X‑ray Lithography on Perovskite Nanocrystals Films: From Patterning with Anion-Exchange Reactions to Enhanced Stability in Air and Water

Films of colloidal CsPbX₃ (X = I, Br or Cl) nanocrystals, prepared by solution drop-casting or spin-coating on a silicon substrate, were exposed to a low flux of X-rays from an X-ray photoelectron spectrometer source, causing intermolecular CC bonding of the organic ligands that coat the surface of the nanocrystals. This transformation of the ligand shell resulted in a greater stability of the film, which translated into the following features: (i) Insolubility of the exposed regions in organic solvents which caused instead complete dissolution of the unexposed regions. This enabled the fabrication of stable and strongly fluorescent patterns over millimeter scale areas. (ii) Inhibition of the irradiated regions toward halide anion exchange reactions, when the films were exposed either to halide anions in solution or to hydrohalic vapors. This feature was exploited to create patterned regions of different CsPbI_<i>x</i>Br_<i>y</i>Cl_<i>z</i> compositions, starting from a film with homogeneous CsPbX₃ composition. (iii) Resistance of the films to degradation caused by exposure to air and moisture, which represents one of the major drawbacks for the integration of these materials in devices. (iv) Stability of the film in water and biological buffer, which can open interesting perspectives for applications of halide perovskite nanocrystals in aqueous environments

PLA/POSS Nanofibers: A Novel System for the Immobilization of Metal Nanoparticles

In this work, a novel catalytic system is developed, consisting of palladium nanoclusters homogenously dispersed on the surface of nanostructured polymer nanofibers based on poly­(L-lactic acid) (PLLA) and polyhedral oligomeric silsesquioxanes (POSS). Indeed, PLLA nanofibers containing amino-functionalized silsesquioxane molecules (POSS-NH₂), potentially capable of interacting with the metal precursor, are prepared by means of electrospinning. Conversely to the polymer matrix, which does not show any tendency to retain the metal precursor, the submicrometric dispersion of POSS-NH₂ in the PLLA nanofibers, as demonstrated by SEM-EDS analysis, turns out to promote the formation of metal nanoclusters. TEM measurements show a uniform distribution of Pd nanoparticles, characterized by an average dimension of ca. 4 nm, along the fibers. The prepared system proves a relevant catalytic activity toward the hydrogenation of stilbene under heterogeneous conditions. Moreover, as demonstrated by XPS measurements, the support is capable of retaining the catalyst during the hydrogenation reaction, thus preventing its leaching

Tic-Tac-Toe Binary Lattices from the Interfacial Self-Assembly of Branched and Spherical Nanocrystals

The self-organization of nanocrystals has proven to be a versatile route to achieve increasingly sophisticated structures of materials, where the shape and properties of individual particles impact the final functionalities. Recent works have addressed this topic by combining various shapes to achieve more complex arrangements of particles than are possible in single-component samples. However, the ability to create intricate architectures over large regions by exploiting the shape of multiply branched nanocrystals to host a second component remains unexplored. Here, we show how the concave shape of a branched nanocrystal, the so-called octapod, is able to anchor a sphere. The two components self-assemble into a locally ordered monolayer consisting of an intercalated square lattice of octapods and spheres, which is reminiscent of the “tic-tac-toe” game. These tic-tac-toe domains form through an interfacial self-assembly that occurs by the dewetting of a hexane layer containing both particle types. By varying the experimental conditions and performing molecular dynamics simulations, we show that the ligands coating the octapods are crucial to the formation of this structure. We find that the tendency of an octapod to form an interlocking-type structure with a second octapod strongly depends on the ligand shell of the pods. Breaking this tendency by ligand exchange allows the octapods to assemble into a more relaxed configuration, which is able to form a lock-and-key-type structure with a sphere, when they have a suitable size ratio. Our findings provide an example of a more versatile use of branched nanocrystals in self-assembled functional materials

Self-Assembly of 1,4-Benzenedimethanethiol Self-Assembled Monolayers on Gold

A study of the self-assembly of 1,4-benzenedimethanethiol (BDMT; HS−CH2−(C6H4)−CH2−SH) monolayers on gold is presented. Self-assembled monolayers (SAMs) are characterized by reflection−absorption infrared spectroscopy (RAIRS), X-ray photoelectron spectroscopy (XPS), and spectroscopic ellipsometry (SE) measurements. The ensemble of measurements consistently shows that well-organized BDMT SAMs, with “standing-up” molecules, can be obtained on high quality gold films with incubation in n-hexane provided that N2-degassed solutions are used and all preparation steps are performed at 60 °C in the absence of ambient light. SE data indicate that the optical interface properties of the BDMT−Au system are different from those of simple alkanethiol SAMs. A possible mechanism for the formation of the “standing-up” phase from the lying-down phase via a hydrogen exchange reaction involving chemisorbed lying-down and free dithiol molecules is discussed

