-
Jensen, Ingvild Julie Thue; Thøgersen, Annett; Cooil, Simon Phillip; Wells, Justin William; Prytz, Øystein & Von Wenckstern, Holger
(2023).
Bandgap and band offset engineering in κ-Ga2O3-based thin films (Invited talk)).
-
Kjeldby, Snorre Braathen; García Fernández, Javier; Nguyen, Phuong Dan; Prytz, Øystein & Vines, Lasse
(2023).
Implantation for polymorphic transformation in Ga2O3: thermal evolution and luminescence.
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.
-
Garcia Fernandez, Javier; 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.
-
Garcia Fernandez, Javier; 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.
-
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.
-
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.
-
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.
-
Kjeldby, Snorre Braathen; Azarov, Alexander; Nguyen, Phuong Dan; Garcia Fernandez, Javier; Venkatachalapathy, Vishnukanthan & Mikšová, Romana
[Show all 10 contributors for this article]
(2022).
Structure and luminescence properties of Si-implanted β-Ga2O3.
-
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.
-
Kjeldby, Snorre Braathen; Nguyen, Phuong Dan; Garcia Fernandez, Javier; 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.
-
Garcia Fernandez, Javier; 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.
-
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.
-
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).
Small.
ISSN 1613-6810.
18(29).
-
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
.
-
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
.
-
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.
-
Aarholt, Thomas; Both, Kevin Gregor; Reinertsen, Vilde Mari & Prytz, Øystein
(2021).
Surface plasmon investigations by STEM-EELS mapping of Au/Ni nanoparticles on STO.
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.
-
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.
-
Elgvin, Cana; Nguyen, Phuong Dan; Both, Kevin Gregor; Vines, Lasse & Prytz, Øystein
(2021).
Crystallographically oriented ZnFe2O4 nanoparticles in ZnO thin films .
-
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.
-
Thøgersen, Annett; Diplas, Spyridon; Michel, Kathrin; Bjørheim, Tor Svendsen; Prytz, Øystein & Norby, Truls Eivind
(2020).
The surface of CeO2 unravelled.
-
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.
-
Song, Xin; Riis, Henrik; Prytz, Øystein & Finstad, Terje
(2019).
Metallization of selected transition metals on ZnSb by electron beam thermal evaporation.
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.
-
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).
-
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.
-
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.
-
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.
-
Aarholt, Thomas; Frodason, Ymir Kalmann & Prytz, Øystein
(2019).
The impact of local relaxation on defect-complex STEM contrast.
-
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
.
-
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.
-
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.
-
Hansen, Per-Anders Stensby; Zikmund, Tomas; Yu, Ting; Nitsche Kvalvik, Julie; Aarholt, Thomas & Prytz, Øystein
[Show all 8 contributors for this article]
(2018).
Aromatic-fluoride nanocomposite materials by atomic layer deposition.
-
Finstad, Terje; Song, Xin; Riis, Henrik & Prytz, Øystein
(2018).
Cu Films on Thermoelectric ZnSb.
Show summary
ZnSb is a semiconductor that is experiencing a renewed interest as a thermoelectric material (as well for other applications). For thermoelectric applications the high abundance of the elements and their low toxicity are favorable. Most of the reports have been on optimizing the material without explicitly addressing the integration into a thermoelectric module. The necessary physical and electrical contacts to the material are important, challenging efficient fabrication, durability, thermal stability, thermal stress etc. The detailed understanding of the thermoelectrical material ZnSb in intimate contacts with metals is lacking. This work is our first step towards studying metal contacts to ZnSb. We start by studying deposited Cu films on ZnSb because Cu may be one of the constituents of a metallization scheme. Some of the reasons for choosing Cu is that its thermal expansion matches that of ZnSb, Cu has low cost and the technology for bonding patterns to insulator substrates like alumina is well established. Further Cu is a p-type dopant for ZnSb yielding optimum thermoelectric characteristics at the solubility limit. The solubility of Cu in ZnSb should thus promote tunneling and low contact resistance.
The Cu/ZnSb interface has been investigated after heat treatments in the temperature range 200 to 350°C. The ZnSb samples were made by hot pressing grains of ZnSb. A 100nm thick layer of Cu was e-beam deposited. The samples are characterized by SEM with EDS and several TEM techniques. The TEM specimens were made by Focused Ion Beam. The elemental distributions and phase formation will be presented. The contact resistance of the samples is also under investigation.
-
Ulvestad, Asbjørn; Koposov, Alexey; Skare, Marte Orderud; Mæhlen, Jan Petter; Andersen, Hanne Flåten & Prytz, Øystein
[Show all 7 contributors for this article]
(2018).
Amorphous Silicon Nitride - A Novel Anode Material for Li-ion Batteries.
-
Riis, Henrik; Song, Xin; Prytz, Øystein & Finstad, Terje
(2018).
Characterization of Cu/ZnSb interfaces.
-
Prytz, Øystein; Karlsen, Ole Bjørn; Nguyen, Phuong Dan; Carvalho, Patricia A. & Lundell, Martin Egge
(2018).
Illustrert vitenskap.
[Journal].
Bilder.
-
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
.
-
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.
-
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
.
