Ab-initio analysis of superstructures revealed by STM on bilayer graphene

In this work we performed density functional theory calculations for a twisted bilayer graphene (BLG). Several conmensurable rotation angles were analyzed and for each one a constant height mode STM image was obtained. These STM images, calculated under the Tersoff-Hamman theory, reproduce the main features experimentally observed, paticularly superstructures and giant corrugations. In this way we confirm that STM characterization of twisted BLG can produce superstructures whose tunneling current intensity maxima occur over regions with $AA$ stacking. Additionally we give new evidence in favour of an electronic origin for the superstructures instead another physical grounds

Moir\'e patterns on STM images of graphite from surface and subsurface rotated layer

We have observed with STM moir\'e patterns corresponding to the rotation of one graphene layer on HOPG surface. The moir\'e patterns were characterized by rotation angle and extension in the plane. Additionally, by identifying border domains and defects we can discriminate between moir\'e patterns due to rotation on the surface or subsurface layer. For a better understanding of moir\'e patterns formation we have studied by first principles an array of three graphene layers where the top or the middle layer appears rotated around the stacking axis. We compare the experimental and theoretical results and we show the strong influence of rotations both in surface and subsurface layers for moir\'e patterns formation in corresponding STM images.Comment: 5 pages, 6 figure

Crustal structure of the Andes from Rayleigh wave dispersion

Records from a Benioff short-period seismograph located at Huancayo, Peru, are digitalized and then passed through a low-pass filter to get the long-period waves. In this way the dispersion curves of Rayleigh waves for paths along the Andes can be computed from seismograms which otherwise would be unusable. The comparison with the empirical curve for a “normal” continental crust (Press 1960) and with specially computed theoretical models indicates a crustal thickness of the order of 50 km. For periods between 20 and 25 sec., the observed group velocity shows abnormally low values