Established and emerging nanocolloids: from synthesis & characterization to applications II

Resume : Administration of autoantigens with the aim to restore immune tolerance to beta cells is among the most attractive approaches to immunotherapy of type 1 diabetes. Such approaches are expected to afford a high degree of security and specificity. However, recent trials in patients have produced disappointing results. One likely reason for these failures is the fact that induction of immune tolerance is unlikely to succeed when autoantigens are administered in the context of the ongoing islet inflammation associated with the disease. A conceivable solution to this problem is the administration of drugs with an anti-inflammatory effect together with the autoantigen. Ideally the drug and the autoantigen should be delivered to the same antigen-presenting cell to make sure that the desired “tolerogenic” response to the autoantigen is produced. We study the effect of targeted nanoparticles (NPs) co-packaging the autoantigen proinsulin together with ITE, a drug conditioning antigen-presenting cells to a functional type that favors induction of immune tolerance. Nanoparticles are 10nm PEGylated spherical γFe2O3 particles, well-known MRI agent and FDA-approved. We study the potential diabetes remission through different NPs batches on non-obese diabetic mice (NOD).

Resume : Magnetic nanoparticles assemblies allow new potential technologies development and many applications in different fields such as data storage or biological devices. Indeed nanoparticles assemblies offer the possibility to tune their collective properties by controlling their spatial arrangement. Therefore the development of new and simple assembly techniques which result in better control of the assembly structure are essential. Hydrogen bonds present the advantage to be more dynamic and flexible in geometry than rigid covalent bonds; they are directional and can be highly selective in the case of functional groups which allow multiple hydrogen bonding.[1-3] Our approach is inspired by Nature who is able to control the formation of complex architectures from simple tools. Here we use self-complementary Watson-Crick multiple hydrogen-bonding interactions between adenine-thymine base pair to assemble magnetite nanoparticles into 2D arrays on gold surfaces. Click chemistry strategy is used to graft nucleosides on both pre functionalized nanoparticles and gold surfaces. Moreover the functionalization step is performed by using micro-wave irradiations which fasten dramatically the “click” reaction kinetics from days down to few minutes.[4] The specific assembly of nanoparticles through self-complementary Watson-Crick multiple hydrogen-bonding is then studied as function of temperature, surface density of nucleosides and solvent polarity. Characterization of theses self-triggered assemblies is achieved by SEM, AFM and ellipsometry [1] Wu, Y.-S.; Wu, Y.-C.; Kuo, S.-W., Polymers, (2014) 6, 1827. [2] Viswanathan, K.; Long, T. E.; Ward, T. C., Langmuir, (2009) 25, 6808. [3] Ronald Zirbs, F. K., Peter Hinterdorfer, and Wolfgang H. Binder, Langmuir, (2005) 21, 8414. [4] Toulemon, D.; Pichon, B. P.; Leuvrey, C.; Zafeiratos, S.; Papaefthimiou, V.; Cattoën, X.; Bégin-Colin, S., Chemistry of Materials, (2013) 25, 2849.

Resume : The development of bacterial strains that are multiresistant to antibiotic treatments has currently reached a critical level, invalidating major antimicrobial drugs for clinical use. These and other considerations have seen an increased interest in the development of non-biocidal anti-infective strategies as alternatives to antibiotics, as these would be expected to show reduced tendency to potentiate resistant strains evolving. Particle based photodynamic therapy (PDT) as well as photo thermal therapy (PTT) holds great promise in disease theranostic applications. Herein, we demonstrate that near-infrared (NIR) plasmonic nanostructures, consisting of gold nanorods enrobed in graphene or silica shells loaded with bacteria targets and/or photosensitizers exhibit high capacities to inactivate different bacteria strains under pulsed laser and/or continous wave light irradiation at 810 or 980 nm. In the case of gold nanorods coated with indocyanine green (ICG)-loaded silica shells, fine tuning the plasmonic structures together with maximizing the loading of the photosensitizer onto the nanostructures allowed optimizing the single oxygen generation capability. The potential of graphene coated gold nanorods as photothermal agent for the suppression of tumor growth and killing of E. coli will be discussed in addition References: K. Turcheniuk, C.-H. Hage, J. Spadavecchia, A. Yanguas Serrano, I. Larroulet, A. Pesquera, A. Zurutuza, M. Gonzales Pisfil, L. Heliot, J. Bouckaert, R. Boukherroub, S. Szunerits, Journal of Materials Chemistry 2015, 3, 375-386 K. Turcheniuk, V. Turcheniuk, C.-H; Hage, T. Dumych, R. Bilyy, J. Bouckaert, L. Héliot, V. Zaitsev, R. Boukherroub, S. Szunerits, Chemical Communications 2015, 51, 16365-16368 K. Turcheniuk, T. Dumych, R. Bilyy, V. Turcheniuk, J. Bouckaert, V. Vovk, V. Chopyak, V. Zaitsev, P. Mariot, N. Prevarskaya, R. Boukherroub, S. Szunerits, RSC Advances, 2016, 6, 16006-1610

Resume : Multimodal imaging combines information from several imaging techniques in order to accurately image and diagnose various medical conditions. A well designed probe can offer imaging prospects using optical imaging, positron emission tomography using a radioactive label and magnetic resonance imaging.[1] Silicon nanoparticles are an interesting material for biological and medical applications. These nanoparticles combine the low toxicity of silicon and the ultrasmall size (< 5 nm) achievable through wet chemistry techniques.[2] The surface termination of silicon nanocrystals can be functionalized from simple amino acid groups to photoemissive dyes, radiotracers and targeting agents, such as peptides, thus making silicon nanoparticles an interesting platform for targeted multimodal imaging. After synthesis and purification, the crucial step towards the utilization of silicon nanoparticles as multimodal probes is the modification of the surface. An accurate quantification of the number of available functional groups is both important and a great challenge to determine. Our research is focused on the surface modification and characterization of silicon nanocrystals and their use as imaging agent in biomedicine. Keywords: silicon nanoparticle, surface modification, multimodal imaging, biomedical application [1]. Louie A. Multimodality Imaging Probes: Design and Challenges. Chem.Rev. 2010, 110, 3146-3195. Doi:10.1021/cr9003538. [2]. Shiohara A., Lai P.-S., Northcote P, Tilley R.D. Sized controlled synthesis, purification, and cell studies with silicon quantum dots. Nanoscale. 2011, 8, 2040-3364. Doi: 10.1039/C1NR10458F.

Resume : This work deals with the identification and quantification of neurotoxic agents in gas phase by combination of Surface Enhanced Raman Spectroscopy (SERS) and resonating Si microcantilevers. In all areas of countermeasures against CBRNE attacks, it is crucial to be able to detect and, if possible, identify the threatening material. The overview of the situation and all actions to be taken depend on a fast, sensitive and reliable detection and identification. Sarin (2-fluoro-methyl-phosphoryl)oxypropane) is a typical organophosphorus nerve agent recognized as one of the most toxic warfare agents. Taking into account the acute toxicity associated to sarin and the Chemical Weapons Convention (CWC), dimethyl methylphosphonate (DMMP) as gas sarin simulant has been herein studied. In this work, MEMS and SERS technologies are simultaneously deployed for on-site and on real time detection and identification of DMMP under relevant conditions by means of Au nanostructures. Plasmonic Gold nanoparticles (20 nm in size) with citrate as stabilizing agent have been used either for the preparation of SERS substrates on Si wafers or for the coating of Si based micro-cantilevers by Dip Pen Nanolithography (DPN). Thus, Si microcantilevers work as tiny microbalances for the quantification of DMPP in vapor phase by adsorption over Au@citrate nanoparticles; and, SERS measurements are performed for label-free ultrasensitive vibrational “fingerprinting” of DMMP molecules found at a favourable position close to plasmonic nanostructures with localized surface plasmon resonance (LSPR) at 526 nm.

Resume : In the field of the synthesis and functionalization of inorganic nanoparticles (NPs) for biomedical applications, most researches aim at developing multifunctional theranostic NPs which can both identify disease states and deliver therapy and allow thus following the effect of therapy by imaging. Iron oxide nanoparticles (NPs) are already commercially used as T2 contrast agent for MRI but they are also currently developed for therapy by magnetic hyperthermia (MH). Therefore the challenge is now to design NPs able to combine both MH and MRI. To be used as T2 MRI contrast agents, NPs should exhibit a high saturation magnetization and be functionalized with suitable molecules for biomedical aplications. In the case of MH, one of the limitations is the low heating power of usual magnetic NPs. Current researches aim at synthesizing NPs optimized for an efficient MH and one important parameter to control to obtain high heating values at low NPs dose is the NP magnetic anisotropy. Therefore the synthesis of ferrite NPs by thermal decomposition was optimized in order to tune their shape and/or composition (doped ferrite or core-shell). By carefully controlling synthesis parameters such as the nature of solvents, of precursors and of ligands, the amount of reactants, the heating rate, we were able to control the synthesis of NPs with different shapes and sizes : nanoplates, nanocubes, octopods, nanocaterpillar... and with different compositions : doped ferrites with Mn and Co and core-shell NPs consisting of a core with a high magnetic anisotropy and a shell with a small magnetic anisotropy. Their structural and magnetic properties have been finely characterized as well as their MRI and MH properties. Some designed NPs were shown to combine very high heating and MRI properties very promising for biomedical applications.

Resume : Specific nanomaterials may overcome the issues related with environmental remediation taking advantage of the peculiar properties of materials at nanoscale. TiO2 is one of the most studied photocatalysts due to its stability, abundance, non-toxicity and high activity. Pulsed laser ablation in liquid (PLAL) is one of the most promising emerging techniques for the synthesis of nanocolloids due to its advantages: industrially compatibility, low environmental impact, high purity of the products. The properties of the nanoparticles obtained by PLAL are determined by the laser parameter as well as by the target material and the liquid environment. This work focuses on the effect of the pH on the synthesis of TiO2 nanocolloids. The structural, morphological, optical and photocatalytic properties as a function of the pH will be presented. The photoactivity was measured by using the discolouration of methylene blue (MB) dye method while the antibacterial activity was measured by using the survival rate of Escherichia coli bacteria. The high activity showed by these nanoparticles is correlated to the surface properties and to the amount of hydroxyl groups, identified as main responsible for an enhancement in the catalytic performance of the nanomaterial. Such high hydrogen content is not observed in commercial TiO2 powders.

Resume : Metal halide perovskites, such as hybrid organic-inorganic CH3NH3PbI3, have attracted enormous attention as solution-deposited absorbing layers in solar cells with power conversion efficiencies reaching 20%. Recently, we have opened a new avenue for halide perovskites by designing highly luminescent perovskite-based colloidal nanocrystals (NCs). A facile one-step synthesis of monodisperse colloidal nanocubes (4-15 nm edge lengths) of fully inorganic cesium lead halide perovskites (CsPbX3, X = Cl, Br, I or Cl/Br and Br/I mixed halide systems) was demonstrated [1]. Post-synthetic chemical transformations of colloidal NCs, such as ion-exchange reactions, provide a pathway to compositional fine tuning or to otherwise inaccessible materials and morphologies. Here we present fast, low-temperature, deliberately partial or complete anion-exchange in highly luminescent CsPbX3 NCs [2]. By adjusting the halide ratios in the colloidal NC solution, the bright photoluminescence can be tuned over the entire visible spectral region (410-700 nm), while maintaining high quantum yields of 20-80% and narrow emission linewidths of 10-40 nm (from blue to red). Furthermore, fast inter-NC anion-exchange is demonstrated as well, leading to uniform CsPb(Cl/Br)3 or CsPb(Br/I)3 compositions simply by mixing CsPbCl3, CsPbBr3 and CsPbI3 nanocrystals in appropriate ratios. References: [1] L. Protesescu et al. Nano Letters 2015, 15, 3692−3696. [2] G. Nedelcu et al. Nano Letters 2015, 15, 5635-5640.

