X-Ray Reflectometry for electrochromic thin film characterization: WO3 as an example

Brandon Faceira (1) , Yves Ménesguen (2) , Marie‐Christine Lépy (2) , Aline Rougier (1)

1 ICMCB - Institut de Chimie de la Matière Condensée de Bordeaux
2 LNHB (CEA, LIST) - Laboratoire National Henri Becquerel (CEA, LIST)

Electrochromic (EC) materials and devices are able to modify their optical properties under the appliance of a voltage. This technology is recognized as one of the key green technology for sustainability and energy saving. The ability of electrochromic materials to maintain their coloured state once the applied voltage is withdrawn associated to its reversibility is called the memory effect. This unusual property on metal oxides allows to reduce power consumption of devices by avoiding to apply a voltage permanently in order to keep the desired colour. WO 3 thin films of ~100 nm were grown by radio-frequency magnetron sputtering using a WO3 ceramic target in an argon and oxygen atmosphere. The control of sputtering conditions as power density, total pressure and oxygen partial pressure allows to adjust the memory effect on WO 3 films. By varying the total pressure from 1 Pa to 2 Pa and 4 Pa, WO3 thin films with an irreversible colouration, a high memory effect or a poor memory effect can be obtained. The presentation will make a focus on WO 3 films deposited at 2 Pa. X-Ray Reflectometry (XRR) is a non-destructive technique which is a useful tool to evaluate thickness and the thin film density, thus the composition. From XRR, density, thickness, surface and interface roughness can be obtained. XRR measurements were performed at the Metrology beamline at SOLEIL synchrotron using CASTOR device. The reflectivity was recorded on a WO 3 thin film deposited on silicon wafer at 8 keV photon energy. Simulation of XRR curves were performed using model based on different layers as substrate, film/substrate interface and thin film.

Mots clés: material characterisation; thin film; X-Ray Reflectometry; Electrochromic material; optical properties; coloured state; metal oxide; radio-frequency magnetron sputtering; ceramic target; sputtering conditions; irreversible colouration; density; thickness; surface; interface roughness; Metrology; SOLEIL; synchrotron; CASTOR; ionizing radiation

Domaines: Matière Condensée [cond-mat]; Optique / photonique

Brandon Faceira, Yves Ménesguen, Marie‐Christine Lépy, Aline Rougier. X-Ray Reflectometry for electrochromic thin film characterization: WO3 as an example. Journées Plénières du GdR Name - "Nanomaterials for Energy Applications", GdR Name, Oct 2022, Lyon, France. ⟨hal-04564367⟩