| 1. |
- Holeňák, Radek, et al.
(författare)
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Assessing trajectory-dependent electronic energy loss of keV ions by a binary collision approximation code
- 2024
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Ingår i: Physical Review Applied. - : American Physical Society. - 2331-7019. ; 21:2
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Tidskriftsartikel (refereegranskat)abstract
- The inelastic energy deposition of energetic ions is a decisive quantity for numerous industrial-scale applications, such as sputtering and ion implantation, yet the underlying physics being governed by dynamic many-particle processes is commonly only qualitatively understood. Recently, transmission experiments on single-crystalline targets (Phys. Rev. Lett. 124, 096601 & Phys. Rev. A 102, 062803) revealed a complex energy scaling of the inelastic energy loss of low-energy ions heavier than protons along different trajectories. We use a Monte Carlo like binary collision approximation code equipped with an impact-parameter-dependent modeling of the inelastic energy losses to assess the role of local contributions to electronic excitations in these cases. We compare angular intensity distributions of calculated trajectories with experimental results for 50-keV 4He and 100-keV 29Si ions transmitted in a time-of-flight setup through single-crystalline silicon (001) foils with nominal thicknesses of 200 and 50 nm, respectively. In these calculations, we employ different models of electronic energy loss, i.e., local and nonlocal forms for light and heavy projectiles. We find that the vast number of projectiles are eventually channeled along their trajectories, regardless of the alignment of the crystal with respect to the incident beam. It is, however, only when local electronic energy loss is considered that the simulated two-dimensional maps and energy distributions show excellent agreement with the experimental results, where channeling leads to significantly reduced stopping, especially for heavier projectiles. We demonstrate the relevance of these effects for ion implantations by assessing the nonlinear and nonmonotonic scaling of the ion range with the thickness of a random surface layer.
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| 2. |
- Holeňák, Radek, et al.
(författare)
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Charge state distributions of Xenon ions with keV kinetic energies transmitted through graphene and carbon self-supporting foils
- 2024
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Ingår i: Nuclear Instruments and Methods in Physics Research Section B. - : Elsevier. - 0168-583X .- 1872-9584. ; 554
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Tidskriftsartikel (refereegranskat)abstract
- We investigated the charge state distributions and energy loss of single and double-charged Xenon ions (20-220 keV) passing through graphene, Quantifoil, and 10 nm thick carbon membranes. Utilizing simultaneous carbon recoil detection on the graphene-containing sample, we determined the areal density of carbon equivalent to 3 monolayers of graphene, indicating only slight contamination by e.g. PMMA, of our exiting surfaces. The charge state distributions revealed notable proportions of higher charge states, up to Xe+5 at higher energies, with mean charge states consistently below 1. The observed exponential decrease in higher charge fractions suggests electron stripping processes play a significant role. Differences in mean charge states are found among the three systems studied.
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| 3. |
- Holeňák, Radek, et al.
(författare)
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Contrast modes in a 3D ion transmission approach at keV energies
- 2020
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Ingår i: Ultramicroscopy. - : Elsevier BV. - 0304-3991 .- 1879-2723. ; 217
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Tidskriftsartikel (refereegranskat)abstract
- We present options for visualizing contrast maps in 3D ion transmission experiments. Simultaneous measurement of angular distributions and flight time of ions transmitted through self-supporting, single-crystalline silicon foils allows for mapping of intensity and different energy loss moments. The transmitted projectiles were detected mainly for random beam-sample orientation using pulsed beams of He ions and protons with incident energies 50 and 200 keV. Differences in contrast, observed when varying the projectile type and energy, can be attributed to sample nuclear and electronic structure and bear witness to impact parameter dependent energy loss processes. Our results provide a base for interpretation of data obtained in prospective transmission studies when for example using a helium ion microscope.
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| 4. |
- Holeňák, Radek, et al.
