DESCRIPTION

BL29 is a soft X-ray beamline dedicated to polarization-dependent spectroscopic investigations of advanced materials of fundamental as well as applied interest. 

  • Experiments performed at BL29 usually involve magnetic materials composed of 3d metals and rare earths, magnetic or superconducting oxides, semiconductors, Silicon and Carbon based materials such as Graphene or organic molecules, ferro-electric, piezo-electric or multiferroic materials.
  • Samples studied are typically in bulk, thin film, multilayered, powder or nanostructured form.
  • Experiments at BL29 are generally relevant at a fundamental and/or applied level for novel micro- and nano-technology devices in fields like spintronics, photonics, sensors, actuators or information storage. In views of the available instrumentation combined with the beamline large photon energy range and polarization control, studies on other materials such as polymers, 2D materials, topological insulators, novel superconductors, etc, are possible and potentially of interest. 
IM-BOREAS_beamline

 BOREAS beamline advanced instrumentation and X-ray optical design make possible soft X-ray (magnetic) circular and linear dichroism (XMCD/XMLD) measurements and other related characterization techniques at the frontier of materials science studies and X-Ray Science.  An X-ray absorption spectra  can be acquired routinely in 2-3 min with high accuracy and repeatability (typically 100-200 eV wide with <0.05 eV step). The beamline allows the full control of X-ray polarization, enabling working modes with adjustment of a partial degree of circular polarization and arbitrary inclination of the X-ray linear polarization. You can see here a presentation with some further details on the beamline instrumentation

ENDSTATIONS 

The beamline is equipped with two state-of-the-art end-stations:

  • High-field vector magnet (HECTOR) for Soft X-ray absorption Spectroscopy and Dichroism techniques such as NEXAFS, XMCD or XMLD
  • UHV reflectometer (MARES) for scattering and reflection approaches including resonant soft X-ray reflectivity, resonant magnetic scattering and GISAXS.

to be updated with better photo by pierlu 

X-ray Absorption Spectroscopy and magnetic circular dichroism endstation (Hector)

HECTOR Station The dichroism end-station consists of a UHV-compatible cryomagnet(Scientific Magnetics Ltd). The samples are in a UHV environment with a base pressure of the order of <1x10-10 mbar, and mount on a sample holder attached to the cold finger of a variable temperature cryostat (3 K - 350 K). The sample insert is electrically insulated in order to perform drain current measurements. Four additional electrical contacts are provided on the sample holder for 4-probe measurements.

The magnet consists on a set of three orthogonal superconducting split-coils allowing maximum fields of up to 6 T in the horizontal plane along the beam direction, with a sweep rate of 2 T/minute, and 2 T in the horizontal plane perpendicular to the X-ray beam and in the vertical plane, with a sweep rate of 0.6 T/minute. Simultaneous operation of the three coils will allow you to cover a sphere of 2 T, with a sweep rate of 0.4 T/minute. 

The system is equipped with a 3-chamber sample preparation/insertion set-up for fast sample exchange, enabling to load up to 4 samples at a time. The preparation chamber below the the magnet is equipped with standard surface preparation tools: a cleaver, a scraper, MBE-evaporators for metals and organic molecules, an e-beam heating stage and an ion sputtering gun. 

Magnetic Resonant Scattering End Station (MaReS)

The scattering endstation is a complex multicomponent instrument based on a double UHV rotary feedthrough (sample and detector circles), a multi-axis cryomanipulator,  a 2 Tesla UHV magnet on a third independent rotary feedthrough, and two detector arms with diodes, channeltron and a custom CCD, all mounted on a highly stable granite support.

IM-BOREAS_Mares1  

An Interstation UHV-Sample Transfer System  (rack&pinion) connects both endstations and also allows transfer from a surface preparation off-line chamber and a travelling UHV Sample-Suitcase.  Find further information on the docs&drawings tab.

