| 1. |
- Eriksson, Peter, et al.
(författare)
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Cerium oxide nanoparticles with antioxidant capabilities and gadolinium integration for MRI contrast enhancement
- 2018
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Ingår i: Scientific Reports. - : Nature Publishing Group. - 2045-2322. ; 8
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Tidskriftsartikel (refereegranskat)abstract
- The chelating gadolinium-complex is routinely used as magnetic resonance imaging (MRI) -contrast enhancer. However, several safety issues have recently been reported by FDA and PRAC. There is an urgent need for the next generation of safer MRI-contrast enhancers, with improved local contrast and targeting capabilities. Cerium oxide nanoparticles (CeNPs) are designed with fractions of up to 50% gadolinium to utilize the superior MRI-contrast properties of gadolinium. CeNPs are well-tolerated in vivo and have redox properties making them suitable for biomedical applications, for example scavenging purposes on the tissue-and cellular level and during tumor treatment to reduce in vivo inflammatory processes. Our near edge X-ray absorption fine structure (NEXAFS) studies show that implementation of gadolinium changes the initial co-existence of oxidation states Ce3+ and Ce4+ of cerium, thereby affecting the scavenging properties of the nanoparticles. Based on ab initio electronic structure calculations, we describe the most prominent spectral features for the respective oxidation states. The as-prepared gadolinium-implemented CeNPs are 3-5 nm in size, have r(1)-relaxivities between 7-13 mM(-1) s(-1) and show clear antioxidative properties, all of which means they are promising theranostic agents for use in future biomedical applications.
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| 2. |
- Pilch, Iris, et al.
(författare)
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Nanoparticle growth by collection of ions : orbital motion limited theory and collision-enhanced collection
- 2016
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Ingår i: Journal of Physics D. - : Institute of Physics Publishing (IOPP). - 0022-3727 .- 1361-6463. ; 49:39
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Tidskriftsartikel (refereegranskat)abstract
- The growth of nanoparticles in plasma is modeled for situations where the growth is mainly due to the collection of ions of the growth material. The model is based on the classical orbit motion limited (OML) theory with the addition of a collision-enhanced collection (CEC) of ions. The limits for this type of model are assessed with respect to three processes that are not included: evaporation of the growth material, electron field emission, and thermionic emission of electrons. It is found that both evaporation and thermionic emission can be disregarded below a temperature that depends on the nanoparticle material and on the plasma parameters; for copper in our high-density plasma this limit is about 1200 K. Electron field emission can be disregarded above a critical nanoparticle radius, in our case around 1.4 nm. The model is benchmarked, with good agreement, to the growth of copper nanoparticles from a radius of 5 nm-20 nm in a pulsed power hollow cathode discharge. Ion collection by collisions contributes with approximately 10% of the total current to particle growth, in spite of the fact that the collision mean free path is four orders of magnitude longer than the nanoparticle radius.
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| 3. |
- Tal, Alexey A., et al.
(författare)
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Correlation between Ethylene Adsorption Energies and Core-Level Shifts for Pd Nanoclusters
- 2019
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Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 123:4, s. 2544-2548
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Tidskriftsartikel (refereegranskat)abstract
- Density functional theory calculations have been used to investigate the adsorption of ethylene on Pd nanoclusters together with shifts in core-level binding energies of Pd atoms bonded to the adsorbate. The adsorption energy is found to correlate with the core-level shifts (CLS), which is consistent with the notion that the core-level binding energy is a measure of differences in cohesion. The correlation between adsorption energies and core-level shifts is found to be stronger than the correlation between adsorption energies and generalized coordination numbers, indicating that descriptors preferably should account for electronic effects explicitly. The advantages of CLS as a descriptor for the screening of adsorption properties is discussed.
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| 4. |
- Tal, Alexey A., et al.
(författare)
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Molecular dynamics simulation of the growth of Cu nanoclusters from Cu ions in a plasma
- 2014
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 90:16, s. 165421-
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Tidskriftsartikel (refereegranskat)abstract
- A recently developed method of nanoclusters growth in a pulsed plasma is studied by means of molecular dynamics. A model that allows one to consider high-energy charged particles in classical molecular dynamics is suggested, and applied for studies of single impact events in nanoclusters growth. In particular, we provide a comparative analysis of the well-studied inert gas aggregation method and the growth from ions in a plasma. The importance to consider of the angular distribution of incoming ions in the simulations of the nanocluster growth is underlined. A detailed study of the energy transfer from the incoming ions to a nanocluster, as well as the diffusion of incoming ions on the cluster surface, is carried out. Our results are important for understanding and control of the nanocluster growth process.
