# OVERVIEW

BACK

The DXAS beamline is an experimental station dedicated to dispersive x-ray absorption spectroscopy (acronym for DXAS) techniques, in the hard x-ray energy range (5 to 14 keV). The peculiarity of this beamline is the capability to collect absorption spectra over an extended range of photon energies without any mechanical movement of its optical elements. The DXAS is especially suited for detecting weak signals in XANES (X-ray Absorption Near-Edge Spectroscopy) and XMCD (X-ray Magnetic Circular Dichroism) experiments and for tracking time-dependent evolution of chemical reactions.

DXAS is installed on a 1.67T bending-magnet source, and it was opened to users in 2005. The beamline is comprised by the synchrotron light source, a vertically focusing bendable mirror, a bent crystal polychromator, and an area detector. The beam path over the optical elements starts when it hits the bendable mirror, used for vertical focusing as well as harmonic rejection. Then the light beam impinges onto a polychromator bent crystal at several different incident angles, resulting in a polychromatic beam after reflection. The reflected beam is selected with a specific bandwidth of hundreds of eV, and is horizontally focused at the sample position. The transmitted signal, after the sample position, reaches an area detector. The photon energy–direction correlation is transformed into an energy–position correlation along the horizontal axis of the detector.

The main features of the beam line are fast acquisition and stability.  A whole X-ray absorption spectrum is acquired in a single detector shot. Thus, it makes the technique especially useful for the study of fast processes. Due to the absence of movement of the optical elements during the data acquisition, the focused beam at the sample position is inherently stable.

The beamline has been used to support studies in the fields of materials science, solution chemistry, heterogeneous and homogeneous catalysis, electrochemistry, magnetism and geosciences.

# CONTACT & STAFF

Beamline Phone Number: +55 19 3512 1141

Coordinator: Gustavo de Medeiros Azevedo
Number: +55 19 3518 3192
E-mail: gustavo.azevedo@lnls.br

# EXPERIMENTAL TECHNIQUES

The following experimental techniques and setups are available to users in this beamline. To learn more about the techniques’ limitations and requirements (sample, environment, etc.) contact the beamline coordinator before submitting your proposal.

###### X-RAY ABSORPTION SPECTROSCOPY (XAS)

X-ray absorption spectroscopy (XAS) is a widely used technique for determining the local geometric on the atomic scale and/or electronic structure of matter. It provides information about a selected element in a material and is very effective for establishing structure-property relationships in any kind of materials.

Setup: Time-resolved XAS measurements in transmission mode

This setup is optimised for time-resolved measurements in transmission mode of homogeneous samples. The high penetration of hard X-rays allows working with a wide variety of sample environments (with gas, liquid, pressure…) in order to perform in situ and even operando time-resolved experiments that are crucial to better understand materials. Only transmission measurements are available on the DXAS beamline and the sample environment must fit within this restriction. Depending of the sample and sample environments, milliseconds time resolution is available.

###### X-RAY MAGNETIC CIRCULAR DICHROISM (XMCD)

X-ray magnetic circular dichroism (XMCD) technique is used to determine the element, orbital and spin magnetic properties of a material as a function of the environmental condition of the sample (temperature, pressure, applied field).

Setup: XMCD in transmission mode

This setup is optimised for transmission detection of XMCD signal, where the sample is between the pole pieces of a electromagnet with field up to 1 T and inside a cryostat allowing temperatures in the range of 20 to 300 K. High pressure anvil cell can also be employed for pressures up to 50 GPa.

Setup: XMCD in reflectivity mode

This setup is optimised for detection of the dichroic signal at the reflectivity of the x-rays from thin film samples, where the sample is between the pole pieces of an electromagnet with field up to 1 T.

