Dr Alexei Kuzmin, Head of the Laboratory of Materials and Structure Investigations,\u00a0discusses the role of X-ray absorption spectroscopy in materials science and the latest\u00a0developments in this field at the Institute of Solid State Physics of the University of Latvia
\n(ISSP UL).<\/p>\n
Establishing the structure of a material is one of the most important goals of any research in\u00a0materials science and nanoscience. It is crucial knowledge for understanding and optimising\u00a0material properties and ultimately influencing their practical applications. The structure is\u00a0also the starting point for theoretical studies, based on numerical simulations and aimed at\u00a0exploration and the prediction of new materials.<\/p>\n
X-ray absorption spectroscopy (XAS) is an excellent probe of the local atomic structure in
\ncrystalline, nanocrystalline, and disordered solids, liquids and gases. Moreover, in
\nmulticomponent materials, X-ray absorption spectroscopy\u00a0allows the independent studying of the local environment\u00a0around atoms of different types. The method is applicable at both high and low\u00a0concentrations of the chemical element of interest and can be implemented in a wide range\u00a0of in-situ and in-operando conditions.<\/p>\n
The success of X-ray absorption spectroscopy\u00a0is based solely on the use of large-scale synchrotron radiation facilities.\u00a016 synchrotron sources are currently available in EU Member States, and there are over 50\u00a0sources worldwide. There are also a number of the laboratory XAS spectrometers, but they\u00a0cannot currently compete with synchrotrons. The advantages of synchrotrons as an X-ray\u00a0source are their wide and continuous spectral range, high flux, and brilliance. Synchrotron\u00a0radiation also has other useful properties as a characteristic polarisation and pulsed\u00a0temporal structure.<\/p>\n
The availability of synchrotron radiation facilities provides scientists from the university
\nlaboratories with access to an innovative infrastructure that allows for competitive research
\nat the forefront of modern science. Such transnational organizations are often the
\nbirthplace of new ideas and the emergence of cooperation. They also play important roles in\u00a0disseminating obtained results and serve as educational centres for new users and,
\nespecially, young researchers.<\/p>\n
ISSP UL, being the leading research centre in the field of material science in Latvia, has a
\nlong tradition in using European synchrotron centres. A significant part of its activities is
\ntraditionally dedicated to X-ray absorption spectroscopy. Pioneering XAS experiments have been conducted in the\u00a01980s and early 1990s at the Frascati ADONE synchrotron radiation source (which closed in\u00a01993) and later at the Orsay LURE storage rings, which stopped in 2006. During that time,\u00a0prominent results were achieved in the field of electrochromic metal oxide materials for\u00a0smart coatings, as well as in studies of superconducting materials and contrast agents for\u00a0medical diagnostics. This was a starting point for the formation of a team in ISSP UL\u00a0specialising in synchrotron-based experiments and XAS. This is now a well-known speciality\u00a0of the Institute.<\/p>\n
In the early 2000s, a collaboration between the ISSP UL team and partners from France,
\nItaly, and Estonia within the European Commission\u2019s Sixth Framework Programme project
\n\u2018X-TIP\u2019 led to the development and demonstration of a new tool for nanoscience which
\ncombines XAS with scanning near-field optical microscopy (SNOM). The XAS-SNOM
\nmicroscope placed at a synchrotron beamline collects the X-ray excited optical
\nluminescence (XEOL) signal in the near field through a tapered optical fibre probe. The latter\u00a0is attached to an oscillating quartz tuning fork and is used to record simultaneously with\u00a0XEOL the topographical image of the sample surface. As a result, element-specific contrast\u00a0becomes attainable in SNOM, and information on the local structure and electronic
\nproperties of materials can be obtained with a spatial resolution down to the nanometre
\nscale.<\/p>\n
An alternative approach, based on the sample mapping using the focused X-ray beam to
\nprobe non-homogeneity of material, has been employed by the ISSP team within the MNT-
\nERA.NET project, which has been realised in collaboration with Forschungszentrum J\u00fclich in
\n2009-2012. It has been demonstrated that X-ray absorption spectroscopy\u00a0at the Fe K-edge is sensitive enough to\u00a0evidence oxygen vacancy clustering around iron ions during resistive switching in Fe-doped\u00a0SrTiO3 thin film memristive devices.<\/p>\n
Simultaneous with experimental activities at large-scale facilities, ISSP UL has been amongst\u00a0the pioneers in the development of advanced data analysis methods. The development over\u00a0the past 10 years is focussed to increase the reliability and amount of structural information\u00a0that one can extract from X-ray absorption spectra (see Fig. 1).<\/p>\n
The currently-available approaches developed by ISSP UL rely on atomistic simulations such\u00a0as molecular dynamics (MD) and reverse Monte-Carlo (RMC) methods, which are employed\u00a0together with ab initio theory of X-ray absorption. However, these simulations are often\u00a0extremely computationally demanding. Therefore, their practical applications are based on\u00a0the intensive use of high-performance computing. The advantage of these methods is that\u00a0they provide a natural way to incorporate static and thermal disorder into the structural\u00a0model. Unlike conventional analysis, which deals with a set of structural parameters, both\u00a0methods give the results in terms of atomic configurations, which include information on\u00a0atom-atom and bond-angle distributions and correlations.<\/p>\n
