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• Mayandi, Jeyanthinath; Madathil, Reshma Krishnan; Abinaya, C; Bethke, Kevin; Venkatachalapathy, Vishnukanthan; Rademann, Klaus; Norby, Truls Eivind & Finstad, Terje (2021). Al-doped ZnO prepared by co-precipitation method and its thermoelectric characteristics. Materials Letters.  ISSN 0167-577X.  288 . doi: 10.1016/j.matlet.2021.129352 Show summary

  We report on structural and electrical characterization of zinc oxide material containing aluminum (Al:ZnO) prepared by a co-precipitation technique using different zinc and aluminum precursors. The as-prepared powders were calcinated and pre-annealed at 600 °C and 1200 °C. These were cold-pressed to pellets and sintered at 1000 °C. We also prepared ZnO material with no Al for comparisons. The electrical and thermal conductivity, as well as the Seebeck coefficient, were measured. These properties were correlated with structural analysis by X-ray diffraction characterization and scanning electron microscopy. The process yields a nanostructured material with much reduced thermal conductivity.

• Song, Xin; Riis, Henrik; Prytz, Øystein & Finstad, Terje (2021). Metallization of ZnSb and contact resistance. Journal of Applied Physics.  ISSN 0021-8979.  130 . doi: 10.1063/5.0043958
• Schrade, Matthias; Berland, Kristian; Kosinskiy, Andrey; Heremans, Joseph P. & Finstad, Terje (2020). Shallow Impurity Band in ZrNiSn. Journal of Applied Physics.  ISSN 0021-8979.  127(4) . doi: 10.1063/1.5112820 Full text in Research Archive. Show summary

  ABSTRACT ZrNiSn and related half Heusler compounds are candidate materials for efficient thermoelectric energy conversion with a reported thermoelectric figure-of-merit of n-type ZrNiSn exceeding unity. Progress on p-type materials has been more limited, which has been attributed to the presence of an impurity band, possibly related to Ni interstitials in a nominally vacant 4d position. The specific energetic position of this band, however, has not been resolved. Here, we report the results of a concerted theory-experiment investigation for a nominally undoped ZrNiSn, based on the electrical resistivity, the Hall coefficient, the Seebeck coefficient, and the Nernst coefficient, measured in a temperature range from 80 to 420 K. The results are analyzed with a semianalytical model combining a density functional theory (DFT) description for ideal ZrNiSn, with a simple analytical correction for the impurity band. The model provides a good quantitative agreement with experiment, describing all salient features in the full temperature span for the Hall, conductivity, and Seebeck measurements, while also reproducing key trends in the Nernst results. This comparison pinpoints the impurity band edge to 40 meV below the conduction band edge, which agrees well with a separate DFT study of a supercell containing Ni interstitials. Moreover, we corroborate our result with a separate study of the ZrNiSn0.9Pb0.1 sample showing similar agreement with an impurity band edge shifted to 32 meV below the conduction band.

• Chandrasekaran, Abinaya; Bethke, Kevin; Andrei, Virgil; Baumann, Jonas; Pollakowski-Herrmann, Beatrix; Kanngießer, Birgit; Beckhoff, Burkhard; Vasquez, Geraldo Cristian; Mayandi, Jeyanthinath; Finstad, Terje & Rademann, Klaus (2020). The effect of post-deposition annealing conditions on structural and thermoelectric properties of sputtered copper oxide films. RSC Advances.  ISSN 2046-2069. . doi: 10.1039/D0RA03906C Full text in Research Archive.
• Heng, C.L.; Zhao, C.N.; Zhang, L; Xiang, W; Su, W.Y.; Yin, H.X.; Gao, Y.K.; Yin, P.G. & Finstad, Terje (2020). Effects of Yb doping on the structure and near band-edge emission of ZnO thin films on Si after high temperature annealing. Journal of Luminescence.  ISSN 0022-2313. . doi: 10.1016/j.jlumin.2020.117153 Full text in Research Archive. Show summary

  n this work, we have investigated the effects of ytterbium (Yb) doping concentration on the structure and near band-edge (NBE) photoluminescence (PL) of ZnO thin films on Si after high temperature annealing. The films were made by magnetron sputtering in an Ar:O2 atmosphere. The structure of the films have been studied by Rutherford backscattering spectrometry, X-ray diffraction (XRD), scanning electron microscopy, and X-ray photoelectron spectroscopy. XRD indicates that the crystallinity of the ZnO improves with annealing temperature in the range 700 -1000 °C; and after the 1000 °C annealing, the crystallinity of the films show overall an improvement for increasing Yb concentration up to 1.35 at.%. At the higher temperatures the films react with Si substrate to form silicates with Zn and Yb, and the Yb has redistributed in the film and piles up towards the Si substrate. The PL measurements show that the NBE PL intensity of the films is correlated with the crystallinity for variations in annealing temperature and Yb concentration. The PL excitation measurements suggest that the films prepared with Yb addition have higher NBE PL efficiency than the un-doped ZnO, while the energy transfer between the host ZnO and Yb ions are not efficient

• Mayandi, Jeyanthinath; Finstad, Terje; Venkatesan, Ragavendran; Vajeeston, Ponniah; Karazhanov, Smagul & Venkatachalapathy, Vishnukanthan (2020). Carbon-dioxide as annealing atmosphere to retain the electrical properties of indium-tin oxide. Materials Letters.  ISSN 0167-577X.  276 . doi: 10.1016/j.matlet.2020.128195 Full text in Research Archive. Show summary

  In practical applications of indium-tin-oxide (ITO) annealing at temperatures ~400 °C without degrading its electrical and optical properties is an important challenge. In the present work, commercial Indium-tin oxide (ITO) coated on glass was subjected to post-annealing treatment in the range of 200-400 °C at different annealing atmospheres; oxygen, nitrogen and carbon-dioxide. The annealed samples were characterized by X-ray diffraction, UV-visible spectroscopy and Hall measurements to evaluate the structural, optical and electrical properties. Both oxygen and nitrogen treated samples degrades the structural, optical and conducting properties of ITO, while carbon-dioxide atmosphere inhibits the degradation of ITO at 400 °C. The obtained results suggest that carbon-dioxide can be well utilized as annealing ambient to retain opto-electronic, structural and electrical properties of ITO and thereby improve the efficiency of ITO based solar cells.

