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Dr. René Heller

Lei­ter Ionen­strahlanalytik
r.hellerAthzdr.de
Tel.: +49 351 260 3617

Publikationen - Ionenstrahlanalytik

Hier finden Sie aktuelle Veröffentlichungen, die aus Nutzerexperimenten und Kollaborationen mit unserer Gruppe entstanden sind.

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First HDZR Author OU: Ionenstrahlanalytik (FWIZ-A)

Tracer diffusion in proton-exchanged congruent LiNbO3 crystals as a function of hydrogen content

Dörrer, L.; Heller, R.; Schmidt, H.

The proton-exchange process is an effective method of fabricating low-loss waveguides based on
LiNbO3 crystals. During proton-exchange, lithium is replaced by hydrogen and Li1 xHxNbO3 is formed.
Currently, mechanisms and kinetics of the proton-exchange process are unclear, primarily due to a lack
in reliable tracer diffusion data. We studied lithium and hydrogen tracer diffusion in proton-exchanged
congruent LiNbO3 single crystals in the temperature range between 130–230 1C. Proton-exchange was
done in benzoic acid with 0, 1, 2, or 3.6 mol% lithium benzoate added, resulting in micrometre thick
surface layers where Li is substituted by H with relative fractions between x = 0.45 and 0.85 as
determined by Nuclear Reaction Analysis. For the diffusion experiments, ion-beam sputtered isotope
enriched 6LiNbO3 was used as a Li tracer source and deuterated benzoic acid as a H tracer source.
Isotope depth profile analysis was carried out by secondary ion mass spectrometry. From the
experimental results, effective diffusivities governing the lithium/hydrogen exchange as well as individual
hydrogen and lithium tracer diffusivities are extracted. All three types of diffusivities can be described by
the Arrhenius law with an activation enthalpy of about 1.0–1.2 eV and increase as a function of hydrogen
content nearly independent of temperature. The effective diffusivities and the lithium tracer diffusivities
are identical within a factor of two to five, while the hydrogen diffusivities are higher by three orders of
magnitude. The results show that the diffusion of Li is the rate determining step governing the protonexchange
process. Exponential dependencies between diffusivities and hydrogen concentrations are
determined. The observed increase of Li tracer diffusivities and effective diffusivities as a function of
hydrogen concentration is attributed to a continuous reduction of the migration enthalpy of diffusion by
a maximum factor of about 0.2 eV. Simulations based on the determined diffusivities can reproduce the
step-like profile of hydrogen penetration during proton-exchange.

Verknüpfte Publikationen


Investigation of matrix independent calibration of oxygen in glow discharge optical emission spectrometry

Hoffmann, V.; Gebel, B.; Heller, R.; Gemming, T.

The performance of glow discharge optical emission spectrometry for matrix independent oxygen determination was
investigated using the spectral lines of atomic oxygen at 130 nm and 777 nm and standard conditions for dc discharge with a
4 mm anode (700 V, 20 mA). Using hot-pressed calibration samples of Cu-, Al- and Mg-powder mixed with their oxides, at
130 nm the dependence of the emission yield on these matrices was confirmed. However, at 777 nm oxygen has the same
emission yield in these matrices. In order to compare the emission yield of oxygen with the emission yield in iron a thick 43
μm FeO-layer was prepared and characterized by Rutherford backscattering spectrometry, X-ray diffraction and glow
discharge optical emission spectrometry. At 130 nm, the emission yield of oxygen in FeO is most similar to that in an Almatrix.
At 777 nm, the calibration revealed a higher emission yield of oxygen in FeO in comparison to the common emission
yield of oxygen in Cu-, Al- and Mg-matrices. © 2022 The Royal Society of Chemistry

Keywords: glow discharge; optical emission spectroscopy; material science

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In situ stability study of WAlSiN based selective absorber under heating and cooling cycles in vacuum up to 800°C

Lungwitz, F.; Niranjan, K.; Munnik, F.; Hübner, R.; Garcia Valenzuela, A.; Escobar Galindo, R.; Krause, M.; Barshilia, H.

In situ measurements using RBS, ERD, and SE are less explored in characterizing solar absorber materials at high temperatures [1, 2]. In the present work, we report the W/WAlSiN/SiON/SiOO2 based spectrally selective solar absorber coating with excellent optical, compositional and structural properties at high temperatures [3, 4]. We have carried out in situ Rutherford backscattering spectrometry, elastic recoil detection and spectroscopic ellipsometry measurements at three different temperatures at 450°C, 650°C, and 800°C. An optical model describing perfectly the reflectance and ellipsometric data was developed. Further, the microstructural properties of the solar absorber coating are evaluated using cross-sectional transmission electron microscopy before and after annealing. Our data obtained before and after the heating experiments demonstrate excellent compositional, optical and structural stability of the coatings under the applied conditions. Furthermore, in situ ellipsometry showed the conservation of the optical properties of the W/WAlSiN/SiON/SiOO2 based spectrally selective solar absorber up to 800 °C, which is crucial for high-temperature applications.
[1] Ramón Escobar Galindo, Matthias Krause, K. Niranjan and Harish Barshilia, in Sustainable Material Solutions for Solar Energy Technologies (ed. Mariana Fraga, Delaina Amos, Savas Sonmezoglu, Velumani Subramaniam, Elsevier, 2021).
[2] Lungwitz, F. et al. Transparent conductive tantalum doped tin oxide as selectively solar-transmitting coating for high temperature solar thermal applications, Solar Energy Mater. Solar Cells 196, 84-93, doi:10.1016/j.solmat.2019.03.012 (2019).
[3] K. Niranjan, A. Soum-Glaude, A. Carling-Plaza, S. Bysakh, S. John, H.C. Barshilia, Extremely high temperature stable nanometric scale multilayer spectrally selective absorber coating: Emissivity measurements at elevated temperatures and a comprehensive study on ageing mechanism, Solar Energy Mater. Sol. Cells 221 (2021) 110905, doi:10.1016/j.solmat.2020.110905.
[4] K. Niranjan, A.C. Plaza, T. Grifo, M. Bordas, A. Soum-Glaude, H.C. Barshilia, Performance evaluation and durability studies of W/WAlSiN/SiON/SiOO2 based spectrally selective solar absorber coating for high-temperature applications: A comprehensive study on thermal and solar accelerated ageing, Solar Energy 227 (2021) 457–467, doi:10.1016/j.solener.2021.09.026.

Keywords: Concentrated solar power; high-temperature solar-selective coatings; nanolaminates; in situ analysis; ion beam analysis; STEM-EDXS imaging

Verknüpfte Publikationen

  • Poster
    PSE 2022 - 18th International Conference on Plasma Surface Engineering, 12.-15.09.2022, Erfurt, Deutschland

Contrast modes in transmission experiments using broad and focussed keV ion beams

Lohmann, S.; Hlawacek, G.; Holeňák, R.; Klingner, N.; Primetzhofer, D.; Serralta, E.

The helium ion microscope (HIM) is an instrument for high-resolution imaging, composition analysis, and materials modification at the nanoscale. Ion transmission experiments could further improve the analytical capabilities of this technique, and multiple contrast modes are possible. We explore the latter at keV ion energies using a HIM in a scanning transmission approach as well as a broad beam in combination with a time-of-flight (ToF) set-up. Both systems employ positionsensitive detectors allowing for analysis of angular distributions.
In the ToF-system, we find a strong trajectory-dependence of the measured specific energy loss attributed to charge-exchange events in close collisions. Channelling and blocking of transmitted ions allows for mapping of intensity as well as different energy loss moments. In the HIM we demonstrate different contrasts, e.g., due to orientation of nanocrystals, channelling in single-crystalline membranes and material contrast for layered films.

Verknüpfte Publikationen

  • Vortrag (Konferenzbeitrag)
    DPG-Tagung der Sektion Kondensierte Materie (SKM), 04.-09.09.2022, Regensburg, Deutschland

Influence of crystal structure on helium-induced tendril formation in an FeCoCrNiV high-entropy alloy

Lohmann, S.; Goodall, R.; Hlawacek, G.; Hübner, R.; Ma, L.; Gandy, A. S.

High-entropy alloys (HEAs) are a relatively new class of metal alloys composed of several principal elements, usually at (near) equiatomic ratios. It has previously been reported that some HEAs dis-play superior radiation damage resistance, with composition and microstructure being cited as con-tributing factors, though the precise mechanism is still unknown. To study the influence of the crys-tal structure on the response to radiation, we have chosen FeCoCrNiV as a model system. While FeCoCrNi has a face-centred cubic (fcc) structure, adding V leads to a structural transformation to-wards a body-centred tetragonal (bct) structure with both phases present at near-stochiometric composition.
The as-cast sample was characterised by energy-dispersive X-ray spectroscopy (EDXS) and electron backscatter diffraction (EBSD) in a scanning electron microscope (SEM) confirming the presence of both phases. Irradiations were performed with a focussed He beam provided by a helium ion mi-croscope (HIM) at temperatures between room temperature and 500°C. The irradiation fluence was varied between 6x10^17 ions/cm² and 1x10^20 ions/cm². High-resolution images of the irradiated areas were taken with the same HIM, and an example is shown in Fig. 1a. Selected irradiated areas were additionally studied by transmission electron microscopy (TEM) in combination with EDXS.
Under irradiation, pores start to be generated in the material with pore sizes differing significantly between the two phases. At higher fluences and above a critical temperature, a tendril structure as exemplary shown for the bct phase in Fig. 1a forms in both phases. We have found that the critical temperature depends on the phase and is lower for fcc. TEM images reveal that the tendrils span the whole depth of the irradiated area and are accompanied by bubbles of various sizes as shown in Fig. 1b for the bct phase. Scanning TEM-based EDXS of these structures indicates a He-induced change in composition.

