Laser-Induced Morphological and Structural Changes of Cesium Lead Bromide Nanocrystals

Metal halide perovskite nanocrystals, an emerging class of materials for advanced photonic and optoelectronic applications, are mainly fabricated with colloidal chemistry routes. On the quest for new properties according to application needs, new perovskite systems of various morphologies and levels of doping and alloying have been developed, often also involving post-synthesis reactions. Recently, laser irradiation in liquids has been utilized as a fast method to synthesize or transform materials and interesting laser-induced transformations on nanocrystals were induced. These studies in general have been limited to small nanocrystals (~15 nm). In the case of halide perovskites, fragmentation or anion exchange have been observed in such laser-based processes, but no crystal structure transformations were actually observed or deliberately studied. Nanocrystals are more sensitive to light exposure compared to the corresponding bulk crystals. Additional factors, such as size, morphology, the presence of impurities, and others, can intricately affect the photon absorption and heat dissipation in nanocrystal suspensions during laser irradiation. All these factors can play an important role in the final morphologies and in the time required for these transformations to unfold. In the present work, we have employed a 513 nm femtosecond (fs) laser to induce different transformations in large nanocrystals, in which two phases coexist in the same particle (Cs4PbBr6/CsPbBr3 nanohexagons of ~100 nm), dispersed in dichlorobenzene. These transformations include: (i) the exfoliation of the primary nanohexagons and partial anion exchange; (ii) fragmentation in smaller nanocubes and partial anion exchange; (iii) side-by-side-oriented attachment, fusion, and formation of nanoplatelets and complete anion exchange; (iv) side-by-side attachment, fusion, and formation of nanosheets. Partial or complete Br-Cl anion exchange in the above transformations was triggered by the partial degradation of dichlorobenzene. In addition to the detailed analysis of the various nanocrystal morphologies observed in the various transformations, the structure–photoluminescence relationships for the different samples were analyzed and discussed.

Special Issue: Perovskite Nanostructures: From Material Design to Applications

In the past decade, perovskite materials have attracted great scientific and technological interest due to their interesting opto-electronic properties. Nanostructuring of the perovskites, due to their reduced dimensions are advantageous in offering large surface area, controlled transport and charge carrier mobility, strong absorption and photoluminescence, and confinement effects. These features, together with the unique tunability in composition, shape, and functionalities in addition to the ability to form efficient, low-cost, and light-active structures make the perovskite nanostructures efficient functional components for multiple applications, ranging from photovoltaics and batteries to lasing and light-emitting diodes. The purpose of this Special Issue is to give an overview of the latest experimental findings concerning the tunability in composition, shape, functionalities, growth conditions, and synthesis procedures of perovskite structures and to identify the critical parameters for producing materials with functional characteristics.

Magnetic Nanoparticle Composites: Synergistic Effects and Applications

Composite materials are made from two or more constituent materials with distinct physical or chemical properties that, when combined, produce a material with characteristics which are at least to some degree different from its individual components. Nanocomposite materials are composed of different materials of which at least one has nanoscale dimensions. Common types of nanocomposites consist of a combination of two different elements, with a nanoparticle that is linked to, or surrounded by, another organic or inorganic material, for example in a core-shell or heterostructure configuration. A general family of nanoparticle composites concerns the coating of a nanoscale material by a polymer, SiO2 or carbon. Other materials, such as graphene or graphene oxide (GO), are used as supports forming composites when nanoscale materials are deposited onto them. In this Review we focus on magnetic nanocomposites, describing their synthetic methods, physical properties and applications. Several types of nanocomposites are presented, according to their composition, morphology or surface functionalization. Their applications are largely due to the synergistic effects that appear thanks to the co-existence of two different materials and to their interface, resulting in properties often better than those of their single-phase components. Applications discussed concern magnetically separable catalysts, water treatment, diagnostics-sensing and biomedicine.

Highly luminescent and ultrastable cesium lead bromide perovskite patterns generated in phosphate glass matrices

