Abstracts Book - IMRC 2018

• SF2-P040
XPS STUDY OF ELECTROCHROMIC WO3 THIN FILMS DEPOSITED BY
DC MAGNETRON SPUTTERING
Pedro Emmanuel Garcia Tinoco 1 , Horacio Crotte Ledesma 1 , Mario Pérez González 1 , Martín
Ponce Mosso 1 , Michael Morales Luna 2 , Sergio Armando Tomás Velázquez 1
1 Centro de Investigación y de Estudios Avanzados del IPN - CINVESTAV, Departamento de
Física, Mexico. 2 Centro de Investigación y de Estudios Avanzados del IPN - CINVESTAV, Facultad
de Quimica, Materiales, Mexico.
Electrochromism is an outstanding technology for energy-saving devices, such
as the so-called “smart windows”, which can efficiently modulate the
transmittance of electromagnetic radiation in different spectral regions. In this
research, amorphous WO 3 thin films were deposited on ITO-coated glass
substrates by dc reactive magnetron sputtering. The effect of two physical
deposition parameters, i.e., the working pressure and O 2 /Ar gas ratio, on the
electrochromic properties was analyzed. The electrochromic performance of
the films was evaluated by cyclic voltammetry for 20 cycles using 0.1 M propionic
acid in aqueous solution as electrolyte. A three-electrode electrochemical cell
was employed, with the sample as working electrode and Ag/AgCl and Pt as
reference and counter electrodes, respectively. The applied voltage range was -
0.5 to 0.7 V vs Ag/AgCl, with a sweep rate of 10 mV/s. UV-vis spectrophotometry
indicated that films deposited at 10 mTorr are highly transparent, with a
transmittance at 550 nm around 90%, and optical modulation close to 30%. The
elemental composition, electronic properties, and oxidation states of the
sample surface were assessed by X-ray photoelectron spectroscopy (XPS). XPS
spectra of samples displayed the spin-orbit splitting for the W 4f core-level
spectra. A detailed analysis revealed W 6+ , W 5+ , and W 4+ oxidation states, which
depend strongly on the deposition conditions. In addition, reduced W 5+
oxidation states appeared in samples subject to electrochromic experiments,
evidencing ion intercalation in the materials. Complementarily, the surface
atomic concentration and elemental mapping were obtained. The highest
coloration efficiency (90 cm 2 /C) was achieved for films synthesized at 10 mTorr
and O 2 /Ar gas ratio of 0.28.
Acknowledgment: This work was supported by CONACyT (projects No. 168605
and No. 205733).
Keywords: Tungsten trioxide, electrochromic films, dc sputtering
Presenting authors email: pgarcia@fis.cinvestav.mx