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Despite its high chemical value, most of lignin is nowadays burnt as low value fuel. It is therefore important to find innovative applications for its use. Copper compounds are used as plant protec...

A tungsten carbide ceramic containing 5 vol% silicon carbide was hot pressed to full density at 1820 °C. A small amount of transient liquid phase based on W-C-Si-O facilitated oxide removal in the reducing environment and favoured the development of a bimodal microstructure containing sub-micrometric grains with square or rod-like morphologies. These microstructural features led to outstanding mechanical properties from room to elevated temperatures. For the first time, WC-materials were characterized up to 1500 °C exhibiting flexural strength over 1 GPa in the whole temperature range and fracture toughness from 7 to 15 MPa⋅√m.

A simple method to obtain highly refractory boride-based ceramic nano-composites is presented. Fundamental requirement for the development of a hierarchical boride composite is the formation of a solid solution around the native MB2 boride grain during the densification step. This can be obtained upon addition of soluble transition metal compounds. In the present case, introduction of WC enabled to form (M,W)B2 shells around the original MB2 cores. Subsequent annealing treatment at high temperature further developed a nano-texturing in the shell, which constituted a nano-composite where metallic W nano-particles were embedded within MB2 grains and displayed unprecedented refractoriness. Here we show the microstructural evolution from the as-sintered to the annealed state of different diboride composite and show how these microstructural change impact on the ultra-high temperature strength. The unique microstructural findings reported open vast opportunities for nano-composite ceramic development, manufacturing and applications.

Bright and nontoxic quantum dots (QDs) are highly desirable in a variety of applications, from solid-state devices to luminescent probes in assays. However, the processability of these species is often curbed by their surface chemistry, which limits their dispersibility in selected solvents. This renders a surface modification step often mandatory to make the QDs compatible with the solvent of interest. Here, we present a new synthetic approach to produce CuInS2 QDs compatible with organic polar solvents and readily usable for the preparation of composite materials. 3-Mercaptopropyl trimethoxysilane (MPTS) was used simultaneously as solvent, sulfur source, and capping agent for the QD synthesis. The synthesized QDs possessed a maximum photoluminescence quantum yield around 6%, reaching approximately 55% after growing a ZnS shell. The partial condensation of MPTS molecules on the surface of QDs was probed by solid-state nuclear magnetic resonance, whose results were used to interpret the interaction of the QDs with different solvents. To prove the versatility of the developed QDs, imparted by the thiolated silane molecules, we prepared via straightforward procedures two nanocomposites of practical interest: (i) silica nanoparticles decorated with QDs and (ii) an inexpensive polymeric film with embedded QDs. We further demonstrate the potential of this composite film as a luminescence thermometer operational over a broad temperature interval, with relative thermal sensitivity above 1% K-1 in the range of biological interest. ©

Magnetic Fe 3 O 4 (magnetite) nanoparticles are synthesized via a chemical precipitation route in different alkaline environments (NH 3 or NaOH) and subsequently functionalized with a (propynylcarbamate)triethoxysilane moiety, with the aim of promoting the nucleation and subsequent stabilization of gold nanoparticles. The propynylcarbamate group is able to capture the gold precursor (HAuCl 4 ), spontaneously reduce it, and stabilize the resulting Au nanoaggregates. The obtained results show that though the dimensions of the starting magnetite substrate depend on the base used in the preparation, they remain unaltered upon the subsequent modification. Conversely, the average Au nanoparticle dimensions can be conveniently tailored as a function of the base used in Fe 3 O 4 preparation and the presence/absence of the organic functionalization. The smallest dimensions (15 nm) are obtained for AuNP supported on propynylcarbamate-functionalized Fe 3 O 4 prepared in the presence of ammonia. Magnetization measurements highlight that all the Au/Fe 3 O 4 nanocomposites display a superparamagnetic behavior and those obtained using ammonia showed consistently smaller Hc and Mr values (av. values of 7.4 Oe and 0.8 emu/g) than those prepared with sodium hydroxide (av. values of 28 Oe and 2.8 emu/g).

Funding: This research was funded by European commission under FP7 LAMP project “Laser Induced Synthesis of Polymeric Nanocomposite Materials and Development of Micro-patterned Hybrid Light Emitting Diodes (LED) and Transistors (LET)” (Grant No. 247928) Many displays involve the use of color conversion layers. QDs are attractive candidates as color converters because of their easy processability, tuneable optical properties, high photoluminescence quantum yield, and good stability. Here, we show that emissive QDs with narrow emission range can be made in-situ in a polymer matrix, with properties useful for color conversion. This was achieved by blending the blue-emitting pyridine based polymer with a cadmium selenide precursor and baking their films at different temperatures. To achieve efficient color conversion, blend ratio and baking temperature/time were varied. We found that thermal decomposition of the precursor leads to highly emissive QDs whose final size and emission can be controlled using baking temperature/time. The formation of the QDs inside the polymer matrix was confirmed through morphological studies using atomic force microscopy (AFM) and transmission electron microscopy (TEM). Hence, our approach provides a cost-effective route to making highly emissive color converters for multi-color displays. Publisher PDF

