Formation ofWell-defined Nanocolumns by Ion Tracking Lithography

Abstract

AbstractLow dimensional systems on the nanometer scale afford a wealth of interesting possibilities including highly anisotropic behavior and quantum effects. Nanocolumns permit electrical and mechanical contact, yet benefit from two confined dimensions. This confinement leads to new optical, mechanical, electrical, chemical, and magnetic properties. We construct nanocolumn arrays with precise definition and independent control of diameter, length, orientation, areal density and composition so that geometry can be directly correlated to the quantum physical property of interest. The precision and control are products of the fabrication technique that we use. The process starts with an ion of sufficient energy to “track” a dielectric such as a film applied uniformly onto a substrate. The energy loss of the ion alters chemical bonding in the dielectric along the ion's straight trajectory. A suitable etchant quickly dