Johannes Bakkelund

• Gong, Weijia; Bakkelund, Johannes; Burba, Svenas; Skomedal, Gunstein & Appiah, Williams Agyei (2026). Multi-scale visualization of the impact of particle morphology on the fast-charging capabilities of graphite-based electrodes. Journal of Energy Storage. ISSN 2352-152X. 178(B). doi: 10.1016/j.est.2026.123733. Fulltekst i vitenarkiv Vis sammendrag

  The major challenge in fast-charging batteries is designing electrodes whose microstructure and composition mitigate slow lithium diffusion in active particles and limited electrolyte transport under high charging current densities, which otherwise cause concentration polarization and lithium plating. To address this issue, an elec­trode design methodology with greater control over particle morphology is proposed for designing graphite anodes. The workflow couples computer-aided design (CAD)-based particle design, where particles of different morphologies are generated from FIB-SEM images of artificial graphite, with 3D-resolved mesoscale electrode reconstruction to build detailed electrode microstructures. A 4D (space + time) electrochemical simulation is then applied to the reconstructed electrodes to quantify how particle morphology, packing, and pore connectivity control lithium transport, spatial lithiation, and rate capability. Using 30 × 30 × 66 μm mesoscale electrode volumes and four morphology-controlled particle populations (e.g., thin-flake particles ≈ 7.3 × 14.9 × 3.9 μm), representative simulations show an average state-of-lithiation (SOL) of ≈ 80% at 1C, with a clear through-thickness gradient and substantially increased ionic heterogeneity and capacity loss at 3C and 5C. This meth­odology provides actionable metrics such as SOL maps, ionic flux distribution, and rate performance, to prioritize particle morphologies and electrode microstructures that enhance cell performance during fast charging, and to guide experimental validation and scale-up for manufacturing anodes for fast charging applications.

• Vita, A. De; Bakkelund, Johannes; Światek, H.; Winiarski, M. J.; Malick, S. & Nielsen, C. V.B. [Vis alle 16 forfattere av denne artikkelen] (2026). Uncovering surface states of the Dirac semimetal BaMg<inf>2</inf>Bi<inf>2</inf>. Physical review B (PRB). ISSN 2469-9950. 113(3). doi: 10.1103/PS93-RFK3. Fulltekst i vitenarkiv Vis sammendrag

  BaMg2⁢Bi2 is a Dirac semimetal characterized by a simple Dirac cone crossing the Fermi level at the center of the Brillouin zone, protected by 𝐶3 rotational symmetry. Together with its Sr-based analog SrMg2⁢Bi2, it has been proposed as a promising candidate for a chemically driven topological switch: while SrMg2⁢Bi2 is an insulator, BaMg2⁢Bi2 exhibits nontrivial topological features. A detailed understanding of its electronic structure is essential to elucidate its electronic and transport properties. Previous photoemission studies confirmed the Dirac nature of BaMg2⁢Bi2, but were limited to high photon energies, which hindered direct comparison with density functional theory calculations (DFT), due to reduced resolution and higher-frequency matrix-element modulation in that regime. In this work, we combine high-resolution angle-resolved photoemission spectroscopy and DFT calculations to get full insight into the valence band states, providing a comprehensive picture of the low-energy electronic structure. Our measurements reveal the presence of previously unobserved surface states. We found that they are topologically trivial, but they unlock a more comprehensive understanding of the material's behavior, reconciling previous discrepancies between experiment and theory.

• Åsland, Anna Cecilie; Bakkelund, Johannes; Cooil, Simon Phillip; Røst, Håkon; Hu, Jinbang & Vescovo, E. [Vis alle 9 forfattere av denne artikkelen] (2025). Overcoming the challenges of accessing topological hallmarks in Sb(112). Electronic Structure. 7(3). doi: 10.1088/2516-1075/adf384. Fulltekst i vitenarkiv Vis sammendrag

  Sb is topologically non-trivial and semi-metallic, but differs from many topological semi-metals because of its continuous band gap. By measuring its (112) surface using angle- and spin-resolved photoemission spectroscopy, Sb(112) was shown to have 1D spin-polarised surface states resembling those on vicinal Bi surfaces and many topological insulators and topological semi-metals. The shape and spin-polarisation of the measured features and the calculated bands agreed. However, the measured features had a slightly steeper energy dispersion and different Fermi-momenta than the calculated bands. Both theoretical and experimental methods were necessary when determining the topology of Sb(112). The presence of projected bulk states near the Fermi-level and varying surface localisation of the electronic states meant it was challenging to deduce the topology of Sb(112) from the number of bands crossing the Fermi-level or a continuous contour in the bulk band gap. Ultimately, the calculations and measurements suggest that there are topological surface states on the Sb(112) surface.

