Browsing by Subject "OXIDE"

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  • Kokkonen, E.; Kaipio, M.; Nieminen, H. -E; Rehman, F.; Miikkulainen, V.; Putkonen, M.; Ritala, M.; Huotari, S.; Schnadt, J.; Urpelainen, S. (2022)
    An ambient pressure cell is described for conducting synchrotron-based x-ray photoelectron spectroscopy (XPS) measurements during atomic layer deposition (ALD) processes. The instrument is capable of true in situ and operando experiments in which it is possible to directly obtain elemental and chemical information from the sample surface using XPS as the deposition process is ongoing. The setup is based on the ambient pressure XPS technique, in which sample environments with high pressure (several mbar) can be created without compromising the ultrahigh vacuum requirements needed for the operation of the spectrometer and the synchrotron beamline. The setup is intended for chemical characterization of the surface intermediates during the initial stages of the deposition processes. The SPECIES beamline and the ALD cell provide a unique experimental platform for obtaining new information on the surface chemistry during ALD half-cycles at high temporal resolution. Such information is valuable for understanding the ALD reaction mechanisms and crucial in further developing and improving ALD processes. We demonstrate the capabilities of the setup by studying the deposition of TiO2 on a SiO2 surface by using titanium(IV) tetraisopropoxide and water as precursors. Multiple core levels and the valence band of the substrate surface were followed during the film deposition using ambient pressure XPS.
  • Seppälä, Sanni; Vehkamäki, Marko; Mizohata, Kenichiro; Noh, Wontae; Räisänen, Jyrki; Ritala, Mikko; Leskelä, Markku (2019)
    Three heteroleptic Zr precursors were studied for atomic layer deposition (ALD) of ZrO2. Films were deposited from Zr(Cp)((t)BuDAD)((OPr)-Pr-i), Zr(MeCp)(TMEA), and Zr(Me5Cp)(TEA) with either water or ozone as the oxygen source {tBuDAD = N, N-bis(tertbutyl) ethene-1,2-diaminato, TMEA = tris[2-(methylamino) ethyl]aminate, TEA = triethoanolaminate}. Self-limiting film growth was confirmed for the Zr(Cp)((t)BuDAD)((OPr)-Pr-i)/O-3 process at 250 degrees C and for the Zr(M(e)5Cp)(TEA)/O-3 process at 375 degrees C, which is among the highest temperatures for advanced heteroleptic precursors. Excellent film purity with C, H, and N levels below the detection limit of the elastic recoil detection analysis was obtained with ozone as the oxygen source. All the studied processes showed the same trend that at low deposition temperatures films were tetragonal ZrO2 and at higher temperatures mixtures of tetragonal and monoclinic ZrO2. With water, the monoclinic phase appeared at higher temperatures than with ozone. In addition to the deposition temperature, the film thickness affected the phase; thinner films favored the tetragonal phase and monoclinic peaks were more clearly seen in thicker films. The high thermal stability and excellent film purity show that from the three studied Zr precursors, Zr(Me5Cp)(TEA) is a noteworthy precursor candidate for ALD of ZrO2. Published by the AVS.
  • Nieminen, Heta-Elisa; Kaipio, Mikko; Ritala, Mikko (2020)
    In this work, a growth mechanism of an intermetallic Co3Sn2 thin film is studied in situ with a quartz crystal microbalance (QCM) and quadrupole mass spectrometer (QMS). The film is deposited by atomic layer deposition (ALD) from CoCl2 (TMEDA) and Bu3SnH precursors (TMEDA = N,N,N' ,N' - tetramethylethylenediamine). Balanced reaction equations are resolved by fitting the QMS and QCM data, and a step-by-step growth mechanism is determined for the process. During the CoCl2 (TMEDA) pulse, only 1-chlorobutane is formed as a byproduct. However, during the Bu3SnH pulse, two byproducts, BuCl and Bu3SnCl, were clearly detected, indicating that two competing reaction pathways exist during that pulse. Preliminary studies on another intermetallic ALD process, Ni3Sn2, revealed that the reactions occur similarly as in the Co3Sn2 process.
