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Research at the VUV

VUV photoemission and its users

The beamline operate in time sharing with SpectroMicroscopy beamline, with 66,6% of time destinated for VUV, i.e. 130 days/year. 35 % of the beamtime is allocated to italian users, 35% is open to general users, and 30% for in-house research, tests, maintenance and commissioning. The average duration of an experiment at VUV is 7 days (21 shifts).
From 2011 to 2014 149 proposals were submitted to VUV photoemission, among them 108 as VUV first choice, and 52 of them were scheduled. In the same period the VUV users published 28 articles with mean impact factor 4.76.

Browse our Publications

Research fields

Research takes place in fields related to surface physics and chemistry, materials science, magnetism, and nanotechnology. Among our topics are graphene-based systems, 1D systems, quantum size effects in thin metal films, electronic structure and transport, magnetic materials, self-assembled molecular layers and many other.

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Recent research activity

Electronic States of Silicene Allotropes on Ag(111)

Silicene, a honeycomb lattice of silicon, presents a particular case of allotropism on Ag(111). Silicene forms multiple structures with alike in-plane geometry but different out-of-plane atomic buckling and registry to the substrate. Angle-resolved photoemission and first-principles calculations show that these silicene structures, with (4×4), (√13×√13)R13.9°, and (2√3×2√3)R30° lattice periodicity, display similar electronic bands despite the structural differences. 


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VUV image gallery





 

Asymmetric band gaps in a Rashba film system

The joint effect of exchange and Rashba spin-orbit interactions is examined on the surface and quantum well states of Ag2Bi-terminated Ag films grown on ferromagnetic Fe(110). The system displays a particular combination of time-reversal and translational symmetry breaking that strongly influences its electronic structure. Angle-resolved photoemission reveals asymmetric band-gap openings, due to spin-selective hybridization between Rashba-split surface states and exchange-split quantum well states.


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Magnetization-dependent Rashba splitting of quantum well states at the Co/W interface

Exchange and Rashba spin-orbit interactions are expected to couple at ferromagnetic-metal/heavy-metal interfaces and influence their electronic structure. We examine these largely unexplored effects in Co(0001) films on W(110) by angle-resolved photoemission spectroscopy. We find breaking of inversion symmetry in the band dispersion of magnetic quantum well states along structurally equivalent directions of the Co films. 


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Energy-momentum mapping of d-derived Au(111) states in a thin film

The quantum well states of a film can be used to sample the electronic structure of the parent bulk material and determine its band parameters. We highlight the benefits of two-dimensional film band mapping, with respect to complex bulk analysis, in an angle-resolved photoemission spectroscopy study of the 5d states of Au(111). Discrete 5d-derived quantum well states of various orbital characters form in Au(111) films and span the width of the corresponding bulk bands


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Evidence for a diamondlike electronic band structure of Si multilayers on Ag(111)

Silicon multilayers on Ag(111) have been suggested to exhibit the structure of silicene, a material that has been heralded as a novel basis for microelectronic applications. However, our angle-resolved photoemission spectra (ARPES) from silicon multilayers on Ag(111) and of the silver-induced reconstruction of Si(111) demonstrate, from the close match in the valence level band structures, that the films exhibit a sp3 diamondlike structure. 


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Spin-orbit interaction and Dirac cones in d-orbital noble metal surface states

Here, we report a joint photoemission and ab initio study of spin-orbit effects in the deep d-orbital surface states of a 24-layer Au film grown on Ag(111) and a 24-layer Ag film grown on Au(111), singling out a conical intersection (Dirac cone) between two surface states in a large surface-projected gap at the time-reversal symmetric M bar points. Unlike the often isotropic dispersion at Γ bar point Dirac cones, the M bar point cones are strongly anisotropic. 


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Silicene on Ag(111): A honeycomb lattice without Dirac bands

By means of angle-resolved photoemission spectroscopy and density-functional theory calculations we show that the π-symmetry states lose their local character and the Dirac cone fades out. The formation of an interface state of free-electron-like Ag origin is found to account for spectral features that were theoretically and experimentally attributed to silicene bands of π character.


