uu.seUppsala University Publications
Change search
Link to record
Permanent link

Direct link
BETA
Björneholm, Olle
Alternative names
Publications (10 of 100) Show all publications
Tchaplyguine, M., Zhang, C., Andersson, T. & Björneholm, O. (2018). Ag-Cu oxide nanoparticles with high oxidation states: towards new high T-c materials. Dalton Transactions, 47(46), 16660-16667
Open this publication in new window or tab >>Ag-Cu oxide nanoparticles with high oxidation states: towards new high T-c materials
2018 (English)In: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, Vol. 47, no 46, p. 16660-16667Article in journal (Refereed) Published
Abstract [en]

In Ag-Cu oxides possible to fabricate so far, superconductivity has not been detected, but high conductivity was. In the quest for superconductivity the demand is to create a high and peculiar copper-oxygen coordination. Such coordination makes it non-trivial to determine Cu oxidation states, which may be several and co-existing. Another reason for uncertainty is in oxygen deficiency typical for superconducting crystals. Finally, Cu oxidation is influenced by the other metals in the substance. For chemical fabrication the difficulty is to tune the relative abundances of elements in a fine way. Ag-Cu oxides have been also produced by reactive co-sputtering of Cu and Ag, but the composition with high Cu oxidation states necessary for high conductivity has not been realized. In the present work we have fabricated Ag-Cu-oxide nanoparticles containing Cu and Ag in high oxidation states actual for superconductivity. The fabrication includes reactive sputtering of Ag and Cu metals, their vapour oxidation and aggregation into nanoparticles. The ability to create different and high oxidation states, also co-existing, is demonstrated. The fabrication approach also allows overcoming the poor miscibility of Cu and Ag. The nanoparticle composition and the oxidation states could be determined due to an experimental arrangement in which photoelectron spectroscopy is applied to free nanoparticles in a beam in vacuum, what allows avoiding any contact of the particles to a substrate or atmosphere. The combination of the fabrication and characterization methods has proven to be a powerful approach when fine composition tuning and control are desirable.

National Category
Inorganic Chemistry
Identifiers
urn:nbn:se:uu:diva-372754 (URN)10.1039/c8dt04118k (DOI)000451657900034 ()30426128 (PubMedID)
Funder
Swedish Research CouncilKnut and Alice Wallenberg FoundationSwedish Foundation for Strategic Research
Available from: 2019-01-15 Created: 2019-01-15 Last updated: 2019-01-15Bibliographically approved
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
Show others...
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
Richter, C., Hollas, D., Saak, C.-M., Foerstel, M., Miteva, T., Mucke, M., . . . Hergenhahn, U. (2018). Competition between proton transfer and intermolecular Coulombic decay in water. Nature Communications, 9, Article ID 4988.
Open this publication in new window or tab >>Competition between proton transfer and intermolecular Coulombic decay in water
Show others...
2018 (English)In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 9, article id 4988Article in journal (Refereed) Published
Abstract [en]

Intermolecular Coulombic decay (ICD) is a ubiquitous relaxation channel of electronically excited states in weakly bound systems, ranging from dimers to liquids. As it is driven by electron correlation, it was assumed that it will dominate over more established energy loss mechanisms, for example fluorescence. Here, we use electron-electron coincidence spectroscopy to determine the efficiency of the ICD process after 2a(1) ionization in water clusters. We show that this efficiency is surprisingly low for small water clusters and that it gradually increases to 40-50% for clusters with hundreds of water units. Ab initio molecular dynamics simulations reveal that proton transfer between neighboring water molecules proceeds on the same timescale as ICD and leads to a configuration in which the ICD channel is closed. This conclusion is further supported by experimental results from deuterated water. Combining experiment and theory, we infer an intrinsic ICD lifetime of 12-52 fs for small water clusters.