• Venkatesan, Ragavendran; Mayandi, Jeyanthinath; Søndenå, Rune; Finstad, Terje & Venkatachalapathy, Vishnukanthan (2020). Investigating antireflection properties of hybrid silicon nanostructures comprising rod-like nanopores and nano-textured surface. Materials Letters.  ISSN 0167-577X.  275 . doi: 10.1016/j.matlet.2020.128087 Full text in Research Archive. Show summary

  In the present work, we have fabricated hybrid silicon (Si) nanostructures comprising vertical rod-like nanopores and nano-textured surface by metal assisted chemical etching (MACE) method at room temperature. The as-received p-type Upgraded Metallurgical grade (UMG) Si wafers were chemical polished, prior to investigating the etching effects at the metal nanoparticle semiconductor interface. The influence of metal silver nanoparticle (AgNPs) concentration on the formation of hybrid nanostructures were studied systematically. Depending on the surface morphology, the hybrid structures exhibited constant 10% average reflectance in the UV–Visible spectral region or average 7.5% reflectance in range of 200–400 nm

• Heng, C.L.; Xiang, W.; Su, W.Y.; Gao, Y.K.; Yin, P.G. & Finstad, Terje (2019). Effect of Eu doping on the near band edge emission of Eu doped ZnO thin films after high temperature annealin. Journal of Luminescence.  ISSN 0022-2313.  210C, s 363- 370 . doi: 10.1016/j.jlumin.2019.02.062 Full text in Research Archive.
• Schrade, Matthias & Finstad, Terje (2018). Using the Callaway Model to Deduce Relevant Phonon Scattering Processes: The Importance of Phonon Dispersion. Physica status solidi (b).  ISSN 0370-1972.  255(12), s 1- 6 . doi: 10.1002/pssb.201800208
• Heng, Chenglin; Wang, T.; Su, W.Y.; Wu, H.C.; Yang, M.C.; Deng, L.G.; Yin, P.G. & Finstad, Terje (2017). Intense ultraviolet photoluminescent emission from Yb doped ZnO thin films on Si after high temperature annealing. Journal of Alloys and Compounds.  ISSN 0925-8388.  695, s 2232- 2237 . doi: 10.1016/j.jallcom.2016.11.072
• Heng, Chenglin; Xiang, W.; Su, W.Y.; Wu, H.C.; Gao, Y.K.; Yin, P.G. & Finstad, Terje (2017). Strong near band edge emission of (Ce, Yb) co-doped ZnO thin films after high temperature annealing. Optical Materials Express.  ISSN 2159-3930.  7(8), s 3041- 3050 . doi: 10.1364/OME.7.003041 Full text in Research Archive.
• Malik, Nishant; Venkatachalapathy, Vishnukanthan; Dall, Wilhelm; Schjølberg-Henriksen, Kari; Poppe, Erik Utne; Taklo, Maaike M. Visser & Finstad, Terje (2017). Texture of Al films for wafer-level thermocompression bonding. Superlattices and Microstructures.  ISSN 0749-6036.  106, s 216- 233 . doi: 10.1016/j.spmi.2017.03.053 Full text in Research Archive. Show summary

  Properties of aluminum thin films for thermocompression bonding have been studied in terms of surface roughness, grain size, and grain orientation by AFM, SEM, XRD and EBSD for thermocompression bonding. Al films were sputter deposited directly on Si and thermally oxidized Si wafers, respectively. The resulting Si/Al and Si/SiO2/Al sample types were compared after annealing (300–550 °C) in vacuum. The Si/SiO2/Al film samples showed higher surface roughness than the Si/Al samples. The as-deposited films had (111) preferred orientation, while (100) and (110) oriented Al grains were also present in Si/SiO2/Al samples. The Si/SiO2/Al samples and Si/Al sample annealed at 550 °C had a conical <111> texture. The observed evolution of the grain structure with annealing temperature is discussed in terms of native oxide, surface roughness, diffusivity and grain orientation dependent mechanical properties in order to shine light on previously observed differences in Alsingle bondAl thermocompression wafer-level bonding with Si/SiO2/Al and Si/Al wafers.

• Schrade, Matthias; Berland, Kristian; Eliassen, Simen Nut Hansen; Guzik, Matylda Natalia; Echevarria-Bonet, Cristina; Sørby, Magnus Helgerud; Jenus, Petra; Hauback, Bjørn; Tofan, Raluca; Gunnæs, Anette Eleonora; Persson, Clas; Løvvik, Ole Martin & Finstad, Terje (2017). The role of grain boundary scattering in reducing the thermal conductivity of polycrystalline XNiSn (X=Hf, Zr, Ti) half-Heusler alloys. Scientific Reports.  ISSN 2045-2322.  7 . doi: 10.1038/s41598-017-14013-8 Full text in Research Archive.
• Song, Xin & Finstad, Terje (2017). A study of S doped ZnSb. Materials Science in Semiconductor Processing.  ISSN 1369-8001.  71, s 421- 426 . doi: 10.1016/j.mssp.2017.09.007 Show summary

  We report on S-doping of ZnSb for S concentrations ranging from 0.02 at% to 2.5 at%. There are no previous reports on S-doping. ZnSb is a thermoelectric material with some advantages for the temperature range 400 K - 600 K. The solid solubility of S in ZnSb was estimated to be lower than 0.1% from observations of precipitates by scanning microscopy. Hall and Seebeck measurements were performed as a function of temperature from 6K to 623 K. The temperature dependence of the electrical properties suggests that S introduces neutral scattering centers for holes in the p-type material. An increase in hole concentration by S is argued by defect reactions involving Zn vacancies.

• Song, Xin; Schrade, Matthias; Maso Carcases, Nahum & Finstad, Terje (2017). Zn vacancy formation, Zn evaporation and decomposition of ZnSb at elevated temperatures: Influence on the microstructure and the electrical properties. Journal of Alloys and Compounds.  ISSN 0925-8388.  710, s 762- 770 . doi: 10.1016/j.jallcom.2017.03.339 Full text in Research Archive. Show summary

  The influence of annealing on the microstructure and electrical properties of undoped polycrystalline ZnSb samples has been investigated by different experimental techniques. In situ XRD in an argon at- mosphere showed that ZnSb powders decompose at 300 C, which is attributed to Zn evaporation. In situ SEM in a moist atmosphere showed fast surface deterioration at 450 C and above, reflecting decom- position of ZnSb and the formation of metallic Sb precipitates. The rate of Zn loss in a reducing atmo- sphere was determined by thermogravimetry and related to the Zn partial vapor pressure. The increase of the hole carrier concentration of ZnSb measured at room temperature after heat treatment was correlated with Zn evaporation at elevated temperature. The carrier concentration after annealing at 400 C is consistent with an activation energy for Zn vacancy formation of 0.4 eV and a maximum Zn deficiency x of Zn1-xSb of 1 10 3.

• Taklo, Maaike M. Visser; Schjølberg-Henriksen, Kari; Malik, Nishant; Poppe, Erik Utne; Moe, Sigurd T. & Finstad, Terje (2017). Al-Al Wafer-Level Thermocompression Bonding applied for MEMS, In  2017 5th International Workshop on Low Temperature Bonding for 3D Integration (LTB-3D), Tokyo, 16-18 May 2017.  IEEE.  ISBN 978-4-904743-03-4.  artikkel.  s 11 - 11 Full text in Research Archive. Show summary

  Wafer-level thermocompression bonding (TCB) using aluminum (Al) is presented as a hermetic sealing method for MEMS. The process is a CMOS compatible alternative to TCB using metals like gold (Au) and copper (Cu), which are problematic with respect to cross contamination in labs. Au and Cu are commonly used for TCB and the oxidation of these metals is limited (Au) or easily controlled (Cu). However, despite Al oxidation, our experimental results and theoretical considerations show that TCB using Al is feasible even at temperatures down to 300−350 °C using a commercial bonder without in-situ surface treatment capability.

