Holger Von Wenckstern

• Grandcolas, Mathieu; Løvoll, Marte; Dahl, Øystein; Thøgersen, Annett; Svenum, Ingeborg-Helene & Wenckstern, Holger Von [Vis alle 7 forfattere av denne artikkelen] (2026). Rapid thermal processing of photoanodes for solar water splitting: status, challenges and opportunities. Solar Energy Materials and Solar Cells. ISSN 0927-0248. 309, s. 1–9. doi: 10.1016/j.solmat.2026.114728. Fulltekst i vitenarkiv Vis sammendrag

  Rapid thermal processing (RTP) is gaining attention as an efficient alternative to conventional annealing of materials for photoelectrochemical (PEC) water splitting. By delivering ultrafast heating and precise temperature control, RTP introduces non-equilibrium conditions that enable metastable phase formation, defect engineering, and interfacial control, while preserving transparent conductive oxides (TCOs) essential for PEC architectures. These advantages improve crystallinity, activate dopants, and enhance interfacial quality without the drawbacks of prolonged furnace treatments. Recent studies report two- to fourfold increases in photocurrent density and negative onset potential shifts up to 300 mV for RTP-treated photoanodes, highlighting RTP's potential to accelerate PEC performance toward industrial benchmarks. Despite these advantages, RTP remains underutilized in PEC research, with challenges in process optimization, atmosphere control, and scalability still unresolved. This review summarizes current progress on RTP for several oxide photoanodes, compares its performance with that of conventional annealing processes, and discusses mechanistic insights. Future directions include hybrid thermal strategies, real-time diagnostics, and data-driven design to enable scalable PEC device manufacturing and sustainable solar hydrogen production.

• Andreassen, Magnus; Rosnes, Andreas; Petersen, Clemens; Schenk, Richard Justin; Both, Kevin Gregor & Bergum, Kristin [Vis alle 7 forfattere av denne artikkelen] (2026). Combinatorial Synthesis and Characterization of Lattice-Matched Ga2O3–Cr2O3 and Ga2O3–V2O3 Sesquioxide Alloys for Ultrawide-Bandgap Semiconductor Applications. Physica Status Solidi (a) applications and materials science. ISSN 1862-6300. 223(15). doi: 10.1002/pssa.70437. Fulltekst i vitenarkiv Vis sammendrag

  Gallium sesquioxide is a wide‐bandgap semiconductor of high interest for power electronics and deep UV‐sensing applications. The α‐phase ( E g  = 5.6 eV) can be synthesized with excellent crystal quality on isostructural Al 2 O 3 substrates, removing the need for expensive homoepitaxial growth that is required for the thermodynamically stable β‐phase ( E g  = 4.9 eV). Here, continuous composition spread material libraries of (Ga 1‐ x V x ) 2 O 3 and (Ga 1‐ x Cr x ) 2 O 3 with 0.05 <  x  < 0.45 are synthesized by pulsed laser deposition, and characterized structurally and optically with the aim of decreasing the optical absorption edge of α‐Ga 2 O 3 to expand the range of potential optoelectronic applications. The (Cr x Ga 1‐ x ) 2 O 3 material library remained stable in the rhombohedral α‐phase throughout the investigated compositional range, exhibiting high crystal quality with minimal changes to the unit cell parameters. A systematic shift in optical absorption edge from 5.5 to 3.9 eV is observed, as determined by spectrophotometry. The (Ga 1‐ x V x ) 2 O 3 material library exhibits a systematic shift from 5.2 to 2.9 eV with increasing x V , but a region of decreased crystal quality is observed for 0.11 ≤  x V  ≤ 0.20. Additionally, a secondary V 2 O 5 phase is observed for x V  > 0.23. Overall, bandgap engineering of α‐(Ga 1‐ x V x ) 2 O 3 and α‐(Ga 1‐ x Cr x ) 2 O 3 is demonstrated, and chromium substitution is identified as especially promising due to high crystallinity and systematic change of optical absorption edge.

