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The AlCoCrFeNi_2.1 eutectic high entropy alloy (EHEA) features a dual-phase lamellar microstructure composed of ordered L1₂ and B2 phases, offering a unique combination of strength, ductility, and thermal stability. This study investigates the microstructural evolution, phase stability, and irradiation resilience of AlCoCrFeNi_x alloys with x = 1.9, 2.1, and 2.6. Advanced electron microscopy techniques revealed composition-dependent microstructure and confirmed the eutectic nature of the x = 2.1 alloy. Thermomechanical processing via cold rolling and annealing preserved phase ordering and enhanced mechanical properties. Irradiation of transmission electron microscopy (TEM) samples with Ne ions at doses up to 1.5 dpa enabled precise microstructure and defect analysis by comparing pre- and post-irradiation states of the same samples. The L1₂ phase exhibited dose-dependent disordering (assessed via evaluation of the fraction of 〈110〉-type dislocations), while the B2 phase retained its ordered structure, showing localized disorder and anti-phase boundaries. As a function of dose, a significant decrease in the network dislocation density (excluding dislocation loops) was observed in L1₂. On the other hand, this phase exhibited dose-dependent increase in both the density and size of dislocation loops. The B2 phase exhibited a similar effect, although the change was more moderate compared to L1₂. Semi-coherent L1₂/B2 boundaries, initially rich in dislocations, retained the Kurdjumov–Sachs orientation relationship post-irradiation, although dislocations vanished and stacking faults occasionally formed. These findings elucidate phase-specific radiation damage mechanisms and confirm the superior irradiation tolerance and structural integrity of AlCoCrFeNi_2.1, highlighting its potential for nuclear structural applications.

Accurate knowledge of the energy deposition of slow ions in solids is essential for modelling plasma-material interactions. While nuclear stopping can be reliably predicted through simulations electronic stopping at very low energies remains challenging to determine. Using molecular dynamics simulations, we investigate how crystallographic structure and surface orientation affect the backscattering probability and impact parameters of low-energy He in fcc and bcc metals. On this basis we evaluate challenges for typical approaches to assess electronic stopping. Close-packed surface orientations yield higher backscattering and smaller mean impact parameters due to reduced channel sizes, with characteristic differences for different crystal structures. For fcc Au, the (1 1 1) surface behaves similarly to a pseudo-amorphous target, whereas for bcc W, the (1 1 0) surface shows a significantly lower backscattering probability. These structural effects can explain the observed energy scaling of the electronic stopping power in some bcc material systems extracted from relative measurements using fcc reference materials. The results furthermore highlight that crystallographic orientation and impactparameter selectivity can strongly bias measurements of electronic stopping at low energies, severely challenging the applicability of a single global electronic stopping cross section.

We measure the photon emission induced by energetic Ne and He ions transmitted through thin single crystalline Si foils. The emitted photons are detected with a delay line microchannel plate detector. Our measurements show that photon emission detectable from the rear surface of the membranes is multiple times more likely than photon emission from the front surface of the membrane. It can be deduced that photon emission from electronic deexcitation of the sample can only play a minor role, while the vast majority of detected photons are emitted by excited projectiles freely decaying behind the sample. Utilizing shadowing effects, we can show that a large proportion of excited projectiles travels several centimeters before decaying. The photons observed in the present approach are another accessible observable reporting on ultrafast processes during ion-matter interaction.

A bilayer of V0.49N0.51/V0.56N0.44 has been grown epitaxially on MgO(001) by reactive high-power pulsed magnetron sputtering in an industrial-scale deposition system at a temperature of 400 degrees C, and it is demonstrated that the defect structure and interfacial strain are governed by the N concentration. Based on the lattice mismatch between MgO and V0.49N0.51 with V vacancies, an interfacial strain of -2.3(1)% is expected. From ab initio calculations, X-ray diffraction, and transmission electron microscopy data, it is inferred that the V0.49N0.51 layer exhibits V vacancies, N Frenkel pairs, and a high dislocation density of approximate to 0.20 nm(-2), causing an interfacial strain of -1.4(5)% at the MgO/V0.49N0.51 interface. The phase formation of understoichiometric V0.56N0.44 is governed by N vacancy formation, while the dislocation density is reduced to approximate to 0.04 nm(-2) at the V0.49N0.51/V0.56N0.44 interface and to < 0.01 nm(-2) within V0.56N0.44 at a distance of approximate to 35 nm from the interface. Based on ab initio calculations, a strain of -1.7(6)% is predicted at the V0.49N0.51/V0.56N0.44 interface in very good agreement with the experimentally obtained value of -1.6(8)%. It is evident that control of the N concentration allows for the design of layered architectures with well-defined strained interfaces and tailored defect structures.