  • Chen, Zhijie; Setala, Heikki; Geng, Shicong; Han, Shijie; Wang, Shuqi; Dai, Guanhua; Zhang, Junhui (2017)
    Purpose Anthropogenic-induced greenhouse gas (GHG) emission rates derived from the soil are influenced by long-term nitrogen (N) deposition and N fertilization. However, our understanding of the interplay between increased N load and GHG emissions among soil aggregates is incomplete. Materials and methods Here, we conducted an incubation experiment to explore the effects of soil aggregate size and N addition on GHG emissions. The soil aggregate samples (0-10 cm) were collected from two 6-year N addition experiment sites with different vegetation types (mixed Korean pine forest vs. broad-leaved forest) in Northeast China. Carbon dioxide (CO2), nitrous oxide (N2O), and methane (CH4) production were quantified from the soil samples in the laboratory using gas chromatography with 24-h intervals during the incubation (at 20 degrees C for 168 h with 80 % field water capacity). Results and discussion The results showed that the GHG emission/uptake rates were significantly higher in the micro-aggregates than in the macro-aggregates due to the higher concentration of soil bio-chemical properties (DOC, MBC, NO3-, NH4+, SOC and TN) in smaller aggregates. For the N addition treatments, the emission/uptake rates of GHG decreased after N addition across aggregate sizes especially in mixed Korean pine forest where CO2 emission was decreased about 30 %. Similar patterns in GHG emission/uptake rates expressed by per soil organic matter basis were observed in response to N addition treatments, indicating that N addition might decrease the decomposability of SOM in mixed Korean pine forest. The global warming potential (GWP) which was mainly contributed by CO2 emission (>98 %) decreased in mixed Korean pine forest after N addition but no changes in broad-leaved forest. Conclusions These findings suggest that soil aggregate size is an important factor controlling GHG emissions through mediating the content of substrate resources in temperate forest ecosystems. The inhibitory effect of N addition on the GHG emission/uptake rates depends on the forest type.
  • Yli-Halla, Markku; Virtanen, Seija; Regina, Kristiina; Österholm, Peter; Ehnvall, Betty; Uusi-Kämppä, Jaana (2020)
    Besides causing acidification, acid sulfate (AS) soils contain large nitrogen (N) stocks and are a potential source of N loading to waters and nitrous oxide (N2O) emissions. We quantified the stocks and flows of N, including crop yields, N leaching, and N2O emissions, in a cultivated AS soil in western Finland. We also investigated whether controlled drainage (CD) and sub-irrigation (CDI) to keep the sulfidic horizons inundated can alleviate N losses. Total N stock at 0-100 cm (19.5 Mg ha(-1)) was smaller than at 100-200 cm (26.6 Mg ha(-1)), and the mineral N stock was largest below 170 cm. Annual N leaching (31-91 kg N ha(-1)) plus N in harvested grain (74-122 kg N ha(-1)) was 148% (range 118-189%) of N applied in fertilizers (90-125 kg N ha(-1)) in 2011-2017, suggesting substantial N supply from soil reserves. Annual emissions of N2O measured during 2 years were 8-28 kg N ha(-1). The most probable reasons for high N2O emission rates in AS soils are concomitant large mineral N pools with fluctuating redox conditions and low pH in the oxidized subsoil, all favoring formation of N2O in nitrification and denitrification. Although the groundwater level was higher in CD and CDI than in conventional drainage, N load and crop offtake did not differ between the drainage methods, but there were differences in emissions. Nitrogen flows to the atmosphere and drainage water were clearly larger than those in non-AS mineral soils indicating that AS soils are potential hotspots of environmental impacts.