An electrochemical synthesis which has been optimized to produce layered double hydroxides (LDHs) intercalated with carbon nanomaterials is proposed for the first time. It is based on a one-step procedure which contemporaneously allows for the Ni/Al-LDH synthesis, the reduction of graphene oxide (ERGO) and its intercalation inside the structure. The LDH/ERGO composites were thoroughly characterized by a comprehensive multi-techniques approach in order to verify their structure and morphology. The results confirmed that a LDH structure was observed only if the GO concentration was not higher than 0.2 mg/mL. All the characterizations led to propose a theorization of the synthetic and growth mechanisms of the composites. The best performing material was employed as cathode for the development of a hybrid supercapacitor. The device had a discharge specific capacitance of 880 F g(-1). The promising results obtained in this work embrace the necessity of development of low environmental impact systems; in fact, the proposed hybrid supercapacitor is binder-free, safe, composed of earth abundant elements and able to work in aqueous electrolyte. (c) 2020 Elsevier Ltd. All rights reserved.

After cellulose, lignin is the most abundant plant-derived polymer in nature. It provides mechanical support to plants, but it has also a defense role against pests and diseases, thanks to antioxidant, bactericidal, and antifungal properties, deriving from its polyphenolic nature. Huge quantities of technical lignins are obtained during several industrial processes and they actually represent a waste of paper pulp and bioethanol industry. Although in the last decades many efforts have been directed to obtain lignin valorization in several fields and for diverse applications, this biobased polymer is still largely underutilized. In particular, very little is known about the possibility to exploit its antioxidant, antifungal, and antibacterial properties in the agronomical field. On the other hand, pest control is often achieved by using copper-based pesticides, but environmental and health issues urge for novel solutions implying reduced copper content. We here describe novel hybrid organic-inorganic materials obtained by combining copper(II) salts with two types of technical lignins. Cu-containing materials (lignin@Cu) have been characterized by different techniques, including X-ray powder diffraction and transmission electron spectroscopy analyses, revealing nanocrystals of brochantite (Cu4SO4(OH)(6)) grown in the lignin matrix. Lignin@Cu was tested for its antifungal and antibacterial profile against a vast panel of pathogens of agronomical interest. Furthermore, preliminary tests on crops in a greenhouse were performed: lignin@Cu had better performances than a commercial pesticide based on copper(II) hydroxide on tomato plants against Rhizoctonia solani, indicating a great potential of these materials as plant protection products.

