Multilayered composite Au-NiO x electrochromic films F.F. Ferreira, M.C.A. Fantini * Instituto de Fı ´sica-Universidade de Sa ˜o Paulo, Caixa Postal 66318, 05315-970, Sa ˜o Paulo, SP, Brazil Received 30 April 2003; accepted 12 January 2004 Abstract In this work is reported the growth of multilayered composite Au-NiO x films by sputtering, using different deposition pressures that allow varying the Au content inside the oxide matrix. The films were characterized by RBS, XRD, TEM, cyclic voltammetry and spectral transmittance measurements. The films present anodic electrochromism, and those containing Au show a selective absorption in the green region of the visible spectrum in the bleached state, which was observed after the intercalation/deintercalation process. Au reduction process occurs during electrochemical cycling. D 2004 Elsevier B.V. All rights reserved. PACS: 85.60.Pg; 78.20.-e; 78.67.Bf; 78.70.Ck; 42.79.Wc Keywords: Electrochromism; Gold-nickel oxide; Selective absorption; Multilayer films; Sputtering 1. Introduction The possibility to obtain electrochromics that transmit colors other than the original tint opens up their range of applications [1–3]. For example, cathodic colored composite films were successfully achieved in the Au-WO 3 [4,5] and Au-MoO 3 [6,7] systems. The aim of this work was to grow anodic colored (blue, violet, red) Au-NiO x films, different from pure NiO x (transparent, gray), due to the presence of Au particles (Rb2.5 nm) inside the oxide matrix. Theoretical calculations of the optical properties of nickel oxide films inserted with gold particles were performed, demonstrating theirs poten- tial use as selective absorbers [8]. 2. Experimental Electrochromic nickel oxide (NiO x ) and composite gold- nickel oxide (Au-NiO x ) thin films were deposited by reactive DC magnetron sputtering, using metallic targets of Ni and Au in an Ar +O 2 atmosphere at room temperature. The films’ characterization techniques were Rutherford backscattering spectrometry (RBS), cyclic voltammetry and in situ spectral transmittance, transmission electron microscopy (TEM), X-ray diffraction (XRD) and ex situ spectral transmittance in the visible range. The substrates were (i ) Corning glass 7059 plates covered with In 2 O 3 :Sn (ITO-resistance b10 ohm/square, nominal coating thickness: 120–160 nm, Delta Technologies) for the electrochemical experiments, spectral transmittance and XRD measure- ments, (ii ) ultra dense amorphous carbon (UDAC) for the RBS measurements and (iii ) copper grid covered with carbon for the TEM analyses. The films were deposited at constant power at the Ni and Au targets, respectively, 200 and 10 W. The oxygen and argon flows were also kept constant at, respectively, 6 and 20 sccm. The samples were deposited as a multilayered system having nine layers of NiO x and eight layers of Au. The gold content in the films was varied by changing the deposition time of each layer (1V 30U,2V 10U and 5V 10U) together with the pressure ( p ) inside the chamber, being 2.0, 5.0 and 10.0 mTorr. Table 1 depicts some of the samples’ characteristics such as composition and thickness, determined by RBS. The simultaneous measurement of the I vs. V plot and in situ spectral transmittance of the films cycled in a 0.1M 0167-2738/$ - see front matter D 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.ssi.2004.01.071 * Corresponding author. Tel.: +55 11 3091 6882; fax: +55 11 3091 6749. E-mail address: mfantini@if.usp.br (M.C.A. Fantini). Solid State Ionics 175 (2004) 517 – 520 www.elsevier.com/locate/ssi