Resume : Synthesis and characterization of highly emissive shell-alloyed Mn-doped ZnSeS nanoparticles using a modified selenium precursor. Most of the methods to synthesize high-quality ZnSe:Mn nanoparticles, involve the use of toxic and expensive alkylphosphines, such as tributylphosphine (TBP) and trioctylphosphine (TOP) which require the use of a glovebox. Various attempts have been made to replace these alkylphosphines as a solvent with fatty alkylamines like oleylamine. During our investigations on the influence of coordinating solvents (like Oleylamine) for the reduction of selenium, we found that the tendency for oxidation of the reduced selenium (Se2-) limits the stability and the resulting optical properties of the synthesized ZnSe:Mn nanoparticles. [1] These observation inspired us to develop a modified selenium-precursor solution for the fabrication of high quality and stable ZnSe:Mn nanoparticles. It is well known that the photostability of metal selenide nanoparticles is improved by depositing a ZnS shell on the core in a two-step approach. However, the passivation step of the ZnSe:Mn core decreases the PL QY after the injection of the elemental S-precursor and Ying et al. found that the elemental sulfur was responsible for the decrease of the QY. [2] To avoid this problem during the passivation step, we bypass the use of elemental sulfur by using a long-chain-thiol:1-Dodecanthiol right in the beginning of the synthesis. The modified Se/S precursor prepared by dissolving Se powder in the mixture of DDT, NaBH4 and OLA (Oleylamine) at room temperature is suitable for the synthesis of high-quality shell-alloyed zinc selenide nanoparticles. Our novel approach is based on simultaneous reduction of selenium and formation of seleno(poly)sulphide which eases the reduction and dissolution process of elemental selenium in oleylamine and at the same time generates a homogenous sulfur source for the protective shell. A additional sulfid rich layer prevents energy transfer to surface states or to the medium and prevents the migration of the dopant ions, which leads to nanoparticles with high optical properties. Hitherto, the synthesis of core/shell and shell-alloyed ZnSe:Mn nanoparticles has required at least two steps. We report on a selenium/sulfur precursor solution with NaBH4, which enables the synthesis of high-quality shell-alloyed ZnSeS:Mn nanoparticles in a one-pot synthesis The nanoparticles obtained in this approach were found to have high optical quality (PL QY 42 %). Remarkably, the PL QY was affected by the amount of DDT which turned out to be a key factor for obtaining high PL QY oft he shell-alloyed ZnSeS:Mn nanoparticles. Distinctive features in the PL spectra allowed for an estimate of the role of DDT. Besides this, the ratio of DDT to Se significantly affected the PL QY of the nanoparticles. HR-TEM, XRD, ICP-MS/OES and XPS were performed to explore the structure of the nanoparticles and furthermore, to acquire proof of an alloyed structure. Paper is in progress. [1] Zimdars, J.; Bredol, M. New J. Chem. 2016 , in press. [2] Wei, Y.; Yang, J.; Lin, A. W. H.; Ying, J. Y. Chem. Mater. 2010, 20, 5672?5677.

Resume : Quasi 2D CdSe nanoplatelets (NPL) with only few monolayer thickness as well as the heterostructures achieved from these quantum wells by growing metal domains on its surface have strengthened the colloidal chemistry of II-VI compound in recent years. (1, 2) Here, we report the synthesis of highly porous, fluorescent aerogel monoliths from strongly quantum confined CdSe and CdSe/CdS NPL. The NPL are synthesized in organic medium and transferred to aqueous solution by a ligand exchange reaction.(3, 4) Controlled destabilization of the aqueous solution of the NPL is achieved with H2O2. The voluminous hydrogels obtained are converted to aerogels by supercritical drying with liquid CO2. SEM and TEM microscopic analysis prove that the nanoplatelets form a self supported fractal type network consisting of pores with diameters ranging from the mesoporous (2 to 50 nm) to the macroporous (> 50 nm) regime. Higher resolution TEM micrographs reveal a random orientation of the NPL with (111) as the exposed crystal facet. The luminescent aerogels exhibit quantum yields up to 10 % and extremely low densities of ~ 0.038 g•cm-3. The nitrogen sorption measurements reveal a significantly large BET specific surface area in the range of 1.8x10^2 – 2.2x10^2 m2•g-1. The unique properties of the here developed aerogels such as high porosity, low density, strong quantum confinement as well as (111) as the exposed crystal facet are promising for future applications in the field such as optical sensing, facet selective catalysis, light emitting diodes and in photovoltaics. References: 1. Ithurria, S. et.al. J. Am. Chem. Soc. 2008, 130, 16504-16505. 2. Naskar, S. et.al. Chem. Mater. 2015, 27, 3159-3166. 3. Kodanek, T. et.al. Nanoscale 2015, 7, 19300-19309. 4. Sánchez-Paradinas, S. et.al. Adv. Mater. 2015, 27, 6152-6156. *nadja.bigall@pci.uni-hannover.de

Resume : Silicon Nanocrystals (Si NCs) are an interesting class of semiconductor nanocrystals due to their unique optical properties, high natural abundance, and low toxicity.1 The size and surface dependent optical properties of Si NCs combined with its low toxicity give it a strong future in applications ranging from bioimaging to LEDs and solar cells.1 Tuning the optical properties of Si NCs is a significant synthetic challenge. Key areas to improve include tuning the emission range, which if addressed will lead to dramatic improvements in Si NC applications such as optoelectronic devices (LEDs) and bioimaging. Doping of semiconductor nanocrystals has been particularly successful at tuning the optoelectronic properties, unlocking a new range of emissions beyond simple size tunability (Cu2+ in InP), and enhancing quantum yields (Ag+ in CdSe).2-3 Doping of Si NCs to tune the optical properties is a promising and relatively unexplored method, with few examples in the literature.1,4 This presentation will discuss the synthesis and characterization of Mn, Ni, and Cu doped Si NCs, highlighting their unique dopant dependent optical properties.4 Doped Si NCs were produced through use of strong hydride reducing agents to co-reduce metal dopant and silicon salt in the presence of a quaternary amine surfactant.4 Doped Si NCs were shown to be highly monodisperse with comparable size to pure Si NCs by transmission electron microscopy.4 The optical properties of doped Si NCs were studied by ultraviolet-visible spectroscopy, photoluminescence spectroscopy (PL), and both ultrafast transient absorption and TCSPC (Time-Correlated Single Photon Counting) PL spectroscopy.4 Doped Si NCs demonstrate distinctive optical properties such as enhanced absorption and emission redshifts of over 50 nm compared to pure Si NCs.4 References 1) M. P. Singh, T. M. Atkins, E. Muthuswamy, S. Kamali, C. Tu, A. Y. Louie and S. M. Kauzlarich, ACS Nano, 2012, 6, 5596-5604. 2) R. Xie and X. Peng, J. Am. Chem Soc., 2009, 131, 10645-10651. 3) A. Sahu, M. S. Kang, A. Kompch, C. Notthoff, A. W. Wills, D. Deng, M. Winterer, C. D. Frisbie, and D. J. Norris Nano Lett. 2012, 12, 2587-2594. 4) B. F. P. McVey, J. Butkus, J. E. Halpert, J. M. Hodgkiss and R. D. Tilley J. Phys. Chem. Lett. 2015, 6, 1573-1576.

Resume : We demonstrate the relation between the optical blinking of colloidal semiconductor nanocrystals (NCs) and their electrical charge blinking for which we provide the first experimental observation of power-law statistics. To show this, we harness the performance of CdSe/ZnS NCs coupled with carbon nanotube field-effect transistors (CNTFETs), used here as single charge-sensitive electrometers with submillisecond time resolution, at room temperature. A random telegraph signal (RTS) associated with the NC single-trap charging is observed, which exhibits power-law temporal statistics (t^−α, with α in the range of ∼1−3), and a Lorentzian current noise power spectrum with a well-defined 1/f^2 corner. The spectroscopic analysis of the NC−CNTFET devices is consistent with the charging of NC defect states with a charging energy of Ec ≥ 200 meV. Reference : E. Zbydniewska et al., Nano Letters 2015, 15 (10), pp 6349–6356.

Resume : Dot-in-bulk CdSe/CdS nanocrystals (DiB-NCs) comprise a CdSe core embedded into a thick CdS shell. As a result of a thin core/shell interfacial potential barrier and electrostatic hole-hole repulsion (dynamic Coulomb blockade) DiB-NCs show two-color core and shell emission under low-level excitation. The exact nature of core-blocking mechanism and its connection to the interfacial structure is, however, not fully understood. Whilst the large shell volume seems to be a necessary condition, taken alone it cannot explain efficient shell emission, suggesting a key role of the interface potential exact shape on dual emission process. To unravel such intimate connection, we perform optic studies on identical DiB-NCs with abrupt core/shell interfaces differing from each other only for the absence/presence of core/shell potential barrier. Dual emission is observed in both cases due to reduced relaxation rate of shell holes into the core with respect to CdSe/CdS NCs with graded interfaces. However, the core-blocking mechanism is active exclusively in NCs with interfacial barrier, leading to suppression of Auger recombination and extending shell-exciton lifetimes. This allows for achieving ASE from shell states using ns-pulsed excitation, while in NCs with a homogeneous shell population inversion is achieved exclusively using fs-pulsed excitation. These results hence provide important guidelines for the realization of next generation NCs with highly controlled dual-emitting capability.

Resume : The advantages of using quantum dots (quantum-confinement effects) and perovskites (high emission efficiencies and low production costs) are combined in all-inorganic cesium lead halide (CsPbX3, X = Cl, Br, I, and mixed Cl/Br and Br/I) nanocrystals (NCs) with perovskite structure, a new promising material for photovoltaic and optoelectronic applications. We synthesize CsPbX3 colloidal nanocrystals dispersed in non-polar solvents with high quantum photoluminescence yields of 50-90%. Here we report on some advances in our current effort to make them water-stable, in order to get an easy-to-handle material with application fields enhanced to bio-imaging and ink-jet printing, among others. For this purpose, we encapsulate the inorganic perovskite NCs in solid lipid nanoparticles (SLN) of stearic acid. Encapsulated perovskite NCs remain stable in water for a period longer than a month. At the same time, their advantageous optical properties of efficient and size-tunable emission and large cross-section for light absorption remain intact after the encapsulation treatment. In addition, the encapsulation avoids anion-exchange between CsPbX3 NCs making possible to get a stable mixture of diverse inorganic perovskite NCs.

Resume : We report on the progress on the partial cation exchange on nanowires. The cation exchange as a post-synthesis treatment for colloidal nanocrystals allows for the alternation of the material composition whilst preserving the shape of the particles.(1, 2) In our experiments, we demonstrate that this treatment can be restrained also to small sections of the isolated particles. This allows us to fabricate hybrid nanostructures that are cannot be produced by chemical synthesis. This work builds on the partial blocking of the cation exchange in films of CdSe/CdS nanoparticles.(3) By exposure to an electron beam areas of the films could be excluded from the cation exchange, while the other particles were transformed into Cu(2-x)Se/Cu(2-x)S. The nanowires are deposited onto a substrate, and partially treated with high-energy radiation. The irradiated parts of the wires are effectively blocked for the cation exchange. The success of this treatment can be demonstrated by elemental mapping in an SEM. We performed electrical characterization of the sectioned wires. 1. Rivest, J. B. & Jain, P. K. Chem Soc Rev 42, 89–96 (2013). 2. Beberwyck, B. J., Surendranath, Y. & Alivisatos, A. P. J. Phys. Chem. C 117, 19759–19770 (2013). 3. Miszta, K. et al. Nano Lett 14, 2116–2122 (2014).

Resume : The controlled growth of nanoparticles (NPs) on surfaces is a powerful tool to create nanostructured materials with desired properties for several technological applications. In particular, metal NPs have attracted much interest due to their potential application in many areas (plasmonics, photovoltaics, etc.). The key step towards reliable solid-state technological applications of metal NPs-based systems is the development of simple, versatile, low-cost, high-throughput methods for the fabrication and manipulation of metal NPs directly on surface. Key requirement is the quantitative understanding of the physical mechanisms governing the NPs growth dynamics. So, we present an investigation on the growth dynamics, induced by thermal processes, of colloidal Au NPs on SiO2. We deposited size-mono-dispersed Au colloidal NPs on SiO2 surface and performed annealing processes in the 573-1173 K temperature (T) range and 900-3600 s time (t) range. The evolution of the mean NPs size was quantified as a function of T and t. In particular, we studied the experimental temporal evolution of the NPs size using the relations prescribed by the particles coalescence theoretical framework. Fits of the experimental data by such relations allowed us to determine a size-dependent activation energy for the coalescence process of the SiO2-supported Au NPs. The size-dependence of the activation energy is discussed on the basis of the size-dependent cohesive energy of the atoms in the NPs.