Introduction Recently, great attention has been paid to solid solutions and composite materials based on metal oxides in order to obtain nanostructures with enhanced sensing performance with respect to those of single-oxide counterparts [1]. Tin and titanium dioxides (SnO2 and TiO2) are wide-gap n-type semiconductors extensively investigated for the fabrication of solid-state devices for gas sensing applications. Albeit SnO2-based gas sensors exhibit high response to reducing gases, they suffer of poor selectivity and degradation of electrical properties at low oxygen partial pressure and high operating temperatures upon prolonged exposure to reducing gases [2]. Instead, TiO2 is more thermally stable than SnO2, but it has a lower sensitivity due to a higher density of surface states, that entails the pinning of the Fermi level [3]. SnO2 and TiO2 would easily form solid solutions because they can exhibit a rutile type structure where octahedrally coordinated Ti4+ and Sn4+ have similar ionic radii (i.e. 0.605 Å and 0.69 Å, respectively) [4,5]. In an earlier investigation, the sensing properties of Sn1-x TixO2 (0.21-xTixO2 solid solution showed better sensing performances than SnO2 and TiO2 under different target gases, with the Sn0.7Ti0.3O2 solid solution overperforming with respect to the other investigated compounds [6]. Despite the Sn1-x Ti x O2 good sensing performances, a further improvement on the sensing aptitude of these materials has been attempted by means of a Nb doping. The incorporation of Nb5+ within the Sn0.7Ti0.3O2 lattice would increase the conductivity of the material, as niobium acts as donor dopant in n-type semiconductors and it can inhibit grain growth [7]. Scope and Methods The aim of this work was to study the sensing properties and the structural features of solid solutions based on Sn, Ti and Nb oxides. According to what reported in a previous investigation [6], different sample of (Sn,Ti,Nb)xO2 were synthesized keeping constant the Sn/Ti stoichiometric ratio (70/30) at different Nb doping of 2, 3.5 and 5% of the total metal amount, and hereafter labelled as STN 2, STN 3.5 and STN 5. As synthetized powders were heated at 650 and 850 °C for 2h (STN Nb% 650, STN Nb% 850) to investigate the possible influence of the temperature on grain size, Nb percolation and sensing properties. Observations at SEM microscopy revealed that the morphology of the samples consists of rounded nanoparticles. Samples heated at 650 °C are composed by grains with diameters from 10 to 30 nm, while those heated at 850 °C showed a more uniform grain size distribution (30-40 nm). Along with a small fraction of TiO2 nanocrystalline phase (about 2.5% on average), X-ray powder diffraction analyses confirm that the (Sn,Ti,Nb)xO2 with rutile-type structure is the main phase in all the investigated samples. On the base of the refined unit-cell parameters a 17% substitution of Ti4+ (i.r. 0.605Å) and Nb5+ (i.r.=0.64Å) for the bigger Sn4+ (i.r.=0.69Å) was estimated. The sensing performance of (Sn,Ti,Nb)xO2 sensors were investigated toward various gases (H2, CO, ethanol, NO2, CH4 and acetaldehyde) at their optimal working temperature of 450 °C. As shown in figure 1a, it was found that the STN 2 650 sample exhibit a response to hydrogen 6 to 8 times higher than STN 2 850 and SnO2 650, respectively. Moreover, STN 2 650 displays a better stability in wet conditions (Fig 1b). Despite the increase of relative humidity (RH%) affects the response to hydrogen, the dynamic response to H2 of the sample heated at 650 °C remains still high (Fig. 1c). Thanks to its outstanding characteristics, (Sn,Ti,Nb)xO2 solid solution is a promising candidate for hydrogen detection. The sensing properties towards other gases will be considered. References [1] A. Dey Materials Science & Engineering B, 229 (2018) 206-217 [2] M.Radwcka, K. Zakrzewska, M. Rekas, Sensors and Actuators B, 47, (1998) 194 [3] C. Malagù, V. Guidi, M.C. Carotta, G. Martinelli, Appl. Phys. Lett. 84, (2004) 4158 [4] Shannon, R. Acta Crystallographica A, 32, (1976) 751-767 [5] Hirata, T., Journal of the American Ceramic Society, 83, (2000) 3205-3207 [6] M.C. Carotta, et al., Sensors and Actuators B 139 (2009) 329–339 [7] Ferroni, M., et al. Sensors and Actuators B: Chemical 68.1-3 (2000) 140-145 Figure 1

This work aims at investigating the impact behavior of an additively manufactured AlSi10Mg alloy subjected to different heat-treatment conditions. The commonly used heat-treatment routes were compared with a novel route (HPT6), which combines hot isostatic pressing (HIP), gas quenching, and ageing at high pressures. The as-built and treated alloy was characterized by Charpy impact testing and several microstructural and fractographic techniques, such as scanning electron microscopy, transmission electron microscopy (TEM), and X-ray diffraction. The as-built material displayed a very fine non-equilibrium microstructure, which led to a high impact strength but limited absorbed energy. Low-temperature annealing severely modified the starting microstructure of the alloy and restored its equilibrium condition. Even though this alloy did not suffer from strength loss, its absorbed energy increased significantly, resulting in an excellent impact performance. HIP application inhibited the growth of gas-hosting pores in the alloy when treated at high temperatures, yielding a material with a final relative density higher than 99%. TEM demonstrated that the novel HPT6 route induced precipitation strengthening in the alloy, thus increasing its impact strength when compared to the HIP route. Moreover, the HPT6 alloy and the alloy subjected to standard heat-treatment exhibited comparable impact performance. This suggests that the novel route proposed in this study can possibly replace the standard heat-treatment protocol, which would reduce the processing duration and cost of production of the additively manufactured AlSi10Mg alloy.

Incorporation of dopants in semiconductors is commonly used to modify the optical response and improve the efficiency of related devices. A physical understanding with elemental and local sensitivity of the electron excitation and trapping channels which follow photoexcitation is a prerequisite for knowledge-based materials design. By using high-resolution x-ray absorption methods we show that, in V-doped TiO2 nanoparticles, subband-gap visible light absorption is predominantly due to excitation of electrons from V ions to defective and long-lived Ti sites. We thus identify an element-specific photoexcitation channel.

Crack-free, ligand-free, phase-pure nanostructured solids, using colloidal nanocrystals as precursors, are fabricated by a scalable and facile approach. Films produced by this approach have conductivities comparable to those of bulk crystals over more than 1 cm (1.370 S cm-1 for PbS films).

