That is clear the moment you approach the main entrance's widened steps on Central Park West and see a bronze, life-size statue of Abraham Lincoln standing in casual welcome.
Four types of high aspect ratio nanoporous anodic alumina funnels with one, two, three and four segments are fabricated by following sequentially anodizing and pore widening steps.
Three bridges along the way have just been rebuilt and widened, with steps removed to make them more bike-friendly, thanks to a lottery grant.
Thus, by combining a cyclic anodization voltage with a subsequent pore-widening step, tunable in-depth modulation of the pore diameter and effective refractive index variations are obtained.
After the anodization, a wet etching to increase pore radius (pore-widening step) was performed with 5 wt.% phosphoric acid (H3PO4) at 35°C.
It was also shown that the application of a pore-widening step after anodization is crucial in order to obtain well-defined stop bands with low transmittance and high reflectance.
Our aim is to show that although porosity of as-anodized layers is very similar for all anodization voltages, if a subsequent pore-widening step is applied, the rate at which porosity increases is indeed different.
NAA-based DBR can be achieved by taking advantage of the fact that a wet etching applied after the anodization to enlarge the pore diameter (pore-widening step) has a different rate depending on the used anodization voltage [23].
We also study how the pore-widening step (necessary to obtain the well-defined photonic stop bands) can be combined with these parameters in order to adjust the stop band position of the fabricated structures.
Other authors have reported on the fabrication of DBR structures by applying a cyclic anodization voltage [19, 20, 24] although they did not stress the importance of the pore-widening step in order to obtain the photonic stop bands.
What I can't forget is how the 37 stone steps, widening as they descend, were transformed by undreamed of dance imagery, nowhere more so than when, soon after the start, the nine dancers rolled up those stairs.