• Berland, Kristian; Song, Xin; Carvalho, Patricia; Persson, Clas; Finstad, Terje & Løvvik, Ole Martin (2016). Enhancement of thermoelectric properties by energy filtering: Theoretical potential and experimental reality in nanostructured ZnSb. Journal of Applied Physics.  ISSN 0021-8979.  119(12) . doi: 10.1063/1.4944716 Full text in Research Archive. Show summary

  Energy filtering has been suggested by many authors as a means to improve thermoelectric properties. The idea is to filter away low-energy charge carriers in order to increase Seebeck coefficient without compromising electronic conductivity. This concept was investigated in the present paper for a specific material (ZnSb) by a combination of first-principles atomic-scale calculations, Boltzmann transport theory, and experimental studies of the same system. The potential of filtering in this material was first quantified, and it was as an example found that the power factor could be enhanced by an order of magnitude when the filter barrier height was 0.5 eV. Measured values of the Hall carrier concentration in bulk ZnSb were then used to calibrate the transport calculations, and nanostructured ZnSb with average grain size around 70 nm was processed to achieve filtering as suggested previously in the literature. Various scattering mechanisms were employed in the transport calculations and compared with the measured transport properties in nanostructured ZnSb as a function of temperature. Reasonable correspondence between theory and experiment could be achieved when a combination of constant lifetime scattering and energy filtering with a 0.25 eV barrier was employed. However, the difference between bulk and nanostructured samples was not sufficient to justify the introduction of an energy filtering mechanism. The reasons for this and possibilities to achieve filtering were discussed in the paper.

• Hansen, Per-Anders; Fjellvåg, Helmer; Finstad, Terje & Nilsen, Ola (2016). Luminescence properties of lanthanide and ytterbium lanthanide titanate thin films grown by atomic layer deposition. Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films.  ISSN 0734-2101.  34:01A130 . doi: 10.1116/1.4936389
• Heng, Chenglin L.; Wang, T.; Su, W.Y.; Wu, H.C.; Yin, P.G. & Finstad, Terje (2016). Down-conversion luminescence from (Ce, Yb) co-doped oxygen-rich silicon oxides. Journal of Applied Physics.  ISSN 0021-8979.  119(12) . doi: 10.1063/1.4945111 Show summary

  We have studied down-conversion photoluminescence (PL) from (Ce, Yb) co-doped “oxygen rich” silicon oxide films prepared by sputtering and annealing. The Ce3þ 510 nm PL is sensitive to the Ce concentration of the films and is much stronger for 3 at. % Ce than for 2 at. % Ce after annealing at 1200 C. The PL emission and excitation spectroscopy results indicate that the excitation of Yb3þ is mainly through an energy transfer from Ce3þ to Yb3þ, oxide defects also play a role in the excita- tion of Yb3þ after lower temperature (800 C) annealing. The Ce3þ 510 nm photon excites mostly only one Yb3þ 980nm photon. Temperature-dependent PL measurements suggest that the energy transfer from Ce3þ to Yb3þ is partly thermally activated. VC 2016 AIP Publishing LLC.

• Heng, Chenglin; Wang, T.; Li, H.; Liu, J.J.; Zhu, J.W.; Ablimit, A.; Su, W.Y.; Wu, H.C.; Yin, P.G. & Finstad, Terje (2016). Strong enhancement of ultra-violet emission by Ce doping of ZnO sputtered films. Materials Letters.  ISSN 0167-577X.  162, s 53- 55 . doi: 10.1016/j.matlet.2015.09.125 Show summary

  We report that ultra-violet (UV) emission of ZnO can be made much more intense by incorporating Ce in the ZnO films. After annealing at 1100 °C in N2 gas, the UV peak (≈3.34 eV, width 133 meV) – intensity for the film doped with Ce is two order of magnitude stronger than that of un-doped ZnO films. The large enhancement is correlated with improved crystallinity and appears due to fewer non-radiative recombination pathways. The improved crystallinity can be related to Ce affecting the self-texturing of ZnO during sputter deposition and annealing.

• Malik, Nishant; Carvalho, Patricia; Poppe, Erik & Finstad, Terje (2016). Interfacial characterization of Al-Al thermocompression bonds. Journal of Applied Physics.  ISSN 0021-8979.  119(20) . doi: 10.1063/1.4952709 Full text in Research Archive. Show summary

  Interfaces formed by Al-Al thermocompression bonding were studied by the transmission electron microscopy. Si wafer pairs having patterned bonding frames were bonded using Al films deposited on Si or SiO2 as intermediate bonding media. A bond force of 36 or 60 kN at bonding temperatures ranging from 400–550 °C was applied for a duration of 60 min. Differences in the bonded interfaces of 200 μm wide sealing frames were investigated. It was observed that the interface had voids for bonding with 36 kN at 400 °C for Al deposited both on Si and on SiO2. However, the dicing yield was 33% for Al on Si and 98% for Al on SiO2, attesting for the higher quality of the latter bonds. Both a bond force of 60 kN applied at 400 °C and a bond force of 36 kN applied at 550 °C resulted in completely bonded frames with dicing yields of, respectively, 100% and 96%. A high density of long dislocations in the Al grains was observed for the 60 kN case, while the higher temperature resulted in grain boundary rotation away from the original Al-Al interface towards more stable configurations. Possible bonding mechanisms and reasons for the large difference in bonding quality of the Al films deposited on Si or SiO2 are discussed.

• Schrade, Matthias; Magraso, Anna; Galeckas, Augustinas; Finstad, Terje & Norby, Truls (2016). The Band Gap of BaPrO3 Studied by Optical and Electrical Methods. Journal of The American Ceramic Society.  ISSN 0002-7820.  99(2), s 492- 498 . doi: 10.1111/jace.13961 Full text in Research Archive.
• Song, Xin & Finstad, Terje (2016). Review of research on the thermoelectric material ZnSb, In Sergey Skipidarov & Mikhail Nikitiin (ed.),  Thermoelectrics for Power Generation - A Look at Trends in the Technology.  IntechOpen.  ISBN 978-953-51-2846-5.  Kapittel 6.  s 117 - 145 Full text in Research Archive.
• Heinrich, Christophe P.; Schrade, Matthias; Cerretti, Giacomo; Lieberwirth, Ingo; Leidich, Patrick; Schmitz, Andreas; Fjeld, Harald; Müller, Eckhard; Finstad, Terje; Norby, Truls & Tremel, Wolfgang (2015). Tetragonal tungsten bronzes Nb8-xW9+xO47-d: optimization strategies and transport properties of a new n-type thermoelectric oxide. Materials Horizons.  ISSN 2051-6347.  2(5), s 519- 427 . doi: 10.1039/c5mh00033e Full text in Research Archive.
• Heng, Chenglin; Li, J.T.; Su, W.U.; Han, Z.; Yin, P.G. & Finstad, Terje (2015). The formation of Yb silicates and its luminescence in Yb heavily doped silicon oxides after high temperature annealing. Optical materials (Amsterdam).  ISSN 0925-3467.  42, s 17- 23 . doi: 10.1016/j.optmat.2014.12.013 Show summary

  We report on the formation of ytterbium (Yb) silicates and its photoluminescence (PL) properties for heavily Yb doped Si oxide films after various annealings. X-ray diffraction patterns and transmission electron microscopy indicate that different Yb silicates have formed in the oxides upon 1100 and 1200°C annealing. The Yb PL intensities after the high temperature annealings are much stronger than those after lower temperatures, which indicates that the Yb silicates have higher emission efficiency than the Yb configurations found for lower temperature annealing. The PL intensities of the films can be altered considerably by secondary oxidizing or annealing in forming gas (N2+7% H2) ambience.