The chemical and physical properties of the double perovskite Pb2FeMoO6 are systematically studied by means of structural and magnetic characterization. The compound crystallizes in the cubic Fm3¯m space group, with partial cation order involving iron and molybdenum at the perovskite B site. Structural and Mössbauer characterization points to the presence of nanometer-sized antiphase domains within the ordered matrix giving rise to two iron populations, characterized by different chemical environments, with the same weight but different valence (0.3 electrons) and inequivalent magnetic anisotropy. This structural feature deeply affects the properties of the compound: Mössbauer and EPR measurements show a high-temperature superparamagnetic-like behavior ascribed to weak magnetic interactions occurring between the antiphase domains and the rest of the sample. However, below 270 K ferrimagnetic ordering of the atomic moments is observed by neutron diffraction and SQUID magnetometry, with the onset of blocked long range magnetic interactions on the Mössbauer timescale involving both the antiphase domains and the ordered matrix below 230 K. The superparamagnetic-like behavior is ascribed to the presence of low anisotropy barriers, giving rise to an extremely thin hysteresis loop at 5 K, with a very small coercive field and remnant magnetization. The observed saturation magnetization of 1.75 µB per f.u. is in agreement with the magnetic structure determined by neutron diffraction, with the two symmetry independent sites producing a ferrimagnetic resultant µS = 1.59 µB.

Rechargeable batteries based on magnesium virtually provide high volumetric capacity, safety, and cost savings thanks to the abundance, dendrite-free electrodeposition, and environmentally green properties of Mg metal anode. The lack of cathodes that can deliver high currents at high potential is one of the principal bottlenecks that limit the entrance of Mg batteries into the market. Here we report the synthesis and characterization of a novel cathode for magnesium secondary batteries based on graphene oxide (GO) and vanadium (V) active species. Thermogravimetric analysis, structural and vibrational analyses, and high-resolution electron microscopies elucidate the complex architecture that characterizes the proposed material and that bestows exceptional electrochemical properties to the cathode. The proposed synthesis is able to give rise to V-based nanoparticles with a very porous surface and wrapped inside a chrysalis-like GO ordered superstructure. Finally, a coin cell device is assembled using a Mg metal anode and the proposed material as cathode. This prototype is able to deliver good capacities when cycled at high current rates (1000 mA g−1) in a higher potential range with respect to classical cathodes for Mg batteries. Thus, a sufficient power (1.70 W g−1) is obtained, making this battery promising towards the substitution of lithium batteries.

This paper demonstrates that when InGaN LEDs are submitted to a constant reverse bias, they can show a time-dependent breakdown, that leads to the catastrophic failure of the devices. By submitting green and blue LEDs to constant voltage stress in the range between -40 V and -60 V we demonstrate that: (i) under reverse bias conditions, current is focused on localized paths, whose positions can be identified by electroluminescence measurements, and that originate from the presence of extended defects; (ii) during a constant voltage stress, the reverse current of the LEDs gradually increases; (iii) for longer stress times, all devices show a time-dependent breakdown; (iv) time-to-failure has an exponential dependence on stress voltage, and is Weibull-distributed.

Reversible hydrogen sorption coupled with the MgH2 Mg phase transformation was achieved in the remarkably low 340-425 K temperature range using MgH2-TiH2 composite nanoparticles obtained by reactive gas-phase condensation of Mg Ti vapors under He/H-2 atmosphere. The equilibrium pressures determined by in situ measurements at low temperature were slightly above those predicted using enthalpy Delta H and entropy Delta S of bulk magnesium. A single van't Hoff fit over a range extended up to 550 K yields the thermodynamic parameters Delta H = 68.1 0.9 kJ/molH(2) and Delta S = 119 2 J/(Kmo1H2) for hydride decomposition. A desorption rate of 0.18 wt % H-2/min was measured at T = 423 K and p(H-2) approximate to 1 mbar, i.e., close to equilibrium, without using a Pd catalysts. The nanoparticles displayed a small absorption desorption pressure hysteresis even at low temperatures. We critically discuss the influence exerted by nanostructural features such as interface free energy, elastic clamping, and phase mixing at the single nanopartide level on equilibrium and kinetic properties of hydrogen sorption.