Resume : Lead halide perovskites have attracted considerable attention in the context of optoelectronic applications. Nanocrystals (NCs) of CsPbX3 (X = Cl, Br, I) exhibit bright photoluminescence, with emission tunable over the entire visible spectral region. However, previous studies on CsPbX3 NCs did not address key aspects such as surface chemistry and quantitative light absorption. Here[1] we elaborate on the synthesis of CsPbBr3 NCs and their surface chemistry. In addition, the intrinsic absorption coefficient was determined experimentally via ICP-MS measurements, combined with optical absorption measurements. 1H solution NMR was used to characterize sample purity, to elucidate the surface chemistry and to evaluate the influence of purification methods on the surface composition. We find that ligand binding to the NC surface is highly dynamic, and therefore, ligands are easily lost during the isolation and purification procedures. However, when a small amount of both oleic acid and oleylamine are added, the NCs can be purified, maintaining optical, colloidal and material integrity. In addition, we find that a high amine content in the ligand shell increases the quantum yield due to the improved binding of the carboxylic acid. This work sheds thus more light on the surface chemistry of CsPbBr3 NCs and opens the way for further surface modifications, required for the optoelectronic applications of these NCs. [1] De Roo, J. et al. ACS Nano 2016 Accepted

Resume : Quantum Dots (QDs) emitting in the visible are of particular interest for lighting and display applications. To make the use of QDs in these fields feasible, InP QDs are studied as alternatives for the well-characterized Cd-based QDs. We recently proposed protocols based on aminophosphine precursors that allow for a cost efficient synthesis of InP QDs of different sizes. This new phosphorus precursor is cheap and is safe-to-use under ambient. Most notably, this method can be used to make InP/ZnS or InP/ZnSe core/shell QDs with a narrow (45-60 nm FWHM) photoluminescence tunable from 480 nm to 670 nm and a quantum yield ranging from 30-80 %. Here, we present a complete investigation of chemical reactions leading to the formation of InP starting from aminophosphine-type precursors and we link the precursor chemistry to the properties of the QDs eventually obtained. To this end, we identified several specific molecules involved in the reaction by different methods: NMR spectroscopy, mass-spectrometry, etc. This study allows us to propose a chemical mechanism based on a nucleophile attack of the phosphorous on an amino group. This mechanism is innovative in the sense that it points out a double role of the phosphorus precursor in the reaction as both a reducing agent and the source of the phosphorous needed to form InP. Moreover, this detailed understanding of the aminophosphine reaction chemistry will further the general use of aminopnictogens for the synthesis of III-V QDs.

Resume : Colloidal nanostructures based on multinary I2-II-IV-VI4 semiconductors (e.g. Cu2ZnSnS4 and Cu2ZnGeS4) have spawned considerable interest in recent years due to their technologically applicable properties that render them useful in the areas of photovoltaics, thermoelectrics and photocatalysis. Moreover, their low toxicity makes them promising alternative materials to the more widely studied cadmium- and lead-containing semiconductor nanostructures. With the use of a facile colloidal synthetic strategy, we were able to prepare nanostructures of Cu2ZnSnS4 and Cu2ZnGeS4 with elongated morphologies (e.g. nanorods, nanoworms). We find that the use of an appropriate combination of coordinating solvents and precursors is crucial to the formation of the metastable wurtzite-derived phase of these multinary sulfides in solution. We propose possible formation mechanisms on the basis of our experimental results.

Resume : Nanoparticles of noble metals demonstrate interesting properties of local enhancement of electromagnetic field, catalytic activity and many other unique properties finding multiple applications. Properties of such nanoparticles depend on their size distribution, mutual position and surrounding material. In the current work mono‐dispersed silver nanoparticles of original and controllable shape were synthesized. In addition to the traditional spherically symmetrical silver nanoparticles, polyhedral silver nanocrystals were synthesized and investigated employing SEM, UV-VIS spectrometry as well as employing transient absorption spectrometer (HARPIA, Light Conversion Ltd.). Polyhedral shaped nanoparticles that are especially interesting because they assemble into different and more complicated configurations than spheres, with unique orientations and connectivity, were synthesized at the size range (60‐300 nm) that are most useful for plasmonic and photo‐catalytic device applications. Ultrafast energy relaxation measurements were used to describe plasmonic properties of the originally shaped silver nanoparticles for the optimization process of technology and further applications in photo‐catalysis.

Resume : In southwestern Taiwan, the western foothill in Tainan-Kaohsiung county is the exposed area of Pliocene to the early Pleistocene strata composed of a mudstone series which is from 5.3 million years ago to 1.6 million years ago, named as Gutingkeng Formation which is 5000 meters in depth. The appearance of this formation is specifically called as “Moon World”. The mineral compositions of Gutingkeng Formation are mainly contained quartz (40%~60%), feldspar (<5%), and clay minerals. The clay minerals consist of illite (~ 50%), clinochlore (~ 40%) and a small amount of swelling clays (~ 10%). The large lenses of Gutingkeng Formation do not have any important economic applications. Furthermore, its grain size is small and it has low permeability, and thus these muds became sticky or resulted in landslide when it rains. To avoid this disaster, the mudstone was modified to promote its economic application in this study. It is known that the nano-silica is widely used in mirrors, chromatography, catalysis and chemical mechanical polishing, electrical insulators, heat-resistant materials, humidity sensors, and so on. In this study the silicon dioxide nanoparticles were prepared from the mudstone of Gutingkeng Formation. Firstly, we purified the mudstone by acid treatment. Next, the sodium hydroxide was used to extract sodium silicate from silica muds. Finally, the hydrochloric acid was titrated to sodium silicate solution until pH=7, and then the SiO2 nanoparticles would be obtained. From the result, it shows that the parameters of titration step are the main factor for the particle size of SiO2 nanoparticles. When the temperature of titration is at 65ºC, the size of nanoparticle will have higher energy to grow up, but a little agglomerated around 20-30 nm. And the titration rate is also the important factor for preparation of SiO2 nanoparticles. The related studies will be further investigated.

Resume : Strontium titanate (SrTiO3) is a very versatile material suitable for a wide range of applications from catalysis to electronics. With special regard to catalysis, surface area, pore topology and matrix crystallinity are decisive parameters. Standard hard templating strategies, such as nanocasting, present several limitations for the synthesis of porous perovskite systems. In this work, a novel hard templating approach for the synthesis of nanoporous SrTiO3 is proposed. The synthesis is realized by mixing a SiO2 precursor solution together with a citrate-metal complex and glycerol. After calcination at temperatures as low as 500 °C, nanoporous SrTiO3 was obtained through etching treatment with NaOH to the resultant nanocomposite. By varying the molar ratio of the SiO2 template, systems with different porosity and crystallinity could be prepared. The materials were characterized comprehensively through a multitechnique approach to address the structure/function relationships. The XRD confirms pure SrTiO3 phase for all the samples whereas N2 physisorption show type IV isotherms with specific surface areas up to 330 m2/g. Furthermore, the catalytic activity of the materials has been tested by photodegradation of methylene blue under UV light. Compared to the bulk reference sample obtained without templating, the nanoporous SrTiO3 systems demonstrate enhanced catalytic activity with a maximum for the material prepared with 50% of SiO2.

Resume : Despite the fact that surfaces and interfaces of colloidal ZnO nanoparticle systems have a key influence on their optoelectronic properties, their chemical and physical properties have remained unspecified for most cases. Considering that minor changes in colloidal processing correspond to substantial changes in the interfacial properties, a particularly unsatisfactory situation is created where an increasing number of publications report discrepant results for one and the same well-established nanomaterial.[1] In this contribution we will discuss for vapor phase grown ZnO nanoparticles how defect related spectroscopic fingerprints such as photoluminescence emission from oxygen interstitials [2] or paramagnetic oxygen vacancies in the surface and subsurface region can be used as probes for interfacial changes in the colloidal system. We will focus on the interplay between particle interface condition and spectroscopic properties for originally dry nanoparticle systems that became converted into colloids by step wise water addition via the gas phase. Aiming at a more consistent and robust assessment of ZnO nanoparticle properties in aqueous dispersions this work also explores the spectroscopic response of nanoparticle interfaces to small molecules such as oxygen and formic acid. [1] Berger and Diwald, Defects in Oxide Nanoparticles Systems, Springer Ser. Surf. Sci., 58 (2015) 273-301 [2] Gheisi et al. PhysChemChemPhys 16 (2014) 23922-23929. [3] Kocsis et al. submitted (2016)

Resume : Photocatalytic properties of TiO2 make them useful materials in a wide range of applications such as waste water purification, antimicrobial surfaces, and self-cleaning surfaces. Consequently it attracts much scientific interest. Photocatalytic efficiency of titanium dioxide depends on many factors such as band gap, surface area, particle size and crystallinity. We demonstrate the synthesis of a unique nanostructured octahedral TiO2/Fe2O3 heterojunctions by using hydrothermal methods. While these methods expose the photocatalytically active (101) and (001) surfaces of anatase, the material also shows activity under visible light. With this novel design, incomparable photocatalytic activity can be obtained due to effective electron and hole separation. The structural, physical and morphological properties of nanocomposites are studied using various characterization tools such as XRD, BET, SEM and TEM. Furthermore, the photocatalytic activities are tested with methylene blue solution under UV/Vis radiation for potential applications in waste water treatment.

Resume : Recently, great attention has been devoted to the passivation of porous III-V semiconductor surfaces. Since the defect states are harmfully affect the optical and electrical properties of the materials, the role of efficient passivants is crucial in enhancing the performance of III-V based devices. In this work, we report the improvement of optical and thermal properties of porous GaAs layers passivated using a simple and effective method by immersing the porous GaAs sample in a dilute LiBr aqueous solution for different concentrations. Thermal conductivity of LiBr-porous GaAs layers was studied using the photothermal deflection technique, by comparing the experimental amplitude and phase of the photothermal signal to the corresponding theoretical one. The optical loss was studied using Spectral Reflectance showing that the oxidation of porous silicon is a good way to obtain lower optical loss of such porous structure. Moreover, photothermal deflection spectroscopy is used to investigate the optical absorption spectrum then the band gap energy. A slight variation of light absorption that is probably due to the newly formed layer during the chemical deposition of the Li metal. Therefore, we consider that LiBr treatment is a promising way to passivate the surface of porous GaAs samples.

Resume : Heterojuction induced from different-sized bipyramidal anatase TiO2 with {101}-exposed facets results in electron/hole separation, which exhibits outstanding photocatalytic performance on methylene blue (MB). The TiO2 was synthesized by hydrothermal process, using sodium titanate as the precursor in lithium salt solution at 200 oC. The obtained anatase TiO2 powder consists of different-sized bipyramids ranging from 100 to 800 nm. In this work, the main influences of photocatalytic performance, such as surface active sites and heterojunction are investigated. In addition, the photocatalytic degradation mechanism was also studied. Conventionally, the rate constants were analyzed by fitting the degradation curves with the first-order decomposition reaction. However, in this work, the curve could not fit well with the first-order kinetic reaction even in the initial 10 minutes, which indicates the existence of another reaction pathway. This shifting-order type kinetics, which may arise from the reactant concentration or the degradation mechanism, are discussed. The photocatalytic results show that the initial degradation rate constant of bipyramidal anatase TiO2 is 0.1899 min-1, which significantly larger than that of commercial P25 TiO2, which is only 0.0927 min-1. Even in the long period experiment, bipyramidal anatase TiO2 still has better photocatalytic performance than commercial P25 TiO2. In conclusion, different-sized bipyramidal anatase TiO2 is a promising photocatalytic material.

Resume : Using uniform TiO2 submicrospheres as an additive markedly enhances scattering of light with short wavelength, resulting in absorption of UVA and UVB effectively, which leads to significantly improved performance of sunscreen. In order to reduce the cost of ingredient in commercial sunscreen product, mass production of highly uniformity PS/TiO2 submicrospheres with well UV absorption will be a primary problem to be tackled. In this study, the PS/TiO2 submicrospheres were synthesized via a facile reflux process at 85 C for 2 hours using industrial TiOSO4 solution as the titanium source and polystyrene (PS) as the hard template. To prepare industrial TiOSO4 solution, TiOSO4 was dissolved in deionized water for 2 hours to become a clear solution. TiO2 can be produced by adjusting pH value in the solution, so, NaOH was chosen to induce hydrolysis of TiOSO4 solution. The obtained uniform PS/TiO2 submicrospheres were 100 nm in diameter with 5-10 nm shell, and moreover, its UV absorption of 250-300 nm was good as commercial ZnO. Furthermore, the size of PS/TiO2 submicrospheres, which related to how well the UV absorption of 250-300 nm light could be adjust by prolonging the reaction time.

Resume : Mesoporous oxide films with nanoparticles inclusions have improved photocatalytic properties due to a controlled porosity and presence of light absorbing metallic catalyzers, but the exact mechanism of improvement is yet to be clarified as several phenomenons occurs concomitantly like charge carrier, surface catalysis, plasmon enhancement, and exciton relaxation. We studied nanostructured electrodes made of metallic nanoparticles (Au, Ag) inside a semi-conductor oxide (TiO2/Fe2O3) with a control of porosity and particle dispersion as an improved photocatalytic system. We performed electrochemical experiments under various ranges of light irradiation, from UV to visible, to determine the variations of redox potentials and photocurrent and thus getting some insights on the photochemical mechanism and the influence of material structure on photocatalytic properties. Porosity is introduced by using block copolymer self assembly process and the nanoparticles are grown using a salt impregnation strategy followed by reduction of the metallic salt inside the porous oxide matrix. Once electrodes are realized, they are fully characterized by SEM, TEM, XRD, UV-visible spectroscopy, and profilometry. The electrochemical properties and photocatalytic performances are then studied in a three-electrode configuration photoelectrochemical cell in order to determine the exact influence of nanoparticles as a catalyzer or as a photonic enhancer through plasmon absorption.

