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• 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.

• 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.

• 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.

• Granerød, Cecilie Skjold; Bilden, Sindre Rannem; Aarholt, Thomas; Yao, Yu-Feng; Yang, C. C. & Look, David C. [Show all 9 contributors for this article] (2018). 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 (PRB). ISSN 2469-9950. 98(11). doi: 10.1103/PhysRevB.98.115301. Full text in Research Archive Show summary

  The combination of high optical transparency and low electrical resistivity has made transparent conductive oxides (TCOs) a key technology in many optoelectronic applications. Furthermore, the study of TCOs yields insight into many fundamental parameters of semiconductors. For example, the high charge carrier concentration results in an apparent shift in the band gap, the so-called Burstein-Moss shift, in addition to plasmonic resonances in the near infrared regime. While both effects are related to the carrier concentration and band structure, their lateral distribution and interaction with boundary conditions such as interfaces and surfaces are difficult to assess, and a direct observation of the local distribution has remained elusive. Here we employ electron energy-loss spectroscopy in scanning transmission electron microscopy (STEM-EELS) for direct observation of spatially resolved plasmonic resonances and Burstein-Moss shift in gallium doped zinc oxide (GZO), one of the most widely used TCOs. A 25 nm thick GZO film with a carrier concentration of 7× 10 20 cm − 3 has been grown epitaxially on a nominally undoped ZnO film. The GZO film shows a renormalized Burstein-Moss shift of ∼ 0.5 eV, in accordance with that expected from Hall effect measurements. The plasma resonance of the conduction band electrons is located at 0.82 eV in the bulk GZO, and with a substantial increase in intensity towards the sample surface, where a surface plasmon energy of 0.54 eV is observed. Hence we have directly measured differences in optical properties between the two films, the local variation across the GZO film has been studied, and we are also directly observing the difference between bulk and surface properties of GZO. © 2018 American Physical Society

• Granerød, Cecilie Skjold; Galeckas, Augustinas; Johansen, Klaus Magnus H; Vines, Lasse & Prytz, Øystein (2018). 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. ISSN 0021-8979. 123(14), p. 1–6. doi: 10.1063/1.5023316. Full text in Research Archive Show summary

  The optical band gap of ZnO has been measured as a function of temperature using Electron Energy-Loss Spectroscopy (EELS) in a (Scanning) Transmission Electron Microscope ((S)TEM) from approximately 100 K up towards 1000 K. The band gap narrowing shows a close to linear dependency for temperatures above 250 K and is accurately described by Varshni, Bose-Einstein, Pässler and Manoogian-Woolley models. Additionally, the measured band gap is compared with both optical absorption measurements and photoluminescence data. STEM-EELS is here shown to be a viable technique to measure optical band gaps at elevated temperatures, with an available temperature range up to 1500 K and the benefit of superior spatial resolution. © 2018 AIP Publishing

• Granerød, Cecilie Skjold; Zhan, Wei & Prytz, Øystein (2018). Automated approaches for band gap mapping in STEM-EELS. Ultramicroscopy. ISSN 0304-3991. 184(A), p. 39–45. doi: 10.1016/j.ultramic.2017.08.006. Full text in Research Archive Show summary

  Band gap variations in thin film structures, across grain boundaries, and in embedded nanoparticles are of increasing interest in the materials science community. As many common experimental techniques for measuring band gaps do not have the spatial resolution needed to observe these variations directly, probe-corrected Scanning Transmission Electron Microscope (STEM) with monochromated Electron Energy-Loss Spectroscopy (EELS) is a promising method for studying band gaps of such features. However, extraction of band gaps from EELS data sets usually requires heavy user involvement, and makes the analysis of large data sets challenging. Here we develop and present methods for automated extraction of band gap maps from large STEM-EELS data sets with high spatial resolution while preserving high accuracy and precision.

• Zhan, Wei; Granerød, Cecilie Skjold; Venkatachalapathy, Vishnukanthan; Johansen, Klaus Magnus H; Jensen, Ingvild Julie Thue & Kuznetsov, Andrej [Show all 7 contributors for this article] (2017). Nanoscale mapping of optical band gaps using monochromated Electron Energy Loss Spectroscopy. Nanotechnology. ISSN 0957-4484. 28(10). doi: 10.1088/1361-6528/aa5962. Full text in Research Archive Show summary

  Using monochromated electron energy loss spectroscopy in a probe-corrected scanning transmission electron microscope we demonstrate band gap mapping in ZnO/ZnCdO thin films with a spatial resolution below 10 nm and spectral precision of 20 meV.