In recent years, the lack of high-performing electrical energy storage systems is seriously bottlenecking the operation of appliances in several fields, that include portable electronics, electric automotive, and stationary devices [1]. Until now, lithium batteries (LiBs) are the highest-performing systems that could address satisfactorily all the requirements of such appliances [2]. Indeed, LiBs show a high specific capacity, a high efficiency, and a long lifespan [3]. However, improvements are still needed in the operating potential (that influences the specific energy and power of the LiBs) and in the rate capability properties of the cathodes. Indeed, electric vehicles need high power during acceleration, and a large amount of stored energy to achieve a sufficient mileage. Herein we describe the synthesis and the study of an innovative family of high-energy and high-rate cathodes for application in LiBs. The structure of a high-performing olivine material of the type LiMPO4 (M = Fe, Ni, and Co) [4] has been doped with high-valence transition metal ions (V(V), Nb(IV), or Ta(IV)). In a first step, the synthesis procedure has been optimized. Five different materials have been obtained, as follows: (i) LFNCVP is a vanadium-doped olivine obtained under oxidizing conditions; (ii) LFNCVP/C is a vanadium-doped olivine obtained under partially reducing conditions (graphite is added during the pyrolysis); (iii) LFNCVP/H is a vanadium-doped olivine obtained under reducing conditions (pyrolysis is carried out under a hydrogen atmosphere); (iv) LFNCNP is a niobium-doped olivine obtained under oxidizing conditions; and (v) LFNCTP is a tantalum-doped olivine obtained under oxidizing conditions. The effects of the different synthesis protocols and ion insertion on the structural, morphological, and electrochemical properties of the cathodes have been thoroughly investigated. The composition of the cathodes has been evaluated by means of Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES), the morphology and size distribution have been gauged by Scanning Electron Microscopy (SEM) and High-Resolution Transmission Electron Microscopy (HR-TEM); the structure has been revealed through powder X-Ray Diffraction (XRD) and IR spectroscopy techniques. The electrochemical performance has been investigated by Cyclic Voltammetry (CV), Electrochemical Impedance Spectroscopy (EIS), and coin battery charge/discharge tests at different current rates. As expected (see Figure 1), the proposed materials reveal a high performance in terms of working potential (4.0÷5.0 V vs. Li/Li+), specific capacity (149 mAh∙g-1), and specific energy (656 mWh∙g-1). Moreover, the insertion of high-valence transition metals is able to boost the rate capability of the cathodes, allowing for fast charge and discharge processes without depleting the cathodes. References [1] B. Dunn, H. Kamath, J. M. Tarascon, Science 334 (2011) 928-935. [2] V. Di Noto, T. A. Zawodzinski, A. M. Herring, G. A. Giffin, E. Negro, S. Lavina, Int. J. Hydrogen Energy 37 (2012) 6120-6131. [3] B. Scrosati, J. Garche, J. Power Sources 195 (2010) 2419-2430. [4] G. Pagot, F. Bertasi, G. Nawn, E. Negro, G. Carraro, D. Barreca, C. Maccato, S. Polizzi, V. Di Noto, Adv. Funct. Mater. 25 (2015) 4032-4037. Figure 1

The three-dimensional tomographic reconstruction of a biological sample, namely collagen fibrils in human dermal tissue, was obtained from a set of projection-images acquired in the Scanning Electron Microscope. A tailored strategy for the transmission imaging mode was implemented in the microscope and proved effective in acquiring the projections needed for the tomographic reconstruction. Suitable projection alignment and Compressed Sensing formulation were used to overcome the limitations arising from the experimental acquisition strategy and to improve the reconstruction of the sample. The undetermined problem of structure reconstruction from a set of projections, limited in number and angular range, was indeed supported by exploiting the sparsity of the object projected in the electron microscopy images. In particular, the proposed system was able to preserve the reconstruction accuracy even in presence of a significant reduction of experimental projections.

Faulted face-centred cubic platinum nanocrystals, grown within a nanoporous silica matrix, have been extensively characterized by the Debye function analysis method applied to wide-angle synchrotron X-ray total scattering data. A method for building databases of sampled interatomic distances of weakly faulted materials is proposed, maintaining statistical significance and allowing complete populations of differently sized and shaped nanocrystals to be used within the DEBUSSY approach. This study suggests that anisotropic Pt nanoclusters are formed in the presence of a shape-directing (templating) agent, and tentatively describes the effects of post-synthetic temperature treatments on fault probability, size, shape and dispersion of the nanocrystal populations. Surface relaxation effects are also observed in the smallest particles.An algorithm enabling the active use of deformation fault probabilities in face-centred cubic metals within the Debye scattering equation approach implemented in the DEBUSSY suite and the subsequent characterization of Pt nanocrystals grown in a nanoporous silica matrix are presented.

Antireflecting–passivating TiO2–SiO2 double layers on crystalline silicon (Si) were optimized and characterized for space solar cells applications. In the numeric optimization, the MgF2–glass–adhesive–TiO2–SiO2–Si structure was considered. In order to fabricate the TiO2–SiO2 double layer, titanium films were deposited on Si wafers in a vacuum chamber, and then, the sample was annealed in oxygen at high temperatures. Glasses with evaporated MgF2 thin films were bonded to the TiO2–SiO2–Si samples so as to obtain the complete structure. A gain of up to 23.5% in the maximum power is demonstrated for simulated c-Si solar cells using the optimized structure. Characterization of the TiO2–SiO2–Si structure using transmission electron microscopy (TEM) and X-ray reflectivity (XRR) as well as optical characterization are presented.