• Burba, Svenas; Bakkelund, Johannes; Kumar, Rikesh; Singh, Ankit; Parmanada, Mukul & Appiah, Williams Agyei (2025). Data-Driven Entropy Coefficient Estimation for Large Format Lithium-Ion Batteries. Batteries & Supercaps. 0. doi: 10.1002/batt.202500533. Fulltekst i vitenarkiv Vis sammendrag

  Large format lithium-ion cell operations are nonisothermal and require an additional entropy term to the open-circuit potential expression in physics-based electrochemical models to accurately predict and optimize cell designs for a given application. However, the experimental estimation of entropy coefficient via potentiometric and colorimetric methods is time-consuming and expensive. A fast method based on parameter optimization of empirical expressions and data-driven approaches is presented to accelerate the estimation of the entropy coefficient term. This involves the use of (dis) charge and hybrid pulse power characterization (HPPC) data from a 100 Ah prismatic cell comprising lithium iron phosphate and graphite electrodes to determine the entropy coefficient via least-squares method. The estimated entropy coefficient is implemented in the Doyle–Fuller–Newman model to predict the voltage profiles at different temperatures and validated against experiments. Complex empirical functions and data-driven estimated entropy from the HPPC data give the best model predictions, especially at low temperatures.

• Strand, Frode Sneve; Cooil, Simon Phillip; Campbell, Quinn T.; Flounders, John J.; Røst, Håkon & Åsland, Anna Cecilie [Vis alle 16 forfattere av denne artikkelen] (2025). Direct Observation of 2DEG States in Shallow Si:Sb δ-Layers. Journal of Physical Chemistry C. ISSN 1932-7447. 129(2), s. 1339–1347. doi: 10.1021/acs.jpcc.4c07331. Fulltekst i vitenarkiv Vis sammendrag

  We investigate the electronic structure of high-density layers of Sb dopants in a silicon host, so-called Si:Sb δ-layers. We show that, in spite of the known challenges in producing highly confined Sb δ-layers, sufficient confinement is created such that the lowest conduction band states (Γ states, studied in depth in other silicon δ-layers), become occupied and can be observed using angle-resolved photoemission spectroscopy. The electronic structure of the Si:Sb δ-layers closely resembles that of Si:P systems, where the observed conduction band is near-parabolic and slightly anisotropic in the k∥ plane. The observed Γ state extends ∼1 nm in the out-of-plane direction, which is slightly wider than the 1/3 monolayer thick dopant distribution. This is caused by a small segregation of the dopant layer, which is nevertheless minimal when comparing with earlier published attempts. Our results serve to demonstrate that Sb is still a feasible dopant alternative for use in the semiconductor δ-layer platform, providing similar electronic functionality to Si:P systems. Additionally, it has the advantages of being less expensive, more controllable, safer to handle, and more compatible with industrial patterning techniques. Si:Sb is therefore a viable platform for emerging quantum device applications.

• Åsland, Anna Cecilie; Cooil, Simon Phillip; Mamedov, Damir; Røst, Håkon; Bakkelund, Johannes & Li, Z. [Vis alle 8 forfattere av denne artikkelen] (2024). Initial stages of water absorption on CeO2 surfaces at very low temperatures for understanding anti-icing coatings. Materials Research Express. 11(11). doi: 10.1088/2053-1591/ad913e. Fulltekst i vitenarkiv Vis sammendrag

  Anti-icing coatings are intended to prevent ice formation on surfaces, minimising the risk of surface-related damage and also reducing ice-related hazards in society. We demonstrate the usefulness of x-ray photoelectron spectroscopy (XPS) as a tool for investigating the anti-icing properties of surfaces simultaneously with their chemical composition by looking at the initial stages of water absorption on the surface of CeO2 coatings. CeO2 coatings are robust, hydrophobic, and transmit light, thus they are suitable for a range of applications. In this work, CeO2 coatings were grown by sputter deposition and transferred to an ultra-high vacuum chamber where they were cooled to ≈ 100 K and exposed to a H2O atmosphere at 1 × 10−8 mbar. XPS measurements were performed before and after the exposure to H2O, in-situ and at cryogenic temperatures. The chemical composition of CeO2 did not change significantly during the experiment. Additionally, XPS revealed that little to no ice formed on the surface of CeO2 after the H2O exposure at ≈ 100 K. In contrast, ice was observed all over the sample holder on which the CeO2 was mounted. These findings suggest CeO2 is a promising candidate for future anti-icing coatings and that XPS is a useful technique to investigate the anti-icing properties of surfaces.

