layer (Brewer Science XHRIC-16) was spun on the sample at 4000 rpm for 30 s and oven prebaked at 175 C for 3 min. Photoresist (PR; Shipley 510A) was spun on the ARC at 4000 rpm and oven prebaked for 3 min at 95 C. IL with 355 nm third-harmonic YAG laser beam was used to produce periodic nanopatterns in the PR [9]. The angle between the two beams determined the 520 nm pattern period while the exposure dose and development time affected the detailed pattern shape. After exposure, the resist was post baked for 2 min at 110 C and developed using a MF-702 developer for 45 s followed by a rinse with deionized (DI) water. Pattern transfer was effected via lift-off of a thin gold film (~30 nm) that was deposited by electronbeam evaporation to form a hard mask and RIE of the underlying ARC and the silicon. Acetone was then used to liftoff the PR leaving a hard Au mask atop the ARC layer. Oxygen plasma was used to etch through the ARC for 3 min with the power of 50 W while a mixture of O 2 and CHF 3 (50:130) was used to etch Si for 3±6 min at a power of 150 W for an etch depth ranging from 30 to 200 nm. Finally, the ARC/Au layer was removed in an ultrasonic bath using piranha. The fabrication of periodic arrays of nanometer-scale cylindrical hole was performed on Si wafer coated with a 60 nm SiO 2 layer. The SiO 2 was thermally grown in a dry-O 2 oxidation furnace. The processing for fabrication 2D patterns was similar to that for groove structures except for double exposures and inductively coupled plasma (ICP) etching of the SiO 2 . After the samples were exposed with a first 1D grating, they were rotated 90 and exposed a second time to obtain 2D photoresist patterns (here posts for positive photoresist). After lift-off of a Au hard mask as above, an ICP system was next used to etch the SiO 2 in the regions where there was no Au hard mask in etching step. A mixture of Ar and CHF 3 (3:1) was used to etch SiO 2 for 2 min at the RF power of 500 W, bias of 150 W, and the pressure of 10 mtorr. The ICP etching could etch selectively SiO 2 with the mixture of Ar and CHF 3 in this case.Two particle sizes were investigated. Both are from Nissan Chemical Industries. Ltd. The larger silica particles (1 wt.-%,~pH 8.8) were prepared by diluting Snowtex ZL (40.9 wt.-%,~pH 9.6, 78 ±16 nm diameter [25]) with DI water. The smaller silica nanoparticles (1 wt.-%, pH 4.8) were prepared by diluting Snowtex OL (20 wt.-%,~pH 3, 50 ±13 nm diameter) with DI water. HCl or NH 4 OH were used to adjust the pH value of the water-based colloidal solutions. Before spin-coating, the treatment of an oxygen plasma RIE was used in order to ensure that the sample surface was hydrophilic. Next, the silica nanoparticle colloidal solution was spun onto the patterned samples. Images were obtained using field emission scanning electron microscopy (FE-SEM) (tilted at 45) at 30 kV with a 10 nm thick Au film to minimize charging.
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