Phuong Dan Nguyen

• 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.

• Larsen, Aleksander Amble; Gorantla, Sandeep; Nguyen, Phuong Dan; Rosnes, Andreas; Xu, Yijiang & Iordanidou, Konstantina [Show all 10 contributors for this article] (2026). Atomic-Resolution EDS Characterization of Ordering in a β–Cu–Zn–Al Alloy. Metallurgical and Materials Transactions A. ISSN 1073-5623. doi: 10.1007/s11661-025-08093-9. Full text in Research Archive Show summary

  Abstract Atomic ordering in single-crystal β –Cu–Zn–Al, relevant to the martensitic transformation and functional properties, is investigated using analytical STEM. Atomic-resolution EDS along the [110] zone axis, where all Wyckoff positions are spatially resolved, reveals three chemically distinct site occupancies. Correlation with HAADF-STEM contrast provides real-space evidence consistent with L2 1 ordering. In agreement with experiments, first-principles calculations show a slight energetic preference for L2 1 over D0 3 , with finite-temperature free-energy calculations indicating that this preference persists at elevated temperatures.

• 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.

• 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.

• 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.

• 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.

• 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 .

• 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.

• Bundli, Silje; Dhak, Prasanta; Jensen, Martin; Gunnæs, Anette Eleonora; Nguyen, Phuong Dan & Fjellvåg, Helmer [Show all 7 contributors for this article] (2019). Controlled alloying of Pt-Rh nanoparticles by the polyol approach. Journal of Alloys and Compounds. ISSN 0925-8388. 779, p. 879–885. doi: 10.1016/j.jallcom.2018.11.301. 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
• Jensen, Ingvild Julie Thue; Gorantla, Sandeep Madhukar; Løvvik, Ole Martin; Gan, Jiantuo; Nguyen, Phuong Dan & Monakhov, Edouard [Show all 9 contributors for this article] (2017). Interface phenomena in magnetron sputtered Cu2O/ZnO heterostructures. Journal of Physics: Condensed Matter. ISSN 0953-8984. 29(43). doi: 10.1088/1361-648X/aa8799. Full text in Research Archive Show summary

  The interface between ZnO and Cu2O has been predicted to be a good candidate for use in thin film solar cells. However, the high predicted conversion efficiency has yet to be fully realized experimentally. To explore the underlying causes of this we investigate the interface between ZnO and Cu2O in magnetron sputtered samples. Two different sample geometries were made: In the first set thin layers of ZnO were deposited on Cu2O (type A), while in the second set the order was reversed (type B). Using x-ray photoelectron spectroscopy (XPS), an intermediate CuO layer was identified regardless of the order in which the Cu2O and ZnO layers were deposited. The presence of a CuO layer was supported by transmission electron microscopy (TEM) results. Changes in the electron hole screening conditions were observed in CuO near the interface with ZnO, manifested as changes in the relative peak-to-satellite ratio and the degree of asymmetric broadness in the Cu 2p peak. The suppression of the Cu 2p satellite characteristic of CuO may cause the CuO presence to be overlooked and cause errors in determinations of valence band offsets (VBOs). For the type A samples, we compare four different approaches to XPS-based determination of VBO and find that the most reliable results are obtained when the thin CuO layer and the altered screening conditions at the interface were taken into account. The VBOs were found to range between 2.5 eV and 2.8 eV. For the B type samples a reduction of the Cu 2p-LMM Auger parameter was found as compared to bulk Cu2O, indicative of quantum confinement in the Cu2O overlayer.

