arXiv subjects

Daniel Primetzhofer

Publications and source records attributed to Daniel Primetzhofer.

At least 19 recordsLinked to original sources

arXiv2026

Charge-State Dependence of Electronic Excitations in keV Ions Transmitted Through Solids Probed by Ion-Photon Coincidence Measurements

Investigating the electronic excitations caused by light keV ions in matter contributes to a better understanding of materials modification such as space weathering or plasma-wall interactions in fusion reactors as well as improved materials analysis methods such as low or medium energy ion scattering. This study investigates the dependence of specific excitations in keV He projectiles, the most common projectile employed in these analytical methods, on the kinetic energy of the ion. We report on photon emission at energies >10eV emitted by projectiles excited upon transmission through different sample systems. We separate exit charge states and report on measurements of ion-photon pairs in coincidence, i.e. we can link a photon to the specific ion emitting it. From these measurements we extracted charge state resolved photon yields and obtained a deep insight into the electronic excitation occurring. Our results show that the electronic excitation of the helium projectile is largely material independent and rising strongly with the kinetic energy of the projectile. The photon yields are in good agreement with a common excitation model initially developed for beam foil spectroscopy. We hence extend the validity of this model to higher photon energies and different sample materials. We further provide a detailed analysis of the employed coincidence approach and necessary corrections to the raw data, as the methodology has a broad applicability in fundamental research and materials analysis.

cond-mat.mtrl-sci↗

arXiv2026

Interface-Controlled Defect Engineering in TiN/TaN Superlattices for Enhanced Hardness and Fracture Toughness

TiNTaN superlattice coatings were designed to investigate how atomic-scale interface chemistry and defect-stabilized TaN layers govern hardness and fracture toughness. Guided by first-principles predictions identifying TaN-based layers as more damage tolerant than TiN, coherent superlattices with a bilayer period of 6 nm were synthesized by reactive magnetron sputtering and interfacially doped with C, B, or Si. Structural and chemical analyses reveal coherent fcc architectures with well-defined interfaces. Si segregates preferentially to the interfaces while incorporating into both TiN and TaN, whereas C and B predominantly diffuse into the TaN layers, modifying coherency strain, bonding, and defect populations. Consequently, hardness increases from 34 GPa for the undoped superlattice to 41 GPa for the Si-doped architecture, whereas fracture toughness increases from 2.8 to 4.0 MPam0.5 for the B-doped superlattice. First-principles calculations show that vacancy-stabilized TaxNy enhances elastic compliance and elastic contrast rather than intrinsic toughness, while the additional toughening induced by B indicates localized defect-assisted energy dissipation at chemically engineered interfaces. Thus, Si maximizes interface strengthening, whereas B provides the most favourable hardness-toughness balance while preserving high hardness, 38 GPa. These findings establish interface chemistry as an additional design parameter for tailoring the mechanical performance of ceramic nitride superlattices.

cond-mat.mtrl-sci↗

arXiv2026

Quantitative Analysis of Composition and Contamination of Atomically Thin Materials by Recoil-Projectile Coincidence in Ion Transmission

Surface contamination strongly affects the intrinsic properties of nanoscale materials, making its reliable identification and quantification crucial for both accurate experimental interpretation and nanofabrication. Although scanning transmission electron microscopy can resolve contaminants at atomic resolution within nanometer-scale regions, it cannot easily provide a quantitative, large-area contamination measure. Here, we introduce a minimally destructive recoil-projectile coincidence method for ion transmission experiments that enables element-specific identification and quantification of surface contaminants with isotopic resolution. We demonstrate this approach by comparing self-supporting graphene samples prepared using either a polymethylmethacrylate (PMMA)-based or a PMMA-free transfer process. Carbon and hydrogen are identified as the dominant surface contaminants. PMMA-free transferred graphene exhibits the lowest native contamination levels. Following in-situ thermal annealing at 400 {\deg}C for 1 h, the measured carbon areal density approaches the value expected for atomically clean single-layer graphene within the experimental uncertainty, while hydrogen coverage is strongly reduced. Unlike PMMA-transferred graphene, which rapidly recontaminates after annealing, PMMA-free transferred graphene remains nearly contamination-free for at least 140 min under ultra-high vacuum conditions ($p_{\mathrm{base}} = 2 \times 10^{-8}$ mbar). Beyond graphene, the presented method establishes a quantitative characterization platform for ultrathin materials, enabling studies of surface cleanliness, adsorption, implantation and surface interaction dynamics in such systems.

