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Transition metal oxide surfaces: Surface structures and molecular interaction
KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.ORCID iD: 0000-0003-0483-0602
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Metal oxides are both corrosion products and useful materials with a wide range of applications. Two of the most used metals today are iron and copper. In this thesis, surface structures and molecular interaction with surfaces of iron oxides and copper oxides are studied using spectroscopy and microscopy methods.

 

The surface structures of iron oxides grown on the low-index iron (Fe) surfaces (100) and (110) have been studied during the initial oxidation phase. The oxidation condition for both iron surfaces was 400 °C and 1×10−6 mbar of oxygen gas. For the Fe(100)-surface, a Fe3O4(100)-film is formed beyond the oxygen adsorbate structures. For the Fe(110)-surface, a FeO(111)-film is first formed. When the FeO(111)-film grows thicker, it transforms into a Fe3O4(111)-film.

 

The surface structures of Cu2O(100) was studied and the main finding is that the most common surface structure that previously in literature has been described to have a periodicity of (3√2×√2)R45° actually has a periodicity described by the matrix (3,0;1,1). Furthermore, the low-binding energy component in the photoelectron spectroscopy O 1s-spectrum is determined to origin from surface oxygen atoms.

 

Sulfur dioxide, a corrosive molecule that in the environment to large share comes from human activities such as burning of fossil fuels, was studied using photoelectron spectroscopy when interacting with surfaces of iron oxide thin films and bulk Cu2O-surfaces. On the iron oxide thin film surfaces under ultra-high vacuum conditions, sulfur dioxide adsorbs partly as SO4-species and partly dissociates and forms FeS2. On the Cu2O-surfaces under ultra-high vacuum conditions, the adsorption of sulfur dioxide is non-dissociative and forms SO3-species. When interacting with near-ambient pressures of water, it is observed in the photoelectron spectroscopy S 2p-region that the sulfur from SO3-species shifts to Cu2S.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2016. , 68 p.
Series
TRITA-ICT, 2016:36
National Category
Physical Sciences Physical Sciences
Research subject
Physics
Identifiers
URN: urn:nbn:se:kth:diva-196130ISBN: 978-91-7729-176-3OAI: oai:DiVA.org:kth-196130DiVA: diva2:1046149
Public defence
2016-12-16, Sal C, Kistagången 16, Kista, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20161114

Available from: 2016-11-17 Created: 2016-11-11 Last updated: 2016-11-17Bibliographically approved
List of papers
1. Oxidation of Fe(100) in oxygen gas at 400 °C
Open this publication in new window or tab >>Oxidation of Fe(100) in oxygen gas at 400 °C
(English)Manuscript (preprint) (Other academic)
Abstract [en]

The oxidation of Fe(100) was studied at an oxygen gas pressure of 1×10−6mbarand a temperature of 400°C. The main findings is that the oxide film, beyond oxy-gen adsorbate structure, is formed by layer-by-layer growth and has a Fe3O4(100)termination.

National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-196125 (URN)
Note

QC 20161114

Available from: 2016-11-11 Created: 2016-11-11 Last updated: 2016-11-14Bibliographically approved
2. Oxidation of Fe(110) in oxygen gas at 400 °c
Open this publication in new window or tab >>Oxidation of Fe(110) in oxygen gas at 400 °c
2016 (English)In: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 644, 172-179 p.Article in journal (Refereed) Published
Abstract [en]

The initial oxidation of Fe(110) in oxygen gas at 400 °C beyond initial adsorbate structures has been studied using X-ray photoelectron spectroscopy, X-ray absorption spectroscopy, low-energy electron diffraction, and scanning tunneling microscopy (STM). Formation of several ordered phases of surface oxides is observed at oxygen coverages between approximately 2.3 and 3.5 oxygen atoms/Fe(110) surface atom. Initially, a FeO(111)-like film is formed with a parallelogram-shaped moiré pattern. It has two mirror domains that are formed symmetrically around the growth direction of a zigzag-shaped adsorbate structure. With increased local oxygen coverage, the moiré structure transforms into a ball-shaped form. Both these moiré structures have equal atomic stacking at the surface and equal apparent height in STM, suggesting oxygen ions diffusing into the film upon oxidation and that the oxide growth takes place at the iron-iron oxide interface. The FeO(111)-like film turns into a Fe3O4(111)-like film with a triangular bistable surface termination as the oxidation proceeds further. The FeO(111)-like film growth proceeds according to the Frank-van der Merwe mechanism while the Fe3O4(111)-like film grows according to the Stranski-Krastanov mechanism.