The reliability of XPS spectra interpretation of heterogeneous materials exhibiting compositionally-driven phase transformations is shown to improve by a comprehensive sample analysis including characterization of microstructure, elemental composition, impurity level, and phase constitution. This approach is demonstrated here for a series of W_1-xN_x films with N content varying in the range 0 ≤ x ≤ 0.65, which results in a complex evolution of W 4f spectra. The reliability of peak models is further enhanced by performing self-consistent XPS analysis from all major core level spectra (W 4f, N 1s, O 1s, and C 1s) in liaison with XRD (for crystalline phase content, lattice parameters, preferred orientation), ToF-ERDA (elemental composition, impurity levels), SEM and TEM (micro- and nano-structural analysis), and SAED (crystalline content down to the nm-level). It is thus found that a phase transformation occurs as x increases from bcc α-W(N) with x = 0.06 to bcc α-W(N) + cubic β-W_yN (0.08 ≲ x ≲ 0.27), cubic β-W_yN + hexagonal W₂N₃ (0.36 ≲ x ≲ 0.56), and finally to cubic β-W_yN + amorphous WN₂ (0.62 ≲ x ≲0.65). The comparison of spectra recorded before and after Ar⁺ etching reveals that sensitivity to sputter damage varies greatly between different phases. This integrated methodology is particularly valuable for transition metal nitrides, carbides, and related compounds exhibiting continuous structural evolution with overlapping XPS signatures.

The oxidation behavior of (Cr_0.47±0.03Al_0.53±0.03)_z(O_yN_1-y)_1-z thin films (z = 0.475 0.015) was investigated as a function of the O concentration with y = 0, 0.15, and 0.40 at 1000 °C to 1200 °C. Three regions were identified after oxidation at 1000 °C and 1100 °C: an Al-rich oxide scale (I) with a Cr-rich oxynitride gradient interlayer (II) is formed, and O levels decrease linearly within the interlayer towards the remaining film (III). Increasing the O concentration in the film reduces the amount of Cr in the oxide scale and significantly increases the stability of the remaining film during oxidation, which can be readily understood by O-induced enhancement of the activation energy of migration. Non-metal mobility is required for the decomposition of (Cr,Al)(O,N) into hexagonal Cr₂N, and the formation of O vacancies is inhibited due to their high vacancy formation energy. All film compositions show a passivating oxidation behavior with comparable oxide scale thickness (I) of ∼130 ± 30 nm after oxidation at 1000 °C for 16 h. In contrast, at 1100 °C, (Cr_0.48Al_0.52)_0.48(O_0.15N_0.85)_0.52 exhibits the thinnest combination of oxide scale and oxynitride interlayer thickness (I+II), while it is 27% and 42% thicker for (Cr_0.50Al_0.50)_0.49N_0.51 and (Cr_0.44Al_0.56)_0.46(O_0.40N_0.60)_0.54, respectively. Oxidation kinetics are reduced for the oxynitride films, however, cracks are formed at the interlayer of (Cr_0.44Al_0.56)_0.46(O_0.40N_0.60)_0.54, eventually causing delamination. Consequently, (Cr_0.48Al_0.52)_0.48(O_0.15N_0.85)_0.52 offers the highest oxidation resistance, while exhibiting lower oxidation kinetics than Cr₂AlC at 1100 °C.

