Spyridon Diplas

• Kalyva, Maria Evangelou; Sunding, Martin Fleissner; Gunnæs, Anette Eleonora; Diplas, Spyridon & Redekop, Evgeniy (2020). Correlation between surface chemistry and morphology of PtCu and Pt nanoparticles during oxidation-reduction cycle. Applied Surface Science.  ISSN 0169-4332.  532, s 1- 6 . doi: 10.1016/j.apsusc.2020.147369 Fulltekst i vitenarkiv. Vis sammendrag

  Process conditions during catalytic reactions induce significant changes in surface chemistry and structure of bi- (mono) metallic nanoparticles leading to their deactivation, and this can ultimately affect the reactions long-term performance. Here PtCu and Pt model nanoparticles are prepared by microwave synthesis and characterized by X-ray diffraction (XRD). Surface chemical and morphological changes of the nanoparticles during high-temperature oxidation and reduction treatments cycle are correlated by near in situ X-ray photoelectron spectroscopy (XPS) and ex situ transmission electron microscopy (TEM) - energy-dispersive X-ray spectroscopy (EDS) studies. At 300 °C the surface atomic composition of the PtCu nanoparticles switches reversibly upon the cycle and at the same time their morphology and composition are maintained. At 400 °C, the surface atomic composition does not fully restore and, while the shape is maintained, the size and composition are not. This occurs by a mechanism of Cu leaching out from the nanoparticles. These data delineate potential operating conditions for stable PtCu nanocatalysts.

• Poulia, Anthoula; S. Azar, Amin; Svec, Peter; Bazioti, Kalliopi; Belle, Branson; Gunnæs, Anette Eleonora; Diplas, Spyridon & Mikheenko, Pavlo (2020). Nanoscale Magnetic Properties of Additively Manufactured FeCoNiAlxMnx High-Entropy Alloys, In  2020 IEEE 10th International Conference on “Nanomaterials: Applications & Properties” (NAP – 2020).  IEEE.  ISBN 978-1-7281-8506-4.  Article.  s 01NMM02-1 - 01NMM02-5 Fulltekst i vitenarkiv. Vis sammendrag

  Magnetic properties of High-Entropy Alloys based on the Fe-Co-Ni-Al-Mn system are reported. High-Entropy Alloys are cutting-edge technological materials containing five or more elements in relatively high concentrations (5–35 at.%) within one or several solid-state solutions. These solutions are stabilized at the nanometer scale due to the high contribution of the mixing entropy to the Gibbs free energy, which can overcome the enthalpic contribution. Two magnetic alloys are found in FeCoNiAlxMnx (1.6 at.%  x  7.8 at.%) samples processed by laser metal deposition. The magnetic techniques used to screen the materials were magneto-optical imaging and magnetic force microscopy. The former allows characterizing magnetic properties within the mm-μm scale, while the latter is efficient down to the nanometer scale. Magnetic screening confirms the importance of the nanostructure in defining magnetic properties of the alloys, and the trends in the magnetic behavior as a function of the alloy composition are revealed. The experimental results suggest that it is possible to form unique alloys, which may outperform conventional magnetic materials used in a variety of applications such as transformers, screening shields and wind power generators.

• Oyama, Kohei; Diplas, Spyridon; M'hamdi, Mohammed; Gunnæs, Anette Eleonora & S. Azar, Amin (2019). Heat source management in wire-arc additive manufacturing process for Al-Mg and Al-Si alloys. Additive Manufacturing.  ISSN 2214-8604.  26, s 180- 192 . doi: 10.1016/j.addma.2019.01.007 Fulltekst i vitenarkiv. Vis sammendrag

  Modelling of wire-arc additive manufacturing process is an effective way for adapting the optimum parameters as well as understanding and managing the sequences of layer-by-layer deposition. Some of these parameters such as toolpath, deposition intervals and heat source power play important roles in improving the process viability and cost efficiency. In this article, we have studied Al-5Mg, Al-3Si alloys as demonstrators, from both experimental and modelling perspectives, to benchmark different deposition parameters and provided guidelines for optimising the process conditions. Physical values such as total distortion and residual stress were selected as indicators for the manufacturability of the structure. The simulations were performed by Simufact Welding software, that is outfitted with the MARC solver and the experiments were executed in a robotic cell. We have introduced a method for optimising the process parameters based on the heat source power modification and selection of unique parameters for each deposition layer. This was performed by monitoring the evolution of the molten pool size and geometry when building a wall structure. The results suggest that achieving an uninterrupted deposition process entails modification of the heat input for each layer. Thus, a simple analytical method was proposed to estimate the heat input reduction coefficient for a wall structure as a function of molten pool geometry and the height at which, a new layer is being deposited. It was also shown that a generic selection of parameters for aluminium alloys may impair the eventual quality for some of the alloys due to their inherent physical properties such as high temperature flowability.

• Vogel, Andreas; Durant, Adam; Cassiani, Massimo; Clarkson, Rory J.; Slaby, Michal; Diplas, Spyridon; Krüger, Kirstin & Stohl, Andreas (2019). Simulation of volcanic ash ingestion into a large aero engine: particle–fan interactions. Journal of turbomachinery.  ISSN 0889-504X.  141(1) . doi: 10.1115/1.4041464 Vis sammendrag

  Volcanic ash (VA) clouds in flight corridors present a significant threat to aircraft operations as VA particles can cause damage to gas turbine engine components that lead to a reduction of engine performance and compromise flight safety. In the last decade, research has mainly focused on processes such as erosion of compressor blades and static components caused by impinging ash particles as well as clogging and/or corrosion effects of soft or molten ash particles on hot section turbine airfoils and components. However, there is a lack of information on how the fan separates ingested VA particles from the core stream flow into the bypass flow and therefore influences the mass concentration inside the engine core section, which is most vulnerable and critical for safety. In this numerical simulation study, we investigated the VA particle–fan interactions and resulting reductions in particle mass concentrations entering the engine core section as a function of particle size, fan rotation rate, and for two different flight altitudes. For this, we used a high-bypass gas-turbine engine design, with representative intake, fan, spinner, and splitter geometries for numerical computational fluid dynamics (CFD) simulations including a Lagrangian particle-tracking algorithm. Our results reveal that particle–fan interactions redirect particles from the core stream flow into the bypass stream tube, which leads to a significant particle mass concentration reduction inside the engine core section. The results also show that the particle–fan interactions increase with increasing fan rotation rates and VA particle size. Depending on ingested VA size distributions, the particle mass inside the engine core flow can be up to 30% reduced compared to the incoming particle mass flow. The presented results enable future calculations of effective core flow exposure or dosages based on simulated or observed atmospheric VA particle size distribution, which is required to quantify engine failure mechanisms after exposure to VA. As an example, we applied our methodology to a recent aircraft encounter during the Mt. Kelud 2014 eruption. Based on ambient VA concentrations simulated with an atmospheric particle dispersion model (FLEXPART), we calculated the effective particle mass concentration inside the core stream flow along the actual flight track and compared it with the whole engine exposure.

• Almeida Carvalho, Patricia; Thøgersen, Annett; Ma, Quanbao; Wright, Daniel Nilsen; Diplas, Spyridon; Galeckas, Augustinas; Azarov, Alexander; Jokubavicius, Valdas; Sun, J; Syväjärvi, Mikael; Svensson, Bengt Gunnar & Løvvik, Ole Martin (2018). Boron-doping of cubic SiC for intermediate band solar cells: a scanning transmission electron microscopy study. SciPost Physics.  ISSN 2542-4653.  5(3) . doi: 10.21468/SciPostPhys.5.3.021
• Bergum, Kristin; Riise, Heine Nygard; Gorantla, Sandeep Madhukar; Lindberg, Per; Jensen, Ingvild Julie Thue; Gunnæs, Anette Eleonora; Galeckas, Augustinas; Diplas, Spyridon; Svensson, Bengt Gunnar & Monakhov, Edouard (2018). Improving carrier transport in Cu2O thin films by rapid thermal annealing. Journal of Physics: Condensed Matter.  ISSN 0953-8984.  30(7) . doi: 10.1088/1361-648X/aaa5f4
• Galeckas, Augustinas; Almeida Carvalho, Patricia; Ma, Quanbao; Azarov, Alexander; Hovden, Sigurd Slettemark; Thøgersen, Annett; Wright, Daniel Nilsen; Diplas, Spyridon; Løvvik, Ole Martin; Jokubavicius, Valdas; Sun, Jianwu; Syväjärvi, Mikael & Svensson, Bengt Gunnar (2018). Optical and microstructural investigation of heavy B-doping effects in sublimation-grown 3C-SiC. Materials Science Forum.  ISSN 0255-5476.  924, s 221- 224 . doi: 10.4028/www.scientific.net/MSF.924.221 Vis sammendrag

  In this work, a complementary microstructural and optical approach is used to define processing conditions favorable for the formation of deep boron-related acceptor centers that may provide a pathway for achieving an intermediate band behavior in highly B-doped 3C-SiC. The crystallinity, boron solubility and precipitation mechanisms in sublimation-grown 3C-SiC crystals implanted to 1-3 at.% B concentrations were investigated by STEM. The revealed defect formation and boron precipitation trends upon thermal treatment in the range 1100-2000°C have been cross-correlated with the optical characterization results provided by imaging PL spectroscopy. We discuss optical activity of the implanted B ions in terms of both shallow acceptors and deep D-centers, a complex formed by a boron atom and a carbon vacancy, and associate the observed spectral developments upon annealing with the strong temperature dependence of the D-center formation efficiency, which is further enhanced by the presence of implantation-induced defects.

