Flower-shaped domains and wrinkles in trilayer epitaxial graphene on silicon carbide.

Trilayer graphene is of particular interest to the 2D materials community because of its unique tunable electronic structure. However, to date, there is a lack of fundamental understanding of the properties of epitaxial trilayer graphene on silicon carbide. Here, following successful synthesis of large-area uniform trilayer graphene, atomic force microscopy (AFM) showed that the trilayer graphene on 6H-SiC(0001) was uniform over a large scale. Additionally, distinct defects, identified as flower-shaped domains and isolated wrinkle structures, were observed randomly on the surface using scanning tunneling microscopy and spectroscopy (STM/STS). These carbon nanostructures formed during growth, has different structural and electronic properties when compared with the adjacent flat regions of the graphene. Finally, using low temperature STM/STS at 4K, we found that the isolated wrinkles showed an irreversible rotational motion between two 60° configurations at different densities of states.

High resolution imaging of superficial mosaicity in single crystals using grazing incidence fast atom diffraction.

A new table top technique is used to simultaneously analyze the local morphology of crystalline surfaces as well as the misalignment of large scale domains at the topmost surface layer. The approach is based on fast atom diffraction at grazing incidence (GIFAD); the diffraction pattern yields the structural characteristics and the topology of the surface electronic density with atomic resolution. If superficial mosaicity is present, diffraction patterns arising from each mosaic domain can be distinguished, providing high sensitivity to the properties of each of the domains. Taking NaCl(001) as an example, we observe a discrete tilt angle distribution of the mosaic domains following an arithmetic progression with a 0.025° ± 0.005° difference; a twist mosaic angle of 0.09° ± 0.01° is also observed.

Growth and dissolution kinetics of ultra thin silicon films on Cu(100).

On Cu(100) surface, Auger electron spectroscopy (AES), Low Energy Electron Diffraction (LEED) and Scanning Tunnelling Microscopy (STM) were used to study (i) at room temperature (RT) the first steps of silicon growth and, (ii) at higher temperature, the dissolution process of silicon in Cu(100). The growth kinetics of Silicon onto Cu(100) at RT monitored by AES shows a quasi perfect layer-by-layer behaviour. After deposition at RT of about 5 silicon monolayers (ML), isochronal dissolution kinetics (rate of annealing of 1.5 degrees C/min) is recorded in a temperatures range [50-400 degrees C]. The slowdown observed in the kinetics dissolution for temperatures between 150 and 340 degrees C, reveals formation of an intermetallic superficial phase thermally stable in this range of temperature. LEED pattern and STM images show large domains of a rectangular (5 x 3) superstructure.