cond-mat.mtrl-sci↗

arXiv2026

Rainbow Scattering from Graphene

We report the experimental observation of atomic rainbow scattering of 40 keV Xe$^+$ ions transmitted through self-supporting single-layer graphene using time-of-flight medium energy ion scattering. Supported by molecular dynamics and binary collision approximation simulations, we show that the rainbow pattern of graphene consists of a small hexagonal inner rainbow, arising from projectiles with characteristic trajectories interacting with multiple carbon atoms, and a larger circular outer rainbow, arising from close binary collisions between projectiles and individual carbon atoms.

cond-mat.mtrl-sci↗

arXiv2026

Impact of O concentration on the thermal stability and decomposition mechanism of (Cr,Al)N compared to (Ti,Al)N thin films

The composition-dependent thermal stability of (Cr$_{0.47 \mp 0.03}$Al$_{0.53 \mp 0.03}$)$_{z}$(O$_{y}$N$_{1-y}$)$_{1-z}$ thin films with O concentrations of y = 0, 0.15, and 0.40 is investigated up to 1200 {\deg}C and then compared to (Ti$_{0.56}$Al$_{0.44}$)$_{z}$(O$_{y}$N$_{1-y}$)$_{1-z}$. X-ray diffraction reveals a thermal stability limit of 1150 {\deg}C independent of the O concentration, as witnessed by the formation of decomposition products, namely h-Cr$_{2}$N for (Cr$_{0.50}$Al$_{0.50}$)$_{0.49}$N$_{0.51}$ and c-Cr for both (Cr$_{0.48}$Al$_{0.52}$)$_{0.48}$(O$_{0.15}$N$_{0.85}$)$_{0.52}$ and (Cr$_{0.44}$Al$_{0.56}$)$_{0.46}$(O$_{0.40}$N$_{0.60}$)$_{0.54}$. Based on TEM and ERDA data, the thermal stability limit is extended to 1100 - 1150 {\deg}C. 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-Cr$_{2}$N and subsequent c-Cr together with N$_{2}$ 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$_{0.47 \mp 0.03}$Al$_{0.53 \mp 0.03}$)$_{z}$(O$_{y}$N$_{1-y}$)$_{1-z}$. 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.

cond-mat.mtrl-sci↗

arXiv2025

Probing formation and epitaxy of ultrathin Titanium Silicide using low and medium energy ion scattering

Titanium silicide is a key contact material in advanced three-dimensional semiconductor device architectures. Here, we examine the formation of ultrathin Ti-silicide on Si(100) using a combination of non-destructive in-situ and ex-situ ion scattering techniques capable of resolving composition and structure at the nanoscale. In-situ Time-of-Flight Low-Energy Ion Scattering (ToF-LEIS) indicates intermixing after annealing at 350 {\deg}C, with further compositional changes after annealing at 500 {\deg}C, including the emergence of a Si terminating layer at the surface. Consecutive ex-situ Time-of-Flight Medium-Energy Ion Scattering (ToF-MEIS) reveals a Ti-rich polycrystalline surface layer and a Si-rich interface layer exhibiting strong ordering along the Si [100] axis. High-Resolution Transmission Electron Microscopy (HR-TEM) images confirm these findings, revealing a $\approx$1.5 nm thick epitaxial silicide layer at the interface. The presence of an epitaxial interface is particularly promising for minimizing contact resistivity in ultrathin contact layers, where interfacial order can dominate electronic performance. In addition, both ToF-MEIS and HR-TEM unveil significant variations in the thickness of the silicide layer, with a substantial interface roughness but no translation of this roughness to the surface.

