Abstract: The increase in nonradiative pathways with decreasing emission energy reduces the luminescence quantum yield (QY) of near-infrared photoluminescent (NIR PL) metal nanoclusters. Efficient surface ligand chemistry can significantly improve the luminescence QY of NIR PL metal nanoclusters. In contrast to the widely reported but modestly effective thiolate ligand-to-metal core charge transfer, we show that metal-to-ligand charge transfer (MLCT) can be used to greatly enhance the luminescence QY of NIR PL gold nanoclusters (AuNCs). We synthesized water-soluble and colloidally stable NIR PL AuNCs with unprecedentedly high QY (similar to 25%) upon introduction of triphenylphosphonium moieties into the surface capping layer. By using a combination of spectroscopic and theoretical methods, we provide evidence for gold core-to-ligand charge transfer occurring in AuNCs. We envision that this work can stimulate the development of these unusually bright AuNCs for promising optoelectronic, bioimaging, and other applications.

Abstract: <script type='text/javascript'>document.write(unpmarked('We show the possibility to tune the pore size of mesoporous TiO2 templated by non-ionic block copolymers by adding different inorganic acids at well-chosen concentration. The effect of the inorganic anions on both the TiO2 cluster formation and the non-ionic block copolymers micelles is investigated to explain the experimental results.'));

Abstract: Nanocomposite systems and nanoparticle (NP) films are crucial for many applications and research fields. The structure-properties correlation raises complex questions due to the collective structure of these systems, often granular and porous, a crucial factor impacting their effectiveness and performance. In this framework, we investigate the optical and morphological properties of Ag nanoparticles (NPs) films and of Ag NPs/TiO₂ porous matrix films, one-step grown by supersonic cluster beam deposition. Morphology and structure of the Ag NPs film and of the Ag/TiO₂ (Ag/Ti 50-50) nanocomposite are related to the optical properties of the film employing spectroscopic ellipsometry (SE). We employ a simple Bruggeman effective medium approximation model, corrected by finite size effects of the nano-objects in the film structure to gather information on the structure and morphology of the nanocomposites, in particular porosity and average NPs size for the Ag/TiO₂ NP film. Our results suggest that SE is a simple, quick and effective method to measure porosity of nanoscale films and systems, where standard methods for measuring pore sizes might not be applicable.

Abstract: <script type='text/javascript'>document.write(unpmarked('Heterostructures consisting of semiconductors with controlled morphology and interfaces find applications in many fields. A range of axial, radial, and diameter-modulated nanostructures have been synthesized primarily using vapor phase methods. Here, we present a simple wet chemical routine to synthesize heterostructures of PbTe/Te using Te nanowires as templates. A morphology evolution study for the formation of these heterostructures has been performed. On the basis of these control experiments, a pathway for the formation of these nanostructures is proposed. Reduction of a Pb precursor to Pb on Te nanowire templates followed by interdiffusion of Pb/Te leads to the formation of a thin shell of PbTe on the Te wires. Controlled dewetting of the thin shell leads to the formation of cube-shaped PbTe that is periodically arranged on the Te wires. Using control experiments, we show that different reactions parameters like rate of addition of the reducing agent, concentration of Pb precursor and thickness of initial Te nanowire play a critical role in controlling the spacing between the PbTe cubes on the Te wires. Using simple surface energy arguments, we propose a mechanism for the formation of the hybrid. The principles presented are general and can be exploited for the synthesis of other nanoscale heterostructures.'));

Abstract: Self-assembly of inorganic nanoparticles has been used to prepare hundreds of different colloidal crystals, but almost invariably with the restriction that the particles must be densely packed. Here,we show that non–close-packed nanoparticle arrays can be fabricated through the selective removal of one of two components comprising binary nanoparticle superlattices. First, a variety of binary nanoparticle superlattices were prepared at the liquid-air interface, including several arrangements that were previously unknown. Molecular dynamics simulations revealed the particular role of the liquid in templating the formation of superlattices not achievable through self-assembly in bulk solution. Second, upon stabilization, all of these binary superlattices could be transformed into distinct “nanoallotropes”—nanoporous materials having the same chemical composition but differing in their nanoscale architectures.

Abstract: Synthetic methods that allow for the controlled design of well-defined Pt nanoparticles are highly desirable for fundamental catalysis research. In this work, we propose a strategy that allows precise and independent control of the Pt particle size and coverage. Our approach exploits the versatility of the atomic layer deposition (ALD) technique by combining two ALD processes for Pt using different reactants. The particle areal density is controlled by tailoring the number of ALD cycles using trimethyl(methylcyclopentadienyl) platinum and oxygen, while subsequent growth using the same Pt precursor in combination with nitrogen plasma allows for tuning of the particle size at the atomic level. The excellent control over the particle morphology is clearly demonstrated by means of in situ and ex situ X-ray fluorescence and grazing incidence small angle X-ray scattering experiments, providing information about the Pt loading, average particle dimensions, and mean center-to-center particle distance.

