Peer-reviewed Publications |
Brand, C., Debiossac, M., Susi, T., Aguillon, F., Kotakoski, J., Roncin P., & Arndt, M. (2019). Coherent diffraction of hydrogen through the 246 pm lattice of graphene. New J. Phys., 21, 033004.
Résumé: We study the diffraction of neutral hydrogen atoms through suspended single-layer graphene using molecular dynamics simulations based on density functional theory. Although the atoms have to overcome a transmission barrier, we find that the de Broglie wave function for H at 80 eV has a high probability to be coherently transmitted through about 18% of the graphene area, contrary to the case of He. We propose an experiment to realize the diffraction of atoms at the natural hexagon lattice period of 246 pm, leading to a more than 400-fold increase in beam separation of the coherently split atomic wave function compared to diffraction experiments at state-of-the art nano-machined masks. We expect this unusual wide coherent beam splitting to give rise to novel applications in atom interferometry.
|
|
Brand, C., Debiossac, M., Susi, T., Aguillon, F., Kotakoski, J., Roncin, P., & Arndt, M. (2019). Coherent diffraction of hydrogen through the 246 pm lattice of graphene. NEW JOURNAL OF PHYSICS, 21(3), 033004.
Résumé: We study the diffraction of neutral hydrogen atoms through suspended single-layer graphene using molecular dynamics simulations based on density functional theory. Although the atoms have to overcome a transmission barrier, we find that the de Broglie wave function for H at 80 eV has a high probability to be coherently transmitted through about 18% of the graphene area, contrary to the case of He. We propose an experiment to realize the diffraction of atoms at the natural hexagon lattice period of 246 pm, leading to a more than 400-fold increase in beam separation of the coherently split atomic wave function compared to diffraction experiments at state-of-the art nano-machined masks. We expect this unusual wide coherent beam splitting to give rise to novel applications in atom interferometry.
|
|
Kleimeier, N. F., Wenzel, G., Urban, A. J., Tchalala, M. R., Oughaddou, H., Dedkov, Y., Voloshina, E., & Zacharias, H. (2019). Unoccupied electronic band structure of pentagonal Si nanoribbons on Ag(110). PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 21(32), 17811–17820.
Résumé: Silicon nanoribbons – one dimensional silicon structures with a pentagonal atomic structure and mixed sp(2)- and sp(3)-hybridisation – grow on Ag(110) upon deposition of silicon. These nanostructures are viewed as promising candidates for modern day electronics as they are comprised of the same element as today's semiconductor devices. Even though they have been studied extensively over the last decade, only little is known about their unoccupied band structure which is important for possible future optoelectronics, semiconductor, and spintronics applications. In order to elucidate the unoccupied band structure of the nanoribbons, k-resolved inverse photoemission spectroscopy (KRIPES) studies were performed on both nanoribbon structures reported in the literature as well as on the bare Ag(110) substrate within the energy range of E-EF = 0-6.5 eV. The obtained experimental results are compared to density functional theory (DFT) calculated band structures to assign individual spectral features to specific bands. Since even small changes in the structural model of the nanoribbons lead to a change in the calculated band structure, this comparison allows us to assess the validity of the proposed structural models.
|
|
Mankos, M., Shadman, K., Hahn, R., Picard, Y. J., Comparat, D., Fedchenko, O., Schonhense, G., Amiaud, L., Lafosse, A., & Barrett, N. (2019). Design for a high resolution electron energy loss microscope. ULTRAMICROSCOPY, 207, 112848.
Résumé: An electron optical column has been designed for High Resolution Electron Energy Loss Microscopy (HREELM). The column is composed of electron lenses and a beam separator that are placed between an electron source based on a laser excited cesium atom beam and a time-of-flight (ToF) spectrometer or a hemispherical analyzer (HSA). The instrument will be able to perform full field low energy electron imaging of surfaces with sub-micron spatial resolution and meV energy resolution necessary for the analysis of local vibrational spectra. Thus, non-contact, real space mapping of microscopic variations in vibrational levels will be made possible. A second imaging mode will allow for the mapping of the phonon dispersion relations from microscopic regions defined by an appropriate field aperture.
|
|
Mery, M., Gonzalez, C., García, C., Romero, C. P., Esaulov, V. A., & Valdés, J. E. (2019). Sputtering yields of tantalum by hydrogen ions in the energy range of 3–11 keV. RADIATION EFFECTS AND DEFECTS IN SOLIDS, 174(1-2), 2–8.
