arXiv subjects

Emilia Olsson

Publications and source records attributed to Emilia Olsson.

10 recordsLinked to original sources

arXiv2026

Statistically Robust Characterization of Polaron and Bipolaron Intrinsic Traps in Amorphous Silica Reveals the Role of Network Flexibility in Electron Localisation

Intrinsic electron localization in amorphous silica (a-SiO2) contributes to charge trapping and defect generation in silica-based electronic materials - a phenomenon that degrades logic-device performance but can be exploited for memory applications. However, the structural distribution of one- and two-electron traps remains incompletely characterized, largely because the disordered covalent network of a-SiO2 spans a vast configurational space. To address this, we perform statistical sampling to select a representative 200-model subset of defect-free bulk a-SiO2 structures from a structurally converged parent set of 2512 models, generated via classical melt-quench molecular dynamics simulations. We then characterize the intrinsic one- and two-electron traps in this subset using HSE06 density functional theory calculations. Analysis of neutral precursor sites shows that trapping propensity is not determined by a universal O-Si-O angle or Si-O bond length; it is controlled by the accessibility of the relaxed trap geometry, requiring both local strain and medium-range network flexibility. Single electrons predominantly form edge-centred polarons on distorted SiO4 tetrahedra, with occupied states 3.1-4.3 eV below the conduction band minimum. Injection of a second electron drives stronger lattice relaxation, most commonly Si-O bond elongation leading to rupture, thereby forming threefold-coordinated-Si (Si3) bipolarons and, in some cases, Si-Si-bonded bipolaron configurations. The calculated bipolaron energy ranges are consistent with optical absorption features at 3.7, 4.7, and 6.4 eV associated with intrinsic electron localization.

cond-mat.mtrl-sci↗

arXiv2026

The role of density in shaping electron trapping in amorphous silicon nitride

The electronic properties of amorphous silicon nitride vary with processing, which often changes stoichiometry and density together. Separating their contributions is essential to connect film structure with electron trapping. Across 499 stoichiometric configurations spanning 2.86-3.19g cm$^{-3}$, porosity controls the trapping mixture. Lower density increases accessible void fraction from 8.4 to 12.6%, expands internal surface and more than triples the supply of free three-coordinate Si precursors. Capture at pre-existing Si dangling bonds (K centres) rises from 9 to 29%, while induced-K and polaronic trapping decline. A neutral precursor fingerprint predicts the trapping mixture in held-out configurations and reproduces its density dependence. Local compensation controls K-centre activation, electronic competition selects capture, and bond strain predicts polaronic relaxation or induced-K formation. Routes involve distinct network volumes but retain their characteristic depths and relaxation energies across the density range. At fixed stoichiometry, density controls the trapping mixture through porosity and precursor availability.

cond-mat.mtrl-sci↗

arXiv2026

State aligned graph wavelet fingerprints of electron trapping in amorphous Si$_3$N$_4$

Classifying charge traps in amorphous materials requires the electronic state and the network response to be resolved together. We develop state-aligned graph-wavelet fingerprints and apply them to electron trapping in a-Si$_3$N$_4$, where intrinsic-polaronic trapping, coordination-driven trapping, and charge-driven conversion coexist within one ensemble. Across 415 pairs of relaxed neutral and negatively charged cells, alignment of the trap state before and after localisation connects electronic identity to multiscale structural fingerprints. Charge-driven conversion produces substantial reorganisation across graph scales and increases the fingerprint amplitude. The fingerprint change identifies the transformation each site undergoes, while the occupation-induced level shift tracks localisation gain and graph deformation tracks stabilisation. Charge-induced defect formation dominates the deepest spectral-trap decile: 69\% form at sites whose Si--N bond breaks on capture, although this route accounts for 44.2\% of the classified traps. The fingerprints unify electronic identity, multiscale network reorganisation and energetic stabilisation in a quantitative framework for resolving charge trapping in amorphous materials.

