42 research outputs found
The big bang of halide perovskites: The starting point of crystallization
Hybrid halide perovskites (HHPs) are very promising absorber materials for solar cells due to their high power conversion efficiency and the low-cost solution-based processing methods. We applied small angle X-ray scattering to MAPbI3, FAPbI3 and MAPbBr3 precursor solutions in different solvents (GBL, DMF, and mixtures) to gain a deeper understanding of the building blocks during the early stage of HHP formation. We present a core–shell model where the core is formed by [PbX6] octahedra surrounded by a shell of solvent molecules, which explains the arrangement of the precursors in solution and how the solvent and the halide influence such arrangement
Traceable GISAXS measurements for pitch determination of a 25 nm self-assembled polymer grating
The feature sizes of only a few nanometers in modern nanotechnology and
next-generation microelectronics continually increase the demand for suitable
nanometrology tools. Grazing incidence small-angle X-ray scattering (GISAXS) is
a versatile technique to measure lateral and vertical sizes in the nm-range,
but the traceability of the obtained parameters, which is a prerequisite for
any metrological measurement, has not been demonstrated so far. In this work,
the first traceable GISAXS measurements, demonstrated with a self-assembled
block copolymer grating structure with a nominal pitch of 25 nm, are reported.
The different uncertainty contributions to the obtained pitch value of 24.83(9)
nm are discussed individually. The main uncertainty contribution results from
the sample-detector distance and the pixel size measurement, whereas the
intrinsic asymmetry of the scattering features is of minor relevance for the
investigated grating structure. The uncertainty analysis provides a basis for
the evaluation of the uncertainty of GISAXS data in a more general context, for
example in numerical data modeling.Comment: 9 pages, 6 figures; submitted to Journal of Applied Crystallograph
Yttria-zirconia coatings studied by grazing-incidence small-angle X-ray scattering during in situ heating
Silver Ion Incorporation and Nanoparticle Formation inside the Cavity of Pyrococcus furiosus Ferritin: Structural and Size-Distribution Analyses
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ASAXS study of CaF2 nanoparticles embedded in a silicate glass matrix
The formation and growth of nanosized CaF2 crystallites by heat treatment of an oxyfluoride glass of composition 7.65Na2O–7.69K2O–10.58CaO–12.5CaF2– 5.77Al2O3–55.8SiO2 (wt%) was investigated using anomalous small-angle X-ray scattering (ASAXS). A recently developed vacuum version of the hybrid pixel detector Pilatus 1M was used for the ASAXS measurements below the Ca K-edge of 4038 eV down to 3800 eV. ASAXS investigation allows the determination of structural parameters such as size and size distribution of nanoparticles and characterizes the spatial distribution of the resonant element, Ca. The method reveals quantitatively that the growing CaF2 crystallites are surrounded by a shell of lower electron density. This depletion shell of growing thickness hinders and finally limits the growth of CaF2 crystallites. Moreover, in samples that were annealed for 10h and more, additional very small heterogeneities (1.6 nm diameter) were found
Solvent and A-Site Cation Control Preferred Crystallographic Orientation in Bromine-Based Perovskite Thin Films
Preferred crystallographic orientation in polycrystalline films is desirable for efficient charge carrier transport in metal halide perovskites and semiconductors. However, the mechanisms that determine the preferred orientation of halide perovskites are still not well understood. In this work, we investigate crystallographic orientation in lead bromide perovskites. We show that the solvent of the precursor solution and organic A-site cation strongly affect the preferred orientation of the deposited perovskite thin films. Specifically, we show that the solvent, dimethylsulfoxide, influences the early stages of crystallization and induces preferred orientation in the deposited films by preventing colloidal particle interactions. Additionally, the methylammonium A-site cation induces a higher degree of preferred orientation than the formamidinium counterpart. We use density functional theory to show that the lower surface energy of the (100) plane facets in methylammonium-based perovskites, compared to the (110) planes, is the reason for the higher degree of preferred orientation. In contrast, the surface energy of the (100) and (110) facets is similar for formamidinium-based perovskites, leading to lower degree of preferred orientation. Furthermore, we show that different A-site cations do not significantly affect ion diffusion in bromine-based perovskite solar cells but impact ion density and accumulation, leading to increased hysteresis. Our work highlights the interplay between the solvent and organic A-site cation which determine crystallographic orientation and plays a critical role in the electronic properties and ionic migration of solar cells
Design of a Nanometric AlTi Additive for MgB2-Based Reactive Hydride Composites with Superior Kinetic Properties
