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Texturing the surface of CR-39 ophthalmic lenses by low energy hydrogen ion shower:Profiling the physicochemical and optical properties of the textured surface vis-a-vis ion shower characteristics

Angela Kirsti A.Lim, Gene Q.Blantocas, Fahad Al-Mufadi

Hydrogen ion showers (Hn +) of current densities 50 to 400 mA/m2 were irradiated on AlyllDiglycol Carbonate (CR-39) ophthalmic lenses. The substrate lenses measured 6×6×2 mm3 and were fabricated through hot deformation polymerization process. Irradiation time was fixed at 15 minutes per sample. The study aimed to correlate Hn + ion beam characteristics to the physicochemical and optical changes of the treated lenses. Beam current densities were measured using a cast steel mass spectrometer and emittance contours at 90 % beam fraction were measured using a single-slit multi-detector emittance meter. Unnormalized emittances ranged from 180 to 310 mm-mrad for 1 to 5 mA discharges. Low energy beams (< 1keV) with elliptic emittance contour shaving H+/H2 + ratio > 8 produced a ubiquitous feature of tapered nanostructures on the surfaces. AFM histograms showed that average substrate surface roughness decreased from 30.91 nm (pristine sample) to 12.94 nm (treated samples) when low energy beams were used, but increased to 20.33 for high energy beams. Lens hydrophobicity improved with contact angles increasing from 61.23o (pristine) to 122.64o (treated). Spectral transmittance improved by about 1.5 times from 60% (pristine) to 90% (treated). An interplay between the roughening action of ion etching and the smoothing action of surface diffusion serves as the physical basis for the formation of sharp-tipped, tapered nanostructures on the lens surfaces. The introduction of nanostructures on the surface effectively created a hydrophobic, antireflective interface. Pre- and post-treatment FTIR-ATR transmittance peaks remained unaltered. Hence surface changes are attributed to physical factors and not to any chemical reactions.