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Al13Fe4 Scientific Result

L. Piccolo
Chemical Communications 49, 9149-9051 (2013)
DOI: 10.1039/c3cc44987d

Abstract : The hydrogenation of butadiene has been investigated for the first time on Al13Fe4.

The model (010) surface of this non-noble metal combination appears both active and selective under mild reaction conditions.

The performances of Al13Fe4 for C=C bond hydrogenation are compared with those of the reference noble metal, palladium.

Last Updated (Tuesday, 14 February 2017 19:24)

 

Morphological instability of the cores in Ag-Cu, Ag-Ni, Ag-Co and Au-Ni nanoalloys

Nanoalloys with core-shell arrangement are of special interest in several applications, such as in optics, catalysis, magnetism, and biomedicine. Despite wide interest in applications, the physical factors stabilizing the structures of these nanoparticles are still unclear to a great extent, especially for what concerns the relationship between geometric structure and chemical ordering patterns. Here, global-optimization searches are performed in order to single out the most stable chemical ordering patterns corresponding to the most important geometric structures, for a series of weakly miscible systems, including AgCu, AgNi, AgCo, and AuCo. The main results are:

(i) the overall geometric structure of the nanoalloy and the shape and placement of its inner core are strictly correlated;

(ii) centered cores can be obtained in icosahedral nanoparticles but not in crystalline or decahedral ones, in which asymmetric quasi-Janus morphologies form;

(iii) in icosahedral nanoparticles, when the core exceeds a critical size, a new type of morphological instability develops, making the core asymmetric and extending it towards the nanoparticle surface. This instability bears resemblance with the Stranski-Krastanov instability occurring in thin-film growth. Its driving force arise from the lattice mismatch between different atoms, causing a change of sign of the strain (from compressive to tensile) as the core size increases.

(iv) multicenter chemical ordering patterns can be obtained in polyicosahedral nanoalloys, and, to a lesser extent, in decahedra.

These issues are crucial for designing strategies to achieve effective coatings of the cores.

D. Bochicchio and R. Ferrando, Phys. Rev. B 87, 165435 (2013)

http://prb.aps.org/abstract/PRB/v87/i16/e165435

 


 

Morphological instability of the cores in icosahedral Au-Co nanoparticles.
For a fixed total cluster size (1415 atoms, diameter of ∼4 nm) we consider increasing sizes of the core (from left to right 13, 55, 147, and 309 atoms) and we look for the lowest-energy configuration by global-optimization searches using exchange moves only. Au atoms are shown as small spheres, whereas core atoms are shown as big spheres. As the core size increases, a morphological instability drives the core from  centered to an asymmetric positions, so that the core touches the cluster surface.

Last Updated (Friday, 26 April 2013 06:29)

 

Recent books on nanoalloys

Recently four very interesting books about nanoalloys have been published. These books have been edited by participants to MP0903 and contains several contributions of participants to MP0903.

Metal Nanoparticles and Nanoalloys, edited by Roy L. Johnston and Jess Wilcoxon, published by Elsevier

Nanoalloys -- Synthesis, Structure and Properties, edited by Damien Alloyeau, Christine Mottet and Christian Ricolleau, published by Springer

Metal Clusters and Nanoalloys, edited by Marcelo Mariscal, Oscar Oviedo and Ezequiel Leiva, published by Springer

Nanoalloys -- From Fundamentals to Emergent Applications, edited by Florent Calvo, published by Elsevier

 


 

 

 

 

Last Updated (Monday, 22 April 2013 12:21)

 

Dramatic change of magnetic order in nanoscale crystals

Our work hints at a tunable antiferro-ferro magnetic (AFM-FM) transition temperature, with great potential for developments in spintronics, heat assisted magnetic data recording, and heat-pumps technology.
In sharp contrast to previous studies on FeRh bulk, thin films, and nanoparticles, we report the persistence of ferromagnetic order down to -270°C for crystals measuring 3.3 nanometers in diameter.
Going nano, the crystal structure relaxes and stabilizes the FM phase, suggesting a rich size-dependent magnetic phase diagram and paving the road for the creation of larger crystals switching from AFM to FM at tunable temperatures, pressures, and magnetic fields.
EPFL professor Harald Brune states: "FeRh nanocrystals give us one more example of how differently matter can behave at the nanoscale: we ascribe the stabilization of the ferromagnetic phase to structural relaxation, which can be controlled by varying the crystal size".
The result was made possible using a combination of cutting-edge experimental techniques, from the production of size-selected nanocrystals, to magnetic and structural characterization using powerful X-ray sources, and atomic-plane electronic imaging.

Low Temperature Ferromagnetism in Chemically Ordered FeRh Nanocrystals

A. Hillion, A. Cavallin, S. Vlaic, A. Tamion, F. Tournus, G. Khadra, J. Dreiser, C. Piamonteze, F. Nolting, S. Rusponi, K. Sato, T. J. Konno, O. Proux, V. Dupuis, and H. Brune

Phys. Rev. Lett. 110, 087207 (2013)

http://prl.aps.org/abstract/PRL/v110/i8/e087207

 

 


 

Last Updated (Tuesday, 05 March 2013 07:20)

 

Unusual chemical arrangement in nanomagnets

Bulk material properties cannot be simply transposed to nanoparticles! This is what researchers (French-Japanese collaboration) have shown by studying the atomic structure of FePt and CoPt nanomagnets. FePt and CoPt magnetic alloys are attractive because they can have a very high magnetic anisotropy. This physical property means that the magnetic moment orientation (the south-north axis of a magnet) is very difficult to modify: it could then allow storing information on nanometer-size magnets, thus increasing dramatically the storage density of our computer hard drives. However, in order to have a large anisotropy, the atoms need to be in a specific arrangement: what is called the L10 chemical order.

Using transmission electron microscopy to determine the atomic structure of FePt and CoPt nanoparticles (around 3 nm diameter), the researchers have found that, in addition to particles showing the desired L10 order, there exist particles with more complex chemical arrangements specific to the nanoscale. In particular, they have clearly observed an exotic structure which was expected from recent theoretical calculations: particles having a pentagonal symmetry (decahedral shape) and chemically ordered, which corresponds to five different L10 domains within a single nanoparticle. Such particles are then locally chemically ordered, but they would only display a very small magnetic anisotropy! These observations give precious information for the understanding of these nano-alloys.

Article: “Multi-L10 Domain CoPt and FePt Nanoparticles Revealed by Electron Microscopy”, F. Tournus, K. Sato, T. Epicier, T. J. Konno and V. Dupuis, Phys. Rev. Lett. 110, 055501 (2013).

http://prl.aps.org/abstract/PRL/v110/i5/e055501

 


 

 

Last Updated (Friday, 01 February 2013 13:05)

 
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