Non classé

Influence of Cracks on the Optical Properties of Silver Nanocrystals Supracrystal Films

J.Wei, C.Deeb, J.L.Pelouard, M.PLPileni ACS Nano DOI: 10.1021/acsnano.8b07435

Physical properties of nanocrystals self-assembled into 3D superlattices called supracrystals are highly specific with unexpected behavior. The best example to support such claim was given, through STM/STS experiments at low temperature, of very thick supracrystals (around 1000 layers) where it was possible to image the surpracrystal surface and study their electronic properties. From previous studies, we know the optical properties of Ag nanocrystals self-assembled in hexagonal network (2D) or forming small 3D superlattices (from around 2 to 7 layers) are governed by dipolar interactions. Here, we challenge to study the optical properties of Ag supracrystals film characterized by large thicknesses (from around 27 to 180 Ag nanocrystals layers). In such experimental conditions, accordingtothe classical Beer-Lambert law, the absorption of Ag films is expected to be very large and the film transmission is closed to zero. Very surprisingly, we observe reduced transmission intensity with an increase of the notch linewidth, in the 300-800 nm wavelength range, as the supracrystal film thickness increased. By calculating the transmission through the supracrystal films, we deduced that the films were dominated by the presence of cracks with wetting layers existing at their bottoms. This result was also confirmed by optical micrographs. The cracks widths increased with increasing the film thickness leading to more complex wetting layers. We also demonstrated the formation of small Ag clusters at the nanocrystal surface. These results pave the way towards a class of plasmonic supracrystals.

 

Non classé

Intrinsic behavior of FCC supra crystals of nanocrystals self organized on mesoscopic scale

M.P. Pileni Chaos,2005,15, 47504-47510.

We describe intrinsic behavior due to the high ordering of nanocrystals at the mesoscopic scale. The first example shows well-defined columns in the formation of cobalt nanocrystals when an applied magnetic field is applied during the evaporation process. Collective breathing properties between nanocrystals are demonstrated. In both cases, these features are observed when the nanocrystals are highly ordered in fcc supra-crystals.

Non classé

From wormlike to spherical palladium nanocrystals: Digestive ripening.

Similar wormlike palladium nanocrystals are produced by various synthetic methods such as reverse micelles and phase-transfer reactions. Palladium nanocrystals, stabilized by dodecylamine as a coating agent, are produced by chemical reduction of PdCl2  by sodium borohydride, NaBH4. A soft digestive ripening process, without any reflux, in which wormlike palladium particles go to sphere is observed in the presence of a rather large amount of dodecanethiol. The wormlike particle diameter is similar to that of the spheres produced.

 

 

source.. From wormlike to spherical palladium nanocrystals: Digestive ripening.
K. Naoe, C. Petit and M.P. Pileni J. Phys. Chem. C,2007,111, 16249-16254.

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