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proved the charge transfer from the perovskite to the carbon nanotube layer upon illumination. These observations may lead to new solar cells with the perovskite as active layer and the carbon nanotubes as hole-transporting layer.
Theory of phase transformations
Hydrodynamic theory of freezing – Nucleation and polycrystalline growth. — Structural aspects of crystal nucleation in undercooled liquids are explored using a nonlinear hydrodynamic theory of crystallization we proposed recently, which is based on combining fluctuating hydrodynamics with the phase-field crystal (PFC) theory. We have shown that in our hydrodynamic approach not only homogeneous and heterogeneous nucleation processes are accessible, but also growth front nucleation, which leads to the formation of new (differently oriented) grains at the solid-liquid front in highly undercooled systems. Formation of dislocations at the solid-liquid interface and interference of density waves ahead of the crystallization front are responsible for the appearance of the new orientations at the growth front that lead to spherulite-like nanostructures (Fig. 2).
Figure 2. Polycrystalline growth in the hydrodynamic model of freezing. Snapshots of the orientation field (upper row), the Voronoi map (bottom row), and coarse-grained density (bottom row central panel: lighter colour denotes higher density) taken at dimensionless times t = 900, 2100, 2900, 3400, and 3900 are shown. Note the spatial variation of the orientation field due to the dislocations shown as red-blue pairs of dots (atoms of 7 and 5 neighbours) in the Voronoi map, and the small crystallite formed close to the interface in the 4th panel from the left. This indicates two mechanisms for growth front nucleation: (i) nucleation of dislocations at the interface, and (ii) crystal nucleation ahead of the growth front.
Grain coarsening in two-dimensional phase-field models with orientation field. — Contradictory results were published regarding the form of the long-time grain size distribution (LGSD) that characterizes grain coarsening in two-dimensional systems: While experiments and the PFC model indicate a log-normal distribution, other works including studies based on phase-field simulations that rely on coarse-grained fields, like the multi-phase-field and orientation field (OF) models, yield significantly different distributions. We investigated this problem, and demonstrated for the OF models that an insufficient resolution of the small-angle grain boundaries leads to a log-normal distribution close to those seen in the experiments. Our work also indicates that the LGSD is critically sensitive to the details of
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the evaluation, and raises the possibility that the differences among the LGSD results from different sources originate from differences in the detection of small-angle grain boundaries.
Topological defects in two-dimensional orientation-field models. — In 2D, a continuous scalar field is used to represent crystallographic orientation. The respective order parameter space is the unit circle, which is not simply connected. This property has important consequences for the multigrain structures: (i) trijunctions may be singular; (ii) for each pair of grains, there exist two different interfacial solutions that cannot be continuously transformed to each another; (iii) if both solutions appear along a grain boundary, a topologically stable singular point defect forms between them. While (i) can be interpreted in the classical picture of grain boundaries, (ii) and, therefore, (iii) cannot. To overcome these problems, we proposed two solutions. The first is based on a three-component unit vector field, while in the second we utilize a two-component vector field with an additional potential.
In both cases, the additional degree of freedom makes the order parameter space simply connected, which removes the topological stability of these defect.
X-ray-related methods
We have continued our studies on structure determination by inside x-ray sources. We have carried out a series of experiments at ESRF, and measured atomic resolution holograms and also Kossel line patterns. The atoms which we used as point sources were exited by a very intense, synchrotron-generated focused X-ray beam. The diffraction patterns and the holograms were detected by a new 2D position sensitive detector allowing the collection of higher quality data then in earlier measurements. The evaluation of the data is under way.
This type of measurements open the way to single-pulse structure determination at X-ray free-electron lasers.
Grants
OTKA NK-105691, Science in nanolaboratories (K. Kamarás 2013-2017)
OTKA K-115504. Structure determination of biological particles with x-ray free electron laser (M. Tegze 2015- 2019).
NKFI K-115959, Pattern formation in far-from equilibrium systems (L. Gránásy, 2016–2019).
NKFI SNN-118012 Correlated electrons in confined molecular systems (K. Kamarás 2016-2019)
NKFI PD-121320 Spectroscopic study of low-dimensional materials (Á. Pekker 2016-2019) NKFI FK-125063 Spectroscopic study of chemically modified low-dimensional materials (Á.
Pekker 2017-2021)
NKFI NN-127069 Pb-free perovskite solar cells with long-term stability (K. Kamarás 2018-2020)
ESA PECS Contract No. 40000110759/11/NL/KML: GRADECET - Phase-field modelling of columnar to equiaxed transition with fluid flow (L. Gránásy, 2015–2017).
VEKOP-2.3.3-15-2016-00001 Determination of atomic structure of nanosystems (K. Kamarás 2016-2018)
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VEKOP-2.3.2-16-2016-00011 Strategic workshop for the technological challenges of renewable energy systems (K. Kamarás 2017-2020)
International cooperations
Institut de Physique de la Matière Complexe, EPFL, Lausanne, Switzerland, Prof. László Forró Institut Jozef Stefan, Ljubljana, Slovenia, Prof. Denis Arcon
Department of Chemistry, University of Nottingham, United Kingdom, Prof. Andrei N.