• Thøgersen, Annett; Jensen, Ingvild Julie Thue; Stange, Marit Synnøve Sæverud; Kjeldstad, Torunn; Martinez-Martinez, Diego; Løvvik, Ole Martin; Ulyashin, Alexander & Diplas, Spyridon (2018). Formation of nanoporous Si upon self-organized growth of Al and Si nanostructures. Nanotechnology.  ISSN 0957-4484.  29(31) . doi: 10.1088/1361-6528/aac36a Fulltekst i vitenarkiv.
• Thøgersen, Annett; Jensen, Ingvild Julie Thue; Stange, Marit Synnøve Sæverud; Røyset, Arne Karstein; Løvvik, Ole Martin; Ulyashin, Alexander & Diplas, Spyridon (2018). Valence charge distribution in homogenous silicon-aluminium thin-films. Journal of Physics: Condensed Matter.  ISSN 0953-8984.  30:35502(33), s 1- 11 . doi: 10.1088/1361-648X/aad216 Fulltekst i vitenarkiv.
• Jensen, Ingvild Julie Thue; Gorantla, Sandeep Madhukar; Løvvik, Ole Martin; Gan, Jiantuo; Nguyen, Phuong Dan; Monakhov, Edouard; Svensson, Bengt Gunnar; Gunnæs, Anette Eleonora & Diplas, Spyridon (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 Fulltekst i vitenarkiv.
• Ma, Quanbao; Carvalho, Patricia; Galeckas, Augustinas; Azarov, Alexander; Hovden, Sigurd Slettemark; Thøgersen, Annett; Wright, Daniel Nilsen; Diplas, Spyridon; Løvvik, Ole Martin; Jokubavicius, Valdas; Sun, Jianwu; Syväjärvi, Mikael & Svensson, Bengt Gunnar (2017). Characterization of B-implanted 3C-SiC for intermediate band solar cells. Materials Science Forum.  ISSN 0255-5476.  897, s 299- 302 . doi: 10.4028/www.scientific.net/MSF.897.299 Vis sammendrag

  Sublimation-grown 3C-SiC crystals were implanted with B ions at elevated temperature (400 °C) using multiple energies (100 to 575 keV) with a total dose of 1.3×1017 atoms/cm2 in order to form intermediate band (IB) in 3C-SiC. The samples were then annealed at 1400 °C for 60 min. An anomalous area in the center was observed in the PL emission pattern. The SIMS analysis indicated that the B concentration was the same both within and outside the anomalous area. The buried boron box-like concentration profile can reach ~3×1021 cm-3 in the plateau region. In the anomalous area a broad emission band (possible IB) emerges at around ~1.7-1.8 eV, which may be associated with B-precipitates having a sufficiently high density. Sublimation-grown 3C-SiC crystals were implanted with B ions at elevated temperature (400 °C) using multiple energies (100 to 575 keV) with a total dose of 1.3×1017 atoms/cm2 in order to form intermediate band (IB) in 3C-SiC. The samples were then annealed at 1400 °C for 60 min. An anomalous area in the center was observed in the PL emission pattern. The SIMS analysis indicated that the B concentration was the same both within and outside the anomalous area. The buried boron box-like concentration profile can reach ~3×1021 cm-3 in the plateau region. In the anomalous area a broad emission band (possible IB) emerges at around ~1.7-1.8 eV, which may be associated with B-precipitates having a sufficiently high density.

• Vogel, Andreas; Diplas, Spyridon; Durant, Adam; S. Azar, Amin; Sunding, Martin Fleissner; Rose, William I.; Sytchkova, Anna Krasilnikova; Bonadonna, Costanza; Krüger, Kirstin & Stohl, Andreas (2017). Reference data set of volcanic ash physicochemical and optical properties. Journal of Geophysical Research (JGR): Atmospheres.  ISSN 2169-897X.  122(17), s 9485- 9514 . doi: 10.1002/2016JD026328 Fulltekst i vitenarkiv.
• Angelopoulos, Panagiotis M.; Maliachova, C.; Papakonstantinou, Konstantinos G.; Taxiarchou, Maria & Diplas, Spyridon (2016). Structural and physical characteristics of fine perlite expanded with a novel method in a vertical electric furnace. Transactions of the Institution of Mining and Metallurgy Section C - Mineral Processing and Extractive Metallurgy.  ISSN 0371-9553.  125(2), s 71- 80 . doi: 10.1080/03719553.2016.1156244 Vis sammendrag

  Expanded perlite is a popular lightweight material widely used due to its outstanding insulating properties. The expansion conditions directly affect perlite characteristics and its suitability for use in various applications. The conventional industrial expansion technique suffers disadvantages that adversely affects product quality and limit the range of expanded perlite applications. To overcome the drawbacks of the traditional technique, a new expansion process has been developed based on a novel vertical electric furnace (VEF). The use of the novel VEF process enables detailed knowledge and better control of expansion conditions, which together with raw material physicochemical properties directly affect the expanded perlite quality. In the present work, an extended experimental campaign was performed to investigate the physical properties and morphology of fine perlite expanded in the VEF. Expansion experiments were also performed in a pilot-scale, conventional furnace and the properties of products from both processes were compared. The novel expanded perlite particles have superior properties, namely significantly increased compression strength, size homogeneity, competitive water and oil absorption capacity, decreased surface porosity and thermal conductivity compared to conventionally expanded samples.

• Gan, Jiantuo; Gorantla, Sandeep Madhukar; Riise, Heine Nygard; Fjellvåg, Øystein Slagtern; Diplas, Spyridon; Løvvik, Ole Martin; Svensson, Bengt Gunnar; Monakhov, Edouard & Gunnæs, Anette Eleonora (2016). Structural properties of Cu2O epitaxial films grown on c-axis single crystal ZnO by magnetron sputtering. Applied Physics Letters.  ISSN 0003-6951.  108:152110(15), s 1- 5 . doi: 10.1063/1.4945985 Vis sammendrag

  Epitaxial Cu2O films grown by reactive and ceramic radio frequency magnetron sputtering on single crystalline ZnO (0001) substrates are investigated. The films are grown on both O- and Zn-polar surface of the ZnO substrates. The Cu2O films exhibit a columnar growth manner apart from a ∼5 nm thick CuO interfacial layer. In comparison to the reactively sputtered Cu2O, the ceramic-sputtered films are less strained and appear to contain nanovoids. Irrespective of polarity, the Cu2O grown by reactive sputtering is observed to have (111)Cu2O||(0001)ZnO epitaxial relationship, but in the case of ceramic sputtering the films are found to show additional (110)Cu2O reflections when grown on O-polar surface. The observed CuO interfacial layer can be detrimental for the performance of Cu2O/ZnO heterojunction solar cells reported in the literature.

• Gunnæs, Anette Eleonora; Gorantla, Sandeep Madhukar; Løvvik, Ole Martin; Gan, Jiantuo; Carvalho, Patricia; Svensson, Bengt Gunnar; Monakhov, Edouard; Bergum, Kristin; Jensen, Ingvild Julie Thue & Diplas, Spyridon (2016). Epitaxial strain-induced growth of CuO at Cu2O/ZnO interfaces. Journal of Physical Chemistry C.  ISSN 1932-7447.  120(41), s 23552- 23558 . doi: 10.1021/acs.jpcc.6b07197 Vis sammendrag

  Cu2O/ZnO has been envisaged as a potential material system for the next generation thin film solar cells. So far, the experimental efforts to obtain conversion efficiencies close to the theoretically predicted value have failed. Combining aberration-corrected (scanning) transmission electron microscopy and density functional theory modelling, we have studied the interfaces between single crystal c-axis oriented ZnO and high-quality magnetron sputtered Cu2O films. Strikingly, our study shows that the first ~5 nm of the Cu-oxide films have the structure of the monoclinic CuO phase. The CuO layer is textured with the (111), (11¯1), (¯111), (1¯1 ¯1), (¯1 ¯11), (1¯11), (¯11¯1) and (100) planes parallel to the (0001) and (000¯1) ZnO interfaces. The ionic arrangement on these planes resembles the hexagonal arrangement of the ZnO interface and epitaxy exists across the interface. A continued epitaxial growth of [111] oriented Cu2O follows resulting in epitaxial 180o rotation twins in the Cu2O layer. For the case with the (100)CuO interfacial plane we have: (111)[1¯10]Cu2O II (100)[011]CuO II (0001)[11¯20]ZnO. Because of a closer lattice matching of CuO with ZnO and Cu2O, the total strain and energy is reduced compared to a pure (111)Cu2O II (0001)ZnO interface. The existence of CuO is anticipated to be a contributing factor for the low conversion efficiencies obtained experimentally.

