Technological insights on the Early-Middle Bronze Age pottery of Monte Meana cave (Sardinia, Italy).

An important Bronze Age settlement was discovered during an archaeological excavation in the Monte Meana karst cave in south-western Sardinia (Italy) between 2007 and 2012. In this region, the caves were used since the Neolithic for different purposes, such as burials or other rituals. The dig highlighted a rare example of domestic use of a cave and showed a case study of household space of the Early -Middle Bronze Age, at the beginning of the Nuragic civilization. This provided the opportunity to investigate through a multidisciplinary approach, the empirical knowledge of ancient potters and technological characters of local pottery production especially in relation to domestic use, in a context at that time devoid of external cultural interferences. For this purpose, a selection of 24 pottery sherds related to vessel forms for cooking, storage, and eating were studied through macroscopic surveys and archaeometric analysis by petrography, scanning electron microscopy, X-ray powder diffraction, and Fourier transform infrared spectroscopy. The results revealed some discriminant variables (shape, wall thickness, features of the paste, surface smoothing, presence of diagnostic mineralogical phases, and tempers), within the ceramic products of this Sardinian Bronze Age site, showing skillful management of firing temperatures.

Defect-assisted synthesis of magneto-plasmonic silver-spinel ferrite heterostructures in a flower-like architecture.

Artificial nano-heterostructures (NHs) with controlled morphology, obtained by combining two or more components in several possible architectures, make them suitable for a wide range of applications. Here, we propose an oleate-based solvothermal approach to design silver-spinel ferrite flower-like NHs. Small oleate-coated silver nanoparticles were used as seeds for the growth of magnetic spinel ferrite (cobalt ferrite and spinel iron oxide) nanodomains on their surface. With the aim of producing homogeneous flower-like heterostructures, a careful study of the effect of the concentration of precursors, the reaction temperature, the presence of water, and the chemical nature of the spinel ferrite was carried out. The magnetic and optical properties of the NHs were also investigated. A heterogeneous growth of the spinel ferrite phase on the silver nanoparticles, through a possible defect-assisted mechanism, was suggested in the light of the high concentration of stacking faults (intrinsic and twins) in the silver seeds, revealed by Rietveld refinement of powder X-ray diffraction patterns and High-Resolution electron microscopy.

Magnetocrystalline and Surface Anisotropy in CoFe2O4 Nanoparticles.

The effect of the annealing temperature Tann on the magnetic properties of cobalt ferrite nanoparticles embedded in an amorphous silica matrix (CoFe2O4/SiO2), synthesized by a sol-gel auto-combustion method, was investigated by magnetization and AC susceptibility measurements. For samples with 15% w/w nanoparticle concentration, the particle size increases from ~2.5 to ~7 nm, increasing Tann from 700 to 900 °C. The effective magnetic anisotropy constant (Keff) increases with decreasing Tann, due to the increase in the surface contribution. For a 5% w/w sample annealed at 900 °C, Keff is much larger (1.7 × 106 J/m3) than that of the 15% w/w sample (7.5 ×105 J/m3) annealed at 700 °C and showing comparable particle size. This indicates that the effect of the annealing temperature on the anisotropy is not only the control of the particle size but also on the core structure (i.e., cation distribution between the two spinel sublattices and degree of spin canting), strongly affecting the magnetocrystalline anisotropy. The results provide evidence that the magnetic anisotropy comes from a complex balance between core and surface contributions that can be controlled by thermal treatments.

Coupled hard-soft spinel ferrite-based core-shell nanoarchitectures: magnetic properties and heating abilities.

Bi-magnetic core-shell spinel ferrite-based nanoparticles with different CoFe2O4 core size, chemical nature of the shell (MnFe2O4 and spinel iron oxide), and shell thickness were prepared using an efficient solvothermal approach to exploit the magnetic coupling between a hard and a soft ferrimagnetic phase for magnetic heat induction. The magnetic behavior, together with morphology, stoichiometry, cation distribution, and spin canting, were investigated to identify the key parameters affecting the heat release. General trends in the heating abilities, as a function of the core size, the nature and the thickness of the shell, were hypothesized based on this systematic fundamental study and confirmed by experiments conducted on the water-based ferrofluids.

Oleate-Based Solvothermal Approach for Size Control of MIIFe2IIIO4 (MII ═ MnII, FeII) Colloidal Nanoparticles.

