Deconvoluting Energy Transport Mechanisms in Metal Halide Perovskites Using CsPbBr3 Nanowires as a Model System

Understanding energy transport in metal halide perovskites is essential to effectively guide further optimization of materials and device designs. However, difficulties to disentangle charge carrier diffusion, photon recycling, and photon transport have led to contradicting reports and uncertainty regarding which mechanism dominates. In this study, monocrystalline CsPbBr₃ nanowires serve as 1D model systems to help unravel the respective contribution of energy transport processes in metal-halide perovskites. Spatially, temporally, and spectrally resolved photoluminescence (PL) microscopy reveals characteristic signatures of each transport mechanism from which a robust model describing the PL signal accounting for carrier diffusion, photon propagation, and photon recycling is developed. For the investigated CsPbBr₃ nanowires, an ambipolar carrier mobility of μ = 35 cm² V⁻¹ s⁻¹ is determined, and is found that charge carrier diffusion dominates the energy transport process over photon recycling. Moreover, the general applicability of the developed model is demonstrated on different perovskite compounds by applying it to data provided in previous related reports, from which clarity is gained as to why conflicting reports exist. These findings, therefore, serve as a useful tool to assist future studies aimed at characterizing energy transport mechanisms in semiconductor nanowires using PL.     

Effect of Hyaluronic Acid on the Self-Assembly of a Dipeptide-Based Supramolecular Gel

The combination of polymers and low molecular weight (LMW) compounds is a powerful approach to prepare new supramolecular materials. Here we prepare two-component hydrogels made by a well-known and biologically active polymer, hyaluronic acid ( HA ), and a dipeptide-based supramolecular gelator. We undertake a detailed study of materials with different compositions including macroscopic (hydrogel formation, rheology) and micro/nanoscopic characterization (electron microscopy, X-ray powder diffraction). We observe that the two components mutually benefit in the new materials: a minimum amount of HA helps to reduce the polymorphism of the LMW network leading to reproducible hydrogels with improved mechanical properties; the LMW component network holds HA without the need for an irreversible covalent crosslinking. These materials have a great potential for biomedical application as, for instance, extracellular matrix mimetics for cell growth. As a proof of concept, we have observed that this material is effective for cell growth in suspension and avoids cell sedimentation even in the presence of competing cell-adhesive surfaces. This may be of interest to advanced cell delivery techniques.     

Evaluating the risk of fish stranding due to hydropeaking in a large continental river

With the continuous development of hydropower on a global scale, stranding of freshwater fishes is of growing concern, and an understanding of the mechanisms and variables affecting fish stranding in hydropeaking rivers is urgently needed. In particular, a methodology is required to identify the magnitude and timing at which fish stranding occurs in relation to environmental conditions. Here, we studied fish stranding in three reaches downstream of a hydropeaking generation station in the Saskatchewan River, Saskatchewan, Canada, using an innovative remote photography approach with 45 trail cameras and traditional transect monitoring, conducting 323 transects. We observed that juvenile sport and commercial fish species are stranding at a higher proportion than small bodied fish species. The remote photography approach provided more precise fish stranding timing and associated the environmental and physical conditions with a given stranding event, but captured fewer fish and only rarely allowed species identification. The comparison of the two methodologies resulted in similar stranded fish densities, but the remote photography allowed for continuous observations whereas the transect monitoring was limited by the observer availability in the field. Remote photography allowed for additional information on the scavenging of stranded fish, with scavenging occurring on average within 240 minutes of the fish being stranded. The probability of fish stranding increased significantly with increasing water temperature and substrate particle size resulted in greater stranding on finer substrates. Our findings have important implications for hydroelectric flow management by introducing an innovative, standardized method to study the effects of hydropeaking events on fish stranding that can be applied to increase our understanding of the impacts of hydropeaking on fish communities.     

