Øystein Prytz

• A. Azarov, J. García-Fernández, J. Zhao, R. He, J.H. Park, D. W. Jeon, Ø. Prytz, F. Djurabekova, and A. Kuznetsov. Phase glides and self-organization of atomically abrupt interfaces out of stochastic disorder in α-Ga2O3. Nature Communications 16, 3245 (2025).

• J. Zhao, J. García-Fernández, A. Azarov, R. He, Ø. Prytz, K. Nordlund, M. Hua, F. Djurabekova, and A. Kuznetsov. Crystallization Instead of Amorphization in Collision Cascades in Gallium Oxide. Physical Review Letters 134, 126101 (2025).

• J. García-Fernández, S. B. Kjeldby, L. J. Zeng, A. Azarov, A. Pokle, P. D. Nguyen, E. Olsson, L. Vines, A. Kuznetsov, and Ø. Prytz. In-situ atomic-resolution study of transformations in double polymorph γ/β-Ga2O3 structures.  Materials Advances 5, 3824 (2024).

• D. A. Leon, C. Elgvin, P. D. Nguyen, Ø. Prytz, F. S. Hage, and K. Berland. Unraveling many-body effects in ZnO: Combined study using momentum-resolved electron energy-loss spectroscopy and first-principles calculations. Physical Review B 109, 115153 (2024).

• S. Montag, D. Splith, M. Kneiß, M. Grundmann, J. Garcia Fernandez, Ø. Prytz, and H. von Wenckstern. Cation segregation observed in an (In,Ga)2O3 material thin film library beyond the miscibility limit of the bixbyite structure. Physical Review Materials 7, 094603 (2023).

• A. Azarov, J. García-Fernández, J. Zhao, F. Djurabekova, H. He, R. He, Ø. Prytz, L. Vines, U. Bektas, P. Chekhonin, N. Klingner, G. Hlawacek, and A. Kuznetsov. Universal radiation tolerant semiconductor. Nature Communications 14, 4855 (2023).

• K. G. Both, V. M. Reinertsen, T. Aarholt, I. J. T. Jensen, D. Neagu, Ø. Prytz, T. Norby, A. Chatzitakis. Ni-doped A-site excess SrTiO3 thin films modified with Au nanoparticles by a thermodynamically driven restructuring for plasmonic activity. Catalysis Today 413-415, 113950 (2023).

• N. S. Genz, A. J. Kallio, R. Oord, F. Krumeich, A. Pokle, Ø. Prytz, U. Olsbye, F. Meirer, S. Huotari, B. M. Weckhuysen. Operando Laboratory-based Multi-edge X-ray Absorption Near-Edge Spectroscopy of Solid Catalysts. Angewandte Chemie Int. Ed. 61, e202209334 (2022).

• X. Kang, V. M. Reinertsen, K. G. Both, A. Galeckas, T. Aarholt, Ø. Prytz, T. Norby, D. Neagu, and A. Chatzitakis. Galvanic Restructuring of Exsolved Nanoparticles for Plasmonic and Electrocatalytic Energy Conversion. Small 18, 2201106 (2022).
• S. B. Kjeldby, A. Azarov, P. D. Nguyen, V. Venkatachalapathy, R. Mikšová, A. Mackova, A. Yu. Kuznetsov, Ø. Prytz, and L. Vines. Radiation-induced defect accumulation and annealing in Si-implanted gallium oxide. Journal of Applied Physics 131, 125701 (2022).
• B. L. Aarseth, C. Granerød, A. Galeckas, A. Azarov, P. D. Nguyen, Ø. Prytz, and L. Vines. Formation and functionalization of Ge-nanoparticles in ZnO. Nanotechnology 32, 505707 (2021).
• C. Bazioti, V. S. Olsen, A. Y. Kuznetsov, L. Vines, and Ø. Prytz . Formation of N₂ bubbles along grain boundaries in (ZnO)_1−x(GaN)_x: nanoscale STEM-EELS studies Physical Chemistry Chemical Physics 22, 3779 (2020).
• T. Aarholt, Y. K. Frodason, and Ø. Prytz. Imaging defect complexes in scanning transmission electron microscopy: Impact of depth, structural relaxation, and temperature investigated by simulations Ultramicroscopy 209, 112884 (2020).
• T. Bondevik, H. H. Ness, C. Bazioti, T. Norby, O. M. Løvvik, C. T. Koch, and Ø. Prytz. Investigation of the electrostatic potential of a grain boundary in Y-substituted BaZrO₃ using inline electron holography Physical Chemistry Chemical Physics 21, 17662 (2019).
• C. Bazioti, A. Azarov, K. M. Johansen, B. G. Svensson, L. Vines, A. Y. Kuznetsov, and Ø. Prytz. Role of Nitrogen in Defect Evolution in Zinc Oxide: STEM–EELS Nanoscale Investigations The Journal of Physical Chemistry Letters 10, 4725 (2019).
• C. S. Granerød, B. L. Aarseth, P. D. Nguyen, C. Bazioti, A. Azarov, B. G. Svensson, L. Vines, and Ø. Prytz. Structural and optical properties of individual Zn₂GeO₄ particles embedded in ZnO. Nanotechnology 30, 225702 (2019).
• C. S. Granerød, A. Galeckas, K. M. H. Johansen, L. Vines, and Ø. Prytz. The temperature-dependency of the optical band gap of ZnO measured by electron energy-loss spectroscopy in a scanning transmission electron microscope. Journal of Applied Physics 123, 145111 (2018).
• C. S. Granerød, S. R. Bilden, T. Aarholt, Y. F. Yao, C. C. Yang, D. C. Look, L. Vines, K. M. Johansen, and Ø. Prytz. Direct observation of conduction band plasmons and the related Burstein-Moss shift in highly doped semiconductors: A STEM-EELS study of Ga-doped ZnO. Physical Review B 98, 115301 (2018).
• C. Granerød, W. Zhan, and Ø. Prytz. Automated approaches for band gap mapping in STEM-EELS. Ultramicroscopy 184, 39 (2018).
• W. Zhan, C. S. Granerød, V. Venkatachalapathy, K. M. H. Johansen, I. J. T. Jensen, A. Yu. Kuznetsov, and Ø. Prytz. Nanoscale mapping of optical band gaps using monochromated Electron Energy Loss Spectroscopy. Nanotechnology 28, 105703 (2017).

• Thøgersen, Annett; Muntingh, Agnar Georg Peder; Vines, Lasse; Prytz, Øystein; Kneiß, Max & Grundmann, Marius [Show all 8 contributors for this article] (2026). Decoupling composition and band gap in κ-Ga<inf>2</inf>O<inf>3</inf>heterostructures via STEM-EELS. Ultramicroscopy. ISSN 0304-3991. 286. doi: 10.1016/j.ultramic.2026.114417. Full text in Research Archive
• Rosnes, Andreas; Jiang, Bo; Nguyen, Phuong D.; Wang, Luyang; Wenckstern, Holger Von & Prytz, Øystein [Show all 7 contributors for this article] (2026). Multiple Stages of Metal Exsolution from Nonstoichiometric Perovskites. Journal of the American Chemical Society. ISSN 0002-7863. 148(31), p. 33486–33495. doi: 10.1021/jacs.6c08762. Full text in Research Archive Show summary

  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), p. 4582–4588. doi: 10.1021/acsaelm.6c00284. Full text in Research Archive Show summary

  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.

• Elgvin, Cana; Hage, Fredrik Sydow; Prytz, Øystein; Elyas, Khairi; Höflich, Katja & Koch, Christoph T. [Show all 7 contributors for this article] (2026). Advances in momentum-resolved EELS of phonons, excitons and plasmons in 2D materials and their heterostructures. PHYSICAL REVIEW MATERIALS. 10. doi: 10.1103/8wwb-lxk2. Full text in Research Archive Show summary

  Momentum-resolved electron energy-loss spectroscopy (q-EELS) enables the study of 2D materials by simultaneously capturing energy and momentum transfer with nanometer spatial resolution, probing excitations beyond the light cone and outside the first Brillouin zone. This technique provides unrivaled detail in the investigation of plasmons, excitons, phonons, and their coupling in 2D materials and across interfaces in heterostructures. This review covers the fundamentals of q-EELS, including resolution limits and detectability challenges. Current applications in graphene, hexagonal boron nitride, and transition metal dichalcogenides are surveyed. Emerging frontiers including magnons, cryogenic operation, and in situ capabilities promise to advance our understanding of low-dimensional materials.

• Wen, Yabing; Rosnes, Andreas; Jiang, Bo; Prytz, Øystein; Norby, Truls & Haugsrud, Reidar [Show all 7 contributors for this article] (2025). Nickel-Induced Lattice Defects Limit Proton Uptake in Barium Zirconate Electrolytes. Journal of the American Chemical Society. ISSN 0002-7863. 148. doi: 10.1021/jacs.5c13935. Full text in Research Archive Show summary

  Nickel provides essential catalytic properties for hydrogen electrodes in proton-conducting ceramic electrochemical cells. However, Ni diminishes the hydration capability and proton conductivity when incorporated into electrolyte materials including BaZr0.8Yb0.2O3−δ studied here. Through semiquantitative atomic-resolution scanning transmission electron microscopy, density functional theory simulations, X-ray total scattering, and absorption spectroscopy, we reveal that Ni forms point defect clusters with the Yb acceptors wherein oxygen vacancies are trapped and resist hydration. The resulting effective acceptor concentration is described by point defect reactions in quantitative agreement with thermogravimetric measurements of hydration for samples substituted with 2–5 mol % Ni by BaNiO2 addition. Moreover, excess B-site cations due to NiO addition induce the formation of antiphase boundaries (APBs) that are enriched in Yb and thereby deplete the bulk of acceptors, further suppressing hydration. The adverse effects of Ni are thereby resolved into two novel mechanisms, opening new avenues in point defect engineering for high-performance electrolytes.

• Fernandez, Javier Garcia; Kjeldby, Snorre Braathen; Zeng, L. J.; Olsson, E.; Vines, Lasse & Prytz, Øystein (2025). Formation and stability of Ge nanocrystals in polymorph converted Ga2O3: Temperature-driven journey. Applied Physics Letters. ISSN 0003-6951. 126(5). doi: 10.1063/5.0235371. Full text in Research Archive Show summary

  The influence of germanium (Ge) implantation on β-Ga2O3 followed by ex situ annealing through polymorph conversion in air at various temperatures (600–1100 °C) is studied. Atomic resolution aberration-corrected scanning transmission electron microscopy is employed to examine the structural and microstructural changes induced by the annealing process. The results show that the thermal annealing process leads to the formation of Ge nanocrystals, which subsequently disappear, leaving nano-voids inside the Ge-doped Ga2O3 matrix. In addition, the microstructure displays distinct crystallographic relationships in annealed β-Ga2O3 forming layers with well-defined interfaces. This work reveals the unique effects of Ge-implantation, demonstrating the possible functionalization of Ga2O3 with Ge nanocrystals.