  • Paajanen, Johanna; Weintraub, Saara; Lönnrot, Satu; Heikkilä, Mikko; Vehkamäki, Marko; Kemell, Marianna; Hatanpää, Timo; Ritala, Mikko; Koivula, Risto (2021)
    Nanoscale SnO2 has many important properties ranging from sorption of metal ions to gas sensing. Using a novel electroblowing method followed by calcination, we synthesized SnO2 and composite SnO2/SiO2 submicron fibers with a Sn : Si molar ratio of 3 : 1. Different calcination temperatures and heating rates produced fibers with varying structures and morphologies. In all the fibers SnO2 was detected by XRD indicating the SnO2/SiO2 fibers to be composite instead of complete mixtures. We studied the Co2+ separation ability of the fibers, since Co-60 is a problematic contaminant in nuclear power plant wastewaters. Both SnO2 and SnO2/SiO2 fibers had an excellent Co2+ uptake with their highest uptake/K-d values being 99.82%/281 000 mL g(-1) and 99.79%/234 000 mL g(-1), respectively. Compared to the bare SnO2 fibers, the SiO2 component improved the elasticity and mechanical strength of the composite fibers which is advantageous in dynamic column operation.
  • Lönnrot, Satu; Paajanen, Johanna; Suorsa, Valtteri; Zhang, Wenzhong; Ritala, Mikko; Koivula, Risto (2020)
    Submicron ZrO(2)fibers with three different Sb-doping levels (5, 10 and 15 cation%) were produced with an electroblowing synthesis for removal of(99)TcO(4)(-). The Sb-doped ZrO(2)fibers showed high selectivity toward(99)TcO(4)(-), which was not interfered by ClO4-, NO(3)(-)or Cl(-)ions and showed no selectivity toward ReO4-. The optimal pH range for the(99)Tc separation was 2-6 but the Sb-doped fibers maintained very high uptake level throughout the studied pH range of 1-10. According to the uptake experiments, Sb(III) is assumed to reduce Tc(VII) to Tc(IV) that is then adsorbed by the zirconia surface.
  • Abdulagatov, Aziz I.; Sharma, Varun; Murdzek, Jessica A.; Cavanagh, Andrew S.; George, Steven M. (2021)
    The thermal atomic layer etching (ALE) of germanium-rich SiGe was demonstrated using an oxidation and "conversion-etch" mechanism with oxygen (O-2) or ozone (O-3), hydrofluoric acid (HF), and trimethylaluminum [TMA, Al(CH3)(3)] as the reactants. The crystalline germanium-rich SiGe film was prepared using physical vapor deposition and had a composition of Si0.15Ge0.85. In situ spectroscopic ellipsometry was employed to monitor the thickness of both the SiGe film and the surface oxide layer on the SiGe film during thermal ALE. Using a reactant sequence of O-2-HF-TMA, the etch rate of the SiGe film increased progressively with temperatures from 225 to 290 degrees C. At 290 degrees C, the SiGe film thickness decreased linearly at a rate of 0.57 angstrom /cycle with a surface oxide thickness of 18-19 angstrom. This etch rate was obtained using reactant pressures of 25, 0.2, and 0.4Torr and doses of 1.5, 1.0, and 1.0s for O-2, HF, and TMA, respectively. The TMA and HF reactions were self-limiting and the O-2 reaction was reasonably self-limiting at 290 degrees C. Using an O-3-HF-TMA reaction sequence, the SiGe ALE etch rate was 0.42 angstrom /cycle at 290 degrees C. This etch rate was obtained using reactant pressures of 15, 0.2, and 0.4Torr and dose times of 0.5, 1.0, and 1.0s for O-3, HF, and TMA, respectively. The O-3, TMA, and HF reactions were all self-limiting at 290 degrees C. Atomic force microscopy images revealed that thermal ALE with the O-2-HF-TMA or O-3-HF-TMA reaction sequences did not roughen the surface of the SiGe film. The SiGe film was etched selectively compared with Si or Si3N4 at 290 degrees C using an O-2-HF-TMA reaction sequence. The etch rate for the SiGe film was >10 times faster than Si(100) or Si3N4 that was prepared using low-pressure chemical vapor deposition. This selectivity for the SiGe film will be useful to fabricate Si nanowires and nanosheets using SiGe as the sacrificial layer.