cond-mat.mtrl-sci↗

arXiv2025

Long-Range Magnetic Order in Structurally Embedded Mesospin Metamaterials

Engineered assemblies of interacting magnetic elements-magnetic metamaterials-provide a powerful route to tailor collective magnetic order and dynamics. By structuring matter at the mesoscale, they bridge atomic magnetism and macroscopic functionality, enabling emergent behaviour inaccessible in conventional materials. However, realizing large-area metamaterials that combine high morphological uniformity with intrinsic long-range order has remained challenging, largely due to the structural disorder inherent to lithographic fabrication. Here we demonstrate a scalable route to structurally and magnetically coherent metamaterials by embedding iron-ions to form mesospins within a non-magnetic thin film palladium host matrix. Using controlled implantation, we realize morphologically uniform arrays that spontaneously develop extended antiferromagnetic order in the as-fabricated state - without the need of external annealing or field cycling. Resonant X-ray scattering and microscopy reveal sharp magnetic Bragg peaks modulated by the mesospin form factor, evidencing long-range antiferromagnetic order coupled to structural coherence. This embedded architecture establishes a platform for exploring coherent spin-photon interactions and functional X-ray scattering in magnetic metamaterials free from lithographic topography and disorder.

cond-mat.mes-hall↗

arXiv2025

Kinetics of the photochromic effect in oxygen-containing rare-earth hydrides

The kinetics of the photochromic reaction of oxygen-containing rare-earth hydrides is commonly described by an exponential function assuming a single-step process. In this paper, we elaborate on the origin of the photochromic effect in oxygen-containing rare-earth metal hydrides, considering the kinetics of the reaction as a two-step process. We show that the fit to the experimental data is improved drastically when two processes that cause the photodarkening are assumed: a fast reaction rate-limited - for example, electronic or local - process and a slow, e.g. diffusion-limited process.

cond-mat.mtrl-sci↗

arXiv2025

Role of hydrogen dynamics and deposition conditions in photochromic YHO/MoO$_3$ bilayer films

Oxygen-containing yttrium hydride (YHO) and molybdenum trioxide (MoO$_3$) bilayer films (YHO/MoO$_3$) are produced using reactive magnetron sputtering, and their photochromic properties are investigated in relation to the thickness and density of the MoO$_3$ layer. Compared to single YHO films, the YHO/MoO$_3$ films exhibit faster coloration and larger contrast, with both parameters adjustable by varying the thickness or deposition pressure of the MoO$_3$ layer. Transparent YHO/MoO$_3$ films (~75% at 550 nm) demonstrate a photochromic contrast of up to 60%, significantly higher than the 25-30% contrast observed for single YHO films after 20 hours of UVA-violet light exposure. This enhancement arises from hydrogen intercalation from the (200)-textured polycrystalline YHO film into the X-ray amorphous MoO$_3$, leading to the formation of molybdenum bronze (HxMoO$_3$), as confirmed by X-ray photoelectron and optical spectroscopies. However, the darkened YHO/MoO$_3$ films do not fully recover to their initial transparency after illumination due to the irreversible nature of the coloured MoO$_3$ layer. Most of the hydrogen intercalated into MoO$_3$ originates from the YHO layer during the initial darkening process. Furthermore, the bilayer films are chemically unstable, exhibiting gradual darkening over time even without intentional UV illumination, as confirmed by nuclear reaction analysis.

cond-mat.mtrl-sci↗

arXiv2025

Mobility of single vacancies and adatoms in graphene at room temperature

We investigate the mobility of structural defects, adatoms, and defect-adatom combinations in self-supporting graphene subjected to keV ion irradiation. In the first scenario, homogeneous irradiation using 20 keV Ar$^+$ ions at a dose of $3 \times 10^{14}$ ions/cm$^2$ induces tensile strain of up to 0.8\%. This strain diminishes with increasing defect density at the dose of $5 \times 10^{14}$ ions/cm$^2$, indicating a strain-relaxation mechanism. Contrary to the expected localized behavior, vacancies exhibit long-range interactions, contributing to global strain effects across the lattice. In the second scenario, by employing a nanopore mask, we spatially confined defect generation to periodically aligned circular regions surrounded by non-irradiated material, enabling direct observation of vacancy and adatom dynamics. Selected area electron diffraction (SAED) reveals significant structural damage in areas adjacent to the irradiated regions, suggesting that single vacancies migrate over distances on the order of 100 nm from irradiated to non-irradiated zones even at room temperature. The build-up of lattice strain observed in this study may play a key role in lowering the migration barrier of single vacancies, thereby facilitating their diffusion into pristine lattice regions. Furthermore, the findings highlight the role of pre-existing surface contaminants in preserving lattice integrity through a self-healing mechanism, where adatom-induced lattice reconstruction mitigates defect-induced structural degradation.

