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Publications (10 of 41) Show all publications
Donzel-Gargand, O., Thersleff, T., Keller, J., Törndahl, T., Larsson, F., Wallin, E., . . . Edoff, M. (2018). Deep surface Cu depletion induced by K in high-efficiency Cu(In,Ga)Se2 solar cell absorbers. Progress in Photovoltaics, 26(9), 730-739
Open this publication in new window or tab >>Deep surface Cu depletion induced by K in high-efficiency Cu(In,Ga)Se2 solar cell absorbers
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2018 (English)In: Progress in Photovoltaics, ISSN 1062-7995, E-ISSN 1099-159X, Vol. 26, no 9, p. 730-739Article in journal (Refereed) Published
Abstract [en]

In this work, we used K‐rich glass substrates to provide potassium during the coevaporation of Cu(In,Ga)Se2 (CIGS) absorber layers. Subsequently, we applied a postdeposition treatment (PDT) using KF or RbF to some of the grown absorbers. It was found that the presence of K during the growth of the CIGS layer led to cell effi- ciencies beyond 17%, and the addition of a PDT pushed it beyond 18%. The major finding of this work is the observation of discontinuous 100‐ to 200‐nm‐deep Cu‐ depleted patches in the vicinity of the CdS buffer layer, correlated with the presence of K during the growth of the absorber layer. The PDT had no influence on the forma- tion of these patches. A second finding concerns the composition of the Cu‐depleted areas, where an anticorrelation between Cu and both In and K was measured using scanning transmission electron microscopy. Furthermore, a steeper Ga/(In+Ga) ratio gradient was measured for the absorbers grown with the presence of K, suggesting that K hinders the group III element interdiffusion. Finally, no Cd in‐diffusion to the CIGS layer could be detected. This indicates that if CdCu substitution occurs, either their concentration is below our instrumental detection limit or its presence is contained within the first 6 nm from the CdS/CIGS interface.

Keywords
CIGS, Cu depletion, EELS, OVC, Raman, solar cell, TEM
National Category
Other Materials Engineering Energy Systems
Identifiers
urn:nbn:se:uu:diva-357120 (URN)10.1002/pip.3010 (DOI)000442501000004 ()
Funder
Swedish Research CouncilSwedish Energy AgencyEU, Horizon 2020, 720887
Available from: 2018-08-12 Created: 2018-08-12 Last updated: 2018-11-13Bibliographically approved
Li, H., Papadakis, R., Jafri, S. H., Thersleff, T., Michler, J., Ottosson, H. & Leifer, K. (2018). Superior adhesion of graphene nanoscrolls. Communications Physics, 1, Article ID 44.
Open this publication in new window or tab >>Superior adhesion of graphene nanoscrolls
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2018 (English)In: Communications Physics, E-ISSN 2399-3650, Vol. 1, article id 44Article in journal (Refereed) Published
Abstract [en]

An emerging material in the carbon family, a graphene nanoscroll (GNS) is composed of tubularly scrolled monolayer graphene and has shown superlubricity and large current sustainability, surpassing the properties of monolayer graphene itself. Here we report on the superior adhesion of GNS prepared with a high yield synthesis method that allows for mass production of high quality GNSs. Raman spectra indicate that the GNS still maintains the signature of monolayer graphene, implying the lacking of pi-stacking between adjacent layers. Importantly, adhesion measurements using atomic force microscopy reveal these GNSs with height range of 120-130 nm show a 2.5-fold stronger adhesion force than pristine graphene. This result potentially indicates that the GNS has higher adhesion than monolayer graphene and even higher than the liquid-solid and hydrogen-bonding enhanced interfaces which are essential types of adhesions involved in the field of physical adhesions and thus, GNS could be a new candidate for super-strong and lightweight devices.

