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Adsorbed layers of water are ubiquitously present at surfaces and fill in microscopic pores, playing a central role in many phenomena in such diverse fields as materials science, geology, biology, tribology, nanotechnology. Despite such importance, the crystal structure of nanoconfined water remains largely unknown. Here we report high-resolution electron microscopy of mono- and few- layers of water confined between two graphene sheets, an archetypal example of hydrophobic confinement. Confined water is found to form square ice at room temperature - a phase with symmetry principally different from the conventional tetrahedral geometry of hydrogen bonding. The square ice has a high packing density with a lattice constant of 2.83 angstrom and during TEM observation assembles in bi- and tri- layer crystallites exhibiting AA stacking. Our findings are important for understanding of interfacial phenomena and, in particular, shed light on ultrafast transport of water through hydrophobic nanocapillaries. Our MD simulations show that square ice is likely to be common inside hydrophobic nanochannels, independent of their exact atomic makeup.

Twisted bi-layer graphene (tBLG) has recently attracted interest due to the peculiar electrical properties that arise from its random rotational configurations. Our experiments on CVD-grown graphene from Cu foil and transferred onto Si substrates, with an oxide layer of 100 nm, reveal naturally-produced bi-layer graphene patches which present different colorations when shined with white light. In particular yellow-, pink- and blue- colored areas are evidenced. Combining optical microscopy, Raman spectroscopy and transmission electron microscopy we have been able to assign these colorations to ranges of rotational angles between the two graphene layers. Optical contrast simulations have been carried out, proving that the observation of the different colorations is due to the angle-dependent electronic properties of tBLG combined with the reflection that results from the layered structure tBLG / 100 nm-thick SiO2 / Si. Our results could lead the way to an easy selective identification of bi-layer graphene merely through the observation on an optical microscope., Comment: This paper has been withdrawn by the author due to copyright incompatibility with the journal of final publication

We present an atomic-resolution observation and analysis of graphene constrictions and ribbons with sub-nanometer width. Graphene membranes are studied by imaging side spherical aberration-corrected transmission electron microscopy at 80 kV. Holes are formed in the honeycomb-like structure due to radiation damage. As the holes grow and two holes approach each other, the hexagonal structure that lies between them narrows down. Transitions and deviations from the hexagonal structure in this graphene ribbon occur as its width shrinks below one nanometer. Some reconstructions, involving more pentagons and heptagons than hexagons, turn out to be surprisingly stable. Finally, single carbon atom chain bridges between graphene contacts are observed. The dynamics are observed in real time at atomic resolution with enough sensitivity to detect every carbon atom that remains stable for a sufficient amount of time. The carbon chains appear reproducibly and in various configurations from graphene bridges, between adsorbates, or at open edges and seem to represent one of the most stable configurations that a few-atomic carbon system accomodates in the presence of continuous energy input from the electron beam., Comment: 12 pages, 4 figures