Highly reflective aluminum films on polycarbonate substrates by physical vapor deposition

Nowadays aluminum has a big potential as reflective thin film on polymer substrates to obtain lightly and flexible mirrors to be used in several technological applications, i.e. solar concentration technologies, microelectronic, hemispherical mirrors, telescope mirrors, among others, due to its good corrosion resistance, relatively low cost and high reflectivity behavior. Thin films of aluminum can be obtained by means of vacuum thermal evaporation and good compatibility and homogeneity can be reached through proper surface activation of the polymeric substrate. In this work polycarbonate (PC) sheet was used as substrate for thin films of high purity aluminum. The polymer surface was previously UVO (ultraviolet and ozone) activated during 5 and 10 min. FTIR, water contact angle and AFM analysis were used to validate the effect of the UVO treatment on the PC surface. High purity aluminum was deposited on PC substrates. Total reflectivity and X-ray diffraction were used to evaluate the quality of the films. The results showed that UVO treatment greatly improved the wettability of the substrates and promoted homogeneity of the aluminum films. The UVO treatment times for improvement of the adhesion force between the polymeric substrate and the aluminum film were well stablished, increasing the reflectivity of the aluminum films. Total reflectivity of 90% was obtained for the aluminum thin films. Compared with a typical commercial rigid mirror for solar concentration of 93% reflectivity, to the best of our knowledge, this value represents one of the highest reported for reflective thin films on flexible polymeric substrates.