Project work / Master/Diploma topics in the TEM Gemini Centre, Spring 2012

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1 Project work / Master/Diploma topics in the TEM Gemini Centre, Spring 2012 As a physics/nanotechnology project or diploma student in the transmission electron microscopy (TEM) group you can take an active part in one of the exciting research projects which require finest scale material characterisation. You work together with a PhD student, a SINTEF research team or one of our external collaborators to achieve a common goal. The work can have an applied character and be very practical, or theoretical to support experimental activities within the group. Also a combination of practical and theoretical work is a possibility. In all projects the TEM or input from TEM is used to understand the structure of a material down to the atomic level and relate this to important macroscopic properties. Examples of student projects which are available for the Spring semester 2012 and in which you can participate are: Developing and characterising of new aluminium alloys Studies of nanostructures in functional oxides Analyses of catalyst materials for future applications Studies of solar cell materials (Si, thin films, quantum dots & nanowires) Simulation, quantification and image processing of TEM data. These projects are described in more detail at the end of this document. Earlier, several student projects have led to publications [1-7]. Due to high demand on the research facilities and the intensive supervising we want to give, we can take in max 4 students this semester. People working in the TEM group, on microscopes and with sample preparation. 1

2 We offer: Choice of a project that fits your interests and background. Training in operating advanced scientific equipment (for example TEM) or/and simulation and quantification software (theoretical/modeling). Weekly meetings with a supervisor during the project. Being part of a large and dynamic scientific consortium. Possibility in extending the project (to diploma/phd) or getting a summer job. You are encouraged to contact one of us if you like to hear more details on a specific project, other available projects, options in academia or industry after a diploma in TEM or possibilities to incorporate own research ideas related to TEM. For more information on the current activities within the group, group members, equipment and recent publications, see the TEM Gemini Centre homepage: Contacts: Ton van Helvoort (Room D4-149, Tel , a.helvoort@ntnu.no) Randi Holmestad (Room D4-153, Tel , randi.holmestad@ntnu.no) John Walmsley (Room D4-113, Tel , john.walmsley@sintef.no) References: [1] Butler K.T., Vullum P.E., Muggerud A.M., Cabrera E. and Harding J.H., Structural and electronic properties of silver/silicon interfaces and implications for solar cell performance, Physical Review B, 83, , [2] Todorovic J., Moses A. F., Karlberg T., Dheeraj D. L., Fimland B.-O., Weman H. and van Helvoort A. T. J., Correlated micro-photoluminescence and electron microscopy studies of the same individual heterostructured semiconductor nanowires, Nanotechnology, 22, , [3] van Helvoort, A. T. J., Dheeraj, D. L., Zhou, H., Grønsberg, S., Patriarche, G., Fimland, B. O. and Weman, H., "Dark field transmission electron microscopy techniques for structural characterization of semiconductor nanowire heterostructures", Journal of Physics - Conference Series, 241, , [4] Rørvik P-M, Lyngdal T, Sæterli R, van Helvoort A T J, Holmestad R, Grande T and Einarsrud M-A, "Influence of volatile chlorides on the molten salt synthesis of ternary oxide nanorods and nanoparticles", Inorganic Chemistry, 47, , [5] Marioara CD, Andersen SJ, Birkeland A, Holmestad R, Orientation of Silicon Particles in a Binary Al-Si Alloy, Journal of Materials Science, , [6] Rørvik PM, Almli A, van Helvoort ATJ, Holmestad R, Tybell T, Grande T and Einarsrud MA PbTiO 3 nanorod arrays by self-assembly of nanocrystals, Nanotechnology, 19, , [7] Eberg E, Monsen AF, Tybell T, van Helvoort ATJ and Holmestad R, "Comparison of TEM specimen preparation of perovskite thin films by tripod polishing and conventional ion milling", Journal of Electron Microscopy 57, ,