Résumé: The total sputtering yield of 6nm thick polycrystalline tantalum films resulting from H-2(+) ion bombardment, at normal incidence, has been determined. For this purpose, we study the evolution of the energy loss of protons transmitted through very thin films of tantalum following bombardment with controlled doses of H-2(+). The energy of the incident ions ranges from 3 to 11 keV. Our method allows us to determine how to find the limit of the thin film surface contamination which is important for stopping power measurements of pure samples. It also allows to prepare films of predetermined variable thickness.
|
|
Pommier, D., Bretel, R., López, L. E. P., Fabre, F., Mayne, A., Boer-Duchemin, E., Dujardin, G., Schull, G., Berciaud, S., & Le Moal, E. (2019). Scanning Tunneling Microscope-Induced Excitonic Luminescence of a Two-Dimensional Semiconductor. Phys. Rev. Lett., 123(2), 027402.
Résumé: The long sought-after goal of locally and spectroscopically probing the excitons of two-dimensional (2D) semiconductors is attained using a scanning tunneling microscope (STM). Excitonic luminescence from monolayer molybdenum diselenide (MoSe2) on a transparent conducting substrate is electrically excited in the tunnel junction of an STM under ambient conditions. By comparing the results with photoluminescence measurements, the emission mechanism is identified as the radiative recombination of bright A excitons. STM-induced luminescence is observed at bias voltages as low as those that correspond to the energy of the optical band gap of MoSe2. The proposed excitation mechanism is resonance energy transfer from the tunneling current to the excitons in the semiconductor, i.e., through virtual photon coupling. Additional mechanisms (e.g., charge injection) may come into play at bias voltages that are higher than the electronic band gap. Photon emission quantum efficiencies of up to 10−7 photons per electron are obtained, despite the lack of any participating plasmons. Our results demonstrate a new technique for investigating the excitonic and optoelectronic properties of 2D semiconductors and their heterostructures at the nanometer scale.
|
|
Tiouitchi, G., Ali, M. A., Benyoussef, A., Hamedoun, M., Lachgar, A., Benaissa, M., Kara, A., Ennaoui, A., Mahmoud, A., Boschini, F., Oughaddou, H., El Kenz, A., & Mounkachi, O. (2019). An easy route to synthesize high-quality black phosphorus from amorphous red phosphorus. MATERIALS LETTERS, 236, 56–59.
Résumé: The development of an easy and efficient process for producing black phosphorus (BP) remains a bottleneck for the use of BP in large-scale applications. In this work, we present a simple, potentially scalable, and economically viable method for the preparation of high-quality BP from amorphous red phosphorus. BP was synthesized under low pressure and temperature conditions from red phosphorus via the addition of small quantities of copper, tin, and tin(IV) iodide. Characterization by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectrometry (EDX), high-resolution transmission electron microscopy (HR-TEM), and Raman spectroscopy were performed to confirm the high quality and purity of the formed BP.
|
|
Tong, Y., Fuhr, J. D., Martiarena, M. L., Oughaddou, H., Enriquez, H., Nicolas, F., Chaouchi, K., Kubsky, S., & Bendounan, A. (2019). Properties of NTCDA Thin Films on Ag(110): Scanning Tunneling Microscopy, Photoemission, Near-Edge X-ray Fine Structure, and Density Functional Theory Investigations. JOURNAL OF PHYSICAL CHEMISTRY C, 123(1), 379–386.
Résumé: It is well proven that the properties of organic/metal interfaces play an utmost role in the performance of organic devices. Here we present a study on structural and electronic properties of high-quality 1,4,5,8-naphthalene tetracarboxylic dianhydride (NTCDA) films grown on an Ag(110) surface. High-resolution scanning tunneling microscopy and low-energy electron diffraction show the presence of two molecular domains. Density functional theory calculations indicate that the most stable location of NTCDA corresponds to anhydride oxygen attached to the Ag atoms along the [110] direction. Photoemission results of the C 1s and O 1s core levels demonstrate a strong interfacial bonding, inducing a charge transfer from the Ag metal to the molecular monolayer. An angular-dependent study of the C K-edge near-edge X-ray fine structure spectra provides detailed information concerning the evolution of the NTCDA orientation with the film thickness.
|
|
Xiao, Y., Shi, Y., Liu, P., Zhu, Y., Gao, L., Guo, Y., Chen, L., Chen, X., & Esaulov, V. A. (2019). Neutralization of keV-energy alkali-metal ions colliding at gold surfaces. NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS, 450, 73–76.
Résumé: Li+ and Na+ ions are scattered from Au(1 1 0) and Au(1 1 1) surfaces in the keV-energy range, respectively. The pronounced Li degrees and Na degrees fractions non-monotonically vary with incident energy and exit angle for high work function gold surfaces. In particular, the azimuthal angle dependence of Li degrees fraction has been observed at low incident energies for a grazing exit angle. The simple calculations are presented to compare with the experimental data. Our findings clearly indicate that both the perpendicular and parallel exit velocity affect the final neutral fraction.
|
|
