Master Projects in Materials Physics, 2010 / 2011

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1 Master Projects in Materials Physics, 2010 / 2011 X-ray based characterization of functional materials Dag W. Breiby & Ragnvald Mathiesen The X-ray group headed by Breiby and Mathiesen constitutes the leading national competence centre in general X-ray science. The group was founded recently (2007), but has already gained sizable momentum both in terms of laboratory facilities, external funding and group activities. Presently, the group has three PhD students, one post-doc, several project and master students and an engineer (part time), all working on activities related to the projects described here. The group has an excellent international network, and (NB!) is also regularly assisting MSc students in finding appropriate locations for a semester or two abroad. We are convinced that a project in our group is a wise choice for clever students who enjoy experimental work. A certain aptitude for data analysis and computer programming is a benefit. It is possible to combine elements from different projects to tailor the project to the interests of the student. Through these projects, you get a unique possibility of doing experimental work using first-class experimental facilities. Students tending to favour more theoretical problems also get their fair share many of the suggested studies are mathematically complex and involve rather challenging computer programming. That a considerable touch of materials science and nanotechnology is involved goes without saying. In any case, the projects are real problems with an obvious practical relevance, making them suitable both for students seeking a continued academic career, but also for those who consider a position in industry their next step. Dag W. Breiby started working as associate professor at the Department of Physics in July Breiby holds a PhD in materials physics from NTNU (2003), and has later on been working at Risø DTU, the University of Copenhagen and Vestfold University College. Focus has been on X-ray characterization of functional organic films. Breiby has supervised about ten Danish and Norwegian MSc students, on problems ranging from diffraction studies of nano-particles and organic films to measurements and computer simulations of scattering characteristics from ferroelectric films and liquid crystals. Office D4-145, Dag.Breiby@ntnu.no, (735) Ragnvald Mathiesen is employed as associate professor at the Department of Physics since September Mathiesen has MSc and PhD (1997) academic degrees in materials physics from NTNU. After obtaining his PhD, Mathiesen worked as post doc at NTNU and at the ESRF in Grenoble, later as scientist at the Department of Inorganic Chemistry, UiO. From 2001 to 2007 Mathiesen was a senior scientist and group leader within SINTEF Materials. Mathiesen has worked both on diffraction physics and with the use of synchrotron X-ray radiation for studying a long range of different materials and areas within solid state physics. Office D4-133, Ragnvald.Mathiesen@ntnu.no, (735)

2 X-rays scattering is an exciting scientific field with tremendous impact on society, via "standard" applications in industry and at hospitals, but also by branching into virtually all fields of the natural sciences. X-ray scattering is currently going through rapid development, which can largely be ascribed to radical experimental improvements, both at synchrotron installations and at the more traditional X-ray laboratories at the universities, and the projects proposed here should be understood in this context. The suggested topics are suitable for students interested in nanotechnology, who enjoy experimental work and computer programming. The projects can be modified according to the particular wishes of the students, and can be adapted for 9 th semester project and final Master projects. For all the suggested projects it is an expressed aim that resulting high quality work should get incorporated in academic publications co-authored by the student. For exceptional students, participation in synchrotron experiments can be envisioned. The projects are suitable for students with a background in physics, nanotechnology, materials science and physical electronics (some also for computer science students). Figure 1 Maps of diffuse scattering in reciprocal space. From the intensity distribution of the diffuse scattering, new knowledge concerning the domain structures in ferroelectric materials can be obtained (J.B. Fløystad, Master thesis, 2010).

3 Theme: X-ray physics (and quite a lot of computer programming!) Project: X-ray Talbot interferometry! X-ray radiation from traditional X-ray sources is incoherent, with the limitations this imposes on imaging and holography. Quite recently, optical interference methods have been explored to partially circumvent this problem [Pfeiffer et al, Nature Phys. 2, 258 (2006)]. An obvious near-future application of this technique is improved CT ( computed tomography ) images in medicine. Later on, the further developments of this technique is expected to be used for studies of functional materials at the nanoscale, and an ultimate goal is to achieve single molecule imaging using the forthcoming free-electron X-ray lasers being developed for example in Hamburg. In this MSc project, which involves computer programming and experimental studies, coherent imaging is addressed using laser setups. Project: X-ray raster scanning. New equipment developments (here: mainly micro-focus sources, fast-readout area detectors, and precise sample positioning stages) facilitate raster scanning scattering experiments. The concept is simple: by making a series of X-ray scattering measurements with a narrow beam (~10 μm), with each new measurement slightly offset from the previous, systematic variations in the measured signal (e.g., modifications of unit cell dimensions and orientations) can be related to macroscopic features of the sample. Samples of particular interest for this project include polymer samples subjected to various mechanical treatment, and also, of course, biological samples. A conceptually simple example of raster scanning is shown to the left, with the X-ray absorption of a spider mounted on a vertical needle (S. von Kaminietz, project 2009). Some internal structure of the spider is readily seen. The image is made from a large number (> 10 3 ) of point measurements. More advanced information, like the growth direction of fibrous tissue, can be obtained by synthesizing similar images based on the scattered signal (rather than just from the transmitted beam intensity, as shown here). Project: Fibre diffraction. ColdWear (see is a project involving Sintef, NTNU and Norwegian textile industry, with possibilities for MSc students interested in applied material science. Polymers ("plastics") in general are of immense industrial importance, and conjugated polymers are also promising as functional materials for use in organic electronics. By incorporating sensors into textiles, the aim is to improve user safety and comfort when working in the High North. Specifically, the MSc student will be working with characterization of fibres, membranes and stimuli-responsive materials, primarily based on AFM and X-ray scattering methods.