cond-mat.mtrl-sci↗

arXiv2026

Vitriflow: calibrated amorphous structure ensembles from melt-quench simulation

Many structure-property relations in amorphous materials are encoded not only in the mean structure, but in the prevalence, correlations and spatial organisation of minority environments across length scales. Yet atomistic models are commonly validated against bulk averages and a nominal number of structures, without establishing whether the finite population resolves the motifs invoked to explain material behaviour. We present an auditable framework, implemented in the Vitriflow software package, that connects calibrated melt-quench generation to explicit populations and quantity-specific uncertainty. This approach is demonstrated on three distinct benchmark systems. In a-SiO$_2$, strain is followed from intra-tetrahedral deformation through compressed Si--O--Si bridges to primitive 3-ring topology, showing that the lower angular tail is an organised medium-range population rather than undifferentiated variation about the network mean. In matched a-Si$_3$N$_4$ refinements, DFT redistributes density and first-neighbour length scale, sharpens the force-field first shell and repairs marginal contacts, while the two DFT descendants retain essentially the same first-neighbour topology. In a-Sm$_2$O$_3$, the amount and connectivity of partially ordered domains are quantified as they emerge from the disordered parent population, while the mixed coordination characteristic of the amorphous oxide remains robust. Mean structure, distribution tails, inherited topology and connected order are therefore distinct materials variables with distinct uncertainties. There is no universal ensemble size: the Vitriflow package records what was generated, which population was analysed and what that finite population establishes, providing a reproducible route from amorphous structure datasets to quantitatively supported structure-property hypotheses.

cond-mat.mtrl-sci↗

arXiv2026

Constraint residuals, graph posteriors, and determinant-corrected full-space targets in Bayesian inverse problems

Bayesian inverse problems constrained by state equations are often sampled in a full parameter-state space by penalising the residual, rather than in a reduced space where the state is eliminated. We show that these formulations are not automatically equivalent as posterior measures. For finite-dimensional discretisations of equality-constrained inverse problems, assume the state equation $c(θ,u)=0$ has a unique solution $u=G(θ)$ and nonsingular state Jacobian $\D_u c$. The reduced posterior, its graph lift, and the zero-noise residual posterior are then distinct. A local change of variables shows that an uncorrected Gaussian residual penalty converges, after marginalisation over $u$, to the reduced density multiplied by $\abs{\det \D_u c(θ,G(θ))}^{-1}$. Thus algebraically equivalent residuals can define the same feasible set but different limiting posteriors. We derive determinant corrections for unweighted, weighted, and rescaled residual penalties that have the graph-lifted reduced posterior as their hard-constraint limit. The result separates feasibility from posterior calibration: driving the residual to zero is not sufficient for exact sampling of the graph-lifted reduced posterior unless the sampling or correction step targets the corresponding corrected density.

math.ST↗

arXiv2026

Topology-Directed Silicide Formation: An Explanation for the Growth of C49-TiSi$_2$ on the Si(100) Surface

Designing metal-semiconductor junctions is essential for optimizing the performance of modern nanoelectronic devices. A widely used material is TiSi$_2$, which combines low electronic resistivity with good endurance. However, its multitude of polymorphs continues to pose a challenge for device fabrication. In particular, the naturally occurring formation of the metastable C49-TiSi$_2$ modification remains poorly understood and is problematic due to its unfavorable electronic properties. Based on extensive DFT calculations, we present a comprehensive model of Ti adsorption on Si(100) that highlights the pivotal role of surface topology for the initial stages of the interfacial TiSi$_2$ formation process. We show that the interplay between Si surface dimers, the symmetry of the Si(100) surface, and the incorporation of Ti adsorbates below the surface drives an adsorption pattern that yields a nucleation template for the C49-TiSi$_2$ phase. Our atomistic model rationalizes experimental observations like the Stranski-Krastanov growth mode, the preferential formation of C49-TiSi$_2$ despite it being less favorable than the competing C54 phase, and why disruption of the surface structure restores thermodynamically driven growth of the latter. Ultimately, this novel perspective on the unique growth of TiSi$_2$ will help to pave the way for next-generation electronic devices.