# LAYOUT & OPTICAL ELEMENTS

ElementTypePosition[m]Description
SourceBending magnet0.00Bending Magnet D06 exit A (4°), 1.67 T, 750 $\mu \rm m$ x 168 $\mu \rm m$
MirrorVertical focusing mirror6.50800 mm long Rh coated
CrystalCrystal polychromator9.75Water-cooled Si(111)

# PARAMETERS

ParameterValueCondition
Energy range [keV]5 - 14Si(111)
Energy resolution [$\Delta$E/E]$13.1 \times 10^{-5}$Si(111)
Energy band-pass [eV]Hundreds of eV-
Beam size at sample [$\mu \rm m^2$, FWHM]150 x 200at 8 keV
Photon flux at sample [ph/s]$2 \times 10^{11}$at 8 keV

# INSTRUMENTATION

InstrumentTypeModelSpecificationsManufacturer
DetectorArea detectorPylon2048F-Princeton Instruments
FurnaceCapillary, provide attachments to gas lines-Max. temp.: 1000°C Max. heating ramp: 20°C/min Quartz capillary inner/outer diameters [mm]: 0.8/1.0; 1.0/1.2 and 2.0/2.4LNLS in-house development
FurnaceTubular, provide attachments to gas lines-Max. temp.: 1000°C Max. heating ramp: 20°C/min Pellet sample with a diameter of 13 or 6 mmLNLS in-house development
Mass flow controllers--Gas flow [mL.$\rm{min}^{-1}$]: 0.2 - 750BROOKS
Gas cylinders--Pure gases: Ar, He, N2, synthetic air Gas mixture (% diluted in He): CO (20%), O2 (5 and 40%), H2 (5%), CO (5%), NO (5%), CH4 (20%), C3H8 (20%), C4H10 (30%), C2H4 (3%), C3H6 (5%), H2S (5%)-
Thermoregulated bath-TE2005Down to -10°C and up to 80°C. Control accuracy of 0.1°CTecnal
Mass spectrometerGas analysis systemOmniStarTungsten (standard) filament. Mass range 1-100 amu. Gas flow rate 1-2 sccm. Qualitative and quantitative gas analysisPfeiffer Vacuum
Liquid cell--Optic path length [mm]: 0.3 – 7.5LNLS in-house development
Potentiostats/Galvanostats-N series 273A-Autolab EG&G
Diffractometer4 circle424-511.1For sample alignment ($\theta$, $2\theta$, $\phi$, $\chi$) = 0.001°Huber
Electromagnetic coilsMagnetic field-Up to 1.5 TLNLS in-house development
Rotary permanent magnetMagnetic field-Up to 0.9 TMagnetic Solutions
Voltage/Current power source-BOP-GL 1KW4 quadrant bipolar power supply. ($0 \rm to \pm 50 \rm V_{dc}$) ($0 \rm to \pm 20 \rm A_{dc}$)Kepco
Picoammeter-6485-Keithley
Cryostats--Down to 15 K and up to 420 KARS
High-pressure cellHigh-pressure Diamond anvil cellMembrane and screw drivenUp to 80 GpaLNLS in-house development, Syntek, Princeton

# 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 the SOL group. MEDM (Motif Editor and Display Manager) and Python are 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.

It is recommended that the proposer contact the beamline staff to obtain any information required for preparing their proposal prior to submission and for preparing for beamtime. For time-resolved XAS studies, please contact Amélie Rochet (amelie.rochet@lnls.br), for XMCD studies, please contact Narcizo M. Souza Neto (narcizo.souza@lnls.br).

# HOW TO CITE THIS BEAMLINE

Users are required to acknowledge the use of LNLS facilities in any publications and to inform the Laboratory about any publications, thesis and other published materials. Users must also cooperate by supplying this information upon request.

Support text for acknowledgements:

This research used resources of the Brazilian Synchrotron Light Laboratory (LNLS), an open national facility operated by the Brazilian Centre for Research in Energy and Materials (CNPEM) for the Brazilian Ministry for Science, Technology, Innovations and Communications (MCTIC). The _ _ _ beamline staff is acknowledged for the assistance during the experiments.

Additionally, in publications related to this facility, please cite the following publication.