• Heng, Chenglin; Li, J.T.; Su, W.Y.; Yin, P.G. & Finstad, Terje (2015). The photoluminescence and structural properties of (Ce, Yb) co-doped silicon oxides after high temperature annealing. Journal of Applied Physics.  ISSN 0021-8979.  117 . doi: 10.1063/1.4906444
• Malik, Nishant; Poppe, Erik; Schjølberg-Henriksen, Kari; Taklo, Maaike Margrete Visser & Finstad, Terje (2015). Environmental Stress Testing of Wafer-Level Al-Al Thermocompression Bonds: Strength and Hermeticity. ECS Journal of Solid State Science and Technology.  ISSN 2162-8769.  4(7), s P251- P257 . doi: 10.1149/2.0181507jss Full text in Research Archive. Show summary

  Hermeticity, reliability and strength of Al-Al thermocompression bonds realized by applying different bonding parameters have been investigated. Laminates of diameter 150 mm were realized by bonding wafers containing membrane structures to wafers with patterned bonding frames. The laminates were bonded applying a bond force of 36 or 60 kN at temperatures ranging from 300 to 400°C for 15, 30 or 60 minutes. The hermetic properties were estimated by membrane deflection measurements with white-light interferometry after bonding. Reliability was tested by exposing the laminates to a steady-state life test, a thermal shock test, and a moisture resistance test. Bond strength was measured by shear test and pull tests. Laminates bonded applying a bond force of 60 kN at temperatures of 350 or 400°C resulted in hermetic bonds. No significant change in membrane deflection was observed after the steady-state life test or the thermal shock test. However, a gross leakage was observed in 1–11% of the dies after exposure to the moisture resistance test. The maximum leakage rate (MLR) estimated from membrane deflection measurements was below 10−11 mbar·l·s−1 for all laminates. The measured average bond strength of dies from selected laminates ranged from 28 to 190 MPa.

• Malik, Nishant; Schjølberg-Henriksen, Kari; Poppe, Erik; Taklo, Maaike Margrete Visser & Finstad, Terje (2015). Impact of SiO2 on Al–Al thermocompression wafer bonding. Journal of Micromechanics and Microengineering (JMM).  ISSN 0960-1317.  25:035025(3) . doi: 10.1088/0960-1317/25/3/035025 Full text in Research Archive. Show summary

  Al–Al thermocompression bonding suitable for wafer level sealing of MEMS devices has been investigated. This paper presents a comparison of thermocompression bonding of Al films deposited on Si with and without a thermal oxide (SiO2 film). Laminates of diameter 150 mm containing device sealing frames of width 200 µm were realized. The wafers were bonded by applying a bond force of 36 or 60 kN at bonding temperatures ranging from 300–550 °C for bonding times of 15, 30 or 60 min. The effects of these process variations on the quality of the bonded laminates have been studied. The bond quality was estimated by measurements of dicing yield, tensile strength, amount of cohesive fracture in Si and interfacial characterization. The mean bond strength of the tested structures ranged from 18–61 MPa. The laminates with an SiO2 film had higher dicing yield and bond strength than the laminates without SiO2 for a 400 °C bonding temperature. The bond strength increased with increasing bonding temperature and bond force. The laminates bonded for 30 and 60 min at 400 °C and 60 kN had similar bond strength and amount of cohesive fracture in the bulk silicon, while the laminates bonded for 15 min had significantly lower bond strength and amount of cohesive fracture in the bulk silicon.

• Malik, Nishant; Tofteberg, Hannah Rosquist; Poppe, Erik; Finstad, Terje & Schjølberg-Henriksen, Kari (2015). Environmental Stress Testing of Wafer-Level Au-Au Thermocompression Bonds Realized at Low Temperature: Strength and Hermeticity. ECS Journal of Solid State Science and Technology.  ISSN 2162-8769.  4(7), s P236- P241 . doi: 10.1149/2.0201507jss Full text in Research Archive. Show summary

  Hermeticity, reliability and strength of four laminates bonded at different temperatures by Au-Au thermocompression bonding have been investigated. Laminates with a diameter of 150 mm were realized by bonding a wafer containing membrane structures to a Si wafer with patterned bond frames. A bond tool pressure of 2266 mbar was applied for 15 minutes at temperatures ranging from 150–300°C. The hermetic properties were estimated by membrane deflection measurements applying white-light interferometry after bonding. Reliability was tested by exposing the laminates to a steady-state life test, a thermal shock test, and a moisture resistance test. Bond strength was estimated by pull test measurements. A dicing yield above 90% was obtained for all laminates. Laminates bonded at 200°C and above had significantly higher hermetic yield than the laminate bonded at 150°C. No degradation in hermeticity was observed after the reliability tests. The maximum leakage rate (MLR) was estimated from two measurements of membrane deflection executed at two different times and was below 10−11 mbar ⋅ l ⋅ s−1. The average bond strength ranged from 44 to 175 MPa.

• Ruoho, Mikko; Valset, Kjetil; Finstad, Terje & Tittonen, Ilkka (2015). Measurement of thin film thermal conductivity using the laser flash method. Nanotechnology.  ISSN 0957-4484.  26(19) . doi: 10.1088/0957-4484/26/19/195706
• Schrade, Matthias; Norby, Truls & Finstad, Terje (2015). Hall effect measurements on thermoelectric Ca3Co4O9: On how to determine the charge carrier concentration in strongly correlated misfit cobaltites. Journal of Applied Physics.  ISSN 0021-8979.  117(20) . doi: 10.1063/1.4921861 Full text in Research Archive.
• Song, Xin; Valset, Kjetil; Graff, Joachim Seland; Thøgersen, Annett; Gunnæs, Anette Eleonora; Luxsacumar, Sivakanesar; Løvvik, Ole Martin; Snyder, Jeffrey G. & Finstad, Terje (2015). Nanostructuring of undoped ZnSb by Cryo-Milling. Journal of Electronic Materials.  ISSN 0361-5235.  44(8), s 2578- 2584 . doi: 10.1007/s11664-015-3708-6 Show summary

  We report the preparation of nanosized ZnSb powder by cryo-milling. The effect of cryo-milling then hot-pressing of undoped ZnSb was investigated and compared with that of room temperature ball-milling and hot-pressing under different temperature conditions. ZnSb is a semiconductor with favorable thermoelectric properties when doped. We used undoped ZnSb to study the effect of nanostructuring on lattice thermal conductivity, and with little contribution at room temperature from electronic thermal conductivity. Grain growth was observed to occur during hot-pressing, as observed by transmission electron microscopy and x-ray diffraction. The thermal conductivity was lower for cryo-milled samples than for room-temperature ball-milled samples. The thermal conductivity also depended on hot-pressing conditions. The thermal conductivity could be varied by a factor of two by adjusting the process conditions and could be less than a third that of single-crystal ZnSb.

• Valset, Kjetil; Song, Xin & Finstad, Terje (2015). A Study of Transport Properties in Cu and P doped ZnSb. Journal of Applied Physics.  ISSN 0021-8979.  117(045709) . doi: 10.1063/1.4906404 Full text in Research Archive. Show summary

  ZnSb samples have been doped with copper and phosphorus and sintered at 798 K. Electronic transport properties are interpreted as being influenced by an impurity band close to the valence band. At low Cu dopant concentrations, this impurity band degrades the thermoelectric properties as the Seebeck coefficient and effective mass are reduced. At carrier concentrations above 1 × 1019 cm−3, the Seebeck coefficient in Cu doped samples can be described by a single parabolic band.

