Functionalization of conducting oxides by ion beam and defect engineering (FUNCTION) (avsluttet)

• 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. Fulltekst i vitenarkiv Vis sammendrag

  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.

• Fernandez, Javier Garcia; Kjeldby, Snorre Braathen; Zeng, L. J.; Azarov, Alexander; Pokle, Anuj & Nguyen, Phuong Dan [Vis alle 10 forfattere av denne artikkelen] (2024). In situ atomic-resolution study of transformations in double polymorph γ/β-Ga2O3 structures. Materials Advances. 5, s. 3824–3831. doi: 10.1039/D3MA01011B. Fulltekst i vitenarkiv Vis sammendrag

  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.

• 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. Fulltekst i vitenarkiv Vis sammendrag

  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 [Vis alle 13 forfattere av denne artikkelen] (2023). Universal radiation tolerant semiconductor. Nature Communications. 14, s. 1–8. doi: 10.1038/s41467-023-40588-0. Fulltekst i vitenarkiv Vis sammendrag

  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 [Vis alle 7 forfattere av denne artikkelen] (2023). Cation segregation observed in an (In,Ga) 2 O3 material thin film library beyond the miscibility limit of the bixbyite structure. PHYSICAL REVIEW MATERIALS. 7(9). doi: 10.1103/PhysRevMaterials.7.094603. Fulltekst i vitenarkiv Vis sammendrag

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

• Kjeldby, Snorre Braathen; Nguyen, Phuong Dan; Fernández, Javier García; Haug, Kristian; Galeckas, Augustinas & Jensen, Ingvild Julie Thue [Vis alle 9 forfattere av denne artikkelen] (2023). Optical properties of ZnFe2O4 nanoparticles and Fe-decorated inversion domain boundaries in ZnO. Nanoscale Advances. 5(7), s. 2102–2110. doi: 10.1039/d2na00849a. Fulltekst i vitenarkiv Vis sammendrag

  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.

• Kang, Xiaolan; Reinertsen, Vilde Mari; Both, Kevin Gregor; Galeckas, Augustinas; Aarholt, Thomas & Prytz, Øystein [Vis alle 9 forfattere av denne artikkelen] (2022). Galvanic Restructuring of Exsolved Nanoparticles for Plasmonic and Electrocatalytic Energy Conversion. Small. ISSN 1613-6810. 18(29). doi: 10.1002/smll.202201106. Fulltekst i vitenarkiv Vis sammendrag

  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. [Vis alle 9 forfattere av denne artikkelen] (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. Fulltekst i vitenarkiv Vis sammendrag

  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 [Vis alle 9 forfattere av denne artikkelen] (2022). Plasmonic properties of aluminium nanowires in amorphous silicon. Journal of Physics: Condensed Matter. ISSN 0953-8984. 35(6), s. 1–10. doi: 10.1088/1361-648X/aca30e. Fulltekst i vitenarkiv Vis sammendrag

  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 [Vis alle 8 forfattere av denne artikkelen] (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. Fulltekst i vitenarkiv Vis sammendrag

  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. Fulltekst i vitenarkiv Vis sammendrag

  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 .

• Aarseth, Bjørn Lupton; Granerød, Cecilie Skjold; Galeckas, Augustinas; Azarov, Alexander; Nguyen, Phuong Dan & Prytz, Øystein [Vis alle 7 forfattere av denne artikkelen] (2021). Formation and functionalization of Ge-nanoparticles in ZnO. Nanotechnology. ISSN 0957-4484. 32(50). doi: 10.1088/1361-6528/ac264a. Fulltekst i vitenarkiv Vis sammendrag

  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.

