455 research outputs found
Unprecedented severe atomic redistribution in germanium induced by MeV self-irradiation
No full textWe present a pronounced unprecedented surface modification of a crystalline Ge layer under ion irradiation with a Ge ion beam at the energy of 2.5 MeV. Samples were covered by a thin SiN-protection layer to protect from sputtering and surface redeposition phenomena. Under the irradiation conditions, the Ge layer did not become porous as observed for other projectiles and lower energies but develops into a severely uneven morphology with characteristic length scales of several hundred nanometers. The observed roughness monotonically increases with the irradiation doses. We show that this phenomenon is caused neither by the surface erosion effect nor by a non-uniform volumetric expansion. Rather, atomic redistribution in the bulk of the material is the major drive for the uneven surface. Furthermore, the deformation of the Ge layer likely occurs to the largest extent after irradiation, as indicated by the very flat interface around the end-of-range region. The observed morphology modification is discussed based on irradiation-induced plastic flow, coupled with a larger contribution of the electronic component in the ion-solid interactions.& nbsp;(C) 2022 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/)
Electronic stopping power of slow Ne-20 ions in Au obtained from TOF-MEIS and Monte-Carlo computer simulations
No full textThe electronic stopping power of slow Ne ions (v > 0.6 a.u. per nucleon, i.e. 180 keV) in polycrystalline Au was investigated in a backscattering approach. Spectra were recorded in a Time-Of-Flight Medium-Energy Ion Scattering (TOF-MEIS) experiment using a gold thin film of several nm thickness deposited on Si. The stopping power was extracted from fitting energy converted TOF-spectra by Monte-Carlo simulations for the ion trajectories. This permits an accurate disentanglement of elastic losses and inelastic losses which are due to nuclear collisions and interactions of the ion with the electronic system of the solid, respectively. The resulting electronic stopping cross section is found to exhibit excellent velocity proportionality in the whole investigated energy range. Data is compared to other experimental datasets for similar ion energies.</p
Chemical state and atomic structure in stoichiovariants photochromic oxidized yttrium hydride thin films
No full textJP, IA, and SZK acknowledge SWEB project 101087367 funded by the HORIZON-WIDERA-2022-TALENTS-01-01. The research leading to this result has been supported by the RADIATE project under the Grant Agreement 824096 from the EU Research and Innovation programme HORIZON 2020. Support of experiments using the tandem accelerator at Uppsala University by the Swedish Research Council VR-RFI (grant # 2019-00191) is gratefully acknowledged. Dmitrii Moldarev acknowledges a postdoctoral fellowship by the foundation Olle Engkvist Byggmästare (grant # 207-0423).The Institute of Solid State Physics of the University of Latvia, which as a center of excellence has received funding from the European Union framework program Horizon 2020 H2020-WIDESPREAD-01-2026-2017-TeamingPhase2 within the framework of grant agreement No. 739508 of the CAMART2 project.We investigate the effective oxidation state and local environment of yttrium in photochromic YHO thin film structures produced by e-beam evaporation, along with their chemical structure and optical properties. Transmission electron microscopy images reveal the oxidized yttrium hydride thin film sample exhibiting a three-layered structure. X-ray photoelectron spectroscopy (XPS) measurements manifest that the oxidation state of yttrium is modified, dependent on the film's composition/depth. Furthermore, Ion beam analysis confirms that this variability is associated with a composition gradient within the film. X-ray absorption spectroscopy at the Y K-edge reveals that the effective oxidation state of yttrium is approximately +2.5 in the transparent/bleached state of YHO. Spectroscopic ellipsometry investigations showed a complex non-linear optical depth profile of the related sample confirming the dominant phase of YHO and the presence of Y2O3 and Y towards the middle of the film. The first evidence of (n; k) dispersion curves for e-beam sputtered photochromic YHO thin films are reported for transparent and dark states. © 2024 the author(s), published by De Gruyter, Berlin/Boston. --//-- This is an open-access article Arslan, Halil, Kuzmin, Alexei, Aulika, Ilze, Moldarev, Dmitrii, Wolff, Max, Primetzhofer, Daniel, Pudza, Inga, Kundzins, Karlis, Sarakovskis, Anatolijs, Purans, Juris and Karazhanov, Smagul Zh. "Chemical state and atomic structure in stoichiovariants photochromic oxidized yttrium hydride thin films" Zeitschrift für Physikalische Chemie, vol. 238, no. 11, 2024, pp. 2075-2100. https://doi.org/10.1515/zpch-2023-0507.HORIZON-WIDERA-2022-TALENTS-01-01, project 101087367 (SWEB); EU Research and Innovation programme HORIZON 2020 824096, project RADIATE; foundation Olle Engkvist Byggmästare 207_0423; Swedish Research Council VR-RFI 2019_00191; the Institute of Solid State Physics of the University of Latvia, which as a center of excellence has received funding from the European Union framework program Horizon 2020 H2020-WIDESPREAD-01-2026-2017-TeamingPhase2 within the framework of grant agreement No. 739508 of the CAMART2 project