• Azarov, Alexander; Fernandez, Javier Garcia; Zhao, Junlei; He, Ru; Park, Ji-Hyeon & Jeon, Dae-Woo [Show all 9 contributors for this article] (2025). Phase glides and self-organization of atomically abrupt interfaces out of stochastic disorder in α-Ga2O3. Nature Communications. 16. doi: 10.1038/s41467-025-58516-9. Full text in Research Archive Show summary

  Disorder-induced ordering and remarkably high radiation tolerance in γ-phase of gallium oxide is a recent spectacular discovery at the intersection of the fundamental physics and electronic applications. Importantly, by far, these data were collected with initial samples in form of the thermodynamically stable β-phase of this material. Here, we investigate these phenomena starting from metastable α-phase and explain radically new trend occurring in the system. We argue that in contrast to that in β-to-γ disorder-induced transitions, the O sublattice in α-phase exhibits hexagonal close-packed structure, so that to activate α-to-γ transformation significant structural rearrangements are required in both Ga and O sublattices. Moreover, consistent with theoretical predictions, α-to-γ phase transformation requires accumulation of the substantial tensile strain to initiate otherwise impossible lattice glides. Thus, we explain the experimentally observed trends in term of the combination of disorder and strain governed process. Finally, we demonstrate atomically abrupt α/γ interfaces paradoxically self-organized out of the stochastic disorder.

• Zhao, Junlei; Fernandez, Javier Garcia; Azarov, Alexander; He, Ru; Prytz, Øystein & Nordlund, Kai [Show all 9 contributors for this article] (2025). Crystallization Instead of Amorphization in Collision Cascades in Gallium Oxide. Physical Review Letters. ISSN 0031-9007. 134. doi: 10.1103/PhysRevLett.134.126101. Full text in Research Archive
• Fernandez, Javier Garcia; Kjeldby, Snorre Braathen; Zeng, L. J.; Azarov, Alexander; Pokle, Anuj & Nguyen, Phuong Dan [Show all 10 contributors for this article] (2024). In situ atomic-resolution study of transformations in double polymorph γ/β-Ga2O3 structures. Materials Advances. 5, p. 3824–3831. doi: 10.1039/D3MA01011B. Full text in Research Archive Show summary

  Disorder-induced formation of metastable Ga2O3 polymorphs as well as the recovery of the stable state upon annealing attract attention because of the fundamental novelty and rapidly increasing interest in the use of Ga2O3 in practical applications. In this study, double polymorph γ/β-Ga2O3 structures fabricated by the radiation-induced disorder approach were used as a starting point for systematic in situ annealing electron microscopy experiments. We show that, under the conditions of the TEM in situ annealing, double γ/β-Ga2O3 polymorph structures remained stable up to 300 °C, when onsets of the γ-to-β transformation become traceable, leading to a prominent γ- and β-mixture already at 500 °C. Interestingly, the recrystallization of the β-Ga2O3 occurs throughout the whole γ-film and the preferential alignments at the newly emerging γ/β-interfaces are different from that of the initial γ/β-interface formed as a result of the disorder-induced ordering. The alignments of the two polymorphs are maintained as a function of temperature – with a reduction in the volumetric ratio of γ-domains for increasing annealing temperature. Finally, at 1100 °C, γ-Ga2O3 fully transforms into β-Ga2O3, without dominating crystallographic relationships or preferred orientations, indicating that energy barriers are not any longer implied limiting factors, because of a sufficiently high thermal energy supply. Thus, these TEM in situ measurements enable a new level of accuracy for assessing polymorphic transformations in Ga2O3.

• Both, Kevin Gregor; Neagu, Dragos; Prytz, Øystein; Norby, Truls & Chatzitakis, Athanasios (2024). Exsolution of Ni nanoparticles in A-site excess STO films. Nanoscale Advances. doi: 10.1039/d4na00213j. Full text in Research Archive Show summary

  Exsolution is a technique to create metal nanoparticles embedded within a matrix. The phenomenon has previously predominantly been studied in A-site deficient and stoichiometric perovskite powders. Here, we present a systematic study of an A-site excess perovskite oxide based on SrTiO3 thin films, doped with nickel and exsolved under different conditions. The study aims to shed light on particle formation in these novel systems, including the effects of (i) the thin film thickness, (ii) pre-exsolution annealing in an oxidative atmosphere, (iii) a reductive atmosphere during the exsolution step, and (iv) exsolution time on the particle size and particle density. Our results indicate that exsolution occurs quickly, forming nanoparticles both on the surface and in the bulk of the host perovskite. The findings indicate that pre-annealing in an ambient atmosphere leads to fewer but larger exsolved particles compared to samples without pre-annealing. Consequently, while crystallization of the thin film occurs in both atmospheres, the simultaneous crystallization of the thin film and formation of the nanoparticles leads to a smaller apparent average radius. Moreover, we present evidence that metal particles can be found beyond the originally doped region. These findings are a step towards realizing tunable functional materials using exsolution to create metallic nanostructures within a thin film in a predictable manner.

• 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. Full text in Research Archive
• Valido, Dario Alejandro Leon; Elgvin, Cana; Nguyen, Phuong Dan; Prytz, Øystein; Hage, Fredrik Sydow & Berland, Kristian (2024). Unraveling many-body effects in ZnO: Combined study using momentum-resolved electron energy-loss spectroscopy and first-principles calculations. Physical review B (PRB). ISSN 2469-9950. 109(11). doi: 10.1103/PhysRevB.109.115153. Full text in Research Archive Show summary

  We present a detailed study of the dielectric response of ZnO using a combination of low-loss momentum- resolved electron energy-loss spectroscopy (EELS) and first-principles calculations at several levels of theory, from the independent particle and the random phase approximation with different variants of density functional theory (DFT), including hybrid and DFT + U schemes; to the Bethe-Salpeter equation (BSE). We use a method based on the f -sum rule to obtain the momentum-resolved experimental loss function and absorption spectra from EELS measurements. We characterize the main features in the direct and inverse dielectric functions of ZnO and their dispersion, associating them to single-particle features in the electronic band structure, while highlighting the important role of many-body effects such as plasmons and excitons. We discuss different signatures of the high anisotropy in the response function of ZnO, including the symmetry of the excitonic wave functions.

• Madathil, Reshma; Thoreton, Vincent; Prytz, Øystein & Norby, Truls Eivind (2023). On the high-temperature oxidation of ZnSb for thermoelectric applications. Corrosion Science. ISSN 0010-938X. 210. doi: 10.1016/j.corsci.2022.110826. Full text in Research Archive Show summary

  Thermoelectric ZnSb has a native surface oxide layer of Sb2O5 +ZnO, while HT oxidation in air resulted in selective oxidation to ZnO, with no detectable Sb by STEM-EDS. The ZnO consisted of an inner nano-granular and a more columnar outer layer. Thermogravimetry showed parabolic oxidation kinetics at 200–325 °C with an activation energy of 117 kJ/mol, comparing well with literature for oxidation of Zn. Two-stage 16O2 +18O2 oxidation followed by SIMS suggests growth by mixed Zn and O diffusion through a protective ZnO layer that still cannot prevent considerable high temperature oxidation in air, with formation of insulating electrical contacts, unless metallised.

• Azarov, Alexander; Fernández, Javier García; Zhao, Junlei; Djurabekova, Flyura; He, Huan & He, Ru [Show all 13 contributors for this article] (2023). Universal radiation tolerant semiconductor. Nature Communications. 14, p. 1–8. doi: 10.1038/s41467-023-40588-0. Full text in Research Archive Show summary

  Abstract Radiation tolerance is determined as the ability of crystalline materials to withstand the accumulation of the radiation induced disorder. Nevertheless, for sufficiently high fluences, in all by far known semiconductors it ends up with either very high disorder levels or amorphization. Here we show that gamma/beta (γ/β) double polymorph Ga 2 O 3 structures exhibit remarkably high radiation tolerance. Specifically, for room temperature experiments, they tolerate a disorder equivalent to hundreds of displacements per atom, without severe degradations of crystallinity; in comparison with, e.g., Si amorphizable already with the lattice atoms displaced just once. We explain this behavior by an interesting combination of the Ga- and O- sublattice properties in γ-Ga 2 O 3 . In particular, O-sublattice exhibits a strong recrystallization trend to recover the face-centered-cubic stacking despite the stronger displacement of O atoms compared to Ga during the active periods of cascades. Notably, we also explained the origin of the β-to-γ Ga 2 O 3 transformation, as a function of the increased disorder in β-Ga 2 O 3 and studied the phenomena as a function of the chemical nature of the implanted atoms. As a result, we conclude that γ/β double polymorph Ga 2 O 3 structures, in terms of their radiation tolerance properties, benchmark a class of universal radiation tolerant semiconductors.

• Montag, S.; Splith, D.; Kneiß, M.; Grundmann, M.; Fernandez, Javier Garcia & Prytz, Øystein [Show all 7 contributors for this article] (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. Full text in Research Archive Show summary

  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.

• Kjeldby, Snorre Braathen; Nguyen, Phuong Dan; Fernández, Javier García; Haug, Kristian; Galeckas, Augustinas & Jensen, Ingvild Julie Thue [Show all 9 contributors for this article] (2023). Optical properties of ZnFe2O4 nanoparticles and Fe-decorated inversion domain boundaries in ZnO. Nanoscale Advances. 5(7), p. 2102–2110. doi: 10.1039/d2na00849a. Full text in Research Archive Show summary

  The maximum efficiency of solar cells utilizing a single layer for photovoltaic conversion is given by the single junction Shockley–Queisser limit. In tandem solar cells, a stack of materials with different band gaps contribute to the conversion, enabling tandem cells to exceed the single junction Shockley–Queisser limit. An intriguing variant of this approach is to embed semiconducting nanoparticles in a transparent conducting oxide (TCO) solar cell front contact. This alternative route would enhance the functionality of the TCO layer, allowing it to participate directly in photovoltaic conversion via photon absorption and charge carrier generation in the nanoparticles. Here, we demonstrate the functionalization of ZnO through incorporation of either ZnFe2O4 spinel nanoparticles (NPs) or inversion domain boundaries (IDBs) decorated by Fe. Diffuse reflectance spectroscopy and electron energy loss spectroscopy show that samples containing spinel particles and samples containing IDBs decorated by Fe both display enhanced absorption in the visible range at around 2.0 and 2.6 eV. This striking functional similarity was attributed to the local structural similarity around Fe-ions in spinel ZnFe2O4 and at Fe-decorated basal IDBs. Hence, functional properties of the ZnFe2O4 arise already for the two-dimensional basal IDBs, from which these planar defects behave like two-dimensional spinel-like inclusions in ZnO. Cathodoluminescence spectra reveal an increased luminescence around the band edge of spinel ZnFe2O4 when measuring on the spinel ZnFe2O4 NPs embedded in ZnO, whereas spectra from Fe-decorated IDBs could be deconvoluted into luminescence contributions from bulk ZnO and bulk ZnFe2O4.

