VUV photoemission beamline description

The beamline

Insertion device

The VUV has been designed primarily for surface and solid state experiments involving high resolution photoemission. The light source is an undulator with a range of 20 to 750 eV, while the minimum energy at a ring energy of 2.4 GeV is about 25 eV. The undulator for the VUV beamline consists of 36 periods, divided in three sections. With minimum gap (K=5.3) the high energy part of the spectrum is like that of a wiggler, i.e. continuous and fairly smooth. The light available here has reduced brightness and a lower degree of polarisation compared with an undulator.


Between 100 and 900 eV, the measured flux on the sample varies from 1.4 x 1013 to 5 x 1010 photons/sec/0.1%bw/200mA, in a spot of maximum size 0.5 mm. Test experiments at a second generation light source and on this beamline indicated at least two orders of magnitude higher count rates at higher resolution.
The monochromator is provided with baffles to reduce stray light and filters will be installed to reduce higher order radiation. Measurements of the higher order contribution are in progress and indicate that the contamination is a few %.


The beamline is controlled by the Beamline Control System (BCS) except for the monochromator (including the entrance optics and the exit slit position) which is under the experimental station software control.  


The Kirkpatrick-Baez entrance optics focus the light after which it enters the entrance slit of the monochromator. The monochromator is a Spherical Grating Monochromator with five interchangeable gratings and pre- and post-focusing optics. The set of five gratings provides a resolving power of 10,000 over the whole energetic range. The light emerges from the movable exit slit and is then refocused by a post-focusing mirror onto the sample. For lower photon energies (< ca.130 eV), the angle of deflection of the light at the grating is increased from 7° to 20° by means of an additional pair of plane mirrors, one of which is fixed and the other removable.

The resolution has been measured using gas phase absorption at a number of energies. The resolving power is estimated to be as follows:

Threshold Energy(eV)

Resolving power
He double ionization
Argon L2,3 (244.4) 
Nitrogen K(400.9) 
Ne K(867.1)

All spectra were taken using the first order of diffraction and the appropriate harmonic of the undulator. The accuracy with which the resolution can be determined is limited by the natural widths of the absorption lines because, except for He, the lines are much broader than the resolution.


Two of evaporation sources can be replaced without venting the preparation chamber as they are mounted on an independently pumped section. Another three are mounted directly to the chamber. The minimum distance to an independently pumped source is about 25 cm. Moreover an Omicron triple evaporator is mounted directly to the chamber, with the minimum distance from the source to the sample about 15 cm. 
Note that to change a directly mounted source (Omicron source included) we need to vent and then to bake the chamber which will require about 2 days.
There is a possibility to grow wedges (ask your local contact for more details).

Resistively heated source

Omicron source 

Samples and sample holders

The samples must be conductive.
The dimensions are usually from 0.3 to 1.0 cm.

We use sample mounting on Ta or Cu sample holder plates.

Detailed sample holder dimensions (in mm)
images/Documents/VUV/portacampioni 2.PDF


Preparation chamber

 The base pressure of the preparation chambe is 2·10-10 mbar. The horizontal manipulator has five degrees of freedom (there is no azimuthal rotation anymore), allowing the sample preparation, LEED analysis and photoemission measurements. The sample can be cooled down to 77K and heated up to 500K. Sputtering facility as well as LEED optics are available in the preparation chamber; there are also gas dosing facilities and sources for overlayer deposition.
The manipulator can host one sample only. 

Please note that we can not allow pressures higher than 5·10-6 mbar of Ar in the preparation chamber.

Heating station

The load lock was modified in an independently baked chamber, destinated for the high temperature annealing.

  • In case no high temperature/pressure treatment is required (load lock mode) the chamber can house up to 3 samples.
  • High pressures - up to 10+2 mbar of oxygen - were successfully tested together with direct current annealing (up to 500°C). In this case the chamber can house one sample only.
  • The high temperature annealing allows to heat the sample above 2000°C by electron bombardement. In this case the chamber can house one sample only.

Changing a sample which does not require high temperature annealing and/or low pressures can be done within 3-4 hours, in another case it will take about 12 hours, since the heating station need to be baked.
The chamber normally has gas dosing facilities and magnetizing coil. There is a possibility to have the sample parking.

Measurement chamber

The main chamber operates in 10-11 mbar regime. It is equipped with vertical a 5 degree of freedom manipulator. The lowest temperature range is 9K for the fixed stage and 13K for rotatable stage. The azimuthal angle motion of rotatable stage is motorized and allows to acquire automatically Fermi surfaces with angle step less than 0.01° with angular range ±160°. The polar angle can span 100° and has 0.1° resolution.  Read more...

Fermi surface measurements are performed by Labview 10.0 and analyzed by Wavemetrics Igor 6.2 procedures. Read more...

The electron analyser is a Scienta R4000-WAL with variable acceptance angle (7-30 degrees). It is mounted at 45° to the beam direction. Read more... 

Please note that we can not allow pressures higher than 10-9 mbar while measuring.

New manipulator

In 2015 we installed and tested a new manipulator with liquid Helium closed-cycle cryostat.

The stage (Vab Vacuum) allows linear motion along the X, Y, and Z axes and polar rotation (360°) with 0.2° accuracy.

The closed-cycle cryostat, provided by ARSCryo, works in the temperature range 9-450K. There is no He consumption (the autonomy of the compressor is 12000 hours). 

Azimuthal rotation (±160°) is performed with 0.01° accuracy through piezoelectric rotary stage (AttoCube ANR24rotary stepper positioner).  




Fermi surface measurements

The way to study Fermi surface which we use at the VUV beamline is the azimuthal rotation, when by changing the azimuthal angle one changes together kx and ky. It is illustrated below.


Last Updated on Tuesday, 12 May 2020 07:18