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Soldemo, M., Vandichel, M., Gronbeck, H. & Weissenrieder, J. (2019). Initial Fe3O4(100) Formation on Fe(100). The Journal of Physical Chemistry C, 123(26), 16317-16325
Open this publication in new window or tab >>Initial Fe3O4(100) Formation on Fe(100)
2019 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 123, no 26, p. 16317-16325Article in journal (Refereed) Published
Abstract [en]

The initial oxidation of Fe(100) at 400 degrees C has been studied by X-ray photoelectron spectroscopy (XPS), scanning tunneling microscopy (STM), and low-energy electron diffraction, in combination with density functional theory calculations. The first observed well-ordered surface oxide is formed at a coverage of similar to 3 oxygen atoms per unreconstructed surface Fe(100) atom. STM shows that this surface oxide is terminated by straight atomic rows exhibiting a p(2 X 1) periodicity. However, already for oxide films with a coverage of similar to 4 oxygen atoms (corresponding to one Fe3O4 unit cell thickness), wiggly atomic rows appear similar to the c(2 X 2) reconstructed Fe3O4 (100)-surface with the Fe3O4 unit vectors rotated 45 degrees to Fe(100). The wiggly rows are a consequence of subsurface cation iron vacancies, which previously have been observed for bulk surfaces. The formation of subsurface vacancies is supported by the XPS O is signature, which is modeled by considering the core-level shifts for all oxygen atoms in the film. Throughout the oxidation series, the microscopy results reveal a layer-by-layer (Frank-van der Merwe) growth.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2019
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-255382 (URN)10.1021/acs.jpcc.9b04625 (DOI)000474796600046 ()
Note

QC 20190730

Available from: 2019-07-30 Created: 2019-07-30 Last updated: 2019-07-30Bibliographically approved
Ghadami Yazdi, M., Lousada, C. M., Evertsson, J., Rullik, L., Soldemo, M., Bertram, F., . . . Göthelid, M. (2019). Structure dependent effect of silicon on the oxidation of Al(111) and Al(100). Surface Science, 684, 1-11
Open this publication in new window or tab >>Structure dependent effect of silicon on the oxidation of Al(111) and Al(100)
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2019 (English)In: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 684, p. 1-11Article in journal (Refereed) Published
Abstract [en]

The effect of sub-monolayer silicon on the oxidation of Al(111) and Al(100) surfaces was investigated using X-ray Photoelectron Spectroscopy (XPS) and density functional theory (DFT) calculations. On both surfaces the adatom site is preferred over substituting Si into the Al-lattice; on Al(100) the four fold hollow site is vastly favored whereas on Al(111) bridge and hollow sites are almost equal in energy. Upon O 2 exposure, Si is not oxidized but buried at the metal/oxide interface under the growing aluminum oxide. On Al(111), Si has a catalytic effect on both the initial oxidation by aiding in creating a higher local oxygen coverage in the early stages of oxidation and, in particular, at higher oxide coverages by facilitating lifting Al from the metal into the oxide. The final oxide, as measured from the Al2p intensity, is 25–30% thicker with Si than without. This observation is valid for both 0.1 monolayer (ML) and 0.3 ML Si coverage. On Al(100), on the other hand, at 0.16 ML Si coverage, the initial oxidation is faster than for the bare surface due to Si island edges being active in the oxide growth. At 0.5 ML Si coverage the oxidation is slower, as the islands coalesce and he amount of edges reduces. Upon oxide formation the effect of Si vanishes as it is overgrown by Al 2 O 3 , and the oxide thickness is only 6% higher than on bare Al(100), for both Si coverages studied. Our findings indicate that, in addition to a vanishing oxygen adsorption energy and Mott potential, a detailed picture of atom exchange and transport at the metal/oxide interface has to be taken into account to explain the limiting oxide thickness.

Place, publisher, year, edition, pages
Elsevier, 2019
Keywords
Aluminum, Density functional theory, Oxidation, Silicon, X-ray photoelectron spectroscopy
National Category
Other Chemistry Topics
Identifiers
urn:nbn:se:kth:diva-246413 (URN)10.1016/j.susc.2019.02.005 (DOI)000470192900001 ()2-s2.0-85061563000 (Scopus ID)
Note