The versatility of a promising and repeatable oleate-based solvothermal approach has been explored through the synthesis of MnFe2O4 and λ-Fe2O3/Fe3O4 nanoparticles in form of colloidal dispersions and the tuning of the particle and crystallite sizes. Spinel ferrite nanoparticles with controlled-size in the range 7-14 nm with dispersity below 15% was reached for both MnFe2O4 and λ-Fe2O3/Fe3O4. The size-tuning was obtained with three different pathways: (i) direct approach by changing the solvent polarity or the precursor concentration; (ii) post-synthesis solvothermal treatment in the presence of metal oleates; (iii) post-synthesis solvothermal treatment in the absence of metal oleates.

57Fe Mössbauer Spectroscopy for the Study of Nanostructured Mixed Mn-Co Spinel Ferrites.

An oleate-based solvothermal approach has been employed to produce pure CoFe2O4 and MnFe2O4 and mixed Co-Mn ferrites having manganese content in the range 0.13-0.65 and crystallite size of about 8-9 nm. The structural and magnetic properties, studied by powder X-ray diffraction and room temperature 57Fe Mössbauer spectroscopy, have allowed to ascertain the formation of a unique spinel phase in which cobalt and manganese are present and to get insights on the cation distribution and the correlated magnetic properties.

Spinel Ferrite Core-Shell Nanostructures by a Versatile Solvothermal Seed-Mediated Growth Approach and Study of Their Nanointerfaces.

An easy, low-cost, repeatable seed-mediated growth approach in solvothermal condition has been proposed to synthesize bimagnetic spinel ferrite core-shell heterostructures in the 10-20 nm particle size range. Cobalt ferrite and manganese ferrite nanoparticles (CoFe2O4 and MnFe2O4) have been coated with isostructural spinel ferrites like maghemite/magnetite, MnFe2O4, and CoFe2O4 with similar cell parameters to create different heterostructures. The conventional study of the structure, morphology, and composition has been combined with advanced techniques in order to achieve details on the interface at the nanoscale level. Clear evidence of the heterostructure formation have been obtained (i) indirectly by comparing the 57Fe Mössbauer spectra of the core-shell samples and an ad hoc mechanical mixture and (ii) directly by mapping the nanoparticles' chemical composition by electron energy loss spectroscopy (EELS) and energy-dispersive X-ray spectroscopy (EDX) in the scanning transmission electron microscopy mode (STEM). In addition, chemical-sensitive electron tomography in STEM-EDX mode has been applied in order to obtain detailed 3D images with a sub-nanometer spatial resolution.

Hierarchical Formation Mechanism of CoFe2O4 Mesoporous Assemblies.

The development of synthetic hybrid organic-inorganic approaches and the understanding of the chemico-physical mechanisms leading to hierarchical assembly of nanocrystals into superstructures pave the way to the design and fabrication of multifunction microdevices able to simultaneously control processes at the nanoscale. This work deals with the design of spherical mesoporous magnetic assemblies through a surfactant assisted water-based strategy and the study of the formation mechanism by a combined use of transmission electron microscopy, X-ray diffraction, and time-resolved small angle X-ray scattering techniques. We visualize the hierarchical mechanism formation of the magnetic assemblies in the selected sodium dodecylsulfate (SDS)-assisted water-based strategy. At the first stage, an intermediate lamellar phase (L) represented by ß-Co(OH)2 and FeOOH hexagonal plates is formed. Then, the nucleation of primary CoFe2O4 (N1) nanocrystals of about 6-7 nm occurs by the dissolution of FeOOH and the reaction of Fe(III) ions coordinated to the SDS micelles, at the reactive sites provided by vertices and edges of the ß-Co(OH)2 plates. The intermediate phase consumes as the primary crystalline nanoparticles form, confined by the surfactant molecules around them, and assembly in spherical mesoporous assemblies. The key role of the surfactant in the formation of porous assemblies has been evidenced by an experiment carried out in the absence of SDS and confirmed by the pore size diameter of the assemblies (about 2-3 nm), that can be correlated with the length of the surfactant dodecylsulfate molecule.

Correlated electron-hole plasma in organometal perovskites.

Organic-inorganic perovskites are a class of solution-processed semiconductors holding promise for the realization of low-cost efficient solar cells and on-chip lasers. Despite the recent attention they have attracted, fundamental aspects of the photophysics underlying device operation still remain elusive. Here we use photoluminescence and transmission spectroscopy to show that photoexcitations give rise to a conducting plasma of unbound but Coulomb-correlated electron-hole pairs at all excitations of interest for light-energy conversion and stimulated optical amplification. The conductive nature of the photoexcited plasma has crucial consequences for perovskite-based devices: in solar cells, it ensures efficient charge separation and ambipolar transport while, concerning lasing, it provides a low threshold for light amplification and justifies a favourable outlook for the demonstration of an electrically driven laser. We find a significant trap density, whose cross-section for carrier capture is however low, yielding a minor impact on device performance.