Verknüpfte Publikationen

  • Vortrag (Konferenzbeitrag)
    FIT4NANO Workshop, 11.-13.07.2022, Krakow, Poland

Helium-induced nano-structuring in an FeCoCrNiV high-entropy alloy

Lohmann, S.; Goodall, R.; Hlawacek, G.; Hübner, R.; Ma, L.; Gandy, A. S.

High-entropy alloys (HEAs) are a relatively new class of metal alloys composed of several principal elements, usually at (near) equiatomic ratios. It has previously been reported that some HEAs display superior radiation damage resistance, with composition and microstructure being cited as contributing factors, though the precise mechanism is still unknown. To study the influence of the crystal structure on the response to radiation, we have chosen FeCoCrNiV as a model system. While FeCoCrNi has a face-centred cubic (fcc) structure, adding V leads to a structural transformation towards a body-centred tetragonal (bct) structure with both phases present at near-stochiometric composition.
The as-cast sample was characterised by energy-dispersive X-ray spectroscopy (EDXS) and electron backscatter diffraction in a scanning electron microscope confirming the presence of both phases. Irradiations were performed with a focussed He beam provided by a helium ion microscope (HIM) at temperatures between 20°C and 500°C. The fluence was varied between 6×10^17 ions/cm² and 1×10^20 ions/cm². High-resolution images of the irradiated areas were taken with the same HIM as shown in Fig. 1a. Selected irradiated areas were additionally
studied by transmission electron microscopy (TEM) in combination with EDXS.
Under irradiation, pores start to be generated in the material with pore sizes differing significantly between the two phases. At higher fluences and above a critical temperature, a tendril structure as exemplary shown for the bct phase in Fig. 1a forms in both phases. TEM images reveal that these tendrils span the whole depth of the irradiated area (Fig. 1b) and are accompanied by bubbles of various sizes. Scanning TEM-based EDXS of these structures indicates a He-induced change in composition.

Verknüpfte Publikationen

  • Vortrag (Konferenzbeitrag)
    29th International conference on atomic collisions in solids & 11th International symposium on swift heavy ions in matter, 19.-24.06.2022, Helsinki, Finnland

Data publication: Examining different regimes of ionization-induced damage in GaN through atomistic simulations

Sequeira, M.; Djurabekova, F.; Nordlund, K.; Mattei, J.-G.; Monnet, I.; Grygiel, C.; Alves, E.; Lorenz, K.

Two Temperature Model - Molecular Dynamics (TTM-MD) simulations describing the interaction of Swift Heavy Ions (0.35-0.54 MeV/amu Xe, 0.6 and 5.8 MeV/amu Pb, and 3.8 MeV/amu U ions. The simulations are discussed in:

Sequeira, M. C., Djurabekova, F., Nordlund, K., Mattei, J.-G., Monnet, I., Grygiel, C., Alves, E., Lorenz, K., Examining Different Regimes of Ionization-Induced Damage in GaN Through Atomistic Simulations. Small 2022, 2102235. https://doi.org/10.1002/smll.202102235

Each zip file contains the input and output corresponding to each ion simulation. The input and output files are those used and generated by PARCAS 5.22 (https://gitlab.com/acclab/parcas). The radial energy profile deposited by the ion, as calculated within the TTM, can be found in the in/track.in file. The file contains two columns: one with the distance to the ion trajectory (in Angstrom) and another with the energy per atom (in eV/atom). For additional information on the simulations (e.g. bulk vs surface), please refer to the methods section of the reference above.

Keywords: Defects; GaN; Molecular Dynamics; Radiation; Recrystallization; Two-Temperature Model

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Advancements in the fabrication and characterization of actinide targets for superheavy element production

Düllmann, C. E.; Artes, E.; Dragoun, A.; Haas, R.; Jäger, E.; Kindler, B.; Lommel, B.; Mangold, K. ‑.; Meyer, C. ‑.; Mokry, C.; Munnik, F.; Rapps, M.; Renisch, D.; Runke, J.; Seibert, A.; Stöckl, M.; Thörle‑Pospiech, P.; Trautmann, C.; Trautmann, N.; Yakushev, A.

The heaviest elements can exclusively be produced in actinide-target based nuclear fusion reactions with intense heavy-ion beams. Ever more powerful accelerators deliver beams of continuously increasing intensity, which brings targets of current technology to their limits and beyond. We motivate efforts to produce targets with improved properties, which calls for a better understanding of targets produced by molecular plating, the current standard method. Complementary analytical methods will help shedding more light on their chemical and physical changes in the beam. Special emphasis is devoted to the aspect of the optimum target thickness and the choice of the backing material.

Keywords: Superheavy elements; Actinide targets; Heavy-ion beam; Target backing; Molecular plating; Thin film analytics

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Sensitive multi-element profiling with high depth resolution enabled by time-of-flight recoil detection in transmission using pulsed keV ion beams

Holeňák, R.; Lohmann, S.; Primetzhofer, D.

The potential of time-of-flight recoil detection for sensitive multi-element profiling of thin membranes and quasi-2D systems in transmission geometry using pulsed keV ion beams is assessed. While the time-of-flight approach allows for simultaneous detection of multiple elements, to the largest extent irrespective of recoil charge states, the keV projectile energies guarantee high recoil-cross sections yielding high sensitivity at low dose. We demonstrate the capabilities of the approach using 22Ne and 40Ar as projectiles transmitted through thin carbon foils featuring optional LiF-coatings and single-crystalline silicon membranes for different sample preparation routines and crystal orientations.
Using a large position-sensitive detector (0.13 sr), a depth resolution below 6 nm and sensitivity below 1014 atoms/cm2 was achieved for H in a 50 nm thick silicon membrane. For crystalline targets, we show how the probability of creation and detection of recoils and their observed angular distribution depend on sample orientation.

Keywords: Recoils; keV ions; Self-supporting films; Time-of-flight

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Examining different regimes of ionization-induced damage in GaN through atomistic simulations

Sequeira, M.; Djurabekova, F.; Nordlund, K.; Mattei, J.-G.; Monnet, I.; Grygiel, C.; Alves, E.; Lorenz, K.

The widespread adoption of gallium nitride (GaN) in radiation-hard semiconductor devices relies on a comprehensive understanding of its response to strongly ionizing radiation. Despite being widely acclaimed for its high radiation resistance, the exact effects induced by ionization are still hard to predict due to the complex phase-transition diagrams and defect creation-annihilation dynamics associated with group-III nitrides. Here, Two-Temperature Model, Molecular Dynamics simulations and Transmission Electron Microscopy, are employed to study the interaction of Swift Heavy Ions with GaN at the atomic level. The simulations reveal a high propensity of GaN to recrystallize the region melted by the impinging ion leading to high thresholds for permanent track formation. Although the effect exists in all studied electronic energy loss regimes, its efficiency is reduced with increasing electronic energy loss, in particular when there is dissociation of the material and subsequent formation of N 2 bubbles. The recrystallization is also hampered near the surface where voids and pits are prominent. The exceptional agreement between the simulated and experimental results establishes the applicability of the model to examine the entire electronic energy loss spectrum. Furthermore, the model supports an empirical relation between the interaction cross sections (namely for melting and amorphization) and the electronic energy loss.

Keywords: Defects; GaN; Molecular Dynamics; Radiation; Recrystallization


Data publication: Stabilization of nanoscale iron films by self-terminated electrodeposition in sulfate electrolyte

Nichterwitz, M.; Duschek, K.; Zehner, J.; Oswald, S.; Heller, R.; Leistner, K.

All RBS Data from measurements with both standard RBS as well as liquid cell RBS, including Simulation files in SIMNRA data format

Keywords: Electrodeposition; sulfate electrolyte; electro chemistry; Rutherford backscattering; iron oxide; nano structures; magnetic properties

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Stabilization of nanoscale iron films by self-terminated electrodeposition in sulfate electrolyte

Nichterwitz, M.; Duschek, K.; Zehner, J.; Oswald, S.; Heller, R.; Leistner, K.

Iron and iron oxide nanostructures are of broad interest for numerous applications, such as in the fields of magnetic data
storage, spintronics, biosensing and catalysis. In all of these cases, defined deposition on nanometer scale is essential for
functionality. For conventional electrodeposition of transition metals, precise thickness control and layer stability at the
nanoscale are difficult due to dissolution tendencies in acidic electrolytes after the voltage is switched off. In contrast to
previous studies that focused on self-termination of Ni and Ni-based alloys, we investigate the thickness control of nanoscale
iron oxide/iron layers using self-terminated electrodeposition from sulfate electrolytes. Electrochemical quartz crystal
microbalance measurements show that self-terminated thickness can be controlled by both deposition potential and iron ion
concentration. Comparison of experimental results with model calculations based on diffusion theory reveal two different
growth modes for self-termination. At low iron ion concentration, self-termination of iron proceeds via the formation of an
ultrathin iron hydroxide layer. At larger iron ion concentration, precipitation of bulk Fe(OH)2 dominates the film growth and
self-termination is shifted to more negative potentials. All self-terminated layers exhibit enhanced stability in the electrolyte
after the voltage is switched off compared to those deposited in the conventional deposition regime. With in situ Rutherford
backscattering spectrometry measurements, we can follow the self-terminating deposition and the stability after voltage
switch-off for longer times online. Surface analytical and morphological analyses show that the self-terminated layers exhibit
a higher iron oxide/iron ratio and are smoother than layers obtained by conventional electrodeposition.