Abstract: <script type='text/javascript'>document.write(unpmarked('By depositing ceria on the surface of yttrium stabilized zirconia (YSZ) nanocrystals and further activation under high-temperature reducing conditions, a 13% mol. CeO2/YSZ catalyst structured as subnanometer thick, pyrochlore-type, ceria-zirconia islands has been prepared. This nanostructured catalyst depicts not only high oxygen storage capacity (OSC) values but, more importantly, an outstandingly stable redox response upon oxidation and reduction treatments at very high temperatures, above 1000 degrees C. This behavior largely improves that observed on conventional ceria-zirconia solid solutions, not only of the same composition but also of those with much higher molar cerium contents. Advanced scanning transmission electron microscopy (STEM-XEDS) studies have revealed as key not only to detect the actual state of the lanthanide in this novel nanocatalyst but also to rationalize its unusual resistance to redox deactivation at very high temperatures. In particular, high-resolution X-ray dispersive energy studies have revealed the presence of unique bilayer ceria islands on top of the surface of YSZ nanocrystals, which remain at surface positions upon oxidation and reduction treatments up to 1000 degrees C. Diffusion of ceria into the bulk of these crystallites upon oxidation at 1100 degrees C irreversibly deteriorates both the reducibility and OSC of this nanostructured catalyst.'));

Abstract: Oxidative etching was used to produce gold seeds of different sizes and crystal habits. Following detailed characterization, the seeds were grown under different conditions. Our results bring new insights toward understanding the effect of size and crystallinity on the growth of anisotropic particles, whilst identifying guidelines for the optimisation of new synthetic protocols of predesigned seeds.

Abstract: <script type='text/javascript'>document.write(unpmarked('The colloidal synthesis and assembly of semiconductor nanowires continues to attract a great deal of interest. Herein, we describe the single-step ligand-mediated synthesis of single-crystalline CsPbBr3 perovskite nanowires (NWs) directly from the precursor powders. Studies of the reaction process and the morphological evolution revealed that the initially formed CsPbBr3 nanocubes are transformed into NWs through an oriented-attachment mechanism. The optical properties of the NWs can be tuned across the entire visible range by varying the halide (Cl, Br, and I) composition through subsequent halide ion exchange. Single-particle studies showed that these NWs exhibit strongly polarized emission with a polarization anisotropy of 0.36. More importantly, the NWs can self-assemble in a quasi-oriented fashion at an air/liquid interface. This process should also be easily applicable to perovskite nanocrystals of different morphologies for their integration into nanoscale optoelectronic devices.'));

Abstract: Shape control in metal-organic frameworks still remains a challenge. We propose a strategy based on the capping agent modulator method to control the shape of ZIF-8 nanocrystals. This approach requires the use of a surfactant, cetyltrimethylammonium bromide (CTAB), and a second capping agent, tris(hydroxymethyl)aminomethane (TRIS), to obtain ZIF-8 nanocrystals with morphology control in aqueous media. Semiempirical computational simulations suggest that both shape-inducing agents adsorb onto different surface facets of ZIF-8, thereby slowing down their crystal growth rates. While CTAB molecules preferentially adsorb onto the {100} facets, leading to ZIF-8 particles with cubic morphology, TRIS preferentially stabilizes the {111} facets, inducing the formation of octahedral crystals. Interestingly, the presence of both capping agents leads to nanocrystals with irregular shapes and higher index facets, such as hexapods and burr puzzles. Additionally, the combination of ZIF-8 nanocrystals with other materials is expected to impart additional properties due to the hybrid nature of the resulting nanocomposites. In the present case, the presence of CTAB and TRIS molecules as capping agents facilitates the synthesis of metal nanoparticle@ZIF-8 nanocomposites, due to synergistic effects which could be of use in a number of applications such as catalysis, gas sensing and storage.

Abstract: Nanorattles are metallic core–shell particles with core and shell separated by a dielectric spacer. These
nanorattles have been identified as a promising class of nanoparticles, due to their extraordinary high
electric-field enhancement inside the cavity. Limiting factors are reproducibility and loss of axial symmetry
owing to the movable metal core; movement of the core results in fluctuation of the nanocavity dimensions
and commensurate variations in enhancement factor. We present a novel synthetic approach for
the robust fixation of the central gold rod within a well-defined box, which results in an axisymmetric
nanorattle. We determine the structure of the resulting axisymmetric nanorattles by advanced transmission
electron microscopy (TEM) and small-angle X-ray scattering (SAXS). Optical absorption and scattering
cross-sections obtained from UV-vis-NIR spectroscopy quantitatively agree with finite-difference
time-domain (FDTD) simulations based on the structural model derived from SAXS. The predictions of
high and homogenous field enhancement are evidenced by scanning TEM electron energy loss spectroscopy
(STEM-EELS) measurement on single-particle level. Thus, comprehensive understanding of
structural and optical properties is achieved for this class of nanoparticles, paving the way for photonic
applications where a defined and robust unit cell is crucial.

