[OPEN ACCESS] Probing planar defects in nanoparticle superlattices by 3D small-angle electron diffraction tomography and real space imaging

Arnaud Mayence, Dong Wang, German Salazar-Alvarez, Peter Oleynikov and Lennart Bergström
Nanoscale, 2014, Accepted Manuscript
DOI: 10.1039/C4NR04156A

Abstract
We demonstrate how the acquisition and processing of 3D electron diffraction data can be extended to characterize structural features on the mesoscale, and show how lattice distortions in superlattices of self-assembled spherical Pd nanoparticles can be quantified using small-angle electron diffraction tomography (3D SA-EDT). Transmission electron microscopy real space imaging and 3D SA-EDT reveals a high density of stacking faults that was related to a competition between fcc and hcp arrangements during assembly. Information of the orientation of the stacking faults was used to make analogies between planar defects in the superlattices and Shockley partial dislocations in metallic systems.

[OPEN ACCESS] Dynamic growth modes of ordered arrays and mesocrystals during drop-casting of iron oxide nanocubes

Cryst. Eng. Comm. 2013
DOI: 10.1039/C3CE41871E
Michael Agthe, Erik Wetterskog, Johanne Mouzon, German Salazar-Alvarez and Lennart Bergström

Abstract:
The growth modes of self-assembled mesocrystals and ordered arrays from dispersions of iron oxide nanocubes with a mean edge length of 9.6 nm during controlled solvent removal have been investigated with a combination of visible light video microscopy, atomic force microscopy and scanning electron microscopy. Mesocrystals with translational and orientational order of sizes up to 10 μm are formed spontaneously during the final, diffusion-controlled, drop-casting stage when the liquid film is very thin and the particle concentration is high. Convection-driven deposition of ordered nanocube arrays at the edge of the drying droplet is a manifestation of the so called coffee-ring effect. Dendritic growth or fingering of rapidly growing arrays of ordered nanocubes could also be observed in a transition regime as the growth front moves from the initial three-phase contact line towards the centre of the original droplet.

Video abstract:


Cover page:
http://pubs.rsc.org.ezp.sub.su.se/en/content/articlepdf/2014/ce/c4ce90010c?page=search

[NEWS] Our review is one of the hotest articles in august!

at the Journal of Materials Chemistry A: http://blogs.rsc.org/jm/2013/08/07/hot-articles-for-august/

Functional hybrids based on biogenic nanofibrils and inorganic nanomaterials

Bernd Wicklein and German Salazar-Alvarez
J. Mater. Chem. A, 2013,1, 5469-5478 
DOI: 10.1039/C3TA01690K, Feature Article

[REVIEW] [OPEN ACCESS] Functional hybrids based on biogenic nanofibrils and inorganic nanomaterials

Bernd Wicklein and German Salazar-Alvarez

J. Mater. Chem. A, 2013, Accepted Manuscript

DOI: 10.1039/C3TA01690K

Abstract:

This feature article reviews some of the recent work on the fabrication of functional hybrids based on biogenic nanofibers and inorganic nanomaterials with an emphasis on the functional properties and suggested potential applications. We also discuss some of the work oriented towards the formation of ordered materials in the pursuit of achieving a hierarchical construction. Besides the academic interest in biogenic nanomaterials, it is anticipated that the use of natural, abundant nanomaterials, e.g., cellulose, chitin, collagen, and silk, could provide affordable functional nanomaterials in developing countries.

[OPEN ACCESS] 2D to 3D crossover of the magnetic properties in ordered arrays of iron oxide nanocrystals - Nanoscale (RSC Publishing)

Nanoscale 5 (2013) 953-960.

Bertrand Faure , Erik Wetterskog , Klas Gunnarsson , Elisabeth Josten , Raphaël P. Hermann , Thomas Brückel , Jens Wenzel Andreasen , Florian Meneau , Mathias Meyer , Alexander P Lyubartsev , Lennart Bergström , German Salazar-Alvarez and Peter Svedlindh

DOI: 10.1039/C2NR33013JD

http://pubs.rsc.org/en/Content/ArticleLanding/2013/NR/c2nr33013j

Abstract:

