Paul Scherrer Institute

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The Thin Films and Interfaces Group

Thin films are nowadays utilized in many applications, ranging from semiconductor devices to optical coatings and are even present in pharmaceuticals (polymers). This wide-spread application of films with thicknesses from atomic monolayers to microns is due to the developments of thin film deposition techniques. Thin films are also important for studies of materials with new and unique properties due to the possibility of tuning their crystallographic and morphological properties. The thin film approach, i.e. the presence of interfaces (to a substrate or the film surface) adds more degrees of freedom for influencing the properties of materials, e.g. by lattice strain or surface functionalization. For these fundamental studies of material properties large research facilities such as synchrotron radiation or neutron spallation sources are one of the keys that the Paul Scherrer Institute (PSI) provides. Read more Top

News


15 November 2018

Woman in Science

Congratulations to our former postdoc, Alexandra Palla-Papavlu (4th from the left), for winning the L’Oreal Prize for Woman in Science in the category Physics in Romania
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Upcoming Conference

April 2019

2019 MRS Spring Meeting & Exhibit

April 22-26, 2019
Phoenix, Arizona, USA
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May 2019

2019 E-MRS Spring Meeting and Exhibit

May 27-31, 2019
Nice, France
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8th International Congress on Laser Advanced Materials Processing

LPM2019 - The 20th International Symposium on Laser Precision Microfabrication
HPL2019 – The 8th International Symposium on High Power Laser Processing
May 21-24, 2019
Hiroshima, Jp
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June 2019

22st International Conference on Solid State Ionics, 2019

June 16-21, 2019
PyeongChang, Korea
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3rd International Conference on Applied Surface Science

June 17-20, 2019
Pisa, Italy
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Deadline for Abstract submission is extended to Friday, 1st. Feb. 2019!


Upcoming Group Seminars

Materials for high efficiency overall CO2 reduction and use in a PV-EC system - Abstract
Speaker: Prof. Victor Mougel
ETH Zürich. Dep. of Chemistry and Applied Biosc.
Date: Monday 25 March 2019 16:00
Room: OFLG/402, TFI-LMX SEMINAR

LMX Seminar
Speaker:
Date: Tuesday 26 March 2019 13:00
Room: OSGA/EG06, LMX

TBA
Speaker: E. Gilardi
Date: Monday 8 April 2019 16:00
Room: OFLG/402, TFI

Scientific Highlights


11 February 2019

Electronic localization in CaVO3 films via bandwidth control

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Understanding and controlling the electronic structure of thin layers of quantum materials is a crucial first step towards designing heterostructures where new phases and phenomena, including the metal-insulator transition (MIT), emerge. Here, we demonstrate control of the MIT via tuning electronic bandwidth and local site environment through selection of the number of atomic layers deposited. We take CaVO3, a correlated metal in its bulk form that has only a single electron in its V4+ 3d manifold, as a representative example. We find that thick films and ultrathin films (≤6 unit cells, u.c.) are metallic and insulating, respectively, while a 10 u.c. CaVO3 film exhibits a clear thermal MIT. Our combined X-ray absorption spectroscopy and resonant inelastic X-ray scattering (RIXS) study reveals that the thickness-induced MIT is triggered by electronic bandwidth reduction and local moment formation from V3+ ions, that are both a consequence of the thickness confinement. The thermal MIT in our 10 u.c. CaVO3 film exhibits similar changes in the RIXS response to that of the thickness-induced MIT in terms of reduction of bandwidth and V 3d–O 2p hybridization.
Facility: SLS

Reference: D.E. McNally et al, npj Quantum Materials 4, 6 (2019)

Read full article: here

8 February 2019

Emergent magnetic monopole dynamics in macroscopically degenerate artificial spin ice

