peer journals

Au nanocrystal superlattices: nanocrystallinity, vicinal surfaces, and growth processes

D.M. Smilgies,Ruipeng Liand M. P. Pileni Nanoscale, 2018, DOI: 10.1039/C8NR04606A

Vicinal Au supracrystal surfaces were prepared  from Ausinglesingle domain nanocrystals (NCs) whereas by replacing Ausingleby their polycrystalline counterparts common low-energy supracrystal surfaces are produced.  By analogy to atomic crystalline surfaces, we propose a mechanism to explain formation of such unexpected supracrystal vicinal surfaces, composed of only AusingleNCs are non-compact (bctstructure) with coherent alignment of the atomic planes oriented along the [111] superlattice axis and a slight tilt configuration  (8.1°) of NCs.  In presence of Co() NCs, these Ausinglesupracrystals loose both the slightly tilted configuration of NCs and their orientational order leading to a superlattice transition from bctto fcc. In contrast, supracrystals of AupolyNCs are unsensitive to the presence of Co() NCs. These intriguing structural changes obtained with Ausinglecompared to Aupolysupracrystals in absence and presence of Co() NCs could explain the formation of vicinal surfaces. Note, the solvent used to disperse the nanocrystals plays a key parameter in the formation of supracrystal vicinal surfaces. Here a new analogy between supracrystals and atomic crystals is presented.

peer journals

Self-organization of inorganic nanocrystals.

Self-organizations of inorganic nanocrystals in 1D, 2D and 3D superlattices are described. In the latter case, supra-crystals with face-centred-cubic (fcc) structure are demonstrated. Collective properties due to the nanocrystal organization are described. These properties are either intrinsic or due to dipolar interactions.

 

Source:

Self-organization of inorganic nanocrystals.  M.P.Pileni J. Phys.: Condens. Matter,2006, 18, S67–S84.

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.