The composition-dependent thermal stability of (Cr_0.47±0.03Al_0.53±0.03)_z(O_yN_1-y)_1-z thin films (z = 0.475 ± 0.015) with O concentrations of y = 0, 0.15, and 0.40 is investigated up to 1200 °C and then compared to (Ti_0.56Al_0.44)_z(O_yN_1-y)_1-z. X-ray diffraction reveals a thermal stability limit of 1150 °C independent of the O concentration, as witnessed by the formation of decomposition products, namely h-Cr₂N for (Cr_0.50Al_0.50)_0.49N_0.51 and c-Cr for both (Cr_0.48Al_0.52)_0.48(O_0.15N_0.85)_0.52 and (Cr_0.44Al_0.56)_0.46(O_0.40N_0.60)_0.54. Based on transmission electron microscopy and elastic recoil detection analysis data, the thermal stability limit is extended to 1100 °C – 1150 °C for all films.Chemical environment-dependent DFT calculations indicate that bond breaking limits the thermal stability. In (Cr,Al)N, N has the lowest activation energy for migration. Furthermore, the O vacancy formation energy is highest in (Cr,Al)(O,N). It has to be overcome to enable diffusion on the non-metal sublattice, which is necessary for forming decomposition products like w-AlN or c-Cr. However, once Cr-N bonds break, decomposition into h-Cr₂N and subsequent c-Cr together with N₂ is triggered. This results in N evaporation, generating sufficient non-metal vacancies that greatly enhance diffusion and render the extensive vacancy formation energies for non-metals irrelevant. This reduction of the activation energy for mass transport on the non-metal sublattice to the migration barrier causes the similar thermal stability in (Cr_0.47±0.03Al_0.53±0.03)_z(O_yN_1-y)_1-z. In contrast, Al bonds break first without creating non-metal vacancies in (Ti,Al)(O,N). Thus, the high O vacancy formation energy in (Ti,Al)(O,N) significantly increases the thermal stability compared to (Ti,Al)N as well as the here investigated films.

Oxidation of B-overstoichiometric Hf_0.13Al_0.18B_0.69 and B-understoichiometric Hf_0.13Al_0.23B_0.64 films at 700°C reveals that both compositions form Al-rich and passivating oxide scales. The superior oxidation resistance of Hf_0.13Al_0.18B_0.69 compared to previously reported B-overstoichiometric Ti_0.10Al_0.19B_0.71 films is attributed to the absence of B-enrichment at grain boundaries, as evidenced by STEM-EDX mapping. These observations align with ab initio calculations, predicting that excess B in Hf_0.13Al_0.18B_0.69 is preferentially incorporated into the lattice as point defects. Formation energies of Al vacancies, transition metal vacancies, and B interstitials are lower on average in the Hf-based system by 43%, 9%, and 19%, respectively. The most plausible scenario involves the formation of Al vacancies, which, among the considered defects, display the lowest energetic barrier and best agreement with experimental lattice parameter data. Consequently, Hf-based films can accommodate higher B concentrations within the grain lattice without developing B-rich grain boundaries, in contrast to Ti-based overstoichiometric films. This significantly improves the processability of Hf-based diboride films by easing the need for strict control of the B-to-metal ratio during synthesis.

We investigate effects of the density of states of condensed matter on the electronic excitations triggered by penetrating keV ions, in a systematic study of energy deposition along multiple well-defined channeling trajectories. We measure the specific energy deposition of ions with keV energies transmitted through Si-a band gap material-in the form of single-crystalline, self-supporting membranes. Energy transfers observed for Ne ions along the < 100 >, < 211 >, and < 111 > channeling orientations agree well in magnitude with predictions from density functional theory for the expected unperturbed electron densities in an electron gas. This agreement indicates that, along channeling trajectories, the interaction is dominated by conduction and valence electrons, with atomic (core-electron) processes largely suppressed. In contrast, for H and He ions, the predicted values are found systematically higher than the measured values. Non-linearities in the energy dependence of the specific energy deposition of Ne ions are found along all studied low-index orientations, with an inverted behavior observable for random in comparison to channeling orientation. In this context, we discuss the experimental challenges of limiting selected trajectories for the lowest velocities studied, which can mask effects of electronic excitation thresholds in the target electronic system. The new insights shed also light on earlier studies reporting a complex scaling of energy deposition with excitation thresholds, or even their apparent absence.

Understanding the influence of helium (He) implantation rate on defect evolution in structural materials is critical for advancing radiation-resistant materials for nuclear applications. In this study, we systematically investigate the effect of He implantation rate on the formation and evolution of nano-bubbles, subsurface fractures, and surface blistering in polycrystalline molybdenum (Mo) at room temperature. Using a combination of Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM), and X-ray Diffraction (XRD), we analyze Mo samples implanted with He at two distinct rates across a range of doses. Our results reveal that higher implantation rates lead to lower densities of He nano-bubbles, wider and deeper projection ranges, and the development of macro-strains, while lower rates result in higher bubble densities and micro-strain formation. These effects are explained by increased diffusion of He atoms, through RED - Radiation Enhanced Diffusion during the higher rate implantations. Furthermore, we propose a novel experimental approach to estimate the annealing time following a collision cascade event, by tracking the effect of implantations at different rates on the target. Through this approach we estimate that the recovery/annealing duration after He collision exceeds 45 ns, which is significantly longer than molecular dynamics simulations predictions.