• Rosnes, Andreas; Jiang, Bo; Nguyen, Phuong D.; Wang, Luyang; Wenckstern, Holger Von & Prytz, Øystein [Vis alle 7 forfattere av denne artikkelen] (2026). Multiple Stages of Metal Exsolution from Nonstoichiometric Perovskites. Journal of the American Chemical Society. ISSN 0002-7863. 148(31), s. 33486–33495. doi: 10.1021/jacs.6c08762. Fulltekst i vitenarkiv Vis sammendrag

  Exsolution enables controlled solid-state precipitation of metal nanoparticles from metal oxides, resulting in materials that exhibit excellent catalytic properties for electrochemical energy conversion. The diverse characteristics of particles exsolved at different temperatures indicate complex mechanisms that remain unresolved. Through a series of in situ electron microscopy, synchrotron X-ray diffraction, and thermogravimetry experiments on La0.2Ca0.7Ti0.9Sc0.05Cu0.05O3−δ across nanoscale wedges to μm-sized powders, multiple stages of exsolution are deconvoluted with increasing thermal activation: (1) minor exsolution of anchored surface nanoparticles, (2) exsolution of endoparticles within the bulk, and (3) diffusion and coalescing in the bulk and at the surfaces. Reconstruction of the perovskite surface by formation of nanoscopic steps and terraces proceeds concurrently with endoparticle growth. Moreover, distinct exsolution characteristics are observed in the near-surface region and deeper within the bulk, resulting in spherically and orthorhombically shaped endoparticles, respectively.

• Fernández, Javier García; Pokle, Anuj; Andreassen, Magnus; Prytz, Øystein; Grundmann, Marius & Wenckstern, Holger Von (2026). Ex Situ and In Situ Thermal Evolution and Crystallization of Amorphous (In,Ga)2O3. ACS Applied Electronic Materials. 8(11), s. 4582–4588. doi: 10.1021/acsaelm.6c00284. Fulltekst i vitenarkiv Vis sammendrag

  The present study investigates the structural evolution of amorphous (In,Ga)2O3 thin films grown by pulsed laser deposition and thermal annealing under vacuum (ex situ) and in situ transmission electron microscopy (TEM). Ex situ annealing results showed that the crystallization starts close to the substrate interface at 500 °C with randomly oriented nanocrystals, nanovoids, and on top of that, columnar grains of cubic c-(In,Ga)2O3. For the in situ TEM studies, we observed the formation of a heterogeneous polycrystalline mixture of elemental indium (In), monoclinic β-Ga2O3, and a minor contribution of c-In2O3 when annealed at 400 °C. Further annealing at 700 °C led to gradual evaporation of indium, resulting in a β-Ga2O3-dominated sample with nanovoids. These findings provide insights into phase stability, evolution, and elemental redistribution, which are critical for optimizing (In,Ga)2O3 thin films for optoelectronic applications.

• Petersen, Clemens; Schultz, Thorsten; Andreassen, Magnus; Vogt, Sofie; Koch, Norbert & Grundmann, Marius [Vis alle 7 forfattere av denne artikkelen] (2025). Toward Ultrawide Bandgap Engineering: Physical Properties of an α-(TixGa1-x)2O3 Material Library. Physica Status Solidi. Rapid Research Letters. ISSN 1862-6254. 19. doi: 10.1002/pssr.202500033. Fulltekst i vitenarkiv Vis sammendrag

  Due to its high bandgap of 5.3–5.6 eV and high predicted breakdown field of 10 MV cm−1, much attention is drawn to the ultrawide bandgap semiconductor α-Ga2O3 for applications in high-power and solar blind optoelectronic devices. In contrast to the thermodynamically most stable β-phase of Ga2O3, various transition metal sesquioxides with rhombohedral crystal structure and similar lattice constants to α-Ga2O3 are available for bandgap engineering toward lower bandgap energies. Therefore the material system α-(TixGa1−x)2O3 in principle offers the possibility to tune the materials bandgap for wavelength selective optoelectronics over an extremely wide range from 5.6 eV (α-Ga2O3) down to 0.14 eV (α-Ti2O3). In this work, high-throughput combinatorial synthesis by pulsed laser deposition is employed to realize a spatially addressable material library covering almost the entire composition range within the ternary (TixGa1−x)yOz solid solution. Phase-pure growth of (TixGa1−x)2O3 up to x = 0.25 is reported, exceeding previously found miscibility limits by a factor of 5. The physical properties of the material system are investigated in relation to x and bandgap engineering within the rhombohedral α-(TixGa1−x)2O3 material system is demonstrated over an up to now unprecedented large spectral range from 4.4 to 5.3 eV.