• Evrin, Tugay; Ilday, Serim; Turan, Rasit & Finstad, Terje (2014). Influence of Ge content and annealing conditions on the PL properties of nc-Si1-xGex embedded in SiO2 matrix in weak quantum confined regime. Journal of Luminescence.  ISSN 0022-2313.  155, s 170- 179 . doi: 10.1016/j.jlumin.2014.06.012 Show summary

  Fabrication of Si (nc-Si), Ge (nc-Ge), and Si1-xGex (nc-Si1-xGex) nanocrystals embedded in SiO2 matrix is achieved by thermal annealing of magnetron-sputtered thin films. Effects of annealing conditions, namely duration and temperature, as well as Ge content on the photoluminescence properties are investigated. Origin and evolution of the photoluminescence signal in the weak quantum confinement regime are discussed. It is found that photoluminescence signals can be decomposed into four Gaussian peaks originating from Ge-related radiative defects located at the sub-oxide (GeOx), either inside the matrix or at the interface region (peak M), nc-Si1-xGex/SiO2 interface-related localized states (peak I), localized states in the amorphous Si1-xGex bandgap (peak A) and quantum confinement of excitons in small nanocrystals (peak Q). The role of small and large nanocrystals in the photoluminescence mechanism is investigated by varying the mean nanocrystal size from 3 nm to 23 nm (from strong to weak quantum confined regime). Our results demonstrate that the quantum confinement effect in Ge nanocrystals manifests though spectral blueshift due to increase in Ge content. We also propose that the decreasing photoluminescence signal intensity with an increase in Ge content may originate from Ge-related nonradiative Pb centers.

• Hansen, Per-Anders; Finstad, Terje & Nilsen, Ola (2014). Luminescent Properties of Multilayered Eu2O3 and TiO2 Grown by Atomic Layer Deposition. Chemical Vapor Deposition.  ISSN 0948-1907.  20(7-8-9), s 274- 281 . doi: 10.1002/cvde.201407113
• Hansen, Per-Anders; Fjellvåg, Helmer; Finstad, Terje & Nilsen, Ola (2014). Luminescence properties of europium titanate thin films grown by atomic layer deposition. RSC Advances.  ISSN 2046-2069.  4(23), s 11876- 11883 . doi: 10.1039/c3ra47469k Full text in Research Archive.
• Heng, Chenglin; Su, Wenyong; Zhang, Qiwei; Ren, Xiaoqian; Yin, Penggan; Pan, Huiping; Yao, Shude & Finstad, Terje (2014). The photoluminescence from (Eu, Yb) co-doped silicon-rich Si oxides. Journal of Luminescence.  ISSN 0022-2313.  154, s 339- 344 . doi: 10.1016/j.jlumin.2014.04.035
• Malik, Nishant; Poppe, Erik; Schjølberg-Henriksen, Kari; Taklo, Maaike Margrete Visser & Finstad, Terje (2014). Hermeticity and Reliability of Al-Al Thermocompression Wafer Bonding, In Hubert Moriceau; H Baumgart; M.S. Goorsky; K.D. Hobart; R. Knechtel; T. Suga & C.S. Tan (ed.),  2014 ECS and SMEQ Joint International Meeting, October 5, 2014 - October 9, 2014 Semiconductor Wafer Bonding 13: Science, Technology, and Applications.  The Electrochemical Society.  ISBN 978-1-62332-185-7.  artikkel.  s 149 - 160 Show summary

  Hermeticity and reliability of laminates bonded by Al-Al thermocompression bonding applying different bonding parameters have been investigated. Laminates of diameter 150 mm were realized by bonding a wafer containing membrane structures to wafers with patterned bonding frames. The laminates were bonded applying a bond force of 36 or 60 kN at temperatures ranging from 300 to 400 °C for 15, 30 or 60 minutes. The hermetic properties were estimated by optical measurement of membrane deflection after bonding. Reliability was tested by exposing the laminates to a steady-state life test, a thermal shock test, and a moisture resistance test. Laminates bonded applying a bond force of 60 kN at temperatures of 350 °C or higher resulted in hermetic and reliable bonds. All the dies on the laminates survived steady-state life test and thermal shock test. Leakage was observed in some dies after exposure to moisture resistance test. Measurements of membrane deflection estimated a maximum leak rate below 10-11 mbar×l×s-1 for all tested bonding parameters.

• Malik, Nishant; Schjølberg-Henriksen, Kari; Poppe, Erik; Taklo, Maaike Margrete Visser & Finstad, Terje (2014). Al-Al thermocompression bonding for wafer-level MEMS sealing. Sensors and Actuators A-Physical.  ISSN 0924-4247.  211, s 115- 120 . doi: 10.1016/j.sna.2014.02.030 Full text in Research Archive. Show summary

  Al–Al thermocompression bonding has been studied using test structures relevant for wafer level sealing of MEMS devices. Si wafers with protruding frame structures were bonded to planar Si wafers, both covered with a sputtered Al film of 1 μm thickness. The varied bonding process variables were the bonding temperature (400, 450 and 550 °C) and the bonding force (18, 36 and 60 kN). Frame widths 100 μm, 200 μm, with rounded or sharp frame corners were used. After bonding, laminates were diced into single chips and pull tested. The effect of process and design parameters was studied systematically with respect to dicing yield, bond strength and resulting fractured surfaces. The test structures showed an average strength of 20–50 MPa for bonding at or above 450 °C for all three bonding forces or bonding at 400 °C with 60 kN bond force. The current study indicates that strong AlAl thermocompression bonds can be achieved either at or above 450 °C bonding temperature for low (18 kN) and medium (36 kN) bond force or by high bond force (60 kN) at 400 °C. The results show that an increased bond force is required to compensate for a reduced bonding temperature for AlAl thermocompression bonding in the studied temperature regime

• Malik, Nishant; Tofteberg, Hannah Rosquist; Poppe, Erik; Finstad, Terje & Schjølberg-Henriksen, Kari (2014). Hermeticity and Reliability of Au-Au Thermocompression Bonds, Realized at Low Temperature, In Hubert Moriceau; H Baumgart; M.S. Goorsky; K.D. Hobart; R. Knechtel; T. Suga & C.S. Tan (ed.),  2014 ECS and SMEQ Joint International Meeting, October 5, 2014 - October 9, 2014 Semiconductor Wafer Bonding 13: Science, Technology, and Applications.  The Electrochemical Society.  ISBN 978-1-62332-185-7.  artikkel.  s 167 - 176 Show summary

  Hermeticity and reliability of four laminates bonded at different temperatures by Au-Au thermocompression bonding have been investigated. Laminates of diameter 150 mm were realized by bonding a wafer containing membrane structures to Si wafers with patterned bond frames. The laminates were bonded applying a bonding pressure of 8.5 MPa at temperatures of 150–300 °C for 15 minutes. The hermetic properties were estimated by measurement of membrane deflection at two different times after bonding. Reliability was tested by exposing the laminates to a steady-state life test, a thermal shock test, and a moisture resistance test. A dicing yield above 90 % was obtained for laminates bonded at or above 150 °C. Laminates bonded at 200 °C and above had significantly higher hermetic yield than the laminate bonded at 150 °C. No degradation in hermeticity was observed after the reliability tests. A maximum leak rate in the range of 10-11 mbar×l×s-1 was estimated.

