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Setup
![Spettrometro SPECS Delta0.5](/sites/default/files/inline-images/HREELS%20spettrometro.jpg)
SPECS Delta0.5 spectrometer
Energy resolution (direct beam) <2 meV with beam current ~10 pA
Primary Electron Energy: 1-100 eV
Specular reflection angle: 53°<θ<90°
Installed on a UHV chamber with XPS spectrometer and connectable to a supersonic molecular beam.
Method
This vibrational spectroscopy exploits the interaction of the surface with a monochromatic electron beam. During the scattering process, an energy transfer from the electron to the surface (or vice versa) can occur with the consequent excitation of surface phonon modes and / or collective electronic excitations (surface plasmons).
This surface-sensitive analytical technique can be applied to conductive or semiconductive samples or supported ultra-thin films and provides information on:
- Surface phonon spectrum
- Phonon spectrum in presence of adsorbates
- Surface phonon dispersion
- Energy and dispersion of surface plasmons (optical and acoustic)
![scheme](/sites/default/files/inline-images/HREELS%20metodo_0.jpg)
Highlights
HREELS spectroscopy applied to bidimensional systems, bare and in presence of adsorbates
The energy loss peaks allow to determine the characteristics of the material, for instance by analising Fuchs-Kliever phonons, if present, and the presence of adsorbates in molecular or dissociated form.
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Characteristic vibrational spectra of several supported bidimensional films. Refs: Appl. Surf. Sci. 2020, Phys. Rev. B 2003 |
Adsorption of CO on graphene monolayers of different defectivity grown on Ni (111). Refs: Appl. Surf. Sci. 2018, Phys. Chem. Chem. Phys. 2016 |
EELS spectroscopy applied to the study of collective electron excitations
![curva di dispersione](/sites/default/files/inline-images/HREELS%20highlight%203_1.jpg)
First measurement of the acoustic surface plasmon of Be(0001). Ref:Nature 2007