• Bergsbak, Ingvild; Nordseth, Ørnulf; Saxegaard, Kjetil Karlsen; Olsen, Vegard Skiftestad; Wenckstern, Holger Von & Bergum, Kristin (2024). Device Simulation of 25.9% Efficient ZnOxNy/Si Tandem Solar Cell. Advanced Theory and Simulations. 7(12). doi: 10.1002/adts.202400252. Fulltekst i vitenarkiv Vis sammendrag

  The novel, high electron mobility material ZnOxNy has been investigated theoretically as an absorber in a two-terminal tandem solar cell. In addition to its high mobility, ZnOxNy can attain sufficiently low carrier concentration to enable pn-junctions, and has a tunable bandgap around the 1.7 eV range. It is therefore suitable for pairing with a Si-based bottom cell. In addition to the ZnOxNy layer, the tandem cell consists of a Cu2O emitter and a Si heterojunction bottom cell. A buffer layer is introduced between the emitter and absorber in the top cell to mediate a large valence band offset that resulted in a poor fill factor, FF. A ZnOxNy buffer layer bandgap of 1.5 eV gave the highest power conversion efficiency (PCE). The objective is to estimate the optimal performance of ZnOxNy in a tandem solar cell. The dependence of current–voltage (J–V) characteristics on thickness, mobility and carrier concentration in the ZnOxNy layer is evaluated, and found to yield maximum performance with 0.35 𝛍m, 250 cm2 Vs–1 and 1016 cm−3, respectively. Using these conditions, the J–V parameters of the device under AM1.5 illumination are short circuit current density, JSC = 17.76 mA cm−2, open circuit voltage, VOC = 1.74 V, FF = 83.8% and PCE = 25.9%. With this, it is reported on, to the best of the knowledge, the first device simulation based on ZnOxNy.

• Rosnes, Andreas; Wenckstern, Holger Von; Polfus, Jonathan & Prytz, Øystein (2024). Identifying transient defects in exsolution of nanoparticles by semi-quantitative ABF STEM imaging. BIO Web of Conferences. ISSN 2273-1709. doi: 10.1051/bioconf/202412925030. Fulltekst i vitenarkiv
• Langørgen, Amanda; Frodason, Ymir Kalmann; Karsthof, Robert Michael; Wenckstern, Holger Von; Jensen, Ingvild Julie Thue & Vines, Lasse [Vis alle 7 forfattere av denne artikkelen] (2023). Defect level in κ-Ga2O3 revealed by thermal admittance spectroscopy. Journal of Applied Physics. ISSN 0021-8979. 134(1), s. 015701-1–015701-6. doi: 10.1063/5.0150994. Fulltekst i vitenarkiv Vis sammendrag

  Defects in pulsed-laser deposition grown have been investigated using thermal admittance spectroscopy and secondary ion mass spectrometry (SIMS). A film was grown on either a tin-doped indium oxide or an aluminum-doped zinc oxide buffer layer on a sapphire substrate functioning as back contact layer in vertical diode structures. In both sample types, a distinct signature in the capacitance signal was observed in the temperature range of 150–260 K. The corresponding defect charge-state transition level, labeled ⁠, was found to exhibit an activation energy of 0.21 eV. Potential candidates for the level were investigated using a combination of SIMS and hybrid-functional calculations. SIMS revealed the main impurities in the sample to be tin, silicon, and iron. The hybrid-functional calculations predict the acceptor levels of substitutional iron to lie 0.7–1.2 eV below the conduction band minimum depending on Ga-site, making an unlikely candidate for the level. Furthermore, Si as well as Sn substituting on the sixfold coordinated Ga2 site and the fivefold coordinated Ga3 and Ga4 sites are all shallow donors in -⁠, similar to that of -⁠. Sn substituting on the fourfold Ga1 site is, however, predicted to have levels in the bandgap at 0.15 and 0.24 eV below the conduction band minimum, in accordance with the extracted activation energy for ⁠. Thus, we tentatively assign as the origin of the level.