Owing to their exceptional optoelectronic properties, all-inorganic lead halide perovskites offer enormous potential for next generation photonic, light-emitting, and optoelectronic devices. However, their usage is significantly limited by their poor stability upon moisture exposure and lead toxicity issues. Moreover, many of the aforementioned applications rely on the development of confined perovskite patterns of various shapes and periodicities. Here we report a simple and low-temperature method enabling the controlled incorporation of photoluminescent all-inorganic metal halide PNCs into a silver phosphate glass (AgPO3) matrix which is transparent in most of the visible range. The developed fabrication protocol is based on a simple melting encapsulation process in which pre-synthesized perovskite crystals are inserted in the glass matrix, following the initial glass quenching. Using this novel approach, two types of composite perovskite glasses are prepared, one that hosts perovskite isles and the second in which a thin perovskite layer is embedded beneath the glass surface. Both types of composite glasses exhibit remarkable photoluminescence stability when compared to the ambient air-exposed perovskite crystals. More importantly, by means of a simple and fast cw-laser processing technique, we demonstrate the development of encapsulated dotted perovskite micropatterns within the composite perovskite glass. The ability of the proposed system to resolve stability and lead toxicity issues, coupled with the facile formation of highly luminescent perovskite patterns pave the way towards the broad exploitation of perovskite crystals in photonic applications.

Laser-Assisted Fabrication for Metal Halide Perovskite-2D Nanoconjugates: Control on the Nanocrystal Density and Morphology

We report on a facile and rapid photo-induced process to conjugate graphene-based materials with metal-halide perovskite nanocrystals. We show that a small number of laser pulses is sufficient to decorate the 2-dimensional (2D) flakes with metal-halide nanocrystals without affecting their primary morphology. At the same time, the density of anchored nanocrystals could be finely tuned by the number of irradiation pulses. This facile and rapid room temperature method provides unique opportunities for the design and development of perovskite-2D nanoconjugates, exhibiting synergetic functionality by combining nanocrystals of different morphologies and chemical phases with various 2D materials.

P1669Frequency and patterns of implantable cardiac defibrillator therapies in patients with ventricular assist devices

Purpose

Durable ventricular assist devices (VADs) use is a life-saving therapy in patients with end-stage heart failure. These patients are at high risk for ventricular arrhythmias. The pattern of ICD therapies in these patients is not well characterized.

Methods

Our single-center retrospective cohort included 86 patients with ICDs and VADs followed at our Centre. Data collected included frequency of ICD therapies, type of therapy (appropriate vs. inappropriate; shocks vs. anti-tachycardia pacing (ATP)), and time-course of therapies.

Results

36 patients (42%) received ICD therapy during a mean follow-up period of 13.6 months. There were 105 episodes (2.9 episodes/patient) during which ICD therapies were delivered, with a total of 379 individual arrhythmias treated (3.6 arrhythmias per episode of therapy). 61.4% of therapies were appropriate, 8.4% were inappropriate, and 31.6% were unknown. Of the 79 episodes treated with appropriate therapy, 36 episodes (46%) required ICD shocks, whereas 43 episodes (54%) were treated with ATP alone. Overall, 33% of the total cohort and 81% of patients who received therapy received at least one ICD shock. Twenty-two patients (61%) received therapy between 1–3 times, while the remainder (14 patients, 39%) received therapy 3–10 times. Eighteen (17%) episodes occurred within the first month after LVAD implantation, with 10 (10%) occurring between 1–3 months, 53 (50%) occurring between 3–12 months, and 24 (23%) occurring more than one year after VAD implantation.

Conclusion

Analysis of our VAD cohort revealed three important findings: 1. ICD therapy is very common (42%) in the first year especially after LVAD implantation; 2. Ventricular arrhythmias are highly clustered in this cohort; 3. ATP is frequently effective. These findings have important implications on device follow-up and programming for this expanding patient population.

Ligand-free all-inorganic metal halide nanocubes for fast, ultra-sensitive and self-powered ozone sensors

Ligand-free all-inorganic lead halide nanocubes have been investigated as ozone sensing materials operating at room temperature. It is found that the nanocubes, crystallined in the orthorhombic CsPbBr₃ structure, can operate at room temperature, be self-powered and exhibit high sensitivity and remarkable repeatability. More importantly, they demonstrate higher sensitivity (54% in 187 ppb) and faster response and recovery times compared to hybrid lead mixed halide perovskite (CH₃NH₃PbI_3-x Cl _x ) layers, which is the only lead halide perovskite material tested for ozone sensing, to date. Following the exposure to an ozone environment, the stoichiometry and the morphology of the nanocubes remain unaltered. The facile and easy fabrication process together with the high responsivity and stability to the ozone environment makes the bare CsPbBr₃ nanocubes a promising material for sensing applications. The sensing properties of the nanoparticulate metal halides presented here provide new exciting opportunities towards engineering reliable and cheap sensing elements for room-temperature operated and self-powered sensors.

