12 research outputs found
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:Â 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
Tailoring Vapor-Phase Fabrication of Mn<sub>3</sub>O<sub>4</sub> Nanosystems: From Synthesis to Gas-Sensing Applications
Supported
p-type α-Mn<sub>3</sub>O<sub>4</sub> nanosystems
were fabricated by means of chemical vapor deposition (CVD) on polycrystalline
alumina substrates at temperatures of 400 and 500 °C, using MnÂ(hfa)<sub>2</sub>·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 O<sub>2</sub> vs O<sub>2</sub> + H<sub>2</sub>O) on the system characteristics.
For the first time, the gas-sensing performances of the obtained CVD
Mn<sub>3</sub>O<sub>4</sub> 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 Mn<sub>3</sub>O<sub>4</sub> 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 Mn<sub>3</sub>O<sub>4</sub> 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 Mn<sub>3</sub>O<sub>4</sub> nanosystems were fabricated
by vapor deposition on Al<sub>2</sub>O<sub>3</sub> substrates, and
their structure/morphology were characterized as a function of the
used growth atmosphere (dry vs. wet O<sub>2</sub>). 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><sub>x</sub></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<sup>(II)</sup>
complexes can lead to Cu<sup>(I)</sup> species in spite of the absence of any
explicit reducing agent is a question only recently answered by investigating
the fragmentation of a Cu<sup>(II)</sup> 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<sup>I</sup>-C-NCCN six-membered ring. Such 6-ring moiety is the
structural motif for a new family of cyclic Cu<sup>(I)</sup> 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<sup>(II)</sup> 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<sup>(II)</sup> 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
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
Au/ε-Fe<sub>2</sub>O<sub>3</sub> Nanocomposites as Selective NO<sub>2</sub> Gas Sensors
A combined
chemical vapor deposition (CVD)/radio frequency (rf) sputtering approach
to Au/Fe<sub>2</sub>O<sub>3</sub> nanocomposites based on the scarcely
investigated ε-ironÂ(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-Fe<sub>2</sub>O<sub>3</sub> interfacial contact along with iron oxide one-dimensional (1D) morphology
resulted in promising performances for the selective detection of
gaseous NO<sub>2</sub> at moderate working temperatures. At variance
with the other ironÂ(III) oxide polymorphs (α-, β-, and
γ-Fe<sub>2</sub>O<sub>3</sub>), that display an <i>n</i>-type semiconducting behavior, ε-Fe<sub>2</sub>O<sub>3</sub> 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<sub>NPs</sub>) suitable
for catalysis applications were conveniently obtained in a straightforward,
one-step synthesis by simply adding an aqueous solution of HAuCl<sub>4</sub> to commercial polyethyleneimine-functionalized silica beads
(SiO<sub>2</sub>-PEI) as the only reactant without any external reducing
agent and/or conventional stabilizing moieties. Six different types
of Au<sub>NPs</sub>/(SiO<sub>2</sub>-PEI) beads termed <b>Au</b><sub><b><i>x</i>–<i>y</i></b></sub><b>h</b>, where <i>x</i> is the initial HAuCl<sub>4</sub> 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><sub><b><i>x</i>–<i>y</i></b></sub><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><sub><b>1–</b></sub><sub><b><i>x</i></b></sub><b>h</b>, 40–70
nm for <b>Au</b><sub><b>5</b><b>–</b></sub><sub><b><i>x</i></b></sub><b>h</b>, and <b>Au</b><sub><b>10</b><b>–</b></sub><sub><b><i>x</i></b></sub><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<sub>NPs</sub>. 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 NaBH<sub>4</sub> 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‑Fe<sub>2</sub>O<sub>3</sub> 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-Fe<sub>2</sub>O<sub>3</sub>) 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-Fe<sub>2</sub>O<sub>3</sub> 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
Fe<sub>2</sub>O<sub>3</sub> nanostructures
Surface Functionalization of Nanostructured Fe<sub>2</sub>O<sub>3</sub> Polymorphs: From Design to Light-Activated Applications
Nanostructured
ironÂ(III) oxide deposits are grown by chemical vapor
deposition (CVD) at 400–500
°C on Si(100) substrates from FeÂ(hfa)<sub>2</sub>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),
yielding the selective formation of α-Fe<sub>2</sub>O<sub>3</sub> or the scarcely studied ε-Fe<sub>2</sub>O<sub>3</sub> polymorphs
under suitably optimized preparative conditions. By using TiÂ(OPr<sup>i</sup>)<sub>4</sub> (OPr<sup>i</sup> = 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<sub>3–<i>x</i></sub>Ti<sub><i>x</i></sub>O<sub>4</sub>) 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