Resume : A relevant area of interest in medical sciences is the in vivo optical bioimaging for the selective identification of tumoral cells. Semiconductor nanoparticles (NPs) or quantum dots (QDs), also doped, are chosen as contrast agents in this field because they show size-dependent optical properties, intense photoluminescence and sharp emission profiles. Ideally, the doped NPs should be selectively luminescent in the near infrared NIR region, since this is the spectral region showing the maximum penetration depth in biological tissues. Therefore we addressed the synthesis of semiconductor NPs based on Ag2S, since it is characterized by a narrow bandgap (0.9-1.1 eV, in the NIR) and low cytotoxicity. Doped Ag2S:Ln (with Ln: NdIII, SmIII, YbIII) NPs were synthesized with two different methods, namely inverse miniemulsion and hydrothermal, and in all routes different concentrations were used, with a fixed molar ratio (2:1). These methods are very suited to control the size and the size dispersion of the nanocrystals, important parameters for NPs and QDs potential application in biomedical labeling. The crystalline NPs were prepared reacting different sulfur precursors, (i.e. Na2S, thiourea, thioacetic acid and ammonium thioglycolate) with silver nitrate, and the resulting materials were thoroughly characterised from a compositional, electronic and structural point of view, using powder X-ray diffraction and synchrotron-based photoemission and X-ray absorption spectroscopies.

Resume : In the past decades, interest for new catalysts and new catalytic reactions increases greatly due to their large applications in several domains such as pharmaceutical and chemical industries. New catalysts were described for an increasing number of organics reactions. Nevertheless, most of the homogenous catalysts are difficult to adapt to industrial process due to separation and regeneration problems. Moreover, though highly efficient, most of the catalysts are containing noble or toxic metals and so new protocols more economically and environmentally friendly need to be developed. Recently, more attention has been paid to the use of nanomaterials as support. In fact, due to their unique properties and their enhanced surface volume ratio putting them at the frontier between heterogeneous and homogeneous catalysis,[1] nanomaterials are quickly becoming the support of choice for catalysis applications. Among them, magnetic nanoparticles appear as an ultimate nano-support due to their easiness of recovery owing to their magnetic properties. The simple use of an external magnet could afford the rapid recovery of the catalyst without the need of filtration or centrifugation. The interest in catalysis using magnetic nanoparticles as a support is increasing dramatically and several nanomagnetic catalysts were described recently.[2] In this context, we proposed to prepare several nanocatalysts based on iron oxide nanoparticles of 10 nm mean diameter bearing two different types of catalysts at their surface: organocatalyst that are small molecules (amino acids, peptides,...) allowing metal free catalysis or Pd catalyst for C-C coupling reactions that played a very important role in a wide range of chemistries. We will first present results obtain with nano-organocatylists on enantioselective Michael addition. We will be showing in these reactions the important role of controlled functionalization of nanoparticles [3-4] and the role played by the nano-support and the chosen surface chemistry used to prepare such nano-organocatalyst.[5] Then we will present a new simple Pd supported magnetic nanocatalyst which turns out to be extremely efficient for Suzuki-Miyaura reaction under microwave, in aqueous media and under aerobic conditions (Figure 1). This very stable catalyst (> 12 months in water under aerobic conditions) is moreover reusable up to 7 times with total conversion and small amount of palladium leaching. This green nano-catalyst prepared with cheap reactant and working under eco-friendly conditions with Pd quantity down to 100 ppm appears to be one of the most efficient up to date for Suzuki-Miyaura cross coupling.[5] Finally preliminary results on its exemplification on other C-C coupling and reduction reactions will be presented. References [1] S. Shylesh, V. Schünemann, W. R. Thiel, Angew. Chem. Int. Ed., 2011, 49, 3428. [2] M. B. Gawande, P. S. Branco, R. S. Varma, Chem. Soc. Rev., 2013, 42, 3371. [3] P. Demay Drouhard, E. Nehlig, J. Hardouin, L. Motte, E. Guénin, Chem. Eur. J., 2013, 19, 8388-8392. [4] E .Nehlig, L. Motte, E. Guénin, Catal. Today,2013 90. [5] E. Nehlig, L.Motte, E. Guenin, RSC Adv. 2015, 5, 104688. [6] E. Nehlig, B. Waggeh, N. Millot, Y. Lalatonne, L. Motte, E Guénin, Dalton Trans., 2015, 44, 2, 501.

Resume : InAsBi layers were elaborated on semi-insulating (100) GaAs substrates misoriented10° by atmospheric pressure metalorganic vapor phase epitaxy (MOVPE) reactor. Spectral reflectance in the range of 200 to 1100 nm was employed to in situ monitor epitaxy. For determining the optical constants of InAsBi films, an optical model incorporating time-dependent surface roughness and time-dependent growth rate was used to simulate the in situ reflectance. A theoretical motivation for the introduction of these two parameters instead of a standard single rms roughness and growth rate is provided Several InAsBi samples grown at different growth temperatures were used to illustrate ways in which the parameters introduced can be evaluated. Reflectivity analysis was ex situ correlated by atomic force microscopy. Keywords: InAsBi, In situ spectral reflectance, optical model, refractive index Corresponding authors: ahmed.rebey@fsm.rnu.tn, hedi.fitouri@fsm.rnu.tn

Resume : Silica powder has been applied to a lot of engineering parts such as reinforcing agent, abrasives, anddehumidifying agent. Such silica powder can be synthesized by sol-gel method which is simple and low cost process. TEOS is the most popular precursor for synthesis of silica powder but its price is high. On the other hand, sodium silicate is much cheaper than TEOS but it includes many impurities, followed to silica powder with low purity. In this work, we studied how to synthesis silica power with high purity from low cost sodium silicate. We achieved to synthesize high purity silica via soxhlet extraction using nitric acid and DI water. To synthesize silica powder, we first prepared 0.3M nitric acid and then dropped sodium silicate into 0.3M nitric acid until its pH became 2, 3, 7, and 10. After adjusting its pH, the solution was stirred for 4h, turning into silica sol. The silica sol was dried at 80℃ for 72h. Then it was dried and cleaned using soxhlet extractor. Cleaning was performed by 1 time with nitric acid and 5 times with DI water. When comparing to silica power synthesized at different pH, silica powder synthesized at pH 2 showed the best cleaning efficiency and purity. In XRD and XPS analysis, silica power synthesized at pH 2 represented a lot of impurity peaks before cleaning. But we did not observe any impurity peak after cleaning process. We observed same results in EDS analysis. Finally we achieved to synthesize high purity silica powder (purity 99.95wt%).

Resume : Quantum Dots (QDs) are part of inorganic nanocolloids relevant to both fundamental and applied sciences. In the latter case, suggested applications include biomedicine and optoelectronics.1 CdTe is a very attractive model material because of successful applications in both medical optical imaging and optelectronic devices such as solar cells due to a relatively high photoluminescence quantum yield and stability at ambient conditions.2-6 Often though, organic solvent based syntheses are based on high temperature synthetic protocols, whist water based syntheses require lower temperature but also lead to more polydisperse products. In this work, we explored the preparation of CdTe QDs near-room temperature. We investigated the impact of several precursors and monitored the properties of the products by steady state and time-resolved optical spectroscopy.7 Along with the QDs characterisation, the challenges associated with such synthetic pathway will be discussed to assist the development of low energy consumption QDs preparation and their use for optoelectonic applications. 1. M. V. Kovalenko et al. ; ACS Nano, 2015, 9, 1012 2. Y. C. Wang et al. ; RSC Adv., 2013, 3, 8899 3. Y. P. Rakovich et al. ; Journal of Materials Chemistry, 2012, 22, 20831 4. A. Ambrosone et al. ; Biomaterials, 2012, 33, 1991 5. N. Gaponik et al. ; Physical chemistry chemical physics : PCCP, 2010, 12, 8685 6. I. Visoly-Fisher et al. ; ChemPhysChem, 2005, 6, 277 7. K. Marbou et al. ; In preparation, 2016

Resume : Recently, nano-fluids with ceramics nanoparticle have been effectively prepared and studied by different researcher. However, more attention should be paid to characterization and investigation of optical properties of oxide particles with the ability of deposition with wet chemical methods. In this work, colloidal solution of ZnO, ZrO2, and SiO2 were prepared and dispersed in water-based solutions. Because of strong interaction between the nanoparticles, they tend to agglomerate in the fluid phase. Therefor different methods like ultrasonication, milling, and surface modification have been used to disperse the nanoparticles and the most concern in this case is stabilization of these additives in host material for. Thin films with different thicknesses were prepared from the dispersed particles. The optical properties of the thin films were studied by measuring reflectance and transmittance. A theoretical method was applied to compare the results of the reflection and transmission which leads us to obtain the thickness and spectral behavior of the refractive index. Structural and morphological properties of these nanocolloids were studied by scanning electron microscopy (SEM) and X-ray diffraction method (XRD). The size of dispersed particles was measured with dynamic light scattering (DLS) which is in a good agreement with the images that obtained by transmission electron microscopy (TEM).

Resume : Metal oxide nanoparticles are an important class of materials for solar cells, gas sensors and as photocatalysts. Recently, ultrathin tungsten oxide nanowires have been reported that have outstanding properties for photochemical reduction of carbon dioxide indicating the high potential of such nanostructures of extremely high surface-to-volume ratios.[1] In this work, we report a synthesis through solvothermal method to produce ultrathin WOx nanowires with precise morphology control over the length and diameter, up to very high aspect ratio (1nm diameter with several hundreds nm length) allowing to fine tune their physical and chemical properties.[2] Interestingly, the morphological control is obtained by modifying the precursor layer structure with different alcohols prior to the solvothermal step. Moreover our novel synthetic approach is based on a non-toxic tungsten precursor (unlike the toxic W(CO)6 commonly used[3]) and allows gram-scale production of these highly soluble nanowires. The ultrathin nanowires having 1nm diameter show the most important effects when used as photocatalysts for the reduction of pollutant Rhodamine B, being considerably more efficient than other morphologies. The possibility to reduce silver precursors directly on the nanowires in order to grow Ag islands on the WOx wires are presented, with the possibility to tune the density and size of Ag islands on WOx by adjusting the synthesis parameters. [1] Guangcheng Xi, et al. Angew. Chem. Int. Ed. 2012, 51, 2395 –2399 [2] Liu J. et al. Adv. Func. Mat., 2014, 24, 6029. [3] Moshofsky, B., & Mokari, T. Chemistry of Materials. 2013, 25, 1384.

Resume : Graphene-related materials due to their properties and perspectives of various applications demand on low-cost synthesis procedure. New methods of graphene and graphene-related materials fabrication in large amounts are intensively elaborated. Electrochemical exfoliation of graphite is one of the most promising. It is should be noted that quality of graphene and its derivatives usually depend on synthetic procedure. Therefore, it is important to study morphology, physical and chemical properties of obtained materials. In this work electro-chemical dispersion was used to produce graphene containing colloid systems. Colloid systems as well as samples of graphene-related materials deposited on substrates (glass, quartz and Si) were characterized by micro-Raman, absorbance and luminescence spectroscopy techniques. Morphology and particles sizes where studied by optical, AFM, STM and SEM microscopy. Dependencies of the characteristics on the concentration, chemical treatment, size, and thickness of carbon micro- and nanoparticle stacking were obtained and analyzed. It was found that large particle in colloids prepared by electrochemical exfoliation reveal graphite-like structure while small particles posses properties of multilayered graphene.

Resume : Incorporation of nanomaterials into various host matrices leads to different effects that can be effectively exploited, in particular, in sensor applications. A prominent example of such nanocomposites is a polymer, containing carbon nanotubes (CNT). It was already demonstrated that the electrical response of polymer-CNT composite is sensitive to the amount of absorbed gamma radiation. In order to provide the efficient radiation shielding, the functionality of these materials can be extended by optimizing the parameters of nanocomposite, such as type, concentration and volume distribution of reinforcing nanomaterial.Utilization of the percolation effect in reinforced nanocomposites can be helpful in the detection of the critical radiation exposure. We focus on systematic studies of physical-chemical properties of epoxy and PEDOT-based nanocomposites under gamma radiation from Radium-226 source. Ideas for the design of a shielding material with the inbuilt radiation exposure sensor will be discussed.

