Substitution and recycling of critical raw materials in optoelectronic, magnetic and energy devices - II

Resume : Perovskites solar cells have emerged as a beacon in thin film photovoltaic technology. The power conversion efficiencies (PCE) has reached to a level of mature thin film technology, which took decades to reach the similar performance of 22.7 %. To improve the inherent challenges, compositional engineering of perovskites as well as molecular engineering of hole transport materials (HTMs) were adopted, without the use of any critical raw materials. Device performance and stability was subsequently enhanced to an extent. However, the intrinsic as well as extrinsic stability of perovskites remains problematic for its real potential applications. Here, the use of an optimized passivation layer is seen as an ideal approach to protect the surface from extrinsic attack, without altering the electro-optical properties. We will describe our findings on the role of passivation layer and compositional engineering approach to protect the perovskite layer from atmospheric attack. An improved PCE was also obtained compare to reference devices, as the passivation layer will restricts the flow of electron towards the HTM layers and lower recombination was obtained. A batch-to-batch reproducibility with ±0.5% PCE was achieved along with very competitive efficiencies of 20%.

Resume : The first perovskite solar cells (PSC) fabricated directly on a paper substrate are here reported. The paper PSCs were developed with a low-temperature Paper/Au/SnO2/meso-TiO2/CH3NH3PbI3/Spiro-OMeTAD/MoOx/Au/MoOx architecture utilizing a Au/SnO2 and MoOx/Au/MoOx stack as electron- and hole- extracting electrodes respectively, delivering state of the art power conversion efficiency of 2.7% for solar cells prepared directly on the opaque paper substrate. The transparent top MoOx/Au/MoOx electrode had a favourable combination of transmittance (62.5%) and sheet resistance (9 Ω/□). Opaque and transparent bottom electrodes were also designed. By comparing performance of cells on paper with those fabricated on glass and plastic films with different electrodes, we identify avenues that can help guide future research for improved performance. All the deposition processes used are scalable and compatible with large area printing or evaporation technologies. Paper represents a lightweight, flexible, inexpensive, ubiquitous, and environmentally friendly material, paving the way for integrating perovskite semiconductor technology with other electronic components as well as for the development of stand-alone PV devices on low-cost and recyclable cellulose paper substrates.

Resume : With the advantages of simple preparation process and high efficiency, perovskite solar cells have become most industrial potentiality in new-type solar cells. However, with the disadvantages of high-cost and low hole mobility on spiro-OMeTAD hole transport materials, inorganic hole transport layer have become significant investigation area of perovskite solar cells. Due to the advantages of high stability, simple preparation process, high hole mobility and size-effect, CuSbS2 quantum dot have been considered as a excellent hole transport materials for perovskite solar cells. In the present work, CuSbS2 quantum dot are prepared with different size and surface passivation process for hole transport layer of perovskite solar cells by spin-coating process. With the size decreasing of quantum dots, the distinction of band energy between hole transport layer and optical absoprtion layer will be increased, which can improve the open-circuit voltage of the solar cells. And CH3CH2I and ZnSe have been introduced for the passivation layer of CuSbS2 quantum dots. It can effectively enhance the photovoltaic conversion efficiency of perovskite solar cells, which have higher short-circuit current density than that of spiro-OMeTAD hole transport materials. These investigations of size and surface passivation process on CuSbS2 quantum dot hole transport materials can provide a perspective area on development of quantum dot hole transport materials.

Resume : An environmental friendly method adopts for the fabrication of anatase titanium dioxide (an-TiO2) as electron transporting layer (ETL) at room temperature was developed for efficient perovskite solar cells (PSCs). Both small and large area device demonstrate the favorable efficiency for PSCs. Grinding TiO2 is a new class of promising material which is suitable for both plastic as well as other flexible substrates manufacturing because of his room-temperature annealing process. The frequently used ETL is an-TiO2 material because of its superior semiconductor characteristics, outstanding optical transmittance and suitable band alignment. Herein, we report for the first time a room-temperature (< 30 ℃), low cost massive production of ETL is developed by grinding of large clumps of an-TiO2 material to achieve suspension of a nanoparticles (NPs) of TiO2 for meso-superstructured PSCs. This process does not required any chemical synthesis, it is purely physical process. Therefore, the weighty nature of oxygen and water protection on an-TiO2 NPs provides a uniform and smooth surface. The lowest unoccupied molecular orbital (LUMO) of the ground an-TiO2 NPs, estimated by ultraviolet photoelectron spectroscopy (UPS), was 4.06 eV, which is salient feature for active layer. When using the solution-processed ground an-TiO2 NPs as the ETL imitative from a 1.5wt % concentration, the resulting CH3NH3PbI3-based PSCs exhibit a champion power conversion efficiency (PCE) at room-temperature (< 30 ℃) of 17.43% with an active area of 0.1cm2. We used same strategy to fabricate a large-area CH3NH3PbI3 film (mask area 25.2 cm2), and achieved a PCE of 14.19%. PSC devices incorporating the ground an-TiO2 NPs as ETLs exhibited attractive long-term device stabilities, with PCEs retaining approximately 85% of their initial values after 80 days, which will open a new paradigm for commercialization for PSCs.

Resume : Thin photovoltaics based on chalcopyrite film, Cu(In,Ga)Se2 (CIGS) and related alloys, have exhibited so far efficiency over 22,3% on the laboratory scale. However, the CIGS solar cells scale-up is expected to be hampered because of the low availability of In and Ga in the Earth crust. The most promising next leader in the chalcogenide thin film technology seems to be the kesterite compound Cu2ZnSnS4 (CZTS), as it is based on earth-abundant elements and it shows the better results when low-cost solution processable techniques are employed in the fabrication. Solution-processed inorganic semiconductors, in fact, offer a rising route for the low-cost mass production of solar cells In this context, we present a new chemical procedure to obtain a superior quality Cu2ZnSnS4 and Cu2FeSnS4 thin films composed of highly soluble and inexpensive precursors in a non-toxic and environmentally friendly solvent. The films were prepared by a Sol-Gel method and the deposition was carried out by in situ gel formation on fluorine doped tin oxide coated glass. The films obtained were characterized by Raman spectroscopy, X-ray diffraction, energy dispersive X-ray analysis, photoluminescence spectroscopy and by electronic scanning microscopy. The developed methodology has successfully identified an innovative way to achieve high-quality kesterite thin films for photovoltaic applications; relate devices optimization is currently underway.

Resume : In the field of renewable energy production, porous Si/eumelanin hybrids are a novel interesting class of organic–inorganic materials for photovoltaic applications. One of the main issues of this junction that prevented the construction of a marketable devices is, however, the photocurrent temporal stability. In the perspective of solving this problem, the understanding of the polymerization mechanisms and of the eumelanin–Si interface formation is needed. We report herein an integrated experimental and computational study to investigate the samples stability. Different experimental strategies have been proposed, both related to the interface modification and to the methods that can be used to impregnate the inorganic porous matrix. Moreover, from the computational point of view, the organic-inorganic interface formation has been simulated, studying the 5,6-dihydroxyindole (DHI) monomer evolution and its adhesion to silicon. A first improvement in the junction stability can be obtained with a mild oxidation of the porous silicon surface because of the enhancement of the DHI–surface interaction, and calculations have shown that the higher oxidation states in DHI oligomers create more favorable conditions for the efficient adhesion of eumelanin on silicon surface. REFERENCES: [1] G. Mula et al., Nanoscale Res Lett 2012, 7, 377; [2] Pinna et al., RSC Advances, 2015, 5, 56704; [3] E. Pinna et al., Int J Mol Sci 2017, 18, 1567; [4] L. Panzella et al. Angew Chem Int Edit 2013, 52.