• Granerød, Cecilie Skjold; Aarseth, Bjørn Lupton; Nguyen, Phuong Dan; Bazioti, Kalliopi; Azarov, Alexander & Svensson, Bengt Gunnar [Vis alle 8 forfattere av denne artikkelen] (2019). Structural and optical properties of individual Zn2GeO4 particles embedded in ZnO. Nanotechnology. ISSN 0957-4484. 30(22), s. 1–6. doi: 10.1088/1361-6528/ab061c. Fulltekst i vitenarkiv

Se alle arbeider i NVA

• Fernandez, Javier Garcia; Montag, S.; Splith, D.; Kneiß, M.; Grundmann, M. & Prytz, Øystein [Vis alle 7 forfattere av denne artikkelen] (2024). Combinatorial PLD Synthesis of (In1−xGax)2O3 Thin Films: Structural, Morphological, and Optical Analysis for Transparent Conducting Oxides. Fulltekst i vitenarkiv
• 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. Fulltekst i vitenarkiv
• 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. Fulltekst i vitenarkiv
• Fernandez, Javier Garcia; Kjeldby, Snorre Braathen; Nguyen, Phuong Dan; Haug, Kristian; Galeckas, Augustinas & Jensen, Ingvild Julie Thue [Vis alle 9 forfattere av denne artikkelen] (2023). Optical properties and structure relationship in ZnO:Fe with inversion domain boundaries and ZnFe2O4/ZnO heterostructures. Fulltekst i vitenarkiv
• Hommedal, Ylva Knausgård; Frodason, Ymir Kalmann; Vines, Lasse & Johansen, Klaus Magnus H (2023). Ge donor diffusion in β-Ga2O3. Fulltekst i vitenarkiv
• Fernandez, Javier Garcia; Kjeldby, Snorre Braathen; Azarov, Alexander; Pokle, Anuj; Nguyen, Phuong Dan & Vines, Lasse [Vis alle 8 forfattere av denne artikkelen] (2023). Polymorph engineering and radiation tolerance in β-Ga2O3. Fulltekst i vitenarkiv
• Kjeldby, Snorre Braathen; Fernández, Javier García; Nguyen, Phuong Dan; Prytz, Øystein & Vines, Lasse (2023). Implantation for polymorphic transformation in Ga2O3: thermal evolution and luminescence. Fulltekst i vitenarkiv Vis sammendrag

  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 [Vis alle 9 forfattere av denne artikkelen] (2022). Structural and optical investigation of Fe-ZnO nanoarchitectures: from inversion domain boundaries to ZnO/ZnFe2O4 heterostructure. Fulltekst i vitenarkiv
• Kang, Xiaolan; Reinertsen, Vilde Mari; Both, Kevin Gregor; Galeckas, Augustinas; Aarholt, Thomas & Prytz, Øystein [Vis alle 9 forfattere av denne artikkelen] (2022). Galvanic restructuring of exsolved nanoparticles for plasmonic and electrocatalytic energy conversion. Fulltekst i vitenarkiv
• Kang, Xiaolan; Reinertsen, Vilde Mari; Both, Kevin Gregor; Galeckas, Augustinas; Aarholt, Thomas & Prytz, Øystein [Vis alle 9 forfattere av denne artikkelen] (2022). Galvanic Restructuring of Exsolved Nanoparticles for Plasmonic and Electrocatalytic Energy Conversion (Small 29/2022 Inside back cover feature). 18(29), s. 2270156–2270156. Fulltekst i vitenarkiv
• 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. Fulltekst i vitenarkiv
• Both, Kevin Gregor; Reinertsen, Vilde Mari; Kang, Xiaolan; Aarholt, Thomas; Neagu, Dragos & Prytz, Øystein [Vis alle 8 forfattere av denne artikkelen] (2022). Improved Photoelectrochemical Performance of SrTiO3 by Plasmonically Active Au Nanoparticles. Fulltekst i vitenarkiv
• Both, Kevin Gregor; Reinertsen, Vilde Mari; Kang, Xiaolan; Neagu, Dragos; Prytz, Øystein & Norby, Truls [Vis alle 7 forfattere av denne artikkelen] (2022). Thin Film Exsolution of Metal Nanoparticles and Their Galvanic Restructuring for Plasmonically Enhanced Photocatalytic Activity. Fulltekst i vitenarkiv
• Kjeldby, Snorre Braathen; Azarov, Alexander; Nguyen, Phuong Dan; Venkatachalapathy, Vishnukanthan; Mikšová, Romana & Macková, Anna [Vis alle 10 forfattere av denne artikkelen] (2022). Structural Transformation of β-Ga2O3 through Si-implantation. Fulltekst i vitenarkiv
• Kjeldby, Snorre Braathen; Nguyen, Phuong Dan; Fernandez, Javier Garcia; Haug, Kristian; Galeckas, Augustinas & Jensen, Ingvild Julie Thue [Vis alle 9 forfattere av denne artikkelen] (2022). Optical properties of Fe-decorated inversion domain boundaries and embedded spinel zinc ferrite nanoparticles in zinc oxide. Fulltekst i vitenarkiv
• Kjeldby, Snorre Braathen; Azarov, Alexander; Nguyen, Phuong Dan; Fernandez, Javier Garcia; Venkatachalapathy, Vishnukanthan & Mikšová, Romana [Vis alle 10 forfattere av denne artikkelen] (2022). Structure and luminescence properties of Si-implanted β-Ga2O3. Fulltekst i vitenarkiv
• Aarholt, Thomas; Both, Kevin Gregor; Reinertsen, Vilde Mari & Prytz, Øystein (2021). Surface plasmon investigations by STEM-EELS mapping of Au/Ni nanoparticles on STO. Fulltekst i vitenarkiv Vis sammendrag