Resume : Magnetic nanoparticles are currently receiving a great deal of attention due to their vast potentials on biomedical applications such as hyperthermia therapy, drug delivery and diagnostic agents among all. So far, the most widely studied magnetic materials are the oxidized forms of iron. Indeed these show attractive features such as superparamagnetism at room temperature and suitable size, and have been approved by Food and Drugs Administration Agency leading their experimentations to in vivo studies. However, for most of the above mentioned application iron oxides nanoparticles are far from ideal since the highest magnetic moment that can be reached is 92 emu/g for magnetite. Conversely, pure metallic Iron shows a higher magnetic moment (217 emu/g), still retaining superparamagnetic behaviour at suitable size and low toxicity, which would increment their performances in biomedical applications. However, the use of Fe nanoparticles is limited due to their quick oxidation process once they are exposed to air and/or biological environment. Indeed, several attempts of coating the iron core to prevent oxidation have been reported in literature but often the protective layer results in non-homogeneous and/or thick non-magnetic mass which increases the size of the particle and reduces their magnetic moment. Therefore the synthesis of stable highly magnetic nanoparticles based on Iron with a suitable coating layer is still an ongoing challenge. In this study we aim to synthesize core@shell nanoparticles with a crystalline bcc Fe core embedded in a protective shell of magnetic FePt. Using FePt as coating layer can increase the stability of the Iron based nanoparticles without adding non-magnetic mass to the system. Furthermore, it has been pointed out that the exchange coupling between magnetically soft and hard materials is a promising strategy to enhance nanoparticles features in biomedical application, i.e. the specific loss power of nanoparticles used for hyperthermia therapy [1]. Thus, since the use of exchange-coupled magnetic material is still at its infancy, the study of this nanoparticles allow also to investigate the heating efficiency of exchange-coupled soft/hard core/shell magnetic nanoparticles. Ref: [1]. J. H. Lee, J.T. Jang, J.S. Choi, S. H. Moon, S.H. Noh, J.W. Kim, J. G. Kim, I. S. Kim, K. I. Park, J. W. Cheon, Nat. Nanotechnol. 6 (2011) 481

Resume : We present various structures of Au@TiO2 hybrid metal - metal oxide nanofibers obtained by electrospinning and ther photochemical properties. We demonstrated that gold particle size and distribution can be modified according to the synthesis procedure, from small particles, embedded in the semiconductor matrix, to large particles strictly on the surface of the fibers. Photochemical properties have also been studied to demonstrate the properties enhancement due to noble particle inclusions. Two experimental approaches are presented, the photooxidation of an organic dye and the electrochemical properties of hybrid electrodes made with these nano-hybrid fibers.

Resume : The current trend in various energy applications, ranging from batteries to electrolizers, lays in the control of physicochemical and morphological properties of materials and their interfaces. Just to give some peculiar examples, due to their insulating nature (e.g. LiFePO4) or their dramatic volume changes (e.g. Si) many materials have been disregarded for decades in battery applications. Nowadays, through nanostructuring and surface coating, LiFePO4 and Si have become among the most promising materials for the next generation batteries that might power our cars. Nanostructuring gave also a new hope to technologies that were discarded such as Li-Air and Li-S. During this seminar, recent strategies for metal oxide synthesis and nanostructuring targeting energy and environmental applications will be discussed. Especially, we will focus on one-pot strategies for the fabrication of hybrid materials by non-hydrolytic sol-gel chemistry1,2 and the synthesis of heterostructured nanocrystals by galvanic replacement reaction.3 We will see that nowadays colloidal chemistry allows a control in terms of composition, crystalline structure, morphology and nanostructuration that would have been unimaginable just 10 years ago. References: [1] Room Temperature Hydrogen Sensing with Hetero-nanostructures Based on Reduced Graphene Oxide and Tin oxide P. A. Russo, N. Donato, S. G. Leonardi, S. Baek, D. E. Conte, G. Neri, N. Pinna Angew. Chem. Int. Ed. 2012, 51, 11053 [2] Efficient and tuneable photoluminescent boehmite hybrid nanoplates lacking metal activator centres for single-phase white-LEDs X. Bai, G. Caputo, Z. Hao, V. T. Freitas, J. Zhang, R. L. Longo, O. L. Malta, R. A. S. Ferreira, N. Pinna Nature Comm. 2014, 5, 5702 [3] Galvanic Replacement Reactions in Metal Oxide Nanocrystals M. H. Oh, T. Yu, S.-H. Yu, B. Lim, K.-T. Ko, M.-G. Willinger, D.-H. Seo, B. H. Kim, M. G. Cho, J.-H. Park, K. Kang, Y.-E. Sung, N. Pinna, T.Hyeon Science 2013, 340, 964

Resume : An overwhelming economic improvement for white LED and photovoltaic (PV) markets is based on the use of lanthanide-free phosphors that are supposed to convert UV light into visible one, thanks to down-conversion (DS) process. ZnO nanoparticles (NPs) have aroused an increasing interest since they possess a variety of intrinsic defects that provide light emission in the visible range without the introduction of any additional impurity. However, high photoluminescent quantum yield (PLQY), stable green/yellow emission and easy scale–up process are expected for industrial applications. Li-doping and polymer surface modifications of ZnO nanoparticles are mainly used in order to reach high PLQY (>30%) but PLQY decay over few days, uses of sophisticated polymers or multi-step reactions are the main issues for industrial implementation. In collaboration with the company Lotus Synthesis, we developed and patented an industry-capable (in terms of legislation concerns) and cost effective chemical solution process to get unique mesospheric self-assembly hybrid ZnO system with intense (PLQY = 40-75%) and stable visible emissions. We also demonstrate that the use of mixture of commercial polyacrylic acid-based polymers can provide large scale amounts of ZnO NPs clear aqueous colloidal suspensions that can be dried and dispersed again in water without compromising the functional performance (e.g. transparency and PLQY) of the final DS layer. We will then address the effects of the ZnO NPs surface functionalization - such as nature, molecular weight, concentration, ratio of the PAA-based polymers- on the stability of the nanocolloids and on the enhancement of their efficiency for LED and PV markets (or even cosmetics one).

Resume : It is well known that control of material structure and properties leads to a better understanding of its properties. The present work reports on sulfated zirconia nanoparticles and is focused on their catalytic properties for biofuel synthesis. Monodispersed zirconia-oxo-alkoxy (ZOA) nanoparticles of 3.6 nm size were prepared by sol-gel method in a rapid micro-mixing reactor with turbulent fluids flow at 20°C [1]. ZOA nanocoatings were deposited on silica gel and impregnated into ultraporous alumina matrixes and ZOA nanopowders were obtained after the nanoparticles precipitation. The ZOA nanopowders and nanocoatings underwent wet impregnation in 0.25 mol/l and 2.5.10-3 mol/l aqueous solution of sulfuric acid forming monodispersed nanoparticulate (MNP) and monodispersed nanocoating (MNC) catalysts. Additionally, polydispersed ZOA nanoparticles were elaborated by conventional sol-gel method and sulfated in the same conditions as monodispersed ZOA nanoparticles to obtain polydispersed nanoparticule (PNP) catalyst. All the prepared materials were subsequently drying at 80°C and calcinated at temperatures between 500 and 1300°C. The X-ray analysis showed that the crystalline structure depends on the nanoparticles agglomeration and the tetragonal phase appears to be stable in the isolated nanoparticles below 1100°C while monoclinic phase appears at much lower temperatures in nanopowders. As a result, MNP, PNP and MNC catalysts were obtained. The catalytic activity of the prepared materials was studied using esterification of palmitic acid in methanol solvent. We show that the mondispersity of ZOA nanoparticles is favourable for the reaction enhancement. In particular, the specific reaction rate ks (min-1.cm-2) of MNP catalyst is higher compared to PNP one. Moreover, the MNC catalyst shows the specific reaction rate km (min-1.g-1) more than 140 times higher compared to PNP. [1] : Nucleation and growth kinetics of zirconium-oxoalkoxy nanoparticles, Sana Labidi, Zixian Jia, Mounir Ben Amar, Khay Chhor and Andrei Kanaev, Phys. Chem. Chem. Phys., 17 (2015) 2651.

Resume : Hybrid nanocomposites (HCs) based on conjugated polymers and colloidal inorganic semiconductor nanocrystals are among the most promising materials for solution-processed photovoltaic devices. Despite the recent developments and the potential advantages, the highest photovoltaic performances reached with such HCs still lag behind those obtained with their organic or inorganic counterparts, due to the chemical and photophysical complexity of the HC systems. Therefore, the comprehension of the operating principles of solar cells based on HCs represents a crucial step towards the realization of high performance photovoltaic devices. In the present work, we investigate the effect of conjugated polymers on hybrid solar cell performances by selectively changing the organic component of the HCs but keeping the same inorganic material, which consist of lead sulfide quantum dots (PbS QDs). Surprisingly, we find that larger photocurrent densities are achieved by using wide-bandgap polymers. A combination of spectroscopic and electro-optical measurements suggest that wide-bandgap polymers promote efficient charge/exciton transfer processes and hinder the population of midgap states on PbS QDs. Our findings underline that in hybrid systems the polymer plays a key role in all the processes involved in the generation of the photocurrent ranging from the light absorption to the activation/deactivation of charge transfer/loss pathways.

Resume : In developing new nanoscale semiconductors for light-driven photocatalytic applications, it is important to choose a semiconducting material that is safe for use in real-world settings and has a high absorption coefficient in the visible spectral range. Among the most promising candidates are the multinary chalcogenide semiconductors, which include the ternary I-III-VI2 (where I = Cu, Ag; III = Ga, In; VI = S, Se) semiconductor family. These inorganic compounds consist of environmentally benign elemental components, exhibit excellent light-harvesting properties, and possess band gap energies that are well-suited for visible photon absorption. Moreover, the band structures of these materials can be conveniently modified through alloying to improve their photocatalytic efficiency. Through a simple non-injection-based synthetic approach, we were able to prepare colloidal nanostructures of the ternary sulfide semiconductors: AgGaS2, CuGaS2 and CuInS2. Our investigation of their photocatalytic properties revealed that colloidal AgGaS2 and CuGaS2 nanostructures display great promise in visible-light-induced degradation of Rhodamine B, a non-biodegradable industrial dye pollutant. Meanwhile, the nanostructures formed by alloying CuInS2 with ZnS (i.e., alloyed ZnS-CuInS2 semiconductor) were found to exhibit remarkable photocatalytic behavior for hydrogen generation from water. The photocatalytic performance of the alloyed ZnS-CuInS2 semiconductor nanostructures were further enhanced through creation of hybrid nanoscale architectures (i.e., hybrid semiconductor-metal system). Undoubtedly, the use of these multinary sulfide semiconductor nanostructures in light-induced photocatalysis holds immense potential in providing possible solutions to a range of environmental and energy-related concerns. In addition, their low toxicity makes them suitable alternatives to the technologically useful yet toxic cadmium-containing semiconductor nanostructures.

Resume : The kesterite material Cu2ZnSn(SxSe1-x)4 (CZTS) is very promising as future thin film solar cell absorber. The material is non-toxic, the elements abundant, and it has a high absorption coefficient. Solution processing allows for comparatively fast and inexpensive fabrication while maintaining a high power conversion efficiency, which makes CZTS a potential candidate also for large-scale applications. For pure-sulfide kesterite phase CZTS nanoparticles (NPs), the highest photovoltaic efficiency was achieved for the largest CZTS NP size (Mkawi et al. Chem. Phys. Lett. 2014 (608) 393). It is well-known that time, temperature and precursor reactivity play a role in NP growth, and preparation of CZTS with a mean particle size between 10-20 nm is typically reported. Higher CZTS particle sizes are difficult to prepare, and new methods are therefore needed. In our work, we study the growth of these chalcogenide NPs – both ligand-coated and ligand-free. The particles are synthesized by the hot-injection method, and bright and dark field transmission electron microscopy allows us to image the NPs and determine their size-distribution. We have shown that controlling the monomer concentration can lead to ligand-coated CZTSe NPs of up to 500 nm in diameter (Engberg et al. RSC Adv. 2015 (5) 96593). In addition, we have, to the best of our knowledge, synthesized the largest ligand-free pure-sulfide phase CZTS NPs with an average diameter of 23 nm ± 11 nm.

Resume : Branched palladium nanoparticles are capturing tremendous research interest as a third plasmonic material and non-palatinum based catalyst in fuel cell applications. However, they face with the challenges of high cost, low catalyst efficiency, and the difficulty in morphology controlled synthesis. Here, highly branched trimetallic PdAgCu nanoparticle is facilely synthesized at room temperature and in aqueous medium based on the galvanic replacement reaction between pre-synthesized silver nanoparticles and palladium ions. We found that the introduction of reducing agent and copper ions trigger the anisotropic growth of high density of small tips on the surface of nanoparticles through kinetically controlling the reaction rate and defect induced growth mechanism. The method allows facilely manipulating size, shape, and optical properties of branched PdAgCu nanoparticles toward the near infrared region by adjusting the experimental conditions such as Pd/Cu molar ratios, seed amount, and halide content. The particle exhibits a high localized surface plasmon resonance sensitivity toward the refractive index change and electrocatalyst activity of formic acid oxidation reaction in alkaline medium, depending on the particle morphology and composition. This result indicates the high potential of branched trimetallic PdAgCu nanoparticles for combined plasmonic and electrocatalytic applications.