Resume : ITO is a unique material with optical and electrical characteristics that at present make it the material of choice in displays, touch screens, solar cells and optoelectronic devices. However, ITO is not suitable for UV and NIR applications and, in addition, is listed among the critical raw materials (CRMs) for EU due to its high supply risk. Therefore alternative materials with similar properties should be identified. In this work we fabricated atomically smooth ultrathin and electrical stable nickel films, by using radio frequency sputtering at room temperature. Continuous films with low resistivity down to 5.6x10-5 Ω·cm and wide spectral range transparency were achieved for thicknesses of a few nanometers without using any seed layer. A novel method based on angle resolved transmittance and reflectance measurements allowed the calculation of the refractive index and extinction coefficient of a Ni films with thickness of about 5 nm.

Resume : Finding an alternative to expensive tin doped Indium oxide as a TCO layer has been a challenge for thin film solar industry. In this regard, doped-TiO2 is a promising alternative to the conventional TCOs, because it is an inexpensive, non-toxic, chemically and electrically stable transparent material with wide optical band gap (Eg; 3.2 eV for anatase). In this study, Ta-doped TiO2 films are successfully fabricated by RF magnetron sputtering by varying a wide range of experimental parameters, such as, dopant concentration, substrate temperature, substrate type, film thickness, post-deposition annealing and microstructure of the seed layer. A detailed microstructural and optoelectronic characterization of all these films are then carried out by using a combination of experimental techniques, like, GI-XRD, AFM, FESEM, XPS, UV-Vis-NIR, PL spectroscopy and Hall effect measurement system. Growth of high quality anatase TiO2 with strong (101) peak and with no presence of rutile, Ta, and/or Ta2O5 is observed. Whereas electrical properties of these films are found to be strongly dependent on the microstructure, all these films are found to be highly transparent with an average transmittance of 80% in the visible range. Blue shift is observed in these films with average Eg being 3.6 eV, which is larger as compared to the bulk Eg of anatase TiO2. Understanding developed in this study might help in tuning the process parameters to design the Ta-doped TiO2 films for the desired application.

Resume : Transparent conducting oxides such as Sn doped In2O3 nanowires (NWs) have been investigated in the past since they are important building blocks for the realization of novel electronic and optoelectronic devices like solar cells, but In is rare and expensive [1]. Similarly Sb doped SnO2 NWs are also transparent and exhibit metallic like conductivities but they are more attractive since Sn is abundant and not expensive. In the past free standing, SnO2 NWs have been grown on c-axis oriented sapphire with a certain degree of alignment while planar and aligned SnO2 NWs have also been obtained sapphire [2] . Here we will describe the growth of highly aligned, free standing and straight Sb doped SnO2 NWs with diameters of a few tens of nm's and lengths reaching up to several tens of um that were obtained by the vapor liquid solid mechanism on r- oriented sapphire using Au as a catalyst. We show that orthogonally oriented Sb doped SnO2 NWs with a highly regular and uniform mesh structure may be obtained on m-oriented sapphire. The electrical and optical properties of the Sb doped SnO2 NWs have been measured by (a) THz conductivity and (b) ultrafast pump probe spectroscopies. More importantly we show that the Sb doped SnO2 NWs can be grown at selective locations thereby forming ordered arrays with definite spacing's. This enables one to tailor the absorption and transmission spectra while maintaining a high conductivity which is important for the development of novel optoelectronic devices in conjunction with other organic or inorganic materials. [1] M.Zervos et al., Broad compositional tunability of indium tin oxide nanowires grown by the vapor liquid solid mechanism', Applied Physics Letters Materials, 2, p.056104 (2014). [2] X.Wang et al., Aligned Epitaxial SnO2 Nanowires On Sapphire : Growth and Device Applications, Nano Letters., 2014, 14 (6), pp 3014–3022

Resume : Bandgap-tunable silicon nanocrystals (Si NCs) have been widely studied towards their application in light-emitting diodes (LEDs). For these devices, the selection of a proper material as top electrode has to meet specific criteria regarding conductivity and transparency. ZnO is currently being employed as transparent conductive oxide (TCO) in solar cell applications because it is a non-toxic and earth abundant material, but it could be also used as top electrode for LEDs. Moreover, because of its luminescence properties, ZnO could also become an interesting candidate as luminescent TCO contact; however, to date, this material has not been exhaustively explored. In this work, we analyse the electroluminescence (EL) properties of Si NC/SiO2 multilayers embedded in a metal-insulator-semiconductor device structure, with ZnO as top contact. DC EL emission is influenced by both the defect states within the ZnO electrode and the quantum-confined contribution from Si NCs. In addition, pulsed electrical excitation was found not only to enhance the total EL intensity by one order of magnitude, but also to modulate the ratio between the ZnO and Si NCs contributions to luminescence. This effect was investigated via recombination dynamics, which allowed modelling the excitation mechanism in terms of sequential carrier injection. Overall, this work highlights the importance of employing luminescent ZnO TCO to expand the EL emission from Si NC-based LEDs towards the visible range.

Resume : Magnetic nanoparticles (NPs) have attracted a great interest in the last decades thanks to their novel fundamental properties emerging from their extremely reduced size. Special attention has been devoted to Co-ferrite (CoxFe3-xO4) NPs due to their cheap manufacturing and high magnetic anisotropy. In particular, the application of Co-ferrite in the realization of permanent magnet has attracted a renewed interest as an alternative to rare-earth base materials in low energy applications. Therefore, a deeper understanding of the structural, size-dependent and morphological effects on final magnetic properties appears necessary. Herein, we present the chemical synthesis of a series of Co-ferrite NPs with a broad range of particle sizes (from 4 to 60 nm). We evaluated the (BH)max product, the figure of merit of permanent magnets, obtaining the maximum values ever reported in the literature for Co-ferrite NPs (i.e., 2.1 MGOe). Moreover, In a second step, we have used these Co-ferrite NPs for building blocks of more complex heterostructures based on antiferromagnetic(AFM)|ferrimagnetic(FiM) core|shell (CS) particles. The CS structure has been generated by topotaxial oxidation of the core region. The sharp interface, the high structural matching between both phases and the good crystallinity of the AFM material have been structurally demonstrated and are corroborated by the robust exchange-coupling between AFM and FiM phases. These properties induce a huge improvement of the capability of storing the energy of the material, a result which suggests that the combination of highly anisotropic AFM|FiM materials can be an effective strategy towards the realization of novel Rare Earth-free permanent magnets.

Resume : Nanoparticles featuring a high magnetic anisotropy are strongly desired for applications related to spintronics such as mass storage media or magneto resistive sensors. Nevertheless, highly anisotropic nanomagnets usually require critical raw materials (CRMs) such as rare earth or platinum group metals. In contrast, abundant materials such as iron oxide (Fe304) nanoparticles are very well-known thanks to their superparamagnetic properties. Therefore, the enhancement of the magnetic anisotropy of Fe3O4 nanoparticles in order to produce blocked magnetic single domain nanoparticles at room temperature is highly challenging. In this context, exchange-coupling in bimagnetic nanoparticles is a very attractive tool. Indeed, a magnetic shell with a high magnetic anisotropy grown onto a Fe3O4 nanoparticle is a very efficient way to enhance their effective magnetic anisotropy. We will report on the design of Fe3O4 nanoparticles which combine additional magnetic components in order to enhance their magnetic anisotropy through exchange coupling. Further, we will present some results on their collective magnetic properties as function of their spatial arrangement when assembled onto substrate.

Resume : MnSb thin films are promising for semiconductor-ferromagnetic structures and spintronic devices. The synthesis was carried out under high vacuum conditions using antimony and manganese films obtained by separate sputtering. The evaporator temperatures were chosen based on the calculation of Mn and Sb vapor flux densities. The stoichiometric composition of MnSb was obtained when the metal condensation fluxes were equal. Sitall and Si wafers were used as the substrates. The speed, evaporation time and substrates temperature were experimentally determined so that the films thickness and the crystallites size composing the film did not exceed 200 and 600 nm, correspondently. Due to high chemical activity of the metal nanolayers, the manganese antimonide growth occurred at temperatures lower than the MnSb peritectic decomposition temperature. Best structures, both the single-crystal MnSb films and their interfaces were obtained on Ge/Si substrates by the MBE. Nanostructures based on MnSb with 1D, 2D, and 3D self-organization can be obtained by Mn and Sb simultaneous deposition in ultrahigh vacuum to highly oriented pyrolytic graphite. The synthesis process was studied by X-ray diffraction, optical and electron microscopy, AFM and MFM. The optimal annealing conditions were determined: 350-400 °C and 3-4 hours. According to the of MFM data, the grown films had ferromagnetic properties.

Resume : Because of the criticality of rare earths (RE), the trend these days is to develop rare earth free/lean magnets as alternatives to Nd-Fe-B (2:14:1 phases) and Sm-Fe(Co) magnets. High performance permanent magnets must have high values of saturation magnetization MS, anisotropy field Ha, Curie temperature Tc (> 300º C) and the proper microstructure that leads to high coercivity. The 1:12 compounds RE-Fe12 with ThMn12 structure have excellent intrinsic properties (MS, Ha, Tc) but it is difficult to develop the proper microstructure that will prevent the nucleation of reversed domains and/or pin the domain walls. In this work, we will present the effects of the microstructure on the coercivity of RE-lean magnets. In samples with the 2:14:1 phase we have obtained large values of coercivity (Hc=2.5T), which is very high regarding its anisotropy field (37%-Ha), after infiltration of nanocrystalline melt-spun alloys. In alloys with 1:12-phases the coercivity is still low, reaching maximum values of Hc=0.5T in samples with Ha>10T. More detailed results of our research work during the past few years will be presented and discussed. This work is supported by the NOVAMAG Project (No. 686056) and DOE.

Resume : Ferrites enjoy a unique position in the group of permanent magnets due to their commercial importance. They are used in low field and low power applications, high-frequency systems... Based on their high demand, recycling of the residues generated in the manufacturing process is beneficial from an environmental point of view but also economically to reduce costs at the magnet company while additionally guarantying sustainability by closing the loop in production line. The Sr-ferrite (SrFe12O19) residue used in this study was collected in the permanent magnet factory in the shape of moisture comprising magnetic powder, water and coolant fluid. Application of a calcination process, under similar parameters to those used by the company in production, results in a recycled Sr-ferrite powder with a high coercivity value (3.3 kOe) above 3.5 times larger than that of the powder acquired by the company for magnets fabrication. The improvement in magnetic properties is the result of an efficient nanostructuration and homogenization of the powder [1]. This has been additionally proven by studying microstructural and magnetic modifications induced by application of a self-developed surfactant-assisted rapid-milling method [2,3] to the commercial Sr-ferrite powder. References [1] A. Bollero et al., ACS Sustainable Chem. Eng. 5, 3243 (2017). [2] J. Rial et al., J. Phys. D: Appl. Phys. 50, 105004 (2017). [3] F.J. Pedrosa et al., Appl. Phys. Lett. 109, 223105 (2016); RSC Adv. 6, 87282 (2016).

Resume : Whenever it comes to applications requiring magnets of highest energy densities, like in e-mobility, wind turbines, robotics etc. rare earth (RE) permanent magnets based on Nd-Fe-B are the material choice. With their outstanding performance they are key components in numerous applications and often not substitutable without performance losses. The transition in energy and transportation sectors as well as automatization will increase significantly the demand for efficient magnet material in the near future. The required RE elements are mainly mined in Asia, with China being by far the dominating player in the market – not only regarding the production of the RE elements and RE permanent magnets, but also as important manufacturer of devices. For Europe, being deprived in RE mineral resources and strategic metals in general but having an economy strongly depending on those materials, this situation should be regarded as highly critical. One way to lower the supply risk for Europe is to make use of the magnet material already circulating in the technosphere: either by reprocessing back to the individual RE elements or their oxides, or by employing functional recycling, i.e. refeeding the permanent magnet intermetallic compound back into the process chain to avoid the costly and energy-intensive separation steps. In this presentation, we highlight current RE criticality aspects and demonstrate how new fully dense sintered, hot-deformed and anisotropic polymer bonded permanent magnets of good quality can be processed from recycled scrap magnet material – at lower economic and ecological costs than magnets made of primary materials.

Resume : There are constant efforts being done to reduce greenhouse gas emissions. Rare earth elements (REEs) play a significant role in these, being essential for green energy production, and for the efficient use of energy. Rare earths are essential constituents of wind turbine generators, fluorescent lamps, LED lamps, electric vehicles, hybrid electric vehicles, and magnetocaloric materials for efficient refrigeration applications. Magnetocaloric refrigeration is expected to replace traditional gas refrigeration, which is responsible for a significant part of the energy consumption. As REEs are at the core of many future-sustainable technologies, they are in high demand, and are considered critical at global level. Current recovery rates of REEs are very low, below 1 %. Recycling of commercial products is an important part of the circular economy, and is needed to assure adequate handling of discarded appliances, and efficient recovery, and re-use of raw materials. So far, recovery of REEs from materials considered for magnetocaloric refrigeration has not been thoroughly addressed. This paper focuses on this topic, and reports on the potential use of hydrometallurgy to recover REEs from genuine magnetocaloric materials comprising cerium, iron, lanthanum, manganese, and silicon. The investigations target leaching with mineral acid solutions (nitric, hydrochloric, and sulfuric acid), and optimizations of leaching in terms of temperature, acid concentration, and solid-to-liquid ratio. Recovery of the REEs from nitric, hydrochloric, and sulfuric acid leachates was investigated using solvent extraction with three types of solvating extractants: tributyl phosphate, mixed trioctylphosphine oxides, and tetraoctyl digylcol amide. A flowsheet comprising leaching of magnetocaloric materials with nitric acid, and solvent extraction of REEs with trioctylphosphine oxides is discussed.

Resume : The search for sustainable, green and environmentally safe approaches to more efficient and economically viable recycling rates of secondary raw materials from end-of-life (EoL) products is at the forefront of modern waste management scenarios. The scarcity of critical raw materials (CRMs) in Europe represents a major challenge to the green growth, sustainability and clean energy objectives of EU industry. However, many of the most economically important metals are present in EoL products of which there are vast amounts in waste repositories and landfills scattered all over Europe awaiting to be efficiently recycled and subsequently reintroduced back in the supply chain. This work addresses more productive, practical and profitable reprocessing techniques oriented to the recovery of CRMs of interest to the nuclear industry, with an eye to their eventual gradual partial substitution. If fusion energy production is ever to reach the market consumers, the amounts of nuclear industry materials needed to build and maintain fusion reactors worldwide will exponentially grow during the second half of this century. Refractory metals will play a leading role, but also lithium, the only practicable precursor of the very scarce tritium, an essential participant of the Deuterium-Tritium typical fusion reaction. Some of these materials present specific complications concerning their disposal as waste, due to proneness to activation, given the very demanding and extreme environments they face during their work life. Such complications have typically excluded them from novel industrial recycling efforts, leaving aside from the value chain relevant metal resources, that in a raw materials scarcity scenario Europe cannot indeed ignore anymore.

Resume : Indium (In) is a crucial raw metal for electronic industry due to its widespread application in electronic boards, solar panels and liquid crystal display (LCD) screens of TVs, laptops, tablets, and mobile phones. Almost 70% of the In in use today is produced for transparent conductive film which is indium-tin-oxide, ITO, for LCD screens. Indium is accepted as one of the scarce material due to its low abundance, and it is in the critical raw materials list for both European Union and US Department of Energy. In this research, recovery of indium from LCD screens by leaching and following separation step were studied. HSC 9 Chemistry software was used for the thermodynamic modeling of the method. The dissolution of the transparent conducting layer from LCD screens were investigated using different acid solutions. Separation of the indium and other valuable metals from leaching solution was studied by solvent extraction and spray pyrolysis methods. Spray pyrolysis method was applied not only for separation purpose, but also to produce fine oxide particles. The separation amount and elemental composition of the powders were analyzed by ICP-OES. The powder properties were characterized by X-ray diffraction and scanning electron microscope.

Resume : Magnesium has been studied as a potential hydrogen storage material for several decades because of its relatively high hydrogen storage capacity, fast sorption kinetics (when doped with transition metal based additives). This research aims to study the possibility to use waste magnesium alloys to produce good quality MgH2 and Mg containing hydride systems. The production costs of hydrogen storage materials is still one of the major barriers disabling scale up for mobile or stationary application. The recycling of magnesium-based waste to produce magnesium hydride will significantly contribute to the cost reduction of this material. This study focuses on the effect of different parameters such as the use of additives as well as the effect of milling time on the material hydrogenation/de-hydrogenation performances.

Resume : Innovation is translating smart ideas or inventions into value for society, for instance, in terms of products, businesses, services or improved social organisation. With more than 120 members coming from the 3 sides of the knowledge triangle - universities, research organisations, and industry - the EIT RawMaterials Knowledge and Innovation Community has initiated radical innovation in the critical materials value chains for the benefit of the European society and beyond - from mine to market.

Resume : 3D-printing of composite materials is an emergent technology which allows the fabrication of functional structures with complex shapes and potential applications in aeronautics, automotive and energy sectors. Successful application of 3D-printing technologies to permanent magnets (PMs) will open the path to novel and more efficient designs, which will undoubtedly benefit to rare earth-free alternatives. This work focuses on the fabrication of polymerized MnAl-based composites in view of their application in 3D-printing technologies. With this aim, polymerized cold compacted magnets and extruded PM filament have been produced. Gas-atomized MnAl-based particles have been recently processed by the ultrafast milling method achieving high coercivities (4.2-5.1 kOe) in record milling times (30-270 s) [1]. Polymerized magnets and filament have been fabricated from composites (ball-milled MnAl-based particles embedded in a polymer matrix), which were chemically synthesized by solution casting and, subsequently extruded. For the composite with the highest filling factor (86.5% content of magnetic particles), the mixture is homogeneous with the polymer covering the particles [2]. MnAl-based filament (12 m in length) with a filling factor of about 75% and PM properties has been fabricated for the first time [2] to be used in advanced 3D-printing technologies. [1] J. Rial et al., J. Phys. D: Appl. Phys. 50, 105004 (2017). [2] E.M. Palmero et al. Submitted.

Resume : A rare-earth free alloy of an optimized composition Mn0.5Bi0.5 offers high-energy-density ferromagnetic properties useful for devising small magnets and devices for various electronic applications. It is a good example to tailor magnetic properties with high magnetocrystalline anisotropy in the low-temperature phase (LTP). In this investigation, a typical Mn0.5Bi0.5 alloy was prepared in small discs using a standard vacuum arc melting and casting method. The as-obtained alloy disc was crushed into small pieces and further ball milled for 5 h using a high-energy ball mill in refining its nanostructure. An as-prepared powder in this way was annealed at an optimized temperature 300 °C for selective periods of 24, 48, 72 and 96 h in vacuum in optimizing the LTP content. A single crystalline phase is formed in these annealed alloys in terms of the X-ray diffraction patterns. An analysis of the EDX spectra with elemental mapping ensures the Mn and Bi atoms distributed uniformly. HRTEM images studied with SEAD patterns and lattice images reveal truncated LTP-Mn0.5Bi0.5 nanocrystals. The ZFC-FC thermograms were recorded over 5-380 K temperatures at a small 500 Oe field, analysing the induced magnetization of 5-35 % on the spin reorientation point TSR at 105 K in a typical sample annealed for 96 h. The M-H hysteresis loop measures a coercivity of 10.5 kOe (35.0 emu/g magnetization) at 300 K, while 14.5 kOe (30.5 emu/g magnetization) at 350 K in an optimally annealed alloy for 48 h. The results demonstrate a simple technique of producing a rare-earth free alloy with tailored structural and magnetic properties as demanded for developing small magnet devices. Keywords: Permanents magnets, Ferromagnetic alloys, Microstructure, Magnetic properties

Resume : Permanent magnets, such as the state-of-the-art Nd-Fe-B supermagnets, are applied as energy convertors in wind turbines and electric vehicles and are thus key materials for a sustainable energy economy. With the growing global demand for highly performant magnetic materials, it is a formidable challenge to discover and develop new rare earth (RE)-lean hard magnetic phases and thus reduce the dependence on these critical raw materials. In this contribution, we present our computational approach to new hard magnetic phases which feature excellent magnetic properties and a lower RE content than Nd-Fe-B. Complementing our combinatorial high-throughput screening (HTS) of RE-containing intermetallics, we now go beyond identifying promising magnetic phases by modelling microstructure effects on the magnetic properties. For selected RE-intermetallics (e.g. of the ThMn12-structure type) the impacts of atomic rearrangements at surfaces and grain boundaries on the local magnetic properties are presented. Just as for Nd-Fe-B magnets, where great scientific efforts have gone into controlling the microstructure for enhanced magnetic performance, there is a huge potential for optimizing new magnetic phases into highly performant materials. By developing microstructure design criteria we aim at building the rational foundations for an accelerated promotion of promising RE-lean phases to application-ready new hard magnets.

Resume : In spintronic device applications, the most commonly used antiferromagnet is an IrMn alloy because of its corrosion resistance and high Néel temperature [1]. However, Iridium is a critical raw material as a platinum group metal, which requires the development of an alternative material [2]. Antiferromagnetic layers have been used to pin its neighbouring ferromagnetic layer in a spin-valve read sensor in a hard disk drive and in a magnetic random access memory for example. The magnetic memories are used in extreme conditions, such as in a bonnet of an automobile and in an aeroplane, due to their robustness against temperature and radiation. In this report, recent efforts to replace a widely used Ir-based alloy with a Heusler alloy consists of common elements [3] are discussed. We found a completely disordered phase with X-Y-Z mixing can still exhibit antiferromagnetic behaviour for Mn-based Heusler alloys [2]. Polycrystalline Mn3Ga layers with thickness in the range from 6-20 nm were deposited at room temperature by a sputtering system [4]. Additional ferromagnetic Co0.6Fe0.4 layer (3.3-9 nm thick) capped with 5 nm Ta were subsequently deposited to investigate the exchange-bias behaviour. X-ray diffraction measurements confirm the presence of Mn3Ga (0002) and (0004) peaks characteristic of the D019 antiferromagnetic ordering. The 6 nm thick Mn3Ga film shows the largest exchange bias of 430 Oe at 120 K with a blocking temperature of 225 K. The magneto-crystalline anisotropy for 6 nm thick Mn3Ga thin film sample is calculated to be 9104 J/m3. Such a binary antiferromagnetic Heusler alloy is compatible with the current memory fabrication process and hence has a great potential for antiferromagnetic spintronics. This work has partially been supported by UK-EPSRC (EP/M02458X/1). [1] A. Hirohata and K. Takanashi, J. Phys. D: Appl. Phys. 47, 193001 (2014). [2] A. Hirohata et al., J. Phys. D: Appl. Phys. 50, 443001 (2017). [3] C. Felser and A. Hirohata, Heusler Alloys (Springer, Berlin, 2015). [4] H. Wu et al., J. Phys. D: Appl. Phys. (submitted).