Abstract:
Thermally activated two-dimensional artificial square ice with height offsets between nanomagnets. (A) Tilted-sample scanning electron microscopy (SEM) image of an artificial square ice with an introduced height offset h, which can be varied from sample to sample, until the competing interactions J<sub>1</sub> and J<sub>2</sub> are equalized and an extensive spin ice degeneracy is achieved. Scale bar, 400 nm. (B) XMCD image of the same artificial square ice array. Nanomagnets with moments pointing toward the incoming x-rays (indicated by a yellow arrow) appear dark, while those opposing the x-ray direction appear with bright contrast. (C) The 16 possible moment configurations on a four-nanomagnet vertex are traditionally listed into four topological types. Without a height offset (h = 0 nm), the ice rule–obeying (two-in-two-out) type I and II configurations have a significantly different energy. Once a critical height offset is introduced, their energies are equalized and spin ice degeneracy is realized. Highlighted with magenta, cyan blue, and yellow frames in (B) and (C) are type I, type II, and type III vertices, respectively.zoom
Thermally activated two-dimensional artificial square ice with height offsets between nanomagnets. (A) Tilted-sample scanning electron microscopy (SEM) image of an artificial square ice with an introduced height offset h, which can be varied from sample to sample, until the competing interactions J1 and J2 are equalized and an extensive spin ice degeneracy is achieved. Scale bar, 400 nm. (B) XMCD image of the same artificial square ice array. Nanomagnets with moments pointing toward the incoming x-rays (indicated by a yellow arrow) appear dark, while those opposing the x-ray direction appear with bright contrast. (C) The 16 possible moment configurations on a four-nanomagnet vertex are traditionally listed into four topological types. Without a height offset (h = 0 nm), the ice rule–obeying (two-in-two-out) type I and II configurations have a significantly different energy. Once a critical height offset is introduced, their energies are equalized and spin ice degeneracy is realized. Highlighted with magenta, cyan blue, and yellow frames in (B) and (C) are type I, type II, and type III vertices, respectively.
Magnetic monopoles, proposed as elementary particles that act as isolated magnetic south and north poles, have long attracted research interest as magnetic analogs to electric charge. In solid-state physics, a classical analog to these elusive particles has emerged as topological excitations within pyrochlore spin ice systems. We present the first real-time imaging of emergent magnetic monopole motion in a macroscopically degenerate artificial spin ice system consisting of thermally activated Ising-type nanomagnets lithographically arranged onto a pre-etched silicon substrate. A real-space characterization of emergent magnetic monopoles within the framework of Debye-Hückel theory is performed, providing visual evidence that these topological defects act like a plasma of Coulomb-type magnetic charges. In contrast to vertex defects in a purely two-dimensional artificial square ice, magnetic monopoles are free to evolve within a divergence-free vacuum, a magnetic Coulomb phase, for which features in the form of pinch-point singularities in magnetic structure factors are observed.
Keywords: artificial spin ice; monopoles; XMCD; thin films;

Facility: Thin Films and Interfaces, LMX, ETHZ, Advanced Light Source, Lawrence Berkeley National Laboratory (LBNL) USA

Reference: A. Farhan et al., Science Advances 5 (2), eaav6380 (2019)

Read full article: [here]

17 January 2019

Improved Photoelectrochemical Water Splitting of CaNbO2N Photoanodes by CoPi Photodeposition and Surface Passivation

Abstract:
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Photoelectrochemical (PEC) solar water splitting is a promising approach to convert solar energy into sustainable hydrogen fuel using semiconductor electrodes. Owing to their visible light absorption properties, oxynitrides have shown to be attractive photocatalysts for this application. In this study, the influence of the preparation method of CaNbO2N particles on their morphological and optical properties, and thereby their PEC performance, is investigated. The best performing CaNbO2N photoanode is produced by ammonolysis of Nb-enriched calcium niobium oxide. The enhanced photoactivity arises from an enlarged surface area and superior visible light absorption properties. The photoactivity of this photoanode was further enhanced by photodeposition of CoPi cocatalyst and by the atomic layer deposition of an Al2O3 overlayer. A photocurrent density of 70 μA cm–2 at 1.23 V versus reversible hydrogen electrode was achieved. The observed enhancement of the PEC performance after CoPi/Al2O3 deposition is the combined effect of the improved kinetics of oxygen evolution because of the CoPi cocatalyst and the reduced surface recombination of the photogenerated carriers at the Al2O3 surface layer.
Keywords: Pulsed laser deposition; Laser induced plasma; Double layer; Plasma plume expansion;

