Browsing by Subject "AL2O3"

Sort by: Order: Results:

Now showing items 1-7 of 7
  • Popov, Georgi; Mattinen, Miika Juhana; Hatanpää, Timo; Vehkamäki, Marko; Kemell, Marianna; Mizohata, Kenichiro; Räisänen, Jyrki; Ritala, Mikko; Leskelä, Markku (2019)
    Atomic layer deposition (ALD) enables the deposition of numerous materials in thin film form, yet there are no ALD processes for metal iodides. Herein, we demonstrate an ALD process for PbI2, a metal iodide with a two-dimensional (2D) structure that has applications in areas such as photo-detection and photovoltaics. This process uses lead silylamide Pb(btsa)(2) and SnI4 as precursors and works at temperatures below 90 degrees C, on a variety of starting surfaces and substrates such as polymers, metals, metal sulfides, and oxides. The starting surface defines the crystalline texture and morphology of the PbI2 films. Rough substrates yield porous PbI2 films with randomly oriented 2D layers, whereas smooth substrates yield dense films with 2D layers parallel to the substrate surface. Exposure to light increases conductivity of the ALD PbI2 films which enables their use in photodetectors. The films can be converted into a CH3NH3PbI3 halide perovskite, an important solar cell absorber material. For various applications, ALD offers advantages such as ability to uniformly coat large areas and simple means to control film thickness. We anticipate that the chemistry exploited in the PbI2 ALD process is also applicable for ALD of other metal halides.
  • Gädda, Akiko; Ott, Jennifer; Karadzhinova-Ferrer, Aneliya; Golovleva, Maria; Kalliokoski, Matti; Winkler, Alexander; Luukka, Panja; Härkönen, Jaakko (2019)
    The suitability of two low-temperature dielectric passivation layer processes for the fabrication of Cadmium Telluride (CdTe) X-ray detectors has been investigated. The CdTe crystals with a size of (10 10 1) mm were coated with sputtered aluminum nitride (AlN) or with aluminum oxide (AlO) grown by the atomic layer deposition (ALD) method. The metallization contacts of the detectors were made by titanium tungsten (TiW) and gold (Au) metal sputtering depositions. The pad detector structures were patterned with proximity-contactless photolithography techniques followed by lift-off patterning of the electrodes. The detector properties were characterized at room temperature by Transient Current Technique (TCT) measurements. The obtained results were compared and verified by numerical TCAD simulations of the detector response. Our results indicate that higher signal charge was collected from samples with AlO. Furthermore, no significant laser light induced signal decay by CdTe material polarization was observed within order of 30 min of continuous illumination.
  • Nyman, Leo; Kestila, Antti; Porri, Paavo; Pudas, Marko; Salmi, Mika; Silander, Rudolf; Miikkulainen, Ville; Kaipio, Mikko; Kallio, Esa; Ritala, Mikko (2021)
    Many fields, including the aerospace industry, have shown increased interest in the use of plastics to lower the mass of systems. However, the use of plastics in space can be challenging for a number of reasons. Ultraviolet radiation, atomic oxygen, and other phenomena specifically associated with space cause the degradation of polymers. Here we show a path toward creation of space-grade components by combining additive manufacturing (AM) and atomic layer deposition (ALD). Our method produced ALD Al2O3 coated thermoplastic parts suitable for space applications. The highlight of this work is a significant reduction in outgassing, demonstrated using residual gas analyzer (RGA) sampling. Compared to uncoated parts, the ALD Al2O3 coating decreased the outgassing of polyether ether ketone (PEEK), acrylonitrile butadiene styrene (ABS), polycarbonate (PC), and nanodiamond-doped polylactide (ND-PLA) by 46%, 49%, 58%, and 65%, respectively. The manufacturing method used in this work enables the use of topology optimization already in the early concept creation phase. The method is ideally suited for spacecraft applications, in which the volume and mass of parts is critical, and could also be adapted for in-space manufacturing. (c) 2021 American Society of Civil Engineers.
