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NANOSOLID Report Summary

Project ID: 306733
Funded under: FP7-IDEAS-ERC
Country: Switzerland

Mid-Term Report Summary - NANOSOLID (Chemically Engineered Nanocrystal Solids)

Many materials in the form of well-defined nanoscale crystals (“nanocrystals”) exhibit unique properties due to size effects and large surface-to-volume ratios. Yet it is clear that the utilization of nanomaterials in modern technologies requires their integration into solid-state structures with programmable electronic, magnetic and optical properties. The clear challenge is the rational design of this novel type of condensed matter, in which the size-tunable individual properties of nanoscale building blocks are enhanced by their interactions and by the macroscopic properties of their ensembles. The project NANOSOLID develops new strategies for the bottom-up assembly of inorganic entities of various dimensionalities into functional inorganic materials. Two objecties are being addressed: (i) the proper design, coupled with the understanding, of nanocrystal surface chemistry, and (ii) the unconventional assembly of nanocrystals into dense nanostructured solids. The union of classical and modern concepts from molecular and supramolecular chemistry is used to develop nanosolids with predictable geometries and functionalities.

A novel class of colloidal semiconductors has been pioneered in this prject. Monodisperse colloidal nanocrystals (NCs, 4-15 nm) of fully inorganic cesium lead halide perovskites (CsPbX3, X=Cl, Br, and I or mixed halide systems Cl/Br and Br/I) using inexpensive commercial precursors. Their bandgap energies and emission spectra are readily tunable over the entire visible spectral region of 410-700 nm. The photoluminescence of CsPbX3 NCs is characterized by narrow emission line-widths of 12-42 nm, wide color gamut covering up to 140% of the NTSC color standard, high quantum yields of up to 90% and radiative lifetimes in the range of 4-29 ns. Post-synthestic chemical transformations of colloidal NCs, such as ion-exchange reactions, provide an avenue to compositional fine tuning or to otherwise inaccessible materials and morphologies. While cation-exchange is facile and commonplace, anion-exchange reactions have not received substantial deployment. A fast, low-temperature, deliberately partial or complete anion-exchange can be observed in CsPbX3 NCs. CsPbX3 NCs exhibit also a low-threshold (5±1 µJ cm-2) for amplified spontaneous emission and lasing in the entire visible spectral range (440-700 nm). At present, the group of M. V. Kovalenko focuses on the understanding of early-stage kinetics of the nucleation and growth of CsPbX3 NCs, their surface chemistry and photophysics.

Novel inorganic capping ligands, such as halometalates and oxometalates, were applied to nanocrystal surfaces in order to impart novel optoelectronic or catalytic functionalities. For the programmable assembly of highly charged inorganic-capped nanocrystals,a simple and general methodology, based on host–guest coordination of chalcogenidometalate-capped NCs with macrocyclic ethers (crown ethers and cryptands), has been developed. It enables the solubilization of inorganic-capped NCs in solvents of any polarity and improving the ability to form NC superlattices. The corona of organic molecules can also serve as a convenient knob for the fine adjustment of charge transport and photoconductivity in films of NCs. In particular, high-infrared-photon detectivities of up to 3.3 × 10e11 Jones with a fast response (3ߙdB cut-off at 3ߙkHz) at the wavelength of 1,200ߙnm were obtained with films of PbS/K3AsS4/decyl-18-crown-6 NCs.

A new kind of long-range ordered binary superlattices comprising atomically defined inorganic clusters and colloidally synthesized nanocrystals was demonstrated. In a model system, surfactant-encapsulated, nearly spherical giant polyoxometalate clusters containing 2.9 nm polyoxomolybdate or 2.5 nm polyoxovanadomolybdate cores were combined with monodisperse colloidal semiconductor nanocrystals (PbS, CdSe, PbS/CdS; 4–11 nm). The results are rationalized on the basis of dense packing principles of sterically stabilized particles with predominantly hard-spherelike interparticle interactions. By varying the size-ratios and relative concentrations of constituents, thermodynamically stable binary packings of hard-spheres isostructural with NaCl, AlB2, and NaZn13 lattices and also CaCu5-type lattice and aperiodic quasicrystals with 12-fold symmetry were obtained. These results suggest that other kinds of cluster materials such as fullerenes and magic-sized metallic and semiconductor clusters can also be integrated into supramolecular assemblies with nanocrystals. Furthermore, synergistic effects are expected from the combination of redox and catalytic properties of polyoxometalates with excitonic and plasmonic properties of inorganic nanocrystals.

For the characterization of nanocrystal surfaces, a novel NMR method that utilizes dynamic nuclear polarization of enhancing the signals has been utilized. Overall, there is a lack of analytical methods to selectively and discriminately probe the core, the surface and capping ligands of nanocrystals. A general concept for studying a broad range of nanocrystals such as CdSe, CdTe, InP, PbSe, PbTe, CsPbBr3, etc., capped with both organic and inorganic surface capping ligands, through DNP NMR has been developed. DNP can enhance surface NMR signals by factors of 10–100, thereby reducing the measurement times by 2–4 orders of magnitude. 1D DNP enhanced spectra acquired in this way are shown to clearly distinguish the surface atoms from those of the core, and environmental effects such as oxidation. Furthermore, 2D NMR correlation experiments, which were previously inconceivable for nanocrystal surfaces, are demonstrated to be readily performed with DNP and provide the bonding motifs between the NC surfaces and the capping ligands.


Maksym Kovalenko, (Assistant Professor)
Tel.: +41 44 633 41 56
Record Number: 183366 / Last updated on: 2016-05-27
Information source: SESAM