Materials with Thickness Dependent Optical Properties

ThickVar materials have optical properties depending on layer thickness. A typical example of this type of materials is metal-island films (Fig. 1).

Usually with the help of characterization the optical properties of such material are determined for several typical thicknesses (Fig. 2).

We assume that they are saved to the Layer Material database with the names reflecting these thicknesses for convenience (Fig. 3).

Fig. 1. Typical structure of a metal-dielectric film: Ag island film is surrounded by two SiO₂ layers (sandwich).

Fig. 2a. Refractive indices of Ag-SiO2 metal-island films for different thicknesses of Ag.

Fig. 2b. Extinction coefficients of Ag-SiO2 metal-island films for different thicknesses of Ag.

Fig. 3. Specification of thickness dependent optical constants in the new ThickVar tab. You specify a dispersion file (left column) and the corresponding Ag-thickness.

Fig. 4. In Preview tab, you can see optical constants for any thickness specified in Layer Thickness field.

Layer materials: SiO₂, TiO₂.

In order to achieve different colors from the front and back sides of the substrate, an absorbing layer is required. Metal-island film is a good solution. It is not clear, however, what thickness of Ag should be. OptiLayer finds this thickness automatically in the course of the design process.

ThickVar Material Ag-SiO₂ (Fig. 3) must be loaded.

• The color coordinates can be specified in color target, for example, in La*b* system:
• a*=25, b*=60 (for reflectance R);
• a*=-60, b*=50 (for back side reflectance BR);
• L*=50% (for R/BR)
• Solar transmittance > 50% (can be specified using integral target).
• Thicknesses of the surrounding SiO₂ layers should be greater than 40 nm.
• The design can contain only one metal-dielectric layer of Ag-SiO₂.

Fig. 5. Color coordinates of reflectance and back side reflectance of the design with the profile shown in Fig. 8.

Fig.6. Solar transmittance of the design shown in Fig. 8 is greater than 50%.

Fig. 7. Reflectance and back side reflectance of the solution shown in Fig. 8.

Fig. 8. A 8-layer metal-dielectric solution satisfying all conditions presented above: the design contains only one Ag-SiO2 layer, this layer is surrounded by SiO₂ layers with thicknesses definitely larger than 40 nm.

Our publications can be interesting:

• V. Janicki, T.V. Amotchkina, J. Sancho-Parramon, H. Zorc, M.K. Trubetskov, and A.V. Tikhonravov, “Design and production of bicolour reflecting coatings with Au metal island fims,” Opt. Express 19, 25521-25527 (2011).
• T. V. Amotchkina, J. Sancho-Parramon, V. Janicki, M. K. Trubetskov, H. Zorc, A.V. Tikhonravov, Design of multilayer coatings containing metal island films, Proc. SPIE. 8168, Advances in Optical Thin Films IV 816809 (2011)
• T.V. Amotchkina, V. Janicki, J. Sancho-Parramon, A.V. Tikhonravov, M.K. Trubetskov, and H. Zorc, “General approach to reliable characterization of thin metal films,” Appl. Opt. 50, 10, 1453-1464 (2011).
• T.V. Amotchkina, V. Janicki, J. Sancho-Parramon, A.V. Tikhonravov, M.K. Trubetskov, and H. Zorc, “General approach to reliable characterization of thin metal films,” Appl. Opt. 50, 10, 1453-1464 (2011).