• Nguyen, Phuong Dan; Gunnæs, Anette Eleonora; Sunding, Martin Fleissner & Olsen, Arne (2014). Heterogeneous nucleation and growth of CrSi2 in sputtered thin films of silicon/silicon nitride. Thin Solid Films. ISSN 0040-6090. 556, p. 200–205. doi: 10.1016/j.tsf.2014.01.080. Full text in Research Archive
• Nguyen, Phuong Dan; Gunnæs, A. E.; Sunding, M. F. & Olsen, Arne (2014). Heterogeneous nucleation and growth of CrSi 2 in sputtered thin films of silicon/silicon nitride. Thin Solid Films. ISSN 0040-6090. doi: 10.1016/j.tsf.2014.01.080. Full text in Research Archive
• Nguyen, Phuong Dan; Kepaptsoglou, D.M.; Erni, Rolf; Ramasse, Q.M. & Olsen, Arne (2013). Quantum Confinement in Germanium Quantum Dots Observed by Electron Energy-Loss Spectroscopy. Microscopy and Microanalysis. ISSN 1431-9276. doi: 10.1017/s1431927613009422. Full text in Research Archive
• Nguyen, Dan Phuong; Kepaptsoglou, Despoina Maria; Ramasse, Q.M. & Olsen, Arne (2012). Direct observation of quantum confinement of Si nanocrystals in Si-rich nitrides. Physical Review B. Condensed Matter and Materials Physics. ISSN 1098-0121. 85(8). doi: 10.1103/PhysRevB.85.085315. Full text in Research Archive
• Kepaptsoglou, Despoina Maria; Erni, R; Ramasse, Q.M.; Olsen, Arne & Nguyen, Dan Phuong (2012). Quantum confinement of volume plasmons and interband transitions in germanium nanocrystals. Physical Review B. Condensed Matter and Materials Physics. ISSN 1098-0121. 86(24). doi: 10.1103/PhysRevB.86.245316. Full text in Research Archive
• Nguyen, Phuong Dan; Olsen, Arne; Kepaptsoglou, D.M. & Ramasse, Q.M. (2012). Quantum confinement of Si nanocrystals in Si-rich nitrides. Microscopy and Microanalysis. ISSN 1431-9276. doi: 10.1017/s1431927612010975. Full text in Research Archive
• Nguyen, Phuong Dan; Kepaptsoglou, D.M.; Ramasse, Q.M. & Olsen, Arne (2012). Direct observation of quantum confinement of Si nanocrystals in Si-rich nitrides. Physical Review B. Condensed Matter and Materials Physics. ISSN 1098-0121. doi: 10.1103/physrevb.85.085315. Full text in Research Archive
• Nguyen, Phuong Dan; Kepaptsoglou, D.M.; Ramasse, Q.M.; Sunding, M. F.; Vestland, L.O. & Finstad, T. G. [Show all 7 contributors for this article] (2012). Impact of oxygen bonding on the atomic structure and photoluminescence properties of Si-rich silicon nitride thin films. Journal of Applied Physics. ISSN 0021-8979. doi: 10.1063/1.4756998. Full text in Research Archive
• Nguyen, Phuong Dan; Kepaptsoglou, D.M.; Erni, Rolf; Ramasse, Q.M. & Olsen, Arne (2012). Quantum confinement of volume plasmons and interband transitions in germanium nanocrystals. Physical Review B. Condensed Matter and Materials Physics. ISSN 1098-0121. doi: 10.1103/physrevb.86.245316. Full text in Research Archive

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• 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
• 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
• 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
• 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
• 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
• 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
• Prytz, Øystein; Karlsen, Ole Bjørn; Nguyen, Phuong Dan; Carvalho, Patricia A. & Lundell, Martin Egge (2018). Illustrert vitenskap. [Journal]. Bilder. Full text in Research Archive
• Aarholt, Thomas; Sky, Thomas Neset; Nguyen, Phuong Dan & Prytz, Øystein (2018). Low-kV EELS band gapmeasurements on indium monolayer structures in ZnO. Full text in Research Archive
• Granerød, Cecilie Skjold; Nguyen, Phuong Dan; Gunnæs, Anette Eleonora & Prytz, Øystein (2016). The Structure Physics group. Full text in Research Archive
• Granerød, Cecilie Skjold; Zhan, Wei; Aarseth, Bjørn Brevig; Nguyen, Phuong Dan; Johansen, Klaus Magnus H & Vines, Lasse [Show all 7 contributors for this article] (2016). Bandgap measurements by STEM-EELS. Full text in Research Archive
• Lervik, Adrian; Bjørheim, Tor Svendsen; Nguyen, Phuong Dan; Diplas, Spyridon; Haugsrud, Reidar & Gunnæs, Anette Eleonora (2016). Chemical and Structural Investigations of Grain Boundaries in Y-Doped BaZrO3. Full text in Research Archive
• Granerød, Cecilie Skjold; Nguyen, Phuong Dan; Zhan, Wei; Monakhov, Edouard & Prytz, Øystein (2015). Band gap measurements by STEM-EELS. Full text in Research Archive
• Granerød, Cecilie Skjold; Nguyen, Phuong Dan; Zhan, Wei; Monakhov, Edouard & Prytz, Øystein (2015). High Energy Resolution EELS on ZnO/Cu2O Heterostructures. Full text in Research Archive
• Roaldset, Elen; Bering, Dag; Aerts, Maarten & Nguyen, Phuong Dan (2014). Kaolinite Group minerals from weathered anorthosite, SW Norway. Full text in Research Archive Show summary