• Genz, Nina; Kallio, Antti-Jussi; Oord, Ramon; Krumeich, Frank; Pokle, Anuj & Prytz, Øystein [Show all 10 contributors for this article] (2022). Operando Laboratory-Based Multi-Edge X-Ray Absorption Near-Edge Spectroscopy of Solid Catalysts. Angewandte Chemie International Edition. ISSN 1433-7851. 61(48). doi: 10.1002/anie.202209334. Full text in Research Archive Show summary

  Laboratory-based X-ray absorption spectroscopy (XAS) and especially X-ray absorption near-edge structure (XANES) offers new opportunities in catalyst characterization and presents not only an alternative, but also a complementary approach to precious beamtime at synchrotron facilities. We successfully designed a laboratory-based setup for performing operando, quasi-simultaneous XANES analysis at multiple K-edges, more specifically, operando XANES of mono-, bi-, and trimetallic CO2 hydrogenation catalysts containing Ni, Fe, and Cu. Detailed operando XANES studies of the multielement solid catalysts revealed metal-dependent differences in the reducibility and re-oxidation behavior and their influence on the catalytic performance in CO2 hydrogenation. The applicability of operando laboratory-based XANES at multiple K-edges paves the way for advanced multielement catalyst characterization complementing detailed studies at synchrotron facilities.

• Kang, Xiaolan; Reinertsen, Vilde Mari; Both, Kevin Gregor; Galeckas, Augustinas; Aarholt, Thomas & Prytz, Øystein [Show all 9 contributors for this article] (2022). Galvanic Restructuring of Exsolved Nanoparticles for Plasmonic and Electrocatalytic Energy Conversion. Small. ISSN 1613-6810. 18(29). doi: 10.1002/smll.202201106. Full text in Research Archive Show summary

  There is a growing need to control and tune nanoparticles (NPs) to increase their stability and effectiveness, especially for photo- and electrochemical energy conversion applications. Exsolved particles are well anchored and can be re-shaped without changing their initial location and structural arrangement. However, this usually involves lengthy treatments and use of toxic gases. Here, the galvanic replacement/deposition method is used, which is simpler, safer, and leads to a wealth of new hybrid nanostructures with a higher degree of tailorability. The produced NiAu bimetallic nanostructures supported on SrTiO3 display exceptional activity in plasmon-assisted photoelectrochemical (PEC) water oxidation reactions. In situ scanning transmission electron microscopy is used to visualize the structural evolution of the plasmonic bimetallic structures, while theoretical simulations provide mechanistic insight and correlate the surface plasmon resonance effects with structural features and enhanced PEC performance. The versatility of this concept in shifting catalytic modes to the hydrogen evolution reaction is demonstrated by preparing hybrid NiPt bimetallic NPs of low Pt loadings on highly reduced SrTiO3 supports. This powerful methodology enables the design of supported bimetallic nanomaterials with tunable morphology and catalytic functionalities through minimal engineering.

• Kjeldby, Snorre Braathen; Azarov, Alexander; Nguyen, Phuong Dan; Venkatachalapathy, Vishnukanthan; Mikšová, R. & MacKová, A. [Show all 9 contributors for this article] (2022). Radiation-induced defect accumulation and annealing in Si-implanted gallium oxide. Journal of Applied Physics. ISSN 0021-8979. 131(12). doi: 10.1063/5.0083858. Full text in Research Archive Show summary

  Defect accumulation and annealing phenomena in Si-implanted monoclinic gallium oxide (β-Ga 2 O 3 ) wafers, having [Formula: see text], (010), and (001) orientations, were studied by Rutherford backscattering spectrometry in channeling mode (RBS/c), x-ray diffraction (XRD), and (scanning) transmission electron microscopy [(S)TEM]. Initially, the samples with different surface orientations were implanted with 300 keV 28 Si + -ions, applying fluences in the range of 1 × 10 14 –2 × 10 16  Si/cm 2 , unveiling interesting disorder accumulation kinetics. In particular, the RBS/c, XRD, and (S)TEM combined data suggested that the radiation disorder buildup in Si-implanted β-Ga 2 O 3 is accompanied by significant strain accumulation, assisting crystalline-to-crystalline phase transitions instead of amorphization. Selected samples having [Formula: see text] orientation were subjected to isochronal (30 min) anneals in the range of 300–1300 °C in air. Systematic RBS/c and XRD characterization of these samples suggested complex structural transformations, which occurred as a function of the fluence and the temperature. Moreover, a detailed (S)TEM analysis of the sample implanted with 2 × 10 16  Si/cm 2 and annealed at 1100 °C was enhanced by applying dispersive x-ray and electron energy-loss spectroscopies. The analysis revealed silicon agglomerations in the form of silicon dioxide particles. Signal from silicon was also detected outside of the agglomerates, likely occurring as substitutional Si on Ga sites.

• Thøgersen, Annett; Jensen, Ingvild Julie Thue; Belle, Branson Delano; Stange, Marit Synnøve Sæverud; Reinertsen, Vilde Mari & Kjeldstad, Torunn [Show all 9 contributors for this article] (2022). Plasmonic properties of aluminium nanowires in amorphous silicon. Journal of Physics: Condensed Matter. ISSN 0953-8984. 35(6), p. 1–10. doi: 10.1088/1361-648X/aca30e. Full text in Research Archive Show summary

  Plasmonic structures can help enhance optical activity in the ultraviolet (UV) region and therefore enhancing photocatalytic reactions and the detection of organic and biological species. Most plasmonic structures are composed of Ag or Au. However, producing structures small enough for optical activity in the UV region has proved difficult. In this study, we demonstrate that aluminium nanowires are an excellent alternative. We investigated the plasmonic properties of the Al nanowires as well as the optoelectronic properties of the surrounding a − Si matrix by combining scanning transmission electron microscopy imaging, electron energy loss spectroscopy and electrodynamic modelling. We have found that the Al nanowires have distinct plasmonic modes in the UV and far UV region, from 0.75 eV to 13 eV. In addition, simulated results found that the size and spacing of the Al nanowires, as well as the embedding material were shown to have a large impact on the type of surface plasmon energies that can be generated in the material. Using electromagnetic modelling, we have identified the modes and illustrated how they could be tuned further.

• Both, Kevin Gregor; Reinertsen, Vilde Mari; Aarholt, Thomas; Jensen, Ingvild Julie Thue; Neagu, Dragos & Prytz, Øystein [Show all 8 contributors for this article] (2022). Ni-doped A-site excess SrTiO3 thin films modified with Au nanoparticles by a thermodynamically-driven restructuring for plasmonic activity. Catalysis Today. ISSN 0920-5861. 413. doi: 10.1016/j.cattod.2022.11.011. Full text in Research Archive Show summary

  Plasmonically active nanoparticles offer a promising pathway to extend the absorption range of photocatalysts. While not necessarily catalytically active themselves, these particles allow the absorption of lower energy photons in wide band gap photocatalysts. Here, we present A-site excess SrTiO3 thin films, doped with Ni, where through a subsequent exsolution process we created well-socketed Ni nanoparticles in the surface of SrTiO3. These were galvanically replaced by Au, resulting in well-socketed Au nanoparticles with variable size on the surface, depending on the galvanic replacement time. Photoelectrochemical measurements and electron energy loss spectroscopy revealed the improved photoresponse of the thin films by plasmonic activity of the nanoparticles. The energy of the plasmon peak suggests that the main improvement results from the injection of hot charge carriers. Our study opens new avenues for the design and synthesis of the next generation of photocatalytic materials.

• Fernandez, Javier Garcia; Kjeldby, Snorre Braathen; Nguyen, Phuong Dan; Karlsen, Ole Bjørn; Vines, Lasse & Prytz, Øystein (2022). Formation of γ-Ga2O3 by ion implantation: Polymorphic phase transformation of β-Ga2O3. Applied Physics Letters. ISSN 0003-6951. 121(19). doi: 10.1063/5.0120103. Full text in Research Archive Show summary

  Ion implantation induced phase transformation and the crystal structure of a series of ion implanted β-Ga 2 O 3 samples were studied using electron diffraction, high resolution transmission electron microscopy, and scanning transmission electron microscopy. In contrast to previous reports suggesting an ion implantation induced transformation to the orthorhombic κ-phase, we show that for 28 Si + , 58 Ni + , and stoichiometric 69 Ga + / 16 O + -implantations, the monoclinic β-phase transforms to the cubic γ-phase. The γ-phase was confirmed for implantations over a range of fluences from 10 14 to 10 16  ions/cm 2 , indicating that the transformation is a general phenomenon for β-Ga 2 O 3 due to strain accumulation and/or γ-Ga 2 O 3 being energetically preferred over highly defective β-Ga 2 O 3 .

• Thøgersen, Annett; Sun, Xinwei; Jensen, Ingvild Julie Thue; Prytz, Øystein & Norby, Truls (2022). In-situ electron loss spectroscopy reveals surface dehydrogenation of hydrated ceria nanoparticles at elevated temperatures. Journal of Physics and Chemistry of Solids. ISSN 0022-3697. 170, p. 1–7. doi: 10.1016/j.jpcs.2022.110955. Full text in Research Archive Show summary

  Ceria (CeO2) exhibits high reversible oxygen storage capacity at intermediate temperatures (500–800 °C) related to an extraordinary and not fully understood reduction of its surfaces. We have investigated pristine and alcohol-dispersed commercially available ceria nanoparticles by in-situ scanning transmission electron microscopy with electron energy loss spectroscopy (STEM-EELS) to examine the dynamic changes during the initial redox reaction process of ceria nanoparticles in an ultra-high vacuum atmosphere using an in-situ heating holder. High spatially resolved EELS was used to estimate the amounts of Ce3+ and Ce4+ in the nanoparticles as a function of temperature, based on the white-line ratios M5/M4 of the EELS spectra. The results show a nm-range thick surface layer rich in Ce3+ on pristine particles prior to heating. During heating, this oxidises to Ce4+. Heating in high vacuum should normally not lead to oxidation, but the observed results can be understood if the surface layer has an oxyhydroxide composition such as CeOOH, which by heating in the vacuum dehydrogenates and hence oxidises to CeO2, a process that requires diffusion of hydrogen only. This process occurred for all samples, but was more pronounced for the particles that were previously dispersed in ethanol. Thermogravimetric analysis (TGA) by heating the pristine powder in dry atmosphere yielded a considerable weight loss confirming the content of hydroxide and probably water in and on the CeO2 particles. The results suggest that CeO2 surfaces are reduced to a layer of oxyhydroxide by hydrogen-containing molecules like water vapour or alcohols.

• Aarseth, Bjørn Lupton; Granerød, Cecilie Skjold; Galeckas, Augustinas; Azarov, Alexander; Nguyen, Phuong Dan & Prytz, Øystein [Show all 7 contributors for this article] (2021). Formation and functionalization of Ge-nanoparticles in ZnO. Nanotechnology. ISSN 0957-4484. 32(50). doi: 10.1088/1361-6528/ac264a. Full text in Research Archive Show summary

  Semiconductor nanocrystals are often proposed as a viable route to improve solar energy conversion in photovoltaics and photoelectrochemical systems. Embedding the nanocrystals in, e.g. a transparent and conducting electrode of a solar cell will promote the photon absorption and subsequent transfer of the generated charge carriers from the nanocrystal, and thereby enhance the function of the electrode. This can be accomplished by embedding a semiconducting nanocrystal with a small bandgap in a transparent conducting oxide (TCO), which is commonly utilized as electrode in new generation solar cells. Here, we demonstrate the incorporation, formation, and functionalization of germanium (Ge) nanocrystals in zinc oxide utilizing ion implantation, where post implantation annealing at 800 °C results in diamond cubic Ge nanocrystals with sizes between 2 and 20 nm. Photoluminecence spectra show a distinct emission around 0.7 eV arising from the Ge nanocrystals, and with additional emission features up to 1.15 eV due to quantum confinement, demonstrating a novel functionalization and tunability of the TCO electrode.