Resume : The Rashba effect, a spin splitting in electronic band structure, attracts much attention for the potential applications in spintronics with no requirement of external magnetic field. Realizing one-dimensional (1D) Rashba system is a big challenge due to the difficulties of growing high-quality heavy-metal nanowires or introducing strong spin-orbit coupling (SOC) and broken inversion symmetry in flexible materials. Here, based on first-principles calculations, we propose a pathway to realize the Rashba spin-split by adsorbing Gd atom on zigzag graphene nanoribbons (Gd-ZGNR) and further investigate the magnetic anisotropy energy (MAE). Perpendicular MAE and unconventional MAE contributions in k-space are found in the self-assembled Gd-ZGNR system, which presents a remarkable Rashba effect (the estimated strength is 1.89 eV Å) due to the strong SOC (~65.6 meV) and the asymmetric adsorption site at nanoribbons edge. Moreover, first-order MAE is connected to the intrinsic Rashba effect beyond the traditional second-order MAE, which is confirmed based on the analysis of electronic structures perturbed with SOC in comparison with metastable Gd-ZGNR at central symmetric adsorption site. The dependence on the ribbon width of first-order MAE as well as Rashba effect in Gd-ZGNRs are also examined. This work not only opens a new gate for designing 1D Rashba system but also provides insight into the unconventional MAE due to the intrinsic Rashba effect, which would be of great significance for searching Majorana fermions and promoting the potential applications in spintronics.

Resume : Over the past few years, indium doped tin oxide has been widely utilized in several optoelectronic devices such as photovoltaic cell, liquid crystal displays and gas sensors because of its unique properties like high conductivity, wide band gap and high electron mobility. However, the main constituent (about 78wt.%) is In which is listed as a critical raw material by EU. Therefore, researchers have been focused on finding out an alternative material to ITO in device applications. Among these effort, the ones based on ZnO has attracted much attention in the past decades due to its suitable and controllable properties for optoelectronic applications. In accordance with this purpose, doping with transition metals has been used to modify and improve the performance of nano materials. In the light of today’s information, it can be said that dopants change the relative characteristics such as structural or morphological properties which affect electrical and optical properties of host materials. Because of this, above mentioned speculation can be seen as a key factor affecting device performance. In this study we conduct our studies on the effect of Co loading on characteristics and device performance of ZnO films prepared by chemical spray pyrolysis technique. Even though also Co is listed among CRMs, its percentage as dopant is very limited (up to 5%).

Resume : A polyaniline-Carbon nanotube (PANI-CNT) composite material was used to replace widely used transparent electrode Indium Tin oxide/Polyethylene terephthalate (ITO/PET) in a flexible electrochromic device. By in situ polymerization of aniline with amine-functionalized CNT, a direct conjugation between PANI and CNT can lead to a high electrical conductivity. This electrode has better bendability than ITO/PET electrode due to its polymeric nature. After electrodeposition of electrochromic PANI, the electrochromic performance of the device is competitive to device with ITO/PET electrode. The PANI-CNT electrode can also contribute to the overall performance. After cycles of bending, the sample can still maintain its electrochromic performance. This may be attributed to good conductivity of electrode after bending and well-bonded interface of electrochromic layer and electrode layer as they use the same type of material. All these advantages enable PANI-CNT a better choice of electrode in a flexible electrochromic device.

Resume : Transparent contacts are critical materials in devices such as touch screens, LCDs, OLEDs and solar cells. The most used are TCOs made of ITO, with state-of-art electrical and optical properties. However, the cost, availability and toxicity of In is driving the quest for alternative TCOs. Many solutions have been proposed, but only a few of them are reliable and compatible with industrial processes. This is the case of the thin TCO/Ag/TCO multilayer that the authors recently developed with high flexibility, low reflectance and electrical resistance [1]. A step ahead is a similar multilayer but with a Ag mesh instead of a film, with benefits in terms of optical transparency and mechanical flexibility. To this end, we studied innovative IZO/Ag_mesh/IZO structures fabricated via colloidal lithography. Well-defined Ag grids were realized by covering an IZO film with a single layer of polystyrene spheres (1.6 m in diameter) through the Langmuir-Blodgett process. Before the Ag deposition, spheres are partially etched by an O2 plasma, thus controlling the spacing in between. Finally, a capping IZO layer is deposited on top. In this way, we fabricated IZO/Ag/IZO multilayers having different Ag grids in terms of thickness and mesh openings. We found excellent electrical properties and a significant enhancement of the infrared transmittance (Rs=16.4 / and ) with respect to state-of-art transparent electrodes. Results on the optical, electrical and mechanical properties of this family of TCO/metal/TCO hybrid materials is reported and discussed. [1] G. Torrisi et al., Solar Energy Materials and Solar Cells 165, 88-93, 2017

Resume : We performed broadband optical reflectance measurements, from 80 cm-1 (~10 meV) to 50,000 cm-1 (~6 eV), on thin films of Ga-doped ZnO (GZO) obtained by ion plating with direct-current arc discharge. The experimental data was reproduced considering reflections at multiple interfaces and assuming a Lorentz-Drude model for both film and substrate, individually. From the fits the main optical functions of GZO were calculated, such as dielectric constant, optical conductivity, reflection or extinction coefficients. Here, we discuss the effects of the deposition parameters, such as the oxygen flow rate and the discharge current between the plasma gun and the source pellet, on optical properties of GZO films.

Resume : ZnO nanorod-based devices have been of increasing interest in the field of flexible electronics, catalyst, optoelectronics and energy harvesting. These devices often contain Zinc oxide film as a seed layer for nanorods and Indium tin oxide (ITO) film as transparent electrode. Since Indium is included in the list of critical raw materials defined by EU commission, the main aims of the present work is the replacement of the preferably-used ITO by an aluminium doped Zinc oxide (AZO) film. The use of polymer flexible substrates usually requires the deposition temperature up to 100 ° C. Moreover, low film thickness is needed to avoid failure of the device due to forming of cracks. Thus the achievement of suitable electrical properties of AZO films deposited on flexible thermally-sensitive substrates is still difficult and therefore it is subject of intense research. In this study, all thin-film depositions were performed using a BOC Edwards TF 600 deposition system equipped with two magnetrons linked to a radio-frequency (RF) and direct current (DC) power supply, which allow to control the oxygen content in the prepared films by co-sputtering from ceramic and metallic target. It was found that the amount of oxygen fundamentally affects the electrical properties of the deposited transparent electrode as well as the seed layer. Various dominant internal defects depending on the different oxygen conditions during the processing was identified as the major reason for these relationships. The control of oxygen amount allows us to achieve lower resistivity of the AZO transparent electrode and also to adjust the seed layer for different types of ZnO nanorod-based devices.

Resume : The developing of lead-free piezoceramics has become one of the most urgent tasks due to the ever-increasing restrictions connected to the use of toxic lead-based materials. In this context, undoped and doped KxNa1-xNbO3 (KNN) systems attracted growing interest as promising candidates due to their excellent piezoelectric properties (390-570 pC/N) by forming new phase boundaries, good electromechanical constants (K33 83%) and high Curie temperature (T 200-420 °C). However, KNN contain 50-55% of Niobium which is considered by the EU as critical raw materials (CRM) with high supply risk. Niobium is in fact expected to have one of the strongest annual demand growths to 2020 among the CRMs. Furthermore, KNN synthesis imposes the use of organic solvents due to the use of alkali elements. To overcome these issues, a new modified Pechini method to synthesize single phase K0.5Na0.5NbO3 powders, from water soluble metal precursors, is presented. The piezo responses of the as calcined systems have been tested by piezoresponse force microscopy (PFM) and compared with similar systems. The piezoelectric coefficient d33 of ~ 80 pm/V, derived by PFM spectroscopy analysis on the local domains, results comparable with the values estimated in the most performing hot-pressed KNN materials, but with the advantage of synthesis at lower temperature and using water soluble precursors.

Resume : This mind opening session will focus on providing an overview of global environmental trends likely to impact CRM uses, it will also discuss the issues and levers to be considered and will be followed by an interactive session with the participants. This session is co-organized with EpE, a company-based environmental think tank and platform for expertise.