Place, publisher, year, edition, pages
NATURE PUBLISHING GROUP, 2018
National Category
Materials Chemistry Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-362689 (URN)10.1038/s42005-018-0043-2 (DOI)000442027400001 ()
Funder
Knut and Alice Wallenberg FoundationWenner-Gren Foundations
Available from: 2018-11-09 Created: 2018-11-09 Last updated: 2019-05-06Bibliographically approved
Spiegelberg, J., Rusz, J., Thersleff, T. & Pelckmans, K. (2017). Analysis of electron energy loss spectroscopy data using geometric extraction methods. Ultramicroscopy, 174, 14-26
Open this publication in new window or tab >>Analysis of electron energy loss spectroscopy data using geometric extraction methods
2017 (English)In: Ultramicroscopy, ISSN 0304-3991, E-ISSN 1879-2723, Vol. 174, p. 14-26Article in journal (Refereed) Published
National Category
Atom and Molecular Physics and Optics Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-328271 (URN)10.1016/j.ultramic.2016.12.014 (DOI)000403342200003 ()28012371 (PubMedID)
Funder
Swedish Research CouncilThe Swedish Foundation for International Cooperation in Research and Higher Education (STINT)Göran Gustafsson Foundation for promotion of scientific research at Uppala University and Royal Institute of Technology
Available from: 2016-12-16 Created: 2017-12-20 Last updated: 2018-04-11Bibliographically approved
Thersleff, T., Giraldo, S., Neuschitzer, M., Pistor, P., Saucedo, E. & Leifer, K. (2017). Chemically and morphologically distinct grain boundaries in Ge-doped Cu2ZnSnSe4 solar cells revealed with STEM-EELS. Materials & design, 122, 102-109
Open this publication in new window or tab >>Chemically and morphologically distinct grain boundaries in Ge-doped Cu2ZnSnSe4 solar cells revealed with STEM-EELS
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2017 (English)In: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 122, p. 102-109Article in journal (Refereed) Published
Abstract [en]

Critical to the future development of Cu2ZnSnSe4 (CZTSe) materials is a comprehensive understanding of the underlying nanoscale mechanisms responsible for reduced performance. Investigating these mechanisms is challenging since they arise on the nanoscale, yet manifest themselves over macroscopic regions. Here, we present an analytical study combining Scanning Transmission Electron Microscopy (STEM), sample preparation, and hyperspectral Electron Energy Loss Spectroscopy (EELS) mapping techniques to meet this challenge. We apply our method to a Ge-doped CZTSe sample with a measured efficiency of 10.1%, revealing that its microstructure is dominated by two distinct types of grain boundaries. The first type appears in the upper half of the absorber separating large grains. These are Cu-enriched, Se-poor, and have varying amounts of . The second type of grain boundary is largely parallel to the substrate and appears predominately in the lower half of the absorber where the Cu/Zn ratio of the kesterite material is slightly lower. These grain boundaries contain voids and Sn oxide nanoparticles, exhibit high concentrations of Na, Cd, and S, and Cu assumes a higher valence state. We conclude with a discussion on the nature of and possible technological implications of these grain boundaries in this system.

Keywords
Cu2ZnSnSe4 (CZTSe), Kesterites, Thin film solar cell, Scanning Transmission Electron Microscopy (STEM), Electron Energy-Loss Spectroscopy (EELS), Grain boundary
National Category
Materials Chemistry Materials Engineering
Identifiers
urn:nbn:se:uu:diva-322518 (URN)10.1016/j.matdes.2017.02.077 (DOI)000400213200008 ()
Funder
EU, FP7, Seventh Framework Programme, FP7-PEOPLE-2012-ITN-316488EU, FP7, Seventh Framework Programme, FP7-PEOPLE-2013-1EF-625840
Available from: 2017-05-30 Created: 2017-05-30 Last updated: 2017-05-30Bibliographically approved
Thersleff, T., Muto, S., Werwinski, M., Spiegelberg, J., Kvashnin, Y., Hjörvarsson, B., . . . Leifer, K. (2017). Towards sub-nanometer real-space observation of spin and orbital magnetism at the Fe/MgO interface. Scientific Reports, 7, Article ID 44802.
Open this publication in new window or tab >>Towards sub-nanometer real-space observation of spin and orbital magnetism at the Fe/MgO interface
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2017 (English)In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 7, article id 44802Article in journal (Refereed) Published
Abstract [en]

