Abstract
Pure tetravinylsilane and its oxygen mixture were used to deposit oxidized plasma polymer films at various effective power (0.1–10 W) and various oxygen fractions (0–0.71) using RF pulsed plasma. The optical properties (refractive index, extinction coefficient, band gap) of the deposited films were investigated by spectroscopic ellipsometry (230–830 nm) using an optical model and Tauc‒Lorentz parametrization. Analyses of chemical and mechanical properties of films allowed for the interpretation of changes in optical properties with deposition conditions. The refractive index was revealed to increase with enhanced effective power due to the increased crosslinking of the plasma polymer network but decreased when increasing the oxygen fraction due to the decrease of polymer crosslinking as the number of carbon bonds in the plasma polymer network was eliminated. A very strong positive correlation was found between the Young’s modulus and the refractive index for oxidized plasma polymer films. The optical properties of films correlated with their chemical properties for the specific deposition conditions used in this study. The band gap (1.9–2.9 eV) was assumed to be widened due to the increased concentration of vinyl groups in oxidized plasma polymer films.
Highlights
Optical coatings are functional materials in the form of thin films that are deposited on optical components to improve and control their optical phenomena in optical and optoelectronic devices.The coatings are applied as a single layer, multilayer, or gradient film, where the optical properties are constant, stepwise changing, or continuously varying across the film, respectively
This study focuses on the optical properties of plasma polymer films deposited from the pure tetravinylsilane monomer and its mixture with oxygen gas using RF pulsed plasma, which were characterized by spectroscopic ellipsometry
The elemental (Si, C, and O) composition of plasma polymer films is plotted in a ternary diagram (Figure 2b), which indicates that the silicon concentration was almost invariant, but the carbon concentration was reduced at the expense of the oxygen concentration
Summary
The coatings are applied as a single layer, multilayer, or gradient film, where the optical properties (refractive index, extinction coefficient) are constant, stepwise changing, or continuously varying across the film, respectively. The optical properties are inevitably related to other functional characteristics such as mechanical properties, adhesion, or thermal stability. Such optical coatings can be used as reflective, antireflective, or transmissive coatings, transparent electrodes, and optical filters in healthcare, military, electronics, transportation, or even construction [1]. Optical coatings are mostly deposited by physical vapor deposition (PVD), e.g., magnetron sputtering [1,2], but chemical vapor deposition (CVD) offers a wider range of technological tools to control optical and other physical, chemical, and surface properties of deposited micro- or nanostructures, since the total coating thickness can range from several nanometers to several micrometers. Among the CVD techniques, plasma-enhanced CVD (PECVD) with low-pressure
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