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Adsorption of molecular thin films on metal and metal oxide surfaces
KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF. (surface physics, surface and corrosion science)ORCID iD: 0000-0002-9828-7753
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 [en]
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: urn:nbn:se:kth:diva-195613ISBN: 978-91-7729-178-7OAI: oai:DiVA.org:kth-195613DiVA: diva2:1044683
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
List of papers
1. Mixed monolayers of alkane thiols with polar terminal group on gold: Investigation of structure dependent surface properties
Open this publication in new window or tab >>Mixed monolayers of alkane thiols with polar terminal group on gold: Investigation of structure dependent surface properties
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2016 (English)In: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 484, no 279, 279-290 p., j.jcis.2016.08.053Article in journal, Editorial material (Refereed) Published
Abstract [en]

Adsorption of thiols with cationic or anionic terminal group on gold has been studied from mixed solutions of 11-Amino-1-undecanethiol (AUT) and 3-Mercaptopropionic acid (MPA) using Quartz Crystal Microbalance with Dissipation (QCM-D), X-ray Photoelectron Spectroscopy (XPS), atomic force microscopy (AFM) and contact angles. The goal is to probe the nature of such layers, and the additivity or otherwise of the pH responsiveness, with a view to evaluate their suitability as smart materials. For each of the two pure (unmixed) cases, ordered molecular monolayers are formed with sulfur binding to gold and the alkane chain pointing out from the surface as expected. Adsorption from the thiol mixtures, however, leads to a more complex behaviour. The surface concentration of thiols from the mixtures, as determined by QCM-D, is considerably lower than for the pure cases and it reaches a minimum at a 3:1 MPA/AUT relative concentration in the solution. The XPS results confirm a reduction in adsorbed amount in mixtures with the lowest overall intensity for the 3:1 ratio. Monolayers formed from mixtures display a wettability which is much lower and less pH sensitive. Collectively these results confirm that for adsorption from mixed systems, the configuration is completely different. Complex formation in the mixed solutions leads to the adsorption of molecules parallel to the surface in an axially in-plane configuration. This parallel layer of thiols is mechanically relatively robust to nano-shaving based on AFM measurements. These results will have a significant impact on the design of biomimetic surface coatings particularly when mixtures of oppositely charged molecules are present on the surface, as is commonly the case in biological, proteinaceous surfaces (e.g. hair and skin).

Place, publisher, year, edition, pages
Academic Press, 2016
Keyword
Self-assembled monolayer (SAM), Thiols, Quartz Crystal Microbalance with Dissipation (QCM-D), Atomic force microscopy (AFM), X-ray Photoelectron Spectroscopy (XPS)
National Category
Composite Science and Engineering
Identifiers
urn:nbn:se:kth:diva-195612 (URN)10.1016/j.jcis.2016.08.053 (DOI)000385690200032 ()2-s2.0-84986258342 (ScopusID)
Funder
Swedish Research Council
Note

QC 20161107

Available from: 2016-11-04 Created: 2016-11-04 Last updated: 2016-11-29Bibliographically approved
2. Se-C cleavage of hexane selenol at steps on Au(111)
Open this publication in new window or tab >>Se-C cleavage of hexane selenol at steps on Au(111)
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(English)Manuscript (preprint) (Other academic) [Artistic work]
Keyword
Self-Assembled monolayer (SAM), hexane selenol, Au(111), Scanning Tunneling Microscopy (STM), Photoelectron Spectroscopy (PES)
National Category
Other Materials Engineering
Identifiers
urn:nbn:se:kth:diva-195641 (URN)
Note

QC 20161107

Available from: 2016-11-07 Created: 2016-11-07 Last updated: 2016-11-07Bibliographically approved
3. In-situ evaluation of dye adsorption on TiO2 using QCM
Open this publication in new window or tab >>In-situ evaluation of dye adsorption on TiO2 using QCM
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(English)Manuscript (preprint) (Other academic) [Artistic work]
Keyword
Sensitized Solar Cell (DSSC), Quartz Crystal Microbalance with Dissipation (QCM-D), Atomic Force Microscopy (AFM) and X-ray Photoelectron Spectroscopy (XPS)
National Category
Engineering and Technology
Research subject
Physics; Chemistry; Materials Science and Engineering
Identifiers
urn:nbn:se:kth:diva-195644 (URN)
Note

QC 20161107

Available from: 2016-11-07 Created: 2016-11-07 Last updated: 2016-11-07Bibliographically 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. Dehydrogenation of methanol on Cu2O(100) and (111)
Open this publication in new window or tab >>Dehydrogenation of methanol on Cu2O(100) and (111)
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(English)Manuscript (preprint) (Other academic) [Artistic work]
Keyword
methanol, metal oxides and catalysis, Cu2O
National Category
Materials Engineering
Research subject
Materials Science and Engineering; Chemistry; Physics
Identifiers
urn:nbn:se:kth:diva-195646 (URN)
Projects
methanol, metal oxides and catalysis, Cu2O
Note

QC 20161107

Available from: 2016-11-07 Created: 2016-11-07 Last updated: 2016-11-07Bibliographically approved

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