While the performance of magnetic tunnel junctions based on metal/oxide interfaces is determined by hybridization, charge transfer, and magnetic properties at the interface, there are currently only limited experimental techniques with sufficient spatial resolution to directly observe these effects simultaneously in real-space. In this letter, we demonstrate an experimental method based on Electron Magnetic Circular Dichroism (EMCD) that will allow researchers to simultaneously map magnetic transitions and valency in real-space over interfacial cross-sections with sub-nanometer spatial resolution. We apply this method to an Fe/MgO bilayer system, observing a significant enhancement in the orbital to spin moment ratio that is strongly localized to the interfacial region. Through the use of first-principles calculations, multivariate statistical analysis, and Electron Energy-Loss Spectroscopy (EELS), we explore the extent to which this enhancement can be attributed to emergent magnetism due to structural confinement at the interface. We conclude that this method has the potential to directly visualize spin and orbital moments at buried interfaces in magnetic systems with unprecedented spatial resolution.

Place, publisher, year, edition, pages
NATURE PUBLISHING GROUP, 2017
National Category
Atom and Molecular Physics and Optics Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-320197 (URN)10.1038/srep44802 (DOI)000397288700001 ()28338011 (PubMedID)
Funder
Swedish Research Council, C0367901The Swedish Foundation for International Cooperation in Research and Higher Education (STINT), IG2009-2017Knut and Alice Wallenberg Foundation, 2013.0020 2012.0031eSSENCE - An eScience Collaboration
Available from: 2017-04-18 Created: 2017-04-18 Last updated: 2019-04-24Bibliographically approved
Mao, F., Nyberg, T., Thersleff, T., Andersson, A. & Jansson, U. (2016). Combinatorial magnetron sputtering of AgFeO2 thin films with the delafossite structure. Materials & design, 91, 132-142
Open this publication in new window or tab >>Combinatorial magnetron sputtering of AgFeO2 thin films with the delafossite structure
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2016 (English)In: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 91, p. 132-142Article in journal (Refereed) Published
Abstract [en]

The main objective of this study is to demonstrate the strength of the combinatorial approach to rapidly and effectively identify suitable process parameters for the synthesis of AgFeO2 filmswith layered delafossite structure. (00l)- textured delafossite AgFeO2 thin films have been successfully deposited for the first time without post-annealing by magnetron sputtering from elemental silver and iron targets in a reactive Ar-O-2 atmosphere. Gradient filmswith a wide composition range were deposited on singlewafers and subsequent screenings of phase- and chemical compositions were employed to optimize process parameters. The optimum deposition temperature for single-phase AgFeO2 growth was 450 degrees C using a Ag target powered at 15 W with a pulsing frequency of 150 kHz and a Fe target powered at constant 120 W at a total pressure of 4 mTorr and a O-2 partial pressure of 0.8 mTorr. Selected films were studied with scanning electron microcopy (SEM), transmission electron microscopy (TEM) and Raman spectroscopy. The optical band gap for the indirect transition in the AgFeO2 film was determined to 1.7 +/- 0.1 eV, and the band gap for the direct transition was 2.5 +/- 0.1 eV. The film showed insulating electrical properties.

