peer journals

Do Binary Supracrystals Enhance the Crystal Stability?

Zhijie Yang, Thomas Altantzis,Sara Bals, Gustaaf Van Tendeloo, Marie-Paule Pileni

We study the oxygen thermal stability of two binary systems. The larger particles are magnetic amorphous Co (7.2 nm) or Fe3O4 (7.5 nm) nanocrystals whereas the smaller ones (3.7 nm) are Au nanocrystals. The nanocrystal ordering, as well as the choice of the magnetic nanoparticles very much influence the stability of the binary system. A perfect crystalline structure is obtained with the Fe3O4/Au binary supracrystals. For the Co/Au binary system, oxidation of Co results in the chemical transformation from Co to CoO, where the size of the amorphous Co nanoparticles increases from 7.2 to 9.8 nm in diameter. During the volume expansion of the Co nanoparticles, Au nanoparticles within the binary assemblies coalesce and are at the origin of the instability of the binary nanoparticle supracrystals. On the other hand, for the Fe3O4/Au binary system, the oxidation of Fe3O4 to Fe2Odoes not lead to a size change of the nanoparticles, which maintains the stability of the binary nanoparticle supracrystals. A similar behavior is observed for an AlB2type Co-Ag binary system: The crystalline structure is maintained, whereas in disordered assemblies, coalescence of Ag nanocrystals is observed

 

 

 

peer journals

Control of the size and shape of inorganic nanocrystals at various scales from nano to macrodomains.

In this paper, we propose the hypothesis that, in highly pure media, the cluster shape can be retained at various scales. Impurities and/or the additives can control the shape of the developing crystals by adsorption on selective sites. We demonstrate that the shape of clusters is retained at the nanoscale. This is supported by structural studies and both experiment and simulated optical properties of nanocrystal assemblies. We compare the data to those obtained by using a large variety of techniques and observation of crystal growth in nature.

Source : Control of the size and shape of inorganic nanocrystals at various scales from nano to macrodomains. M.P. Pileni J. Phys. Chem. C 111, 2007, 9019-9038

peer journals

Self-assembly of inorganic nanocrystals: Fabrication and collective intrinsic properties. 

In this Account, we demonstrate that the ordering of nanocrystals over long distances in 3D superlattices, called supracrystals, can lead to unexpected results: the emergence of collective intrinsic properties. The shape of the nanocrystal organization at the mesoscopic scale also induces new physical properties. In addition, we show that nanocrystals can be used as masks for lithography.

Source : Self-assembly of inorganic nanocrystals: Fabrication and collective intrinsic properties. M.P. Pileni Acc. of Chem. Res., 2007, 40, 685-693.

 

peer journals

Use of reverse micelles to make either spherical or worm-like palladium nanocrystals: Influence of stabilizing agent on nanocrystal shape.

Depending on thewater content, reversemicelles induce the formation of fccmetallic palladiumworm-like nanocrystals made of spheres. After extraction from the nanoreactor, either spheres or worm-like nanocrystals are obtained, and it was found that the binding energy between the coating agent and the Pd surface is a key parameter in shape control (i.e., in the surface reconstruction).

Source : Use of reverse micelles to make either spherical or worm-like palladium nanocrystals: Influence of stabilizing agent on nanocrystal shape. K. Naoe, C. Petit and M.P. Pileni Langmuir, 2008, 24, 2792-2798.

peer journals

2D self-organization of core/shell COhcp/Co nanocrystals.

In this paper we report the preparation of ordered hexagonal 2D arrays of core/shell Cohcp/CoO nanocrystals. A full structural investigation has been carried out using high-resolution transmission electron microscopy, electron diffraction, and electron energy-loss spectroscopy.

Source : 2D self-organization of core/shell COhcp/Co nanocrystals. I. Lisiecki, M. Walls, D. Parker and M.P. Pileni, Langmuir, 2008, 24, 4295-4299.

peer journals

How do self-ordered silver nanocrystals influence their growth into triangular single crystals ?

Thin triangular silver single crystals are obtained by annealing self-ordered 5 nm silver nanocrystals coated with decanethiol at 50 ° C and deposited on highly oriented pyrolitic graphite (HOPG). With the annealing time, the nanocrystals coalesce progressively in the 2D hexagonal arrays and 3D face-centered cubic (fcc) superlattices. By controlling the ordering degree of the nanocrystal assemblies, we observe that the size of the ordered domains tunes the final size of the triangles.

Source : How do self-ordered silver nanocrystals influence their growth into triangular single crystals ? A.I. Henry, A. Courty, N. Goubet and M.P. Pileni J. Phys. Chem. C , 2008, 112, 48-52.

peer journals

Motif Transfer: Down to 3 nm in Resolution Using Individual Nanocrystals.

We demonstrate that individual ferrite nanocrystals used as etching masks are easily transferred on HOPG (High Oriented Pyrolitic Graphite) with a high resolution whereas silicon (SiO2/Si) substrate is too robust compared to the mask to permit the best transfer. There are various procedures for transferring individual ferrite nanocrystals to obtain similar nanostructures with different surfaces. Under the best experimental conditions, the smallest spacing is equal to or less than 3 nm. This distance has, to our knowledge, never been reported in the literature.

Source : Motif Transfer: Down to 3 nm in Resolution Using Individual Nanocrystals. D. Ingert and M-P Pileni Adv. Mat., 2008, 20, 4334-4342.