CEZAR, J. C., SOUZA-NETO, N. M., PIAMONTEZE, C., TAMURA, E., GARCIA, F., CARVALHO, E. J., NEUESCHWANDER, R. T., RAMOS, A. Y., TOLENTINO, H. C. N., CANEIRO, A., MASSA, N. E., MARTINEZ-LOPE, M. J., ALONSO, J. A. & ITIE, J.-P.. Energy-dispersive X-ray absorption spectroscopy at LNLS: investigation on strongly correlated metal oxides. J. Synchrotron Rad. 17, 93-102 (2010). doi:10.1107/S0909049509041119.

An energy-dispersive X-ray absorption spectroscopy beamline mainly dedicated to X-ray magnetic circular dichroism (XMCD) and material science under extreme conditions has been implemented in a bending-magnet port at the Brazilian Synchrotron Light Laboratory. Here the beamline technical characteristics are described, including the most important aspects of the mechanics, optical elements and detection set-up. The beamline performance is then illustrated through two case studies on strongly correlated transition metal oxides: an XMCD insight into the modifications of the magnetic properties of Cr-doped manganites and the structural deformation in nickel perovskites under high applied pressure.

# PUBLICATIONS

Scientific publications produced with data obtained at the facilities of this beamline, and published in journals indexed by the Web of Science, are listed below.

Attention Users: Given the importance of the previous scientific results to the overall proposal evaluation process, users are strongly advised to check and update their publication record both at the SAU Online website and at the For the library, updates can be made by sending the full bibliographic data to the CNPEM library (biblioteca@cnpem.br). Publications are included in the database after being checked by the CNPEM librarians and the beamline coordinators.

MORE PUBLICATIONS

DXAS

Zito, C. A.; Perfecto, T. M.; Volanti, D. P.. Porous CeO2 nanospheres for a room temperature triethylamine sensor under high humidity conditions, New Journal of Chemistry, v. 42, n. 19, p. 15954-15961, 2018. DOI: 10.1039/c8nj03300e

DXAS

Braga, A. H.; Ribeiro, M. C. C.; Noronha, F. B.; Galante, D.; Bueno, J. M. C.; Santos, J. B. O.. Effects of Co Addition to Supported Ni Catalysts on Hydrogen Production from Oxidative Steam Reforming of Ethanol, Energy & Fuels, v. 32, n. 12, p. 12814-12825, 2018. DOI: 10.1021/acs.energyfuels.8b02727

DXAS

Gonçalves, A. M.; Garcia, F.; Lee, H. K.; Smith, A.; Soledade, P. R.; Passos, C. A. C.; Costa, M.; Souza Neto, N. M.; Krivorotov, I. N.; Sampaio, L. C.; Barsukov, I.. Oscillatory interlayer coupling in spin Hall systems, Scientific Reports, v. 8, p. 2318, 2018. DOI: 10.1038/s41598-018-20685-7

DXAS

Chialanza, M. R.; Keuchkerian, R.; Gonçalves, T. S.; de Camargo, A. S. S.; Fornaro, L.. The effect of cation modifier on improving the luminescent properties of borate glasses doped with Yb3+ and Er3+, Journal of Non-Crystalline Solids, v. 483, p. 79-85, 2018. DOI: 10.1016/j.jnoncrysol.2018.01.002

DXAS

Guo, J.; Chen, R.; Zhu, F.-C.; Sun, S.-G.; Villullas, H. M.. New understandings of ethanol oxidation reaction mechanism on Pd/C and Pd2Ru/C catalysts in alkaline direct ethanol fuel cells, Applied Catalysis B-Environmental, v. 224, p. 602-611, 2018. DOI: 10.1016/j.apcatb.2017.10.037

DXAS

Perfecto, T. M.; Zito, C. A.; Mazon, T.; Volanti, D. P.. Flexible room-temperature volatile organic compound sensors based on reduced graphene oxide-WO3 center dot 0.33H(2)O nano-needles, Journal of Materials Chemistry C, v. 6, n. 11, p. 2822-2829, 2018. DOI: 10.1039/c8tc00324f

MORE PUBLICATIONS