Resume : We present the synthetic approaches for triangular Ag-Pd alloy nanoprisms and nanoframes by using silver nanoprisms as sacrificial templates. The galvanic replacement between Ag nanoprism and H2PdCl4 along with co-reduction of Ag /Pd2 is responsible for the formation of final triangular Ag-Pd alloy nanostructures. By adjusting the concentration of H2PdCl4, we could tailor the morphologies of Ag-Pd alloy structures from nanoprisms to nanoframes with tunable thickness. The obtained Ag-Pd alloy nanoprisms exhibited superior electrocatalytic activity for oxygen reduction reaction. Such a high catalytic activity is attributed to not only the alloyed Ag-Pd composition but also the dominant {111} facets of the triangular Ag-Pd nanoprisms. Further, we also demonstrate that the triangular Ag-Pd nanoframes exhibit excellent electrocatalytic activity for methanol oxidation reaction owing the hollow-framed structures with ultrathin Ag-Pd ridges. References: L. Xu and C. Xue* et al., Nanoscale, 2014, 6, 11738-11743; L. Xu and C. Xue* et al., Chem. Eur. J. 2015, 21, 8691-8695.

Resume : The nanochemistry approach has lately attracted lots of interest due to its capability to synthesize nano-objects (NO) with tuneable sizes and shapes. Pt stars and dendrites could be obtained after reduction of chloride salts in presence of oleylamine (OY) under H2 atmosphere and mild temperature. The control of experimental parameters such as Pt concentration, reaction temperature, and dihydrogen pressure, leads to fine-tuning of the kinetics of the reaction and of the nature of seeds formed during the nucleation step. A slow reaction leads to twinned seeds, which evolve into planar tripods (threefold stars) and fivefold stars, while fast reaction leads to cubic seeds and thus to a dendritic growth. High Resolution TEM revealed that these NO were singlecrystalline, exhibiting well defined crystallographic faces of the fcc structure while Electron tomography highlighted their complex 3D morphologies. Combining these leads to quantitative analysis, such as specific surface area, crystallographic preferential orientation and strain distribution, the determination of which being important for further catalysis application. 3-fold stars being of particular interest for logic-gate design, nanotechnology process based on E-Beam lithography is currently optimized to address individual Pt stars. Electron beam deflection from the central branch towards the second or third branch thanks to the application of an external stimulus is expected.

Resume : Atomically flat semiconductor nanoplatelets have superior optical properties compared to zero-dimensional nanocrystals. The absence of inhomogeneous spectral broadening and high photoluminescence efficiency make them very attractive for optoelectronic applications. While the underlying crystal structures provide no explanation for this highly anisotropic growth, existing models relate the formation of nanoplatelets to layered precursor templates or to oriented-attachment of magic-sized nanoclusters. Here we demonstrate the synthesis of zincblende CdSe nanoplatelets from isotropic melts of pure cadmium carboxylates and Se/S in absence of any solvents or additional surfactants, which rules out nanoplatelets formation via templated growth. Furthermore, we obtained alloyed CdSexSy nanoplatelets from mixtures of Se and S rather than binary populations of CdSe and CdS, which speaks against the assembly of preformed magic-sized nanoclusters. We propose instead a simple model that relates the barrier for growth on a crystal surface to its lateral shape. For very narrow surfaces it predicts lowered activation barriers and therefore allows growth at lowered temperatures, which inevitably leads to the formation of nanoplatelets. As the model predicts and our experiments confirm, thicker platelets require higher temperatures and take longer times to grow, but are more stable.

Resume : Nanoparticle filled immiscible polymer blend system has attracted great interest over the recent years due to its potential to combine the attributes of different homopolymer into one composite material, enhanced interfacial area as well as providing various optical enhancement by nanoparticles. With this work, we investigate the influence of fullerene nanoparticles on phase segregated morphology of a spin casted immiscible polymer blend on a flat substrate. For this fundamental study, poly(styrene) (PS) - poly(methylmethaacrylate) (PMMA) were chosen as immiscible polymers. Ascast morphological study of unfilled and nanoparticle filled PS – PMMA blend thin film revealed that on increasing the concentration of fullerene, area fraction of the phase segregated domains significantly increased. Due to presence of coexisting phases and additional polymer – polymer interfaces, migration of nanoparticles occurred which is primarily dependent upon the interfacial and substrate surface energy. Consequently, this led to an enhancement in polymer – polymer interfacial area. Additionally, multiple parameters such as substrate surface energy, molecular weight of the polymers were varied to explain the role of interfacial and substrate surface energy on the separation of fullerene nanoparticles. This fundamental understanding of morphology control via tuning the concentration of nanoparticles in polymer blend thin film can be extended to be used as possible route to enhance the efficiency of bulk heterojunction solar cell which consists of blends of functional polymers.

Resume : our hybrid B3PW calculations show that the F-center diffusion barrier is equal to 1.84, 1.67 and 1.83 eV in SrF2, CaF2 and BaF2 crystals [1-3]. During the F center diffusion, the trapped electron is more delocalized than in the regular F center case, and the gap between the defect level and CB in the alpha spin state decreases. The F center in CaF2, BaF2 and SrF2 is strongly localized inside vacancy, it contrasts with F centers in ABO3 perovskites, for example KNbO3, where two F center electrons are considerably delocalized. The calculation of total energies of different nano-surface H center configurations in BaF2 implies that H centers have a trend to locate near the surface. The energy difference between H centers with different orientations show that the H centers oriented in the [111] direction in SrF2, CaF2 and BaF2 crystals are the most stable configuration. References: 1. H. Shi, L. Chang, R. Jia and R. I. Eglitis, Comput. Mater. Sci. 79, 527 (2013). 2. H. Shi, L. Chang, R. Jia and R. I. Eglitis, J. Phys. Chem. C 116, 4832 (2012). 3. H. Shi, R. Jia and R. I. Eglitis, Solid State Ionics 187, 1 (2011).

Resume : ZnS is a promising material that is capable to combine luminescence properties with good thermal stability and low toxicity. These characteristics makes zinc sulfide one of the most promising material for the development of new quantum dots for bioimaging applications. However, the material must be functionalized not only to be stable and dispersible in physiological conditions, but also for selectively binding the desired targets. To obtain valuable information for the design of effective functionalization strategies, we undertook a comprehensive study based on a tight synergy between spectroscopic investigations and theoretical modelling to study the surface of ZnS nanostructures. ZnS nanostructures were obtained employing a simple, green and highly reproducible hydrothermal method. XRD analysis evidenced the obtainment of crystalline pure sphalerite-phase, with an average crystallite size of 20 nm, whereas XPS and SAED ruled out the presence of zinc oxide traces on the surface. FTIR and Raman spectroscopy pointed out however the presence of adsorbed water and of sulfates, though these latter were not detected by XPS. The surface properties were theoretically investigated using the DFT package Quantum ESPRESSO. We focused on the (110) surface, and considered the interaction with a series of molecular probes, carbon monoxide and dioxide, methanol, and pyridine. The theoretical results were compared with the experimental DRIFT results and with previous DFT calculations.

Resume : The new generation of aberration corrected scanning transmission electron microscope (STEM) instruments optimized for high spatial resolution energy dispersive x-ray (EDX) spectroscopy provide exciting opportunities for elemental analysis of nanoscale objects. Here I will discuss recent example applications where these new analytical capabilities have provided new insights to explain the properties and hence speed up nanomaterial development. It is well known that the properties of nanoparticles depend critically on their structure, morphology and the compositional distribution. Elementally sensitive STEM EDX electron tomography provides a route to understanding the full 3D chemistry and morphology of individual particles, such that structure-property relationships can be established. I will demonstrate results showing the effect of different elemental segregation on catalytic performance as well as discussing the current limitations of this technique [Slater et al, Nano Letters 2014; Slater et al, Ultramicroscopy 2015, Slater et al, Microscopy and Microanalysis 2015]. Recent work demonstrating the application of high spatial resolution STEM EDX spectrum imaging during in-situ gas and liquid phase experiments to track changes in particle morphology as a function of applied stimuli and environmental conditions will also be discussed [Lewis et al, Chemical Communications 2014, Lewis et al Nanoscale, 2014].

Resume : Gold nanoparticles (NPs) have been widely used in sensor and biomedical application due to their unique optical, electrical, and biocompatible properties. These properties mainly related to the shape of Au nanoparticles. According to previous study, the shape of Au NPs would be significantly affected by synthesis method. However, the lack of information that how nanoparticles growing remains unresolved, which should be optimized for studying reactions kinetics. In this work, we prepared Au NPs by reducing HAuCl4 with citrate acid. The solution was sealed in liquid cell and then observed the dynamic growth process of Au NPs via in-situ transmission electron microscopy (TEM). We found that Au NPs nucleated at first and then these nucleuses grew into different shapes such as triangle, parallelogram, hexagon, and sphere. Finally, the Au NPs aggregated, changed their shape, and even twinning. Additionally, we also found the nucleation and growth of sodium chloride which was the byproduct during synthesizing. The in-situ TEM study provides the knowledge of nucleation and growth process, which unravels the thermodynamic and kinetic of Au NPs and sheds light on the design of functional nanostructure.

Resume : Gold nanoparticles (GNPs) have proven to be a versatile platform for a large scope of applications, with potential use in numerous areas including: catalysis, optics and biology. Since the Turkevich study of 1951, the citrate capped GNPs are commonly used for a post functionalization by ligand exchange. Several molecules have been tested to replace citrate as reducing agent and stabilizer for one pot synthesis: carboxylic acids, amines, polysaccharides, thiophene derivatives and polymers. Our project aims to develop new synthetic pathways for the direct synthesis of GNPs allowing easy access to functionalization. This is achieved by using synthesized (1-hydroxy-1-phosphonopent-4-enyl)phosphonic acid, presenting advantages of the well known bisphosphonate coating applied to colloidal gold instead of metal oxides. This molecule is bifunctional: Phosphonate group is able to both reduce gold(III) chloride and to coat the surface of the obtained GNPs. The terminal alkene group will remain inert during the NPs synthesis and will allow further chemoselective GNPs functionalization. We have demonstrated the overall reaction mechanism and the interaction between our bisphosphonate compound and the gold surface by classical analytical chemistry techniques. Optimization of reaction pH has been assessed to yield homogeneous nanospheres of size ranging from 13-20 nm. We have also developed a bioorthogonal approach for the surface functionalization based on an inverse electron demand Diels–Alder cycloaddition reaction with tetrazine that does not require any catalysis by toxic metals. Tetrazines compound have a high potential for biological activity, possessing a wide range of antiviral and antitumor properties. First the click reaction was modelized with the bisphosphonic ligand (1-hydroxy-1-phosphonopent-4-enyl)phosphonic acid in aqueous media. Then the cycloaddition of the tetrazine was carried out on terminal alkene group of our nanoplatform as a proof of concept.

Resume : Colloidal nanomaterials such as semiconductor quantum dots offer unique optical properties, including tunable emission and high photoluminescent quantum yield. However, surface defects and poor surface passivation lead to non-radiative recombination and the on-off blinking of their emission. Core-shell structures, such as CdSe/CdS quantum dots, have therefore attracted a lot of attention, and especially “giant” ones lately, as a better confinement of the excited charge carriers with appropriate larger band gap materials gives higher photoluminescent quantum yield and nonblinking nano-emitters. In this contribution, we present our progress on the “flash” synthesis, initially developed for the fast growth of such giant shells, and highlight its great versatility for the preparation of multi-shell quantum dots and nanorods. Firstly, we report the improved quality and purity of the wurtzite CdSe nanocrystal cores which is the indispensable first step in development of high quality multi-shell nanocrystals. Secondly, we report the advances made on the growth of multi-shells, including CdS, ZnS and even alloyed CdZnS layers, both on isotropic (quantum dots) and anisotropic (nanorods) heterostructures. Thanks to their excellent optical characteristics, these ”flash” grown colloidal nanomaterials have already been employed in a broad range of applications, from lighting and display to lasing and bioimaging applications, which will be showcased in this contribution.