Place, publisher, year, edition, pages
NATURE PUBLISHING GROUP, 2018
National Category
Physical Chemistry Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-372335 (URN)10.1038/s41467-018-07501-6 (DOI)000451176100013 ()30478319 (PubMedID)
Funder
EU, Horizon 2020, 705515The Swedish Foundation for International Cooperation in Research and Higher Education (STINT)
Available from: 2019-01-07 Created: 2019-01-07 Last updated: 2019-01-07Bibliographically approved
Werner, J., Persson, I., Björneholm, O., Kawecki, D., Saak, C.-M., Walz, M.-M., . . . Prisle, N. L. (2018). Shifted Equilibria of Organic Acids and Bases in the Aqueous Surface Region. Physical Chemistry, Chemical Physics - PCCP, 20(36), 23281-23293
Open this publication in new window or tab >>Shifted Equilibria of Organic Acids and Bases in the Aqueous Surface Region
Show others...
2018 (English)In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 20, no 36, p. 23281-23293Article in journal (Refereed) Published
Abstract [en]

Acid-base equilibria of carboxylic acids and alkyl amines in the aqueous surface region were studied using surface-sensitive X-ray photoelectron spectroscopy and molecular dynamics simulations. Solutions of these organic compounds were examined as a function of pH, concentration and chain length to investigate the distribution of acid and base form in the surface region as compared to the aqueous bulk. Results from these experiments show that the neutral forms of the studied acid-base pairs are strongly enriched in the aqueous surface region. Moreover, we show that for species with at least four carbon atoms in their alkyl-chain, their charged forms are also found to be abundant in the surface region. Using a combination of XPS and MD results, a model is proposed that effectively describes the surface composition. Resulting absolute surface concentration estimations show clearly that the total organic mole fractions in the surface region change drastically as a function of solution pH. The origin of the observed surface phenomena, hydronium/hydroxide concentrations in the aqueous surface region and why standard chemical equations, used to describe equilibria in dilute bulk solution are not valid in the aqueous surface region, are discussed in detail. The reported results are of considerable importance especially for the detailed understanding of properties of small aqueous droplets that can be found in the atmosphere.

National Category
Physical Chemistry
Identifiers
urn:nbn:se:uu:diva-341965 (URN)10.1039/c8cp01898g (DOI)000447370600011 ()30191936 (PubMedID)
Funder
Swedish Research Council, 2013-3940EU, Horizon 2020, 717022
Available from: 2018-02-16 Created: 2018-02-16 Last updated: 2019-01-22Bibliographically approved
Ekholm, V., Caleman, C., Bjärnhall Prytz, N., Walz, M.-M., Werner, J., Öhrwall, G., . . . Björneholm, O. (2018). Strong Enrichment of Atmospherically Relevant Organic Ions at the Aqueous Interface: The Role of Ion Pairing and Cooperative Effects. Physical Chemistry, Chemical Physics - PCCP, 20(42), 27185-27191
Open this publication in new window or tab >>Strong Enrichment of Atmospherically Relevant Organic Ions at the Aqueous Interface: The Role of Ion Pairing and Cooperative Effects
Show others...
2018 (English)In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 20, no 42, p. 27185-27191Article in journal (Refereed) Published
Abstract [en]

Surface affinity, orientation and ion pairing are investigated in mixed and single solute systems of aqueous sodium hexanoate and hexylammonium chloride. The surface sensitive X-ray photoelectron spectroscopy technique has been used to acquire the experimental results, while the computational data have been calculated using molecular dynamics simulations. By comparing the single solute solutions with the mixed one, we observe a non-linear surface enrichment and reorientation of the organic ions with their alkyl chains pointing out of the aqueous surface. We ascribe this effect to ion paring between the charged functional groups on the respective organic ion and hydrophobic expulsion of the alkyl chains from the surface in combination with van der Waals interactions between the alkyl chains. These cooperative effects lead to a substantial surface enrichment of organic ions, with consequences for aerosol surface properties.

National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:uu:diva-357368 (URN)10.1039/c8cp04525a (DOI)000451351500042 ()30339167 (PubMedID)
Funder
Swedish Research Council, 2013-3940Swedish Research Council, 2014-04518Carl Tryggers foundation
Available from: 2018-08-15 Created: 2018-08-15 Last updated: 2019-01-07Bibliographically 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
Show others...
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
Show others...
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
Show others...
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
Show others...
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
Organisations

Search in DiVA

Show all publications