52 research outputs found
Quenching the surface electronic structure of P-containing III-V semiconductors via ordered (1x1) Sb overlayers: a P L2,3VV Auger line-shape analysis
No full textInvestigating the activation of passive metals by a combined in-situ AFM and Raman spectroscopy system: a focus on titanium
No full textUnderstanding the main steps involved in the activation of passive metals is an extremely important subject in the mechanical and energy industry and generally in surface science. The titanium-H2SO4 system is particularly useful for this purpose, as the metal can either passivate or corrode depending on potential. Although several studies tried to hypothesise the surface state of the electrode, there is no general consensus about the surface state of Ti in the active-passive transition region. Here by combining in-situ atomic force microscopy (AFM) and Raman spectroscopy, operating in an electrochemical cell, we show that the cathodic electrification of Ti electrodes causes the dissolution of the upper TiO2 portion of the passive film leaving the electrode covered by only a thin layer of titanium monoxide. Fast anodic reactions involved the acidification of the solution and accumulation of sulphur containing anions. This produces a local increase of the solution turbidity, allowing to distinguish favourable regions for the precipitation of TiOSO4 center dot 2H(2)O. These results give a clear answer to the long-stated question of the physical origin behind the formation of negative polarization resistances, sometimes occurring in corroding systems, and a rationale about the proton-induced degradation of passive surfaces in presence of sulphur containing species
The effect of cyclic voltammetry speed on anion intercalation in HOPG
No full textIt is generally accepted that anion intercalation occurs when HOPG is kept at high electrochemical potentials in oxidant electrolytes, such as perchloric and sulfuric acids. The graphite surface undergoes a detriment, made also evident by the swelling of the uppermost layers (blisters formation) caused by gas evolution in standard electrochemical conditions (namely, by cycling the HOPG voltage at speeds up to 25 mV/s). Surface swelling is therefore considered as being indicative of anion intercalation. Recently, suppression of blister formation when the potential is swept at larger speeds (such as 600 mV/s) has been observed, raising the question as to whether this phenomenon might be able to suppress anion intercalation. In this work, by combining atomic force microscopy and X-ray photoemission spectroscopy, we unequivocally show that the HOPG electrode undergoes similar chemical modifications, regardless of the chosen electrochemical conditions and consequently of the morphological evolution at the surface
Esercizi di Fisica - Meccanica e Termodinamica
No full textIl testo affronta esercizi afferenti a due aree tematiche diverse: Meccanica e Termodinamica.
Gli esercizi proposti affrontano lo studio delle grandezze fisiche e relative unità di misura, i vari aspetti della meccanica del punto materiale, la meccanica dei sistemi di punto e quindi il corpo rigido e la gravitazione universale.
Essi proseguono interessando l’ambito della meccanica dei fluidi, dei fenomeni ondulatori e della meccanica relativistica speciale, per poi affrontare i principi della termodinamica, lo studio del gas ideale e la teoria cinetica dei gas.
Gli esercizi sono svolti in forma analitica, e solo nell’ultimo passaggio che porta al risultato finale vengono sostituiti i valori dei parametri in gioco, fornendo pertanto un’idea chiara di come il risultato dipenda da questi ultimi
Template Assisted Nucleation of Cobalt and Gold Nano-clusters on an Ultrathin Iron Oxide Film
No full textBeing the basic building blocks for nano-magnetic and nano-catalytic devices, regular arrays of nano-clusters play a crucial role in modern nanotechnology. One of the possible fabrication methods of periodic nanostructures consists in exploiting nano-patterned substrates as templates for the self-assembly of the deposited atoms. Here, we have investigated the templating properties of a Moiré superlattice formed at the interface between a FeO(111)-like ultrathin film and a Ni/Fe(001) substrate. Co and Au, representative of elements with high and low oxygen affinity, respectively, have been deposited on the iron oxide film. Scanning tunneling microscopy reveals that Co nucleates preferentially along the corrugated regions of the Moiré superstructure, forming stripes with high aspect ratio. On the other hand, Au atoms nucleate randomly distributed three-dimensional islands on the FeO(111) surface
Electronic and spectral properties of clean and C60-covered atom-thick Chromium oxide at the Fe(001) surface
No full textChemisorption of a single atomic layer of oxygen on the Fe(001) surface yields a highly ordered and reproducible benchmark substrate [1] for theoretical and experimental studies, and for the epitaxial growth of metal oxides, including atom-thick CrxOy layers, and hybrid interfaces with foreseen applications e.g. in organic spintronics.
This talk initially presents ab initio investigations that have supplemented microscopy and spectroscopy experiments of the electronic and magnetic properties of two-dimensional Chromium oxides of Cr3O4 and Cr4O5 stoichiometry grown on Fe(001), featuring antiferromagnetic magnetic configurations with underlying Fe(001) [2,3]. Despite Cr / CrO systems are notoriously difficult for mean field approaches, generalized-gradient results are found to explain most experimental findings, with a rigid shift of oxygen bands accounting for electronic correlation effects.
We eventually consider the effect of inserted Cr4O5 layers at the interface between the prototypical C60 organic semiconductor and Fe(001), which is shown to enhance the magnetic hybridization between the molecule and the surface through x-ray magnetic circular dichroism (XMCD) [4,5]. By means of ab initio calculation we characterize the local interface morphology, the magnetic configuration of the surface and the induced spin dependent electronic properties of the molecule, the latter reflecting the magnetic electronic properties of the surface at the relevant energy range. As seen from the substrate, adsorbates can influence the magnitude and even orientation of surface Cr magnetic moments. The interest in this interface is then twofold: on one side the thin magnetic oxide allows tailoring the magnetic properties of the organic layer, on the other side the adsorption of C60 can be envisioned as a tool to control the magnetic ordering of Cr atoms at the interface.
