Beamline Description

The availability of high brightness synchrotron radiation sources has led to the development of spectromicroscopy techniques which involve well-established spectroscopies that make use of x-rays and the high spatial resolution - below 1 micron - afforded by modern synchrotron radiation optical systems.
The beamline houses unique microscope designed for studies of the local band structure of materials. A low photon energy beam (below 100 eV) is focused into a submicrometre spot and electrons arising from the photoemission process are collected and analyzed in terms of their angular and energy distributions (ARPES). Thanks to the beam focusing the photoelectron spectrum is acquired as a function of its origin on a sample surface coordinate system.
The final focusing is obtained by multilayer coated optics of Schwarzschild objectives. The use of multilayers required for high reflectivity at a certain wavelength restricts the photon energy range available after the monochromator (20-200 eV) to specific narrow lines. Currently the beamline is equipped with two Schwarzschild objectives designed for 27 and 74 eV of photon energy.  
The ARPES is then performed by means of internal movable electron energy analyzer mounted on precision two axes goniometer setup. The sample can be measured in the temperature range of 40-470K and the sample focusing and imaging are performed thanks to the XYZR scanning stage on which the sample manipulator is mounted.

Insertion device

The radiation source of the Spectromicroscopy beamline is the U12.5 undulator mounted at the 3.2 section of ELETTRA. Its main parameters at 2.0 GeV/400 mA operation are as follows:

Period 125 mm
B0, max 0.506 T
K max 5.92
N perios 36 (in three sections)
P tot max 1.2 kW
Tunable energy range 17-750 eV

Monochromator and beamline optics

The SpectroMicroscopy beamline comprises the monochromator and the microscope joined at the pinhole "P". The source is the U12.5 undulator mounted at the 3.2 section of ELETTRA and shared with the VUV Photoemission beamline. The beamline is based on a variable angle spherical grating monochromator with  gratings optimized for photon energies engaged. The monochromator uses a variable included angle in the diffraction process by the simultaneous rotation of a spherical grating (SG) and a plane mirror (PM) in front of it, defining a (virtual) movable entrance slit (Padmore design). A set of three gratings covers the energy range of 20-310 eV: 20-62 eV (grating 1), 60-155 eV (grating 2), and 125-310 eV (grating 3).

Besides the monochromatisation action, the beamline performs a predemagnification of the X-rays by forming an intermediate focused image of the source at a pinhole "P" placed at the beginning of the microscope section of the beamline (size = 13 µm H x 9 µm V) by means of a pair of focusing (HFM and VFM) and refocusing (HRM and VRM) mirrors placed before and after the monochromator.

Measurement station

The scheme of the experimental chamber is the following:

Nanospot for microscopy

The measurement station hosts a microscope which is based on a Schwarzschild Objective. Such a device consists of two spherical mirrors which demagnify the beamline focus to a submicron spot onto the sample. High reflectivity of the Schwarzschild Objective is obtained by using periodic multilayer coating. Two objectives are available which operate at photon energies of 27eV and 74eV. The smallest achievable spot size is currently 0.5 µm FWHM.

Photoemission detection

The photoelectrons emitted from the sample are detected by angle-resolved hemispherical electron analyser installed on two-axis goniometer.

Mean radius: 40 mm
Working distance: 15 mm
Entrance slit: 0.5 x 12 mm2
Energy resolution: 12.5 meV
Energy‐dispersive multichannel detection for spectroimaging
Acceptance angle: 16 degrees
Angular modes of operation:
AP or angle to point dispersive modes with 0.37- 2 mm/degree dispersions
Detector: 2D delay line with working area 20x20 mm2

Sample scanning

Scanning stage with three linear axes and rotation around vertical axis
Travel range: 25x25x15 mm
Precision: 100 nm in close loop operation
Accelerations: up to 5 mm sec-2 (20 msec per 500 nm step, 28 msec per 1 μm step)
Ultimate speeds: up to 280 µm sec-1
The sample can be cooled down via copper braid attached to the flow cryostat down to 20 K and warmed up to 450 K.

Last Updated on Friday, 20 January 2012 10:45