| 1. |
- Hautala, Lauri, et al.
(författare)
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Probing RbBr solvation in freestanding sub-2 nm water clusters
- 2017
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Ingår i: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 19:36, s. 25158-25167
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Tidskriftsartikel (refereegranskat)abstract
- Concentration dependent solvation of RbBr in freestanding sub-2 nm water clusters was studied using core level photoelectron spectroscopy with synchrotron radiation. Spectral features recorded from dilute to saturated clusters indicate that either solvent shared or contact ion pairs are present in increasing amount when the concentration exceeds 2 mol kg-1. For comparison, spectra from anhydrous RbBr clusters are also presented.
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| 2. |
- Hautala, Lauri, et al.
(författare)
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Surface site coordination dependent responses resolved in free clusters: applications for neutral sub-nanometer cluster studies
- 2015
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Ingår i: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9084 .- 1463-9076. ; 17:10, s. 7012-7022
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Tidskriftsartikel (refereegranskat)abstract
- In this paper we demonstrate how surface site specific experimental information can be obtained from free low nanometer scale clusters using photoelectron spectroscopy utilising synchrotron radiation. In addition, we show how it can be used to gain insight into the geometry and surface structure of the clusters. The present experiments were conducted on alkali metal halides, RbCl and CsCl, which were chosen as advantageous test cases due to their simple electronic and geometric structures. These heavy alkali metal salts provide additional clarity since the surface and bulk responses can be separated, which is not the case for clusters of lighter alkali metal salts. Computational chemical shift calculations and simple alkali halide cluster size modelling were used to interpret the experimental results.
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| 3. |
- Lin, Jack J., et al.
(författare)
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Pre-deliquescent water uptake in deposited nanoparticles observed with in situ ambient pressure X-ray photoelectron spectroscopy
- 2021
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Ingår i: Atmospheric Chemistry and Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 21:6, s. 4709-4727
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Tidskriftsartikel (refereegranskat)abstract
- We study the adsorption of water onto deposited inorganic sodium chloride and organic malonic acid and sucrose nanoparticles at ambient water pressures corresponding to relative humidities (RH) from 0 % to 16 %. To obtain information about water adsorption at conditions which are not accessible with typical aerosol instrumentation, we use surface-sensitive ambient pressure X-ray photoelectron spectroscopy (APXPS), which has a detection sensitivity starting at parts per thousand. Our results show that water is already adsorbed on sodium chloride particles at RH well below deliquescence and that the chemical environment on the particle surface is changing with increasing humidity. While the sucrose particles exhibit only very modest changes on the surface at these relative humidities, the chemical composition and environment of malonic acid particle surfaces is clearly affected. Our observations indicate that water uptake by inorganic and organic aerosol particles could already have an impact on atmospheric chemistry at low relative humidities. We also establish the APXPS technique as a viable tool for studying chemical changes on the surfaces of atmospherically relevant aerosol particles which are not detected with typical online mass-and volume-based methods.
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| 4. |
- Mikkelä, Mikko-Heikki, et al.
(författare)
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Bismuth-oxide nanoparticles: study in a beam and as deposited
- 2024
-
Ingår i: Physical chemistry chemical physics : PCCP. - 1463-9084. ; 26:13, s. 10369-10381
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Tidskriftsartikel (refereegranskat)abstract
- Bi2O3 is a promising material for solid-oxide fuel cells (SOFC) due to the high ionic conductivity of some phases. The largest value is reached for its δ-phase, but it is normally stable at temperatures too high for SOFC operation, while nanostructured oxide is believed to have more suitable stabilization temperature. However, to manufacture such a material with a controlled chemical composition is a challenging task. In this work, we investigated the fabrication of nanostructured Bi2O3 films formed by deposition of free Bi-oxide nanoparticles created in situ. The particle-production method was based on reactive sputtering and vapour aggregation. Depending on the fabrication conditions, the nanoparticles contained either a combination of Bi–metal and Bi-oxide, or only Bi-oxide. Prior to deposition, the free particles were probed in the beam – by synchrotron-based photoelectron spectroscopy (PES), which allowed assessing their composition “on the-fly”. The nanoparticle films obtained after deposition were studied by PES, scanning electron microscopy, transmission electron microscopy, and electron diffraction. The films' chemical composition, grain dimensions, and crystal structure were probed. Our analysis suggests that our method produced Bi-oxide films in more than one polymorph of Bi2O3.
