Erwan Rauwel

Vanadium Oxide Sensing Layer Grown on Carbon Nanotubes by a New Atomic Layer Deposition Process

A new atomic layer deposition (ALD) process was applied for the homogeneous coating of carbon nanotubes with vanadium oxide. It permits the coating of the inner and outer surface with a highly conformal film of controllable thickness and, hence, the production of high surface area hybrid materials at a so far unprecedented quality. The ALD-coated tubes are used as active component in gas-sensing devices. They show electric responses that are directly related to the peculiar structure, i.e., the p-n heterojunction formed between the support and the film.

A Review on the Green Synthesis of Silver Nanoparticles and Their Morphologies Studied via TEM

Silver has been recognized as a nontoxic, safe inorganic antibacterial/antifungal agent used for centuries. Silver demonstrates a very high potential in a wide range of biological applications, more particularly in the form of nanoparticles. Environmentally friendly synthesis methods are becoming more and more popular in chemistry and chemical technologies and the need for ecological methods of synthesis is increasing; the aim is to reduce polluting reaction by-products. Another important advantage of green synthesis methods lies in its cost-effectiveness and in the abundance of raw materials. During the last five years, many efforts were put into developing new greener and cheaper methods for the synthesis of nanoparticles. The cost decrease and less harmful synthesis methods have been the motivation in comparison to other synthesis techniques where harmful reductive organic species produce hazardous by-products. This environment-friendly aspect has now become a major social issue and is instrumental in combatting environmental pollution through reduction or elimination of hazardous materials. This review describes a brief overview of the research on green synthesis of silver metal nanoparticles and the influence of the method on their size and morphology.

Non-aqueous sol–gel routes applied to atomic layer deposition of oxides

Usually traditional Atomic Layer Deposition (ALD) processes use aqueous sol-gel routes for oxide thin film growth. Typically, transition metal precursors (halides, alkoxide or amide) are reacted with an oxidizing agent (e.g. water, radical oxygen or ozone). More specifically the reaction of such metal complexes with water leads, upon hydrolysis and condensation, to the formation of a metal oxide thin film. The films grown by this traditional way are amorphous; hence a post-synthetic heat treatment is generally required to induce the desired crystallization in order to improve the quality of the film. They also contain large amounts of undesired impurities ranging from unreacted carbon species to halides. Furthermore, as water is a strong oxidizing agent at the typical ALD range of deposition temperatures (200-400 oC) some substrates (e.g. Silicon) are rapidly oxidized. In fact, metal oxide thin films grown on silicon always present a non-negligibly thick oxidized interface layer (silica or silicates) in between the silicon and the deposited metal oxide which usually hinders microelectronic applications. Many solutions are presently proposed to overcome these problems, like using new metal organic precursors [1,2] or by the utilization of plasma during the deposition process. Recently various non-aqueous sol-gel routes were proposed for the formation of metal oxide nanoparticles [3,4] and hybrid materials [5] in solution. They proved to be powerful alternatives, especially because they have the capacity to overcome the main drawbacks of traditional sol-gel routes. However, only a few non-aqueous routes were applied to ALD. The most successful were the ones reported on the reaction of metal alkoxides with metal halides [6] and the formation of silica and silicates [7, 8]. In this work we present a novel non-aqueous approach applied to ALD [9] leading to the formation of high quality metal oxide thin films. Moreover, this approach demonstrates a real ability to reduce the oxide interlayer in the case of deposition on silicon substrates. This process enables to grow metal oxides coating at temperatures as low as 50 °C on various supports including monocrystalline substrates, carbon nanotubes, organic fibers, etc. The characterization of these films will be presented together with their possible formation mechanism. References:

Growth of La1- xCaxMnO3 thin films by atomic layer deposition

Thin films of calcium substituted lanthanum manganite (La1−xCaxMnO3) have been synthesised by the ALD (atomic layer deposition) technique using Mn(thd)3 (Hthd = 2,2,6,6-tetramethylhepta-3,5-dione), La(thd)3, Ca(thd)2, and ozone as precursors. The effect of each of these precursors on the product stoichiometry has been investigated, and ALD type growth was achieved in the temperature range 200–330 °C. A concept on precursor surface area coverage has been applied in order to describe the difference between pulsed and obtained cation stoichiometry. The La1−xCaxMnO3 films are low in carbonate impurities although Ca(thd)2 and ozone alone as precursors would give CaCO3. Mn(thd)3 can be used as a precursor for ALD growth of these oxides for temperatures up to 330 °C when codeposited along with Ca and La, whereas 240 °C is the upper usable temperature for Mn(thd)3 when Mn is deposited alone. Films have been deposited on substrates of (amorphous) soda-lime glass and single crystals of Si(100), MgO(100), SrTiO3(100), and LaAlO3(100). Growth with a cube-on-cube epitaxy has been achieved for SrTiO3(100) and LaAlO3(100) substrates. Magnetoresistive properties are recorded for films with a composition close to La0.7Ca0.3MnO3.

