peer journals

Supra and Nano crystallinity: Specific properties related to crystal growth mechanisms and nanocrystallinity.

The natural arrangement of atoms or nanocrystals either in well-defined assemblies or in a disordered fashion induces changes in their physical properties. For example, diamond and graphite show marked differences in their physical properties though both are composed of carbon atoms. Natural colloidal crystals have existed on earth for billions of years. Very interestingly, these colloidal crystals are made of a fixed number of polyhedral magnetite particles uniform in size. Hence, opals formed of assemblies of silicate particles in the micrometer size range exhibit interesting intrinsic optical properties. A colorless opal is composed of disordered particles, but changes in size segregation within the self-ordered silica particles can lead to distinct color changes and patterning. In this Account, we rationalize two simultaneous supracrystal growth processes that occur under saturated conditions, which form both well-defined 3D superlattices at the air!liquid interface and precipitated 3D assemblies with well-defined shapes. The growth processes of these colloidal crystals, called super- or supracrystals, markedly change the mechanical properties of these assemblies and induce the crystallinity segregation of nanocrystals. Therefore, single domain nanocrystals are the primary basis in the formation of these supracrystals, while multiply twinned particles (MTPs) and polycrystals remain dispersed within the colloidal suspension. Nanoindentation measurements show a drop in the Young’s moduli for interfacial supracrystals in comparison with the precipitated supracrystals. In addition, the value of the Young’s modulus changes markedly with the supracrystal growth mechanism. Using scanning tunneling microscopy/spectroscopy, we successfully imaged very thick supracrystals (from 200 nm up to a few micrometers) with remarkable conductance homogeneity and showed electronic fingerprints of isolated nanocrystals. This discovery of nanocrystal fingerprints within supracrystals could lead to promising applications in nanotechnology.

Source : Supra and Nano crystallinity : Specific properties related to crystal growth mechanisms and nanocrystallinity. M.P.Pileni, Account Chem Res., 2012,45, 1965-1972.

 

peer journals

Modulating the Physical Properties of Isolated and Self-Assembled Nanocrystals by Change in Their Nanocrystallinity

For self-assembled nanocrystals in three-dimensional (3D) superlattices, called supracrystals, the crystalline structure of themetal nanocrystals (either single domain or polycrystalline) or nanocrystallinity is likely to induce signi! cant changes in the physical properties. Previous studies demonstrated that spontaneous nanocrystallinity segregation takes place in colloidal solution upon selfassembling of 5 nm dodecanethiol-passivated Au nanocrystals. This segregation allows the exclusive selection of single domain and polycrystalline nanoparticles and consequently producing supracrystals with these building blocks. Here, we investigate the in » uence of nanocrystallinity on di# erent properties of nanocrystals with either single domain or polycrystalline structure. In particular, the in » uence of nanocrystallinity on the localized surface plasmon resonance of individual nanocrystals dispersed in the same dielectric media is reported. Moreover, the frequencies of the radial breathing mode of single domain and polycrystalline nanoparticles are measured. Finally, the orientational ordering of single domain nanocrystals markedly changes the supracrystal elastic moduli compared to supracrystals of polycrystalline nanocrystals.

Source : Modulating the Physical Properties of Isolated and Self-Assembled Nanocrystals by Change in Their Nanocrystallinity. N. Goubet, C.Yan, D. Polli, H.Portalès, I.Arfaoui, G. Cerullo and M. P. Pileni Nano Lett., 2013,13, 504−508.

peer journals

Soft Supracrystals of Au Nanocrystals with Tunable Mechanical Properties

The elastic properties of highly ordered three-dimensional colloidal crystals of gold nanocrystals (called supracrystals) are reported. This study is based on the simultaneous growth of two kinds of gold nanocrystal supracrystals that range in size from 5 nm to 8 nm: interfacial supracrystals and precipitated supracrystals. The elastic properties are deduced from nanoindentationmeasurements performed with an atomic force microscope. The Young’s modulus of the interfacial supracrystals, which grow layer-by-layer and formwell-defined films, is compared to that of precipitated supracrystals, which are produced by homogeneous growth in solution. For the precipitated supracrystals, characterized by a thickness larger than 1 μ  m, the Oliver and Pharr model is used to determine the elastic moduli, which are in the gigapascal range and decrease with increasing nanocrystal size. For the interfacial supracrystals, with 300 nm average thickness, a second model (plate model) is applied in addition to the Oliver and Pharr model. These two models confirm independently that the interfacial fi lms are very soft with Young’s modulus in the range of 80–240 MPa. This result reveals a totally new feature of nanocrystal solids, never emphasized before. It is shown that these changes in the Young’s modulus are related to the supracrystal growth mechanism.

