Browsing by Author "Ng, S.H."

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    Anisotropic 3D columnar micro-film coating for applications in infrared and visible spectral ranges
    (Elsevier B.V., 2022) Hu, J.; Han, M.; Grineviciute, L.; Ng, S.H.; Anand, V.; Katkus, T.; Ryu, M.; Morikawa, J.; Tobin, M.J.; Vongsvivut, J.; Tolenis, T.
    Polarisation analysis of thin (∼1 μm) SiO2 films deposited via evaporation at a glancing angle of 70◦ to the normal on resist pillar arrays was carried out using synchrotron-based Fourier transform infrared (s-FTIR) microspectroscopy in reflection mode. Changes in intensity of absorption bands were observed to follow the angular dependence of ∼ cos2 𝜃, consistent with the absorption anisotropy. The strongest absorption was found to be the sharp Si–O–Si stretching vibrational mode at 1040 ± 20 cm−1, which can be used for sensor applications, as well as radiative cooling in the atmospheric transparency window, within the range of 8-13 μm (i.e. 1250-769 cm−1). Anisotropy of IR absorbance is correlated with retardance/birefringence of the same patterns in the visible spectral range. Larger period patterns of 3D columnar SiO2 films of ∼1 μm in thickness deposited on polymer/resist pillar arrays provide the possibility to control anisotropy of the form-birefringent 3D columnar films.
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    Optical anisotropy of glancing angle deposited thin films on nano-patterned substrates
    (Optica Publishing Group, 2022) Grineviciute, L.; Moein, T.; Han, M.; Ng, S.H.; Anand, V.; Katkus, T.; Ryu, M.; Morikawa, J.; Tobin, M.J; Vongsvivut, J.; Tolenis, T.
    This study has demonstrated that 3D columnar micro-films/coatings can be deposited over pre-patterned surfaces with sub-micrometer periodic patterns. Four-angle polarisation analysis of thin (0.4 − 1~μm) Si and SiO2 films, evaporated via glancing angle deposition (GLAD) at 70° to the normal, was carried out in reflection mode using synchrotron infrared microspectroscopy at the Australian Synchrotron. The angular dependence of absorbance followed A(θ) ∝ cos 2θ, confirmed for Si substrates patterned by electron beam lithography and plasma etching, which were used to make checkerboard patterns of Λ = 0.4~μm period on Si. Retardance control by birefringence of a patterned SiO2 substrate coated by columnar SiO2 is promising for UV-visible applications due to the use of the same material to endow polarisation control.