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Correlation between stoichiometry and surface structure of the polar MgAl2O4(100) surface as a function of annealing temperature

Jensen, Thomas N.; Rasmussen, Morten K.; Knudsen, Jan LU ; Vlad, Alina; Volkov, Sergey; Lundgren, Edvin LU ; Stierle, Andreas and Lauritsen, Jeppe V. (2015) In Physical Chemistry Chemical Physics 17(8). p.5795-5804
Abstract
The correlation between surface structure, stoichiometry and atomic occupancy of the polar MgAl2O4(100) surface has been studied with an interplay of noncontact atomic force microscopy, X-ray photoelectron spectroscopy and surface X-ray diffraction under ultrahigh vacuum conditions. The Al/Mg ratio is found to significantly increase as the surface is sputtered and annealed in oxygen at intermediate temperatures ranging from 1073-1273 K. The Al excess is explained by the observed surface structure, where the formation of nanometer-sized pits and elongated patches with Al terminated step edges contribute to stabilizing the structure by compensating surface polarity. Surface X-ray diffraction reveals a reduced occupancy in the top two surface... (More)
The correlation between surface structure, stoichiometry and atomic occupancy of the polar MgAl2O4(100) surface has been studied with an interplay of noncontact atomic force microscopy, X-ray photoelectron spectroscopy and surface X-ray diffraction under ultrahigh vacuum conditions. The Al/Mg ratio is found to significantly increase as the surface is sputtered and annealed in oxygen at intermediate temperatures ranging from 1073-1273 K. The Al excess is explained by the observed surface structure, where the formation of nanometer-sized pits and elongated patches with Al terminated step edges contribute to stabilizing the structure by compensating surface polarity. Surface X-ray diffraction reveals a reduced occupancy in the top two surface layers for both Mg, Al, and O and, moreover, vacancies are preferably located in octahedral sites, indicating that Al and Mg ions interchange sites. The excess of Al and high concentration of octahedral vacancies, very interestingly, indicates that the top few surface layers of the MgAl2O4(100) adopts a surface structure similar to that of a spinel-like transition Al2O3 film. However, after annealing at a high temperature of 1473 K, the Al/Mg ratio restores to its initial value, the occupancy of all elements increases, and the surface transforms into a well-defined structure with large flat terraces and straight step edges, indicating a restoration of the surface stoichiometry. It is proposed that the tetrahedral vacancies at these high temperatures are filled by Mg from the bulk, due to the increased mobility at high annealing temperatures. (Less)
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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
in
Physical Chemistry Chemical Physics
volume
17
issue
8
pages
5795 - 5804
publisher
Royal Society of Chemistry
external identifiers
  • wos:000349697200033
  • scopus:84923341212
ISSN
1463-9084
DOI
10.1039/c4cp05878j
language
English
LU publication?
yes
id
d9f0a422-11cb-49b5-8f60-1021c71f9d80 (old id 5169015)
date added to LUP
2015-03-25 09:41:37
date last changed
2017-07-23 04:21:32
@article{d9f0a422-11cb-49b5-8f60-1021c71f9d80,
  abstract     = {The correlation between surface structure, stoichiometry and atomic occupancy of the polar MgAl2O4(100) surface has been studied with an interplay of noncontact atomic force microscopy, X-ray photoelectron spectroscopy and surface X-ray diffraction under ultrahigh vacuum conditions. The Al/Mg ratio is found to significantly increase as the surface is sputtered and annealed in oxygen at intermediate temperatures ranging from 1073-1273 K. The Al excess is explained by the observed surface structure, where the formation of nanometer-sized pits and elongated patches with Al terminated step edges contribute to stabilizing the structure by compensating surface polarity. Surface X-ray diffraction reveals a reduced occupancy in the top two surface layers for both Mg, Al, and O and, moreover, vacancies are preferably located in octahedral sites, indicating that Al and Mg ions interchange sites. The excess of Al and high concentration of octahedral vacancies, very interestingly, indicates that the top few surface layers of the MgAl2O4(100) adopts a surface structure similar to that of a spinel-like transition Al2O3 film. However, after annealing at a high temperature of 1473 K, the Al/Mg ratio restores to its initial value, the occupancy of all elements increases, and the surface transforms into a well-defined structure with large flat terraces and straight step edges, indicating a restoration of the surface stoichiometry. It is proposed that the tetrahedral vacancies at these high temperatures are filled by Mg from the bulk, due to the increased mobility at high annealing temperatures.},
  author       = {Jensen, Thomas N. and Rasmussen, Morten K. and Knudsen, Jan and Vlad, Alina and Volkov, Sergey and Lundgren, Edvin and Stierle, Andreas and Lauritsen, Jeppe V.},
  issn         = {1463-9084},
  language     = {eng},
  number       = {8},
  pages        = {5795--5804},
  publisher    = {Royal Society of Chemistry},
  series       = {Physical Chemistry Chemical Physics},
  title        = {Correlation between stoichiometry and surface structure of the polar MgAl2O4(100) surface as a function of annealing temperature},
  url          = {http://dx.doi.org/10.1039/c4cp05878j},
  volume       = {17},
  year         = {2015},
}