Keywords: Electrodeposition; sulfate electrolyte; electro chemistry; Rutherford backscattering; iron oxide; nano structures; magnetic properties

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Ion-Induced Surface Charge Dynamics in Freestanding Monolayers of Graphene and MoS2 Probed by the Emission of Electrons

Niggas, A.; Schwestka, J.; Balzer, K.; Weichselbaum, D.; Schlünzen, N.; Heller, R.; Sascha, C.; Inani, H.; Tripathi, M.; Speckmann, C.; McEvoy, N.; Susi, T.; Kotakoski, J.; Gan, Z.; George, A.; Turchanin, A.; Bonitz, M.; Aumayr, F.; Wilhelm, R. A.

We compare the ion-induced electron emission from freestanding monolayers of graphene and MoS2 to
find a sixfold higher number of emitted electrons for graphene even though both materials have similar
work functions. An effective single-band Hubbard model explains this finding by a charge-up in MoS2 that
prevents low energy electrons from escaping the surface within a period of a few femtoseconds after ion
impact. We support these results by measuring the electron energy distribution for correlated pairs of
electrons and transmitted ions. The majority of emitted primary electrons have an energy below 10 eVand
are therefore subject to the dynamic charge-up effects at surfaces.

Keywords: Highly charged ions; 2D materials; Graphene; MoS2; Electron Emission; Surface Charge; Ion induced surface modifications


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

Lohmann, S.; Holeňák, R.; Grande, P. L.; Primetzhofer, D.

We measured the electronic energy-loss straggling of protons, helium, boron and silicon ions in silicon using a time-of-flight approach. Ions with velocities 0.25 - 1.6 times the Bohr velocity were transmitted through single-crystalline Si(100) nanomembranes in either channelling or random geometry to study the trajectory dependence of energy-loss straggling. Nuclear and path length contributions 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. For heavier ions, electronic straggling at low velocities does not decrease further but plateaus and even seems to increase again. A satisfying agreement between experiment and transport cross section calculations for helium shows that energy deposition of light ions is dominated by electron-hole pair excitations. 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.


Ion Microprobe analysis of wear processes in ta-C coatings and contact areas on the counter bodies

Munnik, F.; Lorenz, L.; Härtwig, F.; Krause, M.

Solid lubricants, like ta-C (hydrogen-free tetrahedral amorphous carbon) coatings, are an active area of research to replace liquid lubricants. This substitution is important because of the negative environmental impact and high material consumption of liquid lubricants. The influence of soft metal counter bodies on the unlubricated friction behaviour of hydrogen-free carbon coatings has mostly been studied for doped a-C coatings so far. All these studies show that low friction and wear can only be achieved if a tribolayer is formed to protect the contact. Even with a formed tribolayer, its composition is crucial for the frictional behaviour, making the investigation of this composition essential. A study currently underway aims to identify friction-induced surface changes like material loss of the coating, material transfer between the counter body and the coating, or the formation of a tribolayer.
The current work presents Ion Beam Analysis methods to deliver laterally and depth-resolved element analysis of the wear track on the coating and the contact area of the counter bodies (CB). In a first test, a ta-C coating has been subjected to pin-on-disk tests with various metallic and ceramic CBs. He and H ion microbeams have been used to scan over the tracks and the contact areas of the CBs. Both RBS and PIXE have been used and first results are presented. It is shown that, in this case, RBS yields the more useful information. Both, a 2 MeV He ion beam and a 3 MeV H ion beam provide valuable results. The advantages of each type of ion beam depend on the sample and the information needed. As shown in this work, RBS with a 2 MeV He ion beam is useful to determine the transfer layer of a (soft) metal CB to the ta-C coating, whereas 3 MeV H RBS can be used to determine the presence of C and O on the CB because of the increased non-Rutherford cross-sections for these elements.

Verknüpfte Publikationen

  • Poster
    18th International Conference on Nuclear Microprobe Technology and Applications, 11.-16.09.2022, Ljubljana, Slovenia

New correlative microscopy approaches for toxicology studies of nanomaterials

Podlipec, R.; Kriselj, A.; Pirker, L.; Hlawacek, G.; Kelemen, M.; Strancar, J.

A comprehensive understanding of the mechanisms leading to chronic inflammation of tissues after exposure to different types of nanomaterials is greatly lacking. In the case of lung tissue, repeating events of exposure to metal-oxide or carbon nanomaterials can eventually lead to persistent inflammation and further cardiovascular diseases [1,2]. A similar outcome can occur in periprosthetic tissues suffering severe inflammation from the constant influx of metal wear debris from nearby implant materials [3].
To better understand these adverse outcomes, one needs to dig into the initial events that are formed on a molecular, nanoscale, thus requiring an advanced combination of microscopy techniques. Lately, more and more studies in live science are tackled by correlative microscopy (CM) which implements an optimal combination of complementary and advanced techniques on the same sample to be able to reveal new phenomena.
In our recent studies related to both lung and periprosthetic tissue inflammation, we show the new workflow of advanced microscopies and spectroscopies from which we have gained new structural as well as functional insights (Figure 1) [4,5]. With the combination of super-resolution optical microscopy (STED), hyperspectral and fluorescence lifetime imaging (sp-FLIM), Helium Ion Microscopy (HIM), Scanning electron microscopy (SEM-EDS), and Proton Induced X-ray Emission (PIXE) we reveal/present the new mechanisms and impact of nanomaterial interaction with lung epithelium and periprosthetic tissue, which leads to better knowledge and causal relations of the nanotoxicity on such small scales.

References:

1. X. Li, L. Jin, H. Kan, Nature 2019, 570, 437-439.
2. E. Underwood, Science 2017, 355, 342–345.
3. S.B. Goodman, J. Gallo, E. Gibon, M. Takagi, Expert Rev Med Devices 2020, 17, 41–56.
4. H. Kokot, et. al, Advanced Materials, 2020, 32, 2003913-1-15.
5. R. Podlipec, et. al, Materials, 2021, 14, 3048.

Verknüpfte Publikationen

  • Vortrag (Konferenzbeitrag)
    4th SLOVENE MICROSCOPY SYMPOSIUM, 12.-13.05.2022, Ankaran, Slovenia

Differential evolution optimization of Rutherford back-scattering spectra

Heller, R.; Klingner, N.; Claessens, N.; Merckling, C.; Meersschaut, J.

We investigate differential evolution optimization to fit Rutherford back-scattering data. The algorithm helps to find, with very high precision, the sample composition profile that best fits the experimental spectra. The capabilities of the algorithm are first demonstrated with the analysis of synthetic Rutherford back-scattering spectra. The use of synthetic spectra highlights the achievable precision, through which it becomes possible to differentiate between the counting statistical uncertainty of the spectra and the fitting error. Finally, the capability of the algorithm to analyze large sets of experimental spectra is demonstrated with the analysis of the position-dependent composition of a SrxTiyOz layer on a 200 mm silicon wafer. It is shown that the counting statistical uncertainty as well as the fitting error can be determined, and the reported total analysis uncertainty must cover both.

Verknüpfte Publikationen

  • Open Access Logo Journal of Applied Physics 132(2022)16, 165302
    Online First (2022) DOI: 10.1063/5.0096497

Syntetic Spectra Data used in publication "Differential evolution optimization of Rutherford back-scattering spectra"

Heller, R.; Meersschaut, J.; Claessens, N.; Merckling, C.; Klingner, N.

The zip-file contains all synthetic spectra as used for and  described in the publication "Differential evolution optimization of Rutherford back-scattering spectra" and all simulation input files for the code RUTHELDE presented therein. Naming according to the text in the paper. All files are in human readable ASCII format. The simulation input files can be best viewed with any kind of JSON file editor.

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Dataset: spatially resolved temperature distribution in a rare-earth-doped transparent glass-ceramic

Podlipec, R.; Sedmak, I.

Dataset of glass-ceramic temperature-dependent fluorescence emission used for the calibration of the time measurements of spatially resolved temperature distribution in rare-earth-doped glass-ceramic materials for the studies of thermal processes within optically transparent materials.   

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Spatially resolved temperature distribution in a rare-earth-doped transparent glass-ceramic

Sedmak, I.; Podlipec, R.; Urbancic, I.; Strancar, J.; Mortier, M.; Golobic, I.

Knowing the temperature distribution within the conducting walls of various multilayer-type materials is crucial for a better understanding of heat-transfer processes. This applies to many engineering fields, good examples being photovoltaics and microelectronics. In this work, we present a novel fluorescence technique that makes possible the non-invasive imaging of local temperature distributions within a transparent, temperature-sensitive, co-doped Er:GPF1Yb0.5Er glass-ceramic with micrometer spatial resolution. The thermal imaging was performed with a high-resolution, fluorescence microscopy system, measuring different focal planes along the z-axis. This ultimately enabled a precise axial reconstruction of the temperature distribution across a 500-µm-thick glass-ceramic sample. The experimental measurements showed excellent agreement with computer-modeled heat simulations and suggest that the technique could be adopted for the spatial analyses of local thermal processes within optically transparent materials. For instance, the technique could be used to measure the temperature distribution of intermediate, transparent layers of novel ultra-high-efficiency solar cells at the micron and sub-micron levels.