QC 20190402

Available from: 2019-04-02 Created: 2019-04-02 Last updated: 2019-06-25Bibliographically approved
Besharat, Z., Halldin Stenlid, J., Soldemo, M., Marks, K., Önsten, A., Johnson, M., . . . Göthelid, M. (2017). Dehydrogenation of methanol on Cu2O(100) and (111). Journal of Chemical Physics, 146(24)
Open this publication in new window or tab >>Dehydrogenation of methanol on Cu2O(100) and (111)
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2017 (English)In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 146, no 24Article in journal (Refereed) Published
Abstract [en]

Adsorption and desorption of methanol on the (111) and (100) surfaces of  Cu2O have been studied using high-resolution photoelectron spectroscopy in the temperature range 120–620 K, in combination with density functional theorycalculations and sum frequency generation spectroscopy. The bare (100) surfaceexhibits a (3,0; 1,1) reconstruction but restructures during the adsorption process into a Cu-dimer geometry stabilized by methoxy and hydrogen binding in Cu-bridge sites. During the restructuring process, oxygen atoms from the bulk that can host hydrogen appear on the surface. Heating transforms methoxy to formaldehyde, but further dehydrogenation is limited by the stability of the surface and the limited access to surface oxygen. The (√3 × √3)R30°-reconstructed (111) surface is based on ordered surface oxygen and copper ions and vacancies, which offers a palette of adsorption and reaction sites. Already at 140 K, a mixed layer of methoxy, formaldehyde, and CHxOy is formed. Heating to room temperature leaves OCH and CHx. Thus both CH-bond breaking and CO-scission are active on this  surface at low temperature. The higher ability to dehydrogenate methanol on (111) compared to (100) is explained by the multitude of adsorption sites and, in particular, the availability of surfaceoxygen.

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2017
National Category
Physical Chemistry
Identifiers
urn:nbn:se:kth:diva-211786 (URN)10.1063/1.4989472 (DOI)000404302600033 ()2-s2.0-85021446807 (Scopus ID)
Note

QC 20170816

Available from: 2017-08-13 Created: 2017-08-13 Last updated: 2017-11-10Bibliographically approved
Fashandi, H., Soldemo, M., Weissenrieder, J., Gothelid, M., Eriksson, J., Eklund, P., . . . Andersson, M. (2016). Applicability of MOS structures in monitoring catalytic properties, as exemplified for monolayer-iron-oxide-coated porous platinum films. Journal of Catalysis, 344, 583-590
Open this publication in new window or tab >>Applicability of MOS structures in monitoring catalytic properties, as exemplified for monolayer-iron-oxide-coated porous platinum films
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2016 (English)In: Journal of Catalysis, ISSN 0021-9517, E-ISSN 1090-2694, Vol. 344, p. 583-590Article in journal (Refereed) Published
Abstract [en]

Metal Oxide Semiconductor (MOS) capacitor devices comprised of monolayer iron oxide-coated as well as non-coated polycrystalline Pt deposited on oxidized silicon carbide substrates have been fabricated and their usefulness as realistic model systems in catalyst studies development was evaluated. The CO oxidation characteristics of both iron oxide- and non-coated Pt catalysts were investigated using mass spectrometry, monitoring the carbon dioxide production rate for different combinations of carbon monoxide (CO) and oxygen concentrations at various temperatures. Additionally, the output capacitance of the MOS model catalysts was recorded for each individual CO oxidation activity. A low-temperature shift in CO oxidation characteristics for the monolayer-coated compared to the non-coated Pt catalysts was observed, similar to that previously reported for monolayer iron oxide grown on single-crystalline Pt substrates. A strong correlation between the output capacitance of the MOS structures and the CO oxidation characteristics was found for both monolayer- and non-coated model catalysts. Furthermore, the devices exhibit retained MOS electrical output and CO oxidation characteristics as well as an unaffected catalyst surface composition, as confirmed by photoelectron spectroscopy, even after 200 h of continuous model catalyst operation. In addition to the implications on practical applicability of monolayer iron oxide coating on widely used polycrystalline Pt films in real-world catalysts and sensors, the findings also point to new possibilities regarding the use of MOS model systems for in situ characterization, high throughput screening, and tailoring of e.g. catalyst- and fuel-cell-electrode materials for specific applications.