• Borgersen, Jon; Karsthof, Robert Michael; Rønning, Vegard; Vines, Lasse; Wenckstern, Holger Von & Grundmann, Marius [Vis alle 8 forfattere av denne artikkelen] (2023). Origin of enhanced conductivity in low dose ion irradiated oxides. AIP Advances. 13(1), s. 015211-1–015211-5. doi: 10.1063/5.0134699. Fulltekst i vitenarkiv Vis sammendrag

  Significant resistivity variations have previously been observed in oxides subjected to relatively low ion irradiation doses, nominally insufficient to generate the amount of bulk defects needed to explain the phenomena. In an effort to unveil the underlying mechanisms, we performed a systematic comparative study of the resistivity evolution in In 2 O 3 -based oxides as a function of low ion doses and ultraviolet (UV) illumination, observing striking correlations. Specifically, we found that irradiation with ∼3 × 10 12  Si/cm 2 and ∼18 h UV exposure result in similar resistivity drops, interpreted in terms of irradiation/illumination assisted desorption of oxygen containing species from the surface. This was further proven by post-irradiation exposure of one of the samples to an oxygen atmosphere partially restoring the resistivity. Combining the present results with literature data, we conclude that the radiation tolerance of In 2 O 3 -based and similar oxides depends on the surface charge modifications, individual defect contributions, and contributions from defect complexes at low, intermediate, and high doses, respectively.

• Montag, S.; Splith, D.; Kneiß, M.; Grundmann, M.; Fernandez, Javier Garcia & Prytz, Øystein [Vis alle 7 forfattere av denne artikkelen] (2023). Cation segregation observed in an (In,Ga) 2 O3 material thin film library beyond the miscibility limit of the bixbyite structure. PHYSICAL REVIEW MATERIALS. 7(9). doi: 10.1103/PhysRevMaterials.7.094603. Fulltekst i vitenarkiv Vis sammendrag

  Structural, morphological, and optical properties of (In1−xGax)2O3 thin films are reported as a function of the cation composition. A material library with 0.1≤x≤0.64 was fabricated by discrete combinatorial synthesis on r-plane sapphire substrates using pulsed laser deposition. The samples crystallize in the cubic bixbyite phase for x≤0.35. The lattice constant and absorption edge energy systematically decrease and increase, respectively, with increasing Ga content up to x=0.2. For higher Ga admixtures, both saturate. In addition, a significant change in surface morphology occurs at x∼0.2. Transmission electron microscopy examinations of selected samples show a homogeneous incorporation of Ga2O3 into cubic In2O3 for x=0.11, while a segregation of Ga-rich and In-rich regions can be seen for x=0.22 and x=0.35. In the sample with x=0.35, the Ga-rich regions exhibit a preferred orientation with an angle of 45∘–55∘ with respect to the substrate normal, which has been shown to result from a correspondingly faceted In-rich bixbyite layer at the substrate–thin film interface.

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• Amedjkouh, Yani Leo; Jiang, Bo; Rosnes, Andreas; Wenckstern, Holger Von & Polfus, Jonathan M. (2025). Combinatoral PLD of proton ceramic electrode materials with exsolved nanoparticles. Fulltekst i vitenarkiv Vis sammendrag

  Protonic ceramic electrochemical cells (PCECs) are poised to be a critical technology for the electrification of energy and chemical industry using hydrogen. One of the main bottlenecks hodling their widespread adoption back is the sluggish oxygen evolution/reduction reactions (OER/ORR) at the positrode. Wang et al. reported that Ba0.875Fe0.875Zr0.125O3-"δ" (D-BFZ) exhibits remarkable performance as a triple conducting PCFC positrode (Wang 2022). Here, we investigate further improvement of this system by exsolving nanoparticles of Co3O4 or noble metals such as Pt, Ir, Rh and Ru for improved OER/ORR kinetics. Combinatorial pulsed-laser deposition (c-PLD) is a novel thin film deposition technique for obtaining thin films with a continuous composition spread (CCS) (von Wenckstern 2020). D-BFZ doped with the cation species to be exsolved is deposited with a gradient in Ba-deficiency across the film. Spatially resolved synchrotron X-ray diffraction (XRD) and absorption spectroscopy (XAS) is utilized to study the impact of Ba-deficiency on the exsolution process and the resulting nanoparticle characteristics. Further studies involve oxygen exchange kinetics of pristine and exsolved materails using pulsed isotope exchange (PIE). Thus, the impact of the transition metal on the oxygen exchange kinetics can be directly compared between it being exsolved as nanoparticles and incorporated in the perovskite lattice.