Keywords: Temperature-dependent fluorescence; co-doped glass-ceramic; axial temperature distribution; micro-scale temperature measurements


Trajectory-dependent electronic excitations at keV ion energies

Lohmann, S.; Holeňák, R.; Primetzhofer, D.

We present experiments directly demonstrating the significance of charge-state dynamics in close collisions at ion velocities below the Bohr velocity resulting in a drastic trajectory dependence of the specific energy loss.
Experiments were performed with the time-of-flight medium energy ion scattering set-up at Uppsala University [1]. In our 3D-transmission approach [2], pulsed beams of singly charged ions are transmitted through self-supporting Si(100) nanomembranes and detected behind the sample. We record ion energy together with the angular distributions of deflected particles and can additionally insert a deflector to measure exit charge states [3].
We specifically studied the difference in energy loss between channelled (ΔEch) and random trajectories (ΔEr) for ions with masses ranging from 1 (protons) to 40 u (Ar+) as shown in Fig. 1 [4,5]. For protons, the observed effect can be explained with increasing contributions of core-electron excitations in close collisions only attainable in random geometry. For He and heavier ions we observe a reverse trend – a decrease of the ratio ΔEch/ ΔEr with decreasing ion velocity. Due to the inefficiency of core-electron excitations at these velocities, we explain this behaviour by contributions of collision-induced charge-exchange events along random trajectories. The resulting higher mean charge state leads to higher electronic stopping along random trajectories. For heavier ions, local losses due to electron promotion, also including several electrons, are expected to contribute strongly to the energy deposition in random geometry. By studying the trajectory dependence of the statistical distribution of electronic excitations (electronic energy straggling), we present evidence that for heavier ions, individual events with large energy transfer indeed significantly contribute to the energy loss. Finally, we show that our experimental approach leads to results that can serve to benchmark dynamic theories such as time-dependent density functional theory [5].

References
[1] M. A. Sortica et al., Nucl. Instrum. Methods Phys. Res. B 463 (2020) 16-20.
[2] R. Holeňák, S. Lohmann and D. Primetzhofer, Ultramicroscopy 217 (2020) 113051.
[3] R. Holeňák et al., Vacuum 185 (2021) 109988.
[4] S. Lohmann and D. Primetzhofer, Phys. Rev. Lett. 124 (2020) 096601.
[5] S. Lohmann, R. Holeňák and D. Primetzhofer, Phys. Rev. A 102 (2020) 062803.

  • Eingeladener Vortrag (Konferenzbeitrag) (Online Präsentation)
    25th International Conference on Ion Beam Analysis & 17th International Conference on Particle Induce X-ray Emission & International Conference on Secondary Ion Mass Spectrometry, 11.-15.10.2021, Online, Online

Trajectory-dependent electronic excitations of keV ions

Lohmann, S.; Holeňák, R.; Primetzhofer, D.

We present experiments directly demonstrating the significance of charge-exchange events for the energy deposition of ions with velocities below the Bohr velocity. The observed effects lead to a drastic trajectory-dependence of the specific energy loss.
Experiments were performed with the time-of-flight medium energy ion scattering set-up at Uppsala University [1]. We employed pulsed beams of singly charged ions with masses ranging from 1 (H+) to 40 u (Ar+) and energies between 20 and 350 keV. Ions were transmitted through self-supporting Si(100) nanomembranes and detected behind the sample. We assessed the energy and angular distributions of deflected particles for different alignments of the initial beam direction with the crystal axes and planes. A set-up for measuring the exit charge state was constructed to support the analysis [2].
For all ions we observe lower electronic stopping for channelled trajectories as compared to random ones as shown in Fig. 1 [3]. For protons, this difference 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, core-electron excitations at employed ion velocities are inefficient and we, therefore, explain these results by reionisation events occurring in close collisions of ions with target atoms [4]. These events in turn result in trajectory-dependent mean charge states, which heavily affects the energy loss, and could be confirmed by first qualitative measurements of the trajectory dependence of exit charge states. The simplicity of our experimental geometry leads to results that can serve as excellent benchmark systems for calculations using time-dependent density functional theory.

References
[1] M. A. Sortica et al., Nucl. Instrum. Methods Phys. Res. B, 463 (2020) 16-20.
[2] R. Holeňák et al., Vacuum, 185 (2021) 109988.
[3] S. Lohmann et al., Phys. Rev. A, 102 (2020) 062803.
[4] S. Lohmann and D. Primetzhofer, Phys. Rev. Lett., 124 (2020) 096601.

  • Vortrag (Konferenzbeitrag)
    Applied Nuclear Physics Conference, 12.-16.09.2021, Prague, Czech Republic

Ion-electron dynamics studied in a 3D-transmission approach

Lohmann, S.; Holeňák, R.; Grande, P. L.; Primetzhofer, D.

We present experiments demonstrating trajectory-dependent electronic excitations at low ion velocities attributed to charge-exchange events. Experiments were performed with the time-of-flight medium energy ion scattering set-up at Uppsala University [1]. We employed pulsed beams of singly charged ions with masses from 1 (H+) to 40 u (Ar+) and energies between 20 and 300 keV. Ions are transmitted through self-supporting Si(100) nanomembranes and detected behind the sample. Fig. 1 demonstrates our experimental approach, in which ion energy loss is measured together with angular distributions for different beam-crystal alignments. We have analysed both trajectory-dependent electronic stopping and electronic energy-loss straggling. Our results show higher electronic stopping for random than for channelled trajectories for all studied ions [2]. For ions heavier than protons, direct core-electron excitations at employed ion velocities are inefficient. We, therefore, explain our observation by reionisation events occurring in close collisions of ions with target atoms mainly accessible in random geometry [3]. These events result in trajectory-dependent mean charge states, which heavily affects the energy loss. The electronic energy-loss straggling likewise exhibits a strong dependence on ion type, velocity and trajectory. For all ions, straggling in random geometry is higher than in channelling orientation. While for He straggling increases with ion velocity, for B travelling along random trajectories a minimum is observed in the studied velocity range. We compare experimental results for these two ions with predictions by the Chu model and transport cross section calculations (Penn-TCS model). We provide strong evidence that electron-hole pair creation alone cannot explain electronic excitations by slow ions other than protons. Especially for heavy ions, additional energy-loss processes such as charge exchange and autoionisation including possible alterations of the scattering potential [4] have to be taken into account.
References
[1] M. A. Sortica et al., Nucl. Instrum. Methods Phys. Res. B, 463 (2020) 16-20.
[2] S. Lohmann et al., Phys. Rev. A, 102 (2020) 062803.
[3] S. Lohmann and D. Primetzhofer, Phys. Rev. Lett., 124, (2020) 096601.
[4] R. A. Wilhelm and P. L. Grande, Communications Physics, 2 (2019) 89.

  • Eingeladener Vortrag (Konferenzbeitrag) (Online Präsentation)
    27th International Symposium on Ion-Atom Collisions (ISIAC), 14.-16.07.2021, Online, Online

Sputter Deposited Magnetostrictive Layers for SAW Magnetic Field Sensors

Thormählen, L.; Seidler, D.; Schell, V.; Munnik, F.; McCord, J.; Meyners, D.

For the best possible limit of detection of any thin film‐based magnetic field sensor, the functional magnetic film properties are an essential parameter. For sensors based on magnetostrictive layers, the chemical composition, morphology and intrinsic stresses of the layer have to be controlled during film deposition to further control magnetic influences such as crystallographic effects, pinning effects and stress anisotropies. For the application in magnetic surface acoustic wave sensors, the magnetostrictive layers are deposited on rotated piezoelectric single crystal substrates. The thermomechanical properties of quartz can lead to undesirable layer stresses and associated magnetic anisotropies if the temperature increases during deposition. With this in mind, we compare amorphous, magnetostrictive FeCoSiB films prepared by RF and DC magnetron sputter deposition. The chemical, structural and magnetic properties determined by elastic recoil detection, X‐ray diffraction, and magneto‐optical magnetometry and magnetic domain analysis are correlated with the resulting surface acoustic wave sensor properties such as phase noise level and limit of detection. To confirm the material properties, SAW sensors with magnetostrictive layers deposited with RF and DC deposition have been prepared and characterized, showing comparable detection limits below 200 pT/Hz(^1/2) at 10 Hz. The main benefit of the DC deposition is achieving higher deposition rates while maintaining similar low substrate temperatures.

Keywords: Magnetron Sputter Deposition; FeCoSiB; ERDA; XRD; film stress; magnetic field sensor; magnetic prop

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Determination of high-time resolution mineral dust concentration in real-time by optical absorption measurements

Ivančič, M.; Ježek, I.; Rigler, M.; Gregorič, A.; Alföldy, B.; Podlipec, R.; Drinovec, L.; Pikridas, M.; Unga, F.; Sciare, J.; Yus-Díez, J.; Pandolfi, M.; Griša, M.

