Analysis of advanced materials and structures by SIMS method

Bakalářská práce se zabývá studiem pokročilých materiálů metodou SIMS a možnostem kvantitativní analýzy pomocí dat získaných z měření. Byla provedena chemická analýza povrchu keramiky s cílem optimalizace podmínek měření. Zbytek práce využívá datový výstup z měření pro popsání vnitřní mikrostruktury materiálu. Pomocí sofistikovaných metod jsou lokalizovány a popsány Si precipitáty ve vrstvě AlSi a ověřena formace fáze MgAl2O4 ve vzorcích keramiky. Dosažení všech stanovených cílů odhaluje potenciál metody SIMS a především možnosti ve zpracování datového výstupu z měření.Bachelor theasis deals with the study of advanced materials by SIMS method and the possibilities of kvantitative analysis using maesured data. Chemical analysis of the ceramic surface in order to optimize the measurement conditions was performed. The rest of the work uses the data output from the measurement to describe the internal microstructure of the material. Using sophisticated methods, Si precipitates in the AlSi layer are localized and described, and the formation of the MgAl2O4 phase in ceramic samples is confirmed. Achieving all the set goals reveals the potential of the SIMS method and, above all, the possibility of processing the data output from the measurements.

Complex ion beam based depth profiling of anticorrosive layers

Předložená diplomová práce se zabývá implementací metody rentgenové emisne indukované částicemi do experimentálního uspořádání za účelem doplnění rodiny metod založených na iontových technikách, tj. Rutherfordovy zpětné rozptylové spektrometrie, spektrometrie elastického zpětného rozptylu a analýzy detekce doby letu/energie elastického odrazu. Výhoda více-metodického přístupu je demonstrována na vrstvách ze slitin přechodných kovů obsahujících lehké prvky, kde samo-konzistentní analýza poskytuje výrazně zlepšené a přesné informace o stechiometrii, hloubkovém rozložení a tloušťce slitiny. Hmotnostní spektrometrie sekundárních iontů je použita pro porovnání a doplnění získaných výsledků.Presented master’s thesis deals with the implementation of the Particle Induced X-ray Emission method in the experimental setup with the aim to supplement the family of ion beam based techniques, i.e. Rutherford Backscattering Spectrometry, Elastic Backscattering Spectrometry and Time-of-Flight/Energy Elastic Recoil Detection Analysis. The advantage of a multi-method approach is demonstrated on the transition metal alloy films containing light species, where the self-consistent analysis yields significantly improved and accurate information about stoichiometry, depth distribution and thickness of the alloy. Secondary Ion Mass Spectrometry is employed to compare and complement the obtained results.

On the correlation of angular distributions of keV ions and trajectory-dependent electronic excitations in transmission channelling geometry

We use energy discrimination of keV ions transmitted through a thin, single-crystalline silicon membrane to correlate specific angular distribution patterns formed in channelling geometry with trajectory-dependent electronic energy loss. The integral energy and intensity distribution of transmitted ions can thus be dissected into on one side axially channelled projectiles travelling along rather straight trajectories and on the other side dechannelled projectiles predominantly experiencing blocking. Angular distributions of transmitted ions are further simulated with two different Monte-Carlo codes.Comment: 9 pages, 5 figures, conferenc

Trajectory dependence of electronic energy-loss straggling at keV ion energies

We have measured the electronic energy-loss straggling of protons, helium, boron and silicon ions in silicon using a transmission time-of-flight approach. Ions with velocities between 0.25 and 1.6 times the Bohr velocity were transmitted through single-crystalline Si(100) nanomembranes in either channelling or random geometry to study the impact parameter dependence of energy-loss straggling. Nuclear and path length contributions to the straggling were determined with the help of Monte Carlo simulations. Our results exhibit an increase in straggling with increasing ion velocity for channelled trajectories for all projectiles as well as for protons and helium in random geometry. In contrast for heavier ions, electronic straggling at low velocities does not decrease further but plateaus and even seems to increase again. We compare our experimental results with transport cross section calculations. The satisfying agreement for helium shows that electronic stopping for light ions is dominated by electron-hole pair excitations, and that the previously observed trajectory dependence can indeed be attributed to a higher mean charge state for random trajectories. No agreement is found for boron and silicon indicating that local electron-promotion and charge-exchange events significantly contribute to energy loss at low velocities

Simultaneous assessment of energy, charge state and angular distribution for medium energy ions interacting with ultra-thin self-supporting targets: A time-of-flight approach

We demonstrate simultaneous measurements of the charge state, energy and angular distribution of keV ions in transmission experiments through self-supporting foils. Using a time-of-flight approach we have introduced an electrostatic deflection apparatus as an extension to existing medium energy ion scattering (MEIS) instrumentation. Different positive, neutral and negative charge states have been discriminated and quantified for initially singly charged beams of He, N, O and Ne in the energy range from 25 to 250 keV. In parallel, the ion energy after interaction with the target has been assessed for all detected particles, while particles can be discriminated by deflection angle. Self-supporting thin carbon foils were used as samples to benchmark our experiments with literature data where available