Inelastic energy loss of medium energy H and He ions in Au and Pt : Deviations from velocity proportionality
No full textElectronic energy loss of light ions in nm films of Au and Pt has been studied at keV ion energies. For H the electronic stopping power S is found to exhibit the expected velocity proportionality at low ion velocities, which confirms the anticipated excitation mechanisms responsible for the energy transfer between ions and the electrons in the solid. In contrast, for He, S shows a clear deviation from velocity proportionality for both materials at ion velocities below 0.8 atomic units, i.e., 64 keV. This result indicates a change in the interaction mechanisms active at the investigated ion velocities, which cannot exclusively be interpreted from the density of states of the target. Instead, the more complex electronic structure of the He ion enables an additional energy loss channel due to charge exchange by atomic level promotion. Associated energy losses together with a changed equilibrium charge state permit an explanation of the observed phenomenon.</p
Development of W–SiO2 and Nb–TiO2 solar absorber coatings for combined heat and power systems at intermediate operation temperatures
No full textTwo new absorber coatings for mid-temperature operation (300–350 1C) in collectors for solar thermal electricity plants are presented in this study. The absorbers consist of two cermet layers of either W–SiO2 or Nb–TiO2, deposited on a molybdenum infrared reflector and coated with an antireflection layer of silicon oxide. The optimization of the optical performance was made in two steps. First, the layer structure was optimized in model calculations. The optical constants used in this modelling were derived directly from sputtered films of the cermet constituents using reflectance and transmittance measure- ments. The absorber coatings were then sputter-deposited using parameters from the modelling. The results show good agreement between modelled and sputtered optical performance evaluated as solar absorptance and thermal emittance at 350 1C. The optimal values reached for W–SiO2 was 0.91 in combination with 0.08 and 0.93 in combination with 0.09 for Nb–TiO2. The materials characterization from XRD, AES and TEM shows that the composite coatings contain nano-metal inclusions, meaning that they are cermet coatings. Scratch tests show that the coatings adhere well to the substrate of stainless steel. Temperature testing at 350 1C in vacuum for up to 1500 h shows that both coatings are stable under such conditions. Only a slight change occurs during the first 72 h that decreases the emittance but does not change the solar absorptance. ERDA confirms that there is no detectable level of ion migration between layers, only a small decrease in hydrogen content was observed, which indicates outgassing.Digespo projec
Disparate Energy Scaling of Trajectory-Dependent Electronic Excitations for Slow Protons and He Ions
No full textWe have simultaneously measured angular distributions and electronic energy loss of helium ions and protons directly transmitted through self-supporting, single-crystalline silicon foils. We have compared the energy loss along channeled and random trajectories for incident ion energies between 50 and 200 keV. For all studied cases the energy loss in channeling geometry is found lower than in random geometry. In the case of protons, this difference increases with initial ion energy. This behavior can be explained by the increasing contribution of excitations of core electrons, which are more likely to happen at small impact parameters accessible only in random geometry. For helium ions we observe a reverse trend—a decrease of the difference between channeled and random energy loss for increasing ion energy. Because of the inefficiency of core-electron excitations even at small impact parameters at such low energies, another mechanism has to be the cause for the observed difference. We provide evidence that the observation originates from reionization events induced by close collisions of helium ions occurring only along random trajectories
Energy deposition by nonequilibrium charge states of MeV 127I in Au
