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STM imaging, spectroscopy and manipulation of a self-assembled PTCDI monolayer on epitaxial graphene
Yang, H.,Mayne, A. J.,Comtet, G.,Dujardin, G.,Kuk, Y.,Sonnet, Ph.,Stauffer, L.,Nagarajan, S.,Gourdon, A. The Royal Society of Chemistry 2013 Physical chemistry chemical physics Vol.15 No.14
<P>Scanning Tunneling Microscopy (STM), Scanning Tunneling Spectroscopy (STS), and manipulation studies were performed on an ordered self-assembled monolayer (SAM) of <I>N</I>,<I>N</I>′-bis(1-hexylheptyl)perylene-3,4:9,10-bis(dicarboximide) molecules on epitaxial graphene on hexagonal silicon carbide – SiC(0001). Four novel aspects of the molecular SAM on graphene are presented. Molecules adsorb in both armchair and zig-zag configurations, giving rise to six orientations of the molecular layer with respect to the underlying substrate. The interaction between the molecules and the graphene surface shifts the LUMO towards the Fermi level, inducing a charge transfer and the opening of a band gap in the graphene, with the LUMO inside. This decouples the LUMO from the surface rendering it invisible in the d<I>I</I>/d<I>V</I> spectroscopy. The HOMO only becomes visible at short tip-surface distances, as its energy lies within the band gap of the SiC substrate. Finally, the observed molecular defects are very particular, being composed exclusively of molecular dimers. These molecular dimers have a stronger interaction with the graphene than other molecules.</P> <P>Graphic Abstract</P><P>Scanning tunneling microscopy and spectroscopy studies of a self-assembled hexyl heptyl PTCDI monolayer on epitaxial graphene reveal molecules adsorbed in two configurations. Charge transfer induces band gap opening in graphene and decouples the LUMO. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c3cp42591f'> </P>
Kria M.,Varsha,Farkous M.,Prasad V.,Dujardin F,Pérez L.M.,Laroze D.,Feddi E. 한국물리학회 2021 Current Applied Physics Vol.25 No.-
Semi oblate and semi prolate are among the most probable self-organized nanostructures shapes. The optoelectronic properties of such nanostructures are not just manipulated with the height and lateral size but also with the wetting layer element. The practical interest of derivatives of germanium and silicon has a great important role in optoelectronic devices. This study is a contribution to the analysis of linear and nonlinear optical properties of Si0.7Ge0.3/Si. In the framework of the effective mass approximation, we solve numerically the Schr¨odinger equation relative to one particle confined in Si0.7Ge0.3/Si semi prolate and semi oblate quantum dots by using the finite element method and by taking into consideration the effect of the wetting layer. The energy spectrum of the lowest states and the dipolar matrix for the fourth allowed transitions are determined and discussed. We also calculate the detailed optical properties, including absorption coefficients, refractive index changes, second and third harmonic generation as a function of the quantum dot sizes. We found that with the change in the size of prolate and oblate quantum dots, there is a shift in the resonance peaks for the absorption coefficient and refractive index. It is due to the modification in the energy levels with changing size. The study proves a redshift in the second harmonic generation and third harmonic generation coefficients with an increase in the height/radius of the oblate/prolate quantum dot, respectively. We also demonstrated the variation of wavefunction inside the quantum dot with the change in wetting layer thickness.
E. Feddi,N. Aghoutane,M. El-Yadri,F. Dujardin,A. El Aouami,C.A. Duque 한국물리학회 2018 Current Applied Physics Vol.18 No.4
The system formed by an electron and a hole coupled by Coulomb interactions with an ionized donor is the least known among the excitonic complexes. This complex is usually described as an exciton bound to an ionized donor. Strictly speaking, the exact mechanism of formation of this complex remains unclear. Two processes of formation giving rise to this system can be imagined. In a first process labeled A, the complex may be regarded as an exciton trapped by an ionized donor while in the second mechanism labeled B, this complex can be derived from the binding of a neutral donor and a hole. From a theoretical point of view both protocols can occur, with different probabilities and different binding energies, and consequently lead to different lines in the optical absorption spectra. In our hypothesis, we assume that the statistical mixture contains the two species coming from different origins and which were formed randomly. In this context of uncertainty and mixing processes, we propose to determine the absorption coefficient in the framework of the two possible hypotheses. In the aim to contribute with a valid description of the absorption spectrum, we report in this paper a full theoretical analysis of the optical and magneto-optical phenomena accompanying the two possible processes of formation, taking into account the dot sizes, the magnetic field strength, and the effect of the dielectric constant of the host material.
Yang, H.,Boudrioua, O.,Mayne, A. J.,Comtet, G.,Dujardin, G.,Kuk, Y.,Sonnet, Ph.,Stauffer, L.,Nagarajan, S.,Gourdon, A. The Royal Society of Chemistry 2012 Physical chemistry chemical physics Vol.14 No.5
<P>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. Scanning tunneling microscopy experiments and density functional theory calculations are used to study a perylene molecule derivative (DHH-PTCDI), adsorbed on the clean 3 × 3 reconstructed wide band gap silicon carbide surface (SiC(0001)-3 × 3). We find that the LUMO of the adsorbed molecule is invisible in <I>I</I>(<I>V</I>) spectra due to the absence of any surface or bulk states and that the HOMO has a very low saturation current in <I>I</I>(<I>z</I>) 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.</P> <P>Graphic Abstract</P><P>Organic molecule adsorption on the SiC surface forms strong chemical bonds but certain molecular orbitals are electronically decoupled from the substrate. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c2cp23104b'> </P>
Quantum Interference Channeling at Graphene Edges
Yang, Heejun,Mayne, Andrew J.,Boucherit, Mohamed,Comtet, Geneviè,ve,Dujardin, Gé,rald,Kuk, Young American Chemical Society 2010 NANO LETTERS Vol.10 No.3
<P>Electron scattering at graphene edges is expected to make a crucial contribution to the electron transport in graphene nanodevices by producing quantum interferences. Atomic-scale scanning tunneling microscopy (STM) topographies of different edge structures of monolayer graphene show that the localization of the electronic density of states along the C−C bonds, a property unique to monolayer graphene, results in quantum interference patterns along the graphene carbon bond network, whose shapes depend only on the edge structure and not on the electron energy.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/nalefd/2010/nalefd.2010.10.issue-3/nl9038778/production/images/medium/nl-2009-038778_0005.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nl9038778'>ACS Electronic Supporting Info</A></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nl9038778'>ACS Electronic Supporting Info</A></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nl9038778'>ACS Electronic Supporting Info</A></P>