• Ma, Quanbao; Galeckas, Augustinas; Azarov, Alexander; Thøgersen, Annett; Carvalho, Patricia; Wright, Daniel Nilsen; Diplas, Spyridon; Løvvik, Ole Martin; Jokubavicius, Valdas; Liu, Xinyu; Sun, Jianwu; Syväjärvi, Mikael & Svensson, Bengt Gunnar (2016). Boron-implanted 3C-SiC for intermediate band solar cells. Materials Science Forum.  ISSN 0255-5476.  858, s 291- 294 . doi: 10.4028/www.scientific.net/MSF.858.291 Fulltekst i vitenarkiv. Vis sammendrag

  Sublimation-grown 3C-SiC crystals were implanted with 2 atomic percent of boron ions at elevated temperature (400 °C) using multiple energies (100 to 575 keV) with a total dose of 8.5×1016 atoms/cm2. The samples were then annealed at 1400, 1500 and 1600 °C for 1h at each temperature. The buried boron box-like concentration profile can reach ~2×1021 cm-3 in the plateau region. The optical activity of the incorporated boron atoms was deduced from the evolution in absorption and emission spectra, indicating possible pathway for achieving an intermediate band behavior in boron doped 3C-SiC at sufficiently high dopant concentrations.

• Mudu, Federica; Olsbye, Unni; Arstad, Bjørnar; Diplas, Spyridon; Li, Yanjun & Fjellvåg, Helmer (2016). Aluminium substituted lanthanum based perovskite type oxides, non-stoichiometry and performance in methane partial oxidation by framework oxygen. Applied Catalysis A : General.  ISSN 0926-860X.  523, s 171- 181 . doi: 10.1016/j.apcata.2016.05.013 Vis sammendrag

  A series of Rh-promoted La0.75Sr0.25(Fe0.80Co0.20)(1-x)AlxO3-δ (x = 0, 0.10, 0.25, 0.40, 0.60) samples were investigated as oxygen reservoirs for the conversion of CH4 to syngas at 873 K and 1 atm. Neutron powder diffraction studies revealed a decreasing rhombohedral distortion on increasing Al-content. XPS and TEM were employed to investigate surface chemistry and morphology of the Al = 0.25 sample. The influence of Al-substitution on the redox properties was studied by flowing titration whereas catalytic properties were studied by means of transient pulses of CH4 and O2, as well of 13CH4 and CO. The products (CO, H2, CO2 and H2O) of the reaction between CH4 and the studied oxides were successfully tuned by tailoring the redox properties of the reducible oxides through the Al-substitution.

• Syväjärvi, Mikael; Ma, Quanbao; Jokubavicius, Valdas; Galeckas, Augustinas; Sun, Jianwu; Liu, Xinyu; Jansson, Mattias; Wellmann, Peter; Linnarsson, Margareta; Runde, Paal; Johansen, Bertil; Thøgersen, Annett; Diplas, Spyridon; Carvalho, Patricia; Løvvik, Ole Martin; Wright, Daniel Nilsen; Azarov, Alexander & Svensson, Bengt Gunnar (2016). Cubic silicon carbide as a potential photovoltaic material. Solar Energy Materials and Solar Cells.  ISSN 0927-0248.  145, s 104- 108 . doi: 10.1016/j.solmat.2015.08.029 Fulltekst i vitenarkiv. Vis sammendrag

  In this work we present a significant advancement in cubic silicon carbide (3C-SiC) growth in terms of crystal quality and domain size, and indicate its potential use in photovoltaics. To date, the use of 3C-SiC for photovoltaics has not been considered due to the band gap of 2.3 eV being too large for conventional solar cells. Doping of 3C-SiC with boron introduces an energy level of 0.7 eV above the valence band. Such energy level may form an intermediate band (IB) in the band gap. This IB concept has been presented in the literature to act as an energy ladder that allows absorption of sub-bandgap photons to generate extra electron–hole pairs and increase the efficiency of a solar cell. The main challenge with this concept is to find a materials system that could realize such efficient photovoltaic behavior. The 3C-SiC bandgap and boron energy level fits nicely into the concept, but has not been explored for an IB behavior. For a long time crystalline 3C-SiC has been challenging to grow due to its metastable nature. The material mainly consists of a large number of small domains if the 3C polytype is maintained. In our work a crystal growth process was realized by a new approach that is a combination of initial nucleation and step-flow growth. In the process, the domains that form initially extend laterally to make larger 3C-SiC domains, thus leading to a pronounced improvement in crystalline quality of 3C-SiC. In order to explore the feasibility of IB in 3C-SiC using boron, we have explored two routes of introducing boron impurities; ion implantation on un-doped samples and epitaxial growth on un-doped samples using pre-doped source material. The results show that 3C-SiC doped with boron is an optically active material, and thus is interesting to be further studied for IB behavior. For the ion implanted samples the crystal quality was maintained even after high implantation doses and subsequent annealing. The same was true for the samples grown with pre-doped source material, even with a high concentration of boron impurities. We present optical emission and absorption properties of as-grown and boron implanted 3C-SiC. The low-temperature photoluminescence spectra indicate the formation of optically active deep boron centers, which may be utilized for achieving an IB behavior at sufficiently high dopant concentrations. We also discuss the potential of boron doped 3C-SiC base material in a broader range of applications, such as in photovoltaics, biomarkers and hydrogen generation by splitting water

• Thøgersen, Annett; Stange, Marit Synnøve Sæverud; Jensen, Ingvild Julie Thue; Røyset, Arne; Ulyashin, Alexander & Diplas, Spyridon (2016). Structure and optical properties of aSiAl and aSiAlHx magnetron sputtered thin films. APL Materials.  ISSN 2166-532X.  4:036103(3) . doi: 10.1063/1.4944506
• Diplas, Spyridon; Romanyuk, Andriy; Thøgersen, Annett & Ulyashin, Alexander (2015). An in situ XPS study of growth of ITO on amorphous hydrogenated Si: Initial stages of heterojunction formation upon processing of ITO/a-Si:H based solar cell structures. Physica Status Solidi (a) applications and materials science.  ISSN 1862-6300.  212(1), s 47- 50 . doi: 10.1002/pssa.201431773 Vis sammendrag

  In this work we studied the interface growth upon deposition of indium-tin oxide (ITO) on amorphous hydrogenated Si (a-Si:H)/crystalline Si (c-Si) structures. The analysis methods used were X-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS) in combination with in situ film growth with magnetron sputtering. The analysis was complemented with transmission electron microscopy (TEM) of the deposited films. The sputtering equipment was attached to the XPS spectrometer and hence early stage film growth was observed without breaking the vacuum. It was shown that during early deposition stages ITO is reduced by a-Si:H. The reduction is accompanied with formation of metallic In and Sn at the interface. Formation of Sn is more enhanced on a-Si substrates whilst formation of In is more dominant on c-Si substrates. The reduction effect is less intense for amorphous hydrogenated Si as compared to crystalline Si and this is attributed to stronger presence of dangling bonds in the latter than the former.

• Iwu, Kingsley Odinaka; Galeckas, Augustinas; Diplas, Spyridon; Seland, Frode; Kuznetsov, Andrej & Norby, Truls (2014). Effects of temperature, triazole and hot-pressing on the performance of TiO2 photoanode in a solid-state photoelectrochemical cell. Electrochimica Acta.  ISSN 0013-4686.  115, s 66- 74 . doi: 10.1016/j.electacta.2013.10.095 Vis sammendrag

  The photocurrent of hydrogen generating solid-state photoelectrochemical cell utilising a polybenzimidazole proton-conducting membrane and gaseous anode reactants has been enhanced by operation at higher temperatures. With a bias of 0 V for example, photocurrent increased from 15 to 30 μA/cm2 on moving from 25 °C to 45 °C. The increase in photocurrent, which was limited by the dehydration of the cell, was shown to have contribution from improved electrode kinetics. Modification of TiO2 surface with triazole, a conjugated heterocyclic compound, led to significant increase in photocurrent up to 4 fold increase at 0 V and 25 °C. This was attributed to improved separation of photogenerated charge carriers, as confirmed by correspondingly increased carrier lifetimes from 50 ns to 90 ns for triazole-modified TiO2. Assembly of the photoelectrochemical cell by hot-pressing induced a ̴ 0.3 eV red shift in optical absorption edge of TiO2, in agreement with a shift of its valence band maximum to higher binding energy.

• Kytin, V.G; Kulbachinskii, V.A; Reukova, O.V; Galperin, Yuri; Johansen, Tom Henning; Diplas, Spyridon & Ulyashin, Alexander (2014). Conducting properties of In2O3:Sn thin films at low temperatures. Applied Physics A: Materials Science & Processing.  ISSN 0947-8396.  114(3), s 957- 964 . doi: 10.1007/s00339-013-7799-8 Vis sammendrag

  Electrical conductivity, Hall effect and magnetoresistance of In2O3:Sn thin films deposited on a glass substrates at different temperatures and oxygen pressures, have been investigated in the temperature range 4.2–300 K. The observed temperature dependences of resistivity for films deposited at 230 °C as well as at nominally room temperatures were typical for metallic transport of electrons except temperature dependence of resistivity of the In2O3:Sn film deposited in the oxygen deficient atmosphere. The electrical measurements were accompanied by AFM and SEM studies of structural properties, as well as by XPS analysis. It is established that changes of morphology and crystallinity of ITO films modify the low-temperature behavior of resistivity, which still remains typical for metallic transport. This is not the case for the oxygen deficient ITO layer. XPS analysis shows that grown in situ oxygen deficient ITO films have enhanced DOS between the Fermi level and the valence band edge. The extra localized states behave as acceptors leading to a compensation of n-type ITO. That can explain lower n-type conductivity in this material crossing over to a Mott-type hopping at low temperatures. Results for the low temperature measurements of stoichiometric ITO layers indicate that they do not show any trace of metal-to-insulator transition even at 4.2 K. We conclude that, although ITO is considered as a highly doped wide-band gap semiconductor, its low-temperature properties are very different from those of conventional highly doped semiconductors.