• Riley, Jon; Mazzola, Federico; Dendzik, M; Michiardi, M; Takayama, T & Bawden, L [Show all 17 contributors for this article] (2014). Direct observation of spin-polarized bulk bands in an inversion-symmetric semiconductor. Nature Physics. ISSN 1745-2473. 10(11), p. 835–839. doi: 10.1038/nphys3105. Full text in Research Archive

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• 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
• 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
• 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; Granerød, Cecilie Skjold; Olsen, Vegard Skiftestad; Vines, Lasse; Svensson, Bengt Gunnar & Prytz, Øystein (2018). Structural-chemical characterization and bandgap measurements at the nanoscale of (ZnO)1-X(GaN)X thin films using (S)TEM methods. Full text in Research Archive
• Zhan, Wei; Granerød, Cecilie Skjold; Venkatachalapathy, Vishnukanthan; Johansen, Klaus Magnus H; Jensen, Ingvild Julie Thue & Kuznetsov, Andrej [Show all 7 contributors for this article] (2018). Reply to Comment on 'Nanoscale mapping of optical band gaps using monochromated electron energy loss spectroscopy'. Nanotechnology. ISSN 0957-4484. 29(31). doi: 10.1088/1361-6528/aac3ed. Full text in Research Archive
• Olsen, Vegard Skiftestad; Bazioti, Kalliopi; Azarov, Alexander; Granerød, Cecilie Skjold; Svensson, Bengt Gunnar & Kuznetsov, Andrej [Show all 8 contributors for this article] (2018). Bandgap bowing in crystalline (ZnO)1-x(GaN)x thin films. Full text in Research Archive
• Granerød, Cecilie Skjold; Johansen, Klaus Magnus H; Vines, Lasse & Prytz, Øystein (2017). The temperature-dependency of the ZnO band gap measured by STEM-EELS. Full text in Research Archive
• Granerød, Cecilie Skjold; Galeckas, Augustinas; Vines, Lasse; Johansen, Klaus Magnus H & Prytz, Øystein (2017). Temperature-dependency of the ZnO band gap measured by STEM-EELS. Full text in Research Archive
• Bazioti, Kalliopi; Granerød, Cecilie Skjold; Olsen, Vegard Skiftestad; Vines, Lasse; Svensson, Bengt Gunnar & Prytz, Øystein (2017). Structural characterization and nanoscale bandgap measurements of (ZnO)1-X(GaN)X thin films. Full text in Research Archive
• Granerød, Cecilie Skjold; Zhan, Wei & Prytz, Øystein (2017). Methods for Mapping the Band Gap with High Spatial Resolution by STEM-EELS. Full text in Research Archive
• Bazioti, Kalliopi; Granerød, Cecilie Skjold; Olsen, Vegard Skiftestad; Vines, Lasse; Svensson, Bengt Gunnar & Prytz, Øystein (2017). Structural/chemical characterization and bandgap measurements of (ZnO)1-X(GaN)X thin films using (S)TEM methods. Full text in Research Archive
• Bazioti, Kalliopi; Granerød, Cecilie Skjold; Olsen, Vegard Skiftestad; Vines, Lasse; Svensson, Bengt Gunnar & Prytz, Øystein (2017). (S)TEM characterization of magnetron sputtered ZnO:GaN alloy thin films. Full text in Research Archive
• Granerød, Cecilie Skjold; Galeckas, Augustinas; Johansen, Klaus Magnus H; Vines, Lasse & Prytz, Øystein (2017). The temperature-dependency of the ZnO bandgap studied by STEM-EELS. Full text in Research Archive
• Granerød, Cecilie Skjold; Bilden, Sindre Rannem; Zhan, Wei; Vines, Lasse; Johansen, Klaus Magnus H & Prytz, Øystein (2017). Measuring the ZnO bandgap and its temperature dependency with STEM-EELS. Full text in Research Archive
• Bazioti, Kalliopi; Granerød, Cecilie Skjold; Olsen, Vegard Skiftestad; Vines, Lasse; Svensson, Bengt Gunnar & Prytz, Øystein (2017). Structural and chemical characterization of (ZnO)1-X(GaN)X thin films using (S)TEM methods. Full text in Research Archive
• Elanchcelian, Seyon; Granerød, Cecilie Skjold & Prytz, Øystein (2017). TEM-EELS analysis of bandgap properties in 𝛃-Ga2O3. 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; Johansen, Klaus Magnus H; Vines, Lasse & Prytz, Øystein (2016). Band gap measurements by STEM EELS. Full text in Research Archive
• Granerød, Cecilie Skjold & Prytz, Øystein (2016). Advantages of EELS Measurements. 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
• Johansen, Klaus Magnus H; Zhan, Wei; Jensen, Ingvild Julie Thue; Granerød, Cecilie Skjold; Venkatachalapathy, Vishnukanthan & Brillson, Leonard J. [Show all 8 contributors for this article] (2016). Mapping of Optical band gaps using Electron Energy Loss Spectroscopy in ZnCdO-alloys. Full text in Research Archive
• Granerød, Cecilie Skjold (2015). Bandgap of Functional Oxides in STEM-EELS. Full text in Research Archive
• Granerød, Cecilie Skjold; Nilsen, Ola; Monakhov, Edouard & Prytz, Øystein (2015). Bandgaps in the TEM. Full text in Research Archive
• Granerød, Cecilie Skjold; Zhan, Wei; Aarseth, Bjørn Brevig; Vines, Lasse & Prytz, Øystein (2015). Band gap measurements by STEM EELS. Full text in Research Archive
• Granerød, Cecilie Skjold; Zhan, Wei; Venkatachalapathy, Vishnukanthan; Kuznetsov, Andrej; Nilsen, Ola & Monakhov, Edouard [Show all 7 contributors for this article] (2015). Bandgap of Functional Oxides in STEM-EELS. 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
• Zhan, Wei; Venkatachalapathy, Vishnukanthan; Jensen, Ingvild Julie Thue; Granerød, Cecilie Skjold; Flage-Larsen, Espen & Johansen, Klaus Magnus H [Show all 9 contributors for this article] (2015). STEM-EELS Band Gap Measurement in Zn1-XCdXO Thin Films. 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
• Prytz, Øystein; Zhan, Wei & Granerød, Cecilie Skjold (2015). Status of EELS band gap measurements in the monochromated Titan. Full text in Research Archive
• Granerød, Cecilie Skjold; Prytz, Øystein; Monakhov, Eduard & Nilsen, Ola (2018). Measuring optical properties on the nanoscale: a STEM-EELS study of ZnO. Universitetet i Oslo. Full text in Research Archive Show summary

