Nanomechanical Properties of Tungsten Trioxide (WO3) Grown by Atomic Layer Deposition

Tungsten oxide (WO₃) films exhibit interesting properties, making them useful in various thin-film applications, such as smart windows or flat-panel displays [1], in electrochromic devices [2], gas sensors [3], and photocatalysis/photoconductivity [4]. Many of these applications are strongly dependent on tungsten oxide’s crystal morphology, microstructure, and mechanical properties. WO₃ films of 200 and 600 ALD cycles were deposited on p-type Si (100) substrate using atomic layer deposition (ALD) technique and annealed at different temperatures. The 600 ALD cycle samples were annealed at 150, 250, and 300 °C, whereas the 200 ALD cycles sample was annealed at 250 °C. We tested these films for structural, surface morphology, and nanomechanical properties using nanoindentation. The structural and surface properties were explored using X-ray diffraction (XRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM). We discuss the influence of the deposition technique on the structure and properties of the films citing the superiority of the ALD technique that is particularly used in the fabrication of the films that are presented in this study. The results in Figures 1 and 2 depict no significant difference in the hardness among the different films and annealing temperatures. The SEM image of Figure 3 shows radial cracks in the 600 ALD cycles annealed sample at 150 ˚C as an example. All other samples depict similar radial cracks.     

References:

1. C.-G. Granqvist, Handbook of Inorganic Electrochromic Materials, Elsevier, Amsterdam (1995).
2. K. Bange, Sol. Energy Mater. Sol. Cells 58 (1999) 1.
3. M. Boulova, A. Gaskov, G. Lacazeau, Sens. Actuators, B, Chem. 81 (2001) 99.
4. F.B. Li, G.B. Gu, X.J. Li, H.F.Wan, Acta Phys. Chim. Sin. 16 (2000) 997.