Keywords
Combinatorial sputtering, Delafossite, Thin film, AgFeO2
National Category
Materials Engineering
Identifiers
urn:nbn:se:uu:diva-274897 (URN)10.1016/j.matdes.2015.11.092 (DOI)000367235400016 ()
Funder
SweGRIDS - Swedish Centre for Smart Grids and Energy StorageKnut and Alice Wallenberg FoundationSwedish Research Council
Available from: 2016-02-02 Created: 2016-01-26 Last updated: 2018-03-21Bibliographically approved
Giraldo, S., Thersleff, T., Larramona, G., Neuschitzer, M., Pistor, P., Leifer, K., . . . Saucedo, E. (2016). Cu2ZnSnSe4 solar cells with 10.6% efficiency through innovative absorber engineering with Ge superficial nanolayer. Progress in Photovoltaics, 24(10), 1359-1367
Open this publication in new window or tab >>Cu2ZnSnSe4 solar cells with 10.6% efficiency through innovative absorber engineering with Ge superficial nanolayer
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2016 (English)In: Progress in Photovoltaics, ISSN 1062-7995, E-ISSN 1099-159X, Vol. 24, no 10, p. 1359-1367Article in journal (Refereed) Published
Abstract [en]

In our recently published work, the positive effect of a Ge nanolayer introduced into the processing of Cu2ZnSnSe4 absorbers (CZTSe) was demonstrated. In this contribution, the complete optimization of this new approach is presented for the first time. Hence, the optimum Ge nanolayer thickness range is defined in order to achieve an improved performance of the devices, obtaining a record efficiency of 10.6%. By employing this optimized approach, the open-circuit voltage (V-OC) is boosted for our pure selenide CZTSe up to 489 mV, leading to V-OC deficit among the lowest reported so far in kesterite technology. Additionally, two important effects related to the Ge are unambiguously demonstrated that might be the origin of the V-OC boost: the improvement of the grain size and the corresponding crystalline quality, and the interaction between Ge and Na that allows for dynamic control over the CZTSe doping. Finally, evidences pointing to the origin of the deterioration of devices properties for large Ge concentrations are presented.

Keywords
Cu2ZnSnSe4, kesterite, germanium, Na doping, thin-film photovoltaics
National Category
Energy Systems Nano Technology
Identifiers
urn:nbn:se:uu:diva-308777 (URN)10.1002/pip.2797 (DOI)000386072200007 ()
Available from: 2016-12-08 Created: 2016-11-30 Last updated: 2019-04-24Bibliographically approved
Thersleff, T., Rusz, J., Hjörvarsson, B. & Leifer, K. (2016). Detection of magnetic circular dichroism with subnanometer convergent electron beams. Physical Review B, 94(13), Article ID 134430.
Open this publication in new window or tab >>Detection of magnetic circular dichroism with subnanometer convergent electron beams
2016 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 94, no 13, article id 134430Article in journal (Refereed) Published
Abstract [en]

The electron energy-loss spectroscopy technique known as electron magnetic circular dichroism (EMCD) has enormous potential for quantitatively probing the magnetic behavior of materials on the nanoscale. However, the requirement for mostly parallel illumination conditions greatly complicates the extraction of EMCD signals from surface areas under a few square nanometers, because scanning probe methods are limited to around this spatial resolution by the need for higher convergence angles. Here we propose theoretically and demonstrate experimentally that EMCD detection is feasible with convergence angles that are sufficiently large even for atomic resolution spectroscopy. Utilizing scanning transmission electron microscopy we experimentally detect a clear EMCD signal from a 50-nm-thick sample of bcc iron using a convergence semiangle of 8 mrad at 300 keV acceleration voltage, resulting in a probe size of approximately 2 angstrom. We subsequently estimate the number of chirally scattered electrons needed for an unambiguous detection of the EMCD signal and present a method to quantify confidence in signal detection.

