Resonant Photoemission Spectroscopy/Diffraction

Electronic & Chemical & Magnetic Characterization (Electron spectroscopy)

Photoelectron Diffraction (PED) is a structural technique that probes the local atomic arrangement around a chemically selected emitter. On the other hand Resonant photoemission (RESPES) is a spectroscopic technique that provides insight into the contributions of different atomic species to the electronic states in the valence/conduction region, thus allowing to attribute a line component to one or another element in a complex system.

The combination of these two techniques can provide information not only on the electronic properties, but also on the order of the desired components. In addition, the resonance condition enhances the intensity of the specific spectral line thus permitting the measurement of full angular PED patterns also on spectral features that would be normally too faint for a reliable detection with respect to the background of secondary electrons. The latter specific advantage can be exploited not only to enhance the valence band signal, whose photoemission cross-section drops quickly at the photon energy (hence electron kinetic energy) required for an useful PED study, but also to enhance the Auger transitions at the corresponding ionization edge, as may be required in the case of a low coverage of the selected atomic species, or in the case of searching specific electronic effects.

At variance with conventional PED, the photoemission at the resonance of selected ionization thresholds cannot be performed with a standard X-ray lamp, and the fine tuning of the photon energy provided by a Synchrotron radiation source is necessary.

          provided at NFFA-Europe laboratories by:
          provided at Large Scale Facilities by:
XPD/RESPES/RESPED - BACH Beamline @ Elettra Synchrotron
Energy or angle dependent photoelectron diffraction, including resonant photoelectron diffraction
Elettra synchrotron, Apple II undulators; variable polarization (horizontal, vertical, circular ±); beam size on the sample 350x350 (HxV, µm2), vertical size can be reduced on request, flux on sample @10 µm slits (best resolution) (ph./s) 2x1012 - 6x1010; resolving power (E/ΔE): 20000 @44eV -5000 (@1650eV)
35/44 eV - 1650 eV
ScientaR3000 (2D detector with slit perpendicular to the scattering plane, electrons or Auger)
spectral <0.1 eV
x, y, z, θ
Many samples can be accommodated in a 30x30 mm2 area; sample size: 0.5 mm-28 mm; measurement: 40/50K- 500 K; preparation: 40/50K-1200 K
10-10 mbar, magnetic field in remanence, laser and electric field on request
Heating and cooling (ebeam, direct current, PBN), ion gun (VG), 4 evaporator ports (CF40), gas inlet valve (variable leak valve), diamond file scraper, cleaver, LEED (OciLEED); evaporators for organic molecules; e-beam evaporator (Omicron) for metals (evaporation at low sample temperatures is also possible); load lock
XAS in fluorescence and electron yield, ARPES
ARPES, XPD - PEARL Beamline @ Swiss Light Source Synchrotron
The PEARL (Photoemission and atomic resolution laboratory) beamline is dedicated to the structural characterisation of local bonding geometry of molecular adsorbates on metal or semiconductor surfaces, of nanostructured surfaces, and of surfaces of complex materials. It is a soft X-ray beamline with an angle-resolved photoelectron spectrometer for angle-scanned and photon energy-scanned X-ray photoelectron diffraction (XPD)
Bending magnet, linear horizontal, partial circular left/right, flux on sample at 1 keV: 2x1011ph/s, spot size: 170μm H x 73μm V, FWHM, 1mm x1mm
60 - 2000 eV
Scienta EW4000 detector
Up to 7000 at 400 eV (E/ΔE)
6-axis Carving manipulator
Temperatures down to 30K, heating to 650 K
In-situ sample preparation, cooling-heating, LEED, load-lock
STM at temperature of 4K
ResPES, PED @ ALOISA beamline
Aloisa is a spectroscopic beamline (XPS, XAS, ResonantXPS, PED) dedicated to Surface Science. Systems: single crystals, Self Assembled Monolayers, small molecule adsorbates (poly- and hetero-aromatics), ultra-thin films. Phenomena: on-surface synthesis and modification of molecular adsorbates, charge transfer at hybrid organic-inorganic interfaces, molecular orientation at surfaces.
