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Projects / Programmes source: ARIS

Structure and Chemical Composition Study of Surfaces and Interfaces with High-resolution Scanning Transmission Electron Microscopy at Atomic Level

Research activity

Code Science Field Subfield
2.04.00  Engineering sciences and technologies  Materials science and technology   

Code Science Field
P351  Natural sciences and mathematics  Structure chemistry 

Code Science Field
2.10  Engineering and Technology  Nano-technology 
Keywords
AR-STEM, atomic resolution scanning transmission electron microscopy, structure of surfaces and interfaces, crystal structure, microanalysis, energy dispersive X-ray spectroscopy, electron energy loss spectroscopy, fuell-cells, catalysts, photocatalysis
Evaluation (rules)
source: COBISS
Researchers (9)
no. Code Name and surname Research area Role Period No. of publicationsNo. of publications
1.  29158  PhD Elena Chernyshova  Physics  Researcher  2014 - 2017  127 
2.  19029  PhD Nina Daneu  Materials science and technology  Researcher  2014 - 2017  428 
3.  02556  PhD Goran Dražić  Materials science and technology  Head  2014 - 2017  1,046 
4.  34433  PhD Sandra Drev  Geology  Junior researcher  2014 - 2017  123 
5.  35375  PhD Primož Jovanovič  Chemistry  Researcher  2014 - 2016  191 
6.  28561  PhD Jože Moškon  Materials science and technology  Researcher  2014 - 2017  88 
7.  34528  PhD Andraž Pavlišič  Materials science and technology  Junior researcher  2014 - 2015  109 
8.  10083  PhD Aleksander Rečnik  Chemistry  Researcher  2014 - 2017  651 
9.  37457  Tina Zabukovec  Materials science and technology  Junior researcher  2015 
Organisations (2)
no. Code Research organisation City Registration number No. of publicationsNo. of publications
1.  0104  National Institute of Chemistry  Ljubljana  5051592000  21,261 
2.  0106  Jožef Stefan Institute  Ljubljana  5051606000  91,921 
Abstract
Development of new technologies which are consistent with the sustainable development, such as renewable sources of energy, purification of drinking and waste water, low-carbon profile technologies, etc. urge simultaneous research and development of new materials. Studying the properties of these materials it is sometimes obvious that the crystal structure and chemical composition on very small areas, many times on the level of individual atoms, influence the final properties of the material. In last decades beside development of new materials also fast development of devices and methods enabling the microstructural investigation at atomic level could be noticed. As a high-end instrument enabling atomic resolution investigations is probe Cs corrected scanning transmission electron microscope (AR-STEM). With this extremely complex instrument we can observe column of atoms, in some cases individual atoms. From the arrangement of the atoms we can conclude the crystal structure and using energy dispersive X-ray spectroscopy (EDXS) and electron energy loss spectroscopy (EELS) we can determine the chemical composition of practically individual atom column. In addition local bonding, coordination and valence state of individual atoms could be deduced. Using these data we can practically totally describe the structure of nanoparticles, crystal boundaries and planar defects. Using tomography 3D structure could be reconstructed from images taken at different tilt angles. With special sample holders we can perform “in situ” experiments inside the microscope, like heating, cooling, mechanical and electrical testing. In the project we will thoroughly investigate few technologically interesting materials where properties are determined with the structure and chemical composition of outer or internal surfaces or planar defects.   We will concentrate on few acute problems during the development of the materials related to alternative ways of energy production, storage and use. The distribution of Platinum atoms at the surface  of Cu3Pt catalysts, used in low-temperature fuel-cells based on polymer electrolyte membrane (PFMFC) influence strongly on the catalytic properties and finally the efficiency of the fuel-cells. Similarly the 1-2nm sized amorphous layer at the surface of anatase or rutile TiO2 nanoparticles plays an important role in photocatalytic efficiency of the material. Understanding the composition and the formation of the thin amorphous layer on the surface of anatase nanoparticles we could advice Cinkarna Celje how to improve the properties of their products. Next example will be the structure of planar defects in ZnO based materials which is commercially interesting and has potential use in electro-optical devices, solar cells, varistors, etc. Among studied defects will be the stacking faults, ferroelectric domain boundaries, coherent phase boundaries in modern materials like different cobaltates as high-temperature thermoelectrics, doped bismuth ferrites as multiferroics, etc.   We expect that the results of our work will be interesting for a broader scientific audience and that we will be able to publish in upper-class journals. Using state-of-the-art equipment we will be in the position to investigate at the atomic level and to correlate preparation parameters with the microstructure and consequently to understand the processes taking place during the synthesis of the material and their influence on the final properties. The results of the project will have strong potential impact on the industry.
Significance for science