National Category
Condensed Matter Physics Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-308916 (URN)10.1103/PhysRevB.94.134430 (DOI)000387015900003 ()
Funder
Swedish Research CouncilGöran Gustafsson Foundation for promotion of scientific research at Uppala University and Royal Institute of TechnologyThe Swedish Foundation for International Cooperation in Research and Higher Education (STINT), IG2009-2017
Available from: 2016-12-01 Created: 2016-12-01 Last updated: 2019-04-24Bibliographically approved
Bejjani, R., Marianne, C., Thersleff, T. & Stina, O. (2016). Multi-scale study of initial tool wear on textured alumina coating, and the effect of inclusions in low-alloyed steel. Tribology International, 100, 204-212
Open this publication in new window or tab >>Multi-scale study of initial tool wear on textured alumina coating, and the effect of inclusions in low-alloyed steel
2016 (English)In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 100, p. 204-212Article in journal (Refereed) Published
Abstract [en]

When turning low-alloyed steel with hard inclusions, scores and grooves have been observed in the wear of the alumina coating in CVD coated cutting tools. This study focuses on detailed understanding of flank wear in the textured alumina coating and the relation to the workpiece's inclusions. For chip formation studies, a quick stop device has been used. A topography analysis for the worn coating was performed in the micro scale. Studies at lower scales were performed using TEM. This allowed the study of wear on the coating crystalline structure and the embedment of workpiece material on its surface. Based on the results, the mechanism behind the initial wear was analyzed and an abrasion wear model is proposed.

Keywords
Coating, Particles, Abrasive, Machining, TEM
National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Research subject
Engineering Science with specialization in Tribo Materials
Identifiers
urn:nbn:se:uu:diva-285904 (URN)10.1016/j.triboint.2016.01.021 (DOI)000379279600024 ()
Available from: 2016-04-20 Created: 2016-04-20 Last updated: 2018-01-10Bibliographically approved
Donzel-Gargand, O., Thersleff, T., Fourdrinier, L., Leifer, K. & Edoff, M. (2016). Surface defect passivation by a thin metallic barrier for Cu(InxGa1-x)Se2 co-evaporation on Cr-steel substrates. Thin Solid Films, 619, 220-226
Open this publication in new window or tab >>Surface defect passivation by a thin metallic barrier for Cu(InxGa1-x)Se2 co-evaporation on Cr-steel substrates
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2016 (English)In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 619, p. 220-226Article in journal (Refereed) Published
Abstract [en]

The use of Cr-steel substrates for the fabrication of Cu(In,Ga)Se2 (CIGS) solar cells is highly desirable and is a topic of considerable research interest. However, solar cells on non-treated steel substrates often exhibit decreased performance compared to their homologues on soda lime glass substrates. This is partly attributed to out-diffusion of steel components (Fe, Cr, Mn, etc.) into the solar cell. To avoid this contamination, thin film barriers can be added on top of the steel surface, but they do not always prevent the diffusion completely. In this paper we study the potential of using Cr and Ti as thin barrier layers. We find that local surface defects on the steel, several micrometers in height, lead to cracks in the back contact as well as in the barrier layers. Advanced transmission electron microscopy (TEM) techniques reveal that elemental diffusion and chemical reactions occur at these openings during heat treatments in Se atmosphere. TEM-energy dispersive X-ray spectroscopy (TEM-EDX) analysis in combination with calculation of the solid state diffusion coefficient demonstrate that a Cr-barrier sacrificially protects the Cr-steel substrate, blocking most of the Fe out-diffusion, whereas a Ti-barrier is less efficient.

Place, publisher, year, edition, pages
Elsevier, 2016
Keywords
Back contact; Thin film; Solar cell; Steel substrate; CuInGaSe2; Electron microscopy; Diffusion; Barrier
National Category
Metallurgy and Metallic Materials Condensed Matter Physics Energy Systems
Research subject
Engineering Science with specialization in Materials Analysis; Engineering Science with specialization in Materials Science
Identifiers
urn:nbn:se:uu:diva-307368 (URN)10.1016/j.tsf.2016.10.063 (DOI)000389610900033 ()
Available from: 2016-11-14 Created: 2016-11-14 Last updated: 2018-08-12Bibliographically approved
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ORCID iD: ORCID iD iconorcid.org/0000-0002-0999-3569

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