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GENL is a flexible program that can be used to simulate and/or fit x-ray diffraction data from epitaxial thin films exhibiting Laue oscillations. It utilizes differential evolution within a genetic algorithm for the fitting of data and is based on the kinematic theory of diffraction. Effects of polarization, absorption, the Lorentz factor, as well as instrumental resolution and vibrations are taken into account. Useful parameters that can be extracted after fitting include: atomic interplanar spacings, number of coherently scattering atomic planes, strain profiles along the film thickness, and crystal roughness. The program has been developed in MATLAB and employs a graphical user interface. The deployment strategy is twofold whereby the software can either be obtained in source code form and executed within the MATLAB environment, or as a pre-compiled binary for those who prefer not to run it within MATLAB. Finally, GENL can easily be extended to simulate multilayered film systems, superlattices, and films with atomic steps. The program is released under the GNU General Public Licence. 

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.

We demonstrate that thin metallic glasses of VxZr100-x, deposited by direct current magnetron sputtering, closely approximate the structural characteristics of theoretically predicted maximally amorphous materials. Experimentally, x-ray reflectometry reveals atomically flat films with well-defined thickness and low surface roughness, while Rutherford backscattering spectrometry confirms V/Zr stochiometry within 1 at.% and a compact, systematically varying density with composition. Transmission electron microscopy shows no evidence of columnar growth, consistent with fully amorphous and homogeneous films. Using ab initio stochastic quenching to generate representative maximally amorphous configurations, we find excellent agreement with experiment in terms of mass density and pair distribution functions. The calculated structures are mechanically stable, elastically isotropic, and exhibit high Poisson ratios and Pugh ratios indicating a characteristically ductile response. The combination of compactness and ductility suggests potential for applications in mechanically resilient coatings and for hydrogen storage, where deformation tolerance and structural integrity are critical. The agreement between simulation and experiment across structural and compositional descriptors supports the conclusion that sputtered V-Zr metallic glasses can be viewed as experimental realizations of statistically maximally amorphous states within the framework of the random valley approximation. We propose such structures can serve as well defined benchmarks for the maximal degree of amorphousness.

The overillumination correction generally applied in x-ray and neutron reflectometry has been studied in detail with a simple ray tracing program. We find that the validity of the traditional analytical expression for the correction of overillumination depends on the detector field of view. If left untreated, the effect can cause inaccuracies in fitted parameters such as thickness, roughness and density. We give a general expression for the shift of the spill-over angle with the width of the detector slit and the distances involved. The virtual reflectometer program can simulate common scans used for alignment and measurement and can thus serve as an educational tool and to verify proper instrument calibration.

We demonstrate the feasibility of using optical transmission to determine concentration-dependent hydrogen diffusion coefficients and activation energies of thin metallic glass films over a wide range of temperatures and concentrations. The hydrogen concentration's temporal and spatial profiles are simultaneously extracted without requiring a metal-insulator transition or hydride formation. Different contributions to chemical hydrogen diffusion are quantified and compared. The concentration dependence of the activation energy is in stark contrast to the activation energy found in epitaxial vanadium films of similar thickness. The chemical diffusion is found to increase with hydrogen concentration in the glass, whereas it decreases in the crystalline case driven by differences in the activation energy at concentrations below 0.3 H/M and the thermodynamic factor at concentrations above that. This technique provides detailed insight into the concentration dependence of hydrogen diffusion and constrains theories treating the correlated motion of hydrogen and short-range hydrogen-hydrogen interaction. The method can be applied to other materials that show an optical response to hydrogen uptake.

We investigate the influence of hydrogen on the electronic structure of a binary transition metallic glass of V_80⁢Zr₂₀. We examine the hybridization between the hydrogen and metal atoms with the aid of hard x-ray photoelectron spectroscopy. Combined with ab initio density functional theory, we are able to show and predict the formation of 𝑠−𝑑 hybridized energy states. With optical transmission and resistivity measurements, we investigate the emergent electronic properties formed out of those altered energy states, and together with the theoretical calculations of the frequency-dependent conductivity tensor, we qualitatively support the observed strong wavelength-dependency of the hydrogen-induced changes on the optical absorption and a positive parabolic change in resistivity with hydrogen concentration.

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, the effect of proximity on interstitial hydrogen in ultrathin single-crystalline vanadium films is demonstrated 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 a Cr/V-superlattice. Direct measurements of hydrogen site location and thermal vibrations show identical site occupation of octahedral z at room temperature with a vibrational amplitude of 0.20-0.25 & Aring; over a wide range of hydrogen concentrations. These 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.

MAX phases are a family of atomically laminated materials with various potential applications. Mn₂GaC is a prototype magnetic MAX phase, where complex magnetic behaviour arises due to competing interactions. We have resolved the room temperature magnetic structure of Mn₂GaC by neutron diffraction from single-crystal thin films and we propose a magnetic model for the low temperature phase. It orders in a helical structure, with a rotation angle that changes gradually between 120 degrees and 90 degrees depending on temperature.

This study focuses on enhancing the accuracy of hydrogen content verification in hydrogen-rich ultrathin materials relevant for sustainable energy applications. Ion beams are used for distinctive real-space detection leveraging elastic and inelastic interactions with hydrogen atoms. However, the lack of experimental reference data on electronic interactions poses a challenge to the accuracy of analytical techniques. We investigate the effect of absorbed hydrogen on the electronic energy deposition of ¹⁵N-ions in amorphous transition metal compounds, specifically V and Zr, covering concentrations >1H/M. Employing resonant nuclear reactions and Rutherford backscattering, the energy loss is found to increase considerably with hydrogen content, in line with Bragg's additivity. The electronic energy loss cross section for ¹⁵N-ions at 6.5 MeV measured (64.55±3.38) eV cm²/10¹⁵ atoms. Results are compared to semi-empirical and theoretical models. The findings improve hydrogen profiling accuracy using ¹⁵N-nuclear reaction analysis and enable unprecedented methods for hydrogen quantification by other, commonly available ion beams.

We report on the discovery of a boundary-induced body-centered tetragonal iron phase in thin films deposited on MgAl2⁢O4 (001) substrates. We present evidence for this phase using detailed x-ray analysis and ab initio density functional theory calculations. A lower magnetic moment and a rotation of the easy magnetization direction are observed, as compared with body-centered cubic iron. Our findings expand the range of known crystal and magnetic phases of iron, providing valuable insights for the development of heterostructure devices using ultrathin iron layers.