodanes led to the discovery that the monolayers supported on a SiO substrate are considerably more reactive than bilayers as demonstrated by statistical Raman spectroscopy/microscopy. Supported by DFT calculations we show that ditopic addend binding leads to much more stable products than the corresponding monotopic reactions as a result of the much lower lattice strain of the reactions products. The chemical nature of the substrate (graphene versus SiO ) plays a crucial role.

No abstract

Methyl‐substituierte carbocyclische Aromaten der Benzol‐, Diphenyl‐, Terphenyl‐, Stilben‐, 1,4‐Diphenylbutadien‐, Tolan‐, 1,4‐Diphenylbutadiin‐, Naphtalin‐, Anthracen‐und Phenanthren‐Reihe werden mit Anilen aromatischer Aldehyde in Dimethylformamid in Gegenwart von Kaliumhydroxid oder Kalium‐t‐butylat zu Styryl‐Derivaten umgesetzt.

THE CRYSTAL STRUCTURE OF Cu2CdGeS4pounds; however, in five cases ordering could not be determined even if it existed. We note that the patterns all have high symmetry (F-43m for zincblende and P63mc for wurtzite related compounds). Ordering of the cations seems rather unlikely. The composition 122364 is located on the connecting line between 26 and 1362. Examples are known where a complete series of solid solutions exists between 26 and 1362. Goryunova (1965) lists for example CdTe-AglnTe2 and CdTe-CuInTe2 where the zincblende structure type is found over the entire concentration range. The compositions CuCd2InTe4 and AgCd2InTe4 given in Table 7 are, therefore, only selected points of a complete series of solid solutions. For the other compounds given in Table 7 no homogeneity range measurements have been made, and it must be left for further research to determine if these alloys really correspond to independent quaternary compounds or to the quaternary compositions in a solid solution range between a binary and a ternary normal tetrahedral structure compound. (Bond, 1957); es muss daher numerisch bestimmt werden.