3 Nano-structure characterization of aluminium alloys development In studies of light metal alloys there are challenges when it comes to establishing relations between the nano-structure and the mechanical properties, as for example strength and ductility. In Al-Mg-Si/Ge-(Cu) alloys, which are industrially relevant due to their superior mechanical properties (high strength /weight ratio and good corrosion properties), the hardness increase is due to precipitation of nanometre-sized metastable phases that form from solid solution during heat treatment. The student project will consist of experimental testing of mechanical properties (such as hardness) with different heat treatments and alloy compositions, and complementary nanostructure studies by TEM. The heat treatment and hardness measurements will be done at the Department of Materials Science and Engineering (IMT). Background in materials physics (solid state physics) and interest in materials science would be an advantage. We need a student interested in experimental work, and working independently in a larger group of scientists. This project is done in close collaboration with SINTEF and Norwegian Light Metal industry (Hydro Aluminium and Steertec Raufoss), and the student will participate in project meetings in this consortium at Sunndalsøra, Raufoss and Trondheim. Within this field there are possibilities for continuation as a PhD student. Contact persons: Randi Holmestad (randi.holmestad@ntnu.no), Calin Marioara (calin.d.marioara@sintef.no) and Ruben Bjørge (ruben.bjorge@ntnu.no). 3

4 Composition of main hardening precipitates in aluminium alloys While a series of intriguing properties of aluminium (Al) alloys, e.g. their light weight, considerable strength and good corrosion properties tend to be known by quite a few people these days, the basics of the mechanism behind the strength most often is not. Pure Al is quite soft and hence of little use to planes, cars etc. The strength of the Al alloy is derived by incorporation of small amounts (often only 1 2 %) of foreign elements and an appropriate subsequent heat treatment, leading to the nucleation of huge amounts of nanosized structures (precipitates) in the Al host material. These precipitates generally tend to affect the flow of dislocations in the material, thereby increasing its strength, with the efficiency of this process however varying greatly with precipitate type, size and number density. Throughout the last decade, the structures of the precipitates in the Al-Mg-Si alloy system have been determined, largely within our group. Recent investigations (experimental as well as theoretical) suggest, however, that precipitate compositions Mg x Si y Al z are still to be properly clarified. This is of huge potential interest to industry for the main hardening precipitates in particular, as clarification is expected to considerably aid the understanding of the interplay between alloy element concentration, heat treatment and strength properties. The student will investigate theoretically main hardening precipitates in the Al-Mg-Si alloy system. The structure of these precipitates is regarded as clarified, but the range of allowed compositions remains uncertain or even largely unknown. Building upon a recent improved understanding within the group of the requirements for precipitate evolution from the cluster stage, the student will systematically investigate isostructural systems with varying compositions in the range of presumed interest. Calculations will employ density functional theory and the plane wave code VASP. Results will be compared with experimental information already available within the group. We seek one student for this project, with a background from physics or nanotechnology. The ideal candidate will have an interest in solid state physics. The project focus is theoretical, but with the importance of linking experiment and calculations emphasized throughout. Throughout the semester, the student is expected to attend weekly meetings with supervisors and the rest of the group, communicating his/her results. Also, as the project will likely involve communication with SINTEF and the Norwegian Light Metal Industry (Hydro Aluminium and Steertec Raufoss), there will be a chance for the student to participate in a project meeting in this consortium, presenting his/her results. This provides an excellent opportunity to encounter the various aspects of alloy optimization through communication with the people in the business. Our hope is that the results obtained can be published. Contact persons: Flemming Ehlers (flemming.ehlers@ntnu.no) and Randi Holmestad (randi.holmestad@ntnu.no). 4