The magnetic 2D to 3D crossover behavior of well-ordered arrays of monodomain γ-Fe2O3 spherical nanoparticles with different thicknesses has been investigated by magnetometry and Monte Carlo (MC) simulations. Using structural information of the arrays obtained from grazing incidence small-angle X-ray scattering and scanning electron microscopy together with experimentally determined values for the saturation magnetization and magnetic anisotropy of the nanoparticles, we show that MC simulations can reproduce the thickness-dependent magnetic behavior. The magnetic dipolar particle interactions induce a ferromagnetic coupling that increases in strength with decreasing thickness of the array. The 2D to 3D transition in the magnetic properties is mainly driven by a change in the orientation of the magnetic vortex states with increasing thickness, becoming more isotropic as the thickness of the array increases. Magnetic anisotropy prevents long-range ferromagnetic order from being established at low temperature and the nanoparticle magnetic moments instead freeze along directions defined by the distribution of easy magnetization directions.

[OPEN ACCESS] Hard and transparent films formed by nanocellulose-TiO2 nanoparticle hybrids

http://dx.doi.org/10.1371/journal.pone.0045828

PLoS ONE 2012, 7, e45828

Christina Schütz, Jordi Sort, Zoltán Bacsik, Vitaliy Oliynyk, Eva Pellicer, Andreas Fall, Lars Wågberg, Lars Berglund, Lennart Bergström, German Salazar-Alvarez

DOI: 10.1371/journal.pone.0045828

Abstract

The formation of hybrids of nanofibrillated cellulose and titania nanoparticles in aqueous media has been studied. Their transparency and mechanical behavior have been assessed by spectrophotometry and nanoindentation. The results show that limiting the titania nanoparticle concentration below 16 vol% yields a homogeneous hybrids with a very high Young’s modulus and hardness, of up to 44 GPa and 3.4 GPa, respectively, and an optical transmittance above 80 %. Electron microscopy shows that higher nanoparticle contents result in agglomeration and an inhomogeneous hybrid nanostructure with a concomitant reduction of hardness and optical transmittance. Infrared spectroscopy suggests that the nanostructure of the hybrids is controlled by electrostatic adsorption of the titania nanoparticles on the negatively charged nanocellulose surfaces.

[OPEN ACCESS] Quantitative spatial magnetization distribution in iron oxide nanocubes and nanospheres by polarized small-angle neutron scattering

http://stacks.iop.org/1367-2630/14/013025 [OPEN ACCESS]

New Journal of Physics, 2012, 14, 013025

Sabrina Disch, Erik Wetterskog, Raphaël P. Hermann, Albrecht Wiedenmann, Ulla Vainio, German Salazar-Alvarez, Lennart Bergström and Thomas Brückel

DOI: 10.1088/1367-2630/14/1/013025

By means of polarized small-angle neutron scattering, we have resolved the long-standing challenge of determining the magnetization distribution in magnetic nanoparticles in absolute units. The reduced magnetization, localized in non-interacting nanoparticles, indicates strongly particle shape- dependent surface spin canting with a 0.3(1) and 0.5(1) nm thick surface shell of reduced magnetization found for ~9 nm nanospheres and ~8.5 nm nanocubes, respectively. Further, the reduced macroscopic magnetization in nanoparticles results not only from surface spin canting, but also from drastically reduced magnetization inside the uniformly magnetized core as compared to the bulk material. Our microscopic results explain the low macroscopic magnetization commonly found in nanoparticles.

[OPEN ACCESS] Shape Induced Symmetry in Self-Assembled Mesocrystals of Iron Oxide Nanocubes

http://pubs.acs.org/doi/abs/10.1021/nl200126v [OPEN ACCESS]

Nano Lett., 2011, 11 (4), pp 1651–1656
Sabrina Disch, Erik Wetterskog, Raphaël P. Hermann, German Salazar-Alvarez, Peter Busch, Thomas Brückel, Lennart Bergström, and Saeed Kamali

DOI: 10.1021/nl200126v

Abstract:

Grazing incidence small-angle scattering and electron microscopy have been used to show for the first time that nonspherical nanoparticles can assemble into highly ordered body-centered tetragonal mesocrystals. Energy models accounting for the directionality and magnitude of the van der Waals and dipolar interactions as a function of the degree of truncation of the nanocubes illustrated the importance of the directional dipolar forces for the formation of the initial nanocube clusters and the dominance of the van der Waals multibody interactions in the dense packed arrays.