• Song, Xin; Riis, Henrik; Prytz, Øystein & Finstad, Terje (2021). Metallization of ZnSb and contact resistance. Journal of Applied Physics. ISSN 0021-8979. 130(2). doi: 10.1063/5.0043958. Full text in Research Archive Show summary

  We present results on electrical resistance of metal contacts to ZnSb. We synthesized the thermoelectric semiconductor ZnSb with specific doping concentrations by adding Cu as an acceptor to the melt, followed by solidification, crushing, ball-milling, hot-pressing, sawing, and polishing yielding wafers suitable for substrates for further processing. Many batches were made yielding different doping concentrations. We defined transmission line geometries in deposited metal films for specific contact resistance measurements. We prepared sets of Cu, Ti, and Ni films, respectively. We measured the contact resistance vs annealing temperatures. For Cu/ZnSb samples, we observed a specific contact resistance from 5 × 10−7 to 4 × 10−5 Ω cm2. We also measured the carrier concentration of ZnSb. The measurement data of the specific contact resistance had systematic dependence on doping concentration and annealing temperature and were analyzed by a model incorporating different transport mechanisms across the energy barrier at the metal–semiconductor interface. The data were discussed in terms of systematic variation in barrier height and density of states effective mass. We proposed these arising as a consequence of interactions at the interface and a nonparabolic valence band. We have also monitored the interface of the ZnSb substrate and metal films with transmission electron microscopy.

• Gogova-Petrova, Daniela; Olsen, Vegard Skiftestad; Bazioti, Kalliopi; Lee, In-Hwan; Prytz, Øystein & Vines, Lasse [Show all 7 contributors for this article] (2020). High electron mobility single-crystalline ZnSnN2 on ZnO (0001) substrates. CrysteEngComm. 22(38), p. 6268–6274. doi: 10.1039/d0ce00861c. Full text in Research Archive Show summary

  Making a systematic effort, we have developed single-crystalline ZnSnN2 on ZnO (0001) by reactive magnetron co-sputtering. Epitaxial growth was achieved at 350 °C by co-sputtering from metal targets in a nitrogen atmosphere, and confirmed by transmission electron microscopy (TEM) measurements. TEM verified that the layers are single-crystalline of hexagonal phase, exhibiting an epitaxial relationship with the substrate described by: [11−20]ZnSnN2//[11−20]ZnO and [0001]ZnSnN2//[0001]ZnO. The screw-type threading dislocations originating from the ZnSnN2/ZnO interface were identified as the dominant extended defects. More specifically, we report a pioneering measurement of the dislocation density in this material of 1.5 × 1011 cm−2. Even though there are no literature data for direct comparison, such values are typical of heteroepitaxial growth of III-nitride layers without applying defect density reduction strategies. The films demonstrated a high electron mobility of 39 cm2 V−1 s−1 and 63 cm2 V−1 s−1 for stoichiometric and Zn-rich layers, respectively, while the electron carrier density remained in the low 1019 cm−3 range as determined by the Hall effect measurements at room temperature. Optical bandgaps of 1.86 eV and 1.72 eV were determined for the stoichiometric and Zn-rich samples, respectively. As such, we conclude that ZnSnN2 is an earth-abundant, environmentally-friendly semiconductor and is a promising candidate for cost efficient components in optoelectronics and photovoltaics.

• Smalc-Koziorοwska, Julita; Moneta, J.; Chatzopoulou, P.; Vasileiadis, I.G.; Bazioti, Kalliopi & Prytz, Øystein [Show all 9 contributors for this article] (2020). The heterogeneous nucleation of threading dislocations on partial dislocations in III-nitride epilayers. Scientific Reports. 10. doi: 10.1038/s41598-020-74030-y. Full text in Research Archive Show summary

  Abstract III-nitride compound semiconductors are breakthrough materials regarding device applications. However, their heterostructures suffer from very high threading dislocation (TD) densities that impair several aspects of their performance. The physical mechanisms leading to TD nucleation in these materials are still not fully elucidated. An overlooked but apparently important mechanism is their heterogeneous nucleation on domains of basal stacking faults (BSFs). Based on experimental observations by transmission electron microscopy, we present a concise model of this phenomenon occurring in III-nitride alloy heterostructures. Such domains comprise overlapping intrinsic I 1 BSFs with parallel translation vectors. Overlapping of two BSFs annihilates most of the local elastic strain of their delimiting partial dislocations. What remains combines to yield partial dislocations that are always of screw character. As a result, TD nucleation becomes geometrically necessary, as well as energetically favorable, due to the coexistence of crystallographically equivalent prismatic facets surrounding the BSF domain. The presented model explains all observed BSF domain morphologies, and constitutes a physical mechanism that provides insight regarding dislocation nucleation in wurtzite-structured alloy epilayers.

• Hansen, Per-Anders Stensby; Zikmund, Tomas; Yu, Ting; Kvalvik, Julie Nitsche; Aarholt, Thomas & Prytz, Øystein [Show all 8 contributors for this article] (2020). Single-step approach to sensitized luminescence through bulk-embedded organics in crystalline fluorides. Communications chemistry. 3. doi: 10.1038/s42004-020-00410-0. Full text in Research Archive Show summary

  Abstract Luminescent materials enable warm white LEDs, molecular tagging, enhanced optoelectronics and can improve energy harvesting. With the recent development of multi-step processes like down- and upconversion and the difficulty in sensitizing these, it is clear that optimizing all properties simultaneously is not possible within a single material class. In this work, we have utilized the layer-by-layer approach of atomic layer deposition to combine broad absorption from an aromatic molecule with the high emission yields of crystalline multi-layer lanthanide fluorides in a single-step nanocomposite process. This approach results in complete energy transfer from the organic molecule while providing inorganic fluoride-like lanthanide luminescence. Sm 3+ is easily quenched by organic sensitizers, but in our case we obtain strong fluoride-like Sm 3+ emission sensitized by strong UV absorption of terephthalic acid. This design allows combinations of otherwise incompatible species, both with respect to normally incompatible synthesis requirements and in controlling energy transfer and quenching routes.

• Aarholt, Thomas; Frodason, Ymir Kalmann & Prytz, Øystein (2020). Imaging defect complexes in scanning transmission electron microscopy: Impact of depth, structural relaxation, and temperature investigated by simulations. Ultramicroscopy. ISSN 0304-3991. 209. doi: 10.1016/j.ultramic.2019.112884. Full text in Research Archive
• Øien-Ødegaard, Sigurd; Bazioti, Kalliopi; Redekop, Evgeniy; Prytz, Øystein; Lillerud, Karl Petter & Olsbye, Unni (2020). A toroidal Zr70 oxysulfate cluster and its diverse packing structures. Angewandte Chemie International Edition. ISSN 1433-7851. 59, p. 21397–21402. doi: 10.1002/anie.202010847. Full text in Research Archive Show summary

  Herein, we report the discovery of a toroidal inorganic cluster of zirconium(IV) oxysulfate of unprecedented size with the formula Zr70(SO4)58(O/OH)146⋅x(H2O) (Zr70), which displays different packing of ring units and thus several polymorphic crystal structures. The ring measures over 3 nm across, has an inner cavity of 1 nm and displays a pseudo‐10‐fold rotational symmetry of Zr6 octahedra bridged by an additional Zr in the outer rim of the ring. Depending on the co‐crystallizing species, the rings form various crystalline phases in which the torus units are connected in extended chain and network structures. One phase, in which the ring units are arranged in layers and form one‐dimensional channels, displays high permanent porosity (BET surface area: 241 m2 g−1), and thus demonstrates a functional property for potential use in, for example, adsorption or heterogeneous catalysis.

• Bazioti, Kalliopi; Olsen, Vegard Skiftestad; Kuznetsov, Andrej; Vines, Lasse & Prytz, Øystein (2020). Formation of N2 bubbles along grain boundaries in (ZnO)1−x(GaN)x: nanoscale STEM-EELS studies. Physical Chemistry, Chemical Physics - PCCP. ISSN 1463-9076. 22(7), p. 3779–3783. doi: 10.1039/c9cp06025a. Full text in Research Archive Show summary

  Direct evidence of N2 formation after annealing of (ZnO)1−x(GaN)x alloys was revealed. N2 was trapped by VZn+Ga-clusters, forming faceted voids along grain boundaries. This study shows that N–N bonding is a competitive path for nitrogen after annealing, in addition to the increasing Ga–N bonds, indicating that N in O substitution sites (NO) is not a stable configuration.

• Vasquez, Geraldo Cristian; Bathen, Marianne Etzelmüller; Galeckas, Augustinas; Bazioti, Kalliopi; Johansen, Klaus Magnus H & Maestre, D. [Show all 11 contributors for this article] (2020). Strain Modulation of Si Vacancy Emission from SiC Micro- and Nanoparticles. Nano Letters. ISSN 1530-6984. 20(12), p. 8689–8695. doi: 10.1021/acs.nanolett.0c03472. Full text in Research Archive Show summary

  Single-photon emitting point defects in semiconductors have emerged as strong candidates for future quantum technology devices. In the present work, we exploit crystalline particles to investigate relevant defect localizations, emission shifting, and waveguiding. Specifically, emission from 6H-SiC micro- and nanoparticles ranging from 100 nm to 5 μm in size is collected using cathodoluminescence (CL), and we monitor signals attributed to the Si vacancy (VSi) as a function of its location. Clear shifts in the emission wavelength are found for emitters localized in the particle center and at the edges. By comparing spatial CL maps with strain analysis carried out in transmission electron microscopy, we attribute the emission shifts to compressive strain of 2–3% along the particle a-direction. Thus, embedding VSi qubit defects within SiC nanoparticles offers an interesting and versatile opportunity to tune single-photon emission energies while simultaneously ensuring ease of addressability via a self-assembled SiC nanoparticle matrix.

• Olsen, Vegard Skiftestad; Bazioti, Kalliopi; Baldissera, Gustavo; Azarov, Alexander; Prytz, Øystein & Persson, Clas [Show all 9 contributors for this article] (2019). Effects of Substrate and Post-Deposition Annealing on Structural and Optical Properties of (ZnO)1-x(GaN)x Films. Physica status solidi (b). ISSN 0370-1972. 256(6). doi: 10.1002/pssb.201800529. Full text in Research Archive Show summary

  The structural and optical properties of magnetron sputtered thin films of (ZnO)1−x(GaN)x deposited on zinc oxide, sapphire, and silicon oxide are studied as a function of strain accumulation and post‐deposition anneals at 600–800 °C. For the experimental conditions studied, we found that different amounts of tensile strain accumulated in the samples practically does not affect the strong bandbowing effect, that is, optical bandgap, observed in the as‐deposited alloys. In its turn, post‐deposition annealing results in a reduction of the tensile strain and dislocation density in the films, as measured by both X‐ray diffraction and transmission electron microscopy, corroborating an increase in the crystal quality. In addition, the grain size is found to increase with annealing temperature, for example, mean values of 20 nm up to 50 nm were measured for the alloys with x = 0.15. Meanwhile, the full‐width at half maximum of the (0002) X‐ray diffraction reflection increases with annealing temperature, but with only a small increase in bandgap energies for the x = 0.15 sample. However, this observation was explained combining the experimental data and first‐principles calculations based on density functional theory, showing that the increase in the amount of Ga‐N bonds lowers the total energy of the system. As such, we conclude that the thermal treatments increase the Ga‐N ordering, resulting in several contributions or a widening of the diffraction peaks.

