Semester Projects

Prof. Dr. Christof Niedermayer
Laboratory for Neutron Scattering and Imaging (LNS)
+41 56 310 20 86

Frustrated magnetism in α-TeVO4 zig-zag spin S=1/2 chain

Zig-zag spin chains with ferromagnetic nearest and anti-ferromagnetic next nearest neighbour exchange exhibit both reduced dimensionality and frustration. As such they are prone to groundstates and excitations qualitatively different from those of classical, three-dimensional spin systems. This physics has recently been proposed to describe the magnetic properties of α-TeVO4 with S=1/2 V4+ ions. We shall study magnetic ground state and excitations in this system by neutron scattering experiments.

Supervisors: Oksana Zaharko and Alun Biffin

Structural disorder allowing oxygen diffusion in Perovskites and Ruddlesden-Popper phases

In our focus are oxides which show oxygen-ion conductivity at moderate or even at ambient temperatures. Among them, two Perovskite-derivatives, the Brownmillerite ABO2.5+δ and the Ruddlesden-Popper A2BO4+δ phases are of particular interest, as they are non-stoichiometric and are able to accommodate an important amount (~4%) of oxygen on interstitial or regular lattice sites. We are investigating the influence of the disorder to the oxygen conductivity by means of neutron and X-Ray diffraction.

Supervisors: Lukas Keller and Jürg Schefer.

Water diffusion in clays

Clays are application relevant layered porous materials. In this context understanding of water diffusion and molecular ordering of water is of interest. In clay particles water is usually intercalated in a form of integer number of molecular water layers. Recently, a theoretically predicted "1.5" layer state has been observed. In this project the local water diffusion in Li-fluorhectorite (at 1, 1.5 and 2 water layer hydration state) will be measured by means of quasielastic neutron scattering at the FOCUS spectrometer at PSI. Furthermore a novel test experiment on the same instrument will be carried out to measure the structure of the water.

Supervisor: Fanni Juranyi

Water dynamics in maize root mucilage

Water scarcity is the main limit to food production worldwide. Recent studies suggest that mucilage exudation by roots helps plants to better tolerate drought. Wet mucilage is a complex hydrogel, which can take up up to 99.9 % of water. Here the diffusion of water will be measured on a molecular scale by quasielastic neutron scattering at the spectrometer FOCUS at PSI. The focus is on the hydration dependence and to find out whether its main component (polygalacturonicacid) plays a determining role in the dynamics or not. This project is a collaboration with the Georg-August-University Göttingen, Germany.

Supervisor: Fanni Juranyi

Evaluation and characterization of the MICA-monochromator at the cold neutron time-of-flight spectrometer FOCUS@SINQ

The aim of the proposed project is to measure the flux and the energy resolution of the MICA-monochromator, which can be used for neutron wavelengths between 6 and 16 Å. Furthermore the contamination by higher-order reflections and the background shall be checked. The project includes experimental beam-time on FOCUS (4-5 days) and data analysis using state–of–the-art software available in our lab. To demonstrate the performance of the monochromator a standard sample will be investigated.

Supervisor: Jan Peter Embs

Definition and evaluation of a precise calibration standard for the reflectometers at the Swiss Spallation Neutron Source SINQ

High-precision measurements of reference samples on the reflectometers Amor, Morpheus and Narziss are needed to establish a new standard for calibrating these instruments, which are used to investigate thin film samples, heterostructures and bio-membranes. The project involves alignment and neutron reflectivity measurements of several (existing) samples, followed by an analysis using standard simulation tools such as Parratt or MOTOFIT. For the measurements 1 to 2 days on each instrument are necessary. The analysis is performed with state-of-the-art software packages.

Supervisors: Jochen Stahn and Thomas Geue.