Ultrathin (thickness , 2.2 nm) colloidal Sb2S3 nanowires and nanoplatelets were synthesized via a simple solution synthesis. The nanowires and platelets were stable in solution for months and were characterized via SAED, XRD, UV-VIS spectro- scopy, SAXS, XPS and EDAX.

A systematic X-ray absorption spectroscopy investigation of the local coordination in gallium nanostructures has been performed as a function of temperature and particle size. It is shown that the nanostructure strongly affects the polymorphism of solid gallium and the (meta)stability range of the liquid phase (in agreement with previous works) and that the surface tension acts in the same direction as hydrostatic pressure in stabilizing the Ga solid phases. The effect of surface free energy is first to favor the metallic arrangement of the delta phase and then to stabilize a liquid-like phase based on dimeric molecules even at 90 K. The Ga-Ga distance in the dimers is lower in the liquid phase than in the alpha solid. The experimental results are discussed in comparison with molecular dynamic calculations to assess the presence of covalent character of the dimeric Ga-2 units in liquid nanostructured gallium.

In the present work, a series of Au- and Au-Cu-containing catalysts based on different carriers such as TiO2 and CeO2 were studied with a view to increasing the activity and selectivity in 5-hydroxymethylfurfural oxidation by optimizing the interaction both between the metals and with the support. The results obtained demonstrated the high activity in HMF oxidation of gold supported on ceria and titania. Nevertheless, although the particle size of gold on both supports was comparable, Au/CeO2 showed significantly higher activity than Au/TiO2, thus corroborating the theory that not only the gold particle size, but the support also, plays a key role in HMF oxidation in the aqueous phase. Indeed, pre-made uniform nanoparticles, used for catalyst preparation, were surface-bound by poly(N-vinyl-2-pyrrolidone) - the stabilizer used during nanoparticle synthesis - whose presence proved to prevent the interaction of active phases with CeO2, while worsening the catalytic activity of both monometallic and bimetallic systems. The pre-treatment of the prepared catalysts was necessary to activate the materials, by maximizing the contact between the metal and the support and thus suggesting an important role of the ceria defects on 5-hydroxymethylfurfural oxidation to 2,5-furandicarboxylic acid. (C) 2014 Elsevier B.V. All rights reserved.

The BiMnO3 perovskite is a very interesting multiferroic material that, once synthesized at high pressure and high temperature, survives as a metastable phase at ambient conditions. We investigated ceramic samples prepared in different conditions (temperature, pressure, and composition), and the existence of polymorphism at room temperature was clearly evidenced by electron diffraction and high-resolution electron microscopy in all the samples. A new polymorph, characterized by a different distortion of the perovskite basic cell, was found to coexist as a minor phase with the well-known C2 monoclinic form. The new polymorph, which can be described by a triclinic (pseudorhombohedral) superstructure with a = 13.62 angstrom, b = 13.66 angstrom, c = 13.66 angstrom, alpha = 110.0 degrees, beta = 108.8 degrees, and gamma = 108.8 degrees, is mostly segregated at the grain surface. Magnetic characterizations revealed for this second form a critical temperature of 107 K, a few degrees above the ferromagnetic transition of the monoclinic C2 form measured at 99 K. The new phase disappears by reheating the samples at ambient pressure, suggesting the idea of a higher energy polymorph, which kinetically converts in the usual phase once a sufficient temperature has been achieved.

The importance of pure-phase titanium oxide materials as catalysts, sensors, and photonic band-gap materials has been growing steadily. Recently, more attention has been focused on nanostructured titanium oxide showing controlled and periodic porosity on a nanometric scale. The nanocrystal size control of porous nanostructured titanium oxide in an anatase form is a crucial step for the organic template method. Simple template removal by evaporation in an inert atmosphere is reported in this article and compared with the calcination technique usually reported in the literature. The proposed method allows the formation of a double-porous (macro and meso) anatase phase. We demonstrate that it highly preserves the macropore order into a titanium oxide material and induces narrowly dispersed mesopores by controlling the nano-crystal size that is kept around 6 nm. For the proposed method, polystyrene beads are particularly suitable as templates, being evaporated in the temperature range of anatase existence. The final high surface area makes the materials appealing for applications as photocatalysts or sensors.

Transition metal fluorides with tetragonal tungsten bronze (TTB) structure, having general formula KxMIIxMIII1-xF3 with 0.4 < x < 0.6 and M belonging to transition metals, have been studied over the past decades because of the frustrated magnetic ordering arising at low temperature. We investigated the structural properties of TTB fluorides by transmission electron microscopy (TEM). The results, coupled with an accurate structure analysis performed by single-crystal XRD on K0.53FeF3, revealed ferroelectricity and a unified structural description of these materials, where charge order and tilt modulations coexist, each one with its own periodicity differently commensurate to the conventional TTB cell. Whereas the charge order is peculiar of the mixed valence fluorides, the nature of the tilt modulation is clearly associable to the structural features of TTB niobates, suggesting also for the fluoride bronzes the existence of a generalized ferroelectric-ferroelastic behavior at room temperature.

