3. Extension of a Tight Binding Model
3.4. Marching Cubes and Advanced Marching Cubes algorithm
Here we investigated the effect of polymers on optical properties of subpixels. In the process of the replication of the nanostructured substrates, we use two different UV-polymers that will be demonstrated in detail to assess the impact of different UV-polymers, in Figure 7.3.
Figure 7.3 Schematics of UV-NIL process to produce substrates from a quartz stamp. OrmoStamp (MicroChem Corp.) is used as UV-polymer and Acrylate Acrylic Resin (AAR) is applied. The imprinting condition is 28 pounds squared inch (PSI) pressure. UV exposure is applied to cure UV-curable polymer, which its dose larger than 1000mJ/cm2 for (a) and (b).
It can be seen that the only difference between the two processes is applying a different polymer. Figure 7.4 shows the experimental results in printing diluted silver ink (Ag:EG=1:4 ratio) on the AAR polymer NCAs for red diffractive colour. Optical image shows the dots printed in red pixels laminated with a transparent index-matching cover film, as shown in Figure 7.4 (a). The SEM images of the RRC polymer NCAs in Red pixel band are demonstrated in Figure 7.4 (b), (c), (d) and (e). The period of the AAR polymer NCA is 650nm and the average height of the AAR polymer is 550nm for red pixel bands. The diameter of the ARR polymer NCA is 400nm for red pixel bands. The red colour dots inkjet-print on the low-wettability surface leads to a thin silver film coated on the NCAs surface, which assists to preserve the periodic morphology of the printed region as shown in Figure 7.4 (e) and thus leading to remaining printed region active in diffracting light after lamination. The unprinted the AAR polymer NCAs region Figure 7.4
(c) serves as black pixels for diffractive colour after index-matching. The size of individual silver dot printed on the substrate is around 17.74µm to 17.97µm.
Figure 7.4 Experimental results of printing silver ink (Ag:EG=1:4 ratio) nanoparticle weight on the AAR polymer NCA for red diffractive colour. (a) the optical microscope image shows the printed dots in red pixels. (b) a SEM image (tilted angle at 30°) of a silver dot printed on the nanocone array. (e) a SEM image (tilted at 30°)of center of printed dot. (d) a SEM image (tilted at 30°) of the edge of a printed dot. (c) a SEM image (tilted at 30°)of unprinted area. Scale bar: (a) 56µm.
In Figure 7.5, the experimental results in printing diluted silver ink (Ag:EG=1:4 ratio) on the OrmoStamp polymer NCAs for red diffractive colour are examined. The printed samples laminated with a transparent index-matching cover film are shown in Figure 7.5 (a). The SEM images of the OrmoStamp polymer NCAs in Red pixel band are
thin silver film form on the low wettability surface which act as active region in diffracting light as shown in Figure 7.5 (c). The size of individual silver dot printed on the substrate is around 18.54µm.
Figure 7.5 Experimental results of printing silver ink (Ag:EG=1:4 ratio) nanoparticle weight on the OrmoStamp polymer NCA for red diffractive colour. (a) the optical microscope image shows the printed dots in red pixels. (b) a SEM image (tilted angle at 30°) of a silver dot printed on the nanocone array. (c) a SEM image (tilted at 30°)of center of printed dot. (d) a SEM image (tilted at 30°) of the edge of a printed dot. (e) a SEM image (tilted at 30°)of unprinted area. Scale bar: (a) 56µm.
To further illustrate the printing on the AAR polymer NCAs and the OrmoStamp polymer NCAs printing, we also printed two colour images. To implement the experiments, the hydrophobic OrmoStamp polymer and AAR polymer substrate are produced and then generated binary patterns are inkjet-printed with respect to the nanostructured substrate layout. Figure 7.6 shows the resulting images. Then, index matching is used to form the desired colour pattern. In case of printing on the AAR polymer NCAs, silver inks are printed with 20µm dot-to-dot spacing and we managed to print a Simon Fraser University's logo photo as shown in Figure 7.6 (b) and Figure 7.6 (c), on the OrmoStamp polymer NCAs. The photo of the printed picture is shown with the
lighting angle and viewing angle specified in the schematic Figure 7.6 (a). The size of images is 2.0cm × 1.5cm. The effective pixel is 210µm × 210µm that can be seen by naked eyes.
Optical images captured from a region enclosed by white box of the printed picture are shown in Figure 7.6 (c) and (d). It can be observed that printing silver ink (Ag:EG=1:4 ratio) on the OrmoStamp polymer NCAs give brighter and higher contrast colours than the AAR polymer NCAs printing. Figure 7.6 (f) shows the measured normalized diffraction efficiency of the regions indicated by the white circles in Figure 7.6 (c) and Figure 7.6 (d). The displayed colours are confirmed with the measured normalized diffraction efficiency. Measured normalized diffraction efficiency of the OrmoStamp NCA substrate is about 7×10-3 , while the measured normalized diffraction efficiency of the AAR NCA substrate is about 3.5×10-3.
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Figure 7.6 Photo of coat-of-arms of Simon Fraser University printed on the ARR polymer substrate with pixelated nanostructures captured with the lighting angle and viewing angle specified in the schematic at It can be observed that printing silver ink (Ag:EG=1:4 ratio) on the OrmoStamp polymer NCAs give brighter and higher contrast colours than the AAR polymer NCAs printing. (a). (c) Photo of coat-of-arms of Simon Fraser University printed on the OrmoStamp polymer substrate with pixelated nanostructures captured with the lighting angle and viewing angle specified in the schematic at (a) . (d) Optical microscope image of (b) at the region enclosed by white box. (e) Optical microscope image of (c) at the enclosed by white box. (f) Measured normalized diffraction efficiency from the regions enclosed by the white dashed circles in (d) and (e). Scale bars are 56µm.