Nanowire sharpening : application to field ionization

Nanowires show potential for a wide range of fields, from developing next generation solar cells, to detecting viruses, to field ionizing gasses. Their uses in such disparate fields are due to the extreme flexibility in which nanowires can be manufactured and customized to order. The heart of a nanowire, however, is it’s tip. Here surface charges accumulates in extreme densities when the wire is biased, consequently producing large electric fields that are then used in creative ways for exciting applications. My aim for this thesis is three-fold. First, I intend to establish a context for nanowires. Why were these structures studied in the first place? What are some exciting application areas? What makes nanowires unique? Etc... This will set the stage for subsequent sections, and provide the salt and pepper that will make the main course more flavorful. The second is to present an overview of relevant results from the literature that I will later build upon. There are analytical models of varying complexity examining the type of protrusions we are interested in here, as well as numerous numerical studies. We will look at them to get a deeper intuition for whats happening, and use them as a basis for comparison later on. Finally, I will present my results and discuss their consequences. As we will see, sharpening a cylindrical-post nanowire of height H = 1um, starting radius of curvature r₀ = 100nm, and base size b = 2 · r₀ = 200nm can enhance the field further by an order of 100. In addition, the dielectrophoretic (DEP) force present due to strong electric field gradients can significantly alter cooled gas beam trajectories towards the nanowire tips. Non-cooled gas beams also display room temperature trajectory deviations for species with large polarizability to mass ratios. This leads to the conclusion that at lower temperatures (and even at room temperature) the field ionization cross section of a nanowire array is significantly increased under certain conditions when taking into account DEP coupling.