One step synthesis of pure cubic and monoclinic HfO2 nanoparticles: Correlating the structure to the electronic properties of the two polymorphs

Hafnium dioxide is a wide band-gap, high-κ material, and Hafnium based compounds have already been integrated into micro-electronic devices. The pure cubic HfO2 phase is promising as it presents a higher permittivity (κ > 25), but needs to be stabilized by addition of divalent or trivalent dopants, which in turn modify the electronic properties of HfO2. Here, we employ a one-pot synthesis approach to produce undoped cubic and monoclinic HfO2 nanoparticles by choice of solvent alone. The average size of these nanoparticles from transmission electron microscopy studies was estimated to be around 2.6 nm. We present a study of the morphology and microstructure and also demonstrate the presence of a strong visible photoluminescence linked to the nanosize of the particles. Furthermore, the synthesis in equivalent conditions of these two phases of HfO2 provides means for direct comparison of the chemical composition and electronic structures of the two polymorphs. This has therefore allowed us to experimentally ...

Photoluminescent cubic and monoclinic HfO2 nanoparticles: effects of temperature and ambient

We report on the one-pot synthesis and characterization of pure cubic and monoclinic phase HfO2 nanoparticles. An average particles size of 2.6 nm was estimated from transmission electron microscopy studies. The equivalent synthesis conditions of the two polymorphs provided means for direct comparison of their optical absorption and emission properties, which are found to exhibit different behaviors as a function of temperature and ambient environment. The origin of the strong visible luminescence observed from both cubic and monoclinic HfO2 is discussed in terms of surface-defects and nanosize of the particles. The comparative analysis of the PL responses of the two polymorphs suggests that emission at 3.1 eV originates from the oxygen vacancy related defects.

A Review of the Synthesis and Photoluminescence Properties of Hybrid ZnO and Carbon Nanomaterials

Photoluminescent ZnO carbon nanomaterials are an emerging class of nanomaterials with unique optical properties. They each, ZnO and carbon nanomaterials, have an advantage of being nontoxic and environmentally friendly. Their cost-effective production methods along with simple synthesis routes are also of interest. Moreover, ZnO presents photoluminescence emission in the UV and visible region depending on the synthesis routes, shape, size, deep level, and surface defects. When combined with carbon nanomaterials, modification of surface defects in ZnO allows tuning of these photoluminescence properties to produce, for example, white light. Moreover, efficient energy transfer from the ZnO to carbon nanostructures makes them suitable candidates not only in energy harvesting applications but also in biosensors, photodetectors, and low temperature thermal imaging. This work reviews the synthesis and photoluminescence properties of 3 carbon allotropes: carbon quantum or nanodots, graphene, and carbon nanotubes when hybridized with ZnO nanostructures. Various synthesis routes for the hybrid materials with different morphologies of ZnO are presented. Moreover, differences in photoluminescence emission when combining ZnO with each of the three different allotropes are analysed.

Silver Nanoparticles: Synthesis, Properties, and Applications

1Department of Physics, University of Oslo, 24 Sem Saelandsvei, 316 Oslo, Norway 2Institute of Physics, University of Tartu, Ravila 14c, 51014 Tartu, Estonia 3Tartu College, Tallinn University of Technology, Puiestee 78, 51008 Tartu, Estonia 4Department of Physics, University of Minho, 4800-058 Guimaraes, Portugal 5Department of Physics, Brock University, St. Catharines, ON, Canada L2S 3A1 6CWIT Capital Inc., 8 Baker Drive, St. Catharines, ON, Canada L2N 2V8

Biocidal properties study of silver nanoparticles used for application in green housing

We report on the study of surfactant-free silver nanoparticles synthesized using non-hydrolytic sol–gel methods for applications in straw bale constructions. Micro-organism infestation in green constructions is of concern as their proliferation tends to induce health problems. We demonstrate the biocidal properties of these Ag nanoparticles and their efficacy against fungi. Outdoor tests with Ag nanoparticles have demonstrated the effective protection of straw against micro-organisms. Indoor tests using broth liquid are compared with a method of testing we recently developed where the possible nature of the biocidal properties of the silver nanoparticles are further probed. In contrast to the commonly reported results, this study shows that Ag nanoparticles synthesized using non-hydrolytic sol–gel methods have antifungal properties against common fungi in outdoor conditions which demonstrate high potential in related applications.

Metal oxide nanoparticles embedded in rare-earth matrix for low temperature thermal imaging applications

We report on the synthesis and characterization of nanocomposites comprising of oxide nanoparticles (NPs) (ZnO, CaHfO3 and SrHfO3) embedded in rare-earth oxide (Eu2O3, Nd2O3) matrices by using atomic layer deposition. The different oxide surroundings allowed highlighting the role of interface defects in the recombination processes of charge carriers in the NPs. We provide a comparative analysis of optical absorption and emission properties of the constituents: thin films, free-standing and embedded NPs, and discuss the intrinsic and extrinsic nature of the luminescent sites in different nanocomposites. The photoluminescence properties of ZnO nanocomposites are clearly distinguishable from those of free-standing NPs in terms of overall quantum efficiency as well as intensity ratios of the characteristic blue and green emission bands associated with radiative transitions involving excitons and intrinsic defects, respectively. In contrast to PL enhancement due to surface-passivating effect of the surrounding media in the case of ZnO nanocomposites, the embedment of hafnia perovskites into oxide matrices generally leads to suppressed luminescence in the visible range, thus confirming its extrinsic, surface-defect related nature.