  31 Nordic Geological Winter Meeting,Jan. 8-10, 2014. Abstract volume p. 72. Roaldset et al: Investigations of the kaolinite group minerals from in-situ weathered anorthosite at Dydland near Flekkefjord, SW Norway, show the presence of the polymorphs nacrite and/or dickite in addition to kaolinite. The kaolin deposits here were exploited for industrial purposes in the years 1898-1904. Reusch (1901) described the isolated areas of kaolinitic material and interpreted them to be of hydrothermal origin, while they, in the light of today’s geological knowledge, most probably are remnants of preglacial weathering. The basement rocks here are of Proterozoic age, while the time of the deep weathering is difficult to assess. Through geologic eras the region has been subjected to subsidence, sedimentation, uplift, fluvial and glacial erosion. In the Cenozoic the region experienced extensive tectonic movements. The Dydland site is close to the Skagerrak coast and lies about 100 m a.s.l. Detailed mineralogical studies of the Dydland kaolin by XRD, SEM-EDS, TEM and IR are in progress. Verification and characteristics of the kaolinite, dickite and/or nacrite will be presented and discussed in relation to origin and age. Diagenetic mineral transformations may indirectly give information about thickness of a post-weathering sedimentary cover later removed by erosion. Reference: Reusch, H. (1901) En forekomst af kaolin og ildfast ler ved Dydland nær Flekkefjord. Norges geologiske undersøkelse, 32, 99-103.

• 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.

• Langfeldt, Sindre Wiken; Prytz, Øystein; Karlsen, Ole Bjørn & Nguyen, Phuong Dan (2015). Syntese og karakterisering av termoelektriske halv-Heusler materialer av typen (Ti,Zr,Hf)NiSn. Universitetet i Oslo. Full text in Research Archive
• Nguyen, Dan Phuong (2013). Synthesis and Characterisation of Sputtered thin films for renewable energy purposes. Universitetet i Oslo. Full text in Research Archive Show summary

  In the past years, a large body of work has been dedicated to semiconductor quantum dots embedded in thin films of oxide and nitride, as the tailorable electronic and optical properties of these nanostructures make them desirable for various optoelectronic applications. The properties of these low-dimensional semiconductor systems are directly related to the atomic arrangement, distribution and size of the quantum dots, the structure of the surrounding matrices and the distance between the quantum dots. The quantum confinement of carriers in the quantum dots, their interaction, and local states in the matrices are the dominating factors determining the material properties. The present work focuses on studying the atomic structures of these materials, and how their optical and electronic properties vary as a function of size and structure. Two material systems were especially synthesized as part of this work; Si and Ge quantum dots embedded in Si3N4 and SiO2 matrices, respectively. Direct evidence of quantum confinement effects on plasmon energies, interband and conduction band structures as a function of the size and morphologies of the aforementioned Si and Ge quantum dots are provided by exploiting the high spatial and energy resolution of state of the art Scanning Transmission Electron Microscopy (STEM). The discrepancies between earlier theoretical and experimental works on the behavior of confined plasmons and interband transitions are discussed in terms of crystal imperfections, interface states and the chemistry of the surrounding matrix of each system. A comparison between the confinement strength in the system of Si and Ge quantum dots was also brought into discussion. To date, the existing experimental works found in literatures cannot unambiguously identify the correlation between chemical bonding and optical properties of the embedded quantum dots, due to the complexity of these systems. Moreover, the theoretical approaches to this matter are more than often contradictory. The combination of complementary techniques in the present work has drawn a consistent picture of bonding structures and resulting optical properties of Si quantum dots embedded in silicon nitride, and simultaneously highlighted the important impact of oxygen incorporated into the films. A model of gap states and electronic transitions for the silicon nitride films is proposed, which explains adequately the role of QC excitons vs defects in the visible luminescence of silicon nitride films with and without Si quantum dots. These results provide important information for understanding the quantum dots’ physical properties and the possibility for improvements of optoelectronic applications, like solar cells.

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