| 1. |
- Garg, K. B., et al.
(författare)
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Study of Sb substitution for Pr in the Pr0.67Ba0.33MnO3 system
- 2009
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Ingår i: Journal of Magnetism and Magnetic Materials. - : Elsevier BV. - 0304-8853 .- 1873-4766. ; 321:4, s. 305-311
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Tidskriftsartikel (refereegranskat)abstract
- We study the effect of Sb substitution for Pr in the hole-doped system Pr0.67Ba0.33MnO3 (PBMO) for different doping levels of Sb. The two electrical resistivity transitions observed in the pristine sample PBMO shift to low temperatures on Sb doping with an overall increase in the electrical resistivity. The significant local lattice distortion and the grain boundary effects caused by the large cation size mismatch between Pr3+ and Sb3+ suppresses the double-exchange (DE) interaction and enhances the super-exchange (SE) interaction. The compounds show a significant and increasing value of magnetoresistance at temperatures below the Curie temperature, not expected from the DE model. The Curie temperature decreases with increase in Sb content but the saturation magnetization is little affected by the substitution. The spins, however, stay well aligned in the low-temperature regime. Our X-ray near-edge absorption spectra (XANES) and core level photoemission (XPS) data clearly show the Sb cation to be in +3 state and rule out any possibility of e-doping in our compounds.
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| 2. |
- Nappini, S., et al.
(författare)
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Soft x-ray spectroscopies in liquids and at solid-liquid interface at BACH beamline at Elettra
- 2021
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Ingår i: Review of Scientific Instruments. - : American Institute of Physics (AIP). - 0034-6748 .- 1089-7623. ; 92:1
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Tidskriftsartikel (refereegranskat)abstract
- The beamline for advanced dichroism of the Istituto Officina dei Materiali-Consiglio Nazionale delle Ricerche, operating at the Elettra synchrotron in Trieste (Italy), works in the extreme ultraviolet-soft x-ray photon energy range with selectable light polarization, high energy resolution, brilliance, and time resolution. The beamline offers a multi-technique approach for the investigation of the electronic, chemical, structural, magnetic, and dynamical properties of materials. Recently, one of the three end stations has been dedicated to experiments based on electron transfer processes at the solid/liquid interfaces and during photocatalytic or electrochemical reactions. Suitable cells to perform soft x-ray spectroscopy in the presence of liquids and reagent gases at ambient pressure were developed. Here, we present two types of static cells working in transmission or in fluorescence yield and an electrochemical flow cell that allows us to carry out cyclic voltammetry in situ and electrodeposition on a working electrode and to study chemical reactions under operando conditions. Examples of x-ray absorption spectroscopy measurements performed under ambient conditions and during electrochemical experiments in liquids are presented.
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| 3. |
- Baraldi, A., et al.
(författare)
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Thermal stability of the Rh(110) missing-row reconstruction: Combination of real-time core-level spectroscopy and ab initio modeling
- 2005
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. ; 72
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Tidskriftsartikel (refereegranskat)abstract
- The thermal stability of the (1×2) missing-row phase of Rh(110), whose first layer is an ordered array of one-dimensional atomic chains, is investigated using high-resolution core-level spectroscopy and density functional calculations. The time evolution of the spectra indicates that this phase is metastable towards deconstruction into a (1×1) phase. Our calculations unveil the mechanism of this process, which is shown to be ignited by surface defects, and provide a value for the activation energy in good agreement with experimental findings.
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| 4. |
- Clark, Pip C.J., et al.