  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. Fulltekst i vitenarkiv
• Kjeldby, Snorre Braathen; Nguyen, Phuong Dan; Haug, Kristian; Galeckas, Augustinas; Jensen, Ingvild Julie Thue & Thøgersen, Annett [Vis alle 8 forfattere av denne artikkelen] (2021). EELS and SEM-CL investigations of ZnFe2O4 nanoparticles and iron-decorated inversion domain boundaries in bulk ZnO. Fulltekst i vitenarkiv
• Elgvin, Cana; Nguyen, Phuong Dan; Both, Kevin Gregor; Vines, Lasse & Prytz, Øystein (2021). Crystallographically oriented ZnFe2O4 nanoparticles in ZnO thin films. Fulltekst i vitenarkiv
• Nguyen, Phuong Dan; Granerød, Cecilie Skjold; Aarseth, Bjørn Lupton; Bazioti, Kalliopi; Azarov, Alexander & Svensson, Bengt Gunnar [Vis alle 8 forfattere av denne artikkelen] (2019). Structural and optical properties of individual Zn2GeO4 particles embedded in ZnO. Fulltekst i vitenarkiv
• 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. Fulltekst i vitenarkiv
• 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. Fulltekst i vitenarkiv
• Kjeldby, Snorre Braathen; Vines, Lasse & Prytz, Øystein (2024). Polymorph transformations, nanoparticles, and luminescence in ion-implanted gallium oxide. Universitetet i Oslo. Fulltekst i vitenarkiv Vis sammendrag

  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

• Elgvin, Cana & Prytz, Øystein (2021). Characterization and optical properties of ZnFe2O4 nanoparticles in ZnO thin films - A (S)TEM study. Universitetet i Oslo. Fulltekst i vitenarkiv
• Bergli, Jørgen & Prytz, Øystein (2021). Solid state precipitation of spinels in zinc oxide - A microstructure study. Universitetet i Oslo. Fulltekst i vitenarkiv Vis sammendrag

  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.

• Haug, Kristian & Prytz, Øystein (2019). Functionalization of transparent conducting oxides. Zinc ferrite spinel in ZnO. Universitetet i Oslo. Fulltekst i vitenarkiv

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