4 Project: Instrument modelling. This project relates to measuring and simulating the performance (flux, resolution, etc) of the new multipurpose 4-circle diffractometer at the Department of Physics. After having measured the profile and intensity of the X-ray beam at several points along the beam path, statistical methods like Monte Carlo ray tracing will be employed to faithfully model the different components of the instrument (source, monochromating and focusing mirror, slits, collimator, etc). The obtained model will subsequently be employed for optimising the instrument performance and to validate future scattering experiments. This project is particularly adequate for students interested in computer programming and "practical" problems. Project: Scattering simulations using graphics cards. (In collaboration with Prof. Ingve Simonsen). Simulations are central in the analysis of X-ray scattering data, and these simulations are often computationally intensive. Over the last few years, it has been demonstrated that modern graphics cards can speed up many numerical problems times compared to normal CPUs [Editors' Choice, Science 327 (2010)]. The aim of this project is to exploit the vast computational power of modern graphics cards to tackle large simulation problems related to X- ray scattering. Relevant problems include multiparameter fitting of highly non-linear models for reflectivity and diffuse scattering (using genetic algorithms or derivative-based approaches), statistical techniques ("bootstrap") for uncertainty analysis, and model optimization based on weighted data from disparate experimental techniques. The project is suitable for candidates with an interest in physics and excellent programming skills. Theme: Nanoparticles for catalysis Our group collaborates with the group of Prof. Magnus Rønning at the Department of Chemical Engineering. A post-doc and a PhD student are currently being hired on this project, aiming to investigate nanoparticles designed for catalysis. Project: SAXS of nanoparticles, experiment. This is an experimental "hands on" project dealing with small angle X-ray scattering (SAXS) from core-shell nanoparticles. Rønning's group is able to grow low poly-dispersity ("~all same size") nanoparticles of well-defined shape (spherical, ellipsoidal, tetrahedral, etc). In this project, the student is expected to investigate the nanoparticles in solution, and to deduce the structural information from the SAXS signal. A systematic extension of the project might be to subsequently measure the same nanoparticles as deposited on a solid substrate (using grazing incidence SAXS, GISAXS). Particular challenges are related to establishing reproducible measurement schemes for reliable quantitative analysis. Training in Denmark is a likely bonus if choosing this project. If more than one student is interested in this study, a "dual race" with one candidate paying more attention to the equally challenging computer modelling aspects can be arranged.

5 Theme: Ferroelectric thin films Our group collaborates with the group of Prof. Thomas Tybell at the Department of Electronics and Telecommunication on a project on epitaxially grown ferroelectric thin films, typically lead titanate (PbTiO3). Ferroelectrics have a spontaneous electrical polarization which can be switched by applying an electric field. There is a large interest in these materials due to several promising technological applications, with ferroelectric memories as the most exciting. However, many important properties and much interesting physics of these materials in thin film form are still not understood. We focus on characterizing the ferroelectric films using X-ray methods, both using our home laboratory and synchrotron X-ray laboratories abroad. Project: Measuring strain in ferroelectric thin films. Through scattering experiments our group has recently discovered complicated internal strain patterns in ferroelectric films [Fløystad, to be published]. The primary goal of this project is to perform state-of-the-art home lab scattering measurements of lead titanate thin films, partially using our new PILATUS 1M detector. The candidate is challenged to find measurement schemes to maximize the signal-tonoise ratio, while maintaining a reasonable measurement time. A possible extension of the project is to apply a mechanical strain to the film, by placing the sample in a miniature "bending fixture". This will require a custom-made sample holder, which the student should help design together with our engineer. Our home laboratory has all the equipment required for performing reflectivity and related measurements, but if beamtime at synchrotrons abroad becomes available, the student should participate in these experiments. The programming skills required for this project are modest. Theme: Inorganic alloys Project: Ni-based super-alloys are often added considerable amounts of Cr and Fe in solid solution to improve the mechanical and corrosive properties of the material. Generally, these alloys exhibit excellent resistance towards corrosion, even in aggressive environments. However, in the temperature range C and during exposure to carbon and water vapour-containing gas, the corrosive resistance of Ni-based super alloys (as well as certain steel qualities) is strongly reduced. These processes, coined Metal Dusting (MD), can be ascribed to an unfortunate combination of carburization and oxidation, and can in the worst case convert mm-thick metal to fine grained "dust" in the course of just weeks or months. A common feature of MD is that various carbide and oxide particles segregate towards the metal surface. This leaves the bulk material with a significant gradient in concentration and micro-strain that further accelerates the break-down of the material. In this project, the student is challenged to map out the influence of the alloy content of Cr and Fe on the lattice parameters (and thus strain) by using X-ray diffraction. A summer internship at the StatoilHydro Rotvoll research centre may be included as part of the project.