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Geometrical and Electronic Structures at Molecule-Metal Interfaces from Theoretical Modeling
KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.ORCID iD: 0000-0002-3282-0711
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In this thesis, we focus on theoretical investigations on metal interfaces where many heterogeneous chemical reactions take place. Surface-enhanced Raman scattering (SERS) spectroscopy and the modern electrochemical methods are important in-situ techniques that have been widely employed for a variety of applications. Theoretical simulations have become an indispensable tool to infer the molecular details of interfacial structures that are not directly accessible from experimental measurements. In this context, we have proposed several new theoretical models for both SERS and interfacial electrochemistry, which allow us to provide molecular-level understanding of the interfacial structures under the realistic experimental conditions.

 

The first part of the thesis has addressed the basic theory of SERS that offers the vibrational structure of the interfacial molecules. It is well known that the huge enhancement of Raman intensity in this technique can be attributed to two independent factors, namely the physical and chemical enhancements. The former is resulted from the enhanced electromagnetic field induced by the plasmonic excitations, while the latter comes from the changing of interaction between the molecule and the surface. The interplay between these two enhancement factors, which has long been an issue of debate, is revealed in this thesis. They are coupled through molecular polarizability. A practical computational approach is proposed and used to demonstrate the importance of the coupling on different molecular systems. It is found that for certain systems the coupling factor can be as large as 106. This finding is of great importance towards a comprehensive understanding of the SERS mechanisms and a quantitative prediction of the enhancement factor.

 

The other part of the thesis is devoted to the theory of interfacial electrochemistry, in particular the effects of water solution. A novel protocol that combines classical molecular dynamics (MD) and the first principles density functional theory (DFT) calculations is proposed to address the statistical behavior of interfacial properties. Special attention has been paid to the work function of Pt(111) surface and CO adsorption energy on Pt(111) surface in aqueous solution. It has been found that in this case the work function of Pt surface illustrates a surprisingly broad distribution under the room temperature, sheds new light on the understanding of reaction activity of the surface. The proposed protocol is able to provide results in very good agreement with experiments and should be applied routinely in future studies.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2012. , xii, 67 p.
Series
Trita-BIO-Report, ISSN 1654-2312 ; 2012:14
Keyword [en]
SERS, Electrochemistry, DFT, MD
National Category
Physical Chemistry
Research subject
SRA - Energy
Identifiers
URN: urn:nbn:se:kth:diva-94120ISBN: 978-91-7501-372-5 (print)OAI: oai:DiVA.org:kth-94120DiVA: diva2:525377
Public defence
2012-06-07, FB54, Albanova University Center, Roslagstullsbacken 21, Stockholm, 10:00 (English)
Opponent
Supervisors
Funder
StandUp
Note

QC 20120515

Available from: 2012-05-15 Created: 2012-05-07 Last updated: 2013-04-18Bibliographically approved
List of papers
1. Structures of Water Molecules Adsorbed on a Gold Electrode under Negative Potentials
Open this publication in new window or tab >>Structures of Water Molecules Adsorbed on a Gold Electrode under Negative Potentials
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2010 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 114, no 9, 4051-4056 p.Article in journal (Refereed) Published
Abstract [en]

Two stable conformations of water hexamer Clusters on gold electrode under negative potentials have been identified by density functional theory calculations. Both form a ring Structure but with different orientations of free CH bonds. Ill one of the Structures, labeled as F-Type, four free OH bonds of the water molecules point toward the gold surface and remain stable over a wide range of the negative potential. The other Structure, labeled as S-Type, starts with five Such free OH bonds pointing toward the gold surface at the low negative potential and ends LIP with six of them at higher negative potential. From the energetic point of view, the S-Type Structure is more stable than the F-Type under the same Potential. By comparing the calculated Raman spectra with the experiment, it is found that S-Type Structures are the most possible surface adsorption state of water molecules at the electrochemical interface under very negative electrode potentials. It is believed that such a novel water Structure Could also exist Oil other negative charged Surfaces.