Resume : Laser ablation in liquids can produce biocompatible nanoparticles for medical applications. A complex series of steps extended over many orders of magnitude in time involves e.g. ablation, plasma expansion inside a bubble, the penetration of condensed nano-sized phases into the liquid, but also secondary beam-colloid interaction. A quantification and modelling of the multi-pulse incubation of laser ablation exist only for air contact [1], and therefore was undertaken in this study in various fluids. The role of oxidic and carbonaceous conversion layers, plasma shielding, and the action of cavitation processes is considered. Recent investigations of the laser generation of pure aqueous and non-aqueous colloidal fluids are presented. The influence of wavelength and pulse repetition rate on colloidal core-shell properties characterized by TEM, EDX, XRD, and selected area electron diffraction are discussed. [1] A. Naghilou, O. Armbruster, M. Kitzler, and W. Kautek, J. Phys. Chem. C 119, 22992 (2015).

Resume : A general route to produce rare earth(III) fluoride nanoparticles in water media, using co-precipitation methodology has been applied to different metals such as Y, Gd, La and Ce. Due to their potential application in biological fields, citrate was used as a biocompatible capping ligand, stabilizing the obtained nanoparticles in water. In order to characterize chemical and physical features, final size, shape, composition and crystal structure have been studied. According to the obtained experimental results, cubic phase (Y and Gd) gave rise to both supraparticles and nanoparticles depending on the temperature. On the other hand, hexagonal phase (La and Ce) formed only hexagonal nanoplatelets of 7-10 nm size. Experiments were focused on YF3 nanoparticles, where the studies performed at different temperatures show us the possibility of controlling the formation of both nanoparticles and supraparticles hence providing a thermodynamic control of the process. This mechanism has been studied by dynamic simulation of systems at experimental condition in order to understand the mechanism formation of rare earth(III) fluoride nanoparticles in water with citrate stabilization. Obtained knowledge will allow to synthesise high-quality and tuneable nanoparticles for materials and biological fields. The economical support received from EU-FP7 NMP-LA-2012-280432 EUROTAPES project is acknowledged. J.M.E. acknowledges Departament de Química from UAB for the financial support of PIF scholarship.

Resume : The paradigms of green and sustainable chemistry are currently catalysing sharply growing interest in all fields of chemistry1. In particular inorganic chemistry represents an exciting playground for the design and optimization of green chemistry-inspired routes. The implementation of green chemistry paradigms to inorganic chemistry represents one of most bewitching developments. This should be achieved by applying sustainable and green procedures, involving the lowest amount of toxic chemical and/or solvents, safe procedures which are easy to implement and to scale-up and, last but not least, low temperature. In this framework, in these last years, in our group we have developed different low temperature (T<150°C) wet chemistry routes to prepare different inorganic functional nanomaterials in crystalline form, ranging from ferrites and manganites, to pure and doped metal oxides, sulphides, and halogenides, to metal/metal oxide nanocomposites. The adopted wet chemistry routes ranged from 1) miniemulsions to 2) coprecipitation combined with hydrothermal route to 3) classical colloidal routes. This contribution provides an overview of the pros and cons of the proposed routes for the obtainment of targeted inorganic colloids, also outlining as the role of a combination of analytical tools can unravel the complex interplay among experimental parameters and microstructure of the materials. 1- S. Diodati, P. Dolcet, M. Casarin and S. Gross, Chem. Rev., 2015, 115, 11449–11502

Resume : The mechanisms leading to the adhesion of particles of nano sizes in the depletion layer under what would be non-equilibrium conditions, due to the conflicting influence of the mechanical diffusive collisions and the attractive Hamaker forces at the boundaries, are of major interest. We have hence investigated in this paper a theoretical model to calculate the restitution coefficient from basic physical principles. The objective is to quantify the energy balance during the process of a diffusive collision of a nano particle (under the influence of the repulsive forces due to the Pauli principle via mechanical bounce on one hand, and the attractive Hamaker forces acting on the nano particle on the other. This is done by developing a model, to account for the energy losses during collisions, and for the energy gains due to the Hamaker interactions. Adhesion becomes an outcome if the energy balance permits this. Our theoretical model is developed by proposing a special analytic approach based on the Hamaker potential. We derive from the theoretical analysis a characteristic nonlinear equation for the restitution coefficient, and analyze its properties which determine under given physical conditions the outcome for adhesion or not.

Resume : Quantum dots (QDs) are successfully integrated in a wide range of applications such as optoelectronic devices or biological imaging thanks to their unique optical and electronic properties.(1,2) Up to now, II-VI cadmium-based nanocrystals have been the most studied materials. However because of their high toxicity, their commercial use is strongly slowed down. An excellent non-toxic alternative to cadmium-based materials for fluorescence applications are InP nanocrystals. Indeed, the bulk band-gap of InP (1.344 eV) allows to tune their emission across the whole visible spectral range up to the near-infrared. Despite their important attractiveness, the synthesis of high-quality InP nanocrystals with a good monodispersity is still very challenging.(3,4) So far, tris(trimethylsilyl)phosphine (P(TMS)3) is the most commonly used phosphorus precursor but its high reactivity strongly limits a good control of the syntheses. Moreover P(TMS)3 is pyrophoric and expensive. Since 2013, a new precursor is using instead of P(TMS)3, Tris(dimethylamino)phosphine which is cheaper and less toxic.(5,6) In this work, we present a comprehensive study of the formation of InP nanocrystals synthesized with this low-cost and easy-to-handle synthesis. In order to synthesize high quality InP nanocrystals, we proposed a combined molecular and materials approach with the group of Mézailles. Thanks to these analyses, we propose a complex mechanism involved in the formation of InP nanocrystals. In particular, we performed kinetic studies in order to understand the nucleation/growth process by varying the temperature, the nature of the ligands or the ratio between indium and phosphorus precursors. For example, we show that high temperature reaction yield nanocrystals with a size reaching 5 nm. All nanocrystals were well characterized by absorption spectroscopy, TEM and XRD measurements. This study is a first step toward the formation of high quality luminescent core/shell nanocrystal with excellent optical properties. 1. Murray, C.; Norris, D.; Bawendi, M. J. Am. Chem. Soc. 1993, 115, 8706–8715. 2. Xie, R.; Battaglia, D.; Peng, X. J. Am. Chem. Soc. 2007, 129, 15432–3. 3. Buhro, W. E. Polyhedron 1994, 13, 1131–1148. 4. Gary, D. C.; Cossairt, B. M. Chem. Mater. 2013, 25, 2463–2469. 5. Song, W.-S.; Lee, H.-S.; Lee, J. C.; Jang, D. S.; Choi, Y.; Choi, M.; Yang, H. J. Nanoparticle Res. 2013, 15, 1750. 6. Tessier, M. D.; Dupont, D.; Nolf, K. De; Roo, J. De; Hens, Z. Chem. Mater. 2015, 27, 4893–4898.

Resume : In the present study, we use metastable undercooled core-shell (metal/oxide shell-acetate) particles that enables heat-free joining and manufacturing at ambient conditions. First, undercooled metals are encapsulated by a thin complex oxide shell on which a stabilizing organic ligand is chelated. Heat-free soldering and fabrication involves fracturing of outer layers through mechanical stressing or shearing that initiates fluid flow with concomitant deformation, alloying, shaping and solidification. Such a simple and low cost technique offers various applications including joining at nano- and micro- scale, metal repair, potential catalytic surfaces, coatings, and manufacturing of various shape of particles and sheets. This presentation focuses on fabrication of metastable undercooled colloids from metal melt and demonstration of examples from its use in joining and manufacturing. Control over the mechanical stress, leads to metal products with shapes ranging from spheres to half spheres, disks or sheets with varying size and thicknesses, thus offers a new approach to manufacturing of metal devices at ambient conditions without the need for skilled manpower, high tech-instrumentation, or complicated sample preparation procedures.

Resume : The nonstoichiometry of colloidal nanocrystals such as CdSe and PbS is typically explained by attributing a formal charge, equal to its most common oxidation state, to each constituent atom and capping ligand. A neutral nanocrystal is obtained by the zero sum of these formal charges. Despite its simplicity this “oxidation-number sum rule” has little theoretical support within current literature. We introduce the ligand addition energy, defined as the energy gained or expended upon the transfer of one ligand from a reservoir to a metal-rich surface. By calculating successive addition energies, using ab initio methods, the thermodynamically stable surface composition is determined as the last exothermic addition step. This has been calculated for the combination of CdSe, ZnSe and InP surfaces with chalcogen, halogen and hydrochalcogen ligands. In many cases, the oxidation-number sum rule is valid, but exceptions occur for each studied material, most notably when the surface is exposed to small oxidative ligands. For InP these violations are more severe and extend to the entire chalcogen family. We also find that electronegativity rather than chemical hardness is a reasonable predictor for ligand addition energies; the most exothermic addition energies being obtained for the most electronegative ligands. We propose the ligand addition energy to be a valuable quantity for future computational studies on the structure, stability and reactivity of nanocrystal surfaces.

Resume : Non-stoichiometric tungsten oxide nanocrystals represents an interesting candidate for manifesting localized surface plasmon resonance (LSPR) arising from its oxygen-deficient stoichiometry which implying an excess of free-charges (electrons) in the conduction band. Therefore, non-stoichiometric tungsten oxide (WO3-x) represents a self-doped n-type semiconductor and a case of interest for the wide variety of applications in which can be involved. Beside size and stoichiometry, the shape of nanocrystals has an influence as well on the optical response (LSPR). In analogy with metal nanoparticles, non-spherical plasmonic NCs are expected to show multiples resonances, depending on size and shape. We introduce a one-pot colloidal route to achieve size- and shape-tailored WO(3−δ) ultrathin 1D nanocrystals characterized by an unusual hemi-tubular shape, with a tunable aspect-ratio which manifest a correlated tunable LSPR in a wide range of IR region, from 1000 nm to 3000 nm. From the best of our knowledge, this represent the first example reported in literature of these low-symmetry colloidal nanocrystals obtained by a direct synthetic route. The formation mechanism of those hemitubular colloidal nanostructures is unconventional as well and summarized in a synergic effect between a non-hydrolytic reaction together with a stress releasing topochemical conversion of micrometers hybrid organic-inorganic intermediate in situ produced. Synthesis and optical characterization of WO(3−δ) nanocrystals will be discussed together with a structural and compositional characterization where a phase-structural variation can occur under an external stimulus. The experimental extinctions spectra supports the theoretical calculation performed within the frame of discrete dipole approximation.

Resume : The assembly of semiconducting and magnetic nanoobjects into ordered superstructures, e.g., mesocrystals,[1] is attractive from the scientific and technological viewpoints due to their symmetry and potential applications. Specifically, the synthesis and self-assembly of non-spherical nanoparticles has been identified as one of the major challenges, and opportunities, for tomorrow’s materials.[2] In previous work, we presented the rich phase diagram of large, well-ordered three-dimensional mesocrystals based on truncated iron oxide nanocubes (IONs) where we showed that extracting detailed information from small-angle x-ray scattering (SAXS) and electron microscopy measurements allows the reconstruction of the dominant phases.[3,4] The formation of this ordered arrays was dependent upon the monodispersity of the nanoparticle shape and size contigent upon the purity of the reagents.[5] In this talk I will present: (i) how monodisperse iron oxide nanocubes and nanospheres with average sizes between 5 and 27 nm can be synthesized by thermal decomposition and the synthesis conditions that generate nanocubes suitable for producing large ordered arrays, (ii) the time-dependent growth of ION mesocrystals on flat substrates studied by image analysis where it is found that the quasi 2D-growth of the individual mesocrystals can be approximated by single exponential functions whereas the total conversion rate adopts a sigmoidal character, similar to conversion curves for crystallizing polymers, and (iii) the self-assembly IONs followed by time-resolved SAXS experiments on levitating droplets where the acoustic levitator enabled substrate-free evaluation of reaction kinetics within a droplet and on the liquid-air interface. Several stages during droplet drying can be identified from transitions in the scattering behaviour and correlated with existing nucleation theories. [1] L. Bergström, E. V. Sturm (née Rosseeva), G. Salazar-Alvarez, H. Cölfen, E. V Sturm Née Rosseeva, G. Salazar-Alvarez, H. Cölfen, Acc. Chem. Res. 2015, 48, 1391. [2] S. C. Glotzer, M. J. Solomon, Nat. Mater. 2007, 6, 557. [3] S. Disch, E. Wetterskog, R. P. Hermann, G. Salazar-Alvarez, P. Busch, T. Brückel, L. Bergström, S. Kamali, Nano Lett. 2011, 11, 1651. [4] S. Disch, E. Wetterskog, R. P. Hermann, D. Korolkov, P. Busch, P. Boesecke, O. Lyon, U. Vainio, G. Salazar-Alvarez, L. Bergström, T. Brückel, Nanoscale 2013, 5, 3969. [5] E. Wetterskog, M. Agthe, A. Mayence, J. Grins, D. Wang, S. Rana, A. Ahniyaz, G. Salazar-Alvarez, L. Bergström, Sci. Technol. Adv. Mater. 2014, 15, 055010.