• Mayandi, Jeyanthinath; Finstad, Terje; Foss, Steinar; Galeckas, Augustinas & Stange, Marit Synnøve Sæverud (2014). A comparative study of 1.5 μm photoluminescence from (Er, Si) and (Er, Ge) co-sputtered with Al2O3 on Si. Journal of Alloys and Compounds.  ISSN 0925-8388.  590, s 5- 8 . doi: 10.1016/j.jallcom.2013.12.060 Show summary

  We present a comparative study of the 1.54lm photoluminescence (PL) from Al2O3:(Er, Si) and Al2O3:(Er, Ge) films co-sputtered on Si substrates using a composite target. The PL yield of Si- and Ge- doped films subjected to different thermal treatment in the range 500–1100 °C is referenced against that of a control Al2O3:(Er) structure. The Er-related emission reaches maximum upon annealing at 700 °C for the Al2O3:(Er, Si) and 500 °C for the Al2O3:(Er, Ge) films, in both cases decreasing at higher annealing tem- peratures. Ge co-doped films are found to be approximately 20 times less luminous than the reference Al2O3:(Er) structure, whereas Si co-doping leads to greatly enhanced emission at 1.54 lm. By adapting energy filtered transmission electron microscopy (EFTEM), the presence of ����2 nm Si nanoclusters was revealed, whereas no indications of Ge clusters or crystals could be observed implying that mere presence of Ge in the Al2O3 matrix can dramatically reduce the luminescence efficiency. We discuss the possible reasons for not forming the Ge nanoclusters in the Al2O3 host and the apparent quenching of the Er- related emission.

• Schrade, Matthias; Casolo, Simone; Graham, Paul J.; Ulrich, Clemens; Li, Sean; Løvvik, Ole Martin; Finstad, Terje & Norby, Truls (2014). Oxygen nonstoichiometry in (Ca2CoO3)0.62(CoO2): a combined experimental and computational study. Journal of Physical Chemistry C.  ISSN 1932-7447.  118(33), s 18899- 18907 . doi: 10.1021/jp5048437 Full text in Research Archive. Show summary

  The oxygen nonstoichiometry in the misfit calcium cobaltite (Ca2CoO3)0.62(CoO2) has been studied experimentally and by density functional theory (DFT) calculations. The standard oxidation enthalpy ΔH0Ox of oxygen deficient (Ca2CoO3)0.62(CoO2) was measured directly using simultaneous thermogravimetry and differential scanning calorimetry. ΔH0Ox was found to be in agreement with the prediction from a previously published defect chemical model based on purely thermogravimetrical analysis. A series of samples with different oxygen vacancy concentration was prepared by annealing in air, followed by rapid quenching. Room-temperature Raman spectroscopy showed a sharp mode at 700 cm–1 decreasing in intensity with increasing vacancy concentration. We discuss this observation as evidence for oxygen vacancies being preferably formed within the central layer of the Ca2CoO3 subsystem. DFT calculations demonstrated that the calculated electronic structure is sensitive to the chosen model of the crystal structure. Still, for all investigated models, the standard formation enthalpy of oxygen vacancies within the Ca2CoO3 moiety was much lower than that for a site within the CoO2 layer, in agreement with the presented experimental data.

• Schrade, Matthias; Fjeld, Harald; Finstad, Terje & Norby, Truls (2014). Electronic Transport Properties of [Ca2CoO3-δ]q[CoO2]. Journal of Physical Chemistry C.  ISSN 1932-7447.  118(6), s 2908- 2918 . doi: 10.1021/jp409581n
• Schrade, Matthias; Fjeld, Harald; Norby, Truls & Finstad, Terje (2014). Versatile apparatus for thermoelectric characterization of oxides at high temperatures. Review of Scientific Instruments.  ISSN 0034-6748.  85(10) . doi: 10.1063/1.4897489
• Schrade, Matthias; Kabir, Rezaul; Li, Sean; Norby, Truls & Finstad, Terje (2014). High temperature transport properties of thermoelectric CaMnO3-d - Indication of strongly interacting small polarons. Journal of Applied Physics.  ISSN 0021-8979.  115 . doi: 10.1063/1.4868321 Full text in Research Archive.
• Hansen, Per-Anders; Fjellvåg, Helmer; Finstad, Terje & Nilsen, Ola (2013). Structural and optical properties of lanthanide oxides grown by atomic layer deposition (Ln = Pr, Nd, Sm, Eu, Tb, Dy, Ho, Er, Tm, Yb). Dalton Transactions.  ISSN 1477-9226.  42(30), s 10778- 10785 . doi: 10.1039/c3dt51270c Full text in Research Archive.
• Malik, Nishant; Schjølberg-Henriksen, Kari; Poppe, Erik & Finstad, Terje (2013). Al-Al thermocompression bonding for wafer-level MEMS packaging, In  The 17th International Conference on Solid-State Sensors, Actuators and Microsystems (TRANSDUCERS & EUROSENSORS XXVII), 2013 Transducers & Eurosensors XXVII, Barcelona, Spain June 16-20.  IEEE conference proceedings.  ISBN 978-1-4673-5982-5.  Artikkel.  s 1067 - 1070 Show summary

  The Al-Al thermocompression bonding is studied on test structures suitable for wafer level packaging of MEMS devices. Si wafers with protruding frame structures have been bonded to planar Si wafers all covered with a 1 μm sputtered Al film. The varied bonding process variables were temperature (400 °C-550 °C), bonding force (18-36 kN) and frame widths (100 μm, 200 μm, rounded or sharp corners). The delamination caused by dicing and pull tests is systematically studied. It is concluded that bonding is incomplete at 400 °C, with a low dicing yield. The quality of the bonding is increased by increasing bonding temperature and force as expected. The fractured surfaces and the bonding strength have been studied in detail. The test structures showed an average strength of 20-50 MPa for bonding at or above 450 °C. The current study indicates that strong Al-Al thermocompression bonds can be achieved at or above 450 °C for a typical MEMS bond frame.

• Nilsen, Ola; Haug, Kristoffer; Finstad, Terje & Fjellvåg, Helmer (2013). Molecular Hybrid Structures by Atomic Layer Deposition - Deposition of Alq3, Znq2 and Tiq4 (q=8-hydroxyquinoline). Chemical Vapor Deposition.  ISSN 0948-1907.  19(4-6), s 174- 179 . doi: 10.1002/cvde.201207043
• Böttger, Paul Heinrich Michael; Flage-Larsen, Espen; Karlsen, Ole Bjørn & Finstad, Terje (2012). High temperature Seebeck coefficient and resistance measurement system for thermoelectric materials in the thin disk geometry. Review of Scientific Instruments.  ISSN 0034-6748.  83(2) . doi: 10.1063/1.3673474
• Nguyen, Phoung Ngoc; Kepaptsoglou, Despoina Maria; Ramasse, Q.M.; Sunding, Martin Fleissner; Vestland, Lars Olav; Finstad, Terje & Olsen, Arne (2012). Impact of oxygen bonding on the atomic structure and photoluminescence properties of Si-rich silicon nitride thin films. Journal of Applied Physics.  ISSN 0021-8979.  112(7) . doi: 10.1063/1.4756998
• Song, Xin; Böttger, Paul Heinrich Michael; Karlsen, Ole Bjørn; Finstad, Terje & Taftø, Johan (2012). Impurity band conduction in the thermoelectric material ZnSb. Physica Scripta.  ISSN 0031-8949.  T148 . doi: 10.1088/0031-8949/2012/T148/014001
• Valset, Kjetil; Böttger, Paul Heinrich Michael; Taftø, Johan & Finstad, Terje (2012). Thermoelectric properties of Cu doped ZnSb containing Zn3P2 particles. Journal of Applied Physics.  ISSN 0021-8979.  111(2) . doi: 10.1063/1.3675505
• 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
• Böttger, Paul Heinrich Michael; Pomrehn, Gregory S.; Snyder, G. Jeffrey & Finstad, Terje (2011). Doping of p-type ZnSb: Single parabolic band model and impurity band conduction. Physica status solidi. A, Applied research.  ISSN 0031-8965.  208(12), s 2753- 2759 . doi: 10.1002/pssa.201127211
• Mayandi, Jeyanthinath; Finstad, Terje; Foss, Steinar; Klette, H & Sagberg, H. (2011). (Ge, Er) co-doped in SiO2 Sputtered Films with and without Voids and their Stability. Journal of nanoparticle research.  ISSN 1388-0764. Show summary