(författare)
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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
- 2022
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Ingår i: Vacuum. - : Elsevier. - 0042-207X .- 1879-2715. ; 204
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 5. |
- Holeňák, Radek, et al.
(författare)
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Simultaneous assessment of energy, charge state and angular distribution for medium energy ions interacting with ultra-thin self-supporting targets : A time-of-flight approach
- 2021
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Ingår i: Vacuum. - : Elsevier. - 0042-207X .- 1879-2715. ; 185
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate simultaneous measurements of the charge state, energy and angular distribution of keV ions in transmission experiments through self-supporting foils. Using a time-of-flight approach we have introduced an electrostatic deflection apparatus as an extension to existing medium energy ion scattering (MEIS) instrumentation. Different positive, neutral and negative charge states have been discriminated and quantified for initially singly charged beams of He, N, O and Ne in the energy range from 25 to 250 keV. In parallel, the ion energy after interaction with the target has been assessed for all detected particles, while particles can be discriminated by deflection angle. Self-supporting thin carbon foils were used as samples to benchmark our experiments with literature data where available.
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| 6. |
- Lohmann, Svenja, 1990-, et al.
(författare)
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Assessing electron emission induced by pulsed ion beams : a time-of-flight approach
- 2020
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Ingår i: Nuclear Instruments and Methods in Physics Research Section B. - : Elsevier BV. - 0168-583X .- 1872-9584. ; 479, s. 217-221
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- We present a method to measure the kinetic energy of electrons emitted upon ion impact via their time-of-flight. Pulsed beams of H+, D2+, He+ and Ne+ ions with velocities between 0.4 and 3.5 a.u. are transmitted through thin, self-supporting carbon and gold foils. Transmitted ions and secondary electrons are detected with a position-sensitive detector behind the sample and their respective energies are determined via their flight times. A coincidence criterion can be applied in the acquisition software. Measured electron energies range between 10 and 400 eV. Above ion velocities of 1 a.u. the most probable electron energy scales with ion velocity pointing towards a kinetic emission mechanism. At lower ion velocities, the electron energy stays constant and lies above the maximum energy transfer possible in a classical binary collision between ion and electron. Potential applications and technical challenges of measuring electron energies and yields with a time-of-flight approach are discussed.
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| 7. |
- Lohmann, Svenja, 1990-, et al.
(författare)
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Trajectory dependence of electronic energy-loss straggling at keV ion energies
- 2023
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Ingår i: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 107:8
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Tidskriftsartikel (refereegranskat)abstract
- We have measured the electronic energy-loss straggling of protons, helium, boron, and silicon ions in silicon using a transmission time-of-flight approach. Ions with velocities between 0.25 and 1.6 times the Bohr velocity were transmitted through single-crystalline Si(100) nanomembranes in either channeling or random geometry to study the impact parameter dependence of energy-loss straggling. Nuclear and path length contributions to the straggling were determined with the help of Monte Carlo simulations. Our results exhibit an increase in straggling with increasing ion velocity for channeled trajectories for all projectiles as well as for protons and helium in random geometry. In contrast for heavier ions, electronic straggling at low velocities does not decrease further but plateaus and even seems to increase again. We compare our experimental results with transport cross section calculations. The satisfying agreement for helium shows that electronic stopping for light ions is dominated by electron-hole pair excitations, and that the previously observed trajectory dependence can indeed be attributed to a higher mean charge state for random trajectories. No agreement is found for boron and silicon indicating the breakdown of models based solely on electron-hole pair excitations, and that local electron-promotion and charge-exchange events significantly contribute to energy loss at low velocities.
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| 8. |
- Lohmann, Svenja, 1990-, et al.
