M. Di Marino

Bio: M. Di Marino is an academic researcher from University of Padua. The author has contributed to research in topics: Oxide & Amorphous solid. The author has an hindex of 9, co-authored 10 publications receiving 286 citations. Previous affiliations of M. Di Marino include Scuola Normale Superiore di Pisa.

Tuning the catalytic activity of Ag(110)-supported Fe phthalocyanine in the oxygen reduction reaction

Abstract: A careful choice of the surface coverage of iron phthalocyanine (FePc) on Ag (110) around the single monolayer allows us to drive with high precision both the long-range supramolecular arrangement and the local adsorption geometry of FePc molecules on the given surface. We show that this opens up the possibility of sharply switching the catalytic activity of FePc in the oxygen reduction reaction and contextual surface oxidation in a reproducible way. A comprehensive and detailed picture built on diverse experimental evidence from scanning tunnelling microscopy, X-ray photoelectron spectroscopy and X-ray absorption spectroscopy, coupled with density functional theory calculations, sheds new light on the nature of the catalytically active molecule-surface coordination and on the boundary conditions for its occurrence. The results are of relevance for the improvement of the catalytic efficiency of metallo-macrocycles as viable substitutes for platinum in the cathodic compartment of low-temperature fuel cells.

Coverage-Dependent Architectures of Iron Phthalocyanine on Ag(110): a Comprehensive STM/DFT Study

Abstract: Iron(II) phthalocyanine (FePc) self-assembly on Ag(110) has been studied in ultrahigh-vacuum conditions at room temperature by means of scanning tunneling microscopy (STM) and density functional theory (DFT) calculations. For submonolayer to monolayer coverage, FePc molecules lie parallel to the Ag(110) surface, arranged in rows running along the [001] direction. Two similar yet distinct ordered phases are formed, the c(10 × 4) and p(10 × 4) superstructures. The latter is characterized by two equivalent equilibrium configurations of the constituent FePc units, that interconvert by means of a concerted transformation wherein molecules belonging to adjacent rows collectively rotate in opposite directions around the molecular axis perpendicular to the surface. The FePc adsorption site for both superstructures and the transition mechanism between the two configurations in the p(10 × 4) phase have been inferred from high resolution STM images and rationalized by means of DFT calculations. In the case of multil...

Oxidation rate enhancement of SiGe epitaxial films oxidized in dry ambient

Abstract: We present a study on thin oxides obtained by rapid thermal oxidation of Si1−xGex epitaxial layers. The oxidation processes were performed in dry O2 at 1000 °C for times up to 600 s. Our data show an oxide growth rate enhancement with respect to pure Si. Except for a very small amount of GeO2 that is found at the surface, all the Ge is rejected towards the SiO2/SiGe interface, forming a Ge-enriched layer free of extended defects. The comparison of our results for dry processes with those reported in the literature for wet ambient supports the idea that the kinetics of SiGe oxidation is controlled by similar mechanisms in both cases, in contrast with models and interpretations so far proposed.

Silicon interstitial injection during dry oxidation of SiGe∕Si layers

Abstract: The injection of Si self-interstitial atoms during dry oxidation at 815°C of very shallow SiGe layers grown on Si (001) by molecular-beam epitaxy (MBE) has been investigated. We first quantified the oxidation enhanced diffusion (OED) of two boron deltas buried into the Si underlying the oxidized SiGe layers. Then, by simulating the interstitial diffusion in the MBE material with a code developed on purpose, we estimated the interstitial supersaturation (S) at the SiGe∕Si interface. We found that S (a) is lower than that observed in pure Si, (b) is Ge-concentration dependent, and (c) has a very fast transient behavior. After such a short transient, the OED is completely suppressed, and the suppression lasts for long annealing times even after the complete oxidation of the SiGe layer. The above results have been related to the mechanism of oxidation of SiGe in which the Ge piles up at the SiO2∕SiGe interface by producing a thin and defect-free layer with a very high concentration of Ge.

Experimental evidence of B clustering in amorphous Si during ultrashallow junction formation

Abstract: The authors have investigated ultrashallow p+∕n-junction formation by solid-phase epitaxy, by using x-ray absorption near-edge spectroscopy measurements on the B K edge. A clear fingerprint of B–B clusters is detected in the spectra. The authors demonstrate that B clustering occurs during the very early stages of annealing-induced Si recrystallization, i.e., when B is still in an amorphous matrix. After complete regrowth the local structure around B remains the same as in the amorphous phase, implying that B clusters are transferred to the crystalline structure.