CeO₂ Nanoparticles-Loaded pH-Responsive Microparticles with Antitumoral Properties as Therapeutic Modulators for Osteosarcoma

Osteosarcoma is an aggressive form of bone cancer mostly affecting young people. To date, the most effective strategy for the treatment of osteosarcoma is the surgical removal of the tumor with or without combinational chemotherapy. In this study, we present the development of a pH-sensitive drug-delivery system in the form of microparticles, with increased chemotherapeutic action against the osteosarcoma cell line SAOS-2, and with reduced toxicity against the heart myoblastic cell line H9C2. The delivery system is composed of calcium carbonate and collagen type I, and is loaded with cerium dioxide (CeO2) nanoparticles (<25 nm) and the anticancer drug doxorubicin. The fabricated microparticles were fully characterized morphologically and physicochemically, and their ability to induce or inhibit apoptosis/necrosis was assessed using in vitro functional assays and flow cytometry. The results presented in this study show that the highest concentration (250 μg/mL) of the therapeutic microparticles (CaCO3-based therapeutic modulators (C-TherMods)), which corresponds to 6.4 μg/mL of encapsulated doxorubicin, can protect the H9C2 cells even after 120 h, since the percentage of viable cells at this time point is 65%. On the contrary, when H9C2 cells are treated with 0.5 μg/mL of free doxorubicin, 75% of the cells are dead only after 24 h. When SAOS-2 cells are treated with the same concentration of C-TherMods (250 μg/mL), the viability of SAOS-2 cells is 80% after 24 h, while it reduces to 50% after 120 h. At pH 6.0, the synergic effect of the pro-oxidant CeO2 nanoparticles and of the encapsulated doxorubicin leads to almost 100% of cell death, even at the lowest concentration of C-TherMods (50 μg/mL)

Polymer-Free Films of Inorganic Halide Perovskite Nanocrystals as UV-to-White Color-Conversion Layers in LEDs

Polymer-Free Films of Inorganic Halide Perovskite Nanocrystals as UV-to-White Color-Conversion Layers in LED

Reversible Concentration-Dependent Photoluminescence Quenching and Change of Emission Color in CsPbBr₃ Nanowires and Nanoplatelets

We discuss the photoluminescence (PL) of quantum-confined CsPbBr₃ colloidal nanocrystals of two different shapes (nanowires and nanoplatelets) at different concentrations in solution and in solid-state films. Upon increasing the nanocrystal concentration in solution, a constant drop in photoluminescence quantum yield is observed, accompanied by a significant PL red shift. This effect is reversible, and the original PL can be restored by diluting to the original concentration. We show that this effect can be in part attributed to self-absorption and partly to aggregation. In particular, for nanoplatelets, where the aggregation is mostly irreversible, while the self-absorption effect is reversible, the two contributions can be well separated. Finally, when dry solid-state films are prepared, the emission band is shifted into the green spectral region, close to the bulk CsPbBr₃ band gap, thus preventing blue emission from such films

New Stereocomplex PLA-Based Fibers: Effect of POSS on Polymer Functionalization and Properties