  Thin films of SiO2 have been co-doped with Ge and Er during magnetron sputtering. The photo-luminescence (PL) from the samples shows the 1.5 µm Er3+ peak after segregation annealing (600-1000°C) to form Ge nanoclusters. One set of samples was prepared with voids/pores in the film as observed by transmission electron microscopy. The PL yield from these samples showed various kinds of instability, which was monitored over a two years period and compared with samples that did not contain voids. The PL yield varies with storage time for samples that where segregation annealed shortly after film deposition, while the PL is stable for samples stored 6 months before the segregation annealing. The samples were examined by PL, TEM and IR reflectance spectroscopy. The samples with voids have a very high PL yield pr Er atom compared to those without voids (by a factor of 22). The instability is briefly discussed in terms of current research on embedded nanocrystals in oxides.

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• Rahman, Jamil Ur; Almeida Carvalho, Patricia; Guzik, Matylda N.; Soltani, Nayereh; Eleonora Gunnæs, Anette; Karlsena, Ole Bjørn & Finstad, Terje (2021). Synthesis and crystal structure of Sb-based high entropy alloys.
• Rahman, Jamil Ur; Almeida Carvalho, Patricia; Soltani, Nayereh; Schrade, Matthias; Karlson, Ole Bjørn; Eleonora Gunnæs, Anette & Finstad, Terje (2021). A study of new Sb-based high entropy alloys synthesized by non-conventional methods.
• 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. Show summary

  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.

• Løvvik, Ole Martin; Graff, Joachim Seland; Schrade, Matthias; Sunding, Martin Fleissner; Wright, Daniel Nilsen; Song, Xin; Finstad, Terje; Enebakk, Erik; Tollefsen, Torleif Andre & Skomedal, Gunstein (2020). Silicide module produced in the TESil project.
• 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.
• Libassie, Hailu Asmare & Finstad, Terje (2019). PV Installation System: Analysis of Performance and Degradation Mechanisms.
• 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. Show summary

  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; Sunding, Martin Fleissner; Diplas, Spyridon; Almeida Carvalho, Patricia & Finstad, Terje (2019). Oxidation of CrFeCoNiCu sputtered thin films.
• 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.

• 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.

• Riis, Henrik; Song, Xin; Prytz, Øystein & Finstad, Terje (2018). Characterization of Cu/ZnSb interfaces.
• Song, Xin; Graff, Joachim Seland; Götz, Adam; Skomedal, Gunstein & Finstad, Terje (2018). Investigating the influence of synthesis approach on the microstructure and thermoelectric properties for HMS.
• Berland, Kristian; Eliassen, Simen Nut Hansen; Schrade, Matthias; Tofan, Raluca; Guzik, Matylda Natalia; Gunnæs, Anette Eleonora; Finstad, Terje; Katre, Anikta; Madsen, Georg; Persson, Clas & Løvvik, Ole Martin (2017). Using theory to understand thermoelectric materials.
• Finstad, Terje (2017). Cryo-Milled Nanopowders of ZnSb for Reduction of Thermal Conductivity.
• Riis, Henrik; Finstad, Terje & Prytz, Øystein (2017). Metallization of ZnSb.
• Schrade, Matthias; Berland, Kristian; Guzik, Matylda Natalia; Løvvik, Ole Martin & Finstad, Terje (2017). Why does the thermal conductivity of XNiSn vary for nominally identical samples?.
• Taklo, Maaike M. Visser; Schjølberg-Henriksen, Kari; Malik, Nishant; Poppe, Erik Utne; Moe, Sigurd T. & Finstad, Terje (2017). Al-Al Wafer-Level Thermocompression Bonding applied for MEMS.
• Schrade, Matthias; Echevarria-Bonet, Cristina; Eliassen, Simen Nut Hansen; Berland, Kristian; Persson, Clas; Tofan, Raluca; Løvvik, Ole Martin; Gunnæs, Anette Eleonora & Finstad, Terje (2016). Thermal Properties of XNiSn(X = Hf, Zr, Ti) half Heusler Alloys.
• Schrade, Matthias; Echevarria-Bonet, Cristina; Guzik, Matylda Natalia; Tofan, Raluca; Gunnæs, Anette Eleonora; Eliassen, Simen Nut Hansen; Berland, Kristian; Persson, Clas; Løvvik, Ole Martin & Finstad, Terje (2016). Thermal properties of XNiSN (X = Ti, Zr, Hf) half Heusler alloys.
• Heinrich, Christophe P.; Schrade, Matthias; Cerretti, Giacomo; Malerød-Fjeld, Harald; Finstad, Terje; Norby, Truls & Tremel, Wolfgang (2015). Tetragonal Tungsten Bronzes Nb8−xW9+xO47−δ: Optimization Strategies and Transport Properties of a New Group of n-Type Thermoelectric Oxides.
• Malik, Nishant; Venkatachalapathy, Vishnukanthan; Poppe, Erik; Schjølberg-Henriksen, Kari; Taklo, Maaike Margrete Visser & Finstad, Terje (2015). Grain structure of Aluminium films for wafer-level thermocompression bonding.
• Song, Xin; Valset, Kjetil; Graff, Joachim Seland; Thøgersen, Annett; Gunnæs, Anette Eleonora; Carbalho, Partricia; Luxsacumar, Sivakanesar; Løvvik, Ole Martin; Snyder, G. Jeffrey & Finstad, Terje (2015). Nano Improves Thermoelectric Performance. Show summary

  The rule of thumb for improving the performance of thermoelectric materials is to reduce the thermal conduction, which attributes to electron transport and phonon transport. Phonons are characterized by different wavelength, Short wavelength phonons are scattered by impurity atoms in alloyed matels, Mid- and Long wavelength phonns are scattered by the iuinterfaces. Nanostructuring can engineer the phonon transport by introduce numerous grain boundaries, thus increasing phonon scattering, further improving thermal resistance. The aim of the present study is the nano-grains of the thermoelectric material ZnSb and the correlation with thermal transport measurements. We explored cryomilling (by ball-milling powders at Cryogenic temperature) as a technique to created nano—powders of ZnSb for pressing into pellets. The effect of cryomilling flowed by hot-pressing of undoped ZnSb was investigated.