  Denne avhandlingen bidrar til økt kunnskap om målinger av optiske egenskaper i halvledermaterialer gjennom å bruke en relativt ny og avansert målemetode. Denne målemetoden kan gi resultater med en ekstremt høy romlig oppløsning, og har derfor stort potensiale innen videre materialforskning. For å kunne videreutvikle dagens teknologi er det viktig å undersøke nye materialer og sammensetninger. Dette kan resultere i teknologi med høyere effektivitet, utvidede bruksområder, eller helt nye formål, som vil avhenge av materialets egenskaper. Båndgapet er en slik materialegenskap som betegner materialets konvertering mellom energi og strøm eller lys, og er derfor en viktig egenskap innen fornybar energi som solceller, eller i halvledermaterialer som brukes i elektronikk og LED-teknologi. De siste årene har det vært mulig å måle båndgap ved å benytte metoden elektron-energitapsspektroskopi (EELS) i et skanning-transmisjons-elektronmikroskop (STEM). Det unike ved denne metoden er en høy romlig oppløsning, som kan resultere i målinger med oppløsning på en nanometer-skala. Denne metoden kan dermed brukes til å studere båndgap og andre optiske egenskaper, og den romlige variasjonen av disse, og dermed bidra til ny informasjon om kvalitet, bruksområder og effektivitet i materialene. Båndgapsmålinger med denne metoden er ofte krevende å gjennomføre, men også å tolke. Dette arbeidet bidrar derfor med viktig forståelse for hvordan slike målinger og analyser kan gjennomføres, samt påpeke mulighetene og begrensningene ved metoden. Metoden har blitt testet på ulike systemer basert på sinkoksid (ZnO), som er et teknologisk viktig materiale for LED- og solcelleformål, og bidrar dermed også med nyttig informasjon om disse systemene.

• Elanchcelian, Seyon; Prytz, Øystein & Granerød, Cecilie Skjold (2017). TEM-EELS analysis of band gap properties in beta-Ga2O3, Universitetet i Oslo. Full text in Research Archive

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