Search results for "ddc:"
showing 10 items of 3080 documents
Multi-MHz time-of-flight electronic bandstructure imaging of graphene on Ir(111)
2016
In the quest for detailed spectroscopic insight into the electronic structure at solid surfaces in a large momentum range, we have developed an advanced experimental approach. It combines the 3D detection scheme of a time-of-flight momentum microscope with an optimized filling pattern of the BESSY II storage ring. Here, comprehensive data sets covering the full surface Brillouin zone have been used to study faint substrate-film hybridization effects in the electronic structure of graphene on Ir(111), revealed by a pronounced linear dichroism in angular distribution. The method paves the way to 3D electronic bandmapping with unprecedented data recording efficiency.
Domain wall transformations and hopping in La0.7Sr0.3MnO3nanostructures imaged with high resolution x-ray magnetic microscopy
2014
We investigate the effect of electric current pulse injection on domain walls in La(0.7)Sr(0.3)MnO(3) (LSMO) half-ring nanostructures by high resolution x-ray magnetic microscopy at room temperature. Due to the easily accessible Curie temperature of LSMO, we can employ reasonable current densities to induce the Joule heating necessary to observe effects such as hopping of the domain walls between different pinning sites and nucleation/annihilation events. Such effects are the dominant features close to the Curie temperature, while spin torque is found to play a small role close to room temperature. We are also able to observe thermally activated domain wall transformations and we find that,…
Luminescence of nano- and macrosized LaPO4:Ce,Tb excited by synchrotron radiation
2011
Abstract Comparing the luminescence properties of nanosized and macroscopic LaPO4:Ce,Tb powders are performed in wide spectral range using synchrotron radiation. In the present study, LaPO4:Ce,Tb nanopowder was produced by means of a microwave-induced synthesis in ionic liquids, whereas the bulk sample represents a commercial lamp phosphor. Emission and excitation of both, Ce3+ and Tb3+ luminescence, is observed to be different when comparing bulk and nanosized LaPO4:Ce,Tb. In particular, it was shown that the fine structure of the Ce3+ as well as the Tb3+ related emission is poorly resolved for the nanomaterial. It is suggested that the nanoparticles surface plays a key role regarding the …
Noncovalent Functionalization and Passivation of Black Phosphorus with Optimized Perylene Diimides for Hybrid Field Effect Transistors
2020
Amongst the different existing methods to passivate black phosphorus (BP) from environmental degradation, the noncovalent functionalization with perylene diimides (PDI) has been postulated as one of the most promising routes because it allows preserving its electronic properties. This work describes the noncovalent functionalization and outstanding environmental protection of BP with tailor made PDI having peri-amide aromatic side chains, which include phenyl and naphthyl groups, exhibiting a significantly increased molecule-BP interaction. These results are rationalized by density functional theory (DFT) calculations showing that the adsorption energies are mainly governed by van der Waals…
Two birds with one stone: dual grain-boundary and interface passivation enables >22% efficient inverted methylammonium-free perovskite solar cells
2021
Advancing inverted (p���i���n) perovskite solar cells (PSCs) is key to further enhance the power conversion efficiency (PCE) and stability of flexible and perovskite-based tandem photovoltaics. Yet, the presence of defects at grain boundaries and in particular interfacial recombination at the perovskite/electron transporting layer interface induce severe non-radiative recombination losses, limiting the open-circuit voltage (VOC) and fill factor (FF) of PSCs in this architecture. In this work, we introduce a dual passivation strategy using the long chain alkylammonium salt phenethylammonium chloride (PEACl) both as an additive and for surface treatment to simultaneously passivate the grain b…
Monolayer black phosphorus by sequential wetchemical surface oxidation
2018
We report a straightforward chemical methodology for controlling the thickness of black phosphorus flakes down to the monolayer limit by layer-by-layer oxidation and thinning, using water as solubilizing agent.
Reduced Recombination Losses in Evaporated Perovskite Solar Cells by Postfabrication Treatment
2021
The photovoltaic perovskite research community has now developed a large set of tools and techniques to improve the power conversion efficiency (PCE). One such arcane trick is to allow the finished devices to dwell in time, and the PCE often improves. Herein, a mild postannealing procedure is implemented on coevaporated perovskite solar cells confirming a substantial PCE improvement, mainly attributed to an increased open-circuit voltage (V\(_{OC}\)). From a V\(_{OC}\) of around 1.11 V directly after preparation, the voltage improves to more than 1.18 V by temporal and thermal annealing. To clarify the origin of this annealing effect, an in-depth device experimental and simulation character…
High-pressure synthesis of boron-rich chalcogenides B12S and B12Se
2022
The authors thank Drs. I. Dovgaliuk and T. Chauveau for assistance with Rietveld analysis; and Drs. V. Bushlya and A. Jamali for help with EDX/SEM measurements. This work was financially supported by the European Union's Horizon 2020 Research and Innovation Program under Flintstone2020 project (grant agreement No 689279).
Direct observation of half-metallicity in the Heusler compound $Co_{2}MnSi$
2014
Ferromagnetic thin films of Heusler compounds are highly relevant for spintronic applications owing to their predicted half-metallicity, that is, 100% spin polarization at the Fermi energy. However, experimental evidence for this property is scarce. Here we investigate epitaxial thin films of the compound Co2MnSi in situ by ultraviolet-photoemission spectroscopy, taking advantage of a novel multi-channel spin filter. By this surface sensitive method, an exceptionally large spin polarization of () % at room temperature is observed directly. As a more bulk sensitive method, additional ex situ spin-integrated high energy X-ray photoemission spectroscopy experiments are performed. All experimen…
Si nanocrystals embedded in $SiO_2$: Optical studies in the vacuum ultraviolet range
2011
Photoluminescence excitation and transmission spectra of Si nanocrystals of different diameters embeddedin a SiO2 matrix have been investigated in the broad visible-vacuum ultraviolet spectral range usingsynchrotron radiation. The dependence of the photoluminescence excitation spectra on the nanocrystals sizewas experimentally established. It is shown that the photoluminescence excitation and absorption spectra aresignificantly blueshifted with decreasing Si nanocrystal size. A detailed comparison of photoluminescenceexcitation and absorption spectra with data from theoretical modeling has been done. It is demonstrated thatthe experimentally determined blueshift of the photoluminescence exc…