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Ipê Beamline

The IPÊ (Inelastic scattering and PhotoElectron spectroscopy) beamline is dedicated to high resolution resonant Inelastic X-ray scattering (RIXS), X-ray absorption spectroscopy (XAS) and X-ray Photoelectron spectroscopy (XPS) in the soft X-ray range (100 – 2000 eV). These complimentary tools allow characterization of the chemical composition, electronic structure, and elementary excitations in matter in the solid, liquid or gas state.

Analysis of XAS and XPS using soft X-rays allow, quantitative determination of chemical composition of the near surface region of solid samples, which is a crucial information to several areas from thin films and electronics to catalysis and agriculture. XPS and XAS are also important to determine the electronic structure of materials. While XPS probes the occupied states of the core and valence electrons, XAS measure the unoccupied states projected on the absorbing atom. RIXS goes one step further in the understanding of the properties of materials by directly probing the spectrum and dispersion of intrinsic excitations, such as excitons and phonons, which determine several materials´ properties, such as magnetism, electronic conductivity, thermal conductivity, polarizability, among others. This broad view of the electronic structure and excitations provided by IPÊ can be used to fine tune (or refute) theoretical models widely used nowadays in computer simulations that assist not only the understanding of materials properties but also guide the design of new materials with tailored functionalities.

The optics of IPÊ was specifically designed to exploit the fully diffraction limited soft X-ray source at the Sirius storage ring delivering very high resolving power (60.000) and small spot sizes (< 1 μm) required for high resolution experiments. A plane mirror to deflect the X-ray beam into two branches allows the installation of two endstations permanently connected to the beamline. One of these endstations is dedicated to RIXS and the other to XPS, while both can perform XAS measurements.

CONTACT & STAFF

Facility E-mail: ipe@lnls.br

Coordination: Tulio C. R. Rocha
Tel.: +55 19 3512 1292
E-mail: tulio.rocha@lnls.br

Click here  for more information on this Facility team.

EXPERIMENTAL TECHNIQUES

X-RAY PHOTOELECTRON SPECTROSCOPY

X-ray photoelectron spectroscopy (XPS) is a surface-sensitive quantitative spectroscopic technique based on the photoelectric effect that can identify the elements that exist within a material (elemental composition) or are covering its surface, as well as their chemical state, and the overall electronic structure and density of the electronic states in the material. XPS is a powerful measurement technique because it not only shows what elements are present, but also what other elements they are bonded to. Although largely performed using conventional X-ray sources, the use of synchrotron light extends its analytical capabilities. The high photon flux makes it possible to perform XPS experiments from low concentration atomic species, such as dopants, impurities, and molecular surface adsorbates.  The possibility to continuously change the incident X-ray energy allows optimization of the photoionization cross-sections to increase the signal of a particular species of interest.  Variable X-ray energy also let us fine tune the kinetic energy of the emitted electrons enhancing the surface sensitivity to less than 0.5 nm or even perform non-destructive depth profiles. The high spectral resolution improves the accuracy of XPS analysis, particularly for complex samples containing multiple chemical states with small binding energy differences. Additionally, it is also possible to exploit the polarization of the X-rays to probe orientation and chirality of surface adsorbates.

RESONANT INELASTIC X-RAY SCATTERING

Resonant inelastic X-ray scattering is a photon-in/photon-out technique that measures the energy and momentum changes of photons scattered by samples in the solid, liquid and gas state. The energy and momentum lost in the inelastic process are transferred to intrinsic excitations inside the material under study. With recent advances in the design of spectrometers and detectors, it has become possible to distinguish various low energy excitations, such as excitons, plasmons, magnons and phonons, which govern the transport properties of materials. RIXS has some of unique features that distinguish it from other inelastic techniques based on the scattering of neutrons (INS), electrons (EELS) or light (Raman), commonly used to study elementary excitations. It is bulk sensitive, requires only small sample volumes, its is element and orbital specific, polarization dependent and covers a large scattering phase-space. The chemical sensitivity arises by tuning to the absorption edges of the different types of atoms in a material. RIXS can even differentiate between the same chemical element at sites with inequivalent chemical bonding, with different valence or at inequivalent crystallographic positions if the resonances are distinguishable. Another peculiar characteristic of RIXS is that the energy resolution do not depend on the core-hole lifetime (present only in the intermediate state), which leads to intrinsically sharp spectra with energy and momentum resolution determined by the instrumentation. With soft X-rays in the range of 100 to 1200 eV, RIXS is particularly useful for studying first row transition metals and light elements, in materials with strongly correlated electrons, catalysts, organic molecules and polymers.

LAYOUT & OPTICAL ELEMENTS

Element Type Position [m] Description
Source Insertion device 0 Undulator
M1 Toroidal mirror 27 Horizontal focusing and vertical colimation
M2 Plane mirror 28.5 Change grating incidence angle
M3 Diffraction gratings 29 Energy dispersion
M4 Cylndrical mirror 31 Vertical focusing
M5 Plane mirror 33 Branch selection
M6 Elipsoidal mirror 81 Microfocus at XPS endstation
M7 Elipsoidal mirror 91.5 Microfocos at RIXS endstation

PARAMETERS

Parameter Value Condition
Energy range 100 – 2000 eV Horizontal polarization
Resolution power (E/ΔE) 65.000 at 930 eV with cff=5
Harmonic content < 10-4 at 930 eV with cff=2.25
Beam size for RIXS [μm] 0.8 x 3.4 at 930 eV with cff=5
Beam size for XPS [μm] 4 x 5 at 930 eV with cff=2.25