Due to the upcoming ELETTRA 2.0 upgrade, this technique will be unavailable at CNR-IOM(TS) until further notice.
In the last years it has been demonstrated that the surface structure of many heterogeneous catalysts under relevant reaction conditions may differ from those determined by applying traditional high vacuum techniques. In most of the cases, the catalytically active sites tremendously change their properties during the reaction, strongly depending on the applied gas composition, pressure and temperature. This has pushed to the development of the so call in operando spectroscopies or ambient condition spectroscopies.
This process has involved also XAS which is one of the most powerful techniques of investigation of the chemical state of materials. Nowadays, XAS in the hard X-ray regime (typically above 5 keV) is commonly applied to the observation of heterogeneous catalysts under working conditions. On the other side in the soft x-ray range (typically below 2 keV) the availability of setup dedicated to this operando experiments is very recent and essentially stimulated by the commercial availability of thin (and transparent to the x rays) SiN membranes. This opens interesting possibilities because in the soft X-rays have the advantage that their energies cover the range of L or M-edges of most of the transition metals. With respect to XAS at the metals K-edges, L3 and L2 transitions are usually more intense (because formally electric-dipole allowed) and more reach in details. First-row transition-metal L-edges consist of 2p-3d transitions, which directly probe the unoccupied valence density of states. Hence, XAS on metal L-edges is very sensitive to metal-ligand interactions and perfectly complementary to XAS at the metal K-edges. In addition, soft X-rays cover the range of the core level binding energies of light elements (such as C, O, N and many others), potentially allowing the simultaneous observation of the electronic and structural changes underwent by the ligands or by the adsorbed reactants during the catalytic reaction.
X-ray absorption spectroscopy with selectable polarization, catalysis, surface reaction
Elettra Synchrotron, Apple II undulators: variable polarization (horizontal, vertical, circular ±), beam size on the sample 200x200 (HxV, µm2), vertical size can be reduced on request, flux on sample @10 µm slits (best resolution) (ph./s) 2x1012 - 6x1010
250-1500 eV
Total electron yield (measured by a Keithley picoamperometer)
(E/dE) 10000-1000
Many samples can be accommodated in a 25x25 mm2 area
T range: from room temperature to 150 Celsius
From 10-4 mBar to 1 Bar of gas
Gas line
Two degree-of-freedom manipulator
X-ray magnetic circular dichroism (max applied magnetic field 0.3 T)
Possibility to apply electric fields
In TEM/Scanning TEM (STEM) high energy electrons incident on ultra-thin samples, allow imaging, diffraction, electron energy loss spectroscopy and chemical analysis of solid materials with a spatial resolution on the order of 1-2 Å. Samples must have a thickness of a few tens of nanometres and are prepared in sample preparation laboratory.
XRD provides non-destructive information on the structural order of a material. At large scattering angles XRD permits to identify different crystal phases and to quantify lattice distances and crystalline volume fractions. At low angles of incidence the surface roughness of a single crystal and the thickness of a deposition layer can be obtained.
This technique offers the possibility of simulating structural and electronic properties based on the electronic ground state, including electronic charge analysis, energetics of formation, structural and vibrational properties; IR, Raman, EPR, NMR, core-level XAS & XPS, STM & AFM.
Raman spectroscopy (RS) investigates the vibrational properties of a sample and provides chemical as well as structural information. RS does not require any specific sample preparation, size or condition and may be combined with micron/nano spatial resolution when operated using a confocal microscope/TERS or SNOM configuration.
Ultraviolet photoelectron spectroscopy (UPS), also described as photoemission spectroscopy (PES) if applied to measurements on solid surfaces, is suitable for measuring spectral features close to the Fermi level for surfaces or adsorbates, and particularly useful for determining work function and electronic properties of valence band of a material.