Abstract: Large efforts have been made trying to understand the origin of the high catalytic activity of dealloyed nanoporous gold as a green catalyst for the selective promotion of chemical reactions at low temperatures. Residual silver, left in the sample after dealloying of a gold-silver alloy, has been shown to have a strong influence on the activity of the catalyst. But the question of how the silver is distributed within the porous structure has not finally been answered yet. We show by quantitative energy dispersive X-ray tomography measurements that silver forms clusters that are distributed irregularly, both on the surface and inside the ligaments building up the porous structure. Furthermore, we find that the role of the residual silver is ambiguous. Whereas CO oxidation is supported by more residual silver, methanol oxidation to methyl formate is hindered. Structural characterisation reveals larger ligaments and pores for decreasing residual silver concentration.

Abstract: We present a study of the relation between the surface chemistry and nanocrystal shape of PbSe nanocrystals with a variable Pb-to-Se stoichiometry and density of oleate ligands. The oleate ligand density and binding configuration are monitored by nuclear magnetic resonance and Fourier transform infrared absorbance spectroscopy, allowing us to quantify the number of surface-attached ligands per NC and the nature of the surface−Pb−oleate configuration. The three-dimensional shape of the PbSe nanocrystals is obtained from high-angle annular dark field scanning transmission electron microscopy combined with an atom counting method. We show that the enhanced oleate capping results in a stabilization and extension of the {111} facets, and a crystal shape transformation from a truncated nanocube to a truncated octahedron.

Abstract: Nanoporous Pt nanoparticles (NPs) are promising fuel cell catalysts due to their large surface area and increased electrocatalytic activity towards the oxygen reduction reaction (ORR). Herein, we report on the infuence of the growth mechanisms on the surface properties of electrodeposited Pt dendritic NPs with large surface areas. The electrochemically active surface was studied by hydrogen underpotential deposition (HUPD) and compared for the rst time to high angle annular dark eld scanning transmission electron microscopy (HAADF-STEM) quantitative 3D electron tomography of individual nanoparticles. Large nucleation overpotential leads to a large surface coverage of Pt roughened spheroids, which provide large roughness factor (Rf ) but low mass-specic electrochemically active surface area (EASA). Lowering the nucleation overpotential leads to highly porous Pt NPs with pores protruding to the center of the structure. At the expense of smaller Rf , the obtained EASA values of these structures are in the range of these of large surface area supported fuel cell catalysts. The active surface area of the Pt dendritic NPs was measured by electron tomography and it was found that the potential cycling in the H adsorption/desorption and Pt oxidation/reduction region, which is generally performed to determine the EASA, leads to a signicant reduction of that surface area due to a partial collapse of their dendritic and porous morphology. Interestingly, the extrapolation of the microscopic tomography results to macroscopic electrochemical parameters indicated that the surface properties measured by H UPD are comparable to the values measured on individual NPs by electron tomography after the degradation caused by the H UPD measurement. These results highlight that the combination of electrochemical and quantitative 3D surface analysis techniques is essential to provide insights into the surface properties, the electrochemical stability and, hence, the applicability of these materials. Moreover, it indicates that care must be taken with widely used electrochemical methods of surface area determination, especially in the case of large surface area and possibly unstable nanostructures, since the measured surface can be strongly aected by the measurement itself.

Abstract: Copper chalcogenides find applications in different domains including photonics, photothermal therapy and photovoltaics. CuTe nanocrystals have been proposed as an alternative to noble metal particles for plasmonics. Although it is known that deviations from stoichiometry are a prerequisite for plasmonic activity in the near-infrared, an accurate description of the material and its (optical) properties is hindered by an insufficient understanding of the atomic structure and the influence of defects, especially for materials in their nanocrystalline form. We demonstrate that the structure of Cu1.5±xTe nanocrystals canbe determined using electron diffraction tomography. Real-space high-resolution electron tomography directly reveals the three-dimensional distribution of vacancies in the structure. Through first-principles density functional theory, we furthermore demonstrate that the influence of these vacancies on the optical properties of the nanocrystals is determined. Since our methodology is applicable to a variety of crystalline nanostructured materials, it is expected to provide unique insights concerning structure–property correlations.