• Løvvik, Ole Martin; Diplas, Spyridon; Romanyuk, Andriy B. & Ulyashin, Alexander (2014). Initial stages of ITO/Si interface formation: In situ x-ray photoelectron spectroscopy measurements upon magnetron sputtering and atomistic modelling using density functional theory. Journal of Applied Physics.  ISSN 0021-8979.  115(8) . doi: 10.1063/1.4866991 Vis sammendrag

  Initial stages of indium tin oxide (ITO) growth on a polished Si substrate upon magnetron sputtering were studied experimentally using in-situ x-ray photoelectron spectroscopy measurements. The presence of pure indium and tin, as well as Si bonded to oxygen at the ITO/Si interface were observed. The experimental observations were compared with several atomistic models of ITO/Si interfaces. A periodic model of the ITO/Si interface was constructed, giving detailed information about the local environment at the interface. Molecular dynamics based on density functional theory was performed, showing how metal-oxygen bonds are broken on behalf of silicon-oxygen bonds. These theoretical results support and provide an explanation for the present as well as previous ex-situ and in-situ experimental observations pointing to the creation of metallic In and Sn along with the growth of SiO x at the ITO/Si interface.

• Nagayoshi, Hiroshi; Diplas, Spyridon; Walmsley, John; Andersen, Niels Højmark; Karlsson, Arne; Graff, Joachim Seland; Chirvony, Vladimir; Pastor, Juan M. & Ulyashin, Alexander (2014). One-step formation of nanostructures on silicon surfaces using pure hydrogen-radical-initiated reactions. Physica Status Solidi (a) applications and materials science.  ISSN 1862-6300.  211(1), s 231- 238 . doi: 10.1002/pssa.201330220 Vis sammendrag

  One-step formation of silicon nanowires, sheets, and texture surface on a silicon substrate has been achieved using hydrogen-radical etching reactions. Metallic tungsten and for comparison purposes a tungsten hot wire, were used as catalysts for the hydrogen-molecular cracking. It was shown that a variety of surface structures on silicon such as inverted pyramid texture, V-groove texture, dense silicon nanowire growth over texture, and nanosheet structure can be obtained by controlling the process conditions. The obtained results suggested that the formation of nanotungsten silicide particle is an essential prerequisite to obtain these structures. The particles work as an etching mask against hydrogen-radical etching, as well as a catalyst for vapor–solid–solid (VSS) growth. SEM, TEM, micro-RAMAN, and XPS were used for the analysis of the hydrogen-radical-treated Si samples. The Si nanowires growth model, as well as the texturing mechanism initiated by hydrogen-radical treatment of Si surface in the presence of tungsten nanoparticle is discussed. It is concluded that the proposed acid-free method, which is based on a modification of Si surfaces only by hydrogen radicals, can be considered as a “green” technology approach, which can be used for the costeffective fabrication of silicon nanostructures, which can be considered as a base for several types of advanced devices in the future.

• Senel, Esma; Walmsley, John; Diplas, Spyridon & Nisancioglu, Kemal (2014). Liquid metal embrittlement of aluminium by segregation of trace element gallium. Corrosion Science.  ISSN 0010-938X.  85, s 167- 173 . doi: 10.1016/j.corsci.2014.04.012 Vis sammendrag

  The effect of small amounts of gallium on liquid metal embrittlement of model binary AlGa alloys containing 50–1000 ppm2 Ga is studied. Ga segregation did not occur by annealing in the temperature range 300–600 °C because of the high solid solution solubility of Ga in aluminium. Alkaline etching caused significant enrichment of Ga at the surface by dealloying. Diffusion of Ga from the surface into the grain boundaries caused liquid metal embrittlement of samples containing at least 250 ppm Ga. Segregated Ga dissolved back into aluminium by annealing for 1 h at 600 °C after etching, eliminating the grain boundary embrittlement.

• Jensen, Ingvild Julie Thue; Thøgersen, Annett; Løvvik, Ole Martin; Schreuders, Herman; Dam, Bernard & Diplas, Spyridon (2013). X-ray photoelectron spectroscopy investigation of magnetron sputtered Mg-Ti-H thin films. International Journal of Hydrogen Energy.  ISSN 0360-3199.  38(25), s 10704- 10715 . doi: 10.1016/j.ijhydene.2013.05.142 Vis sammendrag

  Thin film samples of Mg80Ti20 (Mg–Ti) and Mg, both with and without H, were investigated in a series of X-ray photoelectron spectroscopy (XPS) measurements. The samples were covered with a thin protective layer of Pd, which was removed by Ar+ sputtering prior to data acquisition. This sputtering was found to reduce both oxides and hydrides. A distinct, previously unknown peak was revealed in the Mg KLL spectrum of the Mg–Ti–H samples, located between the metallic and the MgO component. This peak was attributed to trapping of H in very stable interstitial sites at the interface between Ti nano-clusters and the Mg matrix, based on earlier density functional theory calculations and supported by so-called Bader analysis. The latter was performed in order to study the theoretical charge distribution between Mg, Ti and H, establishing a link between the position of the previously unknown peak and the effect of H on the valence state of Mg. The composition of the samples was studied both by energy dispersive spectroscopy using transmission electron microscopy and by quantitative XPS analysis. Final state Auger parameters (AP) were obtained for metallic Mg, MgO and MgH2, as well as Mg affected by trapped H. No difference between the AP values from the metallic components was found between the Mg and the Mg–Ti samples. The AP values for MgO and MgH2 were consistent with previous reports in literature; several eV lower than the metallic value. Mg in the vicinity of trapped hydrogen, on the other hand, showed a more metallic character, with its corresponding AP value less than 1 eV below the AP for pure Mg.

• Kurt, Köksal; Diplas, Spyridon; Walmsley, John & Nisancioglu, Kemal (2013). Effect of Trace Elements Lead and Tin on Anodic Activation of AA8006 Aluminum Sheet. Journal of the Electrochemical Society.  ISSN 0013-4651.  160(11), s C542- C552 . doi: 10.1149/2.054311jes Vis sammendrag

  Most commercial aluminum alloys, when heat treated in air at 600°C, become activated anodically in chloride solution as a result of segregation of a nanometer size Pb-rich film between the aluminum matrix and thermally-formed γAl2O3. However, certain recycled alloys, such as AA8006, can be activated at lower annealing temperatures. The purpose of this work was to explore the cause of low temperature activation. Alloy 8006 rolled samples in the fully-annealed T0 temper were used in the as-received condition and also mechanically polished to remove the grain-refined surface layer (GRSL) and subsequently annealed for 1 h at 450°C, at which maximum activation was attained. FEG-TEM analysis of cross-sectional sample foils and XPS depth profiling of the polished samples showed the presence of a nanometer size film at the metal-oxide interface, which was enriched in metallic Pb and Sn and which lead to the low temperature activation of the alloy. Pb and Sn segregation was also detected along the grain boundaries of the GRSL on the as-received samples, as interface segregant associated with oxide particles incorporated during hot rolling. Nanofilm segregation of Pb and Sn, and consequently activation, did not occur on the GRSL-free samples prepared by annealing in O2-free environment.

• Thøgersen, Annett; Syre, Marie; Olaisen, Birger Retterstøl & Diplas, Spyridon (2013). Studies of the oxidation states of phosphorus gettered silicon substrates using X-ray photoelectron spectroscopy and transmission electron microscopy. Journal of Applied Physics.  ISSN 0021-8979.  113(4) . doi: 10.1063/1.4775818 Vis sammendrag

  Phosphorus diffusion in p-type silicon wafers with Fe or Cr impurities has been investigated using X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy. Silicon wafers doped with phosphorous are heavily used in semiconductor devices. It is, therefore, of crucial importance to determine their compositions profile. The XPS P2p spectra revealed presence of elemental phosphorus (P0), donor ion (P+), and interstitial or substitutional diffused P− from phosphorus oxides P2O5 and P4O10 as residues of the diffusion process. The surface of the Si wafers was oxidized during the deposition of P2O5 and SiO2 (with a subsequent heating). This resulted in the formation of a 1.3–1.4 nm thick SiOx layer. Pile-up of elemental P was found near the surface of the wafer. This pile-up was larger for Fe contaminated samples compared to Cr contaminated ones. The pile-up may have been caused by a decrease in the diffusion length of P+ donor ions, which could only be found in the first few nm near the surface of the silicon wafer. The observed diffusion length was DLP+<DLP0<DLP−.

• Anawati, Ms; Nordmark, Heidi; Diplas, Spyridon; Walmsley, John & Nisancioglu, Kemal (2012). Surface Segregation of Trace Element Bismuth during Heat Treatment of Aluminum. Journal of the Electrochemical Society.  ISSN 0013-4651.  159(3), s C137- C145 . doi: 10.1149/2.100203jes Vis sammendrag

  Surface segregation of bismuth and resulting oxidation of rolled aluminum bismuth model alloys during heat-treatment were investigated by electron-optical techniques, glow discharge optical emission spectroscopy and X-ray photoelectron spectroscopy. Heat treatment at 600°C caused segregation of liquid Bi in the form of a metallic nanofilm at the oxide-metal interface. Breakdown of thermally-formed -Al2O3 crystalline oxide by the liquid Bi film during subsequent cooling in water produced a composite oxide layer, consisting of remnants of the -Al2O3 layer on top and an amorphous hydrated layer of about 1.5 µm thick between the -Al2O3 layer and the metal. Cooling in laboratory air after heat-treatment gave a slightly thinner (about 1 µm) amorphous layer than that compared to water cooling. Formation of the thick aluminum oxide layer during cooling was attributed to the maintenance of the depassivating BiAl interfacial nanofilm by dealloying of the Al component of the metal. Existence of the BiAl interfacial film in a fluidized state during cooling, which is a necessary condition for oxide growth, was further enhanced by significant depression of the solidification point of the film due to its nanometer order of thickness.