In spite of the fact that the extraction of structural information is the main goal of XAS
\nstudies, the agreement between the experimental and calculated X-ray absorption spectra
\nin combination with methodology developed in ISSP UL can also be used to validate the
\ninteratomic potentials employed in MD simulations of materials. Such an approach is of
\ninterest because XAS experiments can be relatively easily performed at the required
\ntemperature and pressure. In this case, XAS acts as a bridge between experiment and
\ntheory. Currently, this approach is being employed by ISSP UL researchers to study, for
\nexample, oxide-dispersion-strengthened alloys for the future fusion and advanced fission
\nreactors within the framework of the EURATOM\/EUROfusion projects.<\/p>\n
The power of the X-ray absorption spectroscopy\u00a0method is often negated due to the need for a time-consuming\u00a0analysis of experimental data. This issue becomes critical when it is necessary to take a\u00a0quick decision during the experiment to guide some process or reaction. In this case, one\u00a0can rely on the use of machine learning algorithms. In particular, the artificial neural\u00a0network (ANN), pre-trained in advance using thousands of theoretical models generated by\u00a0MD simulations, can be used for rapid X-ray absorption spectra analysis. Such an approach\u00a0has been recently utilised to follow structural changes in iron during a high-temperature\u00a0phase transition from ferritic to austenitic phase. The work performed by ISSP UL in\u00a0collaboration with the researchers from Stony Brook University and Brookhaven National\u00a0Laboratory has attracted remarkable attention of the scientific community. The advantage\u00a0of this approach is that pre-trained ANNs can be easily shared, which allows other\u00a0researchers to analyse their data without having to perform the tedious ANN training\u00a0process on their own.<\/p>\n
There are many other applications of X-ray absorption spectroscopy, which are stimulated by materials demand and\u00a0developments in instrumentation. For example, experiments at extreme conditions and\u00a0time-dependent studies of ultrafast electronic and structural dynamics continuously attract\u00a0considerable interest from researchers. The accessible timescales range from minutes to\u00a0tens of picoseconds at synchrotron sources and go down to femtoseconds at X-ray free-electron laser (X-FEL) facilities. As a result, quantitative structural and kinetic data can be\u00a0obtained on catalytic and photo-induced processes, chemical reactions, and phase\u00a0transitions in the solid and liquid states. These groundbreaking research activities will\u00a0undoubtedly stimulate and promote further developments in the XAS field.<\/p>\n
The Institute of Solid State Physics of the University of Latvia is an internationally-recognised\u00a0leader with 40 years of experience in the material sciences and cross-disciplinary topics in\u00a0Latvia, which provides competitive research and innovative solutions for industrial\u00a0applications. The Institute offers modern infrastructure for different kind of material\u00a0synthesis and analysis that also serve the research needs of scientific and industrial\u00a0partners. Most of the advanced tools are installed in the clean room facilities.<\/p>\n
A H2020 Teaming project, CAMART\u00b2 is one of the largest projects in Latvian science to date,\u00a0and received European Commission funding for strategic development, as well as assistance\u00a0from the top players in the field from Sweden \u2013 Royal Institute of Technologies (KTH) and\u00a0Research Institutes of Sweden (RISE).<\/p>\n
The project’s objective is to strengthen the Institute\u2019s position as a significant regional
\nscience, innovation, and technology transfer centre, as well as within the Latvian state,
\nwithin Europe, and, indeed, internationally. This objective is already being achieved, with
\nthe Institute now world-renowned for the development of knowledge and skills in
\nsynchrotron-based experiments and XAS.<\/p>\n
Project CAMART\u00b2 has received funding from the Horizon 2020 Framework Programme
\nH2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508<\/p>\n
Dr phys Alexei Kuzmin<\/strong> The Institute of Solid State Physics is using\u00a0X-ray absorption spectroscopy for materials science. Dr Alexei Kuzmin, Head of the Laboratory of Materials and Structure Investigations,\u00a0discusses the role of X-ray absorption spectroscopy in materials science and the latest\u00a0developments in this field at the Institute of Solid State Physics of the University of Latvia (ISSP UL). Establishing […]<\/p>\n","protected":false},"author":1,"featured_media":962,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"_monsterinsights_skip_tracking":false,"_monsterinsights_sitenote_active":false,"_monsterinsights_sitenote_note":"","_monsterinsights_sitenote_category":0,"footnotes":""},"categories":[766,24429],"tags":[529,833,821],"acf":[],"yoast_head":"\n
\nHead of the Laboratory<\/strong>
\nInstitute of Solid State Physics<\/strong>
\nUniversity of Latvia<\/strong>
\n+371 (0)67251691<\/strong>
\na.kuzmin@cfi.lu.lv<\/strong><\/a>
\nTweet @LU_CFI<\/strong>
\nwww.cfi.lu.lv\/en\/<\/strong><\/a><\/p>\n","protected":false},"excerpt":{"rendered":"