| 1. |
- Dreiser, Jan, et al.
(författare)
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The Metallofullerene Field-Induced Single-Ion Magnet HoSc2N@C-80
- 2014
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Ingår i: Chemistry - A European Journal. - : Wiley. - 0947-6539 .- 1521-3765. ; 20:42, s. 13536-13540
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Tidskriftsartikel (refereegranskat)abstract
- The low-temperature magnetic properties of the endohedral metallofullerene HoSc2N@C-80 have been studied by superconducting quantum interference device (SQUID) magnetometry. Alternating current (ac) susceptibility measurements reveal that this molecule exhibits slow relaxation of magnetization in a small applied field with timescales in the order of milliseconds. The equilibrium magnetic properties of HoSc2N@C-80 indicate strong magnetic anisotropy. The large differences in magnetization relaxation times between the present compound and the previously investigated DySc2N@C-80 are discussed.
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| 2. |
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| 3. |
- Kostanyan, Aram, et al.
(författare)
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Gadolinium as an accelerator for reaching thermal equilibrium and its influence on the ground state of Dy2GdN@ C80 single-molecule magnets
- 2021
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Ingår i: Physical Review B. - 2469-9950. ; 103:1
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Tidskriftsartikel (refereegranskat)abstract
- Endohedral fullerenes are perfect nanolaboratories for the study of magnetism. The substitution of a diamagnetic scandium atom in Dy2ScN@C80 with gadolinium decreases the stability of a given magnetization and demonstrates Gd to act as a single atom catalyst that accelerates the reaching of thermal equilibrium. X-ray magnetic circular dichroism at the M4,5 edges of Gd and Dy shows that Gd affects the ground state. The Gd magnetic moment follows the sum of the external and the dipolar magnetic field of the two Dy ions and compared to Dy2ScN@C80 a lower exchange barrier is found between the ferromagnetic and the antiferromagnetic Dy configuration. The Arrhenius equilibration barrier as obtained from superconducting quantum interference device magnetometry is more than one order of magnitude larger, though a much smaller prefactor imposes the faster equilibration in Dy2GdN@C80. This sheds light on the importance of angular momentum balance and symmetry in magnetic relaxation.
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| 4. |
- Kostanyan, Aram, et al.
(författare)
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Sub-Kelvin hysteresis of the dilanthanide single-molecule magnet Tb2ScN@ C80
- 2020
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Ingår i: Physical Review B. - 2469-9950. ; 101:13
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Tidskriftsartikel (refereegranskat)abstract
- Magnetic hysteresis is a direct manifestation of nonequilibrium physics that has to be understood if a system is to be used for information storage and processing. The dilanthanide endofullerene Tb2ScN@C80 is shown to be a single-molecule magnet with a remanence time on the order of 100 s at 400 mK. Three different temperature-dependent relaxation barriers are discerned. The lowest 1 K barrier is assigned to intermolecular dipole-dipole interaction, the 10 K barrier to intramolecular exchange and dipolar coupling, and the 50 K barrier to molecular vibrations as was observed for Dy2ScN@C80. The 4 orders of magnitude difference in the prefactor between the Tb and the Dy compound in the decay process across the 10 K barrier is assigned to the lack of Kramers protection in Tb3+. The sub-Kelvin hysteresis follows changes in the magnetization at level crossings of the four possible Tb2 ground-state configurations. Comparison to a hysteresis model, with magnetic relaxation at level crossings only, reveals cooperative action between nearby molecules.
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| 5. |
- Koutsouflakis, Emmanouil, et al.