Facility: Thin Films and Interfaces, LMX, ENE, ETHZ, Center for Nanointegration Duisburg-Essen - University of Duisburg-Essen, Department of Chemistry - University of Zurich

Reference: F. Haydous et al., J. Phys. Chem. C, 123 (2), pp 1059–1068 (2019), online publication 24. 12. 2018, in print 17.01.2019

Read full article: [here]

4 January 2019

Oxynitride Thin Films versus Particle-Based Photoanodes: A Comparative Study for Photoelectrochemical Solar Water Splitting

Abstract:
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The solar water splitting process assisted by semiconductor photocatalysts attracts growing research interests worldwide for the production of hydrogen as a clean and sustainable energy carrier. Because of their optical and electrical properties, several oxynitride materials show great promise for the fabrication of efficient photocatalysts for solar water splitting. This study reports a comparative investigation of particle- and thin-film-based photocatalysts using three different oxynitride materials. The absolute comparison of the photoelectrochemical activities favors the particle-based electrodes because of the better absorption properties and larger electrochemical surface area. However, thin films surpass the particle-based photoelectrodes because of their more suitable morphological features that improve the separation and mobility of the photogenerated charge carriers. Our analysis identifies what specific insights into the properties of materials can be achieved with the two complementary approaches
Keywords: oxynitride; photoanode; photoelectrochemistry; pulsed laser deposition; solar water splitting; thin films;

Facility: Thin Films and Interfaces, LMX, ENE, ETHZ, Center for Nanointegration Duisburg-Essen - University of Duisburg-Essen, International Institute for Carbon-Neutral Energy Research (I2CNER), Kyushu University, Japan

Reference: F. Haydous et al., ACS Appl. Energy Mater. 2 (1), 754-763 (2019), online January 4, 2019

Read full article: [here]

25 October 2018

Rolling dopant and strain in Y-doped BiFeO3 epitaxial thin films for photoelectrochemical water splitting

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We report significant photoelectrochemical activity of Y-doped BiFeO3 (Y-BFO) epitaxial thin films deposited on Nb:SrTiO3 substrates. The Y-BFO photoanodes exhibit a strong dependence of the photocurrent values on the thickness of the films, and implicitly on the induced epitaxial strain. The peculiar crystalline structure of the Y-BFO thin films and the structural changes after the PEC experiments have been revealed by high resolution X-ray diffraction and transmission electron microscopy investigations. The crystalline coherence breaking due to the small ionic radius Y-addition was analyzed using Willliamson-Hall approach on the 2Θ-ω scans of the symmetric (00l) reflections and confirmed by high resolution TEM (HR-TEM) analysis. In the thinnest sample the lateral coherence length (L||) is preserved on larger nanoregions/nanodomains. For higher thickness values L|| is decreasing while domains tilt angles (αtilt) is increasing. The photocurrent value obtained for the thinnest sample was as high as Jph = 0.72 mA/cm2, at 1.4 V(vs. RHE). The potentiostatic scans of the Y-BFO photoanodes show the stability of photoresponse, irrespective of the film’s thickness. There is no clear cathodic photocurrent observation for the Y-BFO thin films confirming the n-type semiconductor behavior of the Y-BFO photoelectrodes.
Reference: F. Haydous et al, Scientific Reports 8, 15826 (2018)