• Hansen, Per-Anders; Fjellvåg, Helmer; Nilsen, Ola & Finstad, Terje (2014). Light conversion materials for solar cells by atomic layer deposition.
• Løvvik, Ole Martin; Song, Xin; Valset, Kjetil; Flage-Larsen, Espen; Fjeld, Harald; Graff, Joachim Seland; Schrade, Matthias; Karlsen, Ole Bjørn; Larsson, Andreas; Casolo, Simone; Prytz, Øystein; Norby, Truls; Finstad, Terje; Gunnæs, Anette Eleonora & Taftø, Johan (2014). Thermoelectric materials from first principles to final applications: Basic and applied thermoelectrics in Oslo.
• Malik, Nishant; Poppe, Erik; Schjølberg-Henriksen, Kari; Taklo, Maaike Margrete Visser & Finstad, Terje (2014). Hermeticity and Reliability of Al-Al Thermocompression Wafer Bonding.
• Malik, Nishant; Poppe, Erik; Schjølberg-Henriksen, Kari; Taklo, Maaike Margrete Visser & Finstad, Terje (2014). Hermeticity and reliability characterization of Al-Al thermocompression bonding.
• Malik, Nishant; Tofteberg, Hannah Rosquist; Poppe, Erik; Finstad, Terje & Schjølberg-Henriksen, Kari (2014). Hermeticity and Reliability of Au-Au Thermocompression Bonds, Realized at Low Temperature.
• Song, Xin; Persson, Clas; Norby, Truls; Flage-Larsen, Espen; Karlsen, Ole Bjørn; Hansen, Vidar; Gunnæs, Anette Eleonora; Prytz, Øystein; Løvvik, Ole Martin; Finstad, Terje; Valset, Kjetil; Cui, Xuemei; Taftø, Johan; Fjeld, Harald; Hauback, Bjørn & Schrade, Matthias (2014). Conversion of Heat and Energy: Thermoelectrics.
• Song, Xin; Valset, Kjetil; Graff, Joachim Seland; Thøgersen, Annett; Gunnæs, Anette Eleonora; Luxsacumar, Sivakanesar; Løvvik, Ole Martin & Finstad, Terje (2014). Nanostructuring by Cryomilling of Undoped ZnSb.
• Valset, Kjetil; Song, Xin & Finstad, Terje (2014). Stability and thermoelectric properties of Cu doped ZnSb.
• Malik, Nishant; Schjølberg-Henriksen, Kari; Poppe, Erik & Finstad, Terje (2013). Al-Al thermocompression bonding for wafer-level MEMS packaging.
• Fjeld, Harald; Schrade, Matthias; Norby, Truls & Finstad, Terje (2013). Defects and transport in thermoelectric calcium cobalt oxide.
• Malik, Nishant; Schjølberg-Henriksen, Kari; Poppe, Erik; Taklo, Maaike Margrete Visser & Finstad, Terje (2013). Optimization of Al-Al thermocompression bonding.
• Norby, Truls; Fjeld, Harald; Schrade, Matthias; Finstad, Terje; Løvvik, Ole Martin & Casolo, Simone (2013). On synthesis, phase purity, and oxygen stoichiometry of sodium and calcium cobaltate thermoelectrics. Show summary

  Relatively high concentrations of oxygen vacancies and effects on thermoelectric properties have been reported in the literature on state-of-the-art thermoelectric sodium cobaltates. However, first principle calculations suggest high energies and low concentrations of such vacancies. Experiments in our laboratory indicate that apparent oxygen non-stoichiometry may have stemmed from secondary phases present after decomposition in two-phase regions during synthesis and measurements. In a similar manner, experimental evaluation and defect-chemical interpretation of non-stoichiometry in calcium cobaltate thermoelectrics are troubled by non-trivial synthesis and sample fabrication. Recent results on these matters are presented and discussed.

• Schrade, Matthias; Fjeld, Harald; Finstad, Terje & Norby, Truls (2013). High temperature electronic transport in (Ca2CoO3-x)q(CoO2).
• Schrade, Matthias; Kabir, Rezaul; Li, Sean; Norby, Truls & Finstad, Terje (2013). Effect of oxygen content on the thermoelectric properties of CaMnO3-x.
• Schrade, Matthias; Kabir, Rezaul; Li, Sean; Norby, Truls & Finstad, Terje (2013). High-temperature thermoelectric properties of CaMnO3-x.
• Song, Xin; Karlsen, Ole Bjørn; Valset, Kjetil; Løvvik, Ole Martin & Finstad, Terje (2013). STUDIES ON SULPHUR DOPING OF ZnSb.
• Song, Xin; Valset, Kjetil; Karlsen, Ole Bjørn; Graff, Joachim Seland; Thøgersen, Annett; Luxsacumar, Sivakanesar; Løvvik, Ole Martin & Finstad, Terje (2013). Characterization methods for nanostructured thermoelectric materials ZnSb.
• Løvvik, Ole Martin; Valset, Kjetil; Rauwel, Protima; Prytz, Øystein; Flage-Larsen, Espen; Song, Xin; Karlsen, Ole Bjørn; Bording, Jan Kåre; Hansen, Vidar; Norby, Truls; Finstad, Terje & Taftø, Johan (2012). Thermoelectricity in Oslo.
• Schrade, Matthias; Fjeld, Harald; Norby, Truls & Finstad, Terje (2012). Influence of oxygen non-stoichiometry on thermoelectric properties of Ca3Co4O9+x.
• Adriyanto, Feri; Finstad, Terje & Schifano, Ramon (2011). Al doped ZnO thin films as a transparent electrode for solar cells applications.
• Algoz, Arif; Genisel, Mustafa; Foss, Steinar; Finstad, Terje & Turan, Rasit (2011). Matrix Density Effect on Morphology of Germanium Nanocrystals Embedded in Silicon Dioxide Thin Films. Materials Research Society Symposium Proceedings.  ISSN 0272-9172.  1337 . doi: 10.1557/opl.2011.976 Show summary

  Flash type electronic memories are the preferred format in code storage at complex programs running on fast processors and larger media files in portable electronics due to fast write/read operations, long rewrite life, high density and low cost of fabrication. Scaling limitations of top-down fabrication approaches can be overcome in next generation flash memories by replacing continuous floating gate with array of nanocrystals. Germanium (Ge) is a good candidate for nanocrystal based flash memories due its small band gap. In this work, we present effect of silicon dioxide (SiO2) host matrix density on Ge nanocrystals morphology. Low density Ge+SiO2 layers are deposited between high density SiO2 layers by using off-angle magnetron sputter deposition. After high temperature post-annealing, faceted and elongated Ge nanocrystals formation is observed in low density layers. Effects of Ge concentration and annealing temperature on nanocrystal morphology and mean size were investigated by using transmission electron microscopy. Positive correlation between stress development and nanocrystal size is observed at Raman spectroscopy measurements. We concluded that non-uniform stress distribution on nanocrystals during growth is responsible from faceted and elongated nanocrystal morphology.

• Algoz, Arif; Genisel, Mustafa; Foss, Steinar; Finstad, Terje & Turan, Rasit (2011). Matrix Density Effect on Morphology of Germanium Nanocrystals Embedded in Silicon Dioxide Thin Films.
• Hansen, Per-Anders; Fjellvåg, Helmer; Nilsen, Ola & Finstad, Terje (2011). Atomic layer deposition of lanthanide oxides.

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