cond-mat.mtrl-sci↗

arXiv2025

The Role of 11B4C Interlayers in Enhancing Fe/Si Multilayer Performance for Polarized Neutron Mirrors

This study investigates the effects of incorporating 11B4C interlayers into Fe/Si multilayers, with a focus on interface quality, reflectivity, polarization, and magnetic properties for polarized neutron optics. It is found that the introduction of 1 {\AA} and 2 {\AA} 11B4C interlayers significantly improves the interface sharpness, reducing interface width and preventing excessive Si diffusion into the Fe layers. X-ray reflectivity and polarized neutron reflectivity measurements show enhanced reflectivity and polarization, with a notable increase in polarization for 30 {\AA} period multilayers. The inclusion of interlayers also helps prevent the formation of iron-silicides, improving both the magnetic properties and neutron optical performance. However, the impact of interlayers is less pronounced in thicker-period multilayers (100 {\AA}), primarily due to the ratio between layer and interface widths. These results suggest that 11B4C interlayers offer a promising route for optimizing Fe/Si multilayer performance in polarized neutron mirrors.

cond-mat.mtrl-sci↗

arXiv2025

Magnetic texture control in ion-implanted metamaterials

We study experimentally the impact of the additive fabrication method on the magnetic properties of Fe$^+$-implanted Pd square artificial spin ice lattices. Our findings show that the lattices exhibit a higher ordering temperature than their continuous film counterparts. This behavior is attributed to the additive fabrication process, which induces an inhomogeneous Fe concentration within the lattice building blocks. Moreover, the implantation process creates a magnetic depth profile, enabling temperature-dependent tunability of the magnetic thickness. These additional internal degrees of freedom broaden the design possibilities for magnetic metamaterials, allowing precise fine-tuning of their static and dynamic properties to achieve complex and customizable behaviors.

cond-mat.mes-hall↗

arXiv2024

Control of Ferrimagnetic Compensation and Perpendicular Anisotropy in Tb$_x$Co$_{(100-x)}$ with H$^{+}$ ion implantation

The tuning of magnetic properties through electrochemical loading of hydrogen has recently attracted significant interest as a way to manipulate magnetic devices with electric fields. In this paper we investigate quantitatively the magneto-ionic effect of hydrogen uptake on the magnetic properties of rare-earth transition metal alloy Tb$_x$Co$_{(100-x)}$ in the composition range of $x=10-39$ at.\% using ion implantation. Using this technique we are able to link changes in magnetic behaviour to exact concentrations of hydrogen, isolated from the movement of any other ions that would be a factor in electrochemical studies. The composition of the alloy has been varied alongside the hydrogen dose to characterize the effect of progressive hydrogen loading on the full range of $x$ displaying out-of-plane magnetic anisotropy. We find large changes in two important properties: the compensation composition and the Co-rich in-plane to out-of-plane magnetic anisotropy transition composition, both of which move by 6 at.\% towards higher Tb concentrations after hydrogen implantation. This shift in composition does not increase with a larger dose. From the changes in magnetization we attribute the change in compensation composition to a significant reduction of the moment on the Tb sublattice.

cond-mat.mtrl-sci↗

arXiv2024

Charge state dynamics of keV ions in solids

Fast dynamic processes between electrons in solids and a foreign atom represent a fundamental challenge for describing interactions in many-body systems and are a prerequisite for modelling materials modification. We experimentally determined the charge state distributions of slow He and Ne projectiles after transmission through thin single-crystalline silicon membranes. We found strong differences in velocity scaling and magnitude of the mean charge along different characteristic particle trajectories, providing direct insight on electron promotion and transfer processes inside the solid. Calculations of characteristic trajectories confirm the frequent spatial and ultrafast temporal accessibility of excitation channels commonly considered characteristic for large angle collisions. The commonly observed excess in energy deposition in amorphous targets compared to channelling trajectories and ab-initio calculations can thus be unambiguously linked to energy dissipation in frequent electron promotion as well as increased ionization density along the trajectory, driven by increased mean charge states. A quantitative comparison of energy loss and observed mean charge states further indicates complex deexcitation mechanisms at large interatomic distances masking the true equilibrium charge states along random trajectories.