Results of a colloidal crystal growth by vertical deposition of nanometric polystyrene beads on a glass substrate under oscillatory shear are reported in this paper. This technique of deposition enabled us to study an early stage of the growth of films as a function of the bead concentration in the water suspension. The surprising analogy between single layer growth and the bulk colloidal crystal behavior has been found. Indeed, the sequence of transitions from low density disordered (LDD) phase to intermediate density ordered phase and then to high density ordered phase with increasing bead concentration has been observed. © 2003 Elsevier Science B.V. All rights reserved.

We have developed a novel method to grow ordered layers of monodisperse colloids on a flat substrate. The evaporation of the colloidal suspension in the presence of the inclined substrate is strengthened by an external gas flux directed on the meniscus. The meniscus oscillations caused by the gas flux have an evident effect on the ordering of the spheres on the substrate. Thick films (more than 150 layers in a single-step deposition) of large area single crystals (∼1 cm 2 ) can be obtained in a very short time (∼1 cm/h maximum growth rate) and from very diluted suspensions (up to 0.022% volume fraction).

We present homojunction and micro-c-Si/a-Si:H/c-Si heterojunction silicon solar cells fabricated by PECVD. The H2 dilution used during the i-layer growth strongly affects the device efficiency. While intermediate H2 dilution of the gas mixture results in V-infinite degradation, the best V-infinite is obtained under zero or very high (= 99.4%) H2 dilution, resulting in totally amorphous or epitaxial i-layer respectively. A maximum value of 638 mV, with 13.7% e.ciency, is observed in the case of an amorphous i-layer, indicating an improvement of interface quality. If the i-layer is deposited using a 99.4% H2 dilution, a 608 mV V-infinite is observed and for homojunction solar cells a 13.1% efficiency is obtained.

Pulsed laser deposition of carbon-based materials has been explored in order to obtain cold cathode flat emitters with high emission current density and low threshold field, and to examine the factors controlling the electron field emission behaviour. In this paper, results on amorphous carbon thin films deposited on silicon by pulsed laser ablation (PLA) from a graphite target, using a KrF excimer laser are presented. The structure and surface morphology of carbon materials have been examined by transmission electron microscopy (TEM) and Raman spectroscopy. I – V characteristics of the carbon films have been measured by a diode technique (below 10 −4 Pa). Some effects of the deposition parameters on thin film uniformity, adhesion, and field emission performances have been investigated. Emission current density as high as 50 mA/cm 2 at an electric field of 70 V/μm has been obtained on 100 nm thick, smooth and glassy carbon films deposited at 150 °C.

The triclinic crystal structure of the φ phase in the structure of the Bi2O3–PbO phase diagram has been recently solved by the synergetic use of electron and X-ray diffraction on a polycrystalline Bi8Pb5O17 sample. In the present work the problem is re-examined on the basis of powder neutron diffraction data: the structure has been confirmed and refined by the Rietveld method. The increased accuracy of the O-atom positions allowed the study of the cationic ordering in this structure by means of bond-valence calculations and charge distribution analysis. The results, confirmed by the refinement of the site occupancies, indicate that the structure is ordered to a large extent, with Bi and Pb atoms occupying preferentially different lattice sites. In this frame, the φ phase being the most ordered one in the considered region of the Bi2O3–PbO phase diagram, it should represent the thermodynamically stable low-temperature polymorph.

Secondary electron emission from diamond films is studied as a function of the primary electron beam energy and bulk material properties. A formulation of a simple model of the secondary electron emission coefficient, as a function of the primary electron beam energy, has been found to be helpful in defining physical criteria able to guide the optimization of the diamond film electron emission performance. The secondary electron mean escape depth deduced from the model is indeed related to the density of defects in the material and represents the main factor in determining the low energy secondary electron yield. These results are supported by Raman spectroscopy measurements, indicating a lower graphitic content and a higher crystalline quality of the diamond phase in films showing better secondary electron and photoemission yields. We demonstrate that a diamond film, acting as a stable and proportional electron multiplier, can be used as a converter of backscattered electrons into secondary electrons in scanning electron microscopy. It will be shown that the use of a diamond film converter is suitable to improve the signal to noise ratio of images providing an enhanced compositional contrast.