Insertion Device: - 1.5 m phase shifting Undulator (constant gap): 21 x 7cm periods. - linear polarization. - fully integrated in the acquistion software suite. Monochromator: - type SX-700 (plane mirror-grating) with collimated beam (2x Paraboloidal Mirrors at 0.5˚ grazing incidence). - multiple working curves for optimization of flux, resolution, rejection of higher orders (depending on specific needs). - linear polarization. - fully integrated in the acquistion software suite. - VERY HIGH TRANSMISSION AT CARBON IONIZATION THRESHOLD (40-50%). - Flux at Sample: ~1x10^12 ph/sec from 200 to 1000 eV in working condition (Exit Slits = 20µm). - photon energy resolving power (E/DE): >5000 from 200 to 900 eV in working condition (10^12 ph/sec).
Monochromator energy range: 130-1500 eV. Undulator First Harmonic:130-450 eV at B.E. = 2.0GeV (140-550 eV at B.E. = 2.4GeV)
XAS: partial electron yield by means of a channeltron equipped with a polarizable grid for low energy secondary electrons rejection (NO drain current measurement available). Simultaneous measurement of drain current on refocussing mirror (i0) for flux normalization and absolute energy calibration at the C, N, O K-edge and Fe, Cr L-edge. XPS: homemade hemisperical analyzer (mean radius 66mm); 2xMCP + 2D-DelayLine detector for very high dynamical range (1 MHz); PED: fully rotatable analyzer with small detection angle (<2˚ FWHM); ResPES: undulator, monochromator, manipulator and analyzer movements fully integrated in the acquistion software suite. FULLY AUTOMATED ACQUISTION SOFTWARE (Labview suite).
XPS: - electron energy resolution: 1% Pass Energy (minimum 35 meV) - standard working conditions: 10-30 eV Pass Energy
MANIPULATOR: - fully motorized six-degrees of freedom with high resolution (<0.01˚ on three rotations; <0.01mm on three translations). - horizontally mounted (coaxial to the photon beam) for grazing incidence measurements. - rotations and translations fully integrated in the acquisition software suite for surface scanning (to prevent radiation damage). XAS: change of surface orientation with respect to polarization from Transverse Magnetic (p-pol) to Transverse Electric (s-pol) by sample rotation around the photon beam at constant grazing angle. XPS: standard XPS at grazing incidence (4˚) and normal emission for high signal yield; fully rotatable analyzer (zenithal angle: 0˚-100˚) for any surface azimuth (±95˚) and surface orientation w.r.t. polarization; analyzer rotation fully integrated in the acquisition software suite.
SOLID samples with polished surface (reflective) for sample alignment (phosphorum plat with TV camera at the end of experimental station for checking the reflected beam. Sample holders (POD) with on-board heating system (radiative or electron bombardment), LN2 cooling, two thermocouples. Sample size: max thickness 3 mm; max width 12-14 mm; min width 4 mm. Minimum temperature: 150 K Max temperature: 1050 K (flash). PID temperature control with programmable ramps. Real time XPS during heating from 150 to 650 K.
UHV experimental chamber (10^-11 mbar); UHV preparation chamber (10^-10 mbar). Praparation chamber in-line between exp. chamber and refocussing mirror (UHV must be recovered before measurements. Manipulator travelling forth and back between exp. and prep. chambers. Max partial pressure for gas dosing 10^-6 mbar. MBE cryovessel (H2O) with four slots for evaporators, shutters and microbalances. Homemade Knudsen cells (two crucibles, either BN or quartz) with inner thermocouple for organic molecules and low vapour tension matyerials (up to 600˚C). Omicron e-beam cells for metal evaporation.
RHEED. Microbalances integrated in the MBE system.
Standard UHV equipment for sample cleaning and ordering.
Dedicated software (freeware) for data analysis and fittings (XPS, NEXAFS, ResPES 2D maps) based on IgorPro platform.
XPS: photoelectron in the 50-1500 eV range
Photon beam transverse size at sample position (h x w): 30-50 µm x 150 µm.
Not allowed to Users.
Not allowed to Users.