Formation of the defect dipoles around dopants demonstrated in dielectric ceramics

A team of international scientists from China, Germany, Norway and Pakistan with SESAME staff have used the BM08 – XAFS/XRF beamline at SESAME for high dielectric constant materials that are of particular interest as indispensable components in electronics. The authors have demonstrated a new approach for optimizing the dielectric properties by acceptor–donor co-doping in (Gax, Cuy) Zn1−x–yO films fabricated with pulse laser deposition (PLD) or, alternatively, exchanging the co-doping step by ion implantation. Exploitation of defect engineering in dielectric ceramics for enhancing performance is an active research area globally. Materials with high dielectric constant (k) and low loss throughout a wide frequency range are among the key components for the device size scale-down in nanoelectronics. The XAFS study performed at SESAME revealed the formation of the defect dipoles around dopants.

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Image: Examples of the X-ray analysis. a) XPS data showing the Cu 2p spectra for the Cu8Zn92O and Ga0.5Cu8Zn91.5O films. b) The X-ray absorption near edge structure (XANES) spectra at the Cu K-edge of Cu8Zn92O and Ga0.5Cu8Zn91.5O samples including reference samples, e.g., Cu foil and CuO powder. c) Magnitude of the Fourier transform of the extended X-ray absorption fine structure (EXAFS) spectra. d) Fourier transform of Real χ at the Zn K-edge of Ga0.5Zn99.5O, Cu8Zn92O, and Ga0.5Cu8Zn91.5O samples compared with theoretical model (black lines).

#SynchroLightAt75 – Historical perspective of catalysis at Elettra

“Catalysis, is a strange principle of chemistry which works in ways more mysterious than almost any other of the many curious phenomena of science” New York Times: June 8, 1923

Heterogeneous catalysis is one of the most extensively studied functional systems since it is in the heart of chemical industry, fuel, energy production and storage and also is part in the devices for environmental protection.

The key processes in heterogeneous catalysis occur at dynamic reactant/catalyst surface interfaces. Since these processes involve coupling between different electronic, structural and mass transport events at time scales from fs to days, and space scales from nm to mm, we are still far from full comprehension how to design and control the catalysts performance. In this respect the ultrabright and tunable light, generated at the synchrotron facilities, has opened unique opportunities for using powerful spectroscopy, spectromicroscopy, scattering and imaging methods for exploring the morphology and chemical composition of complex catalytic systems at relevant length and time scales and correlate them to the fabrication or operating conditions.

The very demanded for catalysis studies is the surface sensitive PhotoElectron Spectroscopy (PES), based on the photoelectric effect, for which Einstein won the 1921 Nobel Prize in Physics, and demonstrated for the first time in 1957 by Kai Siegbahn who was awarded the Nobel Prize in 1981. PES has overcome its time and space limitations for studies of catalytic surface reactions thanks to the synchrotron light, which also added the opportunity for complementary use of X-ray absorption spectroscopy. At Elettra, the first time resolved PES studies with model metal catalyst systems were carried out at SuperESCA beamline in 1993 and few years later PES microscopy instruments, Scanning PhotoElelectron Microscope (SPEM) and X-ray PhotoElectron Emission Microscope (XPEEM) at ESCAMicroscopy and Nanospectroscopy beamlines have allowed for sub-mm space resolved studies, including imaging of dynamic surface mass transport processes as well.

Implementation in the last decade of operando experimental set-ups at APE, BACH and ESCAMicroscopy experimental stations for bridging the pressure gap of PES investigations has led to significant achievements in monitoring in-situ chemical, electrochemical and morphology evolution of all types catalytic systems under reaction conditions. Further complementary studies using X-ray absorption spectroscopy in photon-in/photon-out mode, ongoing at the XAFS and TwinMic beamlines are filling some remaining knowledge gaps for paving the road towards knowledge-based design and production of these complex and very desired functional materials.

M. Amati, L. Bonanni, L. Braglia, F. Genuzio, L. Gregoratti, M. Kiskinova, A. Kolmakov, A.Locatelli, E. Magnano, A. A. Matruglio, T. O. Menteş, S. Nappini, P. Torelli, P. Zeller,” Operando photoelectron emission spectroscopy and microscopy at Elettra soft X-ray beamlines: from model to real functional systems”, J. Electr. Spectr. Rel. Phenom. (2019) doi: 10.1016/j.elspec.2019.146902.