• Hansen, Per-Anders Stensby; Granerød, Cecilie Skjold; Prytz, Øystein & Nilsen, Ola (2019). Controlling luminescence and quenching mechanisms in subnanometer multilayer structure of europium titanate thin films. Journal of Luminescence. ISSN 0022-2313. 215. doi: 10.1016/j.jlumin.2019.116618. Full text in Research Archive Show summary

  We have investigated how layered structures of TiO2 and Eu2O3 on the subnanometer scale control the optical absorption, energy transfer, emission and quenching mechanisms in sensitized lanthanide luminescence systems. By using atomic layer deposition (ALD) as a tool for designing materials with sub nanometer precision, we have been able to make structures ranging from separate (TiO6)8- clusters to bulk TiO2, and series of samples showing transitions from 3D to 2D energy migration. Photoluminescence, excitation and decay measurements have been used alongside transmission electron microscopy (TEM) to investigate how the different structures affect the luminescence. We show that it is possible to drastically suppress concentration quenching compared to solid solutions by designing materials as multilayered structures that confines energy migration in 2D planes. This allows for application of higher concentrations of lanthanides and more defected structures, also enabling use of less pure reactants during synthesis.

• Zhan, Wei; Kosinskiy, Andrey; Vines, Lasse; Johansen, Klaus Magnus H; Carvalho, Patricia Almeida & Prytz, Øystein (2019). ZnCr2O4 Inclusions in ZnO Matrix Investigated by Probe-Corrected STEM-EELS. Materials. 12. doi: 10.3390/ma12060888. Full text in Research Archive Show summary

  The ZnCr2O4/ZnO materials system has a wide range of potential applications, for example, as a photocatalytic material for waste-water treatment and gas sensing. In this study, probe-corrected high-resolution scanning transmission electron microscopy and geometric phase analysis were utilized to study the dislocation structure and strain distribution at the interface between zinc oxide (ZnO) and embedded zinc chromium oxide (ZnCr2O4) particles. Ball-milled and dry-pressed ZnO and chromium oxide (α-Cr2O3) powder formed ZnCr2O4 inclusions in ZnO with size ~400 nm, where the interface properties depended on the interface orientation. In particular, sharp interfaces were observed for ZnO [2 1¯1¯ 3]/ZnCr2O4 [1 1¯ 0] orientations, while ZnO [1 2¯ 10]/ZnCr2O4 [112] orientations revealed an interface over several atomic layers, with a high density of dislocations. Further, monochromated electron energy-loss spectroscopy was employed to map the optical band gap of ZnCr2O4 nanoparticles in the ZnO matrix and their interface, where the average band gap of ZnCr2O4 nanoparticles was measured to be 3.84 ± 0.03 eV, in contrast to 3.22 ± 0.01 eV for the ZnO matrix.

• Sky, Thomas Neset; Johansen, Klaus Magnus H; Frodason, Ymir Kalmann; Aarholt, Thomas; Riise, Heine Nygard & Prytz, Øystein [Show all 8 contributors for this article] (2019). Diffusion of indium in single crystal zinc oxide: a comparison between group III donors. Semiconductor Science and Technology. ISSN 0268-1242. 34(2), p. 1–6. doi: 10.1088/1361-6641/aafa4c. Full text in Research Archive
• Granerød, Cecilie Skjold; Aarseth, Bjørn Lupton; Nguyen, Phuong Dan; Bazioti, Kalliopi; Azarov, Alexander & Svensson, Bengt Gunnar [Show all 8 contributors for this article] (2019). Structural and optical properties of individual Zn2GeO4 particles embedded in ZnO. Nanotechnology. ISSN 0957-4484. 30(22), p. 1–6. doi: 10.1088/1361-6528/ab061c. Full text in Research Archive
• Olsen, Vegard Skiftestad; Baldissera, Gustavo; Zimmermann, Christian; Granerød, Cecilie Skjold; Bazioti, Kalliopi & Galeckas, Augustinas [Show all 11 contributors for this article] (2019). Evidence of defect band mechanism responsible for band gap evolution in (ZnO)1−x(GaN)x alloys. Physical review B (PRB). ISSN 2469-9950. 100(16). doi: 10.1103/PhysRevB.100.165201. Full text in Research Archive Show summary

  It is known that (ZnO)1−x(GaN)x alloys demonstrate remarkable energy band bowing, making the material absorb in the visible range, in spite of the binary components being classical wide band gap semiconductors. However, the origin of this bowing is not settled; two major mechanisms are under debate: Influence of the orbital repulsion and/or formation of a defect band. In the present work, we applied a combination of the absorption and emission measurements on the samples exhibiting an outstanding nanoscale level of (ZnO)1−x(GaN)x homogeneity as monitored by the high resolution electron microscopy equipped with the energy dispersive x-ray analysis and the electron energy loss spectroscopy; moreover the experimental data were set in the context of the computational analysis of the alloys employing density functional theory and quasiparticle GW approximation. A prominent discrepancy in the band gap values as deduced from the absorption and emission experiments was observed systematically for the alloys with different compositions and interpreted as evidence for the absorption gap shrinking due to the defect band formation. Computational data support the argument, revealing only minor variations in the bulk of the conduction and valence band structures of the alloys, except for a characteristic “tail” in the vicinity of the valence band maximum. As such, we conclude that the energy gap bowing in (ZnO)1−x(GaN)x alloys is due to the defect band formation, presumably at the top of the valence band maximum.

• Liu, Xin; Bjørheim, Tor Svendsen; Vines, Lasse; Fjellvåg, Øystein; Granerød, Cecilie Skjold & Prytz, Øystein [Show all 10 contributors for this article] (2019). Highly Correlated Hydride Ion Tracer Diffusion in SrTiO3–xHx Oxyhydrides. Journal of the American Chemical Society. ISSN 0002-7863. 141(11), p. 4653–4659. doi: 10.1021/jacs.8b12985. Full text in Research Archive Show summary

  Mixed oxide hydride anion systems constitute a novel class of materials exhibiting intriguing properties such as solid-state hydride ion conduction and fast anion exchange. In this contribution we derive the kinetics of hydride ion transport in a mixed oxide–hydride system, SrTiO3–xHx, through isotope exchange and depth profiling. Density functional theory (DFT) calculations indicate that migration of H– to neighboring vacant oxygen lattice sites is fast, but that long-range transport is impeded by slow reorganization of the oxygen sublattice. From measured hydride tracer-diffusion coefficients and the correlation factors derived from DFT, we are able to derive the hydrogen self-diffusion coefficients in SrTiO3–xHx. More generally, the explicit description of hydride ion transport in SrTiO3–xHx through combination of experimental and computational methods reported in this work can be applied to explore anion diffusion in other mixed anion systems.

• Birenis, Domas; Ogawa, Yuhei; Matsunaga, Hisao; Takakuwa, Osamu; Yamabe, Junichiro & Prytz, Øystein [Show all 7 contributors for this article] (2019). Hydrogen-assisted crack propagation in α-iron during elasto-plastic fracture toughness tests. Materials Science & Engineering: A. ISSN 0921-5093. 756, p. 396–404. doi: 10.1016/j.msea.2019.04.084. Full text in Research Archive Show summary

  Elasto-plastic fracture toughness tests of a commercially pure iron were performed in air and in hydrogen gas at two different pressures. Some unique characteristics of hydrogen-enhanced cracking were exhibited at both the macroscopic and microscopic length scales, based on the observation of fracture surface, fracture plane, plasticity distribution and dislocation structure. The possible mechanisms responsible for the hydrogen-induced degradation of fracture toughness are discussed.

• Bondevik, Tarjei; Ness, Heine Håland; Bazioti, Kalliopi; Norby, Truls Eivind; Løvvik, Ole Martin & Koch, Christoph T. [Show all 7 contributors for this article] (2019). Investigation of the electrostatic potential of a grain boundary in Y-substituted BaZrO3 using inline electron holography. Physical Chemistry, Chemical Physics - PCCP. ISSN 1463-9076. 21(32), p. 17662–17672. doi: 10.1039/c9cp02676b. Full text in Research Archive Show summary

  We apply inline electron holography to investigate the electrostatic potential across an individual BaZr0.9Y0.1O3 grain boundary. With holography, we measure a grain boundary potential of −1.3 V. Electron energy loss spectroscopy analyses indicate that barium vacancies at the grain boundary are the main contributors to the potential well in this sample. Furthermore, geometric phase analysis and density functional theory calculations suggest that reduced atomic density at the grain boundary also contributes to the experimentally measured potential well.

• Bazioti, Kalliopi; Azarov, Alexander; Johansen, Klaus Magnus H; Svensson, Bengt Gunnar; Vines, Lasse & Kuznetsov, Andrej [Show all 7 contributors for this article] (2019). Role of Nitrogen in Defect Evolution in Zinc Oxide: STEM−EELS Nanoscale Investigations. The Journal of Physical Chemistry Letters. 10(16), p. 4725–4730. doi: 10.1021/acs.jpclett.9b01472. Full text in Research Archive Show summary

  Direct evidence of the formation of nitrogen molecules (N2) after ion implantion of ZnO has been revealed by an atomically resolved scanning transmission electron microscopy (STEM)–electron energy-loss spectroscopy (EELS) investigation. Taking advantage of the possibility of using multiple detectors simultaneously in aberration-corrected STEM, we utilize the detailed correlation between the atomic structure and chemical identification to develop a model explaining the formation and evolution of different defect types and their interaction with N. In particular, the formation of zinc vacancy (VZn) clusters filled with N2 after heat treatment at 650 °C was observed, clearly indicating that N has not been stabilized in the O substitution site, thus limiting p-type doping. Previous results showing an exceptional thermal stability of vacancy clusters only for the case of N-doped ZnO are supported. Furthermore, VZn–N2 stabilization leads to suppression of VZn–Zni recombination; hence, the highly mobile Zn interstitials preferentially condense on the basal planes promoting formation of extended defects (basal stacking faults and stacking mismatched boundaries). The terminations of these defects provide energetically favorable sites for further N2 trapping as a way to reduce local strain fields.

• Zhan, Wei; Venkatachalapathy, Vishnukanthan; Aarholt, Thomas; Kuznetsov, Andrej & Prytz, Øystein (2018). Band gap maps beyond the delocalization limit: correlation between optical band gaps and plasmon energies at the nanoscale. Scientific Reports. 8(848), p. 1–7. doi: 10.1038/s41598-017-18949-9. Full text in Research Archive Show summary

  Recent progresses in nanoscale semiconductor technology have heightened the need for measurements of band gaps with high spatial resolution. Band gap mapping can be performed through a combination of probe-corrected scanning transmission electron microscopy (STEM) and monochromated electron energy-loss spectroscopy (EELS), but are rare owing to the complexity of the experiments and the data analysis. Furthermore, although this method is far superior in terms of spatial resolution to any other techniques, it is still fundamentally resolution-limited due to inelastic delocalization of the EELS signal. In this work we have established a quantitative correlation between optical band gaps and plasmon energies using the Zn1−xCd x O/ZnO system as an example, thereby side-stepping the fundamental resolution limits of band gap measurements, and providing a simple and convenient approach to achieve band gap maps with unprecedented spatial resolution.