5 Studying heterostructured semiconducting nanowires Semiconductor nanowires with high quality are grown Department of Electronics and Telecommunications (IET) for future application in optical devices (laser) and solar cells. Because of their small size, nanowires have to be studied by characterisation techniques with a high resolution as for example TEM. You will study a batch of nanowires with interesting optoelectric properties. Especially the relation between properties and crystal structure / lattice defects are important. You will learn to use basic TEM techniques as electron diffraction and high resolution imaging techniques. SEM and STEM work within NTNU Nanolab could be part of the project. Your own characterization results are relevant to realize and optimize nanowire-based devices. Interest in experimental work at the TEM. Join weekly project meetings with scientists and other project students that grow the nanowires, use others methods to measure the electric and optical properties of single nanowires or nanowire based devices. Being able to clearly communicate and relate your results to others in the project. This is a relatively new field in which different disciplines work together (Nanotechnology, synthesis & different measure/characterisation techniques). We had already 5 project/diploma students working on TEM of semiconducting nanowires. They obtained impressive results within the short duration of their projects. These students results were published in good journals. The obtained practical skills can be applied in the study of other nanostructures. Contact persons: Ton van Helvoort (IFY, a.helvoort@ntnu.no). Other key people in the project: Jelena Todorovic (IFY, Jelena.todorovic@ntnu.no), Vidar Fauske (IFY, vidar.fauske@ntnu.no), Helge Weman (IET) and Bjørn-Ove Fimland (IET). 5

6 TEM studies of catalysts for future applications In collaboration with the Department of Chemical Engineering (IKP) we study different types of porous materials (substrates) with small metal particles which are used as catalysts in a broad range of catalytic processes. To understand the properties of the catalysts it is of crucial importance to know the size (down to a few nanometers) and the structure of the particles, in addition to their composition. We are now establishing a tomography technique which makes it possible to image these particles and substrates in 3D. We also have equipment to study these metal nano particles in reduced states, without exposing them to oxygen. We have in this project collaboration with Statoil-Hydro. Contact persons: John Walmsley (john.walmsley@sintef.no), Dung Trung Tran (dung.tran@ntnu.no), Magnus Rønning (IKP) and Anders Holmen (IKP). TEM characterization of oxide thin films Oxide materials show superior optical, magnetic, dielectric, piezoelectric, and electric conduction (superconductivity, ionic conductivity, semiconductivity) properties, as well as excellent mechanical performance, which make them an important and promising class of functional materials. In the oxide electronics group at Department of Electronics and Telecommunications (IET) they have currently large focus on the effect of interfaces on ferroelectric and piezoelectric materials. The goal is to understand how interfaces can be used to control properties for applications within sensor technologies. Recently they have started to study how to utilize the 2-dimensional-electron gas at the interface between SrTiO 3 and LaAlO 3. Another system is the colossal magneto resistant material (La,Sr)MnO 3. The thin films are grown by the Pulsed Laser Deposition (PLD) technique. Study the crystal structure and the coherence in the thin films using TEM, and correlate this with properties. An important aspect here is to make good cross section samples, and TEM sample preparation will be a considerable part of the work. We seek students with background from physics or nanotechnology. Interest in solid state physics and electronics is needed. We need a student interested in experimental work, and working independently. Accuracy and patience are needed for the sample preparation work. Contact persons: Randi Holmestad (randi.holmestad@ntnu.no) and Thomas Tybell (IET). 6

