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ANDREA STEFANI

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Pubblicazioni

2024 - Chiral Recognition: A Spin‐Driven Process in Chiral Oligothiophene. A Chiral‐Induced Spin Selectivity (CISS) Effect Manifestation [Articolo su rivista]
Stefani, Andrea; Salzillo, Tommaso; Mussini, Patrizia Romana; Benincori, Tiziana; Innocenti, Massimo; Pasquali, Luca; Jones, Andrew C.; Mishra, Suryakant; Fontanesi, Claudio
abstract

In this paper it is experimentally demonstrated that the electron-spin/molecular-handedness interaction plays a fundamental role in the chiral recognition process. This conclusion is inferred comparing current versus potential (I-V) curves recorded using chiral electrode surfaces, which are obtained via chemisorption of an enantiopure thiophene derivative: 3,3 & PRIME;-bibenzothiophene core functionalized with 2,2 & PRIME;-bithiophene wings (BT2T4). The chiral recognition capability of these chiral-electrodes is probed via cyclic voltammetry measurements, where, Ag nanoparticles (AgNPs) capped with enantiopure BT2T4 (BT2T4@AgNP) are used as the chiral redox probe. Then, the interface handedness is explored by recording spin-polarized I-V curves in spin-dependent electrochemistry (SDE) and magnetic-conductive atomic force microscopy (mc-AFM) experiments. The quality of the interfaces is thoroughly cross-checked using X-ray photoemission spectroscopy, Raman, electrodesorption measurements, which further substantiate the metal(electrode)-sulfur(thiophene) central role in the chemisorption process. Spin-polarization values of about 15% and 30% are obtained in the case of SDE and mc-AFM experiments, respectively.It is demonstrated that probing the handedness of a chiral system (here a chiral-electrode-surface/solution interface) by using a spin-polarized current, allows for chiral recognition. This conclusion is inferred by tight comparison with cyclic voltammetry results, where the handedness of the "chiral-electrode-surface/solution interface" is recognized by using an enantiopure chiral redox couple.image

2023 - Spin-dependent charge transmission through chiral 2T3N self-assembled monolayer on Au [Articolo su rivista]
Stefani, Andrea; Innocenti, Massimo; Giurlani, Walter; Calisi, Nicola; Pedio, Maddalena; Felici, Roberto; Favaretto, Laura; Melucci, Manuela; Zanardi, Chiara; Jones, Andrew C; Mishra, Suryakant; Zema, Nicola; Fontanesi, Claudio
abstract

: A gold surface is functionalized by chemisorption of the enantiopure N,N'-bis-[2,2';5',2″]tert-thiophene-5-yl methylcyclohexane-1,2-diamine (2T3N), a chiral oligothiophene derivative, via overnight incubation in a 2T3N ethanol solution. The Au|2T3N interface is characterized by x-ray photoelectron circular dichroism and comparing x-ray photoemission spectroscopy and electro-desorption results. Charge transmission at the Au|2T3N| solution interface is characterized by recording the cyclic voltammetry of the Fe(III)/Fe(II) reversible redox couple, finding a charge transfer rate constant, k°, variation from 1 × 10-1 to 3.3 × 10-2 cm s-1, when comparing the bare Au and the Au|2T3N interfaces, respectively. The "anomalous" high value of k° found for the chiral Au|2T3N interface can be rationalized on the basis of the chiral-induced spin selectivity effect, as further proved by magnetic-conductive atomic force microscopy measurements at room temperature. A spin polarization of about 30% is found.

2022 - Magnetic Field Effect on the Handedness of Electrodeposited Heusler Alloy [Articolo su rivista]
Giurlani, Walter; Vizza, Martina; Pizzetti, Federico; Bonechi, Marco; Savastano, Matteo; Sorace, Lorenzo; Stefani, Andrea; Fontanesi, Claudio; Innocenti, Massimo
abstract

Magneto-electrochemistry (MEC) experiments were carried out in the electrodeposition of a ferromagnetic Heusler alloy. The electrodeposition was carried out in the absence (as a reference) and in the presence of a magnetic field that was applied perpendicularly to the electrode–solution interface. The obtained metallic deposit was characterized by SEM-EDS, XRF, and XRD techniques. The ferromagnetic properties are assessed on the basis of SQUID measurements. The experimental results indicate that the influence of the presence of the magnetic field induces differences in the electrochemical measurements and a macroscopic handedness (chirality) in the deposit, which is a function of magnet orientation. Eventually, the coercivity of the Heusler alloy that was obtained in the presence of the magnetic field was larger compared to that of the deposit that was obtained without a magnetic field.

2022 - PANI-Based Stacked Ferromagnetic Systems: Electrochemical Preparation and Characterization [Articolo su rivista]
Stefani, A; Fonollosa, Nt; Giurlani, W; Giovanardi, R; Fontanesi, C
abstract

In this work, the electropolymerization of polyaniline (PANI) is explored for its action as either a suitable coating or as a substrate for Nickel (Ni) and Magnetite (Fe3O4) surfaces. PANI electropolymerization has been achieved through cyclic voltammetry (CV), potentiostatic and galvanostatic electrochemical methods. The interaction between the obtained surfaces and the ferromagnetic layers (Ni and Fe3O4) has been investigated as a function of the pH of the electrolytic PANI solution, and also a variety of experimental parameters have been optimized in order to achieve the synthesis of PANI coatings (solvent, substrate, concentrations, and cell set-up). Thus, we obtained stable and consistent PANI thick films at the interface of both the nickel and the magnetite ferromagnetic materials.