No full textThe energy loss of iodine ions at initial charge states up to 25+ and energies up to 36 MeV in self-supporting gold foils between 37 and 107 nm of thickness was measured with an electron mirror type time-of-flight detector. An excess energy loss of 130 keV was observed at 36MeV for charge state 25+ compared to 16+, and an energy loss deficit of 100 keV was observed for charge state 8+. The charge state equilibration length for 36-MeV iodine was estimated to lie between 3 and 7 nm, corresponding to an equilibration time between 0.4 and 0.9 fs. This result is relevant both for nanostructure fabrication with MeV ion beams and for depth profiling based on ion beam analysis data in cases where the charge state of the primary ion is far from the equilibrium value in the sample under study. A comparison to published data on charge state equilibration for various projectile-target combinations and energies from 10 keV to 6 GeV indicated that the energy scaling of the equilibration length observed at high energy is invalid for projectile velocities on the order of the Bohr velocity and below. The measurement further provided equilibrium values of the electronic stopping power for iodine in gold at ten energies between 10 and 36 MeV
In-situ measurement of diffusion and surface segregation of W and Ta in bare and W-coated EUROFER97 during thermal annealing
No full textThe near-surface composition of polished EUROFER97 samples was measured by Rutherford backscattering spectrometry while maintaining the analyzed surface at temperatures up to 1188 K. A sample pre-coated with less than a monolayer of tungsten by magnetron sputter deposition was included in the study. A shifting equilibrium due to diffusion and segregation of tungsten and tantalum was observed, with segregation being most important between 900 K and 1040 K, which is near the known transition temperature between the martensitic and austenitic phases. Diffusion counteracted any increase of the near-surface concentration of the elements of interest both above and below the temperature range in which segregation dominated. An asymmetry in the diffusion-segregation balance was observed when approaching the same temperature from above and below. The largest segregation peak measured at elevated temperature in this work indicated an increased amount of tungsten and/or tantalum near the sample surface with an areal atom density corresponding to 70-80% of a monolayer. Additional measurements were performed on bare EUROFER97 after annealing at 1089 K and 1553 K followed by rapid cooling to near room temperature which, if carried out at a critical rate, is expected to restore a martensitic microstructure. In the former case a similar enrichment peak was seen as that measured while the sample temperature was elevated, while in the latter case an increased concentration of tungsten and tantalum from 0.4 to 0.55 atomic percent in a layer of at least 300 nanometers thickness near the surface was observed
Ion beam tools for nondestructive in-situ and in-operando composition analysis and modification of materials at the Tandem Laboratory in Uppsala
No full textIon accelerators have demonstrated tremendous versatility in their research applications throughout several decades. Starting predominantly as nuclear physics tools, they subsequently provided novel insights into fundamental atomic physics. Nowadays small and medium size accelerators are routinely employed in several branches of materials science. As research questions increasingly drive the need for analyses and material modification experiments performed in-situ and/or in-operando, facilities must adapt to service such a need. In this work, we highlight capabilities for in-situ and in-operando composition depth profiling and materials modification, developed with instrumentation at the Tandem Laboratory at Uppsala University. An overview of available ion sources and accelerators is given. We then exemplify the specific capabilities of the available end stations for materials synthesis, sample modification and device operation either during simultaneous ion beam based characterization or with such characterization performed in-situ before and after the application of various modification steps. Describing specific recent examples and potential future applications, we illustrate the impact of the present national research infrastructure
Ion-induced particle desorption in time-of-flight medium energy ion scattering
No full textSecondary ions emitted from solids upon ion impact are studied in a time-of-flight medium energy ion scattering (ToF-MEIS) set-up. In order to investigate characteristics of the emission processes and to evaluate the potential for surface and thin film analysis, experiments employing TiN and Al samples were conducted. The ejected ions exhibit a low initial kinetic energy of a few eV, thus, requiring a sufficiently high acceleration voltage for detection. Molecular and atomic ions of different charge states originating both from surface contaminations and the sample material are found, and relative yields of several species were determined. Experimental evidence that points towards a predominantly electronic sputtering process is presented. For emitted Ti target atoms an additional nuclear sputtering component is suggested
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