 

TECHNICAL SPECIFICATIONS

Photon energy range   80 eV to > 4000 eV
Photon flux at the sample 
(at a resolving power of >7000
and for 100 mA current)
1012 photons/s @ 150-1000 eV
>1011 photons/s @ 1000-2000 eV
1x109 -1x1010 photons/s @ 2000 - 4000 eV
Maximum resolving power >10000 for 80 eV < E < 1500 eV
<5000 for 1500 - 4000 eV
Beam size at the sample variable between < 100 (H)x80(V) micron2 and >1x1 mm2

BL29 state-of-the art beamline optics and elliptical undulator source offers a high flux, high energy resolution, and full polarization control on an extended soft X-ray regime of 80 to 4000 eV. The beam size at sample can be adjusted from approx. < 100x100 um to 1x1 mm thanks to its vertical and horizontal refocusing mirror system with adjustable in-situ mirror benders.

The beamline is optimized to provide the highest photon flux and energy resolution in the range between 150 eV and 2000 eV. However, the monochromator and undulator allow us to reach a lower energy level down to 80 eV in circular polarization, thus covering the Si L edges. Above 2000 eV, the optics of the beamline have a reduced performance when compared to typical hard X-ray beamlines, but the flux and energy resolution has been demonstrated to be high enough to be able to perform X-ray absorption experiments at important edges (L edges of all the 4d metals, etc).

GRATING MIRROR COMBINATIONS

80 – 300 (800)  eV SM1+LEG
250 – 600 (1400) eV  SM2+LEG
380 – 1700   eV SM1+MEG
950 – 3000  eV SM2+MEG
600 – 2100 eV SM1+HEG
1900 – 4500 eV SM2+HEG

Shown below are some plots of the typical beamline photon flux using the different gratings and mirror combinations available at the beamline, and for the various polarizations of the EPU. Flux values are estimated from intensity measurements made using an AUXV100G diode downstream at the location of the last beamline optical component.

In the measurements, the accumulated storage ring current was around 100 mA, and nominal slit settings were used, i.e. 15 micron opening for the vertical entrance (VES) and exit slits (VXS). Resolving power is about 7,500-10,000 with VES/VXS=15/15 micron slits. Higher resolving power, approx 15,000 or greater, can be attained for more extreme exit slit settings, such as 15/5 micron slit settings, whereas intensities are almost linear on the vertical exit slit opening (vertical beam FWHM at the entrance slit is estimated to be typically within 5.5-7.5 micron range). A number of combinations, including choices between Gold or Nickel or Silicon (uncoated) stripes on the first plane mirror, slits, etc...can result in slightly different numbers, but these values are representative.

BOREAS Photon Flux  IM-BOREAS_Flux2

 

SOURCE

The light source is an APPLE II undulator, placed in one of the medium straight sections of the ALBA storage ring.

Parameters

Material  Sm5Co17 Pure Permanent Magnet 
Period 71 mm
Number of periods 22
K at minimum gap 6.19
Source size (FWHM) 133 x 14 µm2 (@ 700eV)
Source div. (FWHM) 52 x 24 µrad2 (@ 700eV)

 

OPTICS LAYOUT

In the figure below, a schematic layout of the optical components of the BOREAS beamline is shown, both from above and side view. A detailed description of the functionality of the various optical elements is given in the Conceptual Design Report of the XMCD beamline.

BOREAS Optics   BOREAS Layout

In brief, the beamline consists of three sections:

1) the first section is composed of the plane and toroidal mirrors (PM and TM, respectively). Their function is to absorb most of the heat load delivered from the source and to prepare the beam for the monochromator by focusing it in the vertical plane (which is the dispersive plane of the monochromator) at the entrance slit (and, in the horizontal plane, 2 m upstream at the exit slit);

2) the second section consists of the monochromator: this is based on variable line spacing (VLS) plane gratings (PGs), working at a fixed included angle (175° in combination with the spherical mirror SM1 or 177° in combination with the spherical mirror SM2). The monochromator is equipped with both entrance and exit slits and is dispersing in the vertical plane;

3) the third section comprises the refocusing optics, consisting of two bendable mirrors arranged in a Kirkpatrick-Baez geometry, where the first mirror (PE1) is vertically focusing, while the second mirror (PE2) is horizontally focusing. This system allows you to focus the beam at either of the two experimental stations.