Low-energy ion scattering (LEIS) probes the outermost atomic layer of a surface by backscattering of noble gas ions. Under certain conditions, also depth profiles up to 5–10 nm depth can be obtained. LEIS spectra of hydrogen containing samples have a background signal at the low energy side of the spectrum due to hydrogen atoms that are sputtered away and ionised by the noble gas ions used for probing the sample. Time-of-Flight (TOF) measurements can separate the hydrogen ion signal from other sputtered elements and backscattered ions. A previous bachelor student project has shown that the thus obtained hydrogen signal is indeed proportional to the hydrogen content of the sample. In this assignment, the focus will be on a better understanding of the detection depth of hydrogen by LEIS, the possibilities for quantification and the detection of hydrogen in sputter depth profiles.
LEIS spectra of clean and hydrogen exposed Pd. The red and blue line show the signal of backscattered He+ ions for Pd cleaned by Ar ion sputtering and after exposure to H atoms, respectively. The green line shows the signal due to sputtered H ions.
To measure X-ray diffraction plots from various thin metallic films optimizing measurement conditions with the goal to select the best measurement scheme and determine the best measurement scheme and determine the instrumental function of different optical elements.
A broadband transmission grating spectrometer approach
The XUV Optics group is undertaking an exciting project based on a newly developed optical component: a nanoscale patterned transmission grating that enables high resolution spectroscopy. The project goal is to do a comprehensive spectral characterization of EUV sources, through measurement of source spectrum in a broad wavelength range, from EUV to visible. Industry has shown interest and a recent grant was received for further optical and technological development of spectrometers. Currently a wealth of spectroscopic data is being gathered from several EUV sources including the most powerful industrial sources in the world.
The goal in this assignment (BSc or MSc) can be designing of new gratings or developing methods for retrieval of the emitted spectra from measurements. A particular challenge in the retrieval is the overlap of several diffraction orders of the grating and contribution of the noise. Candidate solutions include a first method to stitch spectra retrieved from 1st order measurements with several bandpass filters, and a second method to remove all higher order diffraction contributions from measured spectrum. In this project, you can gain experience in principles of spectrometers and spectroscopic analysis.
This project aims for the development of multilayer systems for the use as spectroscopic elements. These serve the purpose of analyzing soft x-ray emission spectra of materials e.g. upon excitation by x-rays or electrons. The analysis then allows the quantitative determination of the x-ray emitting elements in the materials, a technique which in the final application reaches great precision, preferably down to the ppb range. The desired wavelength range for this application is in the 10 to a few nm band, with emphasis on the range below 6 nm, including the so-called water window, below 4.4 nm. To reach substantial reflectivity, the multilayered optics need to have atomically sharp layer interfaces. To meet this extreme requirement, different approaches on layer growth manipulation will be applied: low-energy ion beams during the layer deposition process, thermalized particle deposition, unbalanced magnetron sputtering with high flux of low energy particles. Other new approaches are continuously being proposed and tested. A series of metrology techniques is to be applied: at-wavelength reflectometry, Cu-Kα-reflectometry and diffraction, low energy ion scattering, XPS, AES, AFM, STM, and TEM.
Synthesis of atomically thin multilayer structures with thermalized particles and low energy ions.
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