Da Wang MSc

Ornstein Laboratory, room 0.14
Princetonplein 1, 3584 CC Utrecht
P.O. Box 80 000, 3508 TA Utrecht
The Netherlands
phone: +31(0)30 253 1287
secretariat: +31(0)30 253 2952
e-mail: d.wang@uu.nl

Research

Promotor: Prof.dr. A. van Blaaderen
Employed since August 2012
Funded by EU-ERC Advanced Grant

Self-assembled supraballs from nanocrystals

 

 

Scanning transmission electron microscopy (STEM), Emulsification, Nanocrystal synthesis

Colloidal supraparticles which are assembled from size- and morphology- controlled nanoparticles, combine multi scale properties of the single particles such as quantum confinement and localized plasmon resonances with collective effects resulting from being arranged on a 3D lattice with colloidal properties to be self assembled in a second step. One way to realize such colloidal supraparticles is by suspending nanocrystals in emulsion droplets of a low boiling point solvent in water and slowly evaporating the solvent. In this way the nanocrystals are forced to self-assemble into supraballs. By tuning the concentrations and types of nanocrystals, supraballs with different structures and sizes can be obtained [1-3].

The goal of this research is to extend the spherical confinement method to binary particles systems and anisotropic particles systems. For instance, 6.2 nm Au nanocrystals and 22.0 nm FexO/CoFe2O4 nanocrystals were used to synthesize binary supraballs. GdF3 rhombic shape nanocrystals [4] can also self-assemble the supraballs shown in Fig. 1. After freeze drying, the structure of the supraballs was studied with high-angle annular dark-field scanning transmission electron microscopy (HAADF STEM) and secondary electron scanning transmission electron microscopy (SE STEM) (Fig. 1). Work is in progress to study the structures of more complex supraballs by HAADF STEM tomography.

 

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Figure 1: A) SE STEM image of binary supraballs; B) HAADF STEM image of binary supraballs; C) HAADF STEM image of GdF3 supraballs (inset: TEM image of rhombic shape GdF3 nanocrystals; collaboration with the C. B. Murray group (U. Pennsylvania, USA)). (Scale bars: A and B = 50 nm)

 

[1] V. N. Manoharan et al. Science 301, 483-487 (2003)

[2] T. Wang et al. Science 338, 358-363 (2012)

[3] B. de Nijs et al. Nature Materials Doi:10.1038/nmat4072 (2014)

[4] T. Paik et al. Nano Letters 13, 2952-2956 (2013)

Nanocrystals, Emulsion, HAADF-STEM tomography

Colloidal supraparticles which are assembled from size- and morphology- controlled nanoparticles, combine multi scale properties of the single particles such as quantum confinement and localized plasmon resonances with collective effects resulting from being arranged on a 3D lattice. In addition properties on longer length scales, e.g. photonic, can be controlled by a subsequent self-assembly step. One way to realize such colloidal supraparticles is by suspending nanocrystals in emulsion droplets of a low boiling point solvent in water and slowly evaporating the solvent. In this way the nanocrystals are forced to self-assemble into supraballs. By tuning the concentrations and types of nanocrystals, supraballs and differently shaped supraparticles with different structures and sizes can be obtained.

The goal of this research is to extend the spherical confinement method to binary particles systems and anisotropic particles systems. For instance, 6.5 nm PbSe nanocrystals and 8.5 nm PbSe nanocrystals were used to synthesize binary supraballs with a bulk AB2 phase. GdF3 rhombic shape nanocrystals can also self-assemble into supraballs with liquid-crystal-like interior structure. We found 16.1 nm Ag/8.7 nm Fe3O4 and 6.5 nm PbSe/9.3 nm Au self-assembled into Janus shape binary supraballs or core-shell binary supraballs, respectively, which probably can be ascribed to attractive interactions between different ligands. After freeze drying, the structure of the supraballs was studied with high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) tomography and secondary electron scanning transmission electron microscopy (SE-STEM) (Fig. 1). By coating the supraballs with a thin (~50 nm) layer of porous or non-porous silica, the particles become more robust and do not deform by drying on a substrate. To study how the structure of the more complex supraballs is affected by the spherical confinement, work is in progress by advanced electron microscopy techniques.

Wang_Figure

Figure 1: A) HAADF-STEM image of PbSe/PbSe binary supraballs; B) HAADF STEM image of GdF3 supraballs (inset: TEM image of rhombic shape GdF3 nanocrystals); C) HAADF-STEM image of Ag/Fe3O4 Janus supraballs; D) HAADF-STEM image of PbSe/Au core-shell supraballs; E) SE-STEM image of PbSe/Au core-shell supraballs; F) TEM image of the Au supraballs coated with mesoporous silica shell. (Scale bars: A, B, C and F = 50 nm, D and E= 100 nm) (Supraballs in Fig A, B, D and E: collaboration with the C. B. Murray group (U. Pennsylvania, USA))