I also spent time working with colleagues on campus to create the nano-pillars, which I will updating today as we have made much progress in this area.
Originally the plan was use PolyStyrene NanoSpheres (PSNS) to create the pillars by first placing the spheres on the silicon surface and then performing Reactive Ion Etching (RIE) to etch the areas exposed between the beads and then remove the beads to leave the areas underneath the beads untouched and use them for the adsorption surfaces. In the course of those experiments we found that the beads did not stand up to the power of the RIE process and changed shape during the etching leading the non-uniform shapes instead of pillars. Those results were posted in January of 2013 if one wishes to take a look.
Even if that form of masking were successful, the smallest diameter we have been able to obtain a even somewhat decent monolayer with so far is 80-100 nm, which means the smallest pillars we would end up with would be 100 nm. Our goal, however, is to reach pillars of 10 nm or so and therefore a different approach was needed.
It was later found that a group had already performed this process, with their citation given below
C.-W. Kuo, J.-Y. Shiu, P. Chen, G.A. Somorjai, Fabrication of Size-Tunable Large-Area Periodic Silicon Nanopillar Arrays with Sub-10-nm Resolution, The Journal of Physical Chemistry B, 107 (2003) 9950-9953.
That group used chromium sputtering in between the beads but we have decided to use thermal Nickel evaporation instead as the layer is more uniform and the source acts more like a point source so that the evaporation onto the surface is more anisotropic.
Above is an image of the surface of the silicon with evaporated Ni and beads removed. There is a precleaning step which leads to a slight decrease in the diameter of the beads (and hence an increase in the bead separation and the interstitial spaces) and therefore the dots are roughly 25 to 30 nm instead of 15 nm. However, if the cleaning step is avoided it is believed that smaller more uniform dots will be obtained. There is Ni lace also scattered about the sample, arising from the difficulty in acquiring a widespread hexagonal monolayer of beads across the surface.
Work will continue with these samples to perform the next step, RIE, in order to create the pillars and then remove the Ni with a transene etch.
Work with the trenches is still ongoing, with more difficulty in reaching the silicon bottom of the smallest trench widths. Trenches as small as 30 nm wide have been achieved but still not having a great deal of success in finding the silicon.
Updates will be more frequent in coming from now on.