• Røst, Håkon; Mazzola, Federico; Bakkelund, Johannes; Åsland, Anna Cecilie; Hu, Jinbang & Cooil, Simon Phillip [Vis alle 8 forfattere av denne artikkelen] (2024). Disentangling electron-boson interactions on the surface of a familiar ferromagnet. Physical review B (PRB). ISSN 2469-9950. 109, s. 1–9. doi: 10.1103/PhysRevB.109.035137. Fulltekst i vitenarkiv Vis sammendrag

  We report energy renormalizations from electron-phonon and electron-magnon interactions in spin minority surface resonances on Ni(111). The different interactions are identified, disentangled, and quantified from the characteristic signatures they provide to the complex self-energy and the largely different binding energies at which they occur. The observed electron-magnon interactions exhibit a strong dependence on momentum and the electron energy band position in the bulk Brillouin zone. In contrast, electron-phonon interactions observed from the same bands appear to be relatively momentum and symmetry independent. Additionally, a moderately strong (λ>0.5) electron-phonon interaction is distinguished from a near-parabolic spin majority band not crossing the Fermi level.

• Mamedov, Damir; Åsland, Anna Cecilie; Cooil, Simon Phillip; Røst, Håkon; Bakkelund, Johannes & Allaniyazov, Atabek [Vis alle 8 forfattere av denne artikkelen] (2023). Enhanced hydrophobicity of CeO<inf>2</inf> thin films: Role of the morphology, adsorbed species and crystallography. Materials Today Communications. 35. doi: 10.1016/j.mtcomm.2023.106323. Fulltekst i vitenarkiv Vis sammendrag

  In order to guarantee the long-term efficiency of hydrophobic materials in real-world situations, it is necessary that their surfaces are highly resistant to scratching, fouling and misting. Furthermore, for the specific applications, e.g. in photovoltaic systems, the water-repelling material must necessarily have a large bandage, such that it does not absorb light in the spectral range which is utilized by the underlying photovoltaic cell. One especially promising candidate for this and many other technologically important applications is cerium dioxide (CeO2, ceria). In the current study, we propose the production framework for the manufacturing of CeO2-based thin films with tunable wetting behavior. For obtaining the coatings with various hydrophobicity, ceria is deposited on the substrates with different roughness via reactive magnetron sputtering, with consequent treatment of the films in vapor of different hydrocarbons. By systematic study using the XRD, SEM, XPS and water contact angle (WCA) instruments, we found that surface texturization, different plains at the surface of the films as well as the adsorbed organic molecules all strongly influence on wettability of the CeO2 thin films. In addition, comparison of WCAs for ceria and silicon oxide SiOx is performed. The higher wettability for the former points out the essential role of the surface material despite presence of hydrocarbons. It is demonstrated that by purposeful controlling for all the parameters – surface texturization, the top material and its crystallography, and adsorbed organic molecules – one can reach superhydrophobic state of the surface.

• Åsland, Anna Cecilie; Bakkelund, Johannes; Thingstad, Even; Røst, Håkon; Cooil, Simon Phillip & Hu, Jinbang [Vis alle 11 forfattere av denne artikkelen] (2023). One-dimensional spin-polarized surface states: A comparison of Bi(112) with other vicinal bismuth surfaces. Physical review B (PRB). ISSN 2469-9950. 108(20). doi: 10.1103/PhysRevB.108.205403. Fulltekst i vitenarkiv Vis sammendrag

  Vicinal surfaces of bismuth are unique test beds for investigating one-dimensional (1D) spin-polarized surface states that may one day be used in spintronic devices. In this paper, such states have been observed for the (112) surface when measured using angle- and spin-resolved photoemission spectroscopy, and also when calculated using a tight-binding model and with density functional theory. The surface states appear as elongated Dirac-cones which are 1D and almost dispersionless in the ky direction, but disperse with energy in the orthogonal kx direction to form two ×-like features centered at the ky line through Γ. Unlike many materials considered for spintronic applications, their 1D nature suggests that conductivity and spin-transport properties are highly dependent on direction. The spin polarization of the surface states is mainly in plane and parallel to the 1D states, but there are signs of a tilted out-of-plane spin-vector component for one of the features. The Bi(112) surface states resemble those found for other vicinal surfaces of bismuth, strongly indicating that their existence and general properties are robust properties of vicinal bismuth surfaces. Furthermore, differences in the details of the states, particularly related to their spin polarization, suggest that the electronic band structure may be engineered simply by precise cutting and polishing of the crystal.

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• Åsland, Anna Cecilie; Cooil, Simon Phillip; Mamedov, Damir; Røst, Håkon Ivarssønn; Bakkelund, Johannes & Karazhanov, Smagul [Vis alle 7 forfattere av denne artikkelen] (2024). Initial Stages of Water Absorption on CeO2 Surfaces at Very Low Temperatures for Understanding Anti-Icing Coatings. Fulltekst i vitenarkiv

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