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• Bazioti, Kalliopi; Azarov, Alexander; Vines, Lasse; Prytz, Øystein & Kuznetsov, Andrej (2026). Fundamental insights into polymorphism and defect evolution in ion-irradiated semiconductors by employing atomic-scale Transmission Electron Microscopy. Full text in Research Archive
• 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. Full text in Research Archive
• Fernandez, Javier Garcia; Montag, S.; Splith, D.; Kneiß, M.; Grundmann, M. & Prytz, Øystein [Show all 7 contributors for this article] (2024). Combinatorial PLD Synthesis of (In1−xGax)2O3 Thin Films: Structural, Morphological, and Optical Analysis for Transparent Conducting Oxides. Full text in Research Archive
• Fernandez, Javier Garcia; Kjeldby, Snorre Braathen; Zeng, L. J.; Olsson, E.; Vines, Lasse & Prytz, Øystein (2024). Structural Transformation in Ge+ Implanted β-Ga2O3: Functionalization with Ge Nanoparticles leading to 'Emmental-type' Nano-architecture. Full text in Research Archive
• Fernandez, Javier Garcia; Montag, S.; Andreassen, Magnus; Pokle, Anuj; Splith, D. & Kneiß, M. [Show all 9 contributors for this article] (2024). Probing, microstructure, crystallization and phase segregation in (In1-xGax)2O3 thin films by TEM. Full text in Research Archive
• Holmestad, Randi; Gunnæs, Anette Eleonora; Nord, Magnus; Hage, Fredrik Sydow; Hansen, Vidar Folke & Prytz, Øystein [Show all 7 contributors for this article] (2024). Electron diffraction in physical science in Norway – past, present, and future. Full text in Research Archive
• Kjeldby, Snorre Braathen; Fernandez, Javier Garcia; Galeckas, Augustinas; Jensen, Ingvild Julie Thue; Prytz, Øystein & Vines, Lasse (2024). Cross-sectional cathodoluminescence measurements in implanted and annealed gallium oxide. Full text in Research Archive
• Fernandez, Javier Garcia; Kjeldby, Snorre Braathen; Nguyen, Phuong Dan; Haug, Kristian; Galeckas, Augustinas & Jensen, Ingvild Julie Thue [Show all 9 contributors for this article] (2023). Optical properties and structure relationship in ZnO:Fe with inversion domain boundaries and ZnFe2O4/ZnO heterostructures. Full text in Research Archive
• Fernandez, Javier Garcia; Kjeldby, Snorre Braathen; Azarov, Alexander; Pokle, Anuj; Nguyen, Phuong Dan & Vines, Lasse [Show all 8 contributors for this article] (2023). Polymorph engineering and radiation tolerance in β-Ga2O3. Full text in Research Archive
• 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)). Full text in Research Archive
• Elgvin, Cana; Leon, Dario A.; Hage, Fredrik Sydow; Nguyen, Phuong Dan; Berland, Kristian & Prytz, Øystein (2023). The effects of heavy doping on the band structure of zinc oxide obѕerνed using momentum-resolved EELS. Full text in Research Archive
• Elgvin, Cana; Leon, Dario A.; Hage, Fredrik Sydow; Nguyen, Phuong Dan; Berland, Kristian & Prytz, Øystein (2023). Anisotropy and nature of electronic excitations using ωq-mapping and ab initio calculations. Full text in Research Archive
• Kjeldby, Snorre Braathen; Fernández, Javier García; Nguyen, Phuong Dan; Prytz, Øystein & Vines, Lasse (2023). Implantation for polymorphic transformation in Ga2O3: thermal evolution and luminescence. Full text in Research Archive Show summary

  Dette foredraget presenterer ioneimplantasjonindusert fasetransformasjon i galliumoksid, Ga2O3, fra beta-fasen til gamma-fasen. Den siste tiden har det vært utbredt vitenskaplig interesse i denne transformasjonen, som, basert på tilgjengelige data, ser ut til å være uavhengig av det implanterte speciet. Utover å presentere forsøk som fastslår den termiske stabiliteten til gamma-fasen, opp til 500 eller 700 grader Celsius avhengig av implantasjonsparametre, presenterer vi her også de første luminesensmålingene på slike prøver med høy romlig oppløsning, hovedsaklig fra prøver implantert med germanium, med støttende resultater fra nikkelimplanterte prøver. Både intrinsisk luminesens, fra selvlokaliserte hull og intrinsiske defekter, og ekstrinsisk luminesens fra krom ble studert. Foredraget bidrar til å klargjøre ikke bare strukturen men også egenskapene til fasetransformerte lag i galliumoksid fra ioneimplantasjon.

• Fernandez, Javier Garcia; Kjeldby, Snorre Braathen; Nguyen, Phuong Dan; Haug, Kristian; Galeckas, Augustinas & Jensen, Ingvild Julie Thue [Show all 9 contributors for this article] (2022). Structural and optical investigation of Fe-ZnO nanoarchitectures: from inversion domain boundaries to ZnO/ZnFe2O4 heterostructure. Full text in Research Archive
• 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. Full text in Research Archive
• Kang, Xiaolan; Reinertsen, Vilde Mari; Both, Kevin Gregor; Galeckas, Augustinas; Aarholt, Thomas & Prytz, Øystein [Show all 9 contributors for this article] (2022). Galvanic restructuring of exsolved nanoparticles for plasmonic and electrocatalytic energy conversion. Full text in Research Archive
• Kang, Xiaolan; Reinertsen, Vilde Mari; Both, Kevin Gregor; Galeckas, Augustinas; Aarholt, Thomas & Prytz, Øystein [Show all 9 contributors for this article] (2022). Galvanic Restructuring of Exsolved Nanoparticles for Plasmonic and Electrocatalytic Energy Conversion (Small 29/2022 Inside back cover feature). 18(29), p. 2270156–2270156. Full text in Research Archive
• Kang, Xiaolan; Reinertsen, Vilde Mari; Both, Kevin Gregor; Galeckas, Augustinas; Aarholt, Thomas & Prytz, Øystein [Show all 9 contributors for this article] (2022). Exsolved nanoparticles, galvanically restructured for tunable photo-electrocatalytic energy conversion. Full text in Research Archive
• Elgvin, Cana; Kjeldby, Snorre Braathen; Both, Kevin Gregor; Nguyen, Phuong Dan & Prytz, Øystein (2022). Optical Properties of Zinc Ferrite Nanoparticles Embedded in Zinc Oxide Thin Films Investigated by STEM, EELS and CL. Full text in Research Archive
• Both, Kevin Gregor; Reinertsen, Vilde Mari; Kang, Xiaolan; Aarholt, Thomas; Neagu, Dragos & Prytz, Øystein [Show all 8 contributors for this article] (2022). Improved Photoelectrochemical Performance of SrTiO3 by Plasmonically Active Au Nanoparticles. Full text in Research Archive
• Both, Kevin Gregor; Reinertsen, Vilde Mari; Kang, Xiaolan; Neagu, Dragos; Prytz, Øystein & Norby, Truls [Show all 7 contributors for this article] (2022). Thin Film Exsolution of Metal Nanoparticles and Their Galvanic Restructuring for Plasmonically Enhanced Photocatalytic Activity. Full text in Research Archive
• Kjeldby, Snorre Braathen; Azarov, Alexander; Nguyen, Phuong Dan; Venkatachalapathy, Vishnukanthan; Mikšová, Romana & Macková, Anna [Show all 10 contributors for this article] (2022). Structural Transformation of β-Ga2O3 through Si-implantation. Full text in Research Archive
• Kjeldby, Snorre Braathen; Nguyen, Phuong Dan; Fernandez, Javier Garcia; Haug, Kristian; Galeckas, Augustinas & Jensen, Ingvild Julie Thue [Show all 9 contributors for this article] (2022). Optical properties of Fe-decorated inversion domain boundaries and embedded spinel zinc ferrite nanoparticles in zinc oxide. Full text in Research Archive
• Kjeldby, Snorre Braathen; Azarov, Alexander; Nguyen, Phuong Dan; Fernandez, Javier Garcia; Venkatachalapathy, Vishnukanthan & Mikšová, Romana [Show all 10 contributors for this article] (2022). Structure and luminescence properties of Si-implanted β-Ga2O3. Full text in Research Archive
• Aarholt, Thomas; Both, Kevin Gregor; Reinertsen, Vilde Mari & Prytz, Øystein (2021). Surface plasmon investigations by STEM-EELS mapping of Au/Ni nanoparticles on STO. Full text in Research Archive Show summary

  Metallic nanoparticles have traditionally had sharp absorption peaks between 1 and 5 eV due to the excitation of surface plasmons. Localized surface plasmon resonance (LSPR) is the coherent oscillation of quasi-free electrons excited by the electromagnetic fields of a photon or fast electron1,2. Since the absorption peak energies are in the range of visible light, surface plasmons present a potential pathway for absorbing energy to drive photoelectrochemical reactions or contribute to photovoltaic applications. For driving photoelectrochemical reactions, one difficulty is placing photoactive nanoparticles near the catalyst responsible for a chosen reaction, for example, water splitting. The ideal semiconductor for water splitting has a bandgap of 1.9 – 2.3 eV, although semiconductors in this range are seldom stable during photocatalytic water splitting3. Utilizing plasmonics in wide bandgap semiconductors is a promising alternative, avoiding the stability issue3. In this work, we present a STEM-EELS study of Au nanoparticles created by galvanic replacement of Ni nanoparticles grown by exsolution of a PLD-deposited thin-film of A-site excess strontium titanate (Sr1.07Ti 0.93Ni0.07O 3-δ) (STO). STO is an indirect, wide bandgap (3.2 eV) perovskite, studied as a promising photocatalyst for water splitting 4. Ni can easily substitute the Ti in the STO, making it a suitable candidate for exsolution, while Au cannot substitute Ti5. Simultaneously, Ni nanoparticles barely show any plasmonic activities, while Au particles are second only to Ag nanoparticles6. The presented manufacturing technique results in nanoparticles of gold and nickel freestanding, but socketed, on the surface and embedded in the bulk, with diameters between 50 and 100 nm, which are well-suited for plasmonic applications. As a starting point, STEM-EELS was performed with a monochromated 300kV STEM probe with ZeroLoss Peak (ZLP) full-width at half-maximum of 110 meV on an FEI Titan G2. A peculiarly shaped gold nanocluster was studied. After removing the ZLP, the spectrum image was linearly fitted with Gaussians centered at 1.46, 1.95, and 2.40 eV. The 2.40 eV peak is a well-known Au surface plasmon, whereas the remaining two are investigated in conjunction with modeling approaches. An RGB composite of the fit results can be seen in figure 1. Spectra extracted from the coloured regions can be seen in figure 2.