For first SUPERESCA – A. Baraldi, G. Comelli, S. Lizzit, M. Kiskinova, G. Paolucci “Real-Time X-Ray Photoelectron Spectroscopy of Surface Reactions” Surf. Sci. Reports 49, Nos. 6-8 (2003) 169.

For XPEEM A. Locatelli and M. Kiskinova “Imaging with Chemical Analysis: Adsorbed Structures Formed during Surface Chemical Reactions” A European Journal of Chemistry, 12 (2006) 8890.

Image: From model to real catalysts: structural and chemical complexity

Publication of the first scientific paper

June 1, 2019 marks a historically important accomplishment for SESAME, where the very first scientific paper presenting results using data obtained at SESAME’s X-ray absorption fine structure/X-ray fluorescence (XAFS/XRF) spectroscopy beamline was published in Applied Catalysis B: Environmental.

S: Bac et al. Applied Catalysis B: Environmental, 259, 2019, 117808

Synchrotron measurements performed at SESAME were carried out by the research group of Associate Professor Emrah Ozensoy (Bilkent University Chemistry Department and UNAM-National Nanotechnology Center Ankara, Turkey), in collaboration with the research group of Professor Ahmet Kerim Avcı (Boğaziçi University, Chemical Engineering Department, Istanbul, Turkey) and Dr Messaoud Harfouche (XAFS/XRF beamline scientist, SESAME, Allan, Jordan).
The paper entitled Exceptionally active and stable catalysts for CO2 reforming of glycerol to syngas is the outcome of a measurement campaign at SESAME in July 2018 and focuses on the catalytic valorization of a biomass waste material (i.e. glycerol) to obtain synthesis gas (or syngas, CO + H2). Glycerol is an important renewable feedstock for the large-scale catalytic production of synthetic liquid fuels through a process called Fischer-Tropsch synthesis. In the words of Emrah Ozensoy “XAFS/XRF experiments performed at SESAME were instrumental for us to understand the electronic structure of the Co/CoOx and Ni/NiOx nanoparticles serving as the catalytic active sites. Particularly, complementing the experimental data acquired in our labs with the results obtained at SESAME allowed us to examine the nature of the fresh catalysts and compare them with that of the spent catalysts obtained after the catalytic reaction, revealing crucial molecular-level insights regarding the catalytic aging and poisoning mechanisms.”

>Read more on the SESAME website

Image: Kerem Emre Ercan Some of the researchers who contributed to the publication and data acquisition (from left to right, Yusuf Koçak, Kerem E. Ercan, and M. Fatih Genişel)

SESAME hosts its first users

Mid July, the first users arrived at SESAME to perform experiments using the Centre’s XAFS/XRF (X-ray absorption fine structure/X-ray fluorescence) spectroscopy beamline, SESAME’s first beamline to come into operation.

This was the Finnish Kirsi Lorentz and three of her colleagues at The Cyprus Institute: the Cypriot Grigoria Ioannou, the Japanese Yuko Miyauchi and the Greek/Egyptian Iosif Hafez, who together form a true international team in the spirit of SESAME.

Kirsi is the author of one of the 19 proposals from 5 of the SESAME Members (Cyprus, Egypt, Jordan, Pakistan and Turkey) that have been recommended for a total of 95.8 hour shifts on the XAFS/XRF beamline by SESAME’s Proposal Review Committee (PRC). The PRC is an international advisory body that evaluates the scientific and technological merit of proposals from the General Users and determines their priority using criteria based on IUPAP’s Recommendations for the Use of Major Physics Users Facilities.

“This heralds in a new stage in SESAME’s march forward, and for scientists in the SESAME Members and the region it is the tangible beginning of a moment from when it becomes possible to carry out state-of-the-art research in the region” said Khaled Toukan, Director of SESAME.

 “It is a unique opportunity and a real honour to be the first user of a synchrotron light facility – a research visit to remember” said Kirsi, who is examining ancient human remains from the Eastern Mediterranean and the Near East, adding “we are very excited with the results we obtained at the SESAME XAFS/XRF beamline, and grateful to all those who have worked so hard to bring this crucial research facility into operation in our region”.

>Read more on the SESAME website

Picture: Kirsi Lorentz, The Cyprus Institute: Kirsi Lorentz and her research team (from left to right: Yuko Miyauchi, Grigoria Ioannou, Kirsi Lorentz and Iosif Hafez) at the XAFS/XRF beamline control hutch.