[1] A. Picone, M. Riva, A. Brambilla, A. Calloni, G. Bussetti, M. Finazzi, F. Ciccacci, L. Duò, Surface Science Reports 71, 32 (2016).
[2] A. Picone, G. Fratesi, M. Riva, G. Bussetti, A. Calloni, A. Brambilla, M. I. Trioni, L. Duò, F. Ciccacci, and M. Finazzi, Phys. Rev. B 87, 085403 (2013).
[3] A. Calloni, G. Fratesi, S. Achilli, G. Berti, G. Bussetti, A. Picone, A. Brambilla, P. Folegati, F. Ciccacci, and L. Duò, Phys. Rev. B 96, 085427 (2017).
[4] A. Brambilla, A. Picone, D. Giannotti, A. Calloni, G. Berti, G. Bussetti, S. Achilli, G. Fratesi, M. I. Trioni, G. Vinai, P. Torelli, G. Panaccione, L. Duò, M. Finazzi, and F. Ciccacci, Nano Lett. 17, 7440 (2017).
[5] A. Brambilla, A. Picone, S. Achilli, G. Fratesi, A. Lodesani, A. Calloni, G. Bussetti, M. Zani, M. Finazzi, L. Duò, and F. Ciccacci, Journal of Applied Physics 125, 142907 (2019)
SURFACE LOCAL DENSITY OF STATES OF INP(110) VIA PL2,3VV AUGER LINESHAPE - THE ROLE OF AN ORDERED (1X1) SB OVERLAYER
No full textAn experimental and theoretical investigation on the PL2,3VV Auger lineshape of the InP(110) surface is presented. A band-like picture provides a good description of the spectral features. In addition, deposition of one monolayer of Sb on InP(110) is shown to drive the surface atoms into an environment similar to that present in the bulk, so that a comparison between the PL2,3VV spectrum from the clean and Sb-covered sample allows us to discriminate between the surface contribution and the bulk contribution to this surface-sensitive Auger transition
Observation of a Metastable Honeycomb Arrangement of C60 on Ni(111) with (7 × 7) Periodicity: Tailoring an Interface for Organic Spintronics
No full textHybrid nanostructures in which organic molecules are interfaced with metal surfaces hold promise for the discovery of intriguing physical and chemical phenomena, as well as for the development of innovative devices. In this frame, it is crucial to understand the interplay between the structural details of the interface and the electronic properties of the system. Here, an experimental investigation of the C60/Ni(111) interface is performed by means of scanning tunneling microscopy/spectroscopy (STM/STS) and low-energy electron diffraction (LEED). The deposition of C60 at room temperature, followed by high-temperature annealing, promotes the stabilization of two different phases. A hitherto unreported phase forming a (7 × 7) honeycomb overlayer coexists with the well-known (4 × 4) reconstruction. Highly resolved STM images disclose the adsorption geometry of the molecules for both phases. STS reveals that the electronic properties of C60/Ni(111) are strongly influenced by the morphology of the interface, suggesting the possibility of tuning the electronic properties of the organic/inorganic heterostructures by adjusting the structural coupling with the substrate. This achievement can be important for hybrid magnetic interfaces, where the harmonization between the molecular and the magnetic orders can enhance the development of hybrid magnetic states
Self-organized chromium oxide monolayers on Fe(001)
No full textThe growth of ultrathin epitaxial oxide films on metal supports is attracting
considerable scientific interest both
on a fundamental level and for potential technological applications.
Growth techniques such as reactive deposition (i.e., metal deposition in oxygen
atmosphere) and/or post-oxidation are typically applied, leading to ordered phases
and well defined oxide-metal interfaces on noble metal substrates. On the contrary,
when a more reactive metal, such as Fe, is used as a substrate for the nano-oxide
growth, these procedures fail to produce sharp metal/oxide interfaces. Indeed, during
the metal deposition in oxygen atmosphere, extensive and uncontrolled oxidation of
Fe occurs, preventing the stabilization of long-range ordered oxide monolayers.
An alternative route to obtain a sharp interface between a single layer of transition
metal oxide and a reactive
substrate may be to exploit the oxygen adsorbed on the surface before metal
deposition since, in this case, the
amount of oxygen available is well defined.
The well ordered and defect-free Fe(001)-p(1×1)O surface is an ideal template to
implement this strategy.
The surface is characterized by one oxygen atom per surface unit cell, which can be
used as a reservoir for
the stabilization of two-dimensional transition metal oxides.
In this contribution, by means of a combination of high resolution Scanning Tunneling
Microscopy images, Auger Electron Spectroscopy, and Density Functional Theory
calculations, we show how the Fe(001)-p(1 × 1)O surface can be used as a template
for the self assembly of two dimensional Cr oxides. Cr deposition on this surface
leads to two different phases, depending on the amount of deposited Cr. At 0.75 monolayers coverage a c(4 × 2) overlayer with Cr3O4 formal stoichiometry is
stabilized, while an overlayer with (???5 ×???5)R°27 symmetry and Cr4O5 stoichiometry
is obtained at slightly higher coverages [1].
Furthermore, the magnetic properties of these oxide monolayers are investigated by
means of X-ray magnetic circular dichroism.
References: [1] A. Picone, G. Fratesi, M. Riva, G. Bussetti, A. Calloni, A. Brambilla, M. I. Trioni, L.
Duò, F. Ciccacci, and M. Finazzi, Self-organized chromium oxide monolayers on
Fe(001), Phys. Rev. B 87, 085403 (2013
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