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Björneholm, Olle
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Publications (10 of 97) Show all publications
Ekholm, V., Vazdar, M., Mason, P. E., Bialik, E., Walz, M.-M., Ohrwall, G., . . . Björneholm, O. (2018). Anomalous surface behavior of hydrated guanidinium ions due to ion pairing. Journal of Chemical Physics, 148(14), Article ID 144508.
Open this publication in new window or tab >>Anomalous surface behavior of hydrated guanidinium ions due to ion pairing
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2018 (English)In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 148, no 14, article id 144508Article in journal (Refereed) Published
Abstract [en]

Surface affinity of aqueous guanidinium chloride (GdmCl) is compared to that of aqueous tetrapropylammonium chloride (TPACl) upon addition of sodium chloride (NaCl) or disodium sulfate (Na2SO4). The experimental results have been acquired using the surface sensitive technique X-ray photoelectron spectroscopy on a liquid jet. Molecular dynamics simulations have been used to produce radial distribution functions and surface density plots. The surface affinities of both TPA(+) and Gdm(+) increase upon adding NaCl to the solution. With the addition of Na2SO4, the surface affinity of TPA(+) increases, while that of Gdm(+) decreases. From the results of MD simulations it is seen that Gdm(+) and SO42- ions form pairs. This finding can be used to explain the decreased surface affinity of Gdm(+) when co-dissolved with SO42- ions. Since SO42- ions avoid the surface due to the double charge and strong water interaction, the Gdm(+)-SO42- ion pair resides deeper in the solutions' bulk than the Gdm(+) ions. Since TPA(+) does not form ion pairs with SO42-, the TPA(+) ions are instead enriched at the surface.

National Category
Physical Chemistry
Identifiers
urn:nbn:se:uu:diva-353201 (URN)10.1063/1.5024348 (DOI)000430128600034 ()29655316 (PubMedID)
Funder
Swedish Research Council
Available from: 2018-06-13 Created: 2018-06-13 Last updated: 2018-09-02Bibliographically approved
Pokapanich, W., Björneholm, O., Öhrwall, G. & Tchaplyguine, M. (2017). Core level photoelectron spectroscopy probed heterogeneous xenon/neon clusters. Radiation Physics and Chemistry, 135, 45-48
Open this publication in new window or tab >>Core level photoelectron spectroscopy probed heterogeneous xenon/neon clusters
2017 (English)In: Radiation Physics and Chemistry, ISSN 0969-806X, E-ISSN 1879-0895, Vol. 135, p. 45-48Article in journal (Refereed) Published
Abstract [en]

Binary rare gas clusters; xenon and neon which have a significant contrariety between sizes, produced by a co-expansion set up and have been studied using synchrotron radiation based x-ray photoelectron spectroscopy. Concentration ratios of the heterogeneous clusters; 1%, 3%, 5% and 10% were controlled. The core level spectra were used to determine structure of the mixed cluster and analyzed by considering screening mechanisms. Furthermore, electron binding energy shift calculations demonstrated cluster aggregation models which may occur in such process. The results showed that in the case of low mixing ratios of 3% and 5% of xenon in neon, the geometric structures exhibit xenon in the center and xenon/neon interfaced in the outer shells. However, neon cluster vanished when the concentration of xenon was increased to 10%.

Keywords
Synchrotron, Rare gas, Mixed clusters, Geometric structure, Co-expansion
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:uu:diva-322515 (URN)10.1016/j.radphyschem.2017.02.056 (DOI)000399846700008 ()
Funder
Swedish Research CouncilGöran Gustafsson Foundation for Research in Natural Sciences and MedicineKnut and Alice Wallenberg FoundationThe Swedish Foundation for International Cooperation in Research and Higher Education (STINT)Swedish Foundation for Strategic Research
Available from: 2017-05-30 Created: 2017-05-30 Last updated: 2017-05-30Bibliographically approved
Andersson, T., Zhang, C., Björneholm, O., Mikkela, M.-H., Jankala, K., Anin, D., . . . Tchaplyguine, M. (2017). Electronic structure transformation in small bare Au clusters as seen by x-ray photoelectron spectroscopy. Journal of Physics B: Atomic, Molecular and Optical Physics, 50(1), Article ID 015102.
Open this publication in new window or tab >>Electronic structure transformation in small bare Au clusters as seen by x-ray photoelectron spectroscopy
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2017 (English)In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 50, no 1, article id 015102Article in journal (Refereed) Published
Abstract [en]

