Research Project Electronic Excitation–Driven Defect Engineering in Inorganic and Magnetic Materials under Swift Heavy Ion Irradiation 1. Scientific Context and State of the Art The interaction of energetic ions with solids provides a powerful route to drive matter far from equilibrium. Among ion-based approaches, swift heavy ions (SHI) are particularly effective because they deposit large amounts of energy predominantly into the electronic subsystem of a material. This energy deposition generates intense electronic excitation and ionization within a nanometric cylindrical region surrounding the ion trajectory, followed by ultrafast energy transfer to the lattice. Under such extreme conditions, materials can undergo ion-track formation, amorphization, phase transformations, nanoscale defect clustering, and surface nanostructuring. These phenomena have been investigated extensively in inorganic materials, especially oxides and ceramics, where SHI irradiation is known to produce latent tracks above characteristic electronic stopping thresholds. Well-studied model systems such as SiO₂, Al₂O₃, TiO₂, MgO, CaF₂, and SrTiO₃ have been instrumental in establishing how ion species, energy, fluence, and irradiation geometry affect track formation and structural disorder. In parallel, SHI irradiation has emerged as an efficient tool for modifying thin films and multilayers, where irradiation-induced disorder can alter interface sharpness, strain, magnetic anisotropy, coercivity, and charge transport. More recently, two-dimensional and quasi-two-dimensional materials have attracted growing interest, since irradiation-induced defects in graphene, transition-metal dichalcogenides, and layered van der Waals materials can strongly affect electronic, optical, and magnetic behaviour and are central to defect-engineering strategies. The dominant theoretical framework used to describe SHI-induced damage is the inelastic thermal spike model, often formulated as a two-temperature model. In this approach, the ion first deposits energy into the electronic subsystem, which then transfers part of this energy to the lattice through electron–phonon coupling, potentially leading to transient local melting or structural collapse. This description has successfully explained many experimental observations, including track radii and threshold behaviours in a range of oxides and semiconductors. However, it does not capture all material responses. In wide-bandgap insulators, nanostructured systems, and low-dimensional materials, non-thermal contributions such as Coulomb explosion, excitonic effects, or electronic bond softening may become significant, and the balance between thermal and non-thermal mechanisms remains insufficiently resolved. From an experimental perspective, most SHI studies rely on structural diagnostics such as transmission electron microscopy, X-ray diffraction, atomic force microscopy, Raman spectroscopy, and Rutherford backscattering/channelling. These methods have provided essential information on track morphology, threshold behaviour, phase stability, and defect accumulation over a wide range of materials. By contrast, spectroscopic probes directly sensitive to the local electronic structure of irradiation-induced defects remain comparatively underused. This is a major limitation, because SHI damage is initiated by electronic excitation and should therefore be investigated not only through its structural consequences but also through signatures of local electronic reorganisation and bonding changes. In this context, the MADIR group at CIMAP/GANIL offers a particularly favourable environment. The group has recognised expertise in materials under irradiation, ion-track formation, phase transformations, and defect engineering, as well as access to high-level ion-beam facilities and advanced characterization tools. The proposed project is fully aligned with these activities and aims to establish quantitative links between electronic energy deposition, defect formation mechanisms, and functional property modifications in a set of representative material systems. 2. Scientific Objectives The overarching objective of the project is to develop a quantitative and comparative understanding of defect formation driven by electronic excitation under swift heavy ion irradiation. The work will address three complementary classes of materials: inorganic oxides, magnetic and functional thin films, and two-dimensional or layered materials. A first objective is to determine how electronic stopping power controls defect generation and ion-track formation in model inorganic materials. The aim is not only to identify threshold stopping powers for track formation but also to clarify how these thresholds depend on composition, crystallographic structure, pre-existing disorder, and irradiation geometry. Addressing this question will help rationalise why materials with apparently similar macroscopic properties can exhibit markedly different responses under SHI irradiation. A second objective is to establish how SHI-induced defects alter the magnetic and electronic properties of thin films and multilayers. In such systems, irradiation can modify interface sharpness, strain, local disorder, and defect populations, thereby affecting magnetic anisotropy, coercive field, and charge transport. The project will investigate whether controlled SHI irradiation can be used as a deliberate strategy for functional tuning of magnetic and functional materials, moving beyond the traditional view of irradiation as a source of damage. A third objective is to explore the low-dimensional limit of SHI-induced defect formation in graphene, transition-metal dichalcogenides, and related layered systems. In these materials, reduced dimensionality, lower atomic coordination, and different charge relaxation pathways may significantly modify the balance between thermal and non-thermal damage mechanisms. A key question is whether concepts originally developed for track formation in bulk solids remain applicable in two-dimensional systems or whether new descriptors and models are required. Particular attention will be given to the controlled creation of nanopores and defect complexes for potential functional applications. Finally, a transversal objective is to identify spectroscopic fingerprints of irradiation-induced defects and local electronic reorganisation. High-resolution ion-induced X-ray spectroscopy will be used to probe changes in local coordination, valence state, and excitation conditions in defect-rich regions. These measurements will provide a perspective on SHI damage that is complementary to conventional structural characterization and directly linked to the electronic origin of the processes involved. Together, these objectives are designed to bridge the current gap between energy deposition physics, defect structure, and functional material response across different classes of systems. 