Orientationally ordered silicon nanocrystal cuboctahedra in superlattices

This is an open access article published under an ACS AuthorChoice License. See Standard ACS AuthorChoice/Editors' Choice Usage Agreement - https://pubs.acs.org/page/policy/authorchoice_termsofuse.htmlUniform silicon nanocrystals were synthesized with cuboctahedral shape and passivated with 1-dodecene capping ligands. Transmission electron microscopy, electron diffraction, and grazing incidence wide-angle and small-angle X-ray scattering show that these soft cuboctahedra assemble into face-centered cubic superlattices with orientational order. The preferred nanocrystal orientation was found to depend on the orientation of the superlattices on the substrate, indicating that the interactions with the substrate and assembly kinetics can influence the orientation of faceted nanocrystals in superlattices

Etude du comportement acoustique des nouveaux materiaux piezoelectriques sous pression hydrostatique

SIGLEINIST T 74786 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Etude du comportement acoustique des nouveaux materiaux piezoelectriques sous pression hydrostatique

SIGLEINIST T 74786 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Organisation structurale des accepteurs secondaires dans le photosysteme I des membranes photosynthetiques

SIGLEAvailable from INIST (FR), Document Supply Service, under shelf-number : T 78918 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Directing and characterizing silicon nanocrystal self-assembly

Silicon nanocrystals or quantum dots are non-toxic and exhibit unique size tunable opto-electronic properties. Their bright photoluminescence as well as their ability to generate more than one electron per photon absorbed make them good candidates for both bioimaging and photovoltaics applications. Their surface can be functionalized with different ligands that protect them against oxidation and allow them to be dispersed and stable in a variety of solvents. Dodecane capped silicon nanocrystals can be dispersed in non-polar solvents such as hexane, chloroform or toluene for years without aggregating nor losing their optical properties. When deposited on a substrate under certain conditions, dodecane capped silicon nanocrystals can self-assemble into 2D or 3D periodic arrays of quantum dots called superlattices. These ordered structures of nanocrystals can potentially enhance the conductivity of the nanocrystal thin film which would be helpful for photovoltaic applications. In order to perform charge transport measurements through superlattices, large uniform ordered nanocrystal films must be achieved. Two deposition processes are studied and optimized to lead to the formation of several microns large both 2D and 3D silicon nanocrystals superlattices. A model is developed to understand the superlattice growth mechanism and several parameters are found to influence the superlattice morphology. Silicon nanocrystals can also be functionalized with chromophores to enhance their optical absorption. This can improve efficiencies of self-assembled quantum dots solar devices. Silicon nanocrystals functionalized with pyrene units are studied using transient absorption spectroscopy. They exhibit enhanced optical absorption and efficient carrier multiplication via energy transfer from the pyrene unit to the nanocrystal core. Finally, carboxylate terminated silicon nanocrystals are stable in water over a wide range of pH which makes them suitable for self-assembly in aqueous media. Incorporating biological receptor-substrate sites to the nanocrystal surface can permit recognition-driven self-assembly. Carbodiimide activation is commonly used to biofunctionalize nanoparticles. This chemistry is tested to attach an amine terminated PEG (polyethylene glycol) molecule to silicon nanocrystals. PEG functionalization is found to improve silicon nanocrystal photoluminescence stability.Chemical Engineerin

Bubble Assemblies of Nanocrystals: Superlattices without a Substrate

A method was developed to create free-standing nanocrystal films in the form of solidified bubbles. Bubbles of octadecanethiol-capped gold nanocrystals were studied by in situ grazing incidence small-angle X-ray scattering (GISAXS) to determine how the absence of an underlying substrate influences a disorder–order transition of a nanocrystal superlattice. We find that the presence of the substrate does not significantly change the nature of the disorder–order transition but does lead to reduced interparticle separation and reduced thermal expansion. Bubble assemblies of silicon and copper selenide nanocrystals are also demonstrated

Orientationally ordered silicon nanocrystal cuboctahedra in superlattices

This is an open access article published under an ACS AuthorChoice License. See Standard ACS AuthorChoice/Editors' Choice Usage Agreement - https://pubs.acs.org/page/policy/authorchoice_termsofuse.htmlUniform silicon nanocrystals were synthesized with cuboctahedral shape and passivated with 1-dodecene capping ligands. Transmission electron microscopy, electron diffraction, and grazing incidence wide-angle and small-angle X-ray scattering show that these soft cuboctahedra assemble into face-centered cubic superlattices with orientational order. The preferred nanocrystal orientation was found to depend on the orientation of the superlattices on the substrate, indicating that the interactions with the substrate and assembly kinetics can influence the orientation of faceted nanocrystals in superlattices