The authors investigate the tetragonal(T)-orthorhombic(O) transient zone of YBa 2 Cu 3 O 6+x , in a comparative way on pair samples one of which is produced by deintercalation [D] and the other by intercalation [I] of intrinsic oxygen in the basal Cu(1)O x plane and having the same oxygen content (k) and thermal history. Resistive and electron diffraction measurements, performed on [D] k - [I] k pairs within the composition range 0.28 ≤ k ≤ 0.32, are reported. Direct evidence is provided that the T-OII transient is a structural and electronic two phase region characterized by the (T+OII) [D] 0.30 non-superconducting (non-SC) and (OII+OIII*) [I] 0.30 superconducting (SC) phases. The OII superstructure represents the minority component of [D] 0.30 phase and the majority one of [I] 0.30 and OIII* is a new orthorhombic anti-OIII superstructure. The nature of the non-SC and SC behaviours has been comparatively investigated by NQR analysis at the T-OII borderline. The evaluated different values of the average chain lengths emphasize the role of the Cu-O chain length on the hole doping efficiency in YBCO at constant oxygen content.

The oxygen-order dependent emergence of superconductivity in YBa2Cu3O6+x is studied, for the first time in a comparative way, on pair samples having the same oxygen content and thermal history, but different Cu(1)Ox chain arrangements deriving from their intercalated and deintercalated nature. Structural and electronic non-equivalence of pairs samples is detected in the critical region and found to be related, on microscopic scale, to a different average chain length, which, on being experimentally determined by nuclear quadrupole resonance (NQR), sheds new light on the concept of critical chain length for hole doping efficiency.

A new software package for quantitative electron diffraction data treatment of unknown structures is described. No “a priori” information is required by the package which is able to perform in successive steps the 2-D indexing of digitised diffraction patterns, the extraction of the intensity of the collected reflections and the 3-D indexing of all recorded patterns, giving as results the lattice parameters of the investigated structure and a series of data files (one for each diffraction pattern) containing the measured intensities and the relative e.s.d.s of the 3-D indexed reflections. The software package is mainly conceived for the treatment of diffraction patterns taken with a Gatan CCD Slow-Scan Camera, but it can also deal with generic digitised plates. The program is designed to extract intensity data suitable for structure solution techniques in electron crystallography. The integration routine is optimised for a correct background evaluation, a necessary condition to deal with weak spots of irregular shape and an intensity just above the background.

We report the structure determination, by electron diffraction and high resolution electron microscopy, of two phases, Ba 0.70 CuO 2 and Ba 0.67 CuO 2 , that characterise the Ba x CuO 2 (0.67≤ x ≤0.70) system where 13 K superconductivity has been recently found. Both phases show modulated structures that can be described in terms of composite crystals, resulting from the interpenetration of mutually incommensurate sublattices consisting of Barium atoms and infinite chains of edge sharing CuO 4 planar units. The average Ba 0.70 CuO 2 structure was solved by application of direct methods to electron diffraction data. Starting from this results and on the basis of diffraction patterns and high resolution images, the related Ba 0.67 CuO 2 structure has been described in terms of interpenetration of three mutually incommensurate sublattices associated with twinning. Owing to the extreme complexity of this structure, only a qualitative model has been developed, which is, however, able to describe all the peculiar features of this unusual and interesting structure.

A comparative investigation, performed on Oxygen-Chain-equalised(k) Deintercalated [ OCD ] k and Intercalated [ OCD ] k pair-samples ( k -pairs) of YBa 2 Cu 3 O 6+x by resistive T c and electron diffraction (ED) at steps Δk=0.02-0.03, revealed that equivalent or non-equivalent microscopic oxygen-chain arrangements are produced, at the same oxygen content k, by intercalation and deintercalation of oxygen in the Cu(1)Ox chains. These arrangements manifest in Tc -singularities or Tc -splittings of the k -pairs, whose occurrence can be straightforwardly explained by taking into account the non equivalence of the structural phase diagrams of YBCO, pointed out by electron diffraction, when produced by intercalation of oxygen in the tetragonal T structure or by deintercalation from the orthorhombic OI structure. Tc -singularities are produced in the k ranges for which a superimposition of the phase diagrams occurs, whereas Tc -splitting are pointed out in correspondence of splitted structural regions. The maximum Tc -splitting is observed in proximity of the semiconductor-metal transition with the appearing of superconductivity related to an anti-OIII (OIII*) superstructure in intercalated samples at k =0.30, where the corresponding deintercalated samples are tetragonal and semiconductor. This result confirms that the vanishing of the antiferromagnetic ordering, the emergence of hole doped superconductivity and the symmetry breaking at the T-O transition are nearly coincident phenomena in YBCO. However the related critical oxygen stoichiometry is strictly dependent on the ordering parameter in the Cu(1) plane, i.e. on the formation of extended chains. The OIII* structure, for the first time observed in a systematic way at the T-O transition in intercalated samples, seems to exhibit in analogy with OII and OIII a characteristic Tc .