• Diskus, Madeleine; Nilsen, Ola; Fjellvåg, Helmer; Diplas, Spyridon; Beato, Pablo; Harvey, Clare; Lantman, Evelien van Schrojenstein & Weckhuysen, Bert M. (2012). Combination of characterization techniques for atomic layer deposition MoO3 coatings: From the amorphous to the orthorhombic alpha-MoO3 crystalline phase. Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films.  ISSN 0734-2101.  30(1) . doi: 10.1116/1.3643350 Vis sammendrag

  Thin films of MoO3 deposited on Si(111) and Al2O3(001) substrates by atomic layer deposition have been investigated by x-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and Raman spectroscopy for detailed characterization of composition and morphology. Comparison of angle resolved x-ray photoelectron spectroscopy (ARXPS) and XPS depth profiles based on Ar+ sputtering is reported. Sputtering induces a reduction of molybdenum in MoO3 from +IV to metallic Mo as the interface toward Si is approached, whereas ARXPS on a 10 nm thin film shows that Mo(VI) remains outside the interface toward Si where lower valent molybdenum compounds are formed. Upon annealing, the as-deposited amorphous thin films of MoO3 crystallize into β- or α-MoO3 as identified by x-ray diffraction. The current study provides a convenient route toward formation of metastable β-MoO3 and a full crystallization pathway from amorphous to crystalline α-MoO3. Combined AFM and Raman analysis have been performed on thin films of α-MoO3 deposited on Al2O3(001) and prove that the crystallization proceeds via island growth at 600 °C. The Raman intensity ratios between different bands depend strongly on morphology and size of crystalites

• Jensen, Ingvild Julie Thue; Diplas, Spyridon & Løvvik, Ole Martin (2012). Hydrogen induced stabilization of meta-stable Mg-Ti. Applied Physics Letters.  ISSN 0003-6951.  100(11:111902) . doi: 10.1063/1.3692578 Vis sammendrag

  The hydrogenation of Mg0.8125Ti0.1875 was investigated by density functional calculations, using a model where Ti was segregated into nano-clusters. Introducing small amounts of hydrogen resulted in significant stabilization, with the mixing enthalpy (cohesive energy relative to standard state elements) becoming negative for hydrogen contents exceeding 0.07 H per metal. H prefers sites on the interface between Mg and Ti, with hydrogenation energies down to –115 kJ/(mol H2). Trapping of H on these very stable sites is proposed as an alternative explanation to why the reversibility of Mg-Ti thin films, which are initially meta-stable, can be preserved over many cycles of hydrogenation.

• Jensen, Ingvild Julie Thue; Løvvik, Ole Martin; Schreuders, H; Dam, B & Diplas, Spyridon (2012). Combined XPS and first principle study of metastable Mg-Ti thin films. Surface and Interface Analysis.  ISSN 0142-2421.  44(8), s 986- 988 . doi: 10.1002/sia.4847 Vis sammendrag

  X-ray photoelectron spectroscopy (XPS) was employed to investigate Mg80Ti20 thin film samples prepared by magnetron sputtering and density functional theory (DFT) calculations were performed on atomistic models with similar stoichiometry. As Ti is known to be immiscible in Mg, the microstructure and atomic distribution of Mg–Ti thin films are not fully understood. In this work, it was shown by DFT calculations that the density of states (DOS) depends strongly on whether Ti is arranged in nano-clusters or if it is distributed quasi-randomly. The calculated DOS was compared to valence band spectra measured by XPS, as a new way of indirectly probing short-range order of such thin films. The XPS results of Mg80Ti20 were found to correspond best with the DOS calculated for the nano-cluster model, supporting the view that Ti forms small clusters in such sputtered thin films. Copyright © 2012 John Wiley & Sons, Ltd.

• Long, Ethan Schuyler; Azarov, Alexander; Kløw, Frode; Galeckas, Augustinas; Kuznetsov, Andrej & Diplas, Spyridon (2012). Ge redistribution in SiO2/SiGe structures under thermal oxidation: Dynamics and predictions. Journal of Applied Physics.  ISSN 0021-8979.  111(2) . doi: 10.1063/1.3677987 Fulltekst i vitenarkiv. Vis sammendrag

  Several fundamental aspects of the oxidation-induced redistribution of Ge in thin films of SiGe are studied. This includes the incorporation of Ge into the oxide and the formation of what is alternatively referred to as pile-up, snow-plow, or a germanium-rich layer. Experimental data from the present work shows longer oxidation times leading to an increase of Ge content in the pile-up region and eventually creating a single high Ge content pile-up layer by entirely consuming the initial SiGe layer. The pile-up effect was shown to occur at the oxidation interface, with the highest Ge content occurring at the same interface. For a given oxide thickness, the redistribution of Ge and the formation of a pile-up region was shown experimentally to be independent of temperature in the range between 800 °C and 1000 °C. Simulations using common models for the oxidation of Si and diffusion of Si in SiGe indicate that temperature does have an influence on the composition of the pile-up layer, though the range of achievable compositions is limited. The flux of Si due to diffusion of Si in SiGe relative to the oxidation-induced flux of Si out of the SiGe is integral to the formation and dimensions of a pile-up region. Two predictive relations were derived for describing the dynamics of oxidation of SiGe. The first relation is given for determining the pile-up layer thickness as a function of oxide thickness and the composition of the pile-up layer. The second relation assumes a limited supply of Si and is for determination of the minimum initial thickness of a SiGe layer to avoid oxidation of Ge. The validity of these equations was confirmed experimentally by RBS and XPS data from the present work. The proposed models may be used in nanostructuring of thin films of SiGe by oxidation and in the design of core-shell structures and transistors. This is all done with a focus on oxidation of epitaxial thin films (< 100 nm) of Si1-XGeX in dry O2 at 1 atm between 800 °C and 1000 °C.

• Schifano, Ramon; Schofield, Matthew D.; Vines, Lasse; Diplas, Spyridon; Monakhov, Edouard & Svensson, Bengt Gunnar (2012). Al and Si doping of sputtered ZnO thin films. IOP Conference Series: Materials Science and Engineering.  ISSN 1757-8981.  34 . doi: 10.1088/1757-899X/34/1/012007 Vis sammendrag

  In this work the effect of Al and Si content on the electrical, optical and structural characteristics of Radio Frequency (RF) sputtered ZnO thin films (~ 150 nrn thick) have been investigated. ZnO:Al and ZnO:Si films were deposited on glass through ZnO and Al targets and ZnO and Si targets co-sputtering, respectively. The Al and Si content have been varied between ~ 1018 cm−3 and ~ 4 × 1021 cm−3, as determined by secondary ion mass spectrometry (SIMS) and X-ray photoelectron spectroscopy (XPS) measurements. The X-ray analysis, in the Θ − 2Θ configuration, revealed a surfactant action of both Si and Al in the films, i.e., a reduction of the absolute stress ⊥ to the c axis from ~ 0.6 − 0.8 GPa to ~ 0.4 GPa and ~ 0.2 GPa for Al and Si doping, respectively. In addition, a corresponding decrease of the root mean square (RMS) of the surface roughness with higher Al and Si content has been observed by Atomic Force Micropscope (AFM) measurements. Finally, the electrical characterization of the ZnO films, performed by room temperature Hall measurements, suggested that the best structural conditions in terms of grain size and absolute stress correspond, as expected, to the minimum resistivity.

