Fabrication of Ultralow Stress TiO2/SiO2 Optical Coatings by Plasma Ion-Assisted Deposition

Abstract

Optical and mechanical properties of multilayer coatings depend on the selected layer materials and the deposition technology; therefore, knowledge of the performances of thin films is essential. In the present work, titanium dioxide (TiO2) and silicon dioxide (SiO2) thin films have been prepared by plasma ion-assisted deposition (PIAD). The optical, structural, and mechanical properties of thin films have been investigated using spectrometer/ellipsometer, X-ray diffraction (XRD), atomic force microscopy (AFM), and laser interferometer. The results show that TiO2 film fabricated by PIAD induces a high refractive index, wide optical band gap, amorphous structure, smooth surface, and tensile stress. In the case of SiO2 film, high bias voltage leads to dense structure and compressive stress. As an application, a three-wavelength high reflectance at 632.8, 808, and 1550 nm was optimized and deposited. The dependence of total stress in the multilayer on the substrate temperature was studied as well. In conclusion, it was demonstrated that PIAD is an effective method for the preparation of ultralow stress TiO2/SiO2 multilayer films. The achieved stress was as low as 1.4 MPa. The result could provide guidance to the stress optimization of most optical components without prefiguring, backside coating, and postdeposition treatments.

Multilayers for directed energy accelerated lightsails

“…Luckely, SiO 2 layers usually show a built-in compressive stress, whereas TiO 2 layers show a built-in tensile stress 31 , so that they act in compensation when the SiO 2 /TiO 2 multilayer is deposited. Moreover, by depositing the structure at a specific temperature or treating it with postdeposition annealing cycles, the total built-in stress can be reduced to values lower than 5 MPa 30 . Thermal gradients produce additional stress that adds to the built-in stress.…”

Effect of SILAR Cycles on the Thickness, Structural, Optical Properties of Cobalt Selenide Thin Films

“…From the absorbance (A) obtained from spectrophotometer, other properties such as transmittance, extinction coefficient and band gap were calculated. Transmittance (T) was determine using equation (7) as given by [30,31].…”

Electrostatically Tuned Optical Filters Based on Hybrid Plasmonic-Dielectric Thin Films for Hyperspectral Imaging

“…Deposition of thin film of TiO 2 on glass substrate using electron beam evaporation causes tensile residual stress in the order of 170 MPa [ 38 ]. While deposition of thin film of SiO 2 on a thin film of TiO 2 causes a compression stress in the same order to form [ 39 , 40 ]. Deposition of silver on the other hand causes a tensile stress in the order of 18 Pa which gives a radius of curvature in the range of thousands of kilometers according to Stoney’s equation [ 38 ].…”