(författare)
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The passivating effect of cadmium in PbS/CdS colloidal quantum dots probed by nm-scale depth profiling
- 2017
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Ingår i: Nanoscale. - : Royal Society of Chemistry (RSC). - 2040-3364 .- 2040-3372. ; 9:18, s. 6056-6067
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Tidskriftsartikel (refereegranskat)abstract
- Achieving control of the surface chemistry of colloidal quantum dots (CQDs) is essential to fully exploit their properties in solar cells, but direct measurement of the chemistry and electronic structure in the outermost atomic layers is challenging. Here we probe the surface oxidation and passivation of cation-exchanged PbS/CdS core/shell CQDs with sub nm-scale precision using synchrotron-radiation-excited depth-profiling photoemission. We investigate the surface composition of the topmost 1-2.5 nm of the CQDs as a function of depth, for CQDs of varying CdS shell thickness, and examine how the surface changes after prolonged air exposure. We demonstrate that the Cd is localized at the surface of the CQDs. The surface-localized products of oxidation are identified, and the extent of oxidation quantified. We show that oxidised sulfur species are progressively eliminated as Cd replaces Pb at the surface. A sub-monolayer surface 'decoration' of Cd is found to be effective in passivating the CQDs. We show that the measured energy-level alignments at PbS/CdS colloidal quantum dot surfaces differ from those expected on the basis of bulk band offsets, and are strongly affected by the oxidation products. We develop a model for the passivating action of Cd. The optimum shell thickness (of around 0.1 nm, previously found to give maximised power conversion efficiency in PbS/CdS solar cells) is found to correspond to a trade-off between the rate of oxidation and the introduction of a surface barrier to charge transport.
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| 5. |
- Mohammed Idris Bakhit, Alaa, et al.
(författare)
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A ferromagnetic Eu-Pt surface compound grown below hexagonal boron nitride
- 2023
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Ingår i: Nanoscale. - 2040-3372 .- 2040-3364. ; 15:27, s. 11517-11528
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Tidskriftsartikel (refereegranskat)abstract
- One of the fundamental applications for monolayer-thick 2D materials is their use as protective layers of metal surfaces and in situ intercalated reactive materials in ambient conditions. Here we investigate the structural, electronic, and magnetic properties, as well as the chemical stability in air of a very reactive metal, Europium, after intercalation between a hexagonal boron nitride (hBN) layer and a Pt substrate. We demonstrate that Eu intercalation leads to a hBN-covered ferromagnetic EuPt2 surface alloy with divalent Eu2+ atoms at the interface. We expose the system to ambient conditions and find a partial conservation of the di-valent signal and hence the Eu-Pt interface. The use of a curved Pt substrate allows us to explore the changes in the Eu valence state and the ambient pressure protection at different substrate planes. The interfacial EuPt2 surface alloy formation remains the same, but the resistance of the protecting hBN layer to ambient conditions is reduced, likely due to a rougher surface and a more discontinuous hBN coating.
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| 6. |
- Syres, Karen L., et al.
(författare)
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Adsorbate-Induced Modification of Surface Electronic Structure: Pyrocatechol Adsorption on the Anatase TiO2 (101) and Rutile TiO2 (110) Surfaces
- 2012
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Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 116:44, s. 23515-23525
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Tidskriftsartikel (refereegranskat)abstract
- Photoemission and near-edge X-ray absorption fine structure (NEXAFS) techniques have been used to study the adsorption of pyrocatechol on anatase TiO2 (101) and rutile TiO2 (110) single crystals. Photoemission results suggest the pyrocatechol molecule adsorbs on both surfaces predominantly in a bidentate geometry. Using the searchlight effect, the carbon K-edge NEXAFS spectra recorded for pyrocatechol on anatase TiO2 (101) and rutile TiO2 (110) show the phenyl rings in the pyrocatechol molecule to be oriented at 27 +/- 6 degrees and 2.3 +/- 8 degrees, respectively, from the surface normal. Experimental data and computational models of the pyrocatechol-anatase TiO2 interface indicate the appearance of new occupied and unoccupied states on adsorption due to hybridization between the electronic states of the pyrocatechol molecule and the surface. The atomic character of the new orbitals created facilitates direct photoinjection from pyrocatechol into anatase TiO2 and induces a strong final state effect in the carbon K-edge NEXAFS spectrum.
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