Publication: Ion source-modified polycarbonate substrate for promoting adhesion ofinorganic thin film
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Date
2024-01-01
Authors
Lim Ruo Xuen
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Abstract
Anti-reflective (AR) coatings on polymer substrates play a crucial role to enhance
light transmittance and minimize reflectance loss. However, deposition of multi-layered AR
coatings on polymer substrates present challenges in terms of durability under various
weathering conditions, such as temperature, radiation, and humidity, which can affect
adhesion of the coating to the substrate. Therefore, in the present study, Xenon arc accelerated
weathering test followed ISO 16474-2:2013 guidelines was used to investigate durability of
thermally evaporated SiO2/TiO2 stacking layer as the AR coating on an ion-treated
polycarbonate (PC) substrate by varying anode voltage (80 – 100 V) of the ion treatment,
oxygen flow rate (0 – 10 sccm) during the treatment, and thickness (0, 2.25, and 3.60 nm) of
a binding layer (Chromium silicon monoxide, CrSiO) sandwiched between the AR stacking
layer and PC substrate. Crosshatch tape test based on ASTM D3359-23 was used to evaluate
the adhesion performance. Topography and morphology of the ion-treated PC surface were
respectively, characterized by atomic force microscopy (AFM) and scanning electron
microscopy (SEM). Fourier transform infrared (FTIR) spectroscopy was adopted to identify
chemical function groups of the treated PC surface whereas residual stress and optical
reflection of the total AR coating stacked on the PC substrate was measured by laser
interferometry and UV-Vis spectrophotometry. As the anode voltage increased with no oxygen
flow, an average surface roughness of PC substrate increased but the roughness decreased as
the oxygen flow rate increased when applied the lowest anode voltage (80 V). A reversed trend
of the roughness can be achieved by using at the highest anode voltage (100 V). Amount of
C-O functional group on treated PC substrates increased when the average surface roughness
decreased that led to a better coating adhesion. The adhesion can be improved by incorporating
a CrSiO as a binding layer, by considering the thickness layer is sufficient to smoothen the rough surface resulted from ion treatment. Additional layer of CrSiO can also alter the
compressive residual stress of the material system but not scarify the optical performance that
is used as an AR coating. In general, a better AR coating adhesion can be achieved with PC
surface having a smoother (Ra < 4 nm), higher amount of C-O bonding, and higher overall
residual compressive stress.