The Role of Ligands in the Chemical Synthesis and Applications of Inorganic Nanoparticles

The design of nanoparticles is critical for their efficient use in many applications ranging from biomedicine to sensing and energy. While shape and size are responsible for the properties of the inorganic nanoparticle core, the choice of ligands is of utmost importance for the colloidal stability and function of the nanoparticles. Moreover, the selection of ligands employed in nanoparticle synthesis can determine their final size and shape. Ligands added after nanoparticle synthesis infer both new properties as well as provide enhanced colloidal stability. In this article, we provide a comprehensive review on the role of the ligands with respect to the nanoparticle morphology, stability, and function. We analyze the interaction of nanoparticle surface and ligands with different chemical groups, the types of bonding, the final dispersibility of ligand-coated nanoparticles in complex media, their reactivity, and their performance in biomedicine, photodetectors, photovoltaic devices, light-emitting devices, sensors, memory devices, thermoelectric applications, and catalysis.

All-inorganic lead halide perovskite nanohexagons for high performance air-stable lithium batteries

All-inorganic Cs4PbBr6 perovskite nanohexagons, pre-synthesized by a room temperature co-precipitation method, have been electrochemically investigated in a conventional aqueous electrolyte for potential application as an anode material in Li-ion batteries. The nanohexagons were uniformly deposited on ITO precoated glass substrate and subsequently annealed at ambient air to form a mechanically stable perovskite layer. These perovskite layers showed excellent performance during continuous Li-ion intercalation/deintercalation scans in an aqueous electrolyte, exhibiting a diffusion coefficient of 7.34 × 10-8 cm2 s-1, a specific discharge capacity of 377 mA h g-1, a capacity retention of 75% and coulombic efficiency that deteriorated to 98% after 100 scans. A water-triggered transformation of the Cs4PbBr6 to the CsPb2Br5 was initially observed followed by a reversible Li intercalation/deintercalation in the CsPb2Br5 structure for 40 consecutive scans. Following this period, an irreversible conversion reaction of CsPb2Br5 to CsBr and PbBr2 took place. The excellent electrochemical performance observed is promising towards the potential application of all-inorganic perovskite nanocrystals for air-stable, lithium storage applications.

Unveiling the Structure of MoS x Nanocrystals Produced upon Laser Fragmentation of MoS2 Platelets

Transition-metal dichalcogenide MoS₂ nanostructures have attracted tremendous attention due to their unique properties, which render them efficient nanoscale functional components for multiple applications ranging from sensors and biomedical probes to energy conversion and storage devices. However, despite the wide application range, the possibility to tune their size, shape, and composition is still a challenge. At the same time, the correlation of the structure with the optoelectronic properties is still unresolved. Here, we propose a new method to synthesize various morphologies of molybdenum sulfide nanocrystals, on the basis of ultrashort-pulsed laser fragmentation of MoS₂ platelets. Depending on the irradiation conditions, multiple MoS _x morphologies in the form of nanoribbons, nanospheres, and photoluminescent quantum dots are obtained. Besides the detailed structural analysis of the various crystals formed, the structure-property relation is investigated and discussed.

Iron Oxide Colloidal Nanoclusters as Theranostic Vehicles and Their Interactions at the Cellular Level

Advances in surfactant-assisted chemical approaches have led the way for the exploitation of nanoscale inorganic particles in medical diagnosis and treatment. In this field, magnetically-driven multimodal nanotools that perform both detection and therapy, well-designed in size, shape and composition, are highly advantageous. Such a theranostic material—which entails the controlled assembly of smaller (maghemite) nanocrystals in a secondary motif that is highly dispersible in aqueous media—is discussed here. These surface functionalized, pomegranate-like ferrimagnetic nanoclusters (40⁻85 nm) are made of nanocrystal subunits that show a remarkable magnetic resonance imaging contrast efficiency, which is better than that of the superparamagnetic contrast agent Endorem©. Going beyond this attribute and with their demonstrated low cytotoxicity in hand, we examine the critical interaction of such nanoprobes with cells at different physiological environments. The time-dependent in vivo scintigraphic imaging of mice experimental models, combined with a biodistribution study, revealed the accumulation of nanoclusters in the spleen and liver. Moreover, the in vitro proliferation of spleen cells and cytokine production witnessed a size-selective regulation of immune system cells, inferring that smaller clusters induce mainly inflammatory activities, while larger ones induce anti-inflammatory actions. The preliminary findings corroborate that the modular chemistry of magnetic iron oxide nanoclusters stimulates unexplored pathways that could be driven to alter their function in favor of healthcare.