• Kjeldby, Snorre Braathen; Azarov, Alexander; Aarholt, Thomas; Prytz, Øystein & Vines, Lasse (2021). Defect-annealing in Si+-implanted β-Ga2O3. Full text in Research Archive
• Kjeldby, Snorre Braathen; Nguyen, Phuong Dan; Haug, Kristian; Galeckas, Augustinas; Jensen, Ingvild Julie Thue & Thøgersen, Annett [Show all 8 contributors for this article] (2021). EELS and SEM-CL investigations of ZnFe2O4 nanoparticles and iron-decorated inversion domain boundaries in bulk ZnO. Full text in Research Archive
• Elgvin, Cana; Nguyen, Phuong Dan; Both, Kevin Gregor; Vines, Lasse & Prytz, Øystein (2021). Crystallographically oriented ZnFe2O4 nanoparticles in ZnO thin films. Full text in Research Archive
• Bazioti, Kalliopi; Olsen, Vegard Skiftestad; Azarov, Alexander; Johansen, Klaus Magnus H; Kuznetsov, Andrej & Vines, Lasse [Show all 7 contributors for this article] (2021). Thermal evolution of point and extended defects in N-implanted ZnO and (ZnO)1−x(GaN)x thin films: STEM-EELS investigations. Full text in Research Archive
• Thøgersen, Annett; Diplas, Spyridon; Michel, Kathrin; Bjørheim, Tor Svendsen; Prytz, Øystein & Norby, Truls Eivind (2020). The surface of CeO2 unravelled. Full text in Research Archive
• Bazioti, Kalliopi; Olsen, Vegard Skiftestad; Azarov, Alexander; Johansen, Klaus Magnus H; Svensson, Bengt Gunnar & Kuznetsov, Andrej [Show all 8 contributors for this article] (2020). Role of nitrogren in defect evolution in ZnO and (ZnO)₁−ₓ(GaN)ₓ: STEM-EELS nanoscale investigations. Full text in Research Archive
• Ulvestad, Asbjørn; Koposov, Alexey; Skare, Marte Orderud; Preston, Thomas; Prytz, Øystein & Mæhlen, Jan Petter [Show all 7 contributors for this article] (2019). Amorphous Silicon Nitride-an Anode Material for the Next Generation Li-Ion Batteries. Full text in Research Archive
• Song, Xin; Riis, Henrik; Prytz, Øystein & Finstad, Terje (2019). Metallization of selected transition metals on ZnSb by electron beam thermal evaporation. Full text in Research Archive Show summary

  The thermoelectric module made by ZnSb can be dated back to 1870, even if the performance was considerable low by today’s standard [1]. In recent decades, both the electrical properties and thermal properties of the material have been improved, attributed to introducing proper doping/co-doping and nanostructuring [2]. The figure of merit of ZnSb has been reported close to 1 or even above in a few studies [3], which is considered to be a material with a possible decent thermoelectric performance. In this study, we focus on the electrical contact resistance between ZnSb and metal contact, i.e the metallization of ZnSb. This is a step forward from optimized thermoelectric material to a useful thermoelectric device. For thermoelectric devices, ohmic contact is mostly wanted. In theory, ohmic contacts are derived from Schottly contacts and is dependent on the work function between semiconductor and metal, and doping concentration; while in reality, many other factors can have significant impacts on function and performance, for instance interface defects, adhesion, thermal expansion between semiconductor and metal, inter-diffusion and oxidation. The scope of this work is to test the method for metallization and understand the transport at the contact. In addition, we verified the methodology for measuring contact resistance and estimated the experimental uncertainties. We selected several transition metals that are often used as electrical contact for semiconductor devices. The substrates, i.e. ZnSb with various doping concentration, have been synthesized by the hot-pressing method and prepared by the standard procedure for wafer preparation. We deposited the metal with electron beam thermal evaporation, following post-annealing at different temperatures. The structure at interface was investigated by Transmission Electron Microscopy (TEM). The contact resistance and semiconductor resistivity were extrapolated from transmission line measurements of samples subjected to different post-annealing. We compared the measurements with the idealized models combining thermionic emission, thermionic filed emission and tunneling. Although this model is an idealization, it can provide a guide for further detailed study.

• Nguyen, Phuong Dan; Granerød, Cecilie Skjold; Aarseth, Bjørn Lupton; Bazioti, Kalliopi; Azarov, Alexander & Svensson, Bengt Gunnar [Show all 8 contributors for this article] (2019). Structural and optical properties of individual Zn2GeO4 particles embedded in ZnO. Full text in Research Archive
• Haug, Kristian; Nguyen, Phuong Dan; Karlsen, Ole Bjørn; Aarholt, Thomas; Bazioti, Kalliopi & Prytz, Øystein (2019). Zinc ferrite spinel embedded in ZnO matrix for solar applications. Full text in Research Archive
• Vasquez, Geraldo Cristian; Bazioti, Kalliopi; Galeckas, Augustinas; Johansen, Klaus Magnus H; Granerød, Cecilie Skjold & Nguyen, Phuong Dan [Show all 8 contributors for this article] (2019). Luminescent properties of Zn2GeO4 nanoparticles embedded in ZnO. Full text in Research Archive
• Aarholt, Thomas; Frodason, Ymir Kalmann & Prytz, Øystein (2019). The impact of local relaxation on defect-complex STEM contrast. Full text in Research Archive
• Bazioti, Kalliopi; Olsen, Vegard Skiftestad; Azarov, Alexander; Kuznetsov, Andrej; Vines, Lasse & Prytz, Øystein (2019). Defect formation and thermal evolution in ZnO-based structures (Highlight talk). Full text in Research Archive
• Bondevik, Tarjei; Prytz, Øystein & Norby, Truls Eivind (2019). Investigation of the electrostatic potential of a grain boundary in Y-substituted BaZrO3 using inline electron holography. Full text in Research Archive
• Bazioti, Kalliopi; Olsen, Vegard Skiftestad; Alexander, Azarov; Kuznetsov, Andrej; Vines, Lasse & Prytz, Øystein (2019). STEM-EELS investigation of defect formation and thermal evolution in ZnO. Full text in Research Archive
• Bazioti, Kalliopi; Olsen, Vegard Skiftestad; Johansen, Klaus Magnus H; Azarov, Alexander; Kuznetsov, Andrej & Vines, Lasse [Show all 7 contributors for this article] (2019). Transmission Electron Microscopy methods for atomic-scale investigations of semiconductor properties. Full text in Research Archive
• Bazioti, Kalliopi; Granerød, Cecilie Skjold; Olsen, Vegard Skiftestad; Vines, Lasse; Svensson, Bengt Gunnar & Prytz, Øystein (2018). (ZnO)1-X(GaN)X thin films studied by high-resolution structural and spectroscopic imaging. Full text in Research Archive
• Bazioti, Kalliopi; Azarov, Alexander; Svensson, Bengt Gunnar & Prytz, Øystein (2018). An aberration-corrected (S)TEM study of N-induced defects in ZnO: formation and thermal evolution. Full text in Research Archive
• Riis, Henrik; Song, Xin; Prytz, Øystein & Finstad, Terje (2018). Characterization of Cu/ZnSb interfaces. Full text in Research Archive
• Jones, Ella Randmæl; Prytz, Øystein; Vines, Lasse; Elgvin, Cana & Both, Kevin Gregor (2024). Pulsed laser deposition synthesis of ZnFe2O4 nanostructures embedded in a ZnO thin film for tandem solar cells. University of Oslo, Department of Physics. Full text in Research Archive
• Kjeldby, Snorre Braathen; Vines, Lasse & Prytz, Øystein (2024). Polymorph transformations, nanoparticles, and luminescence in ion-implanted gallium oxide. Universitetet i Oslo. Full text in Research Archive Show summary

  Gallium oxide is a promising ultra wide band gap semiconductor for applications in power electronics, photodetectors, and as a transparent host material or electrical conductor. Ion implantation is a technique used to tailor the properties of semiconductors. For further technological development of gallium oxide, it is therefore essential to understand how the material is affected by ion implantation. Crystalline materials typically lose their crystal structure after high-dose ion implantation, while gallium oxide instead transforms to a different crystal structure. In this thesis, we investigate the transformation, and show that initially monoclinic gallium oxide transforms to the defective spinel polymorph. The results reveal that the polymorph transformation is independent of the implanted species and is caused by the implantation-induced defect formation, rather than the chemistry of the implanted ions. Further, the transformation can be reversed through heat treatments. The work also reveals that germanium and silicon dioxide nanoparticles can be embedded in gallium oxide with ion implantation followed by annealing. The luminescence from implanted and annealed gallium oxide, including Cr-related luminescence, has been probed with high spatial resolution. These results advance the understanding of polymorph transformations from ion implantation and elucidate several important aspects of ion implantation in gallium oxide

• Nguyen, Hao Pierre Quoc & Prytz, Øystein (2023). Structural and Chemical Characterization of ZnGe_xSn_(1-x)N_2 for Solar Cell Applications. Universitetet i Oslo. Full text in Research Archive Show summary

  Nitride semiconductors possess a variety of properties, such as a high dielectric breakdown voltage and bandgap energies ranging from ultraviolet to infrared, favorable for scientific development and application in efficient tandem solar cells. The ideal bandgap for top cells has been calculated to be ∼ 1.75 eV in combination with Si bottom cells, in a two-terminal device. However, some challenges related to materials phase separation and lattice mismatch, as well as cost barriers related to the choice of rare materials and initial growth process, pose problems for consumer implementation. Thin films of ZnGexSn1−xN2 (where x = 0, 0.428 or 0.736) were grown on P:ZnO by reactive co-sputtering of metallic Zn, Sn and Ge targets employing high-power impulse magnetron sputtering (HiPIMS) and conventional RF sputtering. These materials were selected due to their earth-abundance and non-toxic properties. Structural properties were characterized by electron diffraction (ED) and chemical properties were analyzed with energy dispersive X-ray spectroscopy (EDS), both in transmission electron microscopy (TEM). In the present work, high resolution TEM and ED were used in combination to study the atomic structure and strain effects of thin films, which were grown along the [001] direction, perpendicular to the surface of the substrate, and a higher applied Ge target power predictably yields a higher Ge incorporation. A higher Ge content in the alloy is found to produce a more polycrystalline structure, in comparison to pristine ZnSnN2. Additionally, ED indicates that the film structure without Ge has a significant lattice mismatch with the ZnO substrate (a = (0.336 ± 0.004) nm for ZnSnN2, a = (0.319 ± 0.001) nm for ZnO, mismatch ∼ 5.3%) and the induced strain is relaxed through formation of misfit dislocations. In contrast, films with higher Ge incorporation (a = (0.328 ± 0.005) nm for x = 0.74, a = (0.331 ± 0.005) nm for x = 0.43) exhibit a better lattice matching with the substrate (a = (0.326 ± 0.001) nm for ZnO, mismatch ∼ 0.6% and ∼ 1.2% respectively).