Free bare gold clusters in the size range from few tens to few hundred atoms (<= 1 nm dimensions) have been produced in a beam, and the size-dependent development of their full valence band including the 5d and 6s parts has been mapped 'on the fly' by synchrotron-based photoelectron spectroscopy. The Au 4f core level has been also probed, and the cluster-specific Au 4f ionization energies have been used to estimate the cluster size. The recorded in the present work valence spectra of the small clusters are compared with the spectra of the large clusters (N similar to 10(3)) created by us using a magnetron-based gas aggregation source. The comparison shows a substantially narrower 5d valence band and the decrease in its splitting for gold clusters in the size range of few hundred atoms and below. Our DFT calculations involving the pseudopotential method show that the 5d band width of the ground state increases with the cluster size and by the size N = 20 becomes comparable with the experimental width of the valence photoelectron spectrum. Similar to the earlier observations on supported clusters we interpret our experimental and theoretical results as due to the undercoordination of a large fraction of atoms in the clusters with N similar to 10(2) and below. The consequences of such electronic structure of small gold clusters are discussed in connection with their specific physical and chemical properties related to nanoplasmonics and nanocatalysis.

Keywords
Au 5d valence band, Au 4f core level, free bare clusters, synchrotron radiation, x-ray photoelectron spectroscopy, size-dependent electronic structure
National Category
Condensed Matter Physics Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:uu:diva-316008 (URN)10.1088/1361-6455/50/1/015102 (DOI)000391492400001 ()
Funder
Swedish Research CouncilGöran Gustafsson Foundation for promotion of scientific research at Uppala University and Royal Institute of TechnologyKnut and Alice Wallenberg FoundationThe Crafoord FoundationSwedish Foundation for Strategic Research
Available from: 2017-02-24 Created: 2017-02-24 Last updated: 2017-11-29Bibliographically approved
Marinho, R. R. T., Walz, M.-M., Ekholm, V., Ohrwall, G., Björneholm, O. & de Brito, A. N. (2017). Ethanol Solvation in Water Studied on a Molecular Scale by Photoelectron Spectroscopy. Journal of Physical Chemistry B, 121(33), 7916-7923
Open this publication in new window or tab >>Ethanol Solvation in Water Studied on a Molecular Scale by Photoelectron Spectroscopy
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2017 (English)In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 121, no 33, p. 7916-7923Article in journal (Refereed) Published
Abstract [en]