Porphyrins at interfaces

Abstract: Porphyrins and other tetrapyrrole macrocycles possess an impressive variety of functional properties that have been exploited in natural and artificial systems. Different metal centres incorporated within the tetradentate ligand are key for achieving and regulating vital processes, including reversible axial ligation of adducts, electron transfer, light-harvesting and catalytic transformations. Tailored substituents optimize their performance, dictating their arrangement in specific environments and mediating the assembly of molecular nanoarchitectures. Here we review the current understanding of these species at well-defined interfaces, disclosing exquisite insights into their structural and chemical properties, and also discussing methods by which to manipulate their intramolecular and organizational features. The distinct characteristics arising from the interfacial confinement offer intriguing prospects for molecular science and advanced materials. We assess the role of surface interactions with respect to electronic and physicochemical characteristics, and describe in situ metallation pathways, molecular magnetism, rotation and switching. The engineering of nanostructures, organized layers, interfacial hybrid and bio-inspired systems is also addressed.

Iron phthalocyanine with coordination induced electronic localization to boost oxygen reduction reaction

Abstract: Iron phthalocyanine (FePc) is a promising non-precious catalyst for the oxygen reduction reaction (ORR). Unfortunately, FePc with plane-symmetric FeN4 site usually exhibits an unsatisfactory ORR activity due to its poor O2 adsorption and activation. Here, we report an axial Fe–O coordination induced electronic localization strategy to improve its O2 adsorption, activation and thus the ORR performance. Theoretical calculations indicate that the Fe–O coordination evokes the electronic localization among the axial direction of O–FeN4 sites to enhance O2 adsorption and activation. To realize this speculation, FePc is coordinated with an oxidized carbon. Synchrotron X-ray absorption and Mossbauer spectra validate Fe–O coordination between FePc and carbon. The obtained catalyst exhibits fast kinetics for O2 adsorption and activation with an ultralow Tafel slope of 27.5 mV dec−1 and a remarkable half-wave potential of 0.90 V. This work offers a new strategy to regulate catalytic sites for better performance. Iron phthalocyanine with a 2D structure and symmetric electron distribution around Fe-N4 active sites is not optimal for O2 adsorption and activation. Here, the authors report an axial Fe–O coordination induced electronic localization strategy to enhance oxygen reduction reaction performance.

Covalent grafting of carbon nanotubes with a biomimetic heme model compound to enhance oxygen reduction reactions.

Abstract: The oxygen reduction reaction (ORR) is one of the most important reactions in both life processes and energy conversion systems. The replacement of noble-metal Pt-based ORR electrocatalysts by nonprecious-metal catalysts is crucial for the large-scale commercialization of automotive fuel cells. Inspired by the mechanisms of dioxygen activation by metalloenzymes, herein we report a structurally well-defined, bio-inspired ORR catalyst that consists of a biomimetic model compound-an axial imidazole-coordinated porphyrin-covalently attached to multiwalled carbon nanotubes. Without pyrolysis, this bio-inspired electrocatalyst demonstrates superior ORR activity and stability compared to those of the state-of-the-art Pt/C catalyst in both acidic and alkaline solutions, thus making it a promising alternative as an ORR electrocatalyst for application in fuel-cell technology.

Fine-grained and fully ordered intermetallic PtFe catalysts with largely enhanced catalytic activity and durability

Abstract: Catalytic activity and durability improvements are still the main challenges in fuel cell commercialization. To enhance nanocatalyst performance and durability for oxygen reduction reaction (ORR), we prepare 3.6 nm sized PtFe particles with a fully ordered intermetallic structure and entrap them in a porous carbon (PtFe@C). This nanocatalyst toward ORR exhibits 8–10 times enhancement in specific and mass activities over the commercial catalyst of Pt/C. Such a large enhancement is the highest, when compared with all other kinds of intermetallic catalysts reported in the literature. Accelerated durability testing has induced only a small change to the ordered structure and a minor loss of the activity after thousands of potential cycles under harsh electrochemical conditions. The high activity and durability are attributed to the fine-grained and ordered structure of the nanoparticle and the confining effect provided by the porous carbon. The nanoparticle, PtFe@C, represents a new strategy for performance optimization and cost reduction and promoting practical applications of fuel cells.