Place, publisher, year, edition, pages
Academic Press, 2016
Keywords
Monolayer iron oxide, Platinum catalyst, Catalytic activity, CO oxidation, Field effect device, MOS capacitor, CO sensor
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-199751 (URN)10.1016/j.jcat.2016.10.018 (DOI)000390182800057 ()2-s2.0-84996565999 (Scopus ID)
Note

QC 20170123

Available from: 2017-01-23 Created: 2017-01-16 Last updated: 2017-06-28Bibliographically approved
Soldemo, M., Lundgren, E. & Weissenrieder, J. (2016). Oxidation of Fe(110) in oxygen gas at 400 °c. Surface Science, 644, 172-179
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, p. 172-179Article 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
Keywords
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 (Scopus ID)
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: 2017-11-30Bibliographically approved
Grinter, D., Luo, S., Soldemo, M., Piazza, L., Weissenrieder, J., Senanayake, S., . . . Rodriguez, J. (2016). Potassium promotion of a model Au/TiO2 catalyst. Abstracts of Papers of the American Chemical Society, 252
Open this publication in new window or tab >>Potassium promotion of a model Au/TiO2 catalyst
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2016 (English)In: Abstracts of Papers of the American Chemical Society, ISSN 0065-7727, Vol. 252Article in journal, Meeting abstract (Other academic) Published
Place, publisher, year, edition, pages
AMER CHEMICAL SOC, 2016
National Category
Organic Chemistry
Identifiers
urn:nbn:se:kth:diva-242626 (URN)000431460202693 ()
Note

QC 20190225

Available from: 2019-02-25 Created: 2019-02-25 Last updated: 2019-04-09Bibliographically approved
Soldemo, M., Halldin Stenlid, J., Besharat, Z., Ghadami Yazdi, M., Önsten, A., Leygraf, C., . . . Weissenrieder, J. (2016). The Surface Structure of Cu2O(100). The Journal of Physical Chemistry C, 120(8), 4373-4381
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, p. 4373-4381Article 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 (Scopus ID)
Funder
Swedish Research CouncilKnut and Alice Wallenberg Foundation
Note

QC 20160406

Available from: 2016-04-06 Created: 2016-04-01 Last updated: 2017-11-30Bibliographically approved
Soldemo, M. (2016). Transition metal oxide surfaces: Surface structures and molecular interaction. (Doctoral dissertation). Stockholm: KTH Royal Institute of Technology
Open this publication in new window or tab >>Transition metal oxide surfaces: Surface structures and molecular interaction
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. p. 68
Series
TRITA-ICT ; 2016:36
National Category
Physical Sciences Physical Sciences
Research subject
Physics
Identifiers
urn:nbn:se:kth:diva-196130 (URN)978-91-7729-176-3 (ISBN)
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
Soldemo, M., Niu, Y., Zakharov, A., Lundgren, E. & Weissenrieder, J. (2015). A well-ordered surface oxide on Fe(110). Surface Science, 639, 13-19
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, p. 13-19Article 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 (Scopus ID)
Note

QC 20150714

Available from: 2015-07-14 Created: 2015-07-13 Last updated: 2017-12-04Bibliographically approved
Zabel, T., Reuterskiöld Hedlund, C., Gustafsson, O., Karim, A., Berggren, J., Wang, Q., . . . Hammar, M. (2015). Auger recombination in In(Ga)Sb/InAs quantum dots. Applied Physics Letters, 106(1), 013103
Open this publication in new window or tab >>Auger recombination in In(Ga)Sb/InAs quantum dots
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2015 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 106, no 1, p. 013103-Article in journal (Refereed) Published
Abstract [en]

We report on the epitaxial formation of type II In0.5Ga0.5Sb/InAs and InSb/InAs quantum dot ensembles using metal organic vapor phase epitaxy. Employing scanning tunneling spectroscopy, we determine spatial quantum dot dimensions smaller than the de Broglie wavelength of InGaSb, which strongly indicates a three dimensional hole confinement. Photoluminescence spectroscopy at low temperatures yields an enhanced radiative recombination in the mid-infrared regime at energies of 170-200 meV. This luminescence displays a strong excitation power dependence with a blueshift indicating a filling of excited quantum dot hole states. Furthermore, a rate equation model is used to extract the Auger recombination coefficient from the power dependent intensity at 77 K yielding values of 1.35 x 10(-28) cm(6)/s for In0.5Ga0.5Sb/InAs quantum dots and 1.47 x 10(-27) cm(6)/s for InSb/InAs quantum dots, which is about one order of magnitude lower as previously obtained values for InGaSb superlattices.

National Category
Other Physics Topics
Identifiers
urn:nbn:se:kth:diva-160391 (URN)10.1063/1.4905455 (DOI)000347976900047 ()2-s2.0-84923814861 (Scopus ID)
Funder
VINNOVASwedish Foundation for Strategic Research
Note

QC 20150226

Available from: 2015-02-26 Created: 2015-02-19 Last updated: 2017-12-04Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0003-0483-0602

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