• Both, Kevin Gregor; Chatzitakis, Athanasios; Bergum, Kristin; Hansen, Per-Anders Stensby; Prytz, Øystein & Norby, Truls (2023). Plasmonically Enhanced Photocatalysis: Synthesis, Physical Properties, and Applications. Universitetet i Oslo. Full text in Research Archive Show summary

  In this work, plasmonic metal nanoparticles (MNPs) are utilized to improve the photoelectrochemical (PEC) response of strontium titanate (STO). These MNPs were introduced by either direct exsolution, i.e., nickel (Ni), copper (Cu), iron (Fe), ruthenium (Ru), and silver (Ag), or by galvanically replacing exsolved less noble MNPs, i.e., Ni by Gold (Au), or Cu for Ag. Au, Ag, and Cu were the materials chosen with significant plasmonic activity; Fe, Ru, Pt, and Ni were used to make MNPs with minimal plasmonic response. Two different stoichiometries of STO were synthesized. One, La-doped A-site deficient STO (La0.6Sr0.2Ti0.9Ni0.1O3–x), was exclusively doped with Ni and utilized as powder samples. The other stoichiometry was A-site excess STO (Sr1.07Ti0.93M0.07O3±δ, where M is the dopant) was doped with various metals. These excess perovskites were studied in thin film and powder forms. A-site excess STO thin films were deposited by pulsed laser deposition on silicon substrates. The as-deposited thin films appeared nanocrystalline or amorphous until the exsolution process was engaged. The exsolution step was studied explicitly for these A-site excess STO thin films where the formation of MNPs occurred not only at or near the thin film surface but also on grain interfaces and in bulk. Moreover, the dopant diffused significantly during the process. While the size of the template particles depended on the exsolution conditions, the galvanic replacement reaction determined the shapes and sizes of the newly formed MNPs. The replacement time and the form (thin film/powder) of STO influenced the results, both completely replaced particles and partially replaced particles with complex structures were obtained. Additionally, more prolonged galvanic replacement reactions lead to larger particles. In turn, the specific shape of the plasmonic MNPs determined the localized surface plasmon resonance band shape and peak position. Overall, exsolution leads to well-socketed MNPs, a property seemingly inherited by the MNPs created by galvanic replacement. Well-socketed MNPs are extremely difficult to obtain by any other technique and have a favorable localized surface plasmon resonance peak shift. The PEC response revealed that reducing STO first decreases the material’s response. Reducing it further, however, increases the PEC response significantly. Au MNPs increase the PEC performance until the MNPs reach a specific size and subsequently decrease the PEC performance when growing more prominent. This work highlights the ease by which well-socketed plasmonic MNPs can be created, some impossible to synthesize by another technique, and how different reaction conditions can change the shape and size of the MNPs, ultimately tuning the localized surface plasmon resonance band shape and peak position. The method of exsolution and galvanic replacement reaction was generalized by utilizing different elements, implying that the tuning of catalytic activity depends on the choice of elements and reaction conditions.

• Vikne, Martin Schønning; Prytz, Øystein; Nguyen, Phuong Dan & Bergum, Kristin (2022). TEM Characterization of ZnOxNy for Tandem Solar Cell Applications. Universitetet i Oslo. Full text in Research Archive
• Bergli, Jørgen; Prytz, Øystein; Nguyen, Phuong Dan & Karlsen, Ole Bjørn (2021). Solid state precipitation of spinels in zinc oxide - A microstructure study. Universitetet i Oslo. Full text in Research Archive Show summary

  In this work we have investigated the possibility for solid state precipitation of spinel crystals in zinc oxide by separate addition of three different dopant elements. These dopant elements were iron, antimony and vanadium, and were generally introduced as oxide powders. The dopant compounds were mixed with zinc oxide using a powder synthesis route, where the annealing temperature was mostly kept below the solidus temperature in the given system. Some experiments were also performed using a single crystal of zinc oxide embedded in iron oxide and zinc oxide powders. These samples are referred to as diffusion couples. The characterization of samples was carried out by adopting several observation methods. That is light microscopy, x-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy, transmission electron microscopy and scanning transmission electron microscopy. This variety of methods enabled complementary information to be obtained. It was found that the zinc oxide – iron system displays the most promising features in regard to precipitating spinels crystals in the zinc oxide matrix. This property is attributed to a highly temperature dependent solid solubility of iron in zinc oxide. Observations made in this system indicate that two different spinel forming mechanisms are possible. One includes a high solute iron concentration in zinc oxide and consequently precipitation during cooling of the sample. In the other route a second annealing step is added to promote the precipitation from a somewhat low iron concentration in the zinc oxide matrix. The physical appearance of the precipitates was different depending on precipitation route, however the same orientation relationship with adjacent zinc oxide grains/matrix was found for both spinel precipitates. In addition, iron rich inversion domain boundaries were seen in the single crystal. These were explored, and it was found that the spacing between the domains matched the iron concentration profile in the same region. The transition from inversion domain boundaries to spinel grains was probed to understand nucleation mechanisms for both features. In the two other systems, antimony and vanadium doped zinc oxide, no precipitations were found. However, it was found that zinc oxide had low and more or less constant solid solubility when temperature was varied in these systems, which is assumed to be a determining factor in limiting the possibility for precipitations. Therefore, attempts were done in the zinc oxide – vanadium system to increase the solubility. However, despite interesting synthesis development, we were not able to increase the solid solubility. In the zinc oxide – antimony system we show that etching of surfaces could be a way to render inversion domain boundaries visible in scanning electron microscopes. We also confirm the volatility of antimony by the use of x-ray diffraction and energy dispersible spectroscopy.

• Elgvin, Cana & Prytz, Øystein (2021). Characterization and optical properties of ZnFe2O4 nanoparticles in ZnO thin films - A (S)TEM study. Universitetet i Oslo. Full text in Research Archive
• Bergli, Jørgen & Prytz, Øystein (2021). Solid state precipitation of spinels in zinc oxide - A microstructure study. Universitetet i Oslo. Full text in Research Archive Show summary

  In this work we have investigated the possibility for solid state precipitation of spinel crystals in zinc oxide by separate addition of three different dopant elements. These dopant elements were iron, antimony and vanadium, and were generally introduced as oxide powders. The dopant compounds were mixed with zinc oxide using a powder synthesis route, where the annealing temperature was mostly kept below the solidus temperature in the given system. Some experiments were also performed using a single crystal of zinc oxide embedded in iron oxide and zinc oxide powders. These samples are referred to as diffusion couples. The characterization of samples was carried out by adopting several observation methods. That is light microscopy, x-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy, transmission electron microscopy and scanning transmission electron microscopy. This variety of methods enabled complementary information to be obtained. It was found that the zinc oxide – iron system displays the most promising features in regard to precipitating spinels crystals in the zinc oxide matrix. This property is attributed to a highly temperature dependent solid solubility of iron in zinc oxide. Observations made in this system indicate that two different spinel forming mechanisms are possible. One includes a high solute iron concentration in zinc oxide and consequently precipitation during cooling of the sample. In the other route a second annealing step is added to promote the precipitation from a somewhat low iron concentration in the zinc oxide matrix. The physical appearance of the precipitates was different depending on precipitation route, however the same orientation relationship with adjacent zinc oxide grains/matrix was found for both spinel precipitates. In addition, iron rich inversion domain boundaries were seen in the single crystal. These were explored, and it was found that the spacing between the domains matched the iron concentration profile in the same region. The transition from inversion domain boundaries to spinel grains was probed to understand nucleation mechanisms for both features. In the two other systems, antimony and vanadium doped zinc oxide, no precipitations were found. However, it was found that zinc oxide had low and more or less constant solid solubility when temperature was varied in these systems, which is assumed to be a determining factor in limiting the possibility for precipitations. Therefore, attempts were done in the zinc oxide – vanadium system to increase the solubility. However, despite interesting synthesis development, we were not able to increase the solid solubility. In the zinc oxide – antimony system we show that etching of surfaces could be a way to render inversion domain boundaries visible in scanning electron microscopes. We also confirm the volatility of antimony by the use of x-ray diffraction and energy dispersible spectroscopy.

• Kiste, Mikael Bergedalen & Prytz, Øystein (2020). Characterization of electrical properties in ZnO and SiC; A study of semiconductor band structure by automating procedures in a Transmission Electron Microscope. Universitetet i Oslo. Full text in Research Archive
• Musland, Lars; Flage-Larsen, Espen; Prytz, Øystein & Bergli, Joakim (2019). Theory and calculations of thermoelectric transport in heterostructures. Universitetet i Oslo. Full text in Research Archive
• Haug, Kristian & Prytz, Øystein (2019). Functionalization of transparent conducting oxides. Zinc ferrite spinel in ZnO. Universitetet i Oslo. Full text in Research Archive
• Prytz, Øystein; Flage-Larsen, Espen & Bilden, Sindre Rannem (2018). Simulation of momentum resolved Electron Energy Loss Spectroscopy in the low loss region using model band structures. Universitetet i Oslo. Full text in Research Archive Show summary

  One of the key limiting factors to progress within nano science is the ability to measure properties on the relevant length scale. The probe size provided by optical measurements is often larger than the individual nanoscale structures, and the resulting measurement is an average over some large volume, thus other methods must be applied. Electron Energy Loss Spectroscopy (EELS) in a Transmission Electron Microscope (TEM) provides a probe size suitable for measuring on nanoscopic structures, but the physics of the probe change when using electrons instead of photons. The fast electrons passing through the sample carry a significant momentum in addition to energy, and both can be transferred to an electron in the sample. The possible transfer of momentum in addition to energy increases the number of possible excitations immensely thus making the spectra of EELS more complex than its optical equivalent. The EELS-spectra also provide useful information about properties earlier methods could not measure such as excitations resolved by momentum, and a straight measure of transitions across indirect band gaps. However, simulations are key in interpretation of EELS where transitions with momentum transfer contribute. Most simulation software for EELS focus on the optical limit and a production ready software for momentum resolved simulations is so far missing. In the present project a simulation software for EELS is developed for a momentum and energy resolved spectrum. Based on existing theory, a full framework for EELS simulation is developed in the dielectric formulation, strongly depending on the dielectric permittivity. The framework has been implemented with focus on a interactive visualization and interpretation of the result which should be easy to handle. Some limitations have been encountered when it comes to computational cost when mapping both momentum and energy. To limit the computational cost, the permittivity was heavily simplified by treating only its longitudinal component. When applying the software on parabolic bands it was found that the calculated joint density of states reproduced analytically derived results. In calculations of joint density of states of parabolic bands with indirect band gap it was found that the intensity onset had different shape when probing a range of momentum transfers opposed to single momentum transfers. When applied to electronic structure models from tight binding calculations, it was found that the longitudinal permittivity was not sufficient to describe the full response of the systems. The longitudinal permittivity is found insufficient in the presence of transverse electric fields and in non-isotropic systems, thus a correction to the permittivity has been presented, this has not been implemented. To conclude, the developed software indicates that momentum resolved calculations can provide useful information in its simplest manner, and be comparable to experiment with further development.

• Ness, Heine Håland; Prytz, Øystein & Bondevik, Tarjei (2018). Inline Electron Holography - Theoretical and Experimental Aspects. Universitetet i Oslo. Full text in Research Archive Show summary

  In this thesis we study a state of the art inline electron holography technique, titled Full Resolution Wave Reconstruction (FRWR). A rewiev of the reconstruction algorithm is given. We have tested the FRWR capabilities to recover the mean inner potential of Cu2O, and the potential profile across a Cu2O/CuO/ZnO heterojunction.In addition the effects of experimental setup such as objective aperture and energy filtering have been investigated. In addition, theoretical values of the mean inner potential have been calculated from following two different models, a non-binding atom model and an ionized atom model.

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