(författare)
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Metamagnetic transition and a loss of magnetic hysteresis caused by electron trapping in monolayers of single-molecule magnet Tb2@C79N
- 2022
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Ingår i: Nanoscale. - : Royal Society of Chemistry (RSC). - 2040-3364 .- 2040-3372. ; 14:27, s. 9877-9892
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Tidskriftsartikel (refereegranskat)abstract
- Realization of stable spin states in surface-supported magnetic molecules is crucial for their applications in molecular spintronics, memory storage or quantum information processing. In this work, we studied the surface magnetism of dimetallo-azafullerene Tb2@C79N, showing a broad magnetic hysteresis in a bulk form. Surprisingly, monolayers of Tb2@C79N exhibited a completely different behavior, with the prevalence of a ground state with antiferromagnetic coupling at low magnetic field and a metamagnetic transition in the magnetic field of 2.5-4 T. Monolayers of Tb2@C79N were deposited onto Cu(111) and Au(111) by evaporation in ultra-high vacuum conditions, and their topography and electronic structure were characterized by scanning tunneling microscopy and spectroscopy (STM/STS). X-ray photoelectron spectroscopy (XPS), in combination with DFT studies, revealed that the nitrogen atom of the azafullerene cage tends to avoid metallic surfaces. Magnetic properties of the (sub)monolayers were then studied by X-ray magnetic circular dichroism (XMCD) at the Tb-M4,5 absorption edge. While in bulk powder samples Tb2@C79N behaves as a single-molecule magnet with ferromagnetically coupled magnetic moments and blocking of magnetization at 28 K, its monolayers exhibited a different ground state with antiferromagnetic coupling of Tb magnetic moments. To understand if this unexpected behavior is caused by a strong hybridization of fullerenes with metallic substrates, XMCD measurements were also performed for Tb2@C79N adsorbed on h-BN|Rh(111) and MgO|Ag(100). The co-existence of two forms of Tb2@C79N was found on these substrates as well, but magnetization curves showed narrow magnetic hysteresis detectable up to 25 K. The non-magnetic state of Tb2@C79N in monolayers is assigned to anionic Tb2@C79N− species with doubly-occupied Tb-Tb bonding orbital and antiferromagnetic coupling of the Tb moments. A charge transfer from the substrate or trapping of secondary electrons are discussed as a plausible origin of these species.
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| 6. |
- Krylov, Denis S., et al.
(författare)
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Substrate-Independent Magnetic Bistability in Monolayers of the Single-Molecule Magnet Dy2ScN@C80 on Metals and Insulators
- 2020
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Ingår i: Angewandte Chemie - International Edition. - : Wiley. - 1433-7851 .- 1521-3773. ; 59:14, s. 5756-5764
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Tidskriftsartikel (refereegranskat)abstract
- Magnetic hysteresis is demonstrated for monolayers of the single-molecule magnet (SMM) Dy2ScN@C80 deposited on Au(111), Ag(100), and MgO|Ag(100) surfaces by vacuum sublimation. The topography and electronic structure of Dy2ScN@C80 adsorbed on Au(111) were studied by STM. X-ray magnetic CD studies show that the Dy2ScN@C80 monolayers exhibit similarly broad magnetic hysteresis independent on the substrate used, but the orientation of the Dy2ScN cluster depends strongly on the surface. DFT calculations show that the extent of the electronic interaction of the fullerene molecules with the surface is increasing dramatically from MgO to Au(111) and Ag(100). However, the charge redistribution at the fullerene-surface interface is fully absorbed by the carbon cage, leaving the state of the endohedral cluster intact. This Faraday cage effect of the fullerene preserves the magnetic bistability of fullerene-SMMs on conducting substrates and facilitates their application in molecular spintronics.
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| 7. |
- Lee, Wei Chuang, et al.
(författare)
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Monolayer calibration of endofullerenes with x-ray absorption from implanted keV ion doses
- 2024
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Ingår i: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films. - : American Institute of Physics (AIP). - 0734-2101 .- 1520-8559. ; 42:2
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Tidskriftsartikel (refereegranskat)abstract
- X-ray absorption spectroscopy (XAS) has the highest sensitivity for chemical element detection on surfaces. With this approach, small amounts of lanthanide-containing endofullerene molecules (Ho3N@C80) have been measured by total electron yield at a low flux bending magnet beamline. The monolayer coverage is calibrated by extrapolating the signals of constant doses (3 x 1014 cm-2) of Ho ions implanted into SiO2 with energies between 2 and 115 keV. At room temperature, the Ho XAS spectra of the molecules and implanted ions indicate trivalent but not identical Ho ground states. Still, this approach demonstrates a way for calibration of small coverages of molecules containing open core-shell elements.
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| 8. |
- Martinez, Valentina, et al.
(författare)
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Tunable Fulleretic Sodalite MOFs : Highly Efficient and Controllable Entrapment of C-60 Fullerene via Mechanochemistry
- 2020
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Ingår i: Chemistry of Materials. - : American Chemical Society (ACS). - 0897-4756 .- 1520-5002. ; 32:24, s. 10628-10640
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Tidskriftsartikel (refereegranskat)abstract
- Encapsulation and confinement of fullerene guests in metal-organic frameworks (MOFs) lead to a novel class of crystalline fulleretic materials with unique physicochemical properties and a broad field of potential applications. The control over the amount of target guests confined in the MOF structure remains a significant challenge, which is particularly pronounced in the confinement of hardly accessible fullerene derivatives. The main strategies used in constructing fulleretic composites are limited by the solubility of components used and solvent versus guest competition for inhabitation of the framework voids. As mechanochemical procedures often overcome these issues, we developed here solvent-free processing by ball milling to gain control over the encapsulation of bulky and rigid C-60-fullerene into a sodalite MOF with large cages and narrow cage-apertures. A rapid, green, efficient, and stoichiometry-controlled mechanochemical processing afforded four model C-60@zeolitic-imidazolate framework 8 (ZIF-8) crystalline materials containing target 15, 30, 60, and 100 mol % of fullerene entrapped in the accessible cages of the model sodalite zeolitic-imidazolate framework 8 (ZIF-8), in stark contrast to the solution-based strategies that resulted in almost no loading. Varying the fullerene content affects the framework's vibrational properties, color and luminescence of the composites, and the electron-dose radiation stability. The computational and spectroscopic studies show that the fullerene is accommodated in the cage's center and that the cage-to-cage transport is a hardly feasible and energetically unfavored process. However, the fast release of C-60 molecules from ZIF-8 can be effectively controlled by the pH. The entrapment of fullerene molecules in ZIF-8 resulted in their effective isolation even in higher loadings, paving the way to other tunable porous fulleretics containing single-molecule magnets or nanoprobes available on low scales.