Local electronic excitations by slow light ions in tungsten

Accurately predicting the electronic energy deposition of ions in materials is an important challenge in both fundamental and applied research. While employing ab initio simulations to investigate electronic stopping of ions in matter holds promise, its combined use with experimental measurements paves the way for obtaining reliable data. In this paper, we present a collaborative study using real-time time-dependent density functional theory and experimental methods to determine the electronic stopping power of hydrogen and helium ions in tungsten, a primary candidate material for future nuclear fusion devices. While calculated stopping powers in hyperchanneling trajectories are significantly lower than the experimental data, off-center and random geometries demonstrate a better agreement. We show that the deviation from velocity proportionality for both projectiles traversing the hyperchanneling directions can be explained through the existence of a threshold velocity leading to the activation of semicore states. Additionally, we analyse the pseudopotential and the trajectory dependence of computed electronic energy losses. It is demonstrated that the role of including inner-shell electrons varies depending on the velocity range. While these states play a crucial role at high projectile velocities by introducing additional dissipation channels, their impact diminishes in the low-velocity range. Finally, we introduce a simple expression that links electronic energy losses in different trajectories to local electron density, and we show that utilizing this formula allows for quite accurate predictions of stopping powers around the Bragg peak

Analysis of advanced materials and structures by SIMS method

Bachelor theasis deals with the study of advanced materials by SIMS method and the possibilities of kvantitative analysis using maesured data. Chemical analysis of the ceramic surface in order to optimize the measurement conditions was performed. The rest of the work uses the data output from the measurement to describe the internal microstructure of the material. Using sophisticated methods, Si precipitates in the AlSi layer are localized and described, and the formation of the MgAl2O4 phase in ceramic samples is confirmed. Achieving all the set goals reveals the potential of the SIMS method and, above all, the possibility of processing the data output from the measurements

Charge state distributions of Xenon ions with keV kinetic energies transmitted through graphene and carbon self-supporting foils

We investigated the charge state distributions and energy loss of single and double-charged Xenon ions (20-220 keV) passing through graphene, Quantifoil, and 10 nm thick carbon membranes. Utilizing simultaneous carbon recoil detection on the graphene-containing sample, we determined the areal density of carbon equivalent to 3 monolayers of graphene, indicating only slight contamination by e.g. PMMA, of our exiting surfaces. The charge state distributions revealed notable proportions of higher charge states, up to Xe+5 at higher energies, with mean charge states consistently below 1. The observed exponential decrease in higher charge fractions suggests electron stripping processes play a significant role. Differences in mean charge states are found among the three systems studied

Trajectory-dependent electronic excitations by light and heavy ions around and below the Bohr velocity

We present experiments demonstrating trajectory-dependent electronic excitations at low ion velocities, where ions are expected to primarily interact with delocalized valence electrons. Experiments were performed using pulsed beams of singly charged ions incident on self-supporting Si(100) nanomembranes, and energy was measured together with the angular distribution after transmission through the sample. The energy loss of H+, H2+, He+, N+, Ne+, 28/29Si+ and Ar+ was analyzed along channeled and random trajectories. For all ions, we observe a difference in electronic stopping dependent on crystal orientation. For protons, the difference between channeled and random trajectories increases with ion energy, which is explained by increasing contributions of core-electron excitations more likely to happen at small impact parameters accessible only in random geometry. For heavier ions, the energy loss difference between channeling and random geometry is generally found more pronounced, and, different from protons, increases for decreasing ion energy. Due to the inefficiency of core-electron excitations at employed ion velocities, we explain these results by reionization events occurring in close collisions of ions with target atoms, which are heavily suppressed for channeled trajectories. These processes result in trajectory-dependent mean charge states, which strongly affects the energy loss. The strength of the effect seems to exhibit an oscillation with Z1 with an observed minimum for Ne. We, furthermore, demonstrate that the simplicity of our experimental geometry leads to results that can serve as excellent benchmark systems for dynamic calculations of the electronic systems of solids using time-dependent density functional theory

Energy deposition by H and He ions at keV energies in self-supporting, single crystalline SiC foils

The specific energy deposition of H and He ions in SiC has been studied for both random and channeling orientations. The experiments were carried out in transmission geometry using the Time-of-Flight Medium Energy Ion Scattering System at the 350 keV Danfysik Implanter at Uppsala University. The target was a self-supporting, single crystalline cubic 3C-SiC (100) foil with nominal thickness of 200 nm. The measured stopping cross sections are compared with data available from the literature and theoretical predictions. The results for random geometries reveal slightly lower values than predicted by SRIM for H projectiles whereas for He projectiles good agreement was observed over the whole energy range studied. Higher specific energy loss is observed along random trajectories in comparison to channeling geometry, for all measured energies and for both H and He ions. For H ions, however, differences are minor, whereas for He ions, they are found generally more pronounced