Topographic and spectroscopic characterization of electronic edge states in CVD grown graphene nanoribbons

We used scanning tunneling microscopy and spectroscopy (STM/S) techniques to analyze the relationships between the edge shapes and the electronic structures in as-grown chemical vapor deposition (CVD) graphene nanoribbons (GNRs). A rich variety of single-layered graphene nanoribbons exhibiting a width of several to 100 nm and up to 1 μm long were studied. High-resolution STM images highlight highly crystalline nanoribbon structures with well-defined and clean edges. Theoretical calculations indicate clear spin-split edge states induced by electron-electron Coulomb repulsion. The edge defects can significantly modify these edge states, and different edge structures for both sides of a single ribbon produce asymmetric electronic edge states, which reflect the more realistic features of CVD grown GNRs. Three structural models are proposed and analyzed to explain the observations. By comparing the models with an atomic resolution image at the edge, a pristine (2,1) structure was ruled out in favor of a reconstructed edge structure composed of 5-7 member rings, showing a better match with experimental results, and thereby suggesting the possibility of a defective morphology at the edge of CVD grown nanoribbons.     

Growth of large-area single- and Bi-layer graphene by controlled carbon precipitation on polycrystalline Ni surfaces

We report graphene films composed mostly of one or two layers of graphene grown by controlled carbon precipitation on the surface of polycrystalline Ni thin films during atmospheric chemical vapor deposition (CVD). Controlling both the methane concentration during CVD and the substrate cooling rate during graphene growth can significantly improve the thickness uniformity. As a result, one- or two- layer graphene regions occupy up to 87% of the film area. Single layer coverage accounts for 5%–11% of the overall film. These regions expand across multiple grain boundaries of the underlying polycrystalline Ni film. The number density of sites with multilayer graphene/graphite (>2 layers) is reduced as the cooling rate decreases. These films can also be transferred to other substrates and their sizes are only limited by the sizes of the Ni film and the CVD chamber. Here, we demonstrate the formation of films as large as 1 in². These findings represent an important step towards the fabrication of large-scale high-quality graphene samples. Electronic Supplementary Material  Supplementary material is available for this article at and is accessible for authorized users.     

Membrane Tension–Mediated Growth of Liposomes

Recent years have seen a tremendous interest in the bottom‐up reconstitution of minimal biomolecular systems, with the ultimate aim of creating an autonomous synthetic cell. One of the universal features of living systems is cell growth, where the cell membrane expands through the incorporation of newly synthesized lipid molecules. Here, the gradual tension‐mediated growth of cell‐sized (≈10 µm) giant unilamellar vesicles (GUVs) is demonstrated, to which nanometer‐sized (≈30 nm) small unilamellar vesicles (SUVs) are provided, that act as a lipid source. By putting tension on the GUV membranes through a transmembrane osmotic pressure, SUV–GUV fusion events are promoted and substantial growth of the GUV is caused, even up to doubling its volume. Thus, experimental evidence is provided that membrane tension alone is sufficient to bring about membrane fusion and growth is demonstrated for both pure phospholipid liposomes and for hybrid vesicles with a mixture of phospholipids and fatty acids. The results show that growth of liposomes can be realized in a protein‐free minimal system, which may find useful applications in achieving autonomous synthetic cells that are capable of undergoing a continuous growth–division cycle.     

Synthesis, characterization, and optical properties of ordered arrays of III-nitride nanocrystals

A new approach involving self-assembling block copolymer micellar templates and gas-phase reactions to synthesize arrays of monodisperse III-nitrides nanocrystals in the size range of 1-5 nm with uniform spacings between the nanoparticles is demonstrated. The photoluminescence emission spectra revealed the GaN nanocrystals are in the quantum-confined regime. This method not only offers great promise for the controlled synthesis of arrays of ternary III-nitride nanocrystals but may also enable doping in binary nitrides.