Mineral dust is an important natural source of aerosols and significantly influences air quality (Querol et al.,
Environ. Int., 2019) and the global radiation budget (Schepanski, Geosci., 2018). Frequent dust intrusions are
observed in the Mediterranean region (Ealo et al., Atmos. Chem. Phys., 2016; Pikridas et al., Atmos. Environ.,
2018) and Central Europe (Collaud Coen et al., Atmos. Chem. Phys., 2004; Schauer et al., Aerosol Air Qual.
Res., 2016), with high potential to cause exceedances of daily PM10 levels. To separate the influence of
anthropogenic and natural contribution to the PM10 levels, the new method was developed within the DNAAP
project (Detection of non-anthropogenic air pollution – http://www.aerosol.si/dnaap/).
Dust weakly absorbs light in the near ultra-violet and short wavelengths of the visible range, while the light
absorption of dust in longer wavelengths from the visible and near infra-red range is negligible. We used
filter-based photometer Aethalometer AE33 (Drinovec et al., Atmos. Meas. Tech., 2015) to measure the light
absorption at seven wavelengths, from 370 to 950 nm. The mineral dust is not the only light-absorbing aerosol
in the air. Black carbon (BC), a unique primary tracer for combustion emissions, strongly absorbs light across
the entire visual, near infra-red and near ultra-violet spectral range. Since optical absorption of mineral dust is
weaker than the optical absorption of black carbon, the coarse mode mineral particles have to be concentrated
using the high-volume virtual impactor (VI). The method is based on the optical absorption measurements of
the two sample streams, sampling particle size below 1 µm and sample stream with the concentrated coarse
mode particles, where mineral dust contribution is substantial. Experimental configuration includes two
Aethalometers AE33 with different size selective inlets: VI inlet for sampling coarse aerosol mode (mostly
mineral dust) and PM1 inlet for sampling fine mode of aerosols (mainly BC). The optical absorption of mineral
dust can be determined by subtracting the absorption of fine aerosol fraction (PM1) from the absorption of
aerosol sampled by the VI, taking into account the enhancement factor of VI setup (Drinovec et al., Atmos.
Meas. Tech., 2020). The mineral dust mass concentration is then calculated using mass absorption cross-section
(MAC) for dust which could be site and source-region specific.
The results from the measurement campaigns performed at six locations in the Mediterranean region will be
presented. The measurements took place in NE Spain (Barcelona – BCN, Montseny – MSY, Montsec – MSA),
on Cyprus (Nicosia – NI, Agia Marina Xyliatou – AMX), and in Slovenia (Ljubljana – LJ). Two year-long
datasets will be presented, focusing on the analyses of aerosol optical properties of PM1 and VI fractions. The
results were validated using low time resolution chemical specification of offline filters and a statistical
approach where dust was extracted from PM10 measurements for dust intrusions periods determined by models
and back-trajectory studies. For better understanding, helium ion microscopy (HIM) was applied to study the
microscopic differences between mineral dust and black carbon captured on the AE33 filter tapes.
This work was supported by SPIRIT Slovenia – Public Agency for Entrepreneurship, Internationalization,
Foreign Investments and Technology, project DNAAP.

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  • Vortrag (Konferenzbeitrag)
    DUST 2021, 04.-07.10.2021, Torre Cintola Conference Centre, MONOPOLI, Italy

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

Holeňák, R.; Lohmann, S.; Komander, K.; Primetzhofer, D.

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.

Keywords: Channelling; keV ions; Monte-Carlo; Time-of-flight

  • Open Access Logo Beitrag zu Proceedings
    25th International Conference on Ion Beam Analysis & 17th International Conference on Particle Induce X-ray Emission & International Conference on Secondary Ion Mass Spectrometry, 11.10.2021, Online, Online
    Journal of Physics: Conference Series, Volume 2326, 012008
    DOI: 10.1088/1742-6596/2326/1/012008
    arXiv: arXiv:2111.06809

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Indirect bandgap, optoelectronic properties, and photoelectrochemical characteristics of high-purity Ta₃N₅ photoelectrodes

Eichhorn, J.; Lechner, S. P.; Jiang, C.-M.; Folchi, G.; Munnik, F.; Sharp, I. D.

The (opto)electronic properties of Ta3N5 photoelectrodes are often dominated by defects, such as oxygen impurities, nitrogen vacancies, and reduced tantalum centers, impeding fundamental studies of its electronic structure, chemical stability, and photocarrier transport. Here, we synthesize high quality Ta3N5 thin films by reactive magnetron sputtering and subsequent NH3 annealing at varying temperatures. The resulting films are characterized by nearly-ideal N/Ta stoichiometry, low O content, and small Urbach energies. Both the crystallinity and material quality improve with increasing annealing temperatures up to 940 °C, while higher annealing temperatures introduce additional disorder within the Ta3N5 lattice, leading to reduced photoelectrochemical performance. These changes are also reflected in the surface and bulk composition, showing the elimination of oxygen impurities at moderate annealing temperatures and the loss of nitrogen at high annealing temperatures. As a consequence, defect-related sub-gap optical absorption initially decreases due to reduced oxygen impurity concentration, and subsequently increases due to increased formation of nitrogen vacancies. The high material quality enables us to unambiguously identify the nature of the Ta3N5 band gap as indirect, thereby resolving a long-standing controversy regarding the most fundamental characteristic of this material as a semiconductor. The assignment of Ta3N5 as indirect semiconductor is further supported by the suppression of disorder-induced band-edge photoluminescence with improved structural order within the Ta3N5 films.

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Correlated effects of fluorine and hydrogen in fluorinated tin oxide (FTO) transparent electrodes deposited by sputtering at room temperature

Morán-Pedroso, M.; Gago, R.; Julin, J. A.; Salas-Colera, E.; Jimenez, I.; de Andrés, A.; Prieto, C.

The optical and electrical properties of fluorinated tin oxide (FTO) films deposited at room temperature by sputtering have been investigated varying the fluorine content and the hydrogen atmosphere. The complex behavior of the obtained films is disclosed using a wide set of characterization techniques that reveals the combined effects of these two parameters on the generated defects. These defects control the electrical transport (carrier density, mobility and conductivity), the optical properties (band gap and defects-related absorption and photoluminescence) and finally promote the amorphization of the samples. H₂ in the sputtering gas does not modify the H content in the films but induces the partial reduction of tin (from Sn4+ to Sn2+) and the consequent generation of oxygen vacancies with shallow energy levels close to the valence band. A variation of up to four orders of magnitude in electrical conductivity is reported in samples with the appropriate fluorine doping and hydrogen fraction in the sputtering gas, maintaining excellent optical transparency. Optimized room temperature grown electrodes reach sheet resistance ~20 Ω/□ and transparency >90%. This room temperature deposition process enables film preparation on flexible organic substrates, such as polyethylene terephthalate (PET), with identical performance of doubtless interest in flexible and large scale electronics.

Keywords: Transparent conductive materials; Fluorinated tin oxide; Room temperature film preparation

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Impact of Si on the high-temperature oxidation of AlCr(Si)N coatings

Jager, N.; Meindlhumer, M.; Zitek, M.; Spor, S.; Hruby, H.; Nahif, F.; Julin, J.; Keckes, J.; Mitterer, C.; Daniel, R.

The resistance of wear protective coatings against oxidation is crucial for their use at high temperatures. Here, three nanocomposite AlCr(Si)N coatings with a fixed Al/Cr atomic ratio of 70/30 and a varying Si-content of 0 at.%, 2.5 at.% and 5 at.% were analyzed by differential scanning calorimetry, thermogravimetric analysis and X-ray in order to understand the oxidation behavior depending on their Si-content. Additionally, a partially oxidized AlCrSiN coating with 5 at.% Si on a sapphire substrate was studied across the coating thickness by depth-resolved cross-sectional X-ray nanodiffraction and scanning trans-mission electron microscopy to investigate the elemental composition, morphology, phases and residual stress evolution of the oxide scale and the non-oxidized coating underneath. The results reveal enhanced oxidation properties of the AlCr(Si)N coatings with increasing Si-content, as demonstrated by a retarded onset of oxidation to higher temperatures from 1100 °C for AlCrN to 1260 °C for the Si containing coatings and a simultaneous deceleration of the oxidation process. After annealing of the AlCrSiN sample with 5 at.% Si at an extraordinary high temperature of 1400 °C for 60 min in ambient air, three zones developed throughout the coating strongly differing in their composition and structure: (i) a dense oxide layer comprising an Al-rich and a Cr-rich zone formed at the very top, followed by (ii) a fine-grained transition zone with incomplete oxidation and (iii) a non-oxidized zone with a porous structure. The varying elemental composition of these zones is furthermore accompanied by micro-structural variations and a complex residual stress development revealed by cross-sectional X-ray nanodiffraction. The results provide a deeper understanding of the oxidation behavior of AlCr(Si)N coatings depending on their Sicontent and the associated elemental, microstructural and residual stress evolution during high-temperature oxidation.

Keywords: AlCrSiN; Nanocomposite; Cathodic arc; Oxidation behaviour; Cross-sectional X-ray nanodiffraction

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Ion Microprobe analysis of wear processes in tribological ta-C coatings.

Munnik, F.; Habenicht, C.; Lorenz, L.; Krause, M.

