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Accueil du site > Équipes scientifiques > Nanosciences moléculaires > Etudes STM sur Diamant et Carbure de Silicium

Etudes STM sur Diamant et Carbure de Silicium

Etudes STM sur Diamant et Carbure de Silicium

Diamond & Silicon Carbide

Leader : Andrew Mayne

Participants : Gérald Dujardin

Students :

Past Contributors : Geneviève Comtet, Tamara Ovramenko, Heejun Yang, Guillaume Baffou

Surfaces of wide band-gap semiconductors are expected to play a crucial role in many applications ranging from high power micro-electronics, photo-voltaic cells to photo-catalysis. Transparent silicon carbide and diamond surfaces are also ideal for atomic-scale opto-electronic experiments. However, the use of these wide band-gap semiconductor surfaces for molecular nanosciences poses a number of problems such as surface preparation and atomic-scale characterisation, efficient doping, conductivity and adsorption of molecules.

Techniques : UHV NC AFM - RT STM - LEED - Hydrogen Plasma - Atomic Layer Epitaxy (ALE)

Highlights

Single-molecule light emission at room temperature on a wide-band-gap semiconductor. Room-temperature light emission from single chemisorbed perylene based molecules adsorbed on silicon carbide (SiC) is probed by scanning tunneling microscopy (STM). A new approach to STM-induced luminescence of a single molecule is explored using a wide-band-gap semiconductor to decouple electronically the molecule from the surface. The maximum photon energy of the light emission from the molecule shows a fixed shift of 1.5 eV relative to the maximum energy of the tunnel electrons. This is consistent with the photons being generated by inelastic electron tunneling between the HOMO and the unoccupied electronic states of the STM tip.

article : H. Yang, A.J. Mayne, G. Comtet, G. Dujardin, Y. Kuk, S. Nagarajan, A. Gourdon, “Single molecule luminescence induced by STM of chemisorbed PTCDI on silicon carbide”, Phys. Rev. B 90, 125427 (2014)

STM imagery and density functional calculations of C60 fullerene adsorption on the 6H-SiC(0001)-3×3 surface. We show that chemisorption of individual C60 molecules occurs through the formation of one bond to one silicon adatom only in contrast to multiple bond formation on other semiconducting surfaces.We observe three stable adsorption sites with respect to the Si adatoms of the surface unit cell. Comprehensive DFT calculations give different adsorption energies for the three most abundant sites showing that van der Waals forces between the C60 molecule and the neighboring surface atoms need to be considered. The C60 molecules are observed to form small clusters even at low coverage indicating the presence of a mobile molecular precursor state and non negligible intermolecular interactions.

Article : T. Ovramenko, F. Spillebout, F.C. Bocquet, A.J. Mayne, G. Dujardin, Ph. Sonnet, L. Stauffer, Y. Ksari, J.-M. Themlin, "STM imagery and DFT calculations of C60 fullerene adsorption on the SiC(0001)-3x3 surface", Phys. Rev. B 87, 155421 (2013)

Influence of charge transfer doping on the morphologies of C60 islands on hydrogenated diamond C(100)-(2x1). The adsorption and island formation of C60 fullerenes on the hydrogenated C(100)-(2x1):H diamond surface is studied using high-resolution noncontact atomic force microscopy in ultrahigh vacuum. At room temperature, C60 fullerene molecules assemble into monolayer islands, exhibiting a hexagonally close-packed internal structure. Dewetting is observed when raising the substrate temperature above approximately 505 K, resulting in two-layer high islands. In contrast to the monolayer islands, these double-layer islands form extended wetting layers. This peculiar behavior is explained by an increased molecule-substrate binding energy in the case of double-layer islands, which originates from charge transfer doping. Only upon further increasing the substrate temperature to approximately 615 K, the wetting layer desorbs, corresponding to a binding energy of the charge transfer-stabilized film of 1.7 eV.

Article : M. Nimmrich, M. Kittelmann, P. Rahe, W. Harneit, A.J. Mayne, G. Dujardin, A. Kühnle, "Influence of charge transfer doping on the morphology of C60 islands on hydrogenated diamond C(100)-2x1", Phys. Rev. B 85, 035420 (2012)

The paradox of an insulating contact between a chemisorbed molecule and a wide band gap semiconductor surface. Controlling the intrinsic optical and electronic properties of a single molecule adsorbed on a surface requires electronic decoupling of some molecular orbitals from the surface states. Using a combination of Scanning tunniling microscopy and DFT calculations, we find that the LUMO of the DHH-PTCDI molecule adsorbed on the SiC(0001)-3x3 surface molecule is invisible in I(V) spectra due to the absence of any surface or bulk states and that the HOMO has a very low saturation current in I(z) spectra. These results present a paradox that the molecular orbitals are electronically isolated from the surface of the wide band gap semiconductor even though strong chemical bonds are formed.

Article : H. Yang, O. Boudrioua, A.J. Mayne, G. Comtet, G. Dujardin, Ph. Sonnet, L. Stauffer, S. Nagarajan, A. Gourdon, Phys. Chem. Chem. Phys. 14, 1700 (2012)