Low-temperature benchtop-synthesis of all-inorganic perovskite nanowires

A facile, low-temperature precipitation-based method is utilized for the synthesis of ultra-thin and highly uniform cesium lead bromide perovskite nanowires (NWs). The reactions facilitate the NWs' crystalline nature over micron-size lengths, while they impart tailored nanowire widths that range from the quantum confinement regime (∼7 nm) down to 2.6 nm. This colloidal synthesis approach is the first of its kind that is carried out on the work-bench, without demanding chemical synthesis equipment. Importantly, the NWs' photoluminescence is shown to improve over time, with no requirement for tedious post-synthesis surface treatment.

Multicore iron oxide mesocrystals stabilized by a poly(phenylenepyridyl) dendron and dendrimer: role of the dendron/dendrimer self-assembly

We report the formation of multicore iron oxide mesocrystals using the thermal decomposition of iron acetyl acetonate in the presence of the multifunctional and rigid poly(phenylenepyridyl) dendron and dendrimer. We thoroughly analyze the influence of capping molecules of two different architectures and demonstrate for the first time that dendron/dendrimer self-assembly leads to multicore morphologies. Single-crystalline ordering in multicore NPs leads to cooperative magnetic behavior: mesocrystals exhibit ambient blocking temperatures, allowing subtle control over magnetic properties using a minor temperature change.

Assembly-mediated interplay of dipolar interactions and surface spin disorder in colloidal maghemite nanoclusters

Controlled assembly of single-crystal, colloidal maghemite nanoparticles is facilitated via a high-temperature polyol-based pathway. Structural characterization shows that size-tunable nanoclusters of 50 and 86 nm diameters (D), with high dispersibility in aqueous media, are composed of ∼13 nm (d) crystallographically oriented nanoparticles. The interaction effects are examined against the increasing volume fraction, φ, of the inorganic magnetic phase that goes from individual colloidal nanoparticles (φ = 0.47) to clusters (φ = 0.72). The frozen-liquid dispersions of the latter exhibit weak ferrimagnetic behaviour at 300 K. Comparative Mössbauer spectroscopic studies imply that intra-cluster interactions come into play. New insight emerges from the clusters' temperature-dependent ac susceptibility that displays two maxima in χ''(T), with strong frequency dispersion. Scaling-law analysis together with the observed memory effects suggests that a superspin-glass state settles-in at TB ∼ 160-200 K, while at lower-temperatures, surface spin-glass freezing is established at Tf ∼ 40-70 K. In such nanoparticle-assembled systems, with increased φ, Monte Carlo simulations corroborate the role of the inter-particle dipolar interactions and that of the constituent nanoparticles' surface spin disorder in the emerging spin-glass dynamics.

Colloidal assemblies of oriented maghemite nanocrystals and their NMR relaxometric properties

¹H-NMR relaxometric experiments over an extended frequency range show that ferrimagnetic colloidal nanoclusters exhibit enhanced transverse relaxivity, r₂.

Nanocomposite pattern-mediated magnetic interactions for localized deposition of nanomaterials

We present a method to create, align, and locate magnetic wires throughout and on the surface of patterned polymer matrices, following the magnetophoretic transport and self-assembly of ferromagnetic nanoparticles under a static magnetic field during laser photopolymerization of monomer/nanoparticle casted solutions. The resulting films have the ability to attract and immobilize small quantities of magnetic nanomaterials locally on the ferromagnetic wires, as proved by a detailed topography study. Magnetic studies on the films before and after the spontaneous deposition, demonstrate that the deposited nanomaterials alter significantly the magnetic character of the system, making thus possible their macroscopic identification. This offers the possibility to realize sensing devices based on hybrid materials with magnetic properties.

Acute intermittent porphyria in pregnancy: a common misdiagnosis

Acute intermittent porphyria (AIP) is inherited in an autosomal dominant fashion. Only 10% to 15% of the gene carriers have the clinical syndrome. The prevalence of AIP in Europe is 1/20,000. Pregnancy represents an essential risk factor in patients suffering from AIP. The clinical syndrome in AIP presents mainly with acute attacks, especially during the first trimester. Misdiagnosis of AIP unfortunately is very common. Pregnancy in women with AIP is associated with higher rates of spontaneous abortion, hypertension, low birth weight infants and considerable mortality (2-42%). Pregnancy, despite the major hormonal alterations it causes, is seldom associated with porphyric symptoms. There are only limited reports supporting the use of hemin during pregnancy, but experience indicates that it can be safely administered in pregnant women. Until clinical improvement is achieved, symptomatic treatment is recommended. Despite the fact that pregnancy in women suffering from AIP is related to higher rates of morbidity and complications, close management throughout the pregnancy could ensure a good outcome.