Solid lubricants are an active research topic due to many factors, an important one being the elimination of current liquid lubrication because of its environmental impact. The tribological behaviour of different solid lubricants depends on the gas en¬vironment while testing. The most often-used solid lubricant coating is MoS2. A newer one still under research is ta-C (hydrogen-free, tetra-edic, amorphous carbon) that behaves like a polar opposite to MoS2. ta-C relies on free hydrogen and hydroxide ions to passivate free bonds resulting from the wear testing.
In a first test, a ta-C coating has been subjected to tribological tests with counter bodies made of various materials. The aim is to study tribological surface changes like material loss of the coating or material transfer from the counter body, processes which aren’t fully understood yet. Both the wear tracks on the ta-C coating and the counter bodies have been subjected to Ion Beam Analysis using a high energy ion microprobe. Both PIXE (Particle Induced X-ray Emission) and RBS (Rutherford Backscattering Spectrometry) measurements have been performed using a 2 MeV He ion beam and a 3 MeV H ion beam. Results for the wear tracks obtained with a brass and a Al2O3 counter body are presented as well as results on the counter bodies themselves. The advantages and drawbacks of the results obtained with different ions and different methods are presented. These results show that it is important to combine the measurements in order to obtain a complete picture of the damage caused by the wear tests.

Keywords: Tribilogy; Ion beam analysis

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  • Vortrag (Konferenzbeitrag) (Online Präsentation)
    Ion beam workshop 2021 - virtual meeting, 24.-25.03.2021, online, Deutschland

Experimental electronic stopping cross section of tungsten for light ions in a large energy interval

Moro, M. V.; Wolf, P. M.; Bruckner, B.; Munnik, F.; Heller, R.; Bauer, P.; Primetzhofer, D.

Electronic stopping cross section of tungsten for light ions was experimentally measured in a wide energy interval (20 to 6000 keV for protons and 50 to 9000 keV for helium) in backscattering and transmission geometries. The measurements were carried out in three laboratories (Austria, Germany and Sweden) using five different set-ups, the stopping data deduced from different data sets showed excellent agreement amongst each other, with total uncertainty varying within 1.5–3.8% for protons and 2.2–5.5% for helium, averaged over the respective energy range of each data set. The final data is compared to available data and to widely adopted semi-empirical and theoretical approaches, and found to be in good agreement with most adopted models at energies around and above the stopping maximum. Most importantly, our results extend the energy regime towards lower energies, and are thus of high technological relevance, e.g., in fusion research. At these low energies, our findings also revealed that tungsten – featured with fully and partially occupied f- and d-subshells, respectively – can be modeled as an electron gas for the energy loss process.

Keywords: Stopping power; Tungsten; Free electron gas; Bragg peak; Protons; Helium; Fusion

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Reaction Pathways for Atomic Layer Deposition with Lithium Hexamethyl Disilazide, Trimethyl Phosphate, and Oxygen Plasma

Werbrouck, A.; Mattelaer, F.; Minjauw, M.; Nisula, M.; Julin, J. A.; Munnik, F.; Dendooven, J.; Detavernier, C.

Atomic layer deposition (ALD) of lithium-containing films is of interest for the development of next-generation energy storage devices. Lithium hexamethyl disilazide (LiHMDS) is an established precursor to grow these types of films. The LiHMDS molecule can either be used as a single-source precursor molecule for lithium or as a dual-source precursor molecule for lithium and silicon. Single-source behavior of LiHMDS is observed in the deposition process with trimethylphosphate (TMP) resulting in the deposition of crystalline lithium phosphate (Li3PO4). In contrast, LiHMDS exhibits dual-source behavior when combined with O-2 plasma, resulting in a lithium silicate. Both processes were characterized with in situ ellipsometry, in situ time-resolved full-range mass spectrometry, X-ray photoelectron spectroscopy (XPS), and elastic recoil detection analysis (ERDA). When we combined both reactants into a three-step LiHMDS-TMP-O-2* or LiHMDS-O-2*-TMP process, the dual-source nature of LiHMDS emerged again. By carefully combining our measurements, it is shown that film growth with LiHMDS (in combination with TMP and O-2 plasma) is driven by dipole-driven self-saturated surface interactions combined with dissociative chemisorption. We show that when hydroxyl groups are present on the surface, silicon will be incorporated in the films. These insights benefit the general understanding of the behavior of the LiHMDS and TMP precursors and may facilitate their effective use in ternary or quaternary processes.

Keywords: Reaction products; Adsorption; Precursors; Molecules; Plasma

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RBS raw data for publication "Tuning the Co/Sr stoichiometry of SrCoO2.5 thin films by RHEED assisted MBEgrowth"

Schöffmann, P.; Pütter, S.; Schubert, J.; Zander, W.; Barthel, J.; Zakalek, P.; Waschk, M.; Heller, R.; Brückel, T.

RBS raw date for publication "Tuning the Co/Sr stoichiometry of SrCoO2.5 thin films by RHEED assisted MBEgrowth"

Simulation results using SIMNRA included as well

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Tuning the Co/Sr stoichiometry of SrCoO2.5 thin films by RHEED assisted MBEgrowth

Schöffmann, P.; Pütter, S.; Schubert, J.; Zander, W.; Barthel, J.; Zakalek, P.; Waschk, M.; Heller, R.; Brückel, T.

Strontium cobaltite (SrCoO2.5+δ, SCO) is a fascinating material because of its topotactic structural phase transition caused by a change in oxygen stoichiometry. In the brownmillerite phase (δ = 0) it is an insulating antiferromagnet whereas in the perovskite phase (δ = 0.5) it is a conducting ferromagnet. In contrast, the impact of the varying Co/Sr stoichiometry on the structure has not yet been studied in SCO thin films. Using molecular beam epitaxy we have fabricated SCO thin films of varying Co/Sr stoichiometry. Films with Co excess exhibit a brownmillerite crystal structure with CoO precipitates within the thin film and on the surface. Co deficient films are amorphous. Only for 1:1 stoichiometry a pure brownmillerite structure is present. We find a clear dependence of the Reflection High Energy Electron Diffraction (RHEED) pattern of these thin films on the stoichiometry. Interestingly, RHEED is very sensitive to a Co excess of less than 12% while x-ray diffraction fails to reveal that difference. Hence, using RHEED, the stoichiometry of SCO can be evaluated and tuned in-situ to a high degree of precision, which allows for a quick adjustment of the growth parameters during a sample series.

Keywords: This films; SrCoO; Rutherford Backscattering; RHEED; MBE; growth

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MEIS raw data and maps for publication "Stopping and straggling of 60–250-keV backscattered protons on nanometric Pt films"

Selau, F. F.; Trombini, H.; Marmitt, G. G.; de Andrade, A. M. H.; Morais, J.; Grande, P. L.; Alencar, I.; Vos, M.; Heller, R.

MEIS raw data and maps for publication "Stopping and straggling of 60–250-keV backscattered protons on nanometric Pt films"

Including stiched spectra and 2D ESTAT maps

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Stopping and straggling of 60–250-keV backscattered protons on nanometric Pt films

Selau, F. F.; Trombini, H.; Marmitt, G. G.; de Andrade, A. M. H.; Morais, J.; Grande, P. L.; Alencar, I.; Vos, M.; Heller, R.

The stopping power and straggling of backscattered protons on nanometric Pt films were measured at low to medium energies (60–250 keV) by using the medium-energy ion scattering technique. The stopping power results are in good agreement with the most recent measurements by Primetzhofer Phys. Rev. B 86, 094102 (2012) and are well described by the free electron gas model at low projectile energies. Nevertheless, the straggling results are strongly underestimated by well-established formulas up to a factor of two. Alternatively, we propose a model for the energy-loss straggling that takes into account the inhomogeneous electron-gas response, based on the electron-loss function of the material, along with bunching effects. This approach yields remarkable agreement with the experimental data, indicating that the observed enhancement in energy-loss straggling is due to bunching effects in an inhomogeneous electron system. Nonlinear effects are of minor importance for the energy-loss straggling.

Keywords: Stopping cross sections; Rutherford Backscattering; Medium Energy Ion Scattering; Energy Straggling

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RBS raw data for publication "Voltage‐Controlled Deblocking of Magnetization Reversal in Thin Films by Tunable Domain Wall Interactions and Pinning Sites"

Zehner, J.; Soldatov, I.; Schneider, S.; Heller, R.; Khojasteh, N. B.; Schiemenz, S.; Fähler, S.; Nielsch, K.; Schäfer, R.; Leistner, K.

RBS raw data for publication "Voltage‐Controlled Deblocking of Magnetization Reversal in Thin Films by Tunable Domain Wall Interactions and Pinning Sites"

Simulation results using SIMNRA are included as well

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Voltage‐Controlled Deblocking of Magnetization Reversal in Thin Films by Tunable Domain Wall Interactions and Pinning Sites

Zehner, J.; Soldatov, I.; Schneider, S.; Heller, R.; Khojasteh, N. B.; Schiemenz, S.; Fähler, S.; Nielsch, K.; Schäfer, R.; Leistner, K.

High energy efficiency of magnetic devices is crucial for applications such as data storage, computation, and actuation. Redox‐based (magneto‐ionic) voltage control of magnetism is a promising room‐temperature pathway to improve energy efficiency. However, for ferromagnetic metals, the magneto‐ionic effects studied so far require ultrathin films with tunable perpendicular magnetic anisotropy or nanoporous structures for appreciable effects. This paper reports a fully reversible, low voltage‐induced collapse of coercivity and remanence by redox reactions in iron oxide/iron films with uniaxial in‐plane anisotropy. In the initial iron oxide/iron films, Néel wall interactions stabilize a blocked state with high coercivity. During the voltage‐triggered reduction of the iron oxide layer, in situ Kerr microscopy reveals inverse changes of coercivity and anisotropy, and a coarsening of the magnetic microstructure. These results confirm a magneto‐ionic deblocking mechanism, which relies on changes of the Néel wall interactions, and of the microstructural domain‐wall‐pinning sites. With this approach, voltage‐controlled 180° magnetization switching with high energy‐efficiency is achieved. It opens up possibilities for developing magnetic devices programmable by ultralow power and for the reversible tuning of defect‐controlled materials in general.

