# OVERVIEW

BACK

The XAFS2 beamline is an experimental station dedicated to X-ray Absorption Spectroscopy in the hard x-rays energy range (3.5 to 17.0 keV). It focus on the study of the atomic-level structure as well as in the electronic and magnetic properties of matter, with applications in a wide range of scientific fields, such as atomic and molecular physics, chemistry, biology, environmental and geosciences and cultural heritage. Experimental techniques available include Fluorescence Spectroscopy, X-ray Excited Optical Luminescence, X-ray Reflectivity and Combined X-ray Absorption Fine Structure and X-Ray Diffraction.

The XAFS2 is a general-purpose X-ray absorption beamline. Since the completion of the commissioning works in 2007, a large number of users have been using this experimental facility in order to perform several kinds of experiments in different scientific areas. After approximately 7 years in operation this beamline has been substantially updated in order to improve its experimental possibilities. A 4-circle Huber diffractometer has been recently incorporated to perform combined experiments. This equipment collects XRD patterns with the XAFS.

Through the development of a new sample environment, it is now also possible to perform these measurements in situ/operando conditions. Other upgrades include a complete remodeling of the beamline software and its control system. The control system of the beamline has been renovated by the installation of a PXI. The PXI is from National Instruments (PXI-NI) and communicates with Galil/Parker controllers on an EPICS platform. Some parts of the motors were changed in order to improve performance with the upgrade and there were also important changes to the control hardware. The Windows operational system was replaced with Red Hat Linux and the 3-WinDCM control system with EPICS. Furthermore, a new python based script (Py4Syn) was added. This provides high-level abstraction for device manipulation, scan routines, real-time plots and more. This package was created with the aim of providing a simple yet powerful tool to allow scientists and users to develop their own scripts for data acquisition. For user-friendly interface builds a Control System Studio (CS-Studio) is used. The next step with the XAFS2 upgrade, namely, towards a high-throughput XAFS beamline, will involve testing the viability of performing QEXAFS.

## CONTACT

Beamline Email: xafs2@lnls.br

Beamline Telephone Number: +55 19 3512 1246

Coordinator: Santiago J. A. Figueroa

Coordinator Email: santiago.figueroa@lnls.br

Coordinator Telephone Number: +55 19 3517 5063

For more information on the Beamline Team, check out the Beamline Team’s page here

# OPTICAL ELEMENTS

ElementTypePosition[m]Description
SourceBending Magnet0.0Bending Magnet D08 exit B (15°)
$1^{\rm st}$ cooled-slit systemTwo cooled UHV slit systems - vertically and horizontally - based on four independent mechanical feedthroughs, each one supporting at its ends a Ta blade mounted on a copper block.8.0Defines the lateral and vertical dimensions of the polychromatic beam impinging on the first mirror
$1^{\rm st}$ mirrorRh-coated cylindrical vertical collimating mirror with a ~3mrad grazing incidence angle9.2Collimate vertically the white radiation and sends a parallel synchrotron beam onto the two flat Si(111) Double Crystal Monochromator (DCM)
Double Crystal Monochromator (DCM)Flat Si(111) Double Crystal Monochromator10.5The DCM has fixed exit geometry and is the only optical element with thermal stabilization (i.e. water cooled).
$2^{\rm nd}$ slit systemTwo UHV slit systems - vertically and horizontally - based on four independent mechanical feedthroughs, each one supporting at its ends a Ta blade mounted on a copper block.11.6Without refrigeration, these slits are used to eliminate the spurious background radiation.
$2^{\rm nd}$ mirrorRh-coated toroidal bendable mirror12.8It refocuses vertically and horizontally the monochromatic beam of approximately $450 \mu \rm m$ in diameter at the sample position

# PARAMETERS

ParameterValueObs. | Condition
Energy range [keV]3.5 - 17.0Si(111)
Energy resolution [$\Delta$E/E]$1.7 \times 10^{-4}$at 7 keV
Beam size [$\mu \rm m^2$, FWHM]450 x 250at sample position
Flux density at sample [ph/s/$\rm mm^2$]$2.78 \times 10^{9}$ photons/s at 7 keV and 100mAMeasured with a photodiode 100% efficient
Harmonic Content< $3.94 \times 10^{-5}$at 7.5 keV

# INSTRUMENTATION

InstrumentTypeModelSpecificationsManufacturer
DetectorIon Chamber-Two electrodes in a distance of 14 mm. Length of 137 mm, 221 mm and 381 mm. A $25 \mu \rm m$ kapton window with a in/out area of 12 x 30 $\rm mm^2$LNLS in-house development
Detector15-element Germanium Solid State Detector (SSD)G-15 SSDHigh counting rate capability - 300.000cts/s. Si detector total active area - 750 $\rm mm^2$. Element sensitive thickness - 5 mm. $\rm N_2$ liquid cooled.Canberra
DetectorElectron Detector-Collector electrode (He medium) in an electric field produced by a 60V battery. The output is a signal amplification of about two orders of magnitudeLNLS in-house development
DetectorPhotomultiplierModel R928Side-on; V = -1200 V. It output is in current mode.Hamamatsu
DetectorSpectrometerUSB2000+covers the 200-1100 nm range and connects to light sources, optical fibers and other accessoriesOcean Optics
FurnaceTransmission/ FluorescenceCapilarMax Temp.: 900 C, Temp Rate: 10C/s. E5CK-T Ramp/Soak Process Controller-Omron. Sample holder for capillars (ID 0.8 mm/ OD 1mm) (ID 1 mm/ OD 1.2 mm) (ID 2 mm/ OD 2.2 mm)LNLS in-house development
FurnaceTransmissionTubularMax Temp.: 1100 C, Temp Rate: 10C/s. E5CK-T Ramp/Soak Process Controller-Omron. Sample holders of 8 mm and 4 mm diametersLNLS in-house development
Diffractometer4-circle424-511.1Resolution ($\theta$, $2\theta$, $\phi$, $\chi$) = 0.001°Huber
Mass spectrometerGas Analysis SystemOmniStar QMS 200Tungsten (standard) filament. Mass range 1-100 amu. Gas flow rate 1-2 sccm. Qualitative and quantitative gas analysis.Pfeiffer Vacuum
CryostatCryogen free and top loading sample in helium, fast sample change.Omniplex: CS204*F-FMX-19OPHigh cooling power and fast cooldown. 4 K cold head (0.2 W at 4.2 K). 180° Kapton window for x-ray fluorescence detection modeARS
Cryostat for cryo-XEOLCooling power He closed cycle cryocoolerDE-202 Cryocooler series$T_min = 15 K$

# CONTROL AND DATA ACQUISITION

All beamline controls are done through EPICS (Experimental Physics and Industrial Control System), running on a PXI from National Instruments. The data acquisition is done using a Red Hat workstation with the Py4Syn, developed at LNLS by SOL group. CSS (Control System Studio) is used as a graphical interface to display and control the beamline devices.

# APPLYING FOR BEAMTIME

Submission calls are usually announced twice per year, one for each semester. All the academic research proposals must be submitted electronically through the SAU Online portal. Learn more about how to submit a proposal here.