Calcium Adsorption on MgO(100): Energetics, Structure, and Role of Defects.
The adsorption of Ca on the MgO(100) surface at 300 K has been studied using microcalorimetry, in combination with LEED, AES, ISS, work function, sticking probability measurements, and density functional theory (DFT) calculations. The MgO(100) thin films ( 4 nm thick) were grown epitaxially on a 1 μ...
| Publicado en: | Journal of the American Chemical Society Vol. 130; no. 7; pp. 2314 - 2323 |
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| Autores principales: | , , , , , |
| Formato: | Artículo |
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American Chemical Society
2/20/2008
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| Materias: | |
| Acceso en línea: | Ver este registro en EBSCOhost |
| fields | @attributes: recordID: 1 pdfLink: plink: https://search.ebscohost.com/login.aspx?direct=true&db=hlh&AN=31215074&site=ehost-live header: @attributes: shortDbName: hlh uiTerm: 31215074 longDbName: Humanities International Complete uiTag: AN controlInfo: bkinfo: jinfo: jid: 00027863 ACS jtl: Journal of the American Chemical Society issn: 00027863 maglogo: N pubinfo: dt: 2/20/2008 vid: 130 iid: 7 pid: 997 pub: American Chemical Society artinfo: ui: 31215074 10.1021/ja077865y ppf: 2314 ppct: 9 formats: tig: atl: Calcium Adsorption on MgO(100): Energetics, Structure, and Role of Defects. aug: au: Zhu, Junfa Farmer, Jason A. Ruzycki, Nancy Lijun Xu Campbell, Charles T. Henkelman, Graeme affil: Department of Chemistry, University of Washington, Seattle, Washington 98195-1700 Department of Chemistry and Biochemistry, University of Texas, Austin, Texas 78712-0165 su: Calcium Adsorption (Chemistry) Molecular structure Magnesium Oxygen Density functionals Heat of adsorption sug: subj: Calcium Adsorption (Chemistry) Molecular structure Magnesium Oxygen Density functionals Heat of adsorption ab: The adsorption of Ca on the MgO(100) surface at 300 K has been studied using microcalorimetry, in combination with LEED, AES, ISS, work function, sticking probability measurements, and density functional theory (DFT) calculations. The MgO(100) thin films ( 4 nm thick) were grown epitaxially on a 1 μm thick Mo(100) single-crystal. The sticking probability of Ca on MgO(100) at 300 K is unity. On the basis of AES and ISS measurements, it was determined that Ca grows mainly as 3D particles on the MgO(100) surface with a density of 1 × 10 islands/cm. Ca adsorbs initially at defect sites with a very high heat of adsorption ( 410 kJ/mol). DFT calculations attribute this high initial heat to Ca binding to kink sites (376 kJ/mol), step sites (205 kJ/mol), and lower concentrations of stronger binding sites. The heat of adsorption decreases rapidly with coverage, reaching a minimum of 162 kJ/mol at 0.3 ML, where Ca is mainly adding to small 3D Ca clusters. Afterward, it increases to the value of bulk Ca heat of sublimation (178 kJ/mol) at 1.2 ML, attributed to the increase in stability with increasing Ca particle size. A 1.0 eV decrease of the work function with Ca coverage from 0 to 0.3 ML indicates that Ca adsorbed at defects is cationic, in agreement with calculations showing that Ca donates electron density to the MgO. Light ion sputtering of the MgO-(100) surface generates point defects, but these do not change the heat of adsorption versus coverage, implying that they do not nucleate Ca particles. Oxygen vacancies are a likely candidate; DFT calculations show that F and F+ center vacancies bind Ca more weakly than terrace sites. More extensive sputtering creates extended defects (such as steps and kinks) that adsorb Ca with heats of adsorption up to 400 kJ/mol, similar to that at the intrinsic defect sites. pubtype: Academic Journal doctype: Article src: R language: English refInfo: copyright: @attributes: flag: Y dt: @attributes: year: 2008 holdings: @attributes: islocal: N |
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