Resume : In order to protect the environment and critical resources of the next generation society, it is necessary to construct an innovative alternative and circulation cycle of the main materials and components of green devices. In this presentation, we will introduce the materials / components for high heat resistant electronic components for SiC power electronics, transparent conductive film, and LED and LED without using Eu, Ru, In. Also, these components for green devices are manufactured using mixture resin or glass of the functional materials. Such a composite material, for example, leads to deterioration in improving luminescence, and makes recycling difficult. In order to solve these problems, we have developed the photo-induced chemical solution deposition such as Photo-assisted metal organic deposition (PAMOD) for developing the new electronic and luminescent components without using glass or resin. In this process, since a phosphor and electronic components (resistor) can be fabricated on a plastic substrate without using a resin, not only excellent properties but also durability and recyclability can be realized. By using PAMOD method, a high brightness white luminescent thin film by using CsVO3 on PET substrate was successfully obtained. The luminescence intensity of the thin film by PRNP is much higher than that of the commercial available one. In addition, YAG:Ce film without resin was developed for LED applications by using photo-assisted MOD. Moreover, Bi2Sr2CaCu2Oy film resistor for SiC power electronics without glass was developed instead of RuO2 and glass. In this talk, we will give a lecture on substitution and recycling of critical raw materials in optoelectronic, power devices components and displays and the new film process that enables energy saving / resource saving.

Resume : Nowadays the fluorescent inorganic compounds, based on heavy and light rare earths represent the major emitter materials in lighting applications. Their replacement with inexpensive purely organic compounds offers the possibility to develop cheaper and Critical Raw materials free devices. The thermal and morphologic stability, other than its optical properties, are the basic requirements to been considered as feasible candidate in lighting devices that often limited the use of organic compound. On these basis and taking into account the high thermal stability of the aromatic triazine core and its electron donor and acceptor features, a-amino substituted [1,3,5]-triazine derivatives has been synthetized and their optical properties have been investigated. Further chemical modification has been carried out in order to achieve red shift covering the whole spectral region, without compromising the stability of the emitter material. Thermal gravimetric analysis, solid state NMR, X-Ray Diffraction, time resolved fluorescence spectroscopy cyclovoltammetry allow to evaluate the best candidate for optical application. Finally, we achieved also in the preparation and the characterization of Tb-triazine systems showing the feasibility to use the same organic matrix as host for luminescent ion. These systems with reduced, up to totally free of CRM, represent a reliable phosphors alternative to the actual inorganic rare earth based compounds.

Resume : Optically thin copper films are attractive as an alternative to silver window electrodes particularly for application in organic photovoltaics, because copper offers comparable electrical conductivity at one percent of the cost. The primary disadvantage of copper is its lower far-field transparency for wavelengths below 550 nm, stemming from intra-band absorptions which do not occur in silver. For wavelengths above 550 nm the transparency is reduced due to reflection, similar to the case of silver. This talk will present a new approach to simultaneously reducing intra-band absorption losses in copper films for wavelengths below 550 nm and dramatically suppressing reflection for wavelengths above 550 nm, based on incorporation of about 100 million tiny circular apertures per square centimeter into the metal film. A potentially low cost approach to achieving such a high density of apertures in a thin metal film will also be described based on spontaneous phase separation in a polymer blend. The advantage of the method presented is that the metal is deposited by simple vacuum evaporation and all subsequent steps are solution based processes using widely available low-cost chemicals based on earth abundant elements. The utility of these nano-structured copper window electrodes will be demonstrated in organic photovoltaic devices.

Resume : Recently, much attention has been paid to the development of new phosphors for lighting application free from Critical Raw Materials, Rare earths in particular. Materials suitable for applications in this field should guarantee a high chemical stability, easiness and green sintering procedure and optimal optical properties. In this framework Calcium Zinc oxysulfide (CaZnOS) represents one of the most promising materials. Not only it provides an excitation channel in the near UV region with broad emission in the visible part of the spectrum (needed to achieve white emission in LED systems), but the long phosphorescence and the mechano-luminescence constitute a prerogative that still needs to be explored. In this work, we report for the first time the optical properties and the kinetics of radiative recombination upon intrinsic and extrinsic excitation from the nanosecond to the millisecond time window. The analysis of time resolved measurements at room and low temperature (down to 10 K) gives new insight on the distribution and nature of the defects that generate the luminescence as well the long phosphorescence upon external stress. The role of the dopant (Mn, Cu but also Tb and Eu) will be discussed and analysed in view of the achievement of novel phosphor with largely reduced amount or totally free of Critical Raw Materials.

Resume : Recently, the wide color gamut (WCG) of the white LEDs is an important issue for more realistic colors in displays. Therefore, a number of researches are highly focused in developing high color purity luminescence materials. Organic-inorganic halide perovskite (OIP) nanocrystals (NCs) have attained great attention as the candidates for optoelectronic devices due to their outstanding optical properties such as the wide color tunability, narrow full width at half maximum (FWHM) of emission, high photoluminescence quantum yields (PLQYs) and lower materials and synthesis costs. Owing to the high sensitivity to moisture, temperature, light and air environment of OIP, all-inorganic CsPbX3 (X=Cl, Br, I) NCs have been reported with enhanced stability. In this study, we successfully synthesized the high color purity perovskite NCs with enhanced PLQYs of 99.7% and a narrow FWHM of 21 nm by substituting the Cs cations with Rb cations. As synthesized (Cs0.4Rb0.6)PbBr3 NCs were integrated with mesoporous silica (m-SiO2) matrix. The m-SiO2 significantly improved the thermal- and photo- stability of the perovskite NCs. Furthermore a white LED was designed by combining the perovskite NCs@m-SiO2 composite with red-emitting K2SiF6:Mn4 phosphor on blue InGaN LED. The white LEDs showed a wider color gamut of 119% compared with NTSC value.

Resume : Leaching is a serious problem when using metal nanostructure catalysts in liquid phase reactions because it leads to the loss of precious metals and a dramatic reduction in catalytic performance. This is a major problem for industrial catalysts with both economic and environmental implications. The leaching of metal species from catalysts makes it difficult to reuse the catalysts in batch reactors and maintain the desired initial performance in continuous flow catalytic reactors. Dr. Neretina’s laboratory has designed and built a custom experimental setup which allows one to access catalyst leaching. The Neretina group has carried out studies showing the detrimental role that dissolved oxygen within an aqueous solution can have on catalytic performance and the degree to which metal catalysts leach through oxidative etching.

Resume : Catalytic converters are the devices used for purification of exhaust gases of automobile engines, which allow the simultaneous conversion of unburnt hydrocarbons (UHC), carbon monoxide (CO), and nitrogen oxides (NOx) into harmless carbon dioxide (CO2), water (H2O), and nitrogen (N2). The main reason for the usage of catalytic converter is that the respective compounds shall be eliminated before they are released into the surrounding environment, so as to comply with the emission levels imposed by the legislation. Although the catalytic converters had been launched into the market for a long time ago, the development of sustainable three-way catalysts remains a critical research topic especially for the automotive industry due to the increasingly stringent emission regulations together with the cost and scarcity of precious metals. Platinum based catalysts and Palladium based catalysts are used commonly and successfully in this convertors due to high catalytic activities. However, palladium based catalysts are more appropriate for catalytic converters compared to platinum based catalysts because of the higher catalytic activity and lower cost. In addition, mixing Pd with non-precious metals in composites increases their catalytic activities and decreases the cost due to reduced dosage. Also, reducing size to nano-scale increases the surface area and activity of the material. Thus, in this study Pd/Cu nanoparticles are prepared to use in reduction reactions in catalytic converters which are used in gasoline powered cars. The main problem of the usage of these nanoparticles in three-way catalytic converters is that temperature of the exhaust gases can be reach up to 900 C. This high temperatures negatively affect the performance of the nanostructure. Thus, we have used different carrier substrates that have extremely low thermal conductivities such as aluminum oxide foam or Si aerogel to obtain better stability at high temperatures. Resulting materials are characterized using TEM and XRD.