3. Methodology and Technical Approach The project will rely on an integrated methodology that combines irradiation experiments, structural characterization, spectroscopic diagnostics, and modelling. 3.1 Material systems Three families of materials will be investigated. Oxides such as SiO₂, Al₂O₃, TiO₂, and possibly SrTiO₃ will serve as reference systems for track formation and threshold studies. These materials are well documented in the SHI literature, yet they still raise open questions regarding the influence of crystal structure, thermophysical properties, and prior disorder on track formation and damage morphology.pmc.ncbi.nlm.nih+4 Magnetic and functional thin films will include selected metallic, oxide, or multilayer systems, for example NiFe-based, Co-based, or magnetic oxide films. These systems provide a platform to directly connect defect generation and microstructural changes to magnetic anisotropy, coercivity, magnetotransport, and other functional responses. Two-dimensional and layered materials, including graphene and transition-metal dichalcogenides, will be explored to access the low-dimensional regime. In such systems, SHI irradiation can induce vacancy complexes, nanopores, folding, and local phase transformations, offering both a stringent test of existing damage models and a route to controlled defect engineering at the atomic scale. 3.2 Swift heavy ion irradiation Irradiation experiments will be performed at GANIL under conditions where electronic stopping dominates over nuclear stopping. Ion species and incident energies will be selected to scan the electronic stopping power from sub-threshold to above-threshold regimes for track formation in the chosen materials. The main experimental parameters will be: Ion species and energy, to tune the electronic stopping power and energy deposition profile. Ion fluence, from isolated-track conditions to regimes where track overlap and defect accumulation become significant. Incidence angle, to distinguish bulk from near-surface effects, to investigate channeling, and to study surface nanostructuring. Where relevant, broad-beam irradiations will be complemented by microbeam or patterned irradiations using the PELIICAEN platform. This will enable spatially resolved defect engineering and local property modification while maintaining swift heavy ion energies to preserve the predominance of electronic stopping. 3.3 Structural and microstructural characterization Irradiated samples will be analysed using a suite of complementary techniques spanning multiple length scales. Transmission and scanning transmission electron microscopy will provide direct imaging of latent tracks, amorphous regions, interfaces, and nanoscale defect clusters. Cross-sectional and high-resolution observations will be particularly important for thin films and multilayers, where the interplay between interfaces and tracks is critical. X-ray diffraction, including grazing-incidence geometries for thin films, will be employed to quantify phase changes, lattice strain, crystallinity loss, and irradiation-induced disorder through peak shape analysis and structural refinements. Raman spectroscopy will be used in oxides and 2D materials to probe local disorder, defect density, structural phase changes, and phonon-related signatures of irradiation damage. This technique is especially sensitive to bonding changes and layer disorder in layered and two-dimensional systems. Ion-beam analysis techniques such as Rutherford backscattering/channeling, secondary ion mass spectrometry, and time-of-flight ERDA will be applied to investigate compositional stability, impurity redistribution, depth profiles, and damage accumulation. Where possible, in situ methods will be used to monitor damage evolution during irradiation. Taken together, these methods will provide quantitative metrics such as track radius, amorphous fraction, defect density, strain state, and compositional redistribution as functions of irradiation parameters. 3.4 Spectroscopic diagnostics A distinctive element of the project is the use of high-resolution ion-induced X-ray spectroscopy to probe the local electronic structure of irradiated materials. By analysing line positions, line broadening, satellite features, and intensity ratios in core-level and valence-to-core X-ray emission, it will be possible to characterise the electronic environment of atoms in defect-rich regions. These measurements are expected to reveal changes in local bonding, coordination, oxidation state, and multi-electron excitation processes that accompany SHI-induced damage. In magnetic materials, where feasible, these spectroscopic observations may be combined with magnetic-sensitive probes to establish correlations between local defect configurations and magnetic response. This approach will provide a direct experimental window on the electronic consequences of SHI irradiation, which are often inferred only indirectly in most existing studies. 