Core-shell nano-architectures: the incorporation mechanism of hydrophobic nanoparticles into the aqueous core of a microemulsion.

This work presents an in-depth investigation of the molecular interactions in the incorporation mechanism of colloidal hydrophobic-capped nanoparticles into the hydrophilic core of reverse microemulsions. (1)H Nuclear Magnetic Resonance (NMR) was employed to obtain molecular level details of the interaction between the nanoparticles capping amphiphiles and the microemulsion surfactants. The model system of choice involved oleic acid (OAC) and oleylamine (OAM) as capping molecules, while igepal-CO520 was the surfactant. The former were studied both in their "free" state and "ligated" one, i.e., bound to nanoparticles. The latter was investigated either in cyclohexane (micellar solution) or in water/cyclohexane microemulsions. The approach was extremely useful to gain a deeper understanding of the equilibria involved in this complex system (oleic acid capped-Bi2S3 in igepal/water/cyclohexane microemulsions). In difference to previously proposed mechanisms, the experimental data showed that the high affinity of the capping ligands for the reverse micelle interior was the drivingforce for the incorporation of the nanoparticles. A simple ligand-exchange mechanism could be ruled out. The collected information about the nanoparticle incorporation mechanism is extremely useful to develop new synthetic routes with an improved/tuned coating efficiency, in order to tailor the core-shell structure preparation.

Surfactant-assisted route to fabricate CoFe2O4 individual nanoparticles and spherical assemblies.

A surfactant-assisted route in aqueous media has been shown to be suitable to prepare either individual primary CoFe(2)O(4) nanocrystals or secondary spherical nanoporous assemblies with a high surface area. The formation of primary nanoparticles or of spherical assemblies is found to be dependent on the presence of the surfactant and on the particle size, but is shown that the nanoparticle-surfactant interface plays a dominant role. The size of the primary CoFe(2)O(4) particles is controlled by the type of salt, the synthesis temperature and the concentration of the precursors. A detailed characterization evidences the shape and size of the primary particles, the way in which the primary particles assemble and their features in terms of morphological, textural and magnetic properties.

Magnetism in nanoparticles: beyond the effect of particle size.

A set of investigations on selected samples of nanosized cobalt ferrite are reviewed, aimed at studying the various factors affecting the magnetic properties of nanoparticles. Specifically, the effects of inter-particle interactions, of structural and magnetic order, both in the core and on the surface of the particle, have been examined. All factors render the control of the magnetic properties of nanosystems quite difficult, but, at the same time, they also offer the opportunity of tuning them properly, so that materials for specific applications may be created.

Stability of luminescent trivalent cerium in silica host glasses modified by boron and phosphorus.

Ce-doped borosilicate (BSG), phosphosilicate (PSG), and borophosphosilicate (BPSG) glasses (B:P:Si molar ratios 8:0:92, 0:8:92, and 8:8:84; Ce:Si molar ratio 1 x 10(-)(4) to 1 x 10(-)(2)) were prepared by the sol-gel method. High-resolution transmission electron microscopy (HRTEM), (31)P, (29)Si, and (11)B magic angle spinning nuclear magnetic resonance (MAS NMR), electron paramagnetic resonance (EPR), and UV-vis absorption investigations demonstrated that, in PSG and BPSG, Ce(3+) ions interact with phosphoryl, [O=PO(3/2)], metaphosphate, [O=PO(2/ 2)O](-), and pyrophosphate, [O=PO(1/2)O(2)](2)(-), groups, linked to a silica network. This inhibits both CeO(2) segregation and oxidation of isolated Ce(3+) ions to Ce(4+), up to Ce:Si = 5 x 10(-)(3). In BSG, neither trigonal [BO(3/2)] nor tetrahedral [BO(4/2)](-) boron units coordinate cerium; thus, Ce(3+) oxidation occurs even at Ce:Si = 1 x 10(-)(4), as in pure silica glass (SG). The homogeneous rare-earth dispersion in the host matrix and the stabilization of the Ce(3+) oxidation state enhanced the intensity of the photoluminescence emission in PSG and BPSG with respect to BSG and SG. The energy of the Ce(3+) emission band in PSG and BPSG matrixes agrees with the phosphate environment of the rare earth.