Project proposal for the investigation of particle-stabilised emulsions and foams by microgravity experiments

The utilisation of particle-surfactants nanostructures as stabilising agents represents today the technologic and scientific frontier in the stabilisation of liquid films in emulsion and foams. This topic will be addressed by the proposal STEFAN (STabilisation of Emulsions and FoAms by Nanoparticles), proposed by European groups in the framework of the ESA AO-2004 for Life and Physical Sciences and Applied Research projects Similarly to what can be observed for surfactant-stabilised emulsions and foams, microgravity provides ideal conditions for the investigation of the hierarchy of involved objects: interfacial layer, liquid film, dispersed systems foam or emulsion. Microgravity experiments are planned by refurbishing the Experimental Container FASES for the ISS Fluid Science Laboratory and the facility FASTER for the European Drawer Rack, already under development in existing research programmes. Here the scientific guidelines of the project are presented together with examples and preliminary results on the effect of nano-particle-surfactant structures adsorbed at liquid interfaces. First experimental results have been achieved for particle monolayers at the water/air interface and a thermodynamic model was derived to describe the obtained surface pressure-area isotherms.     

Financial and Housing Wealth and Consumption Spending: Cross-Country and Age Group Comparisons

In this study we explore the link between household expenditures and wealth across the age distribution by examining the elasticity of consumption spending from different types of wealth. We use a new source of harmonized wealth micro data for five countries: Canada, Finland, Italy, Germany and the US. Our results indicate that the effect of housing wealth dominates the effect of financial wealth in Finland, Italy, Germany, the US, and also in Canada for certain age groups. We find consumption responsiveness to housing wealth to be statistically significantly lower for younger households. The analysis also confirms the existence of between-country differences.     

A Facet‐Specific Quantum Dot Passivation Strategy for Colloid Management and Efficient Infrared Photovoltaics

Colloidal nanocrystals combine size‐ and facet‐dependent properties with solution processing. They offer thus a compelling suite of materials for technological applications. Their size‐ and facet‐tunable features are studied in synthesis; however, to exploit their features in optoelectronic devices, it will be essential to translate control over size and facets from the colloid all the way to the film. Larger‐diameter colloidal quantum dots (CQDs) offer the attractive possibility of harvesting infrared (IR) solar energy beyond absorption of silicon photovoltaics. These CQDs exhibit facets (nonpolar (100)) undisplayed in small‐diameter CQDs; and the materials chemistry of smaller nanocrystals fails consequently to translate to materials for the short‐wavelength IR regime. A new colloidal management strategy targeting the passivation of both (100) and (111) facets is demonstrated using distinct choices of cations and anions. The approach leads to narrow‐bandgap CQDs with impressive colloidal stability and photoluminescence quantum yield. Photophysical studies confirm a reduction both in Stokes shift (≈47 meV) and Urbach tail (≈29 meV). This approach provides a ≈50% increase in the power conversion efficiency of IR photovoltaics compared to controls, and a ≈70% external quantum efficiency at their excitonic peak.     

3D Scaffolds to Study Basic Cell Biology

Mimicking the properties of the extracellular matrix is crucial for developing in vitro models of the physiological microenvironment of living cells. Among other techniques, 3D direct laser writing (DLW) has emerged as a promising technology for realizing tailored 3D scaffolds for cell biology studies. Here, results based on DLW addressing basic biological issues, e.g., cell‐force measurements and selective 3D cell spreading on functionalized structures are reviewed. Continuous future progress in DLW materials engineering and innovative approaches for scaffold fabrication will enable further applications of DLW in applied biomedical research and tissue engineering.     

Quantum Confinement of Dirac Quasiparticles in Graphene Patterned with Sub-Nanometer Precision

Quantum confinement of graphene Dirac-like electrons in artificially crafted nanometer structures is a long sought goal that would provide a strategy to selectively tune the electronic properties of graphene, including bandgap opening or quantization of energy levels. However, creating confining structures with nanometer precision in shape, size, and location remains an experimental challenge, both for top-down and bottom-up approaches. Moreover, Klein tunneling, offering an escape route to graphene electrons, limits the efficiency of electrostatic confinement. Here, a scanning tunneling microscope (STM) is used to create graphene nanopatterns, with sub-nanometer precision, by the collective manipulation of a large number of H atoms. Individual graphene nanostructures are built at selected locations, with predetermined orientations and shapes, and with dimensions going all the way from 2 nm up to 1 µm. The method permits the patterns to be erased and rebuilt at will, and it can be implemented on different graphene substrates. STM experiments demonstrate that such graphene nanostructures confine very efficiently graphene Dirac quasiparticles, both in 0D and 1D structures. In graphene quantum dots, perfectly defined energy bandgaps up to 0.8 eV are found that scale as the inverse of the dot’s linear dimension, as expected for massless Dirac fermions.