-
Bazioti, Kalliopi; Azarov, Alexander; Svensson, Bengt Gunnar & Prytz, Øystein
(2018).
(S)TEM characterization and thermal evolution of ion-induced defects in ZnO.
-
Aarholt, Thomas; Sky, Thomas Neset; Nguyen, Phuong Dan & Prytz, Øystein
(2018).
Low-kV EELS band gapmeasurements on indium monolayer structures in ZnO.
-
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.
-
-
Nguyen, Hao Pierre Quoc & Prytz, Øystein
(2023).
Structural and Chemical Characterization of ZnGe_xSn_(1-x)N_2 for Solar Cell Applications.
Kjemisk Institutt, Universitetet i Oslo.
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.
University of Oslo Livrary.
ISSN 1501-7710.
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.
-
-
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.
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.
-
-
-
-
-
-
Zhan, Wei; Prytz, Øystein; Kuznetsov, Andrej & Flage-Larsen, Espen
(2018).
Band gap mapping of alloyed ZnO using probe-corrected and monochromated STEM-EELS.
Reprosentralen, University of Oslo.
ISSN 1501-7710.
Show summary
The band gap of semiconducting ZnO can be readily tuned through alloying it with other relevant oxides, such as CdO, consequently extending the performance of the corresponding materials and devices. In this context, one of the challenges is to establish the methodology for two-dimensional band gap measurements on the nanometer scale. Here, monochromated electron energy loss spectroscopy (EELS) in combination with probe-corrected scanning transmission electron microscopy (STEM) can be applied, potentially with much greater success compared to traditional techniques with low spatial resolution. However, up to now, the EELS based band gap mapping technique has not seen widespread use, primarily due to its experimental and data processing complexities.
In this work, utilizing state-of-the-art probe-corrected and monochromated STEM-EELS platform without particular instrumental design, we developed and applied methods for acquiring large band gap maps with high spatial resolution. A newly-developed efficient computing method was employed to extract band gap maps from the EELS data after proper background subtraction. All these advances are highlighted by the band gap mapping of Zn1-xCdxO/ZnO hetero structure with a spatial resolution well below 10 nm and a high spectral precision.
Nevertheless, band gap measurement by EELS are also restricted in spatial resolution, which is fundamentally determined by the delocalization length (L50) of the inelastic scattering process. The origin of this delocalization is the long range electrostatic interactions between the atomic electrons of the sample and the incident high-energy electrons. The EELS plasmon energy map has obviously higher spatial resolution than the band gap map, and its experiment as well as data extraction is also much easier to perform. In order to push the spatial resolving power in EELS band gap analysis further, the relationship between the band gaps and plasmon energies in Zn1-xCdxO was investigated based on the fact that both depend strongly on the unit cell parameter. A robust quantitative correlation was established, providing a simple and straightforward way to calculate the band gap variations just from the easily measured plasmon energy, with improved spatial resolving ability as compared with the conventional EELS approach.
In order to further verify the success of the probe-corrected and monochromated STEM-EELS technique, it was put into application to a new system, namely separate ZnCr2O4 nano-inclusions embedded in ZnO matrix. Band gap mapping of ZnCr2O4 nanoparticles in ZnO matrix and their interface was successfully achieved, confirming the validity of this STEM-EELS approach. In addition, probe-corrected STEM enables sub-ångström imaging, from which the realistic structure can be revealed. We employed atomic-resolution images together with geometric phase analysis (GPA) to analyze the structure and strain at ZnCr2O4/ZnO interfaces, which is of critical importance for thin film growth and may affect band gap.
-
Ness, Heine Håland; Prytz, Øystein & Bondevik, Tarjei
(2018).
Inline Electron Holography - Theoretical and experimental aspects.
Unipub forlag.
Show summary
With ever decreasing size of electronics the need study of sub micrometer structures is prominent. The transmission electron microscope (TEM) gives the possibility to study structures at the nano scale. One technique that the TEM enables is inline electron holography, whith this
technique, the electrostatic potential of a material can be found. By using a defocus series of
electron micrographs, the full electron wavefunction may be recovered by simulating the processes
that take place in the TEM. The phase of the electron wavefunction holds information of
the potential experienced by the electron wave.
In this thesis, we study a state of the art inline electron holography technique, titled Full Resolution Wave Reconstruction (FRWR). A review of the reconstruction algorithm is given, and
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. Furthermore,
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.
The theoretical values for the mean inner potential of Cu2O was found to be 17.29 V for a nonbinding model and 12.78 V for an ionized atom model, whereas the experiential values was
estimated to be 15.46 ± 2.18 V.
For the Cu2O/CuO interface, the theoretical calculations gave a potential of 3.13 V and 2.34 V
for the non-binding and ionic models, respectively. The experimental value was 1.33 ± 0.70 V.
The CuO/ZnO transition gave theoretical values of 3.14 V for the non-binding model and 2.34
V for the ionic model, and an experimental value of 2.60 ± 0.84 V.
-
Musland, Lars; Flage-Larsen, Espen; Prytz, Øystein & Bergli, Joakim
(2018).
Charge carrier transport in multilayered structures; thermoelectric applications.
Unipub forlag.
-
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.
Unipub forlag.
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.