Because of the amphiphilic properties of alcohols, hydrophobic hydration is important in the alcohol water system. In the present paper we employ X-ray photoelectron spectroscopy (XPS) to investigate the bulk and surface molecular structure of ethanol water mixtures from 0.2 to 95 mol %. The observed XPS binding energy splitting between the methyl C is and hydroxymethyl C is groups (BES_[CH3-CH2OH]) as a function of the ethanol molar percentage can be divided into different regions: one below 35 mol % with higher values (about 1.53 eV) and one starting at 60 mol % up to 95 mol % with 1.49 eV as an average value. The chemical shifts agree with previous quantum mechanics/molecular mechanics (QM/MM) calculations [Loytynoja, T.; et al. J. Phys. Chem. B 2014, 118, 13217]. According to these calculations, the BES_[CH3-CH2OH] is related to the number of hydrogen bonds between the ethanol and the surrounding molecules. As the ethanol concentration increases, the average number of hydrogen bonds decreases from 2.5 for water-rich mixtures to 2 for pure ethanol. We give an interpretation for this behavior based on how the hydrogen bonds are distributed according to the mixing ratio. Since our experimental data are surface sensitive, we propose that this effect may also be manifested at the interface. From the ratio between the XPS C is core lines intensities we infer that below 20 mol % the ethanol molecules have their hydroxyl groups more hydrated and possibly facing the solution's bulk. Between 0.1 and 14 mol %, we show the formation of an ethanol monolayer at approximately 2 mol %. Several parameters are derived for the surface region at monolayer coverage.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2017
National Category
Physical Chemistry
Identifiers
urn:nbn:se:uu:diva-335233 (URN)10.1021/acs.jpcb.7b02382 (DOI)000408598300020 ()28715892 (PubMedID)
Available from: 2017-12-05 Created: 2017-12-05 Last updated: 2017-12-05Bibliographically approved
Tchaplyguine, M., Mikkelae, M.-H. -., Marsell, E., Polley, C., Mikkelsen, A., Zhang, W., . . . Björneholm, O. (2017). Metal-passivated PbS nanoparticles: fabrication and characterization. Physical Chemistry, Chemical Physics - PCCP, 19(10), 7252-7261
Open this publication in new window or tab >>Metal-passivated PbS nanoparticles: fabrication and characterization
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2017 (English)In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 19, no 10, p. 7252-7261Article in journal (Refereed) Published
Abstract [en]

Organic-shell-free PbS nanoparticles have been produced in the size range relevant for quantum-dot solar cells (QDSCs) by a vapor aggregation method involving magnetron reactive sputtering. This method creates a beam of free 5-10 nm particles in a vacuum. The dimensions of the particles were estimated after their deposition on a substrate by imaging them using ex situ SEM and HRTEM electron microscopy. The particle structure and chemical composition could be deduced "on the fly", prior to deposition, using X-ray photoelectron spectroscopy (XPS) with tunable synchrotron radiation. Our XPS results suggest that under certain conditions it is possible to fabricate particles with a semiconductor core and 1 to 2 monolayer shells of metallic lead. For this case the absolute energy of the highest occupied molecular orbital (HOMO) in PbS has been determined to be (5.0 +/- 0.5) eV below the vacuum level. For such particles deposited on a substrate HRTEM has confirmed the XPS-based conclusions on the crystalline PbS structure of the semiconductor core. Absorption spectroscopy on the deposited film has given a value of similar to 1 eV for the lowest exciton. Together with the valence XPS results this has allowed us to reconstruct the energy level scheme of the particles. The results obtained are discussed in the context of the properties of PbS QDSCs.

Place, publisher, year, edition, pages
Royal Society of Chemistry, 2017
National Category
Physical Chemistry
Identifiers
urn:nbn:se:uu:diva-321152 (URN)10.1039/c6cp06870g (DOI)000396148600039 ()28239693 (PubMedID)
Available from: 2017-05-02 Created: 2017-05-02 Last updated: 2017-05-02Bibliographically approved
Mocellin, A., de Abreu Gomes, A. H., Araujo, O. C., de Brito, A. N. & Björneholm, O. (2017). Surface Propensity of Atmospherically Relevant Amino Acids Studied by XPS. Journal of Physical Chemistry B, 121(16), 4220-4225
Open this publication in new window or tab >>Surface Propensity of Atmospherically Relevant Amino Acids Studied by XPS
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2017 (English)In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 121, no 16, p. 4220-4225Article in journal (Refereed) Published
Abstract [en]

Amino acids constitute an important fraction of the water-soluble organic nitrogen (WSON) compounds in aerosols and are involved in many processes in the atmosphere. In this-Work, we applied X-ray photoelectron spectroscopy (XPS) to study aqueous solutions of four amino acids, glycine, alanine, Valirie) and methionine, in their zwitterionic forms. We found that amino acids with hydrophilic side chains and smaller size, GLY and ALA, tend to stay in the bulk of the liquid, while the hydrophobic and bigger amino acids, VAL and MET, are found to concentrate more on the surface. We found experimental evidence that the amino acids have preferential orientation relative to the surface, with the hydrophobic side chain being closer to the surface than the hydrophilic carboxylate group. The observed amino acid surface propensity has implications in atmospheric science as the surface interactions play a central role in cloud droplet formation, and they should be considered in climate models.