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| 5. |
- Mikkelä, Mikko Heikki, et al.
(författare)
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Free silver nanoparticles doped by potassium : Work-function change in experiment and theory
- 2021
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Ingår i: Journal of Chemical Physics. - : American Institute of Physics (AIP). - 0021-9606 .- 1089-7690. ; 154:23
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Tidskriftsartikel (refereegranskat)abstract
- The composition-dependent change in the work-function (WF) of binary silver-potassium nanoparticles has been studied experimentally by synchrotron-based x-ray photoelectron spectroscopy (PES) and theoretically using a microscopic jellium model of metals. The Ag-K particles with different K fractions were produced by letting a beam of preformed Ag particles pass through a volume with K vapor. The PES on a beam of individual non-supported Ag-K nanoparticles created in this way allowed a direct absolute measurement of their WF, avoiding several usual shortcomings of the method. Experimentally, the WF has been found to be very sensitive to K concentration: Already at low exposure, it decreased down to approximate to 2 eV-below the value of pure K. In the jellium modeling, considered for Ag-K nanoparticles, two principally different adsorption patterns were tested: without and with K diffusion. The experimental and calculation results together suggest that only efficient surface alloying of two metals, whose immiscibility was long-term textbook knowledge, could lead to the observed WF values.
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| 6. |
- Näslund, Lars-Åke, 1968-, et al.
(författare)
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Chemical bonding of termination species in 2D carbides investigated through valence band UPS/XPS of Ti3C2T xMXene
- 2021
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Ingår i: 2D Materials. - : IOP Publishing. - 2053-1583. ; 8:4
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Tidskriftsartikel (refereegranskat)abstract
- MXenes are technologically interesting 2D materials that show potential in numerous applications. The properties of the MXenes depend at large extent on the selection of elements that build the 2D MX-layer. Another key parameter for tuning the attractive material properties is the species that terminate the surfaces of the MX-layers. Although being an important parameter, experimental studies on the bonding between the MX-layers and the termination species are few and thus an interesting subject of investigation. Here we show that the termination species fluorine (F) bonds to the Ti3C2-surface mainly through Ti 3p - F 2p hybridization and that oxygen (O) bonds through Ti 3p - O 2p hybridization with a significant contribution of Ti 3d and Ti 4p. The study further shows that the Ti3C2-surface is not only terminated by F and O on the threefold hollow face-centered-cubic site. A significant amount of O sits on a bridge site bonded to two Ti surface atoms on the Ti3C2-surface. In addition, the results provide no support for hydroxide (OH) termination on the Ti3C2-surface. On the contrary, the comparison of the valence band intensity distribution obtained through ultraviolet- and x-ray photoelectron spectroscopy with computed spectra by density of states, weighed by matrix elements and sensitivity factors, reveals that OH cannot be considered as an inherent termination species in Ti3C2T x . The results from this study have implications for correct modeling of the structure of MXenes and the corresponding materials properties. Especially in applications where surface composition and charge are important, such as supercapacitors, Li-ion batteries, electrocatalysis, and fuel- and solar cells, where intercalation processes are essential.
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| 7. |
- Partanen, Leena, et al.
(författare)
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Solvation at nanoscale : alkali halides in water clusters
- 2013
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Ingår i: Journal of Chemical Physics. - : American Institute of Physics (AIP). - 0021-9606 .- 1089-7690. ; 138:4, s. 044301-
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Tidskriftsartikel (refereegranskat)abstract
- The solvation of alkali-halides in water clusters at nanoscale is studied by photoelectron spectroscopy using synchrotron radiation. The Na 2p, K 3p, Cl 2p, Br 3d, and I 4d core level binding energies have been measured for salt-containing water clusters. The results have been compared to those of alkali halide clusters and the dilute aqueous salt solutions. It is found that the alkali halides dissolve in small water clusters as ions.