  • Kukli, Kaupo; Kemell, Marianna; Heikkilä, Mikko J.; Castan, Helena; Duenas, Salvador; Mizohata, Kenichiro; Ritala, Mikko; Leskelä, Markku (2020)
    Amorphous SiO2-Nb2O5 nanolaminates and mixture films were grown by atomic layer deposition. The films were grown at 300 degrees C from Nb(OC2H5)(5), Si-2(NHC2H5)(6), and O-3 to thicknesses ranging from 13 to 130 nm. The niobium to silicon atomic ratio was varied in the range of 0.11-7.20. After optimizing the composition, resistive switching properties could be observed in the form of characteristic current-voltage behavior. Switching parameters in the conventional regime were well defined only in a SiO2:Nb2O5 mixture at certain, optimized, composition with Nb:Si atomic ratio of 0.13, whereas low-reading voltage measurements allowed recording memory effects in a wider composition range.
  • Heikkinen, Niko; Keskivali, Laura; Eskelinen, Patrik; Reinikainen, Matti; Putkonen, Matti (2021)
    Atomic layer deposition (ALD) was used to prepare a thin alumina layer on Fischer-Tropsch catalysts. Co-Pt-Si/gamma-Al2O3 catalyst was overcoated with 15-40 cycles of Al2O3 deposited from trimethylaluminum (TMA) and water vapor, followed by thermal annealing. The resulting tailored Fischer-Tropsch catalyst with 35 cycle ALD overcoating had increased activity compared to unmodified catalyst. The increase in activity was achieved without significant loss of selectivity towards heavier hydrocarbons. Altered catalyst properties were assumed to result from cobalt particle stabilization by ALD alumina overcoating and nanoscale porosity of the overcoating. In addition to optimal thickness of the overcoat, thermal annealing was an essential part of preparing ALD overcoated catalyst.
  • Mirhashemihaghighi, Shadi; Swiatowska, Jolanta; Maurice, Vincent; Seyeux, Antoine; Klein, Lorena H.; Salmi, Emma; Ritala, Mikko; Marcus, Philippe (2016)
    Surface smoothening by substrate annealing was studied as a pre-treatment for improving the corrosion protection provided to copper by 10, 20 and 50 nm thick alumina coatings deposited by atomic layer deposition. The interplay between substrate surface state and deposited film thickness for controlling the corrosion protection provided by ultrathin barrier films is demonstrated. Pre-annealing at 750 degrees C heals out the dispersed surface heterogeneities left by electropolishing and reduces the surface roughness to less than 2 nm independently of the deposited film thickness. For 10 nm coatings, substrate surface smoothening promotes the corrosion resistance. However, for 20 and 50 nm coatings, it is detrimental to the corrosion protection due to local detachment of the deposited films. The weaker adherence of the thicker coatings is assigned to the stresses accumulated in the films with increasing deposited thickness. Healing out the local heterogeneities on the substrate surface diminishes the interfacial strength that is bearing the stresses of the deposited films, thereby increasing adhesion failure for the thicker films. Pitting corrosion occurs at the local sites of adhesion failure. Intergranular corrosion occurs at the initially well coated substrate grain boundaries because of the growth of a more defective and permeable coating at grain boundaries. (C) 2016 Elsevier B.V. All rights reserved.
  • Ahaliabadeh, Zahra; Miikkulainen, Ville; Mäntymäki, Miia; Mousavihashemi, Seyedabolfazl; Lahtinen, Jouko; Lide, Yao; Jiang, Hua; Mizohata, Kenichiro; Kankaanpää, Timo; Kallio, Tanja (2021)
    Nickel-rich layered oxides, such as LiNi0.6Co0.2Mn0.2O2 (NMC622), are high-capacity electrode materials for lithium-ion batteries. However, this material faces issues, such as poor durability at high cut-off voltages (>4.4 V vs Li/Li+), which mainly originate from an unstable electrode-electrolyte interface. To reduce the side reactions at the interfacial zone and increase the structural stability of the NMC622 materials, nanoscale (