The basic idea of the project was a detailed study of the structure and chemical composition of model cases at the atomic level, which is possible with a state-of-the-art scanning transmission electron microscope with a spherical aberrations corrector (ARSTEM). The studied materials we have explored were commercially interesting and within the broader context of a low-carbon, sustainable society. The first example of such a material is the copper-platinum-based catalysts. These catalysts are designed for low temperature fuel cells, which could be the basis for zero carbon dioxide emission mobility (in the case that hydrogen is used as a fuel). The basic motivation for the development of fuel cell catalysts is to reduce the price (ie minimize the share of platinum) and increase efficiency and stability. In the Cu3Pt system, which is even more efficient than platinum itself, the crystal structure (ordering), the chemical composition (distribution of Pt and Cu in the catalyst nanoparticles), and the presence of crystal defects, significantly affected the properties. By studying the microstructure at the atomic level, we linked the process parameters in the synthesis of materials through structure and chemistry at the atomic level with the final properties. During the research work we discovered that the increased number of lamellar (polysynthetic) twins positively influenced the properties. During detailed analysis of twins we came to the idea that the normalized intensity of individual columns on HAADF images could be used to determine the chemical composition of individual atomic columns. A similar approach was not known in the literature, it was reported only about the quali or semi-quantitative approaches or the estimation of the number of atoms in nanoparticles based on the intensity of the columns. This method was extended to the field of single atoms in carbon-based supports and the determination of point defects (cation vacancies) in ceramic multiferoics. With the new method for determination of the chemical composition based on the intensities of individual atomic columns, we confirm and quantified the amount of bismuth vacancies on the domain walls in BiFeO3. In parallel, we adapted the method of determining the valence state of iron when it is in the 4 + state. In this case, the EELS ratio methods described in the literature could not be applied. With the discovery that the bismuth vacancies and iron 4+ are located at the domain wall, we were able to solve the decade's old mystery, why the domain walls are more electrically conductive than the bulk grains. We published the work in the prestigious Nature Materials journal. The article was well accepted in the wider research community, which was reflected in a large number of invited lectures. Web of Science ranked this work in the category "Higly Cited", which means that is in the top 1% of the papers cited in the field of material science (September / October 2017). It should be mentioned that the work was entirely done in Slovenia, from the discovery of a method that enabled the determination of the presence of charged defects at the domain walls, through experimental work, and analysis at the atomic level to the interpretation of the conduction mechanism. In the project, we also investigated nanoparticles, thin films and zinc oxide-based ceramics. We connect the synthesis and chemical composition (in fact, the presence of certain impurities) and structural irregularities and, consequently, the change in properties. Similarly, in the investigation of titanium dioxide and its photocatalytic properties, the shape, structure and type of terminal planes were connected to the properties.
Significance for the country
The project topics are in the line with the priorities of the national research program of the Republic of Slovenia, such as energy, nanomaterials and nanotechnologies, and environment and environmental quality (soil, water, air). These areas are particularly important for Slovenia and require the development of knowledge and scientific and economic efficiency. A common feature of all the materials we have been researching within the project is sustainable development, carbonless or low-carbon technologies and modern energy production or utilization. The fuel cell catalyst should allow for high-power production of electricity and, if the input material is hydrogen, such a generator would have a zero carbon footprint. ZnO is an interesting material due to its electrical and optical properties. Various additives can induce the formation of special planar defects - inverse boundaries in the crystal structure - which have a great influence on the growth of crystals or grains in ceramic materials and thus on electrical properties. By tailoring the shape and crystal structure of TiO2 nanoparticles, an improvement in the photocatalytic properties of this material can be achieved. Photocatalysis and related self-cleaning systems and surfaces are recently one of the most important directions for sustainable development. The results obtained from the research work within the project are very interesting for the industry, which has long been involved in the production of such materials. The work on photocatalysis of titanium dioxide would be interesting for one of the largest European manufacturers of TiO2pigmented, and recently also nano-TiO2, which is Cinkarna Celje. Induced defects in zinc oxide can be of interest to Varsi, which has been producing zinc oxide-based varistors for decades, in which these defects play a decisive role in the final properties. By tailoring these properties, we could significantly improve the quality of products and introduce new ones. Mebius, which deals with the development and production of fuel cells, can be the end user of new results from the Cu3Pt-based catalysts.
Most important scientific results Annual report 2015, final report
Most important socioeconomically and culturally relevant results Annual report 2015, final report
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