Applied Surface Science 347 (2015) 861–867 Contents lists available at ScienceDirect Applied Surface Science jou rn al h om ep age: www.elsevier.com/locate/apsusc An iron(II) diketonate–diamine complex as precursor for thin film fabrication by atomic layer deposition Jon E. Bratvold a,∗ , Giorgio Carraro b , Davide Barreca c , Ola Nilsen a a Centre for Materials Science and Nanotechnology (SMN)/Department of Chemistry, University of Oslo, PO Box 1033, Blindern, N-0315 Oslo, Norway b Department of Chemistry, University of Padova and INSTM, via F. Marzolo 1, I-35131 Padova, Italy c CNR-IENI and INSTM, Department of Chemistry, University of Padova, via F. Marzolo 1, I-35131 Padova, Italy a r t i c l e i n f o Article history: Received 22 January 2015 Received in revised form 21 April 2015 Accepted 22 April 2015 Available online 30 April 2015 Keywords: Atomic layer deposition Molecular layer deposition Fe(hfa)2TMEDA Hybrid organic–inorganic materials a b s t r a c t A new divalent Fe precursor has been explored for deposition of iron-containing thin films by atomic layer deposition and molecular layer deposition (ALD/MLD). The Fe(II) -diketonate- diamine complex, Fe(hfa) 2 TMEDA, (hfa = 1,1,1,5,5,5-hexafluoro-2,4-pentanedionate, TMEDA = N,N,N ′ ,N ′ - tetramethylethylenediamine) can be handled in air, and sublimation at 60 ◦ C ensures a satisfactory vaporization rate. The reactivity of the precursor does not allow for direct reaction with water as co- reactant. Nevertheless, it reacts with carboxylic acids, resulting in organic–inorganic hybrid materials, and with ozone, yielding -Fe 2 O 3 . The divalent oxidation state of iron was maintained during deposition when oxalic acid was used as co-reactant, demonstrating the first preservation of Fe(II) from precursor to film during an MLD process. A self-saturating growth mode was proven by in situ quartz crystal microbalance (QCM) measurements, and the films were further characterized by grazing incidence X-ray diffraction (GIXRD), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). © 2015 Elsevier B.V. All rights reserved. 1. Introduction Although used for thousands of years, iron-containing com- pounds are still of great importance for technological applications. The magnetic and electronic properties exhibited by various iron oxides make them strategic candidates for use in biomedicine, lithium ion batteries, photoelectrochemical hydrogen production, and spintronic devices [1–4]. Particularly interesting with respect to spintronics are solid solutions of hematite–ilmenite, -Fe 2 O 3 - FeTiO 3 . Both naturally occurring minerals are antiferromagnetic insulators, but when combined in a layered structure they exhibit very stable magnetization and large exchange bias due to a phe- nomenon known as lamellar magnetism [5,6]. With the coexistence of ferrimagnetic and semiconducting properties [7–9], these sys- tems show great promise for applications in electronics and spintronics [10]. The end-uses require materials in form of thin films/nano-laminates with precise thicknesses, possibly covering complex high aspect ratio surfaces. To this regard, a viable and attractive option is offered by atomic layer deposition (ALD), which enables the tailored growth of ultra-thin, conformal and pin-hole free films with controlled properties even on porous structures. ∗ Corresponding author. Tel.: +47 97668855. E-mail address: j.e.bratvold@kjemi.uio.no (J.E. Bratvold). This technique is already being employed on an industrial scale to fabricate microelectronic devices [11,12]. Although versatile, ALD is usually limited to deposition of either fully reduced phases, i.e. metals, or fully oxidized materials. The possibility to deposit inter- mediate oxidation states by ALD enables the preparation of a wide range of phases with tailored properties. With this in mind, we have investigated the reactivity of a new divalent iron-containing compound as precursor for ALD and molecular layer deposition (MLD). Iron oxide films deposited by ALD were first prepared more than 10 years ago, and since then a variety of differ- ent precursors have been utilized. Pure -Fe 2 O 3 films have been obtained starting from various Fe(III) complexes, includ- ing Fe(acac) 3 (Hacac = 2,4-pentanedione) combined with O 2 [13], Fe(thd) 3 (Hthd = 2,2,6,6-tetramethyl-3,5-heptanedione) with O 3 [14,15], as well as iron(III) tert-butoxide (Fe 2 (O t Bu) 6 ) [16] and FeCl 3 [17], both with H 2 O as co-reactant. Depositions starting from Fe(II) precursors on the other hand require a more careful selection of the oxidizing agent and deposition temperature to produce pris- tine films. Rooth et al. [18] reported that ferrocene [Fe(Cp) 2 ] in combined with oxygen enabled the deposition of pure -Fe 2 O 3 films above 500 ◦ C, whereas a mixture of -Fe 2 O 3 (hematite) and -Fe 2 O 3 (maghemite)/Fe 3 O 4 (magnetite) was obtained at lower temperatures. Conversely, phase-pure -Fe 2 O 3 films could be fab- ricated in a broader temperature range by Martinson et al. using http://dx.doi.org/10.1016/j.apsusc.2015.04.154 0169-4332/© 2015 Elsevier B.V. All rights reserved.