7 Data processing of electron microscope experimental results Electron microscopy can map material properties such as composition with high spatial resolution. One example is when the characteristic x-ray yield that is generated by a focused, scanning electron beam is used to monitor the local composition in a thin foil. Another is three dimensional tomographic reconstruction exploiting the scattering intensity of electrons when a sample volume has been imaged over a range of orientations. These techniques are widely used, but commercial software is often limited in terms of extracting the maximum amount of quantitative information or dealing with difficult data sets. Composition mapping results published in the scientific literature often suffer from these limitations and processing of noise and statistical significance of weak signals are generally ignored. It is possible to take raw data produced during analysis and process them using software packages such as IDL and MATLAB to address this. Also other simulation projects, based on topics such as Electron Energy Loss Spectroscopy fine structure (ELNES), Principle Components Analysis (PCA/MSA), strain analysis (GPA) and simulations of High Angle Annular Dark Field (HAADF)STEM images are available. The student will work with new and existing data sets to develop the type of procedure described above. From this starting point, there are a range of possibilities, ranging from exploring the detailed data extraction to producing a user-friendly interface to make algorithms readily available to other users as an advanced tool. An interest in using and developing software tools is required. The student will be expected to develop an understanding of the problems to be addressed, require good communication and interaction with scientific and academic staff and PhD students. The intention is that final results will form a part of ongoing research programmes and contribute to a publishable result. Contact persons: John Walmsley (john.walmsley@sintef.no), Ragnvald Mathiesen, Randi Holmestad (randi.holmestad@ntnu.no), Ragnhild K. Sæterli (ragnhild.saterli@ntnu.no), Dung Trung Tran (dung.tran@ntnu.no) and Ton van Helvoort (a.helvoort@ntnu.no) References 1. M.H. Larsen, J.C. Walmsley, O. Lunder and K. Nisancioglu, Effect of excess silicon and small copper content in on intergranular corrosion of 6000-series aluminium alloys, 2010, Journal of the Electrochemical Society, 157, 2, C61-C M.H. Larsen, J.C. Walmsley, Otto Lunder, R.H. Mathiesen, and K. Nisancioglu, 2008, Intergranular Corrosion of Copper Containing AA6xxx AlMgSi Aluminum Alloys, Journal of the Electrochemistry Society, 155, 11, C550-C J.C. Walmsley, Ø Sævik, B Graver, R.H. Mathiesen, Y. Yu. and K. Nisancioglu, 2007, Nature of Segregated Lead on Electrochemically Active AlPb Model Alloy, J. Electrochem. Soc. 154 (1) C28-C35. 7

8 TEM characterization of solar cell materials At NTNU there are several ongoing projects for improving conventional Si-based solar cells and develop new, mostly non-si, materials. TEM studies are part of many of these studies as defects, interfaces, size/shape and composition variations at the nm-scale can determine the overall efficiency of the solar cell. Study the crystal structure and different phases in nanostructures or thin films using TEM, and correlate this to process parameters and properties. An important aspect here may be to make good cross section TEM samples, and sample preparation could be a considerable task. The actual work will depend on the type of material. For conventional Si the focus will lie on defect characterization and anomalies at interfaces with electrodes. For quantum dot intermediate band solar cells (QD-IBSC), the focus will lie on QD-density and strain characterization. For the thin films, developing a specimen preparation routine that allows efficient characterization of film size, crystallinity and defects will be important. In the nanowire project effect of doping on crystallinity and morphology in relating to the electro-optical properties is central. We seek students with background from physics or nanotechnology. Interest in solid state physics and nanoscience is needed. We need a student interested in experimental work, working independently and being able to communicate her/his findings efficiently to the research groups synthesizing the materials or measuring the efficiency. There is a large activity at Gløshaugen on solar cell materials, and the student will get the possibility to join this activity, with participation in weekly lunch meetings etc. SEM and STEM work within NTNU Nanolab could be part of some of the suggested projects. Contact persons: Quantum dots solar cells: Ragnhild K. Sæterli (ragnhild.saterli@ntnu.no), Turid Worren Reenaas (IFY), Randi Holmestad (randi.holmestad@ntnu.no), Per Erik Vullum (per.erik.vullum@sintef.no). Silicon solar cells: Randi Holmestad (randi.holmestad@ntnu.no), Per Erik Vullum (per.erik.vullum@sintef.no) and John Walmsley (john.walmsley@sintef.no). Thin film and nanoparticle solar cell materials: Ragnhild K. Sæterli (ragnhild.saterli@ntnu.no), Randi Holmestad (randi.holmestad@ntnu.no), Ton van Helvoort (a.helvoort@ntnu.no), Mari-Ann Einarsrud (IMT) and Tor Grande (IMT). Nanowire solar cell materials: Ton van Helvoort (a.helvoort@ntnu.no) 8