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

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.

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Upcoming Conference

2017 MRS Fall Meeting & Exhibit

November 26-December 1, 2017
Boston, Massachusetts, USA
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Upcoming Group Seminars

TBA
Speaker: E. Gilardi
Date: Monday 25 September 2017 16:30
Room: OFLG/402

TBA
Speaker: LMX Meeting: Susmita Saha
Date: Tuesday 03 Oktober 2017 9:30
Room: OFLG/402

TBA
Speaker: V. Cervetto
Date: Monday 09 Oktober 2017 16:30
Room: OFLG/402

Most recent Paper

M. Pichler, W.P. Si, F. Haydous, H. Téllez, J. Druce, E. Fabbri, M. El Kazzi, M. Döbeli, S. Ninova, U. Aschauer, A. Wokaun, D. Pergolesi, and T. Lippert
LaTiOxNy Thin Film Model Systems for Photocatalytic Water Splitting: Physicochemical Evolution of the Solid–Liquid Interface and the Role of the Crystallographic Orientation
Adv. Funct. Mater., 1605690 (2017)


10 July 2017

LaTiOxNy Thin Film Model Systems for Photocatalytic Water Splitting: Physicochemical Evolution of the Solid–Liquid Interface and the Role of the Crystallographic Orientation

Abstract:
Layer-resolved electronic densities of states for the first and second layer of a) the LaN terminated (001) surface and b) the LaO terminated (001) surface. Dashed vertical lines indicate the top of the valence band in the respective layers and arrows show the migration of holes from the subsurface to the surface layer. Note that the LaO termination compensates polarity by self-doping with electrons, resulting in a Fermi energy in the conduction band, which does however not affect the conclusions drawn here. zoom
Layer-resolved electronic densities of states for the first and second layer of a) the LaN terminated (001) surface and b) the LaO terminated (001) surface. Dashed vertical lines indicate the top of the valence band in the respective layers and arrows show the migration of holes from the subsurface to the surface layer. Note that the LaO termination compensates polarity by self-doping with electrons, resulting in a Fermi energy in the conduction band, which does however not affect the conclusions drawn here.
The size of the band gap and the energy position of the band edges make several oxynitride semiconductors promising candidates for efficient hydrogen and oxygen production under solar light illumination. Intense research efforts dedicated to oxynitride materials have unveiled the majority of their most important properties. However, two crucial aspects have received much less attention: One is the critical issue of compositional/structural surface modifications that occur during operation and how these affect photoelectrochemical performance. The second concerns the relation between electrochemical response and the crystallographic surface orientation of the oxynitride semiconductor. These are indeed topics of fundamental importance, since it is exactly at the surface where the visible-light-driven electrochemical reaction takes place.

In contrast to conventional powder samples, thin films represent the best model system for these investigations. This study reviews current state-of-the-art oxynitride thin film fabrication and characterization, before focusing on LaTiO2N, selected as a representative photocatalyst. An investigation of the initial physicochemical evolution of the surface is reported. Then, it is shown that after stabilization the absorbed photon-to-current conversion efficiency of epitaxial thin films can differ by about 50% for different crystallographic surface orientations, and be up to 5 times larger than for polycrystalline samples.
Keywords: solar water splitting; oxynitride thin film; pulsed laser deposition; photoelectrochemical water splitting;

Facility: Thin Films and Interfaces, LMX, LMU, ENE, ETHZ, Univ. Bern, Kyushu University

Reference: M. Pichler et al., Adv. Funct. Mater., 1605690 (2017)

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