Source : Soft Supracrystals of Au Nanocrystals with Tunable Mechanical Properties C.Yan, I.Arfaoui, N.Goubet and M.P.Pileni Adv.Funct.Mat., 2013, 23, 2315-2321.

peer journals

Assessing the Relevance of Building Block Crystallinity for Tuning the Stiffness of Gold Nanocrystal Superlattices.

We study the influence of the size and nanocrystallinity of dodecanethiol- coated gold nanocrystals (NCs) on the stiffness of 3D selfassembled NC superlattices (called supracrystals). Using single domain and polycrystalline NCs as building blocks for supracrystals, itis shown that the stiffness of supracrystals can be tuned upon change in relative amounts of single and polycrystalline NCs.

Source : Assessing the Relevance of Building Block Crystallinity for Tuning the Stiffness of Gold Nanocrystal Superlattices. C.Yan, H. Portalès, N. Goubet, I. Arfaoui, S. Sirotkin, A. Mermet and M.P. Pileni Nanoscale, 2013, 5, 9523–9527.

peer journals

Mechanical properties of Au supracrystals tuned by flexible ligand interaction. 

Here mechanical properties of face cubic centered colloidal crystals obtained out of equilibrium by solvent evaporation of coated Au nanocrystals suspension, called supracrystals, are reported as a function ligand chain length (n ) and interparticle edge-to-edge distance within the supracrystals (δpp ) for two nanocrystal sizes (d ). Young’ s modulus (E* ) and hardness (H ) are independent of δpp  and of the supracrystal morphology. Both E*  and H  are in the range of few tenths of a MPa to a few GPa. Tuning of δpp  by 50% is achieved by controlling the solvent vapor pressure (Pt ) during the evaporation process. For any nanocrystal size, at Pt  = 0, E*and H  values markedly increase with increasing n  from 12 to14. At Pt = 39% and 75%, such dependency disappears. This trend diff ers from classical nanocomposite materials and is attributed to a change in the conformation of fl exible ligands with n  and to free thiol-containing molecules trapped in the supracrystallattices.

Source : Mechanical properties of Au supracrystals tuned by flexible ligand interaction.  M.Gauvin, Y. Wan, I. Arfaoui and M.P. Pileni J.Phys.Chem.C.,2014, 118, 5005−5012

peer journals

Size and nanocrystallinity controlled gold nanocrystals: synthesis, electronic and mechanical properties.

The influence of nanocrystallinity on the electronic and mechanical properties of metal nanoparticles is still poorly understood, due to the difficulty in synthesizing nanoparticles with a controlled internal structure.Here, we report on a new method for the selective synthesis of Au nanoparticles in either a singledomainor a polycrystalline phase maintaining the same chemical environment. We obtain quasi-sphericalnanoparticles whose diameter is tunable from 6 to 13 nm with a resolution down to ≈0.5 nm and narrow size distribution (4–5%). The availability of such high-quality samples allows the study of the impact of the particle size and nanocrystallinity on a number of parameters, such as plasmon dephasing time, electron– phonon coupling, period and damping time of the radial breathing modes.

Source : Size and nanocrystallinity controlled gold nanocrystals: synthesis, electronic and mechanical properties. N. Goubet,  I. Tempra,  J. Yang,  G. Soavi,  D. Polli,  G. Cerullo  and M. P. Pileni Nanoscale, 2015,7, 3237–3246.

 

peer journals

Morphology, nanocrystallinity and elastic properties of single domain ε-Co supracrystals

We report on the elastic modulus of 3D superlatticesof single domain ε -Co nanocrystals self-assembled in face-centered cubic structures, so-called supracrystals. The effects of nanocrystal size, probe size, and supracrystal morphology on the elasticproperties of supracrystals are investigated by nanoindentation measurements using an atomic force microscope. We show that elastic moduli of supracrystals of single domain ε -Co nanocrystals are invariant on varying the nanocrystal size and supracrystal morphology (fi lms or faceted shape) produced through heterogeneous (solvent evaporation) growth process. A mechanical model is proposed to analyze elastic properties of supracrystals that differ from classical composite materials. These results are explained interms of nanocrystallinity, that is, the crystalline structure of nanocrystals, which is a key parameter in achieving supracrystals of diff erent nanocrystal sizes with robust elastic properties.

Source : Morphology, nanocrystallinity and elastic properties of single domain ε-Co supracrystals. M.Gauvin, N. Yang, E.Barthel, I.Arfaoui, J.Yang,  P.A. Albouy and M.P.Pileni, J.Phys. Chem. C, 2015,119, 7483−7490.