Resume : Tremendous effort has been contributed to the phase-controlled synthesis for inorganic crystals, especially the metallic-phase group-VI transition metal dichalcogenides (TMDs), in which the transition metals are Mo and W, and the chalcogens are S, Se and Te, because of their performance in electrocatalysis and energy storage is much higher than those of their semiconducting counterparts. Notably, the metallic phase TMDs exhibit higher performances in the electrocatalytic hydrogen evolution reaction (HER), and the electrical properties of the group-VI TMDs can be controlled by atomic structures such as 1T (metallic, octahedral structure) and 2H (semiconducting, trigonal prismatic structure) phases. Although several methods have been achieved to prepare the metallic-phase MX2 (M=Mo, W; X=S, Se), it was difficult to avoid from the thermodynamically stable 2H phase or too small lateral size after preparation, severely retarding the research of their properties and applications. Therefore, it is crucial to develop a synthesis method for preparation of metallic-phase MX2 (M=Mo, W; X=S, Se) bulk crystals. Here, we report a synthesis method of metallic-phase 1T'-MoX2 (X=S, Se) bulk crystals with lateral size up to hundreds of micrometers. It has been studied for the distorted octahedral coordination structure (1T') and intrinsic electrical property of 1T'-MoS2 crystals. Importantly, the 1T'-MoS2 can be converted to 2H-MoS2 after thermal treatment and laser irradiation. The results of HER performed in electrochemical microcells demonstrate the crystal phase-dependent HER of MoS2, i.e. the basal plane of 1T'-MoS2 is much more active than that of 2H-MoS2.

Resume : A layered β-NiOOH crystal with under-coordinated facets is an active and economically viable non-noble catalyst for the oxygen evolution reaction (OER) in alkaline electrolytes. However, it is extremely difficult to enclose the β-NiOOH crystal with under-coordinated facets due to its inevitable crystal transformation to γ-NiOOH, resulting in the exfoliation of the catalytic surfaces. Herein, we demonstrate {111}-faceted Ni octahedra as the parent substrates which surfaces are easily transformed to catalytically active β-NiOOH during the alkaline OER. Electron microscopic measurements demonstrate that the horizontally stacked β-NiOOH on the surfaces of Ni octahedra has resistance to further oxidation to γ-NiOOH. By contrast, significant crystal transformation and thus the exfoliation of the γ-NiOOH sheets can be observed on the surfaces of Ni cubes and rhombic dodecahedra (RDs). Electrocatalytic measurements exhibit that the β-NiOOH formed on Ni octahedra performs highly enhanced OER durability compared to the Ni cubes, Ni RDs, and the state-of-the-art Ir/C catalysts.

Resume : Highly active and low-cost electrocatalysts for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) are crucial due to the need for clean and renewable energy. Herein, we report the preparation of porous NiFeV layer double hydroxides (LDHs) grown on Nickel foam (NF) as an efficient bifunctional electrode. The lateral size of the nanosheets is few hundreds nm with the thickness of 10 nm. Among all ratios investigated, the Ni0.75Fe0.125V0.125-LDHs/NF depicts the optimized performance. It displays an excellent catalytic activity with modest overpotentials of 0.23 and 0.12 V, alongside with Tafel slope of 39 and 62 mV/dec for OER and HER, respectively. Also, remarkable durability and stability are observed. Interestingly, with such electrode, a single battery of 1.5 V can drive the water electrolysis, outperforming the state-of-the-art IrO2||Pt and indicating successful water splitting with barely 0.27 V overpotential. The exceptional catalytic activity could be attributed to the synergistically combination of Fe and V in Ni-based LDHs that leads to better intrinsic catalytic activity and higher electrochemical surface area (ECSA). The porous structure of the nanosheets gives enough space for electrolyte penetration and diffusion; as well as provide a higher number of active sites by boosting the accessible ECSA. In addition, the in-situ growth of the hydroxide onto conductive NF benefits the charge transfer, lowering significantly the resistance of the system

Resume : Photocatalytic CO2 reduction to solar fuels by artificial photosynthesis is an attractive and effective research area to solve the energy crisis as well as anthropogenic greenhouse emission problems from CO2 emission. In recent years, it becomes a hot renewable-energy research topic. In the past several years, many semiconductor photocatalysts have been developed for photocatalytic CO2 reduction to hydrocarbons [1,2]. The promising prospect of these semiconductor photocatalyst is far away from the commercial requirement. Thus, it is a great challenge to develop a potential photocatalyst for a high CO2 reduction to solar fuel under visible light. In last few years metal dichalcogenide nanostructures are playing an important role in photocatalysis due to their wide range of optical and electronic properties. Moreover, the high surface area and low charge recombination characteristics of 2D materials can potentially enhance the photocatalyst activity. Among various metal sulfides, SnS2 is a naturally occurred n-type narrow bandgap semiconductor. The narrow bandgap with around 0.19 µm average photocarriers diffusion length and high quantum yield of SnS2 thus possesses two advantages for a good photocatalyst under visible light. Although it has a narrow-band gap, however, the indirect band gap and faster charge recombination remain major challenge in the photocatalytic application. In this work, we propose an in-situ carbon doped SnS2 nanostructure system with limited average lifetime of photo-generated electrons and holes by shortening the diffusion time so that they can reach the reaction sites before losing their energy. In the hybrid system the conductive carbon incorporated into SnS2 provides the opportunities for fast charge transport in the nanostructure with an interconnected planar structure, thus shortening the diffusion time from semiconductor interior to surface reaction sites. The synthesized carbon doped SnS2 photocatalyst shows selective photocatalytic CO2 reduction to acetaldehyde with moderately high photochemical quantum efficiency (QE-0.7%) under visible-light irradiation [3]. The details photocatalytic performance, quantum yield, product selectivity of solar chemicals and theoretical study will be discussed on the presentation. References: [1] H-C. Hsu, I. Shown et al.Nanoscale 5, 262, (2013). [2] I. Shown, H-C. Hsu et al. Nano Letters 14, 6097, (2014). [3] I. Shown, S. Samireddii et al. Nature Communications, 9, 169, 2018

Resume : The environmental treatment and clean energy production represents one of the most hard challenge in the next future and the photo-catalysis represent a reliable promising solution. A part the well-known inorganic semiconductors already utilized, titanium dioxide and zinc oxide, the next step is represented by organic photocatalytic materials, that are in general cheaper, more versatile in chemical and in the flexible designs. However most of them are organometallic complexes, where the ruthenium and iridium are the catalytic metallic centres. The substitution of such materials is mandatory in terms of Critical Raw Materials and for low environmental impact. In this work we propose novel Perylene tetracarboxylic diimide’s (PTCDI) -based hybrid materials for photocatalytic applications. PTCDI is characterized by an excellent photochemical and thermal stability other than high molar absorptivity. The coupling with electron acceptor materials, like TiO2 and/or organic, like 7,7 8,8 tetracyanoquinodimethane (TCNQ) give rise to intriguing hybrid materials with increased photo-catalytic properties. In this work, we present the preparation of novel organic PTCDI-based hybrid materials and their structural, morphological, optical and photocatalyitic characterization. 1H-NMR, 13C-NMR, solid state NMR, high resolution mass spectrometry, X-Ray diffraction, UV, time resolved and steady time photoluminescence, infrared and Raman spectroscopy measurements will be provided and discussed.