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| 5. |
- Tal, Alexey, 1990-
(författare)
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Electronic and structural properties of nanoclusters
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Nanoclusters have gained a huge interest due to their unique properties. They represent an intermediate state between an atom and a solid, which manifests itself in their atomic configurations and electronic structure. The applications of nanoclusters require detailed understanding of their properties and strongly depend on the ability to control their synthesis process. Significant effort has been invested in modelling of nanoclusters properties. However, the complexity of these systems is such that many aspects of their growth process and properties are yet to be understood.My thesis focuses on describing structural and electronic properties of nanoclusters. In particular, the model for nanoparticles growth in plasma condition is developed and applied, allowing to describe the influence of the plasma conditions on the evaporation, growth and morphological transformation processes. The mechanism driving the morphology transition from icosahedral to decahedral phase is suggested based on force-fields models. Spectroscopic methods allow for precise characterization of nanoclusters and constitute an important tool for analysis of their electronic structure of valence band as well as core-states. The special attention in the thesis is paid to the core-states of nanoclusters and influences that affect them. In particular, the effects of local coordination, interatomic distances and confinement effects are investigated in metal nanoclusters by density functional theory methods. These effects and their contribution to spectroscopic features of nanoclusters in X-ray photoemission are modelled. The relation between the reactivity of nanoclusters and their spectroscopic features calculated in different approximations are revealed and explained. Ceria is a very important system for many applications due to the ability of cerium atoms to change their oxidation state depending on the environment. The shift of the oxidation state and its effects on the core-states is examined with X-ray absorption measurements and modelling allowing to build a rigid foundation for interpretation of the measured spectra and characterization of electronic structure of ceria nanoparticles.
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| 6. |
- Tal, Alexey, et al.
(författare)
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Morphology transition mechanism from icosahedral to decahedral phase during growth of Cu nanoclusters
- 2015
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 92:2, s. 020102-
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Tidskriftsartikel (refereegranskat)abstract
- The morphology transition from the thermodynamically favorable to the unfavorable phase during growth of freestanding copper nanoclusters is studied by molecular dynamics simulations. We give a detailed description of the kinetics and thermodynamics of the process. A universal mechanism of a solid-solid transition, from icosahedral to decahedral morphology in the nanoclusters, is proposed. We show that a formation of distorted NC during the growth process with islands of incoming atoms localized in certain parts of the grown particle may shift the energy balance between Ih and Dh phases in favor of the latter leading to the morphology transition deep within the thermodynamic stability field of the former. The role of diffusion in the morphology transition is revealed. In particular, it is shown that fast diffusion should suppress the morphology transition and favor homogeneous growth of the nanoclusters.
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| 7. |
- Tal, Alexey, et al.
(författare)
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Origin of the core-level binding energy shifts in Au nanoclusters
- 2017
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Ingår i: Physical Review B. - : AMER PHYSICAL SOC. - 2469-9950 .- 2469-9969. ; 95:24
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the shifts of the core-level binding energies in small gold nanoclusters by using ab initio density-functional-theory calculations. The shift of the 4f states is calculated for magic-number nanoclusters in a wide range of sizes and morphologies. We find a nonmonotonous behavior of the core-level shift in nanoclusters depending on the size. We demonstrate that there are three main contributions to the Au 4f shifts, which depend sensitively on the interatomic distances, coordination, and quantum confinement. They are identified and explained by the change of the on-site electrostatic potential.
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| 8. |
- Tal, Alexey, et al.
(författare)
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Pressure-induced crossing of the core levels in 5d metals
- 2016
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Ingår i: Physical Review B. - : AMER PHYSICAL SOC. - 2469-9950 .- 2469-9969. ; 93:20, s. 205150-
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Tidskriftsartikel (refereegranskat)abstract
- A pressure-induced interaction between core electrons, the core-level crossing (CLC) transition, has been observed in hcp Os at P approximate to 400 GPa [L. Dubrovinsky et al., Nature (London) 525, 226 (2015)]. By carrying out a systematic theoretical study for all metals of the 5d series (Hf, Ta, W, Re, Os, Ir, Pt, Au) we have found that the CLC transition is a general effect for this series of metals. While in Pt it occurs at approximate to 1500 GPa, at a pressure substantially higher than in Os, in Ir it occurs already at 80 GPa. Moreover, we predict that in Re the CLC transition may take place already at ambient pressure. We explain the effect of the CLC and analyze the shift of the transition pressure across the series within the Thomas-Fermi model. In particular, we show that the effect has many common features with the atomic collapse in rare-earth elements.
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| 9. |
- Xia, Chao, 1986-, et al.
(författare)
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Effects of rhenium on graphene grown on SiC(0001)
- 2018
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Ingår i: Journal of Electron Spectroscopy and Related Phenomena. - : Elsevier. - 0368-2048 .- 1873-2526. ; 222, s. 117-121
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Tidskriftsartikel (refereegranskat)abstract
- We study the effects of Rhenium (Re) deposited on epitaxial monolayer graphene grown on SiC(0001) and after subsequent annealing at different temperatures, by performing high resolution photoelectron spectroscopy (PES) and angle resolved photoelectron spectroscopy (ARPES). The graphene-Re system is found to be thermally stable. While no intercalation or chemical reaction of the Re is detected after deposition and subsequent annealing up to 1200 degrees C, a gradual decrease in the binding energy of the Re 4f doublet is observed. We propose that a larger mobility of the Re atoms with increasing annealing temperature and hopping of Re atoms between different defective sites on the graphene sample could induce this decrease of Re 4f binding energy. This is corroborated by first principles density functional theory (DFT) calculations of the Re core-level binding energy shift. No change in the doping or splitting of the initial monolayer graphene electronic band structure is observed after Re deposition and annealing up to 1200 degrees C, only a broadening of the bands. (C) 2017 Elsevier B.V. All rights reserved.
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