2022 - Resorcinol electropolymerization process obtained via electrochemical oxidation [Articolo su rivista]
Bonechi, M.; Giurlani, W.; Stefani, A.; Marchetti, A.; Innocenti, M.; Fontanesi, C.
abstract

The electrochemical oxidation of resorcinol is experimentally studied on platinum, palladium and glassy carbon (GC) electrodes. The results of an exhaustive electrochemical characterization are presented, and integrated with the outcome of complementary chromatographic analytical techniques: LC-DAD and LC-MS. We demonstrate that upon electrochemical oxidation resorcinol polymerizes following an efficient and facile process, and once the electropolymerization is triggered a polymer film can be easily grown. The latter film features also good adhesion on the electrode surface.

2021 - Electrodeposition of Cu on PEDOT for a Hybrid Solid-State Electronic Device [Articolo su rivista]
Vizza, Martina; Pappaianni, Giulio; Giurlani, Walter; Stefani, Andrea; Giovanardi, Roberto; Innocenti, Massimo; Fontanesi, Claudio
abstract

Conductive polymers are nowadays attracting great attention for their peculiar mechanical, electrical and optical proprieties. In particular, PEDOT can be used in a wide range of innovative applications, from electroluminescent devices to photovoltaics. In this work, the electrochemical deposition of 3,4 ethylenedioxythiophene (EDOT) was performed on various substrates (ITO, thin films of gold and palladium on silicon wafers) by means of both potentiostatic and potentiodynamic techniques. This was intended to further expand the applications of electrochemically deposited PEDOT, particularly regarding the preparation of thin films in tight contact with electrode surfaces. This allows one to obtain systems prone to be used as electrodes in stacked devices. Chronoamperometric experiments were performed to study the nucleation and growth process of PEDOT. SEM, ESEM and AFM analysis allowed the characterization of the morphology of the polymeric films obtained. Raman and visible spectroscopy confirmed the high-quality of the coatings on the different substrates. Then, the PEDOT films were used as the base material for the further electrodeposition of a copper layer. In this way, a hybrid electronic device was obtained, by using electrochemical methods only. The high conductivity and ohmic behavior of the device were confirmed over a wide range of frequencies with electrical impedance spectroscopy analysis.

2021 - Influence of magnetic field on the electrodeposition and capacitive performances of MnO2 [Articolo su rivista]
Girimonte, A.; Stefani, A.; Innocenti, M.; Fontanesi, C.; Giovanardi, R.
abstract

This study focuses on the influence of an applied external magnetic field on the elec-trodeposition process and capacitive performances of MnO2, as pseudo-capacitive active material for supercapacitors electrodes. MnO2 was electrochemically deposited on Si/Au substrates in the presence and in the absence of a 0.5 T magnet, and its capacitive performance was tested via electrochemical characterization. The samples obtained in the presence of the magnetic field show a positive influence on the deposition process: the increase in deposition efficiency leads to more compact and uniform MnO2 coatings, with a decrease in capacitance values for the samples produced with the magnetic field.

2021 - On the Savéant's Concerted/Stepwise Model. The Electroreduction of Halogenated Naphthalene Derivatives as a Case Study [Articolo su rivista]
Stefani, Andrea; Giurlani, Walter; Bonechi, Marco; Marchetti, Andrea; Preda, Giovanni; Pasini, Dario; Innocenti, Massimo; Fontanesi, Claudio
abstract

The electroreduction of 1-Br-2-naphthol is shown to be a not-additive process with respect to the results obtained with two structurally related chiral [1,1′-Binaphthalene]-2,2′-diol, 6,6′-dibromo and 1,1′-Binaphthalene,6,6′-dibromo-2,2′-dimethoxy compounds. The 1-Br-2-naphtol reduction is accompanied by the carbon bromine dissociation, eventually producing a film due to a fast radical-radical cross reaction. The film formation is not observed in the BINOL-like chiral halogen-derivatives.

2021 - On the oxygen reduction reaction mechanism catalyzed by pd complexes on 2d carbon. A theoretical study [Articolo su rivista]
Bonechi, M.; Giurlani, W.; Vizza, M.; Savastano, M.; Stefani, A.; Bianchi, A.; Fontanesi, C.; Innocenti, M.
abstract

Oxygen Reduction Reaction (ORR) is the bottle-neck strategic reaction ruling the fuel cell efficiency process. The slow kinetics of the reaction require highly effective electrocatalysts for proper boosting. In this field, composite catalysts formed by carbon nanotubes functionalized with palladium(II) complexes showed surprising catalytic activity comparable to those of a commercial Pt electrode, but the catalytic mechanisms of these materials still remain open to discussion. In this paper, we propose the combination of experimental and theoretical results to unfold the elementary reaction steps underlying the ORR catalysis.

2020 - Influence of Chiral Compounds on the Oxygen Evolution Reaction (OER) in the Water Splitting Process [Articolo su rivista]
Gazzotti, M.; Stefani, A.; Bonechi, M.; Giurlani, W.; Innocenti, M.; Fontanesi, C.
abstract

Results are presented concerning the influence on the water splitting process of enantiopure tartaric acid present in bulk solution. Stainless steel and electrodeposited nickel are used as working electrode (WE) surface. The latter is obtained by electrodeposition on the two poles of a magnet. The influence and role played by the chiral compound in solution has been assessed by comparing the current values, in cyclic voltammetry (CV) experiments, recorded in the potential range at which oxygen evolution reaction (OER) occurs. In the case of tartaric acid and nickel WE a spin polarization of about 4% is found. The use of the chiral environment (bulk solution) and ferromagnetic chiral Ni electrode allows for observing the OER at a more favorable potential: About 50 mV (i.e., a cathodic, less positive, shift of the potential at which the oxygen evolution is observed).