Keywords: iron films; magnetic domains; magnetoelectrics; magneto‐ionic mechanisms

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RBS raw data for publication "High quality epitaxial Mn2Au (001) thin films grown by molecular beam epitaxy "

Bommanaboyena, S. P.; Bergfeldt, T.; Heller, R.; Kläui, M.; Jourdan, M.

RBS raw data for publication "High quality epitaxial Mn2Au (001) thin films grown by molecular beam epitaxy "

Simulation results using SINRA are included as well.

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High quality epitaxial Mn2Au (001) thin films grown by molecular beam epitaxy

Bommanaboyena, S. P.; Bergfeldt, T.; Heller, R.; Kläui, M.; Jourdan, M.

The recently discovered phenomenon of Néel spin-orbit torque in antiferromagnetic Mn2Au [Bodnar et al., Nat. Commun. 9, 348 (2018); Meinert et al., Phys. Rev. Appl. 9, 064040 (2018); Bodnar et al., Phys. Rev. B 99, 140409(R) (2019)] has generated huge interest in this material for spintronics applications. In this paper, we report the preparation and characterization of high quality Mn2Au thin films by molecular beam epitaxy and compare them with magnetron sputtered samples. The films were characterized for their structural and morphological properties using reflective high-energy electron diffraction, x-ray diffraction, x-ray reflectometry, atomic force microscopy, and temperature dependent resistance measurements. The thin film composition was determined using both inductively coupled plasma optical emission spectroscopy and Rutherford backscattering spectrometry techniques. The MBE-grown films were found to show a superior smooth morphology and a low defect concentration, resulting in reduced scattering of the charge carriers.

Keywords: Atomic force microscopy; Electron diffraction; Epitaxy; Inductively coupled plasma atomic emission spectroscopy; Thin films; Rutherford backscattering spectrometry

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RBS raw data for publication "Solid–liquid interface analysis with in‐situ Rutherford backscattering and electrochemical impedance spectroscopy "

Bergmann, U.; Apelt, S.; Khojasteh, N. B.; Heller, R.

RBS raw data for publication "Solid–liquid interface analysis with in‐situ Rutherford backscattering and electrochemical impedance spectroscopy "

Simulation results using SIMNRA-Code also included

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Solid–liquid interface analysis with in‐situ Rutherford backscattering and electrochemical impedance spectroscopy

Bergmann, U.; Apelt, S.; Khojasteh, N. B.; Heller, R.

A novel Rutherford backscattering spectrometry (RBS) method is presented to investigate the interface between a solid surface and a surrounding liquid. The introduced measurement system allows to observe and quantify adsorption at the solid–liquid interface and the formation of the electrochemical double layer (EDL). BaCl2 as a bicomponent electrolyte and a Si3N4 membrane surface are chosen as a model system to prove the capabilities of the setup. The results of these RBS measurements are combined with electrochemical impedance spectroscopy (EIS) to validate the findings for the solid–liquid interface under study. Complementary results and discrepancies regarding the formation of the EDL are discussed.
Author keywords: electrochemical double layer, electrochemical impedance spectroscopy, Rutherford backscattering spectroscopy, silicon nitride

Keywords: Rutherford backscattering spectrometry; electrochemical double layer; electrochemical impedance spectroscopy; point of zero charge

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RBS Raw data for publication: ""Electrical and Optical Properties of Amorphous SnO2:Ta Films, Prepared by DC and RF Magnetron Sputtering: A Systematic Study of the Influence of the Type of the Reactive Gas"

Mientus, R.; Weise, M.; Seeger, S.; Heller, R.; Ellmer, K.

Raw data for pub. "Electrical and Optical Properties of Amorphous SnO2:Ta Films, Prepared by DC and RF Magnetron Sputtering: A Systematic Study of the Influence of the Type of the Reactive Gas"

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Electrical and Optical Properties of Amorphous SnO2:Ta Films, Prepared by DC and RF Magnetron Sputtering: A Systematic Study of the Influence of the Type of the Reactive Gas

Mientus, R.; Weise, M.; Seeger, S.; Heller, R.; Ellmer, K.

By reactive magnetron sputtering from a ceramic SnO2:Ta target onto unheated substrates, X-ray amorphous SnO:Ta films were prepared in gas mixtures of Ar/O2(N2O, H2O). The process windows, where the films exhibit the lowest resistivity values, were investigated as a function of the partial pressure of the reactive gases O2, N2O and H2O. We found that all three gases lead to the same minimum resistivity, while the width of the process window is broadest for the reactive gas H2O. While the amorphous films were remarkably conductive (ρ ≈ 5 × 10−3 Ωcm), the films crystallized by annealing at 500 °C exhibit higher resistivities due to grain boundary limited conduction. For larger film thicknesses (d ≳ 150 nm), crystallization occurs already during the deposition, caused by the substrate temperature increase due to the energy influx from the condensing film species and from the plasma (ions, electrons), leading to higher resistivities of these films. The best amorphous SnO2:Ta films had a resistivity of lower than 4 × 10−3 Ωcm, with a carrier concentration of 1.1 × 1020 cm−3, and a Hall mobility of 16 cm2/Vs. The sheet resistance was about 400 Ω/□ for 100 nm films and 80 Ω/□ for 500 nm thick films. The average optical transmittance from 500 to 1000 nm is greater than 76% for 100 nm films, where the films, deposited with H2O as reactive gas, exhibit even a slightly higher transmittance of 80%. These X-ray amorpous SnO2:Ta films can be used as low-temperature prepared transparent and conductive protection layers, for instance, to protect semiconducting photoelectrodes for water splitting, and also, where appropriate, in combination with more conductive TCO films (ITO or ZnO).

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Influence of precursor thin-film quality on the structural properties of large-area MoS2 films grown by sulfurization of MoO3 on c-sapphire

Spanková, M.; Sojková, M.; Dobrocka, E.; Hutár, P.; Bodík, M.; Munnik, F.; Hulman, M.; Chromik, S.

In recent years, molybdenum disulfide (MoS2) has been investigated due to its unique electronic, optical, and mechanical properties with a variety of applications. Sulfurization of pre-deposited MoO3 layers is one of the methods of the preparation of large-area MoS2 thin films. The MoO3 layers have been grown on c-sapphire substrates, using two different techniques (rf sputtering, pulsed laser deposition). The films were subsequently annealed in vapors of sulfur at high temperatures what converted them to MoS2 films. The quality of MoS2 is strongly influenced by the properties of the precursor MoO3 layers. The pre-deposited MoO3, as well as the sulfurized MoS2, have been characterized by several techniques including Raman, Rutherford backscattering spectroscopy, atomic force microscopy, scanning electron microscopy, and X-ray diffraction. Here we compare two types of MoS2 films prepared from different MoO3 layers to determine the most suitable MoO3 layer properties providing good quality MoS2 films for future applications.

Keywords: Molybdenum disulfide; Sulfurization; Sputtering; Pulsed laser deposition; Structural properties

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Nanoparticle emission by electronic sputtering of CaF2 single crystals

Alencar, I.; Hatori, M.; Marmitt, G. G.; Trombini, H.; Grande, P. L.; Dias, J. F.; Papaléo, R. M.; Mücklich, A.; Assmann, W.; Toulemonde, M.; Trautmann, C.

Material sputtered from CaF2 single crystals by 180 MeV Au ions impinging at different incidence angles were collected on high-purity amorphous C-coated Cu grids and Si100 wafer catcher surfaces over a broad angular range. These catcher surfaces were characterized complementary by transmission electron microscopy, atomic force microscopy and medium energy ion scattering, revealing the presence of a distribution of partially buried CaF2 nanoparticles in conjunction to a thin layer of deposited CaF2 material. Particle size distributions do not follow simple power laws and depend on the angles of ion incidence and particle detection. It is shown that the particle ejection is directly related to the jet-like component of sputtering, previously observed in ionic crystals, contributing significantly to the total yield. This contribution enhances as the impinging ions approach grazing incidence. Possible scenarios for the emission of particles are discussed in light of these observations.

Keywords: Atomic force microscopyCatcher technique; Nanoparticle; Medium energy ion scattering; Electronic sputtering; Swift heavy ions; Transmission electron microscopy

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High carrier mobility epitaxially aligned PtSe2 films grown by one-zone selenization

Sojkova, M.; Dobročka, E.; Hutár, P.; Tašková, V.; Pribusová-Slušná, L.; Stoklas, R.; Píš, I.; Bondino, F.; Munnik, F.; Hulman, M.