Solid-state hydride compounds are a promising option for efficient and safe hydrogen-storage systems. Lithium reactive hydride composite system 2LiBH4 + MgH2/2LiH + MgB2 (Li-RHC) has been widely investigated owing to its high theoretical hydrogen-storage capacity and low calculated reaction enthalpy (11.5 wt % H2 and 45.9 kJ/mol H2). In this paper, a thorough investigation into the effect of the formation of nano-TiAl alloys on the hydrogen-storage properties of Li-RHC is presented. The additive 3TiCl3·AlCl3 is used as the nanoparticle precursor. For the investigated temperatures and hydrogen pressures, the addition of ∼5 wt % 3TiCl3·AlCl3 leads to hydrogenation/dehydrogenation times of only 30 min and a reversible hydrogen-storage capacity of 9.5 wt %. The material containing 3TiCl3·AlCl3 possesses superior hydrogen-storage properties in terms of rates and a stable hydrogen capacity during several hydrogenation/dehydrogenation cycles. These enhancements are attributed to an in situ nanostructure and a hexagonal AlTi3 phase observed by high-resolution transmission electron microscopy. This phase acts in a 2-fold manner, first promoting the nucleation of MgB2 upon dehydrogenation and second suppressing the formation of Li2B12H12 upon hydrogenation/dehydrogenation cycling.Fil: Le, Thi-Thu. Helmholtz Zentrum Geesthacht; AlemaniaFil: Pistidda, Claudio. Helmholtz Zentrum Geesthacht; AlemaniaFil: Puszkiel, Julián Atilio. Helmholtz Zentrum Geesthacht; Alemania. Comisión Nacional de EnergÃa Atómica. Centro Atómico Bariloche; Argentina. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Centro CientÃfico Tecnológico Conicet - Patagonia Norte; ArgentinaFil: Castro Riglos, Maria Victoria. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Centro CientÃfico Tecnológico Conicet - Patagonia Norte; Argentina. Helmholtz Zentrum Geesthacht; Alemania. Comisión Nacional de EnergÃa Atómica. Centro Atómico Bariloche; ArgentinaFil: Karimi, Fahim. Helmholtz Zentrum Geesthacht; AlemaniaFil: Skibsted, Jørgen. University Aarhus; DinamarcaFil: Gharibdoust, Seyedhosein Payandeh. University Aarhus; DinamarcaFil: Richter, Bo. University Aarhus; DinamarcaFil: Emmler, Thomas. Helmholtz Zentrum Geesthacht; AlemaniaFil: Milanese, Chiara. Università di Pavia; ItaliaFil: Santoru, Antonio. Helmholtz Zentrum Geesthacht; AlemaniaFil: Hoell, Armin. Helmholtz Zentrum Berlin für Materialien und Energie; AlemaniaFil: Krumrey, Michael. Physikalisch Technische Bundesanstalt; AlemaniaFil: Gericke, Eike. Universität zu Berlin; AlemaniaFil: Akiba, Etsuo. Kyushu University; JapónFil: Jensen, Torben R.. University Aarhus; DinamarcaFil: Klassen, Thomas. Helmholtz Zentrum Geesthacht; Alemania. Helmut Schmidt University; AlemaniaFil: Dornheim, Martin. Helmholtz Zentrum Geesthacht; Alemani
Fluoride Chemistry in Tin Halide Perovskites
Tin is the frontrunner for substituting toxic lead in perovskite solar cells. However, tin suffers the detrimental oxidation of SnII to SnIV. Most of reported strategies employ SnF2 in the perovskite precursor solution to prevent SnIV formation. Nevertheless, the working mechanism of this additive remains debated. To further elucidate it, we investigate the fluoride chemistry in tin halide perovskites by complementary analytical tools. NMR analysis of the precursor solution discloses a strong preferential affinity of fluoride anions for SnIV over SnII, selectively complexing it as SnF4. Hard X-ray photoelectron spectroscopy on films shows the lower tendency of SnF4 than SnI4 to get included in the perovskite structure, hence preventing the inclusion of SnIV in the film. Finally, small-angle X-ray scattering reveals the strong influence of fluoride on the colloidal chemistry of precursor dispersions, directly affecting perovskite crystallization
Effect of the particle size evolution on the hydrogen storage performance of KH doped Mg(NH2)2 + 2LiH
In recent years, many solid-state hydride-based materials have been considered as hydrogen storage systems for mobile and stationary applications. Due to a gravimetric hydrogen capacity of 5.6wt% and a dehydrogenation enthalpy of 38.9kJ/molH2, Mg(NH2)2 + 2LiH is considered a potential hydrogen storage material for solid-state storage systems to be coupled with PEM fuel cell devices. One of the main challenges is the reduction of dehydrogenation temperature since this system requires high dehydrogenation temperatures (~ 200°C). The addition of KH to this system significantly decreases the dehydrogenation onset temperature to 130°C. On the one hand, the addition of KH stabilizes the hydrogen storage capacity. On the other hand, the capacity is reduced by 50% (from 4.1 to 2%) after the first 25cycles. In this work, the particle sizes of the overall hydride matrix and the potassium-containing species are investigated during hydrogen cycling. Relation between particle size evolution of the additive and hydrogen storage kinetics is described by using an advanced synchrotron-based technique: Anomalous small-angle X-ray scattering, which was applied for the first time at the potassium K-edge for amide-hydride hydrogen storage systems. The outcomes from this investigation show that, the nanometric potassium-containing phases might be located at the reaction interfaces, limiting the particle coarsening. Average diameters of potassium-containing nanoparticles double after 25cycles (from 10 to 20nm). Therefore, reaction kinetics at subsequent cycles degrade. The deterioration of the reaction kinetics can be minimized by selecting lower absorption temperatures, which mitigates the particle size growth, resulting in two times faster reaction kinetics
Characterization of LiBH4–MgH2 Reactive Hydride Composite System with Scattering and Imaging Methods Using Neutron and Synchrotron Radiation
Reversible solid-state hydrogen storage in metal hydrides is a key technology for pollution-free energy conversion systems. Herein, the LiBH2–MgH2 composite system with and without ScCl3 additive is investigated using synchrotron- and neutron-radiation-based probing methods that can be applied to characterize such lightweight metal–hydrogen systems from nanoscopic levels up to macroscopic scale. Combining the results of neutron- and photon-based methods allows a complementary insight into reaction paths and mechanisms, complex interactions between the hydride matrix and additive, hydrogen distribution, material transport, structural changes, and phase separation in the hydride matrix. The gained knowledge is of great importance for development and optimization of such novel metal-hydride-based hydrogen storage systems with respect to future applications