Laurence Magaud

Electron states of mono and bilayer graphene on SiC probed by scanning-tunneling microscopy

We present a scanning tunneling microscopy (STM) study of a gently-graphitized 6H-SiC(0001) surface in ultra high vacuum. From an analysis of atomic scale images, we identify two different kinds of terraces, which we unambiguously attribute to mono- and bilayer graphene capping a C-rich interface. At low temperature, both terraces show

Rotational disorder in few-layer graphene films on 6 H − Si C ( 000 − 1 ) : A scanning tunneling microscopy study

(sqrt{3}times sqrt{3})

Spontaneous evolution of the Ni/Cu(111) interface at 300 K

quantum interferences generated by static impurities. Such interferences are a fingerprint of

Graphene on the carbon face of SiC: Electronic structure modification by hydrogen intercalation

pi

Co-deposition of In and Sn on the Si(100) 2×1 surface: growth of a one-dimensional alloy?

-like states close to the Fermi level. We conclude that the metallic states of the first graphene layer are almost unperturbed by the underlying interface, in agreement with recent photoemission experiments (A. Bostwick et al., Nature Physics 3, 36 (2007))

Impact of local stacking on the graphene-impurity interaction: Theory and experiments

We have analyzed by Scanning Tunnelling Microscopy (STM) thin films made of few (3-5) graphene layers grown on the C terminated face of 6H-SiC in order to identify the nature of the azimuthal disorder reported in this material. We observe superstructures which are interpreted as Moire patterns due to a misorientation angle between consecutive layers. The presence of stacking faults is expected to lead to electronic properties reminiscent of single layer graphene even for multilayer samples. Our results indicate that this apparent electronic decoupling of the layers can show up in STM data.

Dynamics of Pb deposits on theSi(100)2×1surface at room temperature

Abstract The spontaneous evolution of the structures obtained by submonolayer deposition of Ni on Cu(1xa01xa01) at room temperature has been studied by scanning tunnelling microscopy. The growth of an additional Cu plane on top of Ni-rich monolayer (ML) islands, and the simultaneous development of a characteristic electron standing wave pattern, have been observed in real time. From these observations we could derive the composition of the surface plane of the two kinds of bilayer islands that coexist in the deposit. A simple nucleation model is presented to explain the different evolution of pure and partially covered ML islands.

Ab initio study of boron-hydrogen complexes in diamond and their effect on electronic properties

It has been shown that the first C layer on the SiC(0001)(2{times}2)C surface already exhibits graphene-like electronic structure, with linear pi bands near the Dirac point. Indeed, the (2{times}2)C reconstruction, with a Si adatom and C restatom structure, efficiently passivates the SiC(0001) surface thanks to an adatom/restatom charge transfer mechanism. Here, we study the effects of interface modifications on the graphene layer using density functional theory calculations. The modifications we consider are inspired from native interface defects observed by scanning tunneling microscopy. One H atom per 4 {times} 4 SiC cell (5 {times} 5 graphene cell) is introduced in order to saturate a restatom dangling bond and hinder the adatom/restatom charge transfer. As a consequence, the graphene layer is doped with electrons from the substrate and the interaction with the adatom states slightly increases. Native interface defects are therefore likely to play an important role in the doping mechanism on the C terminated SiC substrates. We also conclude that an efficient passivation of the C face of SiC by H requires a complete removal of the reconstruction. Otherwise, at variance with the Si terminated SiC substrates, the presence of H at the interface would increase the graphene/substrate interaction.

STM investigation of the charge transport mechanisms to nanoscale metallic islands on a semiconductor substrate

Abstract We present a scanning tunneling microscopy (STM) study of the co-deposition of In and Sn in the submonolayer range (typical coverage: 0.1 ML) on the Si(100) 2×1 surface. The pure elements Sn and In are known to form one-dimensional (1D) lines of dimers on this surface. The aim of the present study was to examine the possibility to grow 1D metals by co-deposition of group III (In) and group IV (Sn) elements on the Si(100) 2×1 surface. We have analysed samples with different concentrations prepared at or slightly above room temperature. The position of the Sn and In atoms could be obtained from pairs of opposite bias images due to a strong contrast of electronic origin. The results show that metal atoms still form 1D structures, with In and Sn atoms co-existing in the lines. Measurements of the apparent height of the various structures indicate, however, that «mixed» In–Sn dimers are scarce in our growth conditions. These results will be discussed in connection with ab-initio total energy calculations of the possible structures of the dimers.

Electrically active defects in boron doped diamond homoepitaxial layers studied from deep level transient spectroscopies and other techniques

We investigate the graphene-impurity interaction problem by combining experimental - scanning tunneling microscopy (STM) and spectroscopy (STS) - and theoretical - Anderson impurity model and density functional theory (DFT) calculations - techniques. We use graphene on the SiC(000-1)(2x2)_C reconstruction as a model system. The SiC substrate reconstruction is based on silicon adatoms. Graphene mainly interacts with the dangling bonds of these adatoms which act as impurities. Graphene grown on SiC(000-1)(2x2)_C shows domains with various orientations relative to the substrate so that very different local graphene/Si adatom stacking configurations can be probed on a given grain. The position and width of the adatom (impurity) state can be analyzed by STM/STS and related to its local environment owing to the high bias electronic transparency of graphene. The experimental results are compared to Andersons model predictions and complemented by DFT calculations for some specific local environments. We conclude that the adatom resonance shows a smaller width and a larger shift toward the Dirac point for an adatom at the center of a graphene hexagon than for an adatom just on top of a C graphene atom.