• Fernandez, Javier Garcia; Pokle, Anuj; Andreassen, Magnus; Prytz, Øystein; Grundmann, Marius & Wenckstern, Holger Von (2025). In situ and ex situ thermal evolution, crystallization and optical properties of Amorphous (In,Ga)2O3. Fulltekst i vitenarkiv
• Fernandez, Javier Garcia; Montag, S.; Splith, D.; Kneiß, M.; Grundmann, M. & Prytz, Øystein [Vis alle 7 forfattere av denne artikkelen] (2024). Combinatorial PLD Synthesis of (In1−xGax)2O3 Thin Films: Structural, Morphological, and Optical Analysis for Transparent Conducting Oxides. Fulltekst i vitenarkiv
• Choubey, Anjali; Nilsen, Ola; Wenckstern, Holger Von & Sønsteby, Henrik Hovde (2024). Utilizing low-temperature ALD technique to investigate perovskite nickelates for photovoltaic applications. Fulltekst i vitenarkiv Vis sammendrag

  Photovoltaic (PV) materials currently in use like silicon are well-established but approaching their theoretical limit, and halide-perovskites, even though developing rapidly, are toxic and unstable under environmental conditions. Developing new materials for PV applications is slowly becoming a crucial necessity. In this study, perovskite nickelates are investigated as an alternative to traditional PV materials. Nickelates are not only stable under environmental conditions, but they can also withstand photobleaching and thermal exposures. Additionally, they are well known for their metal-insulator phase transition, magnetic phase transition, and structural transition [1, 2]. This has made them very lucrative for various electronic, magnetic, dielectric, superconducting, and catalytic applications. However, there is not much data on the use of nickelates for PV applications, and we are trying to bridge that gap. Some perovskite nickelates have shown bandgap tuning abilities by A-site substitution control [2-4]. In this work, Terbium nickelate (TbNiO3) and Gadolinium nickelate (GdNiO3) thin films fabricated using low-temperature atomic layer deposition (ALD) techniques were studied and characterized. X-ray diffraction gave information about the structure and crystallinity, x-ray fluorescence and x-ray photoelectron spectroscopy about the composition, and spectroscopic ellipsometry about the thickness and refractive indices of the deposited films. These investigations helped gain valuable insight into the extent of the semiconductive nature of these materials and how to exploit them for PV applications. Reference: 1. Catalano, S., et al., Reports on Progress in Physics, 81(4), 046501 (2018). 2. Mercy, A., et al., Nature Communications, 8(1), (2017). 3. Chang, L., et al., Journal of Physics D: Applied Physics, 49(44), (2016). 4. Chang, L., et al., ACS Applied Materials & Interfaces, 11(17), (2019).

• Fernandez, Javier Garcia; Montag, S.; Andreassen, Magnus; Pokle, Anuj; Splith, D. & Kneiß, M. [Vis alle 9 forfattere av denne artikkelen] (2024). Probing, microstructure, crystallization and phase segregation in (In1-xGax)2O3 thin films by TEM. Fulltekst i vitenarkiv
• Jensen, Ingvild Julie Thue; Thøgersen, Annett; Cooil, Simon Phillip; Wells, Justin William; Prytz, Øystein & Wenckstern, Holger Von (2023). Bandgap and band offset engineering in κ-Ga2O3-based thin films (Invited talk)). Fulltekst i vitenarkiv
• Bazioti, Kalliopi; Kneiβ, Max; Wenckstern, Holger Von; Hage, Fredrik Sydow & Prytz, Øystein (2022). Band Gap Measurements by VEELS of novel κ-(Al0.2Ga0.8)2O3/ κ-(In0.25Ga0.75)2O3 superlattices. Fulltekst i vitenarkiv

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