Resume : Soft magnetic nanoparticles (NPs) are promising candidates for a wide range of applications ranging from microelectronics to nanobiotechnology. Among them, FeCo alloy presents the highest saturation magnetization (Ms = 240 emu/g) combined with a low anisotropy constant (K = 1,5.104 J/m3). However, the chemical synthesis of FeCo NPs remains a challenge. Indeed, the difference of reactivity of the precursors used often leads to poorly crystallized and/or inhomogeneous FeCo NPs, resulting to low Ms. A detrimental to the particle size and shape annealing process is then required to achieve the desired bulk magnetic properties, . We report for the first time the synthesis of monodisperse and chemically homogeneous FeCo NPs, by the co-decomposition of an iron and a cobalt metalloid amide under mild conditions. By adjusting the synthesis parameters we can tune the size (2 to 90 nm), the shape and the composition of the NPs. The obtained NPs are well crystallized and exhibit magnetic properties close to the bulk ones. Under specific conditions, the chemically ordered B2 structure could be stabilized within 11 nm NPs as revealed by a precise structural study coupling zero field 59Co NMR and 57Fe Mossbauer spectroscopy. Such ordered structure is of particular interest for magnetically induced catalysis [1]. [1] A. Meffre et al. Nano Lett. 2015, 15 (5), 3241

Resume : Future advancements in the development of nanodevices are based on the ability to integrate materials in smaller devices with improved properties. The bottom-up approach represents a very attractive strategy to prepare rational nanostructures based on magnetic nanoparticles. Among variety of nanostructures, 1D-assemblies of nanoparticles are certainly one of the most promising to develop new advanced applications related to sensors and spintronics. Indeed, such a low dimensionality of assemblies is featured by high anisotropy which enhances significantly collective properties, and so sensitivity to external stimuli such as magnetic field. We report on a novel approach based on “click” chemistry to address precisely the assembly of iron oxide nanoparticles into chain-like structures. Randomly oriented nanoparticle chains could be obtained within 2D monolayers by tuning the balance between the kinetic of the “click” reaction and dipolar interactions between nanoparticles upon the assembly process.1 Further, “click” chemistry was performed under a magnetic field in order to control the formation of co-aligned single nanoparticle chains separated by regular distances.2 Such a high uniaxial anisotropy results in the strong enhancement of magnetic collective properties in comparison to 2D monolayers or isolated nanoparticles. Furthermore, the fine control on the chain structure allows evidencing a first order intra-chain dipolar interactions and a second order inter-chain magnetic coupling which cannot be discriminated in bundle chains of nanoparticle as usually reported in the literature. This work offers new opportunities to go further into the understanding of the collective properties of 1D assemblies of magnetic nanoparticles. References 1. Toulemon et al. Langmuir, under revision 2. Toulemon et al. Adv. Fucnt. Mater., accepted

Resume : Iron nanocubes (NCs) elaborated by organo-metallic chemistry consist in ideal systems due to their single crystal structure, tunable sizes and bulk magnetic parameters. In such nano-objects, micromagnetic simulations predict that the magnetic configuration changes from single-domain (i.e. flower) to vortex states as the cube size increases. By combining chemical synthesis, electron holography (EH) in a dedicated transmission electron microscope and micromagnetic simulations, here we focus on sufficiently small Fe NCs to reveal this single-domain/vortex transition. Iron nanoparticles are synthesized by decomposition of a precursor under hydrogen atmosphere at 150°C in the presence of long-chain amines and acids. By tuning the amine/acid ratio we control the size and shape of our particles, ranging from 1.3 to 90 nm and evolving from spherical to cubic. Thanks to controlled surface-state, all these particles exhibit bulk magnetization, even the smallest ones. The spin configuration phase diagram in size-controlled single Fe nanocubes is discussed. High sensitivity EH imaging explicitly reveals how three different spin configurations can be stabilized within a 3 nm window. Magnetic maps of easy-axis flower, hard (<111>) and easy-axis (<001>) vortices states are analyzed in isolated Fe NCs of roughly 25, 26 and 27 nm size respectively, and this in good accordance with dedicated calculations. It is the first time that a <001> flower state is observed in a so small magnetic element, and that a stable <111> vortex is measured. This gives a deeper understanding of the single-domain/vortex transition which is more complex than expected with the appearance of a <111> vortex intermediate state. Such measurements and simulations open the door to fine magnetic control of nano-objects which will find applications in fields as wild as spintronics devices, information storage or hyperthermia.

Resume : Controlling the amplitude, phase and frequency of the time dependent magnetization is important for spintronic devices like spin-torque oscillators,[1,2] as well as for medical applications such as cancer therapy.[3,4] One way towards this challenging goal is to tailor the anisotropy of nanostructured materials.[5,6] Here, it is shown that the competition between the shape and magneto-crystalline anisotropies of CoxFe3-xO4 crystalline nano-cubes leads to a phase opposition in the motion of precession induced by femtosecond laser pulses. It occurs for a particular angle of an external static magnetic field, which depends on the concentration x of cobalt, the laser intensity, or the degree of organization of the nano-cubes. We model these dynamical effects using the Landau-Lifshitz-Gilbert equation, taking into account simultaneously the time dependent spin and lattice temperatures, the temperature dependent anisotropy as well as the inter-nano-cube interactions.[7] 1. S. Mangin, et al., Nat. Mater. 5, 210 (2006). 2. D. Houssameddine, et al., Nat. Mater. 6, 447 (2007). 3. J. Dobson, Nat. Mater. 9, 95 (2010). 4. D.H. Kim, et al., Nat. Mater. 9, 165 (2010). 5. S.C. Glotzer, et al., Nat. Mater. 6, 557 (2007). 6. S. Disch, et al., Nano Lett. 11, 1651 (2011). 7. M. Vomir, et al., Submitted (2015).

Resume : Transport in network of nano-objects has been intensively studied for the past ten years but still raises many questions, especially since most of the systems have been studied at very low temperature. However, for any application and extensive study of the factors governing the transport, it is desirable to have an easily accessible and robust system working at room temperature. Here, we report a robust and air-stable hybrid nanomaterial, made of self-assembled ultra-small platinum nanoparticles (1.2 or 1.7 nm). Not only this system displays Coulomb blockade at room temperature, but it can be tuned at a very fine level by changing subtle details of the surface ligands stabilizing the particles: for example by increasing the length of an alkyl chain carbon per carbon, or changing one single substituent on an aryl group. This fine tuning gave us the opportunity to study the structural influence of the nanomaterials on charge transport at an unprecedented subtlety and thus to propose a specific mechanism of the crossing of the electrons through the molecules between two particles. This work is the cornerstone of promising perspectives such as the elaboration of functional materials where the charge of the nanoparticles is tuned by the nature of the ligands, electron per electron, with foreseen applications in electrochemistry, artificial photo-synthesis or molecular electronics.

Resume : We perform electrical transport studies on square PbSe superlattices that we gate using an ionic-liquid.-cite The devices are made from PbSe nanocrystals which are first let to self-assemble on a liquid surface in two dimensional perculative and honeycomb lattices. In the following oriented attachment process the nanocrystals atomically bind, keeping the PbSe atomic structure intact.-cite These single crystalline superstructures are predicted to show band-type transport affected by the superstructure geometry. Daric carriers are predicted in the honeycomb lattice. In this work we take the first steps in a detailed transport study of the superlattices. We contact the material with gold leads, shaping micron sized field effect devices using standard electron beam lithograpy. The liquid gate is contacted by a gold pad defined on-chip. We than cover the devices with an ionic-liquid (DEME-TFSI) or an polymer based electrolyte (PEG with LiClO4). A potential difference is applied between the gate pad and the device, inducing the formation of an electrical double layer on the substrate. This double layer acts as a very strong gate, inducing more than two electrons per nanocrystal. We find a field-effect electron mobility of 20 cm2/Vs; the hole mobility is a factor of ten lower. Future measurements are directed towards low-temperature studies and the incorporation of Hallbar configurations. This work is financed by FOM

Resume : Electrets have important technological application from established ones such as microphones or particulate filters to emerging ones as in powering energy harvesting devices. At smaller length scale, the control in the polarization and charge of the material can be useful for complex bottom-up synthesis, exploited in the self assembly growth of both bio and inorganic materials. Additionally a localized charge can improve the functionalities of nanostructured materials, providing further transduction schemes for MEMS and NEMS devices. However to guarantee the stability of the polarization in microsystems is challenging. Moreover, the fabrication process, modifying the natural neutral state of the material, may induce significant changes in the structural and mechanical properties. In this work, we study the behavior of SiO2 nano and microparticles when charged by injecting electrons by field emission scanning microscope at energy ranging between 3 and 10 keV. Charge stability in time was monitored and the effect of the electronic implantation on the microstructure and on the mechanical properties was evaluated by a joint microRaman and microBrillouin analysis. In particular, we study the correlation between the electron dose and the formation of silica defects, and with the modifications of the elastic constants of the charged material, evaluated by measuring by microBrillouin spectroscopy the acoustic vibrations of the single particle.

Resume : Self-assembled nanoparticle arrays (NPAs) represent a convenient platform for upscaling single molecular junctions to networks with different functionalities [1]. To investigate properties of few nanoparticles molecular devices, we propose to contact NPAs with graphene electrodes. The ultimate flatness of the graphene electrodes makes it possible to fabricate devices with various geometric shapes and without contact steps or inhomogeneities. Simultaneously, we can study the properties of graphene field-effect transistors (GFETs) where the NP array acts as a top-gate for the GFET. By applying different signals to the NP array using graphene contacts, we can control the electrostatic potential of the array and modulate the GFET properties to explore memory-type effects and conductance photoswitching [2,3] in these hybrid devices. [1] J. Liao et al., Ordered nanoparticle arrays interconnected by molecular linkers, Chem. Soc. Rev. 44, 999–1014 (2015), doi:10.1039/c4cs00225c. [2] S. J. van der Molen et al., Light-controlled conductance switching of ordered metal-molecule-metal devices, Nano Letters, 9, 76-80 (2009), doi:10.1021/nl802487j [3] Y. Viero et al., High Conductance Ratio in Molecular Optical Switching of Functionalized Nanoparticle Self-Assembled Nanodevices, The Journal of Physical Chemistry C, 119 (36), 21173–21183 (2015), doi:10.1021/acs.jpcc.5b05839.

Resume : Quantum dot (QD) superlattices, or QD solids, represent an important class of materials holding interesting promises for a variety of high-technological applications such as transistors, solar cells and photodetectors. A true QD solid is built up of separate QDs which are epitaxially connected to one another. Such a structure has a potentially high charge carrier mobility as there is a direct electronic coupling between the QDs. At the same time quantum confinement is preserved, meaning that its optical properties are easily adjusted. Many efforts have been put into making these structures, but so far no robust methods to make long-range QD solids have been reported. As the pristine ligand shell has to be partially removed, the problem of superlattice formation largely boils down to a fine control over the surface chemistry. As such, recent advances in QD ligand chemistry provide new opportunities in the synthesis of these structures. In our study we apply an L-type induced Z-type ligand removal to adjust the QD ligand density, thereby ceasing control over the superlattice formation. We show that the rate at which the superlattice is formed and the initial QD ligand density are controlling factors in obtaining long-range QD superlattices with a high degree of epitaxial connections. Our findings present an important step forwards in the synthesis of QD solids, providing researchers with a platform to further investigate the physics and chemistry of these nanostructures.

Resume : The commercially most viable approach to white light-emitting diodes (LED) is based on the combination of a blue LED with one or more luminescent materials that convert part of the blue light to green and red to make an overall white color spectrum. Recently, we have published an economical synthesis of size-tunable core/shell InP Quantum Dots (QDs) that exhibit excellent emission properties and are well-suited phosphors for white LEDs. There successful application, however, will critically depend on ‘shell engineering’. For example, a ZnS shell coating leads to an emission linewidth broader than for a ZnSe shell coating. On the other hand, better quantum yields are obtained with ZnS shell coating (up to 80%). Here, we present synthesis protocols that lead to different types of II-VI shell materials, priming InP-based QDs for remote phosphor applications. QD-based LEDs also require a long-term photo-stability, a property depending critically on the QD surface termination. We found that the photo-stability of the InP QDs can be considerably improved by changing the ligands capping InP-based QDs. We finally embedded such optimized InP QDs into solid polymer-based layers and analyzed the layers emission efficiencies. We demonstrate that the efficiency of these remote phosphors layers can be markedly increased by incorporating all adaptations described above. These results improve the prospects of using InP-based QDs as a remote phosphor in, for example, display applications.