Place, publisher, year, edition, pages
Elsevier, 2016
Keyword
Fe(110), Iron oxide thin film, Low-energy electron diffraction, Photoelectron spectroscopy, Scanning tunneling microscopy
National Category
Inorganic Chemistry Condensed Matter Physics
Identifiers
urn:nbn:se:kth:diva-180936 (URN)10.1016/j.susc.2015.10.058 (DOI)000367489000027 ()2-s2.0-84949494103 (ScopusID)
Funder
Knut and Alice Wallenberg Foundation, Dnr 2012.0321Swedish Research Council, 621-2008-576
Note

QC 20160205

Available from: 2016-01-26 Created: 2016-01-25 Last updated: 2016-11-11Bibliographically approved
3. A well-ordered surface oxide on Fe(110)
Open this publication in new window or tab >>A well-ordered surface oxide on Fe(110)
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2015 (English)In: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 639, 13-19 p.Article in journal (Refereed) Published
Abstract [en]

A well-ordered surface oxide grown on Fe(110) has been studied using scanning tunneling microscopy (STM), low energy electron diffraction, low energy electron microscopy, and core level photoelectron spectroscopy. The iron oxide film exhibits wide terraces and is formed after exposure to 100-1000 L at 1 x 10(-6) mbar O-2 and 400 degrees C. Two domains, mirror symmetric in the Fe(110)-lattice mirror symmetry planes but otherwise equal, are observed. The surface oxide forms a relatively large coincidence surface unit cell (16.1 angstrom x 26.5 angstrom). Imaging by STM reveals a strong bias dependence in the apparent height within the surface unit cell. The oxygen terminating atomic layer has a hexagonal atomic structure, FeO(111)-like, with the atomic sparing of 3.2 angstrom, that is expanded by similar to 63% relative to bulk FeO(111).

National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-170933 (URN)10.1016/j.susc.2015.04.008 (DOI)000356546000003 ()2-s2.0-84928957900 (ScopusID)
Note

QC 20150714

Available from: 2015-07-14 Created: 2015-07-13 Last updated: 2016-11-11Bibliographically approved
4. The Surface Structure of Cu2O(100)
Open this publication in new window or tab >>The Surface Structure of Cu2O(100)
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2016 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 120, no 8, 4373-4381 p.Article in journal (Refereed) Published
Abstract [en]

Despite the industrial importance of copper oxides, the nature of the (100) surface of Cu2O has remained poorly understood. The surface has previously been subject to several theoretical and experimental studies, but has until now not been investigated by atomically resolved microscopy or high-resolution photoelectron spectroscopy. Here we determine the atomic structure and electronic properties of Cu2O(100) by a combination of multiple experimental techniques and simulations within the framework of density functional theory (DFT). Low-energy electron diffraction (LEED) and scanning tunneling microscopy (STM) characterized the three ordered surface structures found. From DFT calculations, the structures are found to be energetically ordered as (3,0;1,1), c(2 x 2), and (1 x 1) under ultrahigh vacuum conditions. Increased oxygen pressures induce the formation of an oxygen terminated (1 x 1) surface structure. The most common termination of Cu2O(100) has previously been described by a (3 root 2 x root 2)R45 degrees unit cell exhibiting a LEED pattern with several missing spots. Through atomically resolved STM, we show that this structure instead is described by the matrix (3,0;1,1). Both simulated STM images and calculated photoemission core level shifts compare favorably with the experimental results.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2016
National Category
Inorganic Chemistry
Identifiers
urn:nbn:se:kth:diva-184532 (URN)10.1021/acs.jpcc.5b11350 (DOI)000371562000024 ()2-s2.0-84960171601 (ScopusID)
Funder
Swedish Research CouncilKnut and Alice Wallenberg Foundation
Note

QC 20160406

Available from: 2016-04-06 Created: 2016-04-01 Last updated: 2016-11-11Bibliographically approved
5. Cuprous oxide surfaces exposed to sulfur dioxide and near-ambient pressures of water
Open this publication in new window or tab >>Cuprous oxide surfaces exposed to sulfur dioxide and near-ambient pressures of water
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

The interaction of sulfur dioxide with Cu2O(100) and Cu2O(111) at ultra-high vac-uum is studied. It is found that on both surfaces, the sulfur dioxide moleculesbind as SO3-species. Dosing water in UHV does not impact the SO3-species at thedoses used. When dosing water at near-ambient pressure conditions, however, itis observed that the sulfur in the SO3-species shifts to Cu2S when monitoring thePES S 2p-region.

National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-196127 (URN)
Note

QC 20161114

Available from: 2016-11-11 Created: 2016-11-11 Last updated: 2016-11-29Bibliographically approved
6. Sulfur dioxide interaction with oxidized low-index iron surfaces
Open this publication in new window or tab >>Sulfur dioxide interaction with oxidized low-index iron surfaces
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Sulfur dioxide was dosed on thin iron oxides grown on Fe(100) and Fe(110) (fromPaper 1 and Paper 2). It is found that the sulfur dioxide molecules adsorb as SO4-species at room temperature and that some of the adsorbed molecules dissociateupon adsorption and forming FeS2. The oxides corresponding to the lowest dosesof oxygen gas in Paper 1 and Paper 2 were annealed after the sulfur dioxide dos-ing, resulting in increased amount of dissociated molecules. The thicker oxides, onboth surfaces were exposed to another dose of sulfur dioxide, the change of sulfurcoverages show that the surfaces are almost saturated.

National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-196126 (URN)
Note

QC 20161114

Available from: 2016-11-11 Created: 2016-11-11 Last updated: 2016-11-14Bibliographically approved

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