Defect Sites and Their Distributions on MgO(100) by Li and Ca Adsorption Calorimetry
- 9 February 2009
- journal article
- research article
- Published by American Chemical Society (ACS) in Journal of the American Chemical Society
- Vol. 131 (8), 3098-3103
- https://doi.org/10.1021/ja808986b
Abstract
Chemical bonding to oxide surfaces is often dominated by surface defects, but their nature remains elusive. Calorimetric measurements of Ca and Li adsorption energies on MgO(100) and ion-damaged MgO(100), when combined with density functional theory (DFT) calculations and kinetic modeling, are shown to be a powerful way to assess the nature of the defect sites on oxide surfaces and their lateral distributions. While ion sputtering causes a strong increase in the initial adsorption energy for Li on MgO(100) at 300 K, the initial adsorption energy for Ca is independent of the extent of sputtering. This result and the measured coverage dependence of the adsorption energies of Ca and Li on MgO(100) surfaces with ∼5, 12, and 25% defects were simulated with a kinetic model based on DFT input regarding site binding energies and adatom migration barriers. Reproducing the experimental results required models with distinct probability distributions of local defect concentrations for the differing extents of ion damage. A key difference between Li and Ca revealed by DFT and necessary to reproduce their differing adsorption energy versus ion damage measurements is the much greater tendency for a diffusing Li adatom to remain locked in place once it reaches a terrace site neighboring an occupied step or kink site, thus nucleating a 2D island on a terrace. In contrast, Ca adatoms thermally diffuse from such sites quickly, to seek out the remaining defect sites. The model also reproduces the measured Li and Ca film morphology seen by ion scattering spectroscopy.Keywords
This publication has 27 references indexed in Scilit:
- Properties of Alkali Metal Atoms Deposited on a MgO Surface: A Systematic Experimental and Theoretical StudyChemistry – A European Journal, 2008
- Li atoms deposited on single crystalline MgO(001) surface. A combined experimental and theoretical studyChemical Physics Letters, 2008
- Effect of the Specific Surface Area of Li/MgO Catalysts in the Oxidative Coupling of MethaneZeitschrift für Physikalische Chemie, 2007
- Surface Sensitivity in Lithium-Doping of MgO: A Density Functional Theory Study with Correction for on-Site Coulomb InteractionsThe Journal of Physical Chemistry C, 2007
- Alkali Metal Doping of MgO: Mechanisms of Formation of Paramagnetic Surface CentersThe Journal of Physical Chemistry B, 2003
- LDA and GGA calculations of alkali metal adsorption at the (001) surface of MgOThe Journal of Chemical Physics, 2000
- Cs adsorption on oxide films (Al2O3, MgO, SiO2)Surface Science, 1997
- Photoemission study of Na and Cs adsorption on MgO(100)1 × 1Surface Science, 1996
- The Catalytic Oxidative Coupling of MethaneAngewandte Chemie-International Edition, 1995
- Surface colour centres on magnesium oxide generated by magnesium and alkali-metal dopingJournal of the Chemical Society, Faraday Transactions, 1994