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| 8. |
- Tchaplyguine, Maxim, et al.
(författare)
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Gold Oxide Nanoparticles with Variable Gold Oxidation State
- 2015
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Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 119:16, s. 8937-8943
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 9. |
- Tchaplyguine, Maxim, et al.
(författare)
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Valence-band narrowing and metallic-screening disappearance in the metal-to-insulator transition in small Pb clusters—as seen by photoelectron spectroscopy
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- A metal-to-insulator transition in small Pb clusters within the size range from a few tens of atoms up to ~100 atoms is investigated using synchrotron-based photoelectron spectroscopy. The electronic structure is seen to differ increasingly from that of the solid when the cluster size decreases. With the cluster size decrease the valence band narrows gradually -down to 25% of that of the solid-state at the smallest size of few tens of atoms. Simultaneously the Fermi-edge energy increases. The Pb 5d core level binding energy also increases and the spectral features broaden and change the shape. The changes observed for the valence and for the 5d energies and shapes are consistent with the picture of the loss of metallicity in Pb below the critical size of 20-30 atoms/cluster.
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| 10. |
- Wright, Charles, et al.
(författare)
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Tin Oxides : Insights into Chemical States from a Nanoparticle Study
- 2017
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 121:35, s. 19414-19419
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 11. |
- Zhang, Chaofan, et al.
(författare)
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Alloying and oxidation of in situ produced core-shell Al@Yb nanoalloy particles-An "on-the-fly" study.
- 2014
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 141:8
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Tidskriftsartikel (refereegranskat)abstract
- Core-shell-structured nanoalloy particles with an Al-dominated interior covered by few Yb monolayers have been fabricated using a vapor-aggregation method involving magnetron sputtering. The radially segregated structure of the Yb-Al nanoparticles has been disclosed by "on-the-fly" photoelectron spectroscopy monitoring of the nanoparticle beam in Yb 4f and Al 2p electron binding energy regions. Both, the binding energy values and the electron microscopy images taken on the deposited nanoparticles, allow estimating their dimensions to be in the 5-10 nm range. The photoelectron spectroscopy results suggest that in these nanoparticles no trivalent Yb - the typical case for the macroscopic Yb-Al alloy - is present. The oxidation of preformed Yb-Al nanoparticles was successfully attempted, leading to the appearance of divalent Yb surface oxide - in contrast to the bulk macroscopic Yb which is trivalent in the oxide. Our results suggest that at intermediate oxygen exposures "sandwich-like" nanoparticles of YbO/Yb/Al were synthesized. At higher O2 exposures, the oxygen seems to penetrate all the way to the Yb-Al interface. The results of the present study have to be considered when photonic applications of Yb-doped garnet nanoparticles are planned.
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| 12. |
- Zhang, Chaofan, et al.
(författare)
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Ionic bonding in free nanoscale NaCl clusters as seen by photoelectron spectroscopy
- 2011
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 134:12, s. 124507-
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Tidskriftsartikel (refereegranskat)abstract
- The free neutral nanoscale NaCl clusters have been produced in a beam and studied with x-ray photoelectron spectroscopy. High resolution spectra simultaneously containing cluster and molecular-monomer, featuring in both the valence and core-level Na 2p and Cl 2p regions, have been obtained. Cluster-level energy shifts of around 3 eV toward lower binding energy for Na 2p and approximate to 1 eV toward higher binding energy for Cl 2p relative to the monomer levels have been unambiguously established. To rationalize the core-level energy shifts of the nanoscale NaCl clusters, the ionic model taking into account all charge-charge and polarization interactions has been developed and implemented. A satisfactory agreement between the experimental and model results has been obtained. The model calculations have also shed additional light on the size-and site-specific cluster responses.
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