• Anawati, Ms; Diplas, Spyridon; Holme, Børge; Solberg, Jan Ketil; Mathiesen, Ragnvald; Walmsley, John & Nisancioglu, Kemal (2011). Surface Characterization of Heat Treated AlPbCu Model Alloys. Journal of the Electrochemical Society.  ISSN 0013-4651.  158(6), s C178- C184 . doi: 10.1149/1.3579506
• Thøgersen, Annett; Mayandi, Jeyanthinath; Vines, Lasse; Sunding, Martin Fleissner; Olsen, Arne; Diplas, Spyridon; Mitome, Masanori & Bando, Yoshio (2011). Composition and structure of Pd nanoclusters in SiOx thin film. Journal of Applied Physics.  ISSN 0021-8979.  109(8) . doi: 10.1063/1.3561492 Fulltekst i vitenarkiv.
• Anawati, Ms; Diplas, Spyridon & Nisancioglu, Kemal (2011). Effect of copper on anodic activity of aluminum-lead model alloy in chloride solution. Journal of the Electrochemical Society.  ISSN 0013-4651.  158(5), s C158- C163 . doi: 10.1149/1.3562946
• Böttger, Paul Heinrich Michael; Diplas, Spyridon; Flage-Larsen, Espen; Prytz, Øystein & Finstad, Terje (2011). Electronic structure of thermoelectric Zn-Sb. Journal of Physics: Condensed Matter.  ISSN 0953-8984.  23(26) . doi: 10.1088/0953-8984/23/26/265502
• Kumakiri, Izumi; Diplas, Spyridon; Simon, Christian Rone & Nowak, Pavel (2011). Photocatalytic Membrane Contactors for Water Treatment. Industrial & Engineering Chemistry Research.  ISSN 0888-5885.  50(10), s 6000- 6008 . doi: 10.1021/ie102470f
• Sunding, Martin Fleissner; Hadidi, Kianoosh; Diplas, Spyridon; Løvvik, Ole Martin; Norby, Truls & Gunnæs, Anette Eleonora (2011). XPS characterisation of in situ treated lanthanum oxide and hydroxide using tailored charge referencing and peak fitting procedures. Journal of Electron Spectroscopy and Related Phenomena.  ISSN 0368-2048.  184(7), s 399- 409 . doi: 10.1016/j.elspec.2011.04.002
• Thøgersen, Annett; Rein, Margrethe Holmer; Monakhov, Edouard; Mayandi, Jeyanthinath & Diplas, Spyridon (2011). Elemental distribution and oxygen deficiency of magnetron sputtered indium tin oxide films. Journal of Applied Physics.  ISSN 0021-8979.  109(11) . doi: 10.1063/1.3587174
• Tsiourvas, D.; Tsetsekou, A.; Arkas, M.; Diplas, Spyridon & Mastrogianni, E. (2011). Covalent attachment of a bioactive hyperbranched polymeric layer to titanium surface for the biomimetic growth of calcium phosphates. Journal of materials science. Materials in medicine.  ISSN 0957-4530.  22(1), s 85- 96 . doi: 10.1007/s10856-010-4181-7
• Diplas, Spyridon; Moslemzadeh, N; Watts, J.F.; Beamson, G & Tsakiropoulos, P (2010). An XPS study of the interatomic charge distribution in stainless steels. Surface and Interface Analysis.  ISSN 0142-2421.  42(6-7), s 722- 725 . doi: 10.1002/sia.3367
• Flage-Larsen, Espen; Diplas, Spyridon; Prytz, Øystein; Toberer, Eric S. & May, Andrew F. (2010). Valence band study of thermoelectric Zintl-phase SrZn2Sb2 and YbZn2Sb2: X-ray photoelectron spectroscopy and density functional theory. Physical Review B. Condensed Matter and Materials Physics.  ISSN 1098-0121.  81(20) . doi: 10.1103/PhysRevB.81.205204
• Jensen, Ingvild Julie Thue; Diplas, Spyridon; Løvvik, Ole Martin; Watts, J; Hinder, S; Schreuders, H & Dam, B (2010). X-ray photoelectron spectroscopy study of MgH2 thin films grown by reactive sputtering. Surface and Interface Analysis.  ISSN 0142-2421.  42(6-7), s 1140- 1143 . doi: 10.1002/sia.3347
• Diplas, Spyridon; Løvvik, Ole Martin; Nordmark, Heidi; Kepaptsoglou, Despoina Maria; Graff, Joachim Seland; Ladam, Cecile; Tyholdt, Frode; Walmsley, John; Gunnæs, Anette Eleonora; Fagerberg, Ragnar & Ulyashin, Alexander (2010). Characterization of thin and ultrathin transparent conducting oxide (TCO) films and TCO-Si interfaces with XPS, TEM and ab initio modeling. Surface and Interface Analysis.  ISSN 0142-2421.  42(6-7), s 874- 877 . doi: 10.1002/sia.3355
• Foss, Martin Smestad; Diplas, Spyridon & Gulbrandsen, Egil (2010). Mechanistic study of adsroption of cetyltrimethyl ammonium bromide on high purity iron using contact angle, polarization resistance and XPS. Electrochimica Acta.  ISSN 0013-4686.  55(17), s 4851- 4857 . doi: 10.1016/j.electacta.2010.03.071
• Gorzkowska-Sobas, Agnieszka A; Galeckas, Augustinas; Sunding, Martin Fleissner; Diplas, Spyridon & Kuznetsov, Andrej (2010). An investigation of Fe-doped ZnO thin films grown by magnetron sputtering. Physica Scripta.  ISSN 0031-8949.  T141 . doi: 10.1088/0031-8949/2010/T141/014004
• Jensen, Ingvild Julie Thue; Diplas, Spyridon & Løvvik, Ole Martin (2010). Density functional calculations of Ti nanoclusters in the metastable Mg-Ti system. Physical Review B. Condensed Matter and Materials Physics.  ISSN 1098-0121.  82(17) . doi: 10.1103/PhysRevB.82.174121
• Sunding, Martin Fleissner; Kepaptsoglou, Despoina Maria; Diplas, Spyridon; Norby, Truls & Gunnæs, Anette Eleonora (2010). XPS characterisation of the interface between anode and electrolyte in a proton conducting solid oxide fuel cell. Surface and Interface Analysis.  ISSN 0142-2421.  42(6-7), s 568- 571 . doi: 10.1002/sia.3383
• Truong, Thuy le; Larsen, Åge; Holme, Børge; Diplas, Spyridon; Hansen, Finn Knut; Roots, Jaan & Jørgensen, Sissel (2010). Dispersibility of silane-functionalized alumina nanoparticles in syndiotactic polypropylene. Surface and Interface Analysis.  ISSN 0142-2421.  42(6-7), s 1046- 1049 . doi: 10.1002/sia.3166
• Diplas, Spyridon & Løvvik, Ole Martin (2009). Electronic structure studies of Ni–X (X: B, S, P) alloys using x-ray photoelectron spectroscopy, x-ray induced Auger electron spectroscopy and density functional theory calculations. Journal of Physics: Condensed Matter.  ISSN 0953-8984.  21(24)
• Diplas, Spyridon & Løvvik, Ole Martin (2009). Electronic structure studies of Ni-X (X: B, S, P) alloys using x-ray photoelectron spectroscopy, x-ray induced Auger electron spectroscopy and density functional theory calculations. Journal of Physics: Condensed Matter.  ISSN 0953-8984.  21(24) . doi: 10.1088/0953-8984/21/24/245503
• He, W.; Knudsen, Ole Øystein & Diplas, Spyridon (2009). Corrosion of stainless steel 316L in simulated formation water environment with CO2-H2S-Cl-. Corrosion Science.  ISSN 0010-938X.  51(12), s 2811- 2819 . doi: 10.1016/j.corsci.2009.08.010
• Borg, Øyvind; Dietzel, Pascal; Spjelkavik, Aud I.; Tveten, Erik Zakarias; Walmsley, John C.; Diplas, Spyridon; Eri, Sigrid; Holmen, Anders & Rytter, Erling (2008). Fischer-Tropsch synthesis: Cobalt particle size and support effects on intrinsic activity an product distribution. Journal of Catalysis.  ISSN 0021-9517.  259, s 161- 164 . doi: 10.1016/j.jcat.2008.08.017
• Darabara, M; Bourithis, L; Diplas, Spyridon & Papadimitriou, GD (2008). A TiB2 metal matrix composite coating enriched with nitrogen: Microstructure and wear properties. Applied Surface Science.  ISSN 0169-4332.  254, s 4144- 4149 . doi: 10.1016/j.apsusc.2007.12.044

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• Jeyanthinath, Mayandi; Stange, Marit Synnøve Sæverud; Dahl, Øystein; Sunding, Martin Fleissner; Sagvolden, Espen; Flage-Larsen, Espen; Schrade, Matthias; Deuermeier, J.; Fortunato, Elvira; Diplas, Spyridon; Løvvik, Ole Martin; Finstad, Terje & Almeida Carvalho, Patricia (2020). Functional Properties of CrFeCoNiCu and GeFeCoNiCu oxides. Vis sammendrag

  The present work explores the concept of high-entropy alloys to design FeCoNi-based oxides suitable for functional applications. Fundamental changes in electronic behavior produced by metal substitution and variable oxygen content were screened to investigate the potential of these materials for specific applications, such as transparent conductors and thermoelectric materials. Elements with atomic radius similar to the average value expected for FeCoNi have been selected for substitutional replacement: (i) Cr and Cu as relatively abundant commodities with intensive industrial application and (ii) Ge due its semiconductor nature. CrFeCoNiCu and GeFeCoNiCu thin films with variable oxygen concentration were deposited by reactive DC magnetron sputtering onto optically transparent substrates and characterized by structural, spectroscopic and electrical methods. Transmission electron microscopy showed that for low oxygen content the materials adopted an fcc-type structure while the NaCl-structure was found for higher oxygen concentrations. X-ray-photoelectron spectroscopy was used to characterize the oxidation state of the metals. The resistivity measured at room temperature ranged from 10-4 to values above 104 Ω.cm. Hall measurements and Seebeck measurements show that both electrons and holes contribute to conduction and that at room temperature the Hall coefficient and Seebeck coefficient have different sign. This behaviour is discussed in terms of the structural analysis and suggested electronic model of the films.