Resume : Solar energy is one of the most promising technologies due to its potential applications in solving the issues of environmental pollution. Much effort has been focused to study the semi-conductor photocatalysis, which utilizes solar energy to decompose various organic contaminants in waste water. An important example is the Ag3PO4 photocatalyst, which possesses high visible-light photocatalytic activity in O2 evolution and organic contaminant degradation, but the large crystallite size severely limit its practical application. It is highly desirable to expand new photocatalytic Ag3PO4 systems with a nanosized structure, in order to increase the specific surface areas, and to obtain a high photocatalytic activity. In this study, a novel nanosized Ag3PO4 photocatalyst was prepared by Sol Gel method. The products were characterized by X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM) to examine the crystal structure, size and morphology. Fourier transform infrared spectra (FT-IR) have served to characterize and identify the functional groups of the powders while UV-visible spectroscopy for the study of optical properties. Solar energy is one of the most promising technologies due to its potential applications in solving the issues of environmental pollution. Much effort has been focused to study the semi-conductor photocatalysis, which utilizes solar energy to decompose various organic contaminants in waste water. An important example is the Ag3PO4 photocatalyst, which possesses high visible-light photocatalytic activity in O2 evolution and organic contaminant degradation, but the large crystallite size severely limit its practical application. It is highly desirable to expand new photocatalytic Ag3PO4 systems with a nanosized structure, in order to increase the specific surface areas, and to obtain a high photocatalytic activity. In this study, a novel nanosized Ag3PO4 photocatalyst was prepared by Sol Gel method. The products were characterized by X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM) to examine the crystal structure, size and morphology. Fourier transform infrared spectra (FT-IR) have served to characterize and identify the functional groups of the powders while UV-visible spectroscopy for the study of optical properties.

Resume : Carbon dots (CDs) are a versatile nanomaterial with attractive photoluminescent and photocatalytic properties. Here we show that these two functionalities can be easily tuned through simple synthetic means. The CDs were synthesized from citric acid by a microwave irradiation approach, with a varying concentration of nitrogen-containing branched polyethyleneimine (BPEI). The amount of the precursor determines the overall level of nitrogen incorporation and the different inclusion modes within the aromatic domains inside the CDs. At intermediate levels of BPEI, numerous sp2 domains grow with nitrogen in a predominantly graphitic configuration, yielding a high photoluminescence yield. On the other hand, at high (and very low) BPEI content, the nitrogen atoms are located primarily at the edge sites of the aromatic domains. In this form, they attract photogenerated electrons, allowing for an efficient charge separation and an enhanced photocatalytic activity for hydrogen generation from water. The ensuing ability to achieve a controlled trade-off between emissive and photocatalytic behavior of CDs depending on nitrogen atom positioning inside the aromatic domain is expected to bring substantial improvements on their efficiency for on-demand light emission or energy conversion applications. Ref: 1) Nature Communications 8 (1), 1401 (2017) 2) Nano Letters 17 (12), 7710–7716 (2017) 3) Nano Letters 15 (9), 6030-6035 (2015)

Resume : Solid-state lighting (SSL) using light emitting diodes (LEDs) is recognized as a major disruptive technology expected to dominate the public lighting market. The main advantages of SSL sources are the energy saving, their potential stability to produce long lifetime devices and their possibility to develop smart lighting devices. At Néel Institute, we develop a new type of phosphors based on metal aluminum borate powders without any lanthanide as doping. The innovation of these phosphors is to produce broad emission bands extended in the whole visible range from emitting centers (structural defects) trapped in stable glassy grains of a few microns in diameters. Thus, from only one phosphor excited with a near-UV LED chip (365- 390 nm), we can generate intense warm white-light: internal quantum yields around 80-90% and very high color rendering indexes (CRI = 92-94). The main objective of this study was to optimize the chemical compositions, synthesis procedures and thermal treatments for these micrometric powders to enhance their photoluminescence properties. This has been favored by the great versatility of “chimie douce” process such as polymeric precursor methods. Complementary spectroscopic studies (EPR, NMR, FTIR, PL) and structural methods (X-ray Diffraction, Pair Distribution Functions (PDF), coupled with thermal analyses (DSC, DTA, TG-MS) have been used to specify the chemical nature and structural environment of emitting centres.

Resume : Novel fluorescent nanoarchitectures are investigated to engineer organic-inorganic hybrids for applications in photonics, in particular as white LED. The selected fluorescent compounds are Carbon-dots (CDs) whose emission properties can be tuned by quantum confinement and surface functionalization. The fluorescent quantum yields of C-dots in the blue/green range is almost competitive to those of CdSe/ZnS, and the efficiency in the red/IR range could be increased by proper functionalization of the CDs surface. To achieve photonic applications the fluorescent compounds will be embedded in suitable matrices, such mesoporous silica. The chosen host matrix is mesoporous silica because its huge specific surface area allows hosting large concentrations of fluorescent CDs. The analysis of the interaction of CDs with the matrix, in terms of physical and chemical confinement of emitting compounds, is a strategic issue to fill the current knowledge gap about CDs in embedded systems. Structural and optical properties of Carbon dots prepared by facile microwave thermal synthesis and embedded in sol-gel prepared silica matrix are reported. The hybrid structures promotes the emission in the green region, thus envisaging possible applications of these compounds in the lighting field.

Resume : Solid state laser lighting, which combines a laser diode (LD) with a YAG:Ce3 phosphor have been attracted as next-generation light source due to their remarkable characteristics such as environmental-friendly device, long operating time, low energy-consumption and high brightness, compared to conventional light source. For application in solid state lighting phosphors can be designed into various types of packages. For laser-based automotive headlamps, phosphor converters with enhanced stability at high power light energy, is required. Among the various converter types, polycrystalline phosphor plates have better thermal properties than packages using polymers or binders. Particularly in phosphor plates a number of factors including density, grain size, porosity and etc. control the output optical characteristics. These factors can be controlled by using pore forming agent, sintering aid, and precursor. In this study, the YAG:Ce3 ceramic phosphor plates (CPP) were prepared under various conditions, such as amounts of sintering aid, sintering temperature, sintering atmosphere and manufacturing process. We observed the particle size, pore size, yellow ring, density of the fabricated plates, and also compared the optical characteristics difference through laser diode packaging. The sintering temperature and sintering aid content were optimized and the yellow ring was improved by optimizing the precursor and process conditions.

Resume : TiO2 and WO3 are two of the most important earth-abundant materials for electronic and energy applications. Particularly for smart windows, WO3 is one of best performing materials to date. It has been demonstrated that alloying WO3 with TiO2 can improve both performance and stability of such electrochromic devices[1]. While the oxidation of both W and Ti has been discussed in literature, only few works exist on the oxidation of W-Ti alloys. In this work we present an in-depth study of the oxidation behavior in W-Ti alloys using different synthesis routes. Solid solution alloy precursors were deposited using combinatorial sputtering and subsequently oxidized using either thermal oxidation or potentiostatic anodization, which correspond to near-equilibrium and off-equilibrium growth methods, respectively. The oxide formation during thermal oxidation and the thermal stability of the anodic oxide alloys were monitored using real time synchrotron XRD. For both oxidation methods a Ti-enrichment in the surface region of the grown WxTi1-xOy layer is observed, which strongly depends on the oxidation conditions and precursor composition. As evidenced by XPS mapping and TEM, a thin TiO2 overlayer on top of the WxTi1-xOy film can be achieved, resulting in an increased stability in reactive environments. In addition, the optoelectronic properties of the oxide are reported, providing insights into the synthesis-property relationship of WxTi1-xOy. [1] Sol.Energ.Mat.Sol.Cells 125,184-189,2014

Resume : Cadmium germanium arsenide is an interesting compound due to its outstanding properties for nonlinear optical application. The quality of the crystals has a substantial impact on the output characteristics of the devices. It was discovered Cd3Ge2As4, which is a new metastable phase in the Cd-Ge-As compound alloys. It belongs to the Cd-GeAs2 pseudo-binary section, the same as CdGeAs2. The formation of tricadmium digermanium tetraarcenide from the quenched CdGeAs2 stoichiomentic solution is reported in the present paper. The samples were studied by X-ray diffraction, differential thermal analysis (DTA) and scanning electron microscopy (SEM) with energy dispersive X-ray microanalysis. As the crystallization rate increased, the formation probability of a metastable phase increased, too. The Cd3Ge2As4 phase annealing led to double and triple stable eutectic compositions Cd3As2-CdGeAs2 42.2 at.% Cd, 15.7 at% Ge, 42.1 at.% As and Cd3As2-CdGeAs2-CdAs2 - 42.7 at% Cd, 15.1 Ge and 42.2 at.% As, the formation correspondently.