cond-mat.mtrl-sci↗

arXiv2025

Adhesion Control through Electric Field-Induced Water Adsorption at Oxidized Silicon Interfaces

Adhesion plays a pivotal role in computer chip manufacturing, directly affecting the precision and durability of positioning components such as wafer stages. Electrical biasing is widely employed to eliminate floating potential and to enable electrostatic clamping. However, upon electrical grounding adhesion can persist and there is limited knowledge about the nature of this adhesion hysteresis. Here, we investigate potential causes underlying electric field-induced adhesion hysteresis at the interface between an n-type AFM tip and a p-type silicon sample using atomic force microscopy. Our findings reveal that neither charge trapping nor siloxane bond formation significantly impacts the measured adhesion. Surprisingly, we show that adhesion can be tuned through electric field-induced water adsorption under low relative humidity (RH < 10%). Our results provide new insights into adhesion hysteresis and opportunities for adhesion control.

cond-mat.soft↗

arXiv2025

Elucidating the impact of point defects on the structural, electronic, and mechanical behaviour of chromium nitride

Defect engineering offers an important route to property tuning of nanostructured coatings for advanced applications. Transition metal nitrides, such as CrN, are widely used for their mechanical resilience, but their nitrogen-rich analogue CrN2 remains poorly understood, especially at the atomic scale. This study employs density functional theory to investigate the energetics as well as how intrinsic defects (vacancies, interstitials, and anti-sites) and extrinsic impurities (hydrogen and oxygen) influence the structural, electronic, magnetic, and mechanical response of CrN2, in comparison to the more commonly studied CrN. With directional N-N bonding and semiconducting character, CrN2 shows high sensitivity to defect incorporation, including local spin polarisation, gap states, and mechanical softening. In contrast, CrN's metallic character enables effective screening of similar defects, preserving its structural, magnetic, electronic and mechanical integrity. However, hydrogen induces anisotropic distortions and mechanical degradation in CrN, while oxygen enhances hardness. These findings reveal how defect chemistry and bonding anisotropy govern mechanical performance, with implications for nanoscale control in coatings design.

cond-mat.mtrl-sci↗

arXiv2025

Extreme Ultraviolet High-Harmonic Interferometry of Excitation-Induced Bandgap Dynamics in Solids

Interferometry is a fundamental technique in physics, enabling precise measurements through the interference of waves. High-harmonic generation (HHG) in solids has emerged as a powerful method for probing ultrafast electronic dynamics within crystalline structures. In this study, we employed extreme ultraviolet (XUV) high-harmonic interferometry with phase-locked XUV pulse pairs to investigate excitation-induced bandgap dynamics in solids. Our experiments on amorphous SiO2 and crystalline MgO, complemented by analytical modeling and semiconductor Bloch equation simulations, reveal a correlation between transient bandgap modifications and variations in the phase of harmonic emission. These findings suggest a potential pathway for sub-cycle, all-optical control of band structure modifications, advancing prospects for petahertz-scale electronic applications and attosecond diagnostics of carrier dynamics.

physics.optics↗

arXiv2023

Enhanced dendrite nucleation and Li-clustering at vacancies on graphene

An ever present challenge for Li-ion batteries is the formation of metallic dendrites on cycling that dramatically reduces cycle life and leads to the untimely failure of the cell. In this work we investigate the modes of Li-cluster formation on pristine and defective graphene. Firstly, we demonstrate that on a defect free surface the cluster formation is impeded by the thermodynamic instability of \ce{Li_2} and \ce{Li_3} clusters. In contrast, the presence of a vacancy dramatically favours clustering. This provides insights into the two modes of Li-growth observed: for the pristine basal plane if the Li-Li repulsion of the small clusters can be overcome then plating type behaviour would be predicted (rate / voltage dependent and at any point on the surface); whilst dendritic growth would be predicted to nucleate from vacancy sites, either pre-existing in the material or formed as a result of processing.

cond-mat.mtrl-sci↗