National Category
Physical Chemistry
Identifiers
urn:nbn:se:uu:diva-323456 (URN)10.1021/acsjpcb.7b02174 (DOI)000400534200031 ()28358197 (PubMedID)
Funder
Swedish Research CouncilCarl Tryggers foundation Swedish Foundation for Strategic Research
Available from: 2017-07-06 Created: 2017-07-06 Last updated: 2017-07-06Bibliographically approved
Wright, C., Zhang, C., Mikkela, M.-H., Marsell, E., Mikkelsen, A., Sorensen, S., . . . Tchaplyguine, M. (2017). Tin Oxides: Insights into Chemical States from a Nanoparticle Study. The Journal of Physical Chemistry C, 121(35), 19414-19419
Open this publication in new window or tab >>Tin Oxides: Insights into Chemical States from a Nanoparticle Study
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2017 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 121, no 35, p. 19414-19419Article in journal (Refereed) Published
Abstract [en]

Tin oxides are semiconductor materials currently attracting close attention in electronics, photovoltaics, gas sensing, and catalysis. Depending on the tin oxidation state-Sn(IV), Sn(II), or intermediate-the corresponding oxide has either n- or p-type natural conductivity, ascribed to oxygen or metal deficiency in the lattice. Such crystalline imperfections severely complicate the task of establishing tin oxidation state, especially at nanoscale. In spite of the striking differences between SnO2 and SnO in their most fundamental properties, there have been enduring problems in identifying the oxide type. These problems were to a great extent caused by the controversy around the characteristic chemical shift, that is, the difference in electron binding energy of a certain core level in an oxide and its parent metal. Using in situ fabricated bare tin oxide nanoparticles, we have been able to resolve the controversy: Our photoelectron spectroscopic study on tin oxide nanoparticles shows that, in contrast to a common opinion of a close chemical shift for SnO2 and SnO, the shift value for tin(IV) oxide is, in fact, 3 times larger than that for tin(II) oxide. Moreover, our investigation of the nanoparticle valence electronic structure clarifies the question of why previously the identification of oxidation states encountered problems.

National Category
Nano Technology Physical Chemistry
Identifiers
urn:nbn:se:uu:diva-335205 (URN)10.1021/acs.jpcc.7b05013 (DOI)000410597600052 ()
Available from: 2017-12-04 Created: 2017-12-04 Last updated: 2017-12-04Bibliographically approved
Björneholm, O., Hansen, M. H., Hodgson, A., Liu, L.-M., Limmer, D. T., Michaelides, A., . . . Bluhm, H. (2016). Water at Interfaces. Chemical Reviews, 116(13), 7698-7726
Open this publication in new window or tab >>Water at Interfaces
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2016 (English)In: Chemical Reviews, ISSN 0009-2665, E-ISSN 1520-6890, Vol. 116, no 13, p. 7698-7726Article, review/survey (Refereed) Published
Abstract [en]

The interfaces of neat water and aqueous solutions play a prominent role in many technological processes and in the environment. Examples of aqueous interfaces are ultrathin water films that cover most hydrophilic surfaces under ambient relative humidities, the liquid/solid interface which drives many electrochemical reactions, and the liquid/vapor interface, which governs the uptake and release of trace gases by the oceans and cloud droplets. In this article we review some of the recent experimental and theoretical advances in our knowledge of the properties of aqueous interfaces and discuss open questions and gaps in our understanding.