Khlobystov
Department of Mechanical Engineering, University of Tokyo, Prof. Shigeo Maruyama
Walther Meissner Institute, Bavarian Academy of Sciences and Humanities, Garching, Germany, Dr. Rudi Hackl
Cardiff University, School of Chemistry, Cardiff, United Kingdom, Prof. D. Bonifazi
School of Chemical Engineering and Materials Science, Chung Ang University, Seoul, Republic of Korea, Prof. Soo Young Kim
Synchrotron Soleil, Gif-sur-Yvette, France, Dr. Ferenc Borondics
Physique de la Matière Condensée, École Polytechnique, CNRS, 91128 Palaiseau, France, Prof.
Mathis Plapp and Dr. Hervé Henry
NIST, Gaithersburg, Maryland 20899, USA, Prof. James A. Warren
Access e.V., Intzestrasse 5, 52072 Aachen, Germany, Dr. Markus Apel, Dr. Ulrike Hecht German Aerospace Center (DLR), Linder Höhe, 51147 Cologne, Dr. Mathias Kolbe
Publications
Articles
1. Chelwani N, Hoch D, Jost D, Botka B, Scholz J-R, Richter R, Theodoridou M, Kretzschmar F, Böhm T, Kamarás K, Hackl R: Off-axis parabolic mirror optics for polarized Raman spectroscopy at low temperature. APPL PHYS LETT 110:(19) 193504/1-4. (2017)
2. Datz D, Németh G, Tóháti HM, Pekker Á, Kamarás K: High-resolution nanospectroscopy of boron nitride nanotubes. PHYS STATUS SOLIDI B 254:(11) 1700277/1-4. (2017)
3. Németh G, Datz D, Tóháti HM, Pekker Á, Otsuka K, Inoue T, Maruyama S, Kamarás K:
Nanoscale characterization of individual horizontally aligned single-walled carbon nanotubes. PHYS STATUS SOLIDI B 254:(11) 1700433/1-4 (2017)
4. Korbuly B, Pusztai T, Tóth GyI, Henry H, Plapp M, Gránásy L: Orientation-field models for polycrystalline solidification: grain coarsening and complex growth forms. J CRYST GROWTH 457: 32-37 (2017)
5. Korbuly B, Pusztai T, Henry H, Plapp M, Apel M, Gránásy L: Grain coarsening in two-dimensional phase-field models with an orientation field. PHYS REV E 95:(5) 053303/1-12 (2017)
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6. Korbuly B, Plapp M, Henry H, Warren JA, Gránásy L, Pusztai T: Topological defects in two-dimensional orientation-field models for grain growth. PHYSICAL REVIEW E 96:(5) 052802/1-15 (2017)
7. Matyuska F, Szorcsik A, May NV, Dancs Á, Kováts É, Bényei A, Gajda T: Tailoring the local environment around metal ions: A solution chemical and structural study of some multidentate tripodal ligands. DALTON T 46:(26) 8626-8642 (2017)
8. Podmaniczky F, Tóth GI, Tegze G, Pusztai T, Gránásy L: Phase-field crystal modeling of heteroepitaxy and exotic modes of crystal nucleation. J CRYST GROWTH 457: 24-31 (2017)
9. Podmaniczky F, Tóth GyI, Tegze Gy, Gránásy L: Hydrodynamic theory of freezing:
Nucleation and polycrystalline growth. PHYS REV E 95:(5) 052801/1-8 (2017)
10. Rátkai L, Tóth GyI, Környei L, Pusztai T, Gránásy L: Phase-field modeling of eutectic structures on the nanoscale: the effect of anisotropy. J MATER SCI 52: 5544-5558 (2017)
11. Tóháti HM, Pekker Á, Andričević P, Forró L, Náfrádi B, Kollár M, Horváth E, Kamarás K:
Optical detection of charge dynamics in CH3NH3PbI3/carbon nanotube composites.
NANOSCALE 9:(45) 17781-17787 (2017)
12. Tomović AŽ, Savić JJ, Bakić NLj, Bortel G, Faigel G, Zikic R, Jovanović VP: Oxidized pentacene micro-rods obtained by thermal annealing of pentacene thin films in air.
VACUUM 144: 36-42 (2017)
13. Tóth GI, Selvag J, Kvamme B: Phenomenological continuum theory of asphaltene-stabilized oil/water emulsions. ENERG FUEL 31:(2) 1218-1225 (2017)
14. Walker KE, Rance GA, Pekker Á, Tóháti HM, Fay MW, Lodge RW, Stoppiello CT, Kamarás K, Khlobystov AN: Growth of carbon nanotubes inside boron nitride nanotubes by coalescence of fullerenes: Toward the world's smallest coaxial cable.
SMALL METHODS 1:(9) UNSP 1700184/1-9 (2017)
15. Gránásy L: Számítógépes anyagtudomány: tûkristályoktól a komplex polikristályos alakzatokig (Computational materials science: from needle crystals to complex polycrystalline forms, in Hungarian). FIZIKAI SZEMLE 67:(12) 403-406. (2017)
Conference proceedings
16. Podmaniczky F, Tóth GI, Gránásy L: Nucleation and polycrystalline growth in a hydrodynamic theory of freezing. In: Proceedings of SP’17 the 6th Decennial International Conference on Solidification Processing (Old Windsor, UK, 25-28 July 2017) Ed.: Fan Z, London: Brunel University, ISBN:978-1-908549-29-7, 2017. pp. 22-25 See also: S-D.1, S-D.2
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