Browsing by Subject "OPTICAL-CONSTANTS"

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  • 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.
  • Iivonen, Tomi; Heikkilä, Mikko J.; Popov, Georgi; Nieminen, Heta-Elisa; Kaipio, Mikko; Kemell, Marianna; Mattinen, Miika; Meinander, Kristoffer; Mizohata, Kenichiro; Räisänen, Jyrki; Ritala, Mikko; Leskelä, Markku (2019)
    Herein, we report an atomic layer deposition (ALD) process for Cu2O thin films using copper(II) acetate [Cu(OAc)(2)] and water vapor as precursors. This precursor combination enables the deposition of phase-pure, polycrystalline, and impurity-free Cu2O thin films at temperatures of 180-220 degrees C. The deposition of Cu(I) oxide films from a Cu(II) precursor without the use of a reducing agent is explained by the thermally induced reduction of Cu(OAc)(2) to the volatile copper(I) acetate, CuOAc. In addition to the optimization of ALD process parameters and characterization of film properties, we studied the Cu2O films in the fabrication of photoconductor devices. Our proof-of-concept devices show that approx- imately 20 nm thick Cu2O films can be used for photodetection in the visible wavelength range and that the thin film photoconductors exhibit improved device characteristics in comparison to bulk Cu2O crystals.