Read full article: here


Special interview with Prof. Thomas Lippert (PSI and Principle Investigator at I2CNER, Kyushu University) and Prof. Tatsumi Ishihara (Associate Director I2CNER, Kyushu University) on Current and Future Energy Research and Development in Europe: Perspectives from Switzerland, Germany and Japan. The interview is being published in the August 2017 issue of the Energy Outlook of the International Institut for Carbon-Neutral Energy Research, I2CNER.
Prof. Ishihara is heading the Molecular Photoconversion Devices Division within I2CNER. One of the topics Prof. Lippert and Prof. Ishihara are working on is part of the Solid Oxide Interfaces for Faster Ion Transport project from the JSPS Core-to-Core program.
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PhD projects at the Thin Films and Interfaces Group

At present, we do not have open PhD positions available. As soon as we have details will be posted at our open position page. Other open positions are always published on the PSI Open Positions page.

Most recent Paper

Yanuo Shi, Aline Fluri, Inigo Garbayo, J. Jakob Schwiedrzik, Johann Michler, Daniele Pergolesi, Thomas Lippert, Jennifer Lilia Marguerite Rupp;
Zigzag or spiral-shaped nanostructures improve mechanical stability in yttria-stabilized zirconia membranes for micro-energy conversion devices
Nano Energy 59, 674–682 (2019)



11 March 2019

Zigzag or spiral-shaped nanostructures improve mechanical stability in yttria-stabilized zirconia membranes for micro-energy conversion devices

Abstract:
(a) Oblique angle pulsed laser deposition for the fabrication of yttria-stabilized zirconia thin films with varied nanomorphologies and grain-grain connections to form straight columnar, zigzag and spiral-shaped structures. (b) Optical microscopy images of the free-standing membranes with straight, zigzag and spiral-shaped 8YSZ structure. Pt electrodes are on top of the membrane for following electrical characterization. (from Fig. 1)zoom
(a) Oblique angle pulsed laser deposition for the fabrication of yttria-stabilized zirconia thin films with varied nanomorphologies and grain-grain connections to form straight columnar, zigzag and spiral-shaped structures. (b) Optical microscopy images of the free-standing membranes with straight, zigzag and spiral-shaped 8YSZ structure. Pt electrodes are on top of the membrane for following electrical characterization. (from Fig. 1)
Free-standing solid-state ion conducting thin film membranes are key components in micro-energy conversion devices such as micro-solid oxide fuel cells or electrolyzers. Through this work, we explore the design and fabrication of thin film architectures with either straight, zigzag or spiral-shaped columnar grain nanostructures of 8 mol% doped Yttria stabilized zirconia (8YSZ) in order to modify the ceramics elastic properties and mechanical stability for MEMS integration. We report that the zigzag and spiral-shaped nanomorphologies' can be engineered with a ∼44% reduced elastic modulus. Ultimately, this results in an increased fabrication yield when the thin ionic conductor thin film structures are turned into free-standing membranes as required for different micro energy converter applications. Raman spectroscopy reveals that the symmetry is lowered by the existence of monoclinic distortions in the cubic phase which modifies the elastic moduli of films with straight columnar structures. Fundamentally, we show here evidence that for yttria-stabilized zirconia modifications in membrane nano-architectures and strain can lead to phase changes, which agrees well with findings published in the 1970s based on applied external stress's on macroscopic structures (i.e. pellets). The influence of the change in nano-morphology on the cross-plane ionic conductivity is minor. The oxygen ion conducting thin film nanomorphology design exhibits potential to optimize grain connectivity and tortuosity by growth as either columnar, zigzag or spiral-shaped morphologies, in order to obtain membranes with controllable phases and elastic moduli for micro-energy conversion devices.
Keywords: Energy conversion membrane, Zigzag nanomorphology; Mechanical stability; Micro-solid oxide fuel cell;

Facility: Thin Films and Interfaces, LMX, ETHZ, EMPA Thun, Department of Material Science and Engineering, MIT, USA

Reference: Y. Shi et al., Nano Energy 59, 674–682 (2019)

Read full article: [here]
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