Keyword
infrared-absorption spectroscopy, enhanced raman-spectroscopy, au(210), surfaces, interface, clusters, spectra, au, reorientation, adsorption, ag(111)
National Category
Physical Chemistry
Identifiers
urn:nbn:se:kth:diva-19269 (URN)10.1021/jp911072g (DOI)000275045600049 ()2-s2.0-77949305757 (Scopus ID)
Funder
Swedish Research Council
Note
QC 20100525Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2017-12-12Bibliographically approved
2. A density functional theory approach to mushroom-like platinum clusters on palladium-shell over Au core nanoparticles for high electrocatalytic activity
Open this publication in new window or tab >>A density functional theory approach to mushroom-like platinum clusters on palladium-shell over Au core nanoparticles for high electrocatalytic activity
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2011 (English)In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 13, no 12, 5441-5449 p.Article in journal (Refereed) Published
Abstract [en]

Recently, it was found that Pt clusters deposited on Pd shell over Au core nanoparticles (Au@Pd@Pt NPs) exhibit unusually high electrocatalytic activity for the electro-oxidation of formic acid (P. P. Fang, S. Duan, et al., Chem. Sci., 2011, 2, 531-539). In an attempt to offer an explanation, we used here carbon monoxide (CO) as probed molecules, and applied density functional theory (DFT) to simulate the surface Raman spectra of CO at this core-shell-cluster NPs with a two monolayer thickness of Pd shell and various Pt cluster coverage. Our DFT results show that the calculated Pt coverage dependent spectra fit the experimental ones well only if the Pt clusters adopt a mushroom-like structure, while currently the island-like structure is the widely accepted model, which follows the Volmer-Weber growth mode. This result infers that there should be a new growth mode, i.e., the mushroom growth mode as proposed in the present work, for Au@Pd@Pt NPs. We suggest that such a mushroom-like structure may offer novel active sites, which accounts for the observed high electrocatalytic activity of Au@Pd@Pt NPs.

Place, publisher, year, edition, pages
Cambridge: ROYAL SOC CHEMISTRY, 2011
Keyword
ADSORBATE-ADSORBATE INTERACTIONS; SINGLE-CRYSTAL SURFACES; AUGMENTED-WAVE METHOD; OXYGEN-REDUCTION; CARBON-MONOXIDE; FORMIC-ACID; PD(111) SURFACE; AB-INITIO; BIMETALLIC NANODENDRITES; METAL NANOCRYSTALS
National Category
Physical Chemistry
Identifiers
urn:nbn:se:kth:diva-32126 (URN)10.1039/c1cp20096h (DOI)000288219700029 ()2-s2.0-79952649242 (Scopus ID)
Note
QC 20110407Available from: 2011-04-07 Created: 2011-04-07 Last updated: 2017-12-11Bibliographically approved
3. Molecular polarization bridging physical and chemical enhancements in surface enhanced Raman scattering
Open this publication in new window or tab >>Molecular polarization bridging physical and chemical enhancements in surface enhanced Raman scattering
2011 (English)In: Chemical Communications, ISSN 1359-7345, E-ISSN 1364-548X, Vol. 47, no 41, 11438-11440 p.Article in journal (Refereed) Published
Abstract [en]

We present a practical method which demonstrates how the physical and chemical enhancements in SERS for a molecule adsorbed on metal junctions are conceptually coupled through the polarization of the molecule and its surroundings. Calculations with the state-of-the-art density functional reveal that the coupling factor considered in the present work can be as large as 10(6), such that it is indeed important for certain vibrational modes.

Keyword
sers spectra, silver, metal, spectroscopy, modes, gold
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-46869 (URN)10.1039/c1cc14962h (DOI)000295696300012 ()2-s2.0-80053947493 (Scopus ID)
Funder
Swedish Research Council
Note
QC 20111107Available from: 2011-11-07 Created: 2011-11-07 Last updated: 2017-12-08Bibliographically approved
4. A Hybrid Molecular Dynamics and First Principles Study on the Workfunction of a Pt(1 1 1) Electrode Immersed in Aqueous Solution at Room Temperature
Open this publication in new window or tab >>A Hybrid Molecular Dynamics and First Principles Study on the Workfunction of a Pt(1 1 1) Electrode Immersed in Aqueous Solution at Room Temperature
(English)Article in journal (Other academic) Submitted
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-95163 (URN)
Note
QS 2012Available from: 2012-05-15 Created: 2012-05-15 Last updated: 2012-05-15Bibliographically approved
5. Thermal Eects on Electronic Properties of CO/Pt(111) in Water
Open this publication in new window or tab >>Thermal Eects on Electronic Properties of CO/Pt(111) in Water
(English)Article in journal (Other academic) Submitted
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-95164 (URN)
Note
QS 2012Available from: 2012-05-15 Created: 2012-05-15 Last updated: 2012-05-15Bibliographically approved

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