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Two Distinct Phases of Bilayer Graphene Films on Ru(0001)

By combining angle-resolved photoemission spectroscopy and scanning tunneling microscopy we reveal the structural and electronic properties of multilayer graphene on Ru(0001). We prove that large ethylene exposure allows the synthesis of two distinct phases of bilayer graphene with different properties. 

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Electronic structure of epitaxial graphene grown on stepped Pt(997)

Angle-resolved photoemission spectroscopy, low-energy electron diffraction, and density functional theory calculations were employed to investigate the electronic and structural properties of a graphene layer grown on the regularly stepped Pt(997) surface.The measurements show the predominance of a (2×2) multidomain superstructure of graphene, lying flat on the Pt terraces and covering the step edges in a carpetlike mode. Read more...



 



Controlling the Topology of Fermi Surfaces in Metal Nanofilms

The properties of metal crystals are governed by the electrons of the highest occupied states at the Fermi level and determined by Fermi surfaces, the Fermi energy contours in momentum space. Topological regulation of the Fermi surface has been an important issue in synthesizing functional materials, which we found to be realized at room temperature in nanometer-thick films.

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Electronic structure study of ultrathin Ag(111) films modified by a Si(111) substrate and √3×√3-Ag2Bi surface

Angle-resolved photoemission spectroscopy experiments show that the electronic structure of a Ag(111) film grown on Si(111) is markedly perturbed by the formation of a √3×√3-Ag2Bi Rashba-type surface alloy. Four spin-split surface states, with different band dispersions and energy contours, intercept and hybridize selectively with the sp-derived quantum well states of the Ag layer. 


Highly Anisotropic Dirac Cones in Epitaxial Graphene Modulated by an Island Superlattice

We present a new method to engineer the charge carrier mobility and its directional asymmetry in epitaxial graphene by using metal cluster superlattices self-assembled onto the moire´ pattern formed by graphene on Ir(111).Angle-resolved photoemission spectroscopy reveals threefold symmetry in the band structure associated with strong renormalization of the electron group velocity close to the Dirac point giving rise to highly anisotropic Dirac cones.

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Large Band Gap Opening between Graphene Dirac Cones Induced by Na Adsorption onto an Ir Superlattice

We investigate the effects of Na adsorption on the electronic structure of bare and Ir cluster superlattice-covered epitaxial graphene on Ir(111) using angle-resolved photoemission spectroscopy and scanning tunneling microscopy. 
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Probing the electronic transmission across a buried metal/metal interface

We monitored the sp-quantum-well states of Ag films on Pt(111) by angle-resolved photoemission in order to examine the electron transmission across the Ag/Pt interface. For thin layers up to 3.5 nm, the Ag states are characterized by broad quasiparticle peaks and a reversal of the parabolic curvature near the center of the surface Brillouin zone. Remarkable departures from the expected nearly-free-electronlike band dispersion persist in films of more than 14 nm thickness.

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Influence of the substrate bands on the sp-levels topology of Ag films on Ge(111)

Angle-resolved photoemission spectroscopy and first-principles calculations were employed to analyze unusual features in the electronic structure of ultrathin Ag films grown on Ge(111). The Ag sp-derived quantum well states exhibit hexagonal-like constant energy contours with different in-plane orientations near the center of the surface Brillouin zone, in striking contrast to the expectations for a free-standing Ag(111) layer.

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Evidence of graphene-like electronic signature in silicene nanoribbons           

We report on the electronic properties of straight, 1.6 nm wide, silicene nanoribbons on Ag(110), arranged in a one-dimensional grating with a pitch of 2 nm, whose high-resolution scanning tunneling microscopy images reveal a honeycomb geometry.

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Enhanced spin relaxation in an ultrathin metal film by the Rashba-type surface

We measured the magnetoconductance of bare and √3×√3-Bi/Ag-terminated ultrathin Ag(111) films by the micro-four-point probe method as a function of the applied magnetic field. he experimental curves were analyzed by introducing the results of photoemission investigation and band-structure calculations into the Hikami-Larkin-Nagaoka formula, in order to derive the characteristic fields of the two systems.
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Last Updated on Wednesday, 01 February 2017 13:17