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| 9. |
- Mohl, Melinda, et al.
(författare)
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Titania nanofibers in gypsum composites : an antibacterial and cytotoxicology study
- 2014
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Ingår i: Journal of Material Chemistry B. - : Royal Society of Chemistry. - 2050-750X .- 2050-7518. ; 2:10, s. 1307-1316
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Tidskriftsartikel (refereegranskat)abstract
- Further developments of antibacterial coatings based on photocatalytic nanomaterials could be a promising route towards potential environmentally friendly applications in households, public buildings and health care facilities. Hereby we describe a simple chemical approach to synthesize photocatalytic nanomaterial-embedded coatings using gypsum as a binder. Various types of TiO2 nanofiber-based photocatalytic materials (nitrogen-doped and/or palladium nanoparticle decorated) and their composites with gypsum were characterized by means of scanning (SEM) and transmission (TEM) electron microscopy as well as electron and X-ray diffraction (XRD) and energy-dispersive X-ray spectroscopy (EDX) techniques. These gypsum-based composites can be directly applied as commercially available paints on indoor walls. Herein we report that surfaces coated with photocatalytic composites exhibit excellent antimicrobial properties by killing both methicillin-sensitive Staphylococcus aureus (MSSA) and methicillin-resistant Staphylococcus aureus (MRSA) under blue light. In the case of MSSA cells, the palladium nanoparticle-decorated and nitrogen-doped TiO2 composites demonstrated the highest antimicrobial activity. For the MRSA strain even pure gypsum samples were proven to be efficient in eradicating Gram-positive human pathogens. The cytotoxicity of freestanding TiO2 nanofibers was revealed by analyzing the viability of HeLa cells using MTT and fluorescent cell assays.
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| 10. |
- Trunina, Natalia A., et al.
(författare)
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Monitoring of TiO2 and ZnO Nanoparticle Penetration Into Fnamel and Dentine of Human Tooth IN VITRO and Assessment of Their Photocatalytic Ability
- 2014
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Ingår i: IEEE Journal of Selected Topics in Quantum Electronics. - 1077-260X .- 1558-4542. ; 20:3, s. Article Number: UNSP 7300108-
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Tidskriftsartikel (refereegranskat)abstract
- Penetration of nanoparticles into tooth enamel and dentine is of significant interest upon solving problems related to reduction of tooth sensitivity, enamel strengthening, disinfection, restoration as well as cosmetic bleaching. This paper aims at studying the process of nanoparticle penetration into tooth enamel and dentine samples using nonlinear optical microscopy and at investigating the influence of the same nanoparticles on the generation of free radicals using the electronic paramagnetic resonance technique. We presented in vitro measurements demonstrating that nonlinear optical microscopy, namely, two-photon-excited autfluorescence, second harmonic generation, and hyper-Rayleigh scattering-based microscopy can be used for monitoring and imaging TiO2 and ZnO nanoparticle penetration into tooth tissues. The results indicate that ZnO nanoparticles penetrated into the human tooth enamel and dentine up to a depth of 12 and 45 mu m, respectively, and TiO2 nanoparticles penetrated into dentine to a depth of 5 mu m. The penetration mainly- occurs along either enamel rods or dentinal tubules. Permeability of the dentine was found to be higher than that of enamel (for ZnO particles) by one order of magnitude and the diffusion rate was affected by the particle size being higher for smaller, submicron particles (ZnO) than for micronsized aggregates (TiO2 I. Nitrogen-doped TiO2 nanoparticles generate more radicals in the UV-VIS spectral range in comparison to pristine TiO2 (anatase) and ZnO nanoparticles, therefore, they can potentially be used for disinfection purposes of superficial tooth areas (up to 5-mu m deep).
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