Few-layer PtSe2 films are promising candidates for applications in high-speed electronics, spintronics and photodetectors. Reproducible fabrication of large-area highly crystalline films is, however, still a challenge. Here, we report the fabrication of epitaxially aligned PtSe2 films using one-zone selenization of pre-sputtered platinum layers. We have studied the influence of growth conditions onstructural and electrical properties of the films prepared from Pt layers with different initial thickness. The best results were obtained for the PtSe2 layers grown at elevated temperatures (600 °C). The films exhibit signatures for a long-range in-plane ordering resembling an epitaxial growth. The charge carrier mobility determined by Hall-effect measurements is up to 24 cm²/V.s

Keywords: PtSe2; epitaxial films; Laue oscillations; Raman spectroscopy

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Unusual scandium enrichments of the Tørdal pegmatites, south Norway. Part I: Garnet as Sc exploration pathfinder

Steffenssen, G.; Müller, A.; Munnik, F.; Friis, H.; Erambert, M.; Kristoffersen, M.; Rosing-Schow, N.

The granitic pegmatites of the Tørdal area in southern Norway have been known for their Sc enrichment for about 100 years. Scandium is a compatible element in garnet. In this study, 32 garnet samples from 16 pegmatite localities across the Tørdal pegmatite field were investigated to determine the Sc distribution within garnets (crystal scale), within pegmatite bodies (pegmatite scale) and across the Tørdal pegmatite field (regional scale). In the Tørdal pegmatites, Sc content in garnet is representative for the Sc bulk composition of pegmatites, defining garnet as a reliable pathfinder mineral for the exploration of Sc mineralization in pegmatite fields. Garnets with highest Sc concentrations of up to 2197 µg/g have a spessartine component ranging from 50 to 60 mol.%. Since most garnets crystallized during the early stage of pegmatite formation (wall zone stage) Sc decreases in the remaining pegmatite melt, as documented by generally decreasing Sc from core to rim of crystals and by the occurrence of late-stage garnets (albite zone stage) with low Sc. Thus, with progressing crystallization Sc decreases in the melt. The regional Sc distribution in the Tørdal pegmatite field revealed that the Skardsfjell-Heftetjern-Høydalen pegmatites have highest Sc enrichments to sub-economic levels, with an average bulk Sc content of 53 µg/g and an average Sc content in garnet of about 1900 µg/g in the Heftetjern 2 pegmatite.
The assumed resources of the Skardsfjell-Heftetjern-Høydalen area are about 125,000 t ore grading c. 50 µg/g Sc resulting in a total of 625 t Sc, which is too small to have economic potential. However, the strong Sc enrichment of the Tørdal pegmatites is unusual for granitic pegmatites, making them a specific Sc deposit type. The amphibolitic host rocks of the Tørdal pegmatites are identified as the source rocks of Sc. The host rocks, which are part of the Nissedal Outlier supracrustals, are enriched in Sc (mean 34 µg/g) compared to average crustal compositions (mean 14 µg/g). Scandium of amphiboles was preferentially released at the onset of partial melting of the amphibolites. Thus, the Sc content in the pegmatite is strongly dependent on the degree of partial melting.

Keywords: scandium; pegmatite; garnet; Sveconorwegian orogeny; Tørdal

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Silicon Surface Passivation by ALD-Ga₂O₃: Thermal vs. Plasma-Enhanced Atomic Layer Deposition

Hiller, D.; Julin, J. A.; Chnani, A.; Strehle, S.

Silicon surface passivation by gallium oxide (Ga2O3) thin films deposited by thermal- and plasma-enhanced atomic layer deposition (ALD) over a broad temperature range from 75 °C to 350 °C is investigated. In addition, the role of oxidant (O3 or O-plasma) pulse lengths insufficient for saturated ALD-growth is studied. The material properties are analyzed including the quantification of the incorporated hydrogen. We find that oxidant dose pulses insufficient for saturation provide for both ALD methods generally better surface passivation. Furthermore, different Si surface pretreatments are compared (HF-last, chemically grown oxide, and thermal tunnel oxide). In contrast to previous reports, the annealing time to activate the surface passivation is found to be significantly shorter. The best surface saturation current densities (JOs) or surface recombination velocities (Seff) are 6 and 9 fA/cm² or 0.6 and 1.5 cm/s for n- and p-type Si, respectively. We correlate the surface passivation with the negative fixed charge density (Qfix; field-effect passivation) and the interface defect density (Dit; chemical passivation). It turns out that a high Qfix is present, irrespective of the utilized ALD-method, deposition temperature, or postannealing, whereas low Dit is only achieved fo rplasma-enhanced ALD at low temperatures. A critical H-density of∼10¹⁶ cm−2 is identified as a necessary but not sufficient condition for excellent surface passivation. Finally, contact resistivities are measured to investigate the possibility of using ALD-Ga2O3 as passivating contact material. In order to understand the current-voltage measurements, the energetic positions of the band edges and the Fermi level are determined by ultraviolet photoelectron spectroscopy and Kelvin probe.

Keywords: Atomic layer deposition (ALD); gallium oxide(Ga2O3); hydrogen; silicon surface passivation

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Lithium Diffusion in Ion-Beam Sputter-Deposited Lithium-Silicon Layers

Strauss, F.; Hüger, E.; Julin, J. A.; Munnik, F.; Schmidt, H.

Lithium-silicon compounds are used as active material in negative electrodes of Li-ion batteries. The knowledge of Li diffusion in these materials is of importance for an optimization of charging/discharging rates and achievable maximum specific capacity as well as for an understanding of the basic lithiation mechanism. We carried out Li tracer self-diffusion experiments on ion-beam sputter-deposited LixSi(O) thin films for x ~ 0.25 and x ~ 4.5 using LixSi/6LixSi hetero-structures in combination with secondary ion mass spectrometry in line scan like mode. Measurements with elastic recoil detection analysis revealed the presence of a considerable amount of oxygen in the films. The diffusivities follow the Arrhenius law in the temperature range between 300 and 500 °C with an activation energy of 0.8 – 0.9 eV. The film containing a higher amount of Li shows faster diffusion by one order of magnitude. The Li diffusivities in the investigated Li-rich materials are several orders of magnitude higher than in Li-poor LixSi films (x = 0.02 to 0.06) as given in literature because of a lower activation energy. This indicates the presence of a direct interstitial-like mechanism. Oxygen present in samples with the same Li concentration of x = 0.06 also enhances diffusion but does not lead to a reduction in the activation energy.

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Microstructural evolution and thermal stability of AlCr(Si)N hard coatings revealed by in-situ high-temperature high-energy grazing incidence transmission X-ray diffraction

Jäger, N.; Meindlhumer, M.; Spor, S.; Hruby, H.; Julin, J.; Stark, A.; Nahif, F.; Keckes, J.; Mitterer, C.; Daniel, R.

An extensive understanding about the microstructural evolution and thermal stability of the metastable AlCr(Si)N coating system is of considerable importance for applications facing high temperatures, but it is also a challenging task since several superimposed processes simultaneously occur at elevated temperatures. In this work, three AlCr(Si)N coatings with 0 at.%, 2.5 at.% and 5 at.% Si were investigated by in-situ high-temperature high-energy grazing incidence transmission X-ray diffraction (HT-HE-GIT-XRD) and complementary differential scanning calorimetry and thermogravimetric analysis measurements combined with conventional ex-situ X-ray diffraction. The results revealed (i) a change in the microstructure from columnar to a fine-grained nano-composite, (ii) a reduced decomposition rate of CrN to Cr₂N, also shifted to higher onset temperatures from ∼ 1000 ℃ to above 1100 ℃ and (iii) an increase of lattice defects and micro strains resulting in a significant increase of compressive residual strain with increasing Si content. While the Si-containing coatings in the as-deposited state show a lower hardness of 28 GPa compared to AlCrN with 32 GPa, vacuum annealing at 1100℃ led to an increase in hardness to 29 GPa for the coatings containing Si and a decrease in hardness to 26 GPa for AlCrN. Furthermore, the in-situ HT-HE-GIT-XRD method allowed for simultaneously accessing temperature-dependent variations of the coating microstructure (defect density, grain size), residual strain state and phase stability up to 1100℃. Finally, the results established a deeper understanding about the relationships between the elemental composition of the materials, the resulting microstructure including crystallographic phases and residual strain state, and the coating properties from room temperature up to 1100℃.

Keywords: AlCrSiN; nano-composite; cathodic arc; thermal stability

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Thermo-physical properties of coatings in the Ti(B,N) system grown by chemical vapor deposition

Kainz, C.; Schalk, N.; Tkadletz, M.; Saringer, C.; Winkler, M.; Stark, A.; Schell, N.; Julin, J.; Czettl, C.

Hard protective coatings are commonly subjected to temperatures exceeding 1000 °C, which has significant influence on their thermo-physical properties and the associated performance in application. Within the present work, temperature dependent physical properties of coatings within the Ti(B,N) system grown by chemical vapor deposition were correlated with their chemical composition. High-energy X-ray diffraction experiments in inert atmosphere proved that TiN, TiB₂ and ternary TiBxNy coatings with varying B contents are thermally stable up to 1000 °C. First order lattice strains of TiN and TiBxNy coatings diminish during heating, whereas TiB₂ exhibits compressive strain enhancement up to the deposition temperature. Nanocrystalline TiB₂ exhibits more pronounced grain growth during annealing compared to coarse grained columnar TiN. Within the investigated coatings, the mean thermal expansion coefficient decreases as the B content increases. The same trend was observed for the thermal conductivity, which correlates with the grain size of the coatings.

Keywords: Chemical vapor deposition; X-ray diffraction; Ti(B,N); thermal conductivity; strain

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Kontakt

Dr. René Heller

Lei­ter Ionen­strahlanalytik
r.hellerAthzdr.de
Tel.: +49 351 260 3617