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Optical transmittances of spin-coated polymer films with different spin step protocols
(2019-07-01)
Sukjit, Peemases
;
Jaieau, Chatchai
;
Wasapinyokul, Kamol
In this report, we studied the effects of different spin-coating step protocol on the optical transmittance of thin film polymer. Thin films of poly(methylmethacrylate), or PMMA, were spin-coated with two different spin step protocols - the speed-up and speed-down protocols. In each protocol, the spin-coating had two steps, the first and the second steps. In the speed-up protocol, the first step was slow, while the second faster step was faster. In the speed-down protocol, the first step was fast, while the second step was slower. All the films were subsequently characterised for their optical transmittance over the visible region. There were at least three points worth explained from the experimental results. Firstly, for the speedup protocol, when the second-step speed was slower than 4000 rpm, the transmittance of the film were varied and did not show any relation with the first-step speed. However, when the second-step speed was faster, all the films, regardless of the first-step speed, provided roughly equal transmittance. Secondly, for the speed-down protocol, when the second-step speed was slower than 3000 rpm, transmittances from all films were varied. But when the second-step speed was faster, all the films from all first-step speed gave roughly equal transmittance. As the transmittance is related to the film thickness, these results indicated that, regardless of what the protocol was, if the second-step speed was fast, the film thickness from any first-step speeds would be roughly equal to each other. Finally, for the same pair of speeds but with different protocols, a film with a speed-down protocol provided a relatively higher transmittance than one from a speed-up protocol, implying a thinner film. The results from this study could be further developed to understand how the spin-speed protocol could be chosen to provide a thin film with required thickness.
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A study of optical properties of thin film polymer spin-coated with different dispensing methods
(2019-07-01)
Phatcharawutikul, Ronakrit
;
Tangtrakul, Kitbordee
;
Wasapinyokul, Kamol
Thin films of poly(methyl methacrylate), PMMA, were fabricated by using a spin-coating process with two different dispensing methods: static and dynamic ones. In the former and latter methods, the solution was dropped onto the substrate when the substrate was stationary and spinning, respectively. The films were characterised for their optical transmittance. The results show that the films from the dynamic dispensing method would provide higher optical transmittances than those from the static ones, indicating the thinner films. This could be explained as, in the dynamic method, the film would always be in a dynamic state and therefore could not form the film easily, resulting in a thinner film. Another point worth noting is that, in the dynamic method, the dispensing height affected the film's transmittance. The higher the dispensing height, the higher the transmittance. This indicated a thinner film and could be explained that, in the dynamic method, a higher dispensing height would result in a larger proportion of the liquid drop to bounce off the substrate, hence less amount of liquid remained to form the film, leading to a thinner film. Such characteristic did not appear in the static method because in this method, the liquid was dropped carefully and covered all the substrate before the spinning started. The results from this study could help choosing the dispensing method to provide film with required optical properties.
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Effects of quenching process on the optical properties of thin film polymers
(2019-07-01)
Jumpar-Ngern, Jitrin
;
Sompong, Khanisorn
;
Wasapinyokul, Kamol
Polymer is a group of materials applied in several thin film electronic devices. A typical fabrication process of the material consists of coating it as a film onto a substrate by a wet process, followed by the baking and annealing the film to change its molecular structures, and hence its properties. In this study, we reported the effect of the quenching process, or the cooling down process after baking, on the optical transmittance of the film. Thin films of poly(methyl methacrylate), or PMMA, was coated on a substrate and then baked at different temperatures followed by either a quick or slow cool-down quenching process; before they were checked for their optical transmittances. The results showed that the film baked at a temperature slightly higher than the glass transition temperature of the polymer, followed by a slow cool-down quenching process would provide the transmittance apparently lower than those of the films baking and quenching at other conditions. We believe that this was because when the polymer was baked above such temperature, the polymer was in its glassy state. When it was slowly cooled down, the molecules had time to form crystalline structure, hence a lower optical transmittance. The result from this study indicated that the quenching process can be used to control the properties of a polymer film and hence should be carefully practiced.

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