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Atomic Structure of Sub-Monolayer NaCl Grown on Ag(110) Surface Khalid Quertite, Karima Lasri, Hanna Enriquez, Andrew J Mayne, Azzedine Bendounan, Gérald Dujardin, Nicolas Trcera, Walter Malone, Abdallah El Kenz, Abdelilah Benyoussef, Abdelkader Kara, and Hamid Oughaddou J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.7b05150 • Publication Date (Web): 23 Aug 2017 Downloaded from http://pubs.acs.org on August 25, 2017
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The Journal of Physical Chemistry
Atomic Structure of Sub-Monolayer NaCl Grown on Ag(110) Surface
Khalid Quertite1,2,3, Karima Lasri4, Hanna Enriquez1, Andrew J. Mayne1, Azzedine Bendounan2, Gérald Dujardin1, Nicolas Trcera2, Walter Malone4, Abdallah El kenz3, Abdelilah Benyoussef3,5, Abdelkader Kara4 and Hamid Oughaddou1,6,*
1
Institut des Sciences Moléculaires d’Orsay, ISMO-CNRS, Bât. 210, Université Paris-Sud, 91405 Orsay, France 2 Synchrotron Soleil, L’Orme des Merisiers Saint-Aubin, B.P. 48, 91192 Gif-sur-Yvette Cedex, France 3 LMPHE, Faculté des Sciences, Université Mohammed V - Agdal, 10100, Rabat, Morocco 4 Department of Physics, University of Central Florida, Orlando, FL 32816, USA 5 Institute of Nanomaterials and Nanotechnologies, MAScIR, 10100, Rabat, Morocco 6 Département de Physique, Université de Cergy-Pontoise, 95031 Cergy-Pontoise Cedex, France
Abstract: We report results on the growth of an NaCl film on Ag(110) under ultra-high vacuum conditions. At room temperature, Low Energy Electron Diffraction and Scanning Tunneling Microscopy show that the NaCl film forms a (4x1) superstructure. At RT, the film consists of small-sized islands that coalesce into larger islands at 410 K. These large islands preserve the (4x1) superstructure and cover the entire surface. The apparent heights obtained from the STM images show that the initial thickness of the NaCl islands is one atomic layer and they present a very small height corrugation. The density functional theory calculations, with and without the inclusion of van der Waals effects confirm the co-existence of two domains in agreement with the observed structure.
*Corresponding author:
[email protected] 1
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The Journal of Physical Chemistry
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Introduction Thin insulating films have recently received an increasing interest because of their promising applications in the field of nanoscience and nanotechnology. These materials grown on metal surfaces are a solution to the problem of decoupling the electronic states of adsorbed nanostructures or atomic-molecular species from those of the metallic substrate and to decrease charging effects. Ultrathin dielectric films have been employed successfully to study and enhance the intrinsic features of atomic-scale structures. For example, thin insulating films have been used as spacers allowing individual molecular orbitals to be probed, 1, 2 the electronic state of a single adatom to be manipulated, 3 and the catalytic activity of metal nanoparticles to be modified.4 These thin films can support 2D networks5 and 2D layers6 that could be extended to new 2D materials that would otherwise react or strongly interact with the metal.7-9 One of the key advantages of using thin insulating films as substrates is that electron-based surface characterization techniques will work, because charging of thin insulating layers is weak. For example, Scanning Tunneling Microscopy (STM) investigations of these surfaces are possible because the electron wave function penetrates through the ultrathin dielectric layers 1 nm thick or less allowing the current to flow.10 Sodium chloride (NaCl) is a very promising material in this respect, since it can be successfully grown as atomically flat islands on numerous noble metal surfaces, including Cu(111),11 Cu(100),12 Cu(311),13 Ag(100),14 Ag(111),15 Al(100)16 and Au(111)17. Bulk NaCl is a wide band-gap (8.5 eV) ionic material containing Cl- and Na+ ions, 18 with a cubic symmetry of the rock-salt structure. Using the low energy electron diffraction, it was shown previously that deposition of NaCl on Ag(110) for coverages of about 1 ML leads to an epitaxial growth of commensurate NaCl.19 To our knowledge, STM and Density Functional Theory (DFT) analysis of NaCl ultra insulating films grown on Ag(110) surface are currently missing in the literature.
EXPERIMENTAL AND COMPUTATIONAL DETAILS Using LEED, STM and DFT calculations we have fully characterized the deposition of 1 ML of NaCl on Ag(110). Our experiments are performed in an UHV system from Omicron GmbH (base pressure
