The thermal reshaping and its influence on the plasmonic properties of gold nanostars are investigated using a combination of in situ tomography and a state-of-the-art fast acquisition approach.
Colloidal
CsPbBr3 nanocrystals (NCs) have emerged as
promising candidates for various opto-electronic applications, such
as light-emitting diodes, photodetectors, and solar cells. Here, we
report on the self-assembly of cubic NCs from an organic suspension
into ordered cuboidal supraparticles (SPs) and their structural and
optical properties. Upon increasing the NC concentration or by addition
of a nonsolvent, the formation of the SPs occurs homogeneously in
the suspension, as monitored by in situ X-ray scattering measurements.
The three-dimensional structure of the SPs was resolved through high-angle
annular dark-field scanning transmission electron microscopy and electron
tomography. The NCs are atomically aligned but not connected. We characterize
NC vacancies on superlattice positions both in the bulk and on the
surface of the SPs. The occurrence of localized atomic-type NC vacancies—instead
of delocalized ones—indicates that NC–NC attractions
are important in the assembly, as we verify with Monte Carlo simulations.
Even when assembled in SPs, the NCs show bright emission, with a red
shift of about 30 meV compared to NCs in suspension.
Nanoporous Pt based
nanoparticles (NP’s) are promising fuel
cell catalysts due to their high surface area and increased electrocatalytic
activity toward the ORR. In this work a direct double-pulse electrodeposition
procedure at room temperature is applied to obtain dendritic Pt structures
(89 nm diameter) with a high level of porosity (ca. 25%) and nanopores
of 2 nm protruding until the center of the NP’s. The particle
morphology is characterized using aberration-corrected high angle
annular dark field scanning transmission electron microscopy (HAADF-STEM)
and electron tomography (ET) combined with field emission scanning
electron microscopy (FESEM) and macroscopic electrochemical measurements
to assess their activity and stability toward the ORR. Macroscopic
determination of the active surface area through hydrogen UPD measurements
in combination with FESEM and ET showed that a considerable amount
of the active sites inside the pores of the low overpotential NP’s
were accessible to oxygen species. As a result of this accessibility, up to a 9-fold enhancement of
the Pt mass corrected ORR activity at 0.85 V vs RHE was observed at
the highly porous structures. After successive potential cycling upward
to 1.5 V vs RHE in a deaerated HClO4 solution a negative
shift of 71 mV in half-wave potential occurred. This decrease in ORR
activity could be correlated to the partial collapse of the nanopores,
visible in both the EASA values and 3D ET reconstructions.
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