• Thøgersen, Annett; Diplas, Spyridon; Michel, Kathrin; Bjørheim, Tor Svendsen; Prytz, Øystein & Norby, Truls Eivind (2020). The surface of CeO2 unravelled.
• Kalyva, Maria Evangelou; Redekop, Evgeniy; Johansson, Niclas; Urpelainen, Samuli; Gunnæs, Anette Eleonora; Diplas, Spyridon & Olsbye, Unni (2019). AP-XPS study of bimetallic PtCu nanoparticles supported on SiO2 films.
• Mayandi, Jeyanthinath; Stange, Marit Synnøve Sæverud; Sagvolden, Espen; Sunding, Martin Fleissner; Dahl, Øystein; Schrade, Matthias; Deuermeier, J.; Fortunato, E.; Løvvik, Ole Martin; Diplas, Spyridon; Finstad, Terje & Calvaho, Patricia (2019). Development of sputtered HEA thin films and their functional properties.
• Redekop, Evgeniy; Johansson, Niclas; Kalyva, Maria Evangelou; Urpelainen, Samuli; Diplas, Spyridon & Olsbye, Unni (2019). Is Temporal Analysis of Products (TAP) an operando technique? – – Challenges and opportunities of coupling TAP with surface spectroscopies.
• Redekop, Evgeniy; Johansson, Niclas; Kokkonen, Esko; Kalyva, Maria Evangelou; Urpelainen, Samuli; Diplas, Spyridon & Olsbye, Unni (2019). Pt-Cu nanoparticles on 2D and 3D supports: an AP-XPS/TAP study.
• Redekop, Evgeniy; Johansson, Niclas; Urpelainen, Samuli; Kalyva, Maria Evangelou; Affolter, Christopher; Kokkonen, Esko; Øien-Ødegaard, Sigurd; Diplas, Spyridon; Lillerud, Karl Petter & Olsbye, Unni (2019). Combining transient kinetics with surface characterization to better understand complex catalytic materials.
• Mayandi, Jeyanthinath; Stange, Marit Synnøve Sæverud; Dahl, Øystein; Sunding, Martin Fleissner; Sagvolden, Espen; Schrade, Matthias; Deuermeier, J.; Fortunato, Elvira; Diplas, Spyridon; Løvvik, Ole Martin; Finstad, Terje & Almeida Carvalho, Patricia (2019). Exploring functional properties of high entropy oxides. Vis sammendrag

  The present work explores the concept of high-entropy alloys to design FeCoNi-based oxides suitable for functional applications. Fundamental changes in electronic behaviour produced by metal substitution and variable oxygen content were screened to investigate the potential of these materials for specific applications, such as transparent conductors and thermoelectric materials. Elements with atomic radius similar to the average value expected for FeCoNi have been selected for substitutional replacement: (i) Cr and Cu as relatively abundant commodities with intensive industrial application and (ii) Ge due its semiconductor nature. We have sputtered CrFeCoNiCu and of GeFeCoNiCu thin films onto insulating and optically transparent substrates in order to measure electrical and optical properties. The deposition was done by reactive DC magnetron sputtering from targets with equimolar proportions of the metallic elements using atmospheres ranging from 0 to 20 at.% O2 /Ar. The films where characterized by structural, spectroscopic and electrical methods. Transmission electron microscopy showed that for oxygen content up to 8 at.% the materials adopted an fcc-type structure while the NaCl-structure was found for higher oxygen concentrations. X-ray-photoelectron spectroscopy was used to characterize the oxidation state of the metals. Standard absorption analysis by UV-VIS spectrometry revealed that the films had bandgaps ranging from 0.8 to 2.8 eV. The resistivity measured at RT ranged from 10-4 to values above 104 Ω.cm. Hall measurements and Seebeck measurements indicated that both electrons and holes contribute to conduction and at RT the Hall coefficient and Seebeck coefficients have different sign. This behaviour is discussed in terms of the structural analysis and suggested electronic model of the films. In conclusion, the optical band gap and resistivity of the materials produced span over large ranges demonstrating potential for a variety of functional applications.

• Mayandi, Jeyanthinath; Stange, Marit Synnøve Sæverud; Sagvolden, Espen; Sunding, Martin Fleissner; Dahl, Øystein; Schrade, Matthias; Deuermeier, J.; Fortunato, E.; Løvvik, Ole Martin; Diplas, Spyridon; Almeida Carvalho, Patricia & Terje G, Finstad (2019). Structural and Electrical Properties of Sputtered HEA Thin Films of CrFeCoNiCu and their Oxidation Studies. Vis sammendrag

  High-entropy alloys (HEAs) represent a class of materials that is intensively investigated for a range of possible applications. They generally show a high degree of phase stability by the high entropy while the structure is a random atom position disorder unlike other alloys which can influence physical properties differently than regular alloys. In general, there are few studies on oxidation of HEA and studies on adding oxygen during the fabrication of HEA. In this study we have sputtered thin films of CrFeCoNiCu onto insulating and optically transparent substrates in order to measure structural, electrical and optical functional properties. We have varied the oxygen pressure in the sputtering environment as well as oxidizing the samples at elevated temperatures after deposition. Optical and electrical characterization was performed on films sputter deposited on fused quartz wafers. The films were characterized by TEM, XRD and XPS. The films with no intentional oxygen had an FCC structure with a texture showing strong (111) preferred orientation as seen by XRD. TEM analysis showed columnar morphology with twins parallel to (111) planes. Samples sputtered under high oxygen content showed a simple NaCl structure(FeO). The samples were annealed in air and O2 ambient in the temperature range of 300 to 500 °C. This caused an oxide layer growing on top of the FCC structure. XPS was utilized to find the atomic compositions and chemical stated of the elements. Hall measurements and Seebeck measurements were performed on the as prepared and oxidized films from 10 K to 600K. For the FCC structure the resistivity was a factor 104 higher than the elemental metals while can be satisfactory described by electron phonon scattering by the Bloch-Grüneisen description and the low temperature negative temperature effect by the Kondo effect. The sign of the Hall coefficient was positive while the Seebeck coefficient was negative, indicating the Fermi surface containing pockets of electrons and holes and an energy dependent scattering time. A detailed comparison of the as prepared and the oxidized thin films will be discussed in terms of the structural chemical and electrical properties of the grown films. In addition the electric properties will be discussed in terms of a model considering electronic structure and scattering.

• Mayandi, Jeyanthinath; Stange, Marit Synnøve Sæverud; Sunding, Martin Fleissner; Diplas, Spyridon; Almeida Carvalho, Patricia & Finstad, Terje (2019). Oxidation of CrFeCoNiCu sputtered thin films.
• Mayandi, Jeyanthinath; Stange, Marit Synnøve Sæverud; Sunding, Martin Fleissner; Schrade, Matthias; Deuermeier, J.; Fortunato, E.; Løvvik, Ole Martin; Diplas, Spyridon; Almeida Carvalho, Patricia & Terje G, Finstad (2019). Physical properties of sputtered CrFeCoNiCu thin films on quartz substrate. Vis sammendrag

  Equiatomic high entropy alloys (HEA) have attracted considerable interest due to their exceptional properties, which might be closely related to their extreme disorder induced by chemical complexity. We have sputtered thin films of CrFeCoNiCu onto insulating and optically transparent substrates in order to measure electrical and optical functional properties. After several optimizations desired sputtering conditions were obtained for the deposition of CrFeCoNiCu onto fused quartz wafers. All the samples were characterized by structural, chemical and electrical methods. The as prepared films had fcc-type structure. Hall measurements were performed from 10 K to 600K. The resistivity was a factor 104 higher than the elemental metals and the temperature dependence was different. The sign of the Hall coefficient indicates that the film was dominated by holes, while the Seebeck coefficient was negative and dominated by electrons. The electric properties will be discussed in terms of a model considering electronic structure and scattering.

• Redekop, Evgeniy; Johansson, Niclas; Kokkonen, Esko; Urpelainen, Samuli; Kalyva, Maria Evangelou; Affolter, Christopher; Diplas, Spyridon & Olsbye, Unni (2019). X-Ray spectroscopies and time-resolved kinetics for advanced characterization of heterogeneous catalysts.
• Sunding, Martin Fleissner; Jensen, Ingvild Julie Thue; Svenum, Ingeborg-Helene; Ivashenko, Oleksii; Redekop, Evgeniy; Wells, Justin; Fagerberg, Ragnar; Sjåstad, Anja Olafsen; Venvik, Hilde Johnsen; Olsbye, Unni & Diplas, Spyridon (2019). National Surface and Interface Analysis Laboratory (NICE II): From (near) in-situ to operando XPS analysis.
• Sunding, Martin Fleissner; Løberg, Monika; S. Azar, Amin; Stange, Marit Synnøve Sæverud; Almeida Carvalho, Patricia; Karlsen, Ole Bjørn; Pike, Nicholas; Gunnæs, Anette Eleonora; Diplas, Spyridon & Løvvik, Ole Martin (2019). The Need for a Multi-Technique Approach in the Search for New Phase-Transforming Materials. Vis sammendrag