4. Modelling and Quantitative Analysis A central ambition of the project is to move beyond qualitative descriptions and establish a quantitative framework for interpreting SHI-induced defect formation. Stopping-power calculations will be performed using SRIM or equivalent tools to determine the depth dependence of electronic and nuclear stopping and to identify irradiation conditions relevant for threshold and comparative studies. These calculations will guide the choice of ion–material combinations and enable consistent comparisons across different material classes. The experimental programme will be coupled, where possible, with inelastic thermal spike and two-temperature modelling. Such simulations will be used to estimate the temporal evolution of electronic and lattice temperatures, the spatial extent of the heated zone, possible molten radii, and cooling timescales. Material-specific parameters such as heat capacity, thermal conductivity, and electron–phonon coupling strengths will be included whenever reliable values are available, and recent developments in the assessment and comparison of thermal spike models will be taken into account. Model–experiment comparison will be carried out on several levels. Predicted threshold behaviours and track sizes will be confronted with TEM and XRD observations in oxides and thin films. Spectroscopic signatures of defect-modified electronic structure will be examined in light of model-derived local energy densities and excitation conditions. When significant discrepancies arise, they will be analysed as possible indicators of non-thermal contributions, particularly in highly insulating or low-dimensional systems where Coulomb explosion or other non-thermal mechanisms may play a larger role. This modelling effort is essential to identify not only which defects form under given conditions but also why they form, thereby providing a mechanistic understanding that links energy deposition, defect configurations, and macroscopic material response. 5. Expected Results and Scientific Impact The project is expected to generate new insight into the mechanisms governing electronic-excitation-driven defect formation in a broad range of materials. For oxides, it should provide improved determination of track formation thresholds and a clearer understanding of how structural and thermophysical parameters influence damage morphology and stability. For magnetic thin films and functional multilayers, it should establish quantitative links between irradiation-induced disorder, magnetic anisotropy, coercive field, and transport properties, thereby assessing the potential of SHI irradiation as a tool for functional tuning rather than solely as a source of degradation. For two-dimensional and layered materials, it should clarify whether defect creation follows the same principles as in bulk systems or whether reduced dimensionality necessitates revised mechanistic descriptions and new design rules for defect engineering. The integration of high-resolution spectroscopy is expected to provide substantial added value by identifying electronic fingerprints of irradiation-induced defects and by constraining the balance between thermal and non-thermal mechanisms. More broadly, the project should contribute to a comparative, mechanism-based picture of SHI-induced defect engineering across dimensionalities, linking three-dimensional oxides, thin films, and two-dimensional materials within a unified framework. Beyond its fundamental interest, the work may have practical relevance for the design of radiation-tolerant materials for nuclear or space applications, for the nanostructuring and property control of magnetic and functional materials, and for the controlled introduction of defects in two-dimensional systems for electronics, sensing, and membrane technologies. 6. Integration within MADIR and Contribution to GANIL The project is fully consistent with the scientific priorities of the MADIR group, particularly in the areas of ion-track formation, irradiation effects in inorganic materials, and defect engineering. It will reinforce existing activities by introducing a stronger focus on electronic-structure-sensitive diagnostics, thereby complementing the group’s established strengths in structural and microstructural characterization. The project will also contribute to the broader mission of GANIL by exploiting the specific capabilities of its irradiation platforms and by strengthening links between beam physics, materials science, and spectroscopy. Beyond the core research programme, I intend to participate actively in laboratory life through involvement in beamline operation, user support, experimental preparation, and data analysis. Previous experience with accelerator environments, detector systems, and vacuum-based experimental setups provides a solid basis for this integration. In this way, the project combines an ambitious scientific agenda with a strong collective and collaborative dimension within the GANIL community. 7. Provisional Three-Year Work Plan During the first year, the priority will be to establish the experimental framework of the project: selection of initial material systems, definition of irradiation conditions, setup of structural and spectroscopic characterization protocols, and first irradiation campaigns on model oxides and selected thin films. This phase will provide the methodological reference for subsequent comparative studies. During the second year, the work will focus on systematic irradiation campaigns designed to determine threshold behaviours and to quantify correlations between stopping power, defect morphology, and structural disorder. Magnetic and functional thin films will be investigated more extensively in this period, with emphasis on the relationship between defect generation, microstructural evolution, and magnetic response. During the third year, the project will be extended to two-dimensional and layered materials, with particular attention to controlled defect creation and to the integrated use of structural and spectroscopic diagnostics. This final phase will also be devoted to the synthesis of results across material classes, the refinement of modelling approaches, and the preparation of joint publications, conference contributions, and collaborative proposals within the GANIL network.