UCL Promotors : Vincent Bayot, Jean-Christophe Charlier, Benoît Hackens, and Gian-Marco Rignanese
UCL Collaborators : Andrés Botello-Méndez, Sébastien Faniel, Aurélien Lherbier, Sorin Melinte (ICTEAM), Frederico Rodrigues Martins
External Collaborations : X. Blase and V. Olevano (Institut Néel, CNRS-Grenoble, FR), J. Dumont and R. Sporken (FUNDP)
Funding : FNRS - Research Project, Graphene Flagship, ARC Graphene Stresstronics
The aim of the present research project consists in imaging locally various nanostructures using scanning tunneling microscopy (STM) and modeling STM images using the ab initio description (DFT formalism).
STM imaging is based on the quantum tunneling effect, which takes place between the surface of a conducting material and a metallic tip scanning a few angströms above it, in order to probe its local electronic properties. These so-called local probe techniques are tools widely used nowadays, as they give access both to atomic-resolution imaging of the surface of conducting materials, and to spectroscopic information about the surface electron system (the scanning tunneling spectroscopy – or STS - mode). On the experimental side, STM imaging is performed using a LT-STM system from Omicron, down to low temperature (4.2 K) and in ultra-high vacuum conditions. We are focusing on developing new types of scanning probe techniques adapted to image the transport properties of nanodevices, such as scanning gate microscopy (SGM), and combining them with STM. This combination aims at correlating the local behaviour of charge carriers with the atomic structure of nanodevices (including e.g. the position of defects).
Interpreting experimental STM images is always an extremely difficult task which can be tackled with the help of numerical simulations. On the theory/simulation side, the theoretical research objectives of the present project consist in using various available ab initio approaches (integration of the electronic wavefunctions within the Bardeen theory ; simplification of the tip using the Tersoff-Hamann approximation ; full electronic transport calculations between the tip and the surface using Green functions formalism whitin the Landauer-Büttiker approach ; …) to simulate STM images and to predict local densities-of-states that can be compared to STS measurements.
References :
- Quasiparticle effects on tunneling currents: a study of C2H4 adsorbed on the Si(001)-2x1 surface
G.-M. Rignanese, X. Blase, and S. G. Louie
Phys. Rev. Lett. 86, 2110-2113 (2001) - Scanning tunneling microscopy fingerprints of point defects in Graphene : a theoretical prediction
H. Amara, S. Latil, V. Meunier, Ph. Lambin, and J.-C. Charlier
Physical Review B 76, 115423 (2007) - ZnO(0001) surfaces probed by scanning tunneling spectroscopy : Evidence for an inhomogeneous electronic structure
J. Dumont, B. Hackens, S. Faniel, P.-O. Mouthuy, R. Sporken and S. Melinte
Appl. Phys. Lett. 95, 132102 (2009) - One-dimensional extended lines of divacancy-defects in Graphene.
A.R. Botello-Méndez, X. Declerck, M. Terrones, H. Terrones, and J.-C. Charlier
Nanoscale, in press (2011).