Modeling the first activation stages of a Fe(II) CVD precursor on a heated growth surface

<div>Green open access version of the paper:</div><div>"Modeling The First Activation Stages of the Fe(hfa)2 TMEDA CVD Precursor on a Heated Growth Surface"<br></div><div>published in:</div><div>Ceramic Engineering and Science Proceedings (2016) 36(6):83 - Advanced Processing and Manufacturing Technologies for Nanostructured and Multifunctional Materials II: A Collection of Papers Presented at the 39th International Conference on Advanced Ceramics and Composites (eds T. Ohji, M. Singh and M. Halbig), John Wiley & Sons, Inc., Hoboken, NJ, USA. doi: 10.1002/9781119211662.ch10<br></div><div>Which should be cited to refer to this work.</div><div><br></div><div>A popular summary of this paper is available at this link: https://goo.gl/MpdOpn</div

An iron(II) diamine diketonate molecular complex: synthesis, characterization and application in the CVD of Fe2O3 thin films

<div>Green open access version of the paper:</div><div><div>An iron(II) diamine diketonate molecular complex: synthesis, characterization and application in the CVD of Fe2O3 thin films</div></div><div><br></div><div>published in:</div><div><div>Inorganica Chimica Acta, 2012, 380, 161–166  </div><div><div>http://dx.doi.org/10.1016/j.ica.2011.10.036</div></div><div>which should be cited to refer to this work</div></div><div><br></div><div>Short non-technical summary of this paper: https://goo.gl/Fpwws7</div><div><br></div><div><div>This contribution was uploaded during the Open Access Week 2016 and is meant to be a little concrete step to put "Open in Action".</div><div><br></div></div

Nitrate and nitrite electrocatalytic reduction at layer-by-layer films composed of Dawson-type heteropolyanions mono-substituted with transitional metal Ions and silver nanoparticles

A series of Dawson-type heteropolyanions (HPAs) mono-substituted with transitional metal ions (α2-[P2W17O61FeIII]8−, α2-[P2W17O61CuII]8− and α2-[P2W17O61NiII]8−) have exhibited electrocatalytic properties towards nitrate and nitrite reduction in slightly acidic media (pH 4.5). The immobilization of these HPAs into water-processable films developed via layer-by layer assembly with polymer-stabilized silver nanoparticles led to the fabrication of the electrocatalytic interfaces for both nitrate and nitrite reduction. The LBL assembly as well as the changes in the HPA properties by immobilization has been characterized by electrochemical methods. The effects of the substituent ions, outer layers and the cationic moieties utilized for the films assembly of the developed film on the performances of nitrate electrocatalysis has been elucidate

Tailoring Vapor-Phase Fabrication of Mn₃O₄ Nanosystems: From Synthesis to Gas-Sensing Applications

Supported p-type α-Mn₃O₄ nanosystems were fabricated by means of chemical vapor deposition (CVD) on polycrystalline alumina substrates at temperatures of 400 and 500 °C, using Mn­(hfa)₂·TMEDA (hfa = 1,1,1,5,5,5-hexafluoro-2,4-pentanedionate; TMEDA = <i>N</i>,<i>N</i>,<i>N</i>′,<i>N</i>′-tetramethylethylenediamine) as precursor compound. The structure, chemical composition, and morphology of the obtained deposits were characterized in detail, devoting particular attention to the influence of the used reaction atmosphere (dry O₂ vs O₂ + H₂O) on the system characteristics. For the first time, the gas-sensing performances of the obtained CVD Mn₃O₄ nanomaterials were investigated toward ethanol and acetone vapors, with concentrations ranging from 10 to 50 and from 25 to 100 ppm, respectively. The developed systems showed the best activity ever reported in the literature for Mn₃O₄ chemoresistive sensors in the detection of the target gases, a result that, along with their low detection limits and good selectivity, is an appealing starting point for eventual technological applications

Toward the Detection of Poisonous Chemicals and Warfare Agents by Functional Mn₃O₄ Nanosystems