(författare)
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Trajectory-dependent electronic excitations by light and heavy ions around and below the Bohr velocity
- 2020
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Ingår i: Physical review A. Covering atomic, molecular, and optical physics and quantum information. - 2469-9926 .- 2469-9934. ; 102:6
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Tidskriftsartikel (refereegranskat)abstract
- We present experiments demonstrating trajectory-dependent electronic excitations at low ion velocities, where ions are expected to primarily interact with delocalized valence electrons. Experiments were performed using pulsed beams of singly charged ions incident on self-supporting Si(100) nanomembranes, and energy was measured together with the angular distribution after transmission through the sample. The energy loss of H+, H2+, He+, N+, Ne+, 28/29Si+ and Ar+ was analyzed along channeled and random trajectories. For all ions, we observe a difference in electronic stopping dependent on crystal orientation. For protons, the difference between channeled and random trajectories increases with ion energy, which is explained by increasing contributions of core-electron excitations more likely to happen at small impact parameters accessible only in random geometry. For heavier ions, the energy loss difference between channeling and random geometry is generally found more pronounced, and, different from protons, increases for decreasing ion energy. Due to the inefficiency of core-electron excitations at employed ion velocities, we explain these results by reionization events occurring in close collisions of ions with target atoms, which are heavily suppressed for channeled trajectories. These processes result in trajectory-dependent mean charge states, which strongly affects the energy loss. The strength of the effect seems to exhibit an oscillation with Z1 with an observed minimum for Ne. We, furthermore, demonstrate that the simplicity of our experimental geometry leads to results that can serve as excellent benchmark systems for dynamic calculations of the electronic systems of solids using time-dependent density functional theory.
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| 9. |
- Moldarev, Dmitrii, et al.
(författare)
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A new setup for optical measurements under controlled environment
- 2023
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Ingår i: Review of Scientific Instruments. - : American Institute of Physics (AIP). - 0034-6748 .- 1089-7623. ; 94:3
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Tidskriftsartikel (refereegranskat)abstract
- We present a new analytical instrument for studying the optical properties of materials in different gaseous environments at room and controlled elevated temperatures. The system consists of a vacuum chamber, which is equipped with temperature and pressure controllers, a heating band, and a residual gas analyzer and is connected to a gas feeding line via a leak valve. Two transparent view ports located around a sample holder allow for optical transmission and pump-probe spectroscopy using an external optical setup. The capabilities of the setup are demonstrated by conducting two experiments. In the first experiment, we study the photodarkening and bleaching kinetics of photochromic oxygen-containing yttrium hydride thin films illuminated in ultra high-vacuum and correlate it with changes in partial pressures inside the vacuum chamber. In the second study, we investigate changes in the optical properties of a 50 nm V film upon hydrogen absorption.
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| 10. |
- Moro, Marcos V., et al.
(författare)
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Accurate high-resolution depth profiling of magnetron sputtered transition metal alloy films containing light species : A multi-method approach
- 2019
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Ingår i: Thin Solid Films. - : Elsevier BV. - 0040-6090 .- 1879-2731. ; 686
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Tidskriftsartikel (refereegranskat)abstract
- We present an assessment of a multi-method approach based on ion beam analysis to obtain high-resolution depth profiles of the total chemical composition of complex alloy systems. As a model system we employ an alloy based on several transition metals and containing light species. Samples have been investigated by a number of different ion-beam based techniques, i.e., Rutherford Backscattering Spectrometry, Particle-Induced X-ray Emission, Elastic Backscattering Spectrometry and Time-of-Flight/Energy Elastic Recoil Detection Analysis. Sets of spectra obtained from these different techniques were analyzed both independently and following an iterative and self-consistent approach yielding a more accurate depth profile of the sample, including both metallic heavy constituents (Cr, Fe and Ni) as well as the rather reactive light species (C, O) in the alloy. A quantitative comparison in terms of achievable precision and accuracy is made and the limitations of the single method approach are discussed for the different techniques. The multi-method approach is shown to yield significantly improved and accurate information on stoichiometry, depth distribution and thickness of the alloy with the improvements being decisive for a detailed correlation of composition to the material properties such as corrosion strength. The study also shows the increased relative importance of experimental statistics for the achievable accuracy in the multi-method approach.
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