  Introduction/Purpose Reversible diffusionless first-order phase transformations are a fundamental part of phase change materials and shape memory alloys [1]. Some of these materials even possess useful physical characteristics that show abrupt changes e.g. in their electrical[2] and magnetic [3] polarizations. These phase transformations can be studied using multiple techniques, enabling access to different types of information including length scales and time periods, but how should this characterisation be approached? Methods TEM studies give highly relevant data in this field of research, from detailed crystallographic structures, to relative orientations between grains and phases and to the phase transformation temperature. However, TEM analyses are time consuming and requires small sample sizes and ad hoc preparation. High-throughput measurement techniques are thus required in the search for improved compositions and new materials in order to rapidly assess the properties of many samples or samples with graded composition [4]. Optical methods (for example unpolarised and polarised microscopy and thermal imaging) and electric conductivity measurements can for example be used to map phase transformation temperatures much faster and on much larger areas than traditional TEM techniques. XRD and SEM-EDS-EBSD can then be applied to obtain initial crystallographic and microstructure information on an intermediate size scale, before TEM is applied for the in-depth study of the most relevant compositions. Results We applied this multi-pronged approach in the search for Heusler and half-Heusler alloys with a low temperature martensitic phase transformation and with low thermal hysteresis, with potential applications in waste heat energy harvesting. Conclusions Drawing advantage of the strengths of multiple analysis techniques – with respect to the obtainable information, the sample size and/or the time frame of the analyses – renders the search for new phase change materials more effective. It enables faster identification of potential target compositions and of sample areas optimal for in depth studies. Selected references [1] David Dye, Nature Materials14 (8), 760 (2015). [2] M. M. Vopson, Critical Reviews in Solid State and Materials Sciences40 (4), 223 (2015). [3] L. Huang, D. Y. Cong, L. Ma, Z. H. Nie, Z. L. Wang, H. L. Suo, Y. Ren, and Y. D. Wang, Applied Physics Letters108 (3) (2016). [4] M. L. Green, C. L. Choi, J. R. Hattrick-Simpers, A. M. Joshi, I. Takeuchi, S. C. Barron, E. Campo, T. Chiang, S. Empedocles, J. M. Gregoire, A. G. Kusne, J. Martin, A. Mehta, K. Persson, Z. Trautt, J. Van Duren, and A. Zakutayev, Applied Physics Reviews 4 (1), 011105 (2017).

• Diplas, Spyridon; Kyratsi, Theodora; Sun, Jianwu; Pirriera, Monica Della & Ulyashin, Alexander (2018). Materials for Energy Harvesting. Physica Status Solidi (a) applications and materials science.  ISSN 1862-6300.  215(17) . doi: 10.1002/pssa.201800645
• Kepaptsoglou, Despoina Maria; Diplas, Spyridon; Gunnæs, Anette Eleonora & Ulyashin, Alexander (2017). On the evolution of properties of ITO layers deposited on crystalline and amorphous Si upon heat treatments.
• Kepaptsoglou, Despoina Maria; Diplas, Spyridon; Ramasse, Quentin; Gunnæs, Anette Eleonora & Ulyashin, Alexander (2017). A high resolution electron microscopy and spectroscopy study of interfaces in Si-based solar cell heterojunctions.
• Kjeldstad, Torunn; Galeckas, Augustinas; Nilsen, Ola; Azarov, Alexander; Stange, Marit Synnøve Sæverud; Diplas, Spyridon & Thøgersen, Annett (2017). Self-assembly of Al-nanowires in silicon.
• Thøgersen, Annett; Carvalho, Patricia; Pishahang, Mehdi; Sunding, Martin Fleissner; Lind, Anna Maria; Larring, Yngve & Diplas, Spyridon (2017). Characterizating the stability of catalyst materials using in-situ environmental transmission electron microscopy..
• Thøgersen, Annett; Carvalho, Patricia; Sunding, Martin Fleissner; Lind, Anna Maria; Pishahang, Mehdi; Larring, Yngve & Diplas, Spyridon (2017). In-situ environmental Transmission Electron Microscopy characterization of catalyst materials..
• Thøgersen, Annett; Kjeldstad, Torunn; Jensen, Ingvild Julie Thue; Stange, Marit Synnøve Sæverud; Ulyashin, Alexander; Galeckas, Augustinas; Nilsen, Ola; Monakhov, Edouard & Diplas, Spyridon (2017). Growing and characterizing self-organizing aluminium nanowires in amorphous silicon.
• Kjeldstad, Torunn; Galeckas, Augustinas; Nilsen, Ola; Azarov, Alexander; Stange, Marit Synnøve Sæverud; Diplas, Spyridon & Thøgersen, Annett (2016). A new silicon nanostructure.
• 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.
• Lervik, Adrian; Haugsrud, Reidar; Diplas, Spyridon & Gunnæs, Anette Eleonora (2016). Structural- and Compositional Investigations of Grain Boundaries in Y-Doped BaZrO3.
• Ma, Quanbao; Carvalho, Patricia; Galeckas, Augustinas; Azarov, Alexander; Hovden, Sigurd; Thøgersen, Annett; Wright, Daniel Nilsen; Diplas, Spyridon; Løvvik, Ole Martin; Jokubavicius, Valdas; Sun, Jianwu; Syväjärvi, Mikael & Svensson, Bengt Gunnar (2016). Characterization of B-implanted 3C-SiC for intermediate band solar cells.
• Thøgersen, Annett; Stange, Marit Synnøve Sæverud; Røyset, Arne Karstein; Jensen, Ingvild Julie Thue; Ulyashin, Alexander & Diplas, Spyridon (2016). Electronic structure of tunable metastable aSiAl and aSiAlHx thin films.
• Diplas, Spyridon; Walmsley, John; Holmestad, Randi & Prytz, Øystein (2015). An introduction to NORTEM by the NORTEM management group.
• Lervik, Adrian; Haugsrud, Reidar; Diplas, Spyridon & Gunnæs, Anette Eleonora (2015). A TEM approach to BZY.
• Steinsmo, Unni Merete & Diplas, Spyridon (2015, 12. september). Supermikroskop skal få flere i arbeid.  Adresseavisen.
• Jensen, Ingvild Julie Thue; Løvvik, Ole Martin & Diplas, Spyridon (2012). Hydrogen Interface Interactions in Meta-stable Mg-Ti Thin Films.
• Jensen, Ingvild Julie Thue; Thøgersen, Annett; Løvvik, Ole Martin & Diplas, Spyridon (2012). Hydrogen Interface Interactions in Mg-Ti Thin Films - combining calculations and experiment.
• Kurt, Köksal; Walmsley, John; Diplas, Spyridon & Nisancioglu, Kemal (2012). Combined Role of Trace Elements Pb and Sn in Low Temperature Activation of Aluminum.
• Løvvik, Ole Martin; Jensen, Ingvild Julie Thue & Diplas, Spyridon (2012). Hydrogen storage in solid state materials from atomic-scale modeling.
• Løvvik, Ole Martin; Jensen, Ingvild Julie Thue & Diplas, Spyridon (2012). Nanostructures in thin film hydrides - something for hydrogen storage?.
• Jensen, Ingvild Julie Thue; Løvvik, Ole Martin; Schreuders, Herman; Dam, Bernard & Diplas, Spyridon (2011). Combined XPS and first principle study of meta-stable Mg-Ti thin films.
• Böttger, Paul Heinrich Michael; Diplas, Spyridon; Flage-Larsen, Espen; Prytz, Øystein & Finstad, Terje (2010). Electronic structure of the thermoelectric Zn-Sb system.
• Jensen, Ingvild Julie Thue; Diplas, Spyridon; Løvvik, Ole Martin; Schreuders, Herman & Dam, Bernard (2010). Using X-ray Photoelectron Spectroscopy in Investigation of Mg-Based Thin Film Hydrides.
• Sunding, Martin Fleissner; Kepaptsoglou, Despoina Maria; Diplas, Spyridon; Gunnæs, Anette Eleonora & Norby, Truls (2010). Metal-Oxide interfaces in proton conducting fuel cells studied by angle-resolved XPS.
• Fontaine, Marie-Laure; Larring, Yngve; Mei, Sen; Bredesen, Rune; Syvertsen, Guttorm E; Lein, H. L.; Grande, Tor; Sunding, Martin Fleissner; Kepaptsoglou, Despoina Maria; Diplas, Spyridon; Gunnæs, Anette Eleonora; Løvvik, Ole Martin; Olsen, Arne; Magraso Sola, Anna; Skilbred, Anders Werner Bredvei; Haugsrud, Reidar & Norby, Truls (2009). Proton Conducting SOFCs – From Fundamental Understanding to Fuel Cell Stacks.
• Gorzkowska-Sobas, Agnieszka A; Galeckas, Augustinas; Diplas, Spyridon; Nilsen, Ola; Bratvold, Jon Einar & Klepper, Karina Barnholt (2009). PREPARATION AND CHARACTERISATION OF THE MULTILAYERED TiO2/ZnO:Fe THIN FILMS FOR PHOTOELECTROCHEMICAL WATER SPLITTING.
• Gorzkowska-Sobas, Agnieszka A; Galeckas, Augustinas; Sunding, Martin Fleissner; Diplas, Spyridon & Kuznetsov, Andrej (2009). Investigation of Fe-doped ZnO thin films grown by magnetron sputtering.
• Diplas, Spyridon; Løvvik, Ole Martin; Nordmark, Heidi; Kepaptsoglou, Despoina Maria; Graff, Joachim Moe & Gunnæs, Anette Eleonora (2009). Characterisation of transparent conducting oxide (TCO) films and TCO-Si interfaces with XPS, TEM and ab-initio modelling.
• Jensen, Ingvild Julie Thue; Diplas, Spyridon & Løvvik, Ole Martin (2009). X-ray photoelectron spectroscopy study of MgH2 thin films grown by reactive sputtering.
• Finstad, Terje; Mayandi, Jeyanthinath; Galeckas, Augustinas; Diplas, Spyridon; Petersson, Anna Malou & Balasundaraprabhu, R (2008). Visible luminescence from DC magnetron sputtered ZnO with and without Ge.

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