In this work, a novel approach for the functionalization of electrospun stereocomplex polylactide (sc-PLA)-based fibers, prepared from solutions containing equimolar amount of high-molecular-weight poly­(l-lactide) (PLLA) and poly­(d-lactide) (PDLA), was developed. The method, which consists in introducing functionalized polyhedral oligomeric silsesquioxanes (POSS) into the electrospinning solutions, was carried out by employing as a solvent system a 2:1 mixture of chloroform (CHCl₃) and 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP), never applied in the production of sc-PLA fibers, which was found to promote POSS solubilization while simultaneously allowing to obtain an excellent fiber homogeneity. Indeed, the specific effect of the single components of the solvent mixture, CHCl₃ and HFIP, on fiber structuring and morphology was evaluated. Conversely to the fiber morphology, which turned out to be significantly affected by the chosen electrospinning solvent, the PLA stereocomplexation, occurring upon subsequent annealing treatment at 100 °C (as evidenced by differential scanning calorimetry (DSC) and X-ray diffraction analyses), was found to be similar for fibers prepared starting from the different types of solvent. Unlike solution casting, electrospinning allows the exclusive formation of stereocomplex crystallites, simultaneously promoting a submicrometric dispersion of the silsesquioxanes, with the consequent fiber functionalization. In our work, two different kinds of POSSone characterized by hydroxyl groups (POSS–OH) and another one functionalized with an amino-bearing molecule (POSS–NH₂)were exploited to impart hydroxyl and amino functionalities to PLA based nanofibers, while preserving the capability of the polymer system to form a pure stereocomplex on subsequent annealing. In particular, it was found that the amino groups of the sc-PLA fibers functionalized with POSS–NH₂, promote specific interactions with a metal precursor, i.e., PdCl₂, which, as a result of a subsequent reduction, forms metal nanoclusters homogeneously dispersed on the fiber surface. The higher thermal and chemical resistance of the sc-PLA fibers with respect to those based solely on PLLA allowed to significantly broaden the applications of the catalytic system. Indeed, the sc-PLA/Pd fibers turned out to be very active in the Heck reaction, easily recoverable and reusable for multiple catalytic cycles

CO Oxidation on Colloidal Au_0.80Pd_0.20–Fe_<i>x</i>O_<i>y</i> Dumbbell Nanocrystals

We report a colloidal synthesis of Au0.80Pd0.20–FexOy dumbbell nanocrystals (NCs) derived from Au0.75Pd0.25 NCs by metal oxide overgrowth. We compared the catalytic activity of the two types of NCs in the CO oxidation reaction (CO + 1/2O2 → CO2), after they had been dispersed on an alumina nanopowder support. In both cases, the surface active sites were identified by means of in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The enhanced catalytic performance of the dumbbell NCs (Au0.80Pd0.20–FexOy) catalyst over that of the initial Au0.75Pd0.25 NCs could be correlated to the presence of the epitaxial connection between the FexOy and the Au0.80Pd0.20 domains (as the main factor). Such connection should result in an electron flow from the metal oxide (FexOy) domain to the noble metal (Au0.80Pd0.20) domain and appears to influence favorably the nature and composition of the catalytically active surface sites of the dumbbells. Our experiments indicate indeed that, when the metal alloy domain is attached to the metal oxide domain (that is, in the dumbbell), surface Pd species are more active than in the case of the initial Au0.75Pd0.25 NCs and also Auδ− sites are formed that were not present on the initial Au0.75Pd0.25 NCs

Generalized One-Pot Synthesis of Copper Sulfide, Selenide-Sulfide, and Telluride-Sulfide Nanoparticles

Here we report a facile approach to synthesize copper chalcogenide (Cu_2–<i>x</i>S, Cu_2–<i>x</i>Se_<i>y</i>S_1–<i>y</i> and Cu_2–<i>x</i>Te_<i>y</i>S_1–<i>y</i>) nanocrystals without employing hot-injection, at moderate reaction temperatures (200–220 °C) and free of phosphines. Scaling up of the synthesis yields monodisperse nanoparticles without variations in their morphology. We have observed the formation of alloyed copper selenide-sulfide and telluride-sulfide nanocrystals due to the incorporation of sulfur by using 1-dodecanethiol as a ligand along with oleic acid. The materials obtained possess localized surface plasmon resonances in the near-infrared region, which are demonstrated to be widely tunable via a controlled oxidation generating copper vacancies. Copper sulfide nanoparticles with well-defined initial chalcocite crystal phase were subjected to oxidation followed by structural characterization. Structural rearrangement of the oxidized chalcocite Cu_2–<i>x</i>S crystal lattice to roxbyite by aging is proven to release the copper vacancies. Further oxidation again can create new copper vacancies in the roxbyite lattice, however its structure does not evolve into covellite CuS. These findings suggest that besides nonstoichiometry (i.e., the value of <i>x</i>) induced by oxidation, crystal structure is an important factor responsible for plasmonic properties of copper chalcogenide nanocrystals. Furthermore, successful water solubilization of Cu_2–<i>x</i>Te_<i>y</i>S_1–<i>y</i> nanoparticles with preservation of their plasmon band has been realized via a ligand exchange approach employing a mPEG-SH stabilizer