cond-mat.str-el↗

arXiv2024

Inverse spillover and dimensionality effects on interstitial hydrogen

Nanoscaling interstitial metal hydrides offers opportunities for hydrogenation applications by enhancing kinetics, increasing surface area, and allowing for tunable properties. The introduction of interfaces impacts hydrogen absorption properties and distribution heterogeneously, making it however challenging to examine the multiple concurrent mechanisms, especially at the atomic level. Here we demonstrate the effect of proximity on interstitial hydrogen in ultrathin single crystalline vanadium films, by comparing hydride formation in identically strained Fe/V- and Cr/V-superlattices. Pressure concentration and excess resistivity isotherms show higher absolute solubility of hydrogen, higher critical temperature and concentration in the Cr/V-superlattice. Direct measurements of hydrogen site location and thermal vibrations show identical occupation of octahedral z sites at room temperature with a vibrational amplitude of 0.20-0.25 {\AA} over a wide range of hydrogen concentrations. Our findings are consistent with a more extended region of hydrogen depletion in the vicinity of Fe compared to Cr, which showcases an inverse of the hydrogen spillover effect. Advancing the understanding of interface effects resolves previously puzzling differences in the hydrogen loading of Fe/V- and Cr/V-superlattices and is relevant for advancing both catalysis and storage.

cond-mat.mtrl-sci↗

arXiv2024

The influence of geometry and specific electronic and nuclear energy deposition on ion-stimulated desorption from thin self-supporting membranes

We investigate the dependence of the yield of positive secondary ions created upon impact of primary He, B and Ne ions on geometry and electronic and nuclear energy deposition by the projectiles. We employ pulsed beams in the medium energy regime and a large position-sensitive, time-of-flight detection system to ensure accurate quantification. As a target, we employ a single crystalline Si(100) self-supporting 50 nm thick membrane thus featuring two identical surfaces enabling simultaneous measurements in backscattering and transmission geometry. Electronic sputtering is identified as the governing mechanism for the desorption of hydrogen and molecular species found on the surfaces. Nevertheless, larger energy deposition to the nuclear subsystem by heavier projectiles as well as due to the directionality of the collision cascade appears to act in synergy with the electronic energy deposition leading to an overall increase in secondary ion yields. A higher yield of ions sputtered from the matrix is observed in transmission geometry only for B and Ne ions, consistent with the observed role of nuclear stopping.

physics.chem-ph↗

arXiv2024

Magnetic Order and Long-Range Interactions in Mesoscopic Ising Chains

We investigate the design of magnetic ordering in one-dimensional mesoscopic magnetic Ising chains by modulating long-range interactions. These interactions are affected by geometrical modifications to the chain, which adjust the energy hierarchy and the resulting magnetic ground states. Consequently, the magnetic ordering can be tuned between antiferromagnetic and dimer antiferromagnetic phases. These phases are experimentally observed in chains fabricated using both conventional electron-beam lithography and ion implantation techniques, demonstrating the feasibility of controlling magnetic properties at the mesoscale. The ability of attaining these magnetic structures by thermal annealing, underlines the potential of using such systems instead of simulated annealers in tackling combinatorial optimization tasks.

cond-mat.mes-hall↗

arXiv2024

Sputter Yields of the Lunar Surface: Experimental Validation and Numerical Modelling of Solar Wind Sputtering of Apollo 16 Soils

Sputtering by solar wind ions is a key process driving the ejection of high-energy particles into the exospheres of airless bodies like asteroids, Mercury and the Moon. In view of upcoming missions which will deliver new in-situ data on these exospheres like the Artemis program at the Moon and BepiColombo at Mercury, a deeper understanding of sputtering effects is crucial. In this work, we combine sensitive quartz crystal microbalance measurements and numerical simulations to quantify sputter yields of Apollo soil 68501 under solar wind relevant conditions. We find that none of the commonly used simulation codes can reliably predict laboratory sputter yields without experimental benchmarks. All of the employed packages significantly overestimate the sputter yields of flat samples by at least a factor of 2 for the case of hydrogen. When accounting for surface roughness and regolith-like porosity, sputter yields are decreased even further to 7.3E-3 atoms\ion and 7.6E-2 atoms\ion for H and He at solar wind energies of 1 keV\amu, respectively. The reduced yields of porous regolith structures are largely independent of the ion incidence angle, making them applicable across a wide range of lunar latitudes. This study highlights the need for experimental validation of sputtering models to ensure accurate predictions for space weathering and lunar exosphere composition.

astro-ph.EP↗