National Category
Other Chemistry Topics
Identifiers
urn:nbn:se:uu:diva-300655 (URN)10.1021/acs.chemrev.6b00045 (DOI)000379794000012 ()
Funder
The Royal Swedish Academy of SciencesSwedish Research CouncilEU, European Research Council, 616121Swedish Foundation for Strategic Research Carl Tryggers foundation
Available from: 2016-08-10 Created: 2016-08-10 Last updated: 2017-11-28Bibliographically approved
Ohrwall, G., Prisle, N. L., Ottosson, N., Werner, J., Ekholm, V., Walz, M.-M. & Björneholm, O. (2015). Acid-Base Speciation of Carboxylate Ions in the Surface Region of Aqueous Solutions in the Presence of Ammonium and Aminium Ions. Journal of Physical Chemistry B, 119(10), 4033-4040
Open this publication in new window or tab >>Acid-Base Speciation of Carboxylate Ions in the Surface Region of Aqueous Solutions in the Presence of Ammonium and Aminium Ions
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2015 (English)In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 119, no 10, p. 4033-4040Article in journal (Refereed) Published
Abstract [en]

The acid base speciation of surface-active carboxylate ions in the surface region of aqueous solutions was studied with synchrotron-radiation-based photoelectron spectroscopy. The protonated form was found at an extraordinarily large fraction compared to that expected from the bulk pH. When adding salts containing the weak acid NH4+ to the solution, the fraction of the acidic form at the surface increases, and to a Much greatet extent than expected from the bulk pH of the solution. We show that ammonium ions also are overrepresented in the surface region, and propose that the interaction between the surface-active anionic carboxylates and cationic ammonium ions creates a carboxylateammonium bilayer close to the surface, which increases the probability of the protonation of the carboxylae ions. By comparing the situation when a salt of the less volatile amine diethanolatnine is used, We also show that the observed evaporation of ammonia that occurs after such an event only affects the equilibrium marginally.

National Category
Physical Chemistry
Identifiers
urn:nbn:se:uu:diva-251803 (URN)10.1021/jp509945g (DOI)000351188300016 ()25700136 (PubMedID)
Available from: 2015-04-28 Created: 2015-04-24 Last updated: 2017-12-04Bibliographically approved
Tchaplyguine, M., Mikkela, M.-H., Zhang, C., Andersson, T. & Björneholm, O. (2015). Gold Oxide Nanoparticles with Variable Gold Oxidation State. The Journal of Physical Chemistry C, 119(16), 8937-8943
Open this publication in new window or tab >>Gold Oxide Nanoparticles with Variable Gold Oxidation State
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2015 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 119, no 16, p. 8937-8943Article in journal (Refereed) Published
Abstract [en]

Gold-oxide-containing nanoparticles have been produced in a range of partial to full oxidation conditions, where the nanoparticle electronic structure and stoichiometry have been characterized. Our results indicate that with the increase of the oxidation degree in these nanoparticles the gold oxidation state possibly changes from lower oxides with monoor divalent metal to the higher oxide with the trivalent gold. At intermediate oxidation conditions our observations are consistent with a radially segregated structure of such nanopaiticles-with the core containing mainly oxide and the surface covered with few monolayers of metallic gold. These results have been possible to obtain combining the vapor aggregation method for the nanoparticle fabrication and synchrotron-based photoelectron spectroscopy for their characterization. The deposition of the oxidized nanoparticles has showed that the species assigned as containing lower oxide could be preserved in the landing and then studied on a substrate for a limited time. The possible lower oxide formation in nanoparticles is discussed in connection to the enhanced catalytic activity of gold nanoparticles.

National Category
Chemical Sciences
Identifiers
urn:nbn:se:uu:diva-255292 (URN)10.1021/acs.jpcc.5b00811 (DOI)000353603500059 ()
Funder
Swedish Research CouncilKnut and Alice Wallenberg FoundationThe Crafoord Foundation
Available from: 2015-06-22 Created: 2015-06-15 Last updated: 2017-12-04Bibliographically approved
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