Abstract: Here we will demonstrate that the crystallinity of nanoparticles is controlled and plays a marked role both in supracrystal growth mechanism and specific chemical and physical properties are pointed when they are self assembled in 2D and 3D superlattices. These properties (electron, mechanical, vibrational) are observed when nanocrystals are self-ordered in 3D superlattices called supracrystals. Concerning the isolated nanocrystals, the change in the absorption profile of the localized surface plasmon resonance spectrum observed with polycrystalline and single domain nanocrystals is attributed to internal structural defects like twins, whose effect on the optical properties is not accounted for using current models in the literature The nanocrystallinity affects the quadrupolar vibrational modes (l=2) of Au nanocrystals whereas it does not markedly perturb the vibrational breathing mode (l=0) of nanocrystals. The latter was observed for both Au and Co nanocrystals. Note that the nanocrystallinity does not play any role on the formation of CoO when isolated Co nanocrystals on a substrate are subjected to oxygen. When the same nanocrystals are self ordered in a 2D hexagonal compact network, the final structure of Co nanocrystals subjected to oxygen at 200°C, show a marked change with the nanocrystallinity and nanocrystal sizes. The general trend shows that single domain nanocrystals induced hollow CoO nanocrystals whereas polycrystals show the formation of core-shell nanoparticles. Note that such various steps are also control by the nanocrystal size. Very recently we grew binary supracrystals (Co/Ag, Ag/Ag and Co/Co) with the small nanocrystals placed in the interstices of the large ones. Various structures were detected and usually agree with the hard sphere model developed for atomic binary systems. With Co/Ag nanocrystals this agrees by using superparamagnetic Co nanocrystals. With ferromagnetic Co nanocrystals, the magnetic properties markedly change the structure and “quasi”supracrystals are produced. Similarly by using a mixture of single domain Co and Au nanocrystals, Au supracrystals with vicinal facets (high index plane) were observed for the first time. It is demonstrated such usually thermodynamically unstable assemblies depend on the nanocrystallinity of nanocrystals involved in these supracrystals. 

About the Speaker: Prof. M.P Pileni is a Distinguished Professor at University P&M Curie, UPMC, Adjunct Professor of chemistry and biochemistry in the school of chemistry and biochemistry at Georgia Tech, Atlanta, USA and Senior Scientist in Nuclear Center. She is member (1999- at present) and chair (2004-2010) of Institut Universitaire de France, IUF. She has published more 400 articles with 16,997 citations, 49.55 average citations per item and h factor of 67. Prof. Pileni research has been highly interdisciplinary over her entire scientific career. Her major breakthroughs are: (i) A fundamental understanding of the kinetics and mechanisms in colloidal solutions guided me in the preparation of either nanocrystals with different sizes and shapes or the chemical modification of enzymes. (ii) Formation of thermodynamically stables states of self-assemblies either by using surfactant molecules (supraaggregates) or inorganic nanocrystals (supracrystals). (iii) Collective optical and magnetic properties induced by dipolar interactions and due to the nanocrystal arrangements in 1D, 2D and 3D superlattices. (iv) Physical intrinsic properties such as vibrational, magnetic and crystal growth related to the nanocrystals ordering in supracrystals (3D). (v) Chemical intrinsic properties due to nanocrystals ordering. Prof. Pileni received the Langmuir award of the American Chemical Society, the lecture award of the Japanese Chemical Society, the Research Award of the Alexander von Humboldt Foundation in Germany, the Descartes-Huygens Prize of the Royal Netherlands Academy of Arts, Science and Emila Valori from the French Academy of Sciences, Catalán-Sabatier Lectureship award from the Royal Society of Chemistry of Spain (RSEQ) Life Achievement Award. In 2010 from Journal Colloid Interface Science, she received the ERC Advanced Grant Award (European Research Council).  

Date&Time: August 20, 2014 (Wednesday), 10:00-11:00 a.m. 
Location: 606 Conference Room, No.3 Heqing Road, Haidian District