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The Surface Structure of Cu2O(100)
KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.ORCID iD: 0000-0003-0483-0602
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.ORCID iD: 0000-0003-3832-2331
KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.ORCID iD: 0000-0002-9828-7753
KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
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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
Resource type
Text
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. Vol. 120, no 8, 4373-4381 p.
National Category
Inorganic Chemistry
Identifiers
URN: urn:nbn:se:kth:diva-184532DOI: 10.1021/acs.jpcc.5b11350ISI: 000371562000024Scopus ID: 2-s2.0-84960171601OAI: oai:DiVA.org:kth-184532DiVA: diva2:917420
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
In thesis
1. Adsorption of molecular thin films on metal and metal oxide surfaces
Open this publication in new window or tab >>Adsorption of molecular thin films on metal and metal oxide surfaces
2016 (English)Doctoral thesis, comprehensive summary (Other academic) [Artistic work]
Abstract [en]

Metal and metal oxides are widely used in industry, and to optimize their performance their surfaces are commonly functionalized by the formation of thin films. Self-assembled monolayers (SAMs) are deposited on metals or metal oxides either from solution or by gas deposition. Thiols with polar terminal groups are utilized for creating the responsive surfaces which can interact electrostatically with other adsorbates. Surface charge effects wetting and adhesion, and many other surface properties. Polar terminal groups in thiols could be used to modify these factors. Mixed SAMs can provide more flexible surfaces, and could change the resulting surface properties under the influence of factors such as pH, temperature, and photo-illumination. Therefore, in order to control these phenomena by mixed polar-terminated thiols, it is necessary to understand the composition and conformation of the mixed SAMs and their response to these factors. In this work, mixtures of thiols with carboxylic and amino terminal groups were studied. Carboxylic and amino terminal groups of thiol interact with each other via hydrogen bonding in solution and form a complex. Complexes adsorb to the surface in non-conventional orientations. Unmixed SAMs from each type, either carboxylic terminated thiols or amino terminated thiols are in standing up orientation while SAMs from complexes are in an axially in-plane orientation. Selenol is an alternative to replace thiols for particular applications such as contact with biological matter which has a better compatibility with selenol than sulfur. However, the    Se-C bond is weaker than the S-C bond which limits the application of selenol. Understanding the selenol adsorption mechanism on gold surfaces could shed some light on Se-C cleavage and so is investigated in this work. Se-C cleavage happens in the low coverage areas on the step since atoms at steps have lower coordination making them more reactive than atoms on the terraces.  Another area where the self-assembly of molecules is of importance is for dye sensitized solar cells, which are based on the adsorption of the dye onto metal oxides surfaces such as TiO2.The interface between the SAM of dye and the substrate is an important factor to consider when designing dyes and surfaces in dye sensitized solar cells (DSSCs). The quality of the self-assembled monolayers of the dye on the TiO2 surface has a critical influence on the efficiency of the DSSCs.  Creation of just a monolayer of dye on the surface could lead to an efficient current of photo-excited electrons to the TiO2 and degeneration of the dye by redox. This work, T-PAC dye showed island growth with some ad-layer that is not in contact with the surface, whereas the MP13 dye adsorption is laminar growth.  Cuprite (Cu2O) is the initial and most common corrosion product for copper under atmospheric conditions. Copper could be a good replacement for noble metal as catalysts for methanol dehydrogenation. Knowledge about the structure of Cu2O(100) and Cu2O(111) surfaces could be used to obtain a deeper understanding of methanol dehydrogenation mechanisms with respect to adsorption sites on the surfaces. In this work, a detailed study was done of Cu2O(100) surface which revealed the possible surface structures as the result of different preparation conditions. Studies of the structure of Cu2O(100) and Cu2O(111) surfaces show that Cu2O(100) has a comparatively stable surface and reduces surface reactivity. As a consequence, dehydrogenation of methanol is more efficient on the Cu2O(111) surface. The hydrogen produced from methanol dehydrogenation is stored in oxygen adatom sites on both surfaces.

 

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2016. 85 p.
Series
TRITA-ICT, 2016:37
Keyword
Self assembled monolayer (SAM), dye synthesis solar cell (DSSC), thiol, selenol, Cu2O(100), Cu2O(111) and dehydrogenation
National Category
Physical Sciences
Research subject
Physics; Materials Science and Engineering
Identifiers
urn:nbn:se:kth:diva-195613 (URN)978-91-7729-178-7 (ISBN)
Public defence
2016-12-09, Sal C Electrum, Kistagången 16 16440 Kista,, stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20161107

Available from: 2016-11-09 Created: 2016-11-04 Last updated: 2016-12-01Bibliographically approved
2. Transition metal oxide surfaces: Surface structures and molecular interaction
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. 68 p.
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

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