The detection of poisonous chemicals and warfare agents, such as acetonitrile and dimethyl methylphosphonate, is of utmost importance for environmental/health protection and public security. In this regard, supported Mn₃O₄ nanosystems were fabricated by vapor deposition on Al₂O₃ substrates, and their structure/morphology were characterized as a function of the used growth atmosphere (dry vs. wet O₂). Thanks to the high surface and peculiar nano-organization, the target systems displayed attractive functional properties, unprecedented for similar p-type systems, in the detection of the above chemical species. Their good responses, selectivity, and sensitivity pave the way to the fabrication of low-cost and secure sensors for different harmful analytes

Cu(II) Reduction without Reductants: Insights from Theory

<p>A topic issue in sustainable technologies is the production of Cu<i>_x</i>O (<i>x</i>=1,2) nanomaterials with tailored composition and properties. They can be fabricated through bottom-up processes that involve unexpected changes in the metal oxidation state and open intriguing challenges on the copper redox chemistry. How Cu^(II) complexes can lead to Cu^(I) species in spite of the absence of any explicit reducing agent is a question only recently answered by investigating the fragmentation of a Cu^(II) precursor for Cu oxide nanostructures by computer simulations and ESI-MS with multiple collisional experiments (ESI/MS<i>n</i>). Here we show that a Cu-promoted CH bond activation leads to reduction of the metal center and formation of a Cu^I-C-NCCN six-membered ring. Such 6-ring moiety is the structural motif for a new family of cyclic Cu^(I) adducts, characterized by a bonding scheme that may shed unprecedented light on high-temperature Cu chemistry. In particular, in this contribution we describe how collisions with hot atoms may activate Cu^(II) species to a configuration prone to the reduction. Besides its relevance for the fabrication of Cu-oxide nanostructures, the hydrogen-abstraction/proton-delivery/electron-gain mechanism of Cu^(II) reduction described herein could be a general property of copper and might help to understand its redox reactivity.</p><p>Poster presented at the 39th International Conference and Expo on Advanced Ceramics and Composites - Daytona Beach (FL) 25-31 Jan 2015</p

Au/ε-Fe₂O₃ Nanocomposites as Selective NO₂ Gas Sensors

A combined chemical vapor deposition (CVD)/radio frequency (rf) sputtering approach to Au/Fe₂O₃ nanocomposites based on the scarcely investigated ε-iron­(III) oxide polymorph is reported. The developed materials, analyzed by field emission-scanning electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDXS), X-ray photoelectron spectroscopy (XPS), and secondary ion mass spectrometry (SIMS), consisted of iron oxide nanorods decorated by gold nanoparticles (NPs), whose content and distribution could be tailored as a function of sputtering time. Interestingly, the intimate Au/ε-Fe₂O₃ interfacial contact along with iron oxide one-dimensional (1D) morphology resulted in promising performances for the selective detection of gaseous NO₂ at moderate working temperatures. At variance with the other iron­(III) oxide polymorphs (α-, β-, and γ-Fe₂O₃), that display an <i>n</i>-type semiconducting behavior, ε-Fe₂O₃ exhibited a <i>p</i>-type response, clearly enhanced by Au introduction. As a whole, the obtained results indicate that the sensitization of <i>p</i>-type materials with metal NPs could be a valuable tool for the fabrication of advanced sensing devices

Straightforward Synthesis of Gold Nanoparticles Supported on Commercial Silica-Polyethyleneimine Beads

Stable silica-supported gold nanoparticles (Au_NPs) suitable for catalysis applications were conveniently obtained in a straightforward, one-step synthesis by simply adding an aqueous solution of HAuCl₄ to commercial polyethyleneimine-functionalized silica beads (SiO₂-PEI) as the only reactant without any external reducing agent and/or conventional stabilizing moieties. Six different types of Au_NPs/(SiO₂-PEI) beads termed <b>Au</b>_{<b><i>x</i>–<i>y</i></b>}<b>h</b>, where <i>x</i> is the initial HAuCl₄ concentration (1, 5, or 10 mM) and <i>y</i> is the reaction time (1 or 24 h), were prepared and characterized by UV–vis diffuse reflectance spectroscopy, X-ray fluorescence, FE-SEM microscopy, and X-ray absorption spectroscopy. The SEM micrographs of <b>Au</b>_{<b><i>x</i>–<i>y</i></b>}<b>h</b> samples showed that the particle size distribution decreases with the increase of the starting gold concentration, i.e., 70–100 nm for <b>Au</b>_<b>1–</b>_{<b><i>x</i></b>}<b>h</b>, 40–70 nm for <b>Au</b>_{<b>5</b><b>–</b>}_{<b><i>x</i></b>}<b>h</b>, and <b>Au</b>_{<b>10</b><b>–</b>}_{<b><i>x</i></b>}<b>h</b>, whereas on passing from 1 to 24 h the aggregation phenomena overcome the nucleation ones, promoting the formation of bigger aggregates at the expense of small Au_NPs. The XAS analysis as a combination of XANES and EXAFS studies provided detailed structural information regarding the coordination geometry and oxidation state of the gold atoms present on the beads. Moreover, the catalytic activity of the modified silica beads in the reduction of 4-nitrophenol to 4-aminophenol by NaBH₄ was investigated and in one case the XAS analysis was repeated after recovery of the catalyst, demonstrating further reduction of the Au site to Au(0)

Vapor Phase Processing of α‑Fe₂O₃ Photoelectrodes for Water Splitting: An Insight into the Structure/Property Interplay

Harvesting radiant energy to trigger water photoelectrolysis and produce clean hydrogen is receiving increasing attention in the search of alternative energy resources. In this regard, hematite (α-Fe₂O₃) nanostructures with controlled nano-organization have been fabricated and investigated for use as anodes in photoelectrochemical (PEC) cells. The target systems have been grown on conductive substrates by plasma enhanced-chemical vapor deposition (PE-CVD) and subjected to eventual ex situ annealing in air to further tailor their structure and properties. A detailed multitechnique approach has enabled to elucidate the interrelations between system characteristics and the generated photocurrent. The present α-Fe₂O₃ systems are characterized by a high purity and hierarchical morphologies consisting of nanopyramids/organized dendrites, offering a high contact area with the electrolyte. PEC data reveal a dramatic response enhancement upon thermal treatment, related to a more efficient electron transfer. The reasons underlying such a phenomenon are elucidated and discussed by transient absorption spectroscopy (TAS) studies of photogenerated charge carrier kinetics, investigated on different time scales for the first time on PE-CVD Fe₂O₃ nanostructures

Surface Functionalization of Nanostructured Fe₂O₃ Polymorphs: From Design to Light-Activated Applications

Nanostructured iron­(III) oxide deposits are grown by chemical vapor deposition (CVD) at 400–500 °C on Si(100) substrates from Fe­(hfa)₂TMEDA (hfa = 1,1,1,5,5,5-hexafluoro-2,4-pentanedionate; TMEDA = <i>N</i>,<i>N</i>,<i>N</i>′,<i>N</i>′-tetramethylethylenediamine), yielding the selective formation of α-Fe₂O₃ or the scarcely studied ε-Fe₂O₃ polymorphs under suitably optimized preparative conditions. By using Ti­(OPrⁱ)₄ (OPrⁱ = iso-propoxy) and water as atomic layer deposition (ALD) precursors, we subsequently functionalized the obtained materials at moderate temperatures (<300 °C) by an ultrathin titanomagnetite (Fe_3–<i>x</i>Ti_<i>x</i>O₄) overlayer. An extensive multitechnique characterization, aimed at elucidating the system structure, morphology, composition and optical properties, evidenced that the photoactivated hydrophilic and photocatalytic behavior of the synthesized materials is dependent both on iron oxide phase composition and ALD surface modification. The proposed CVD/ALD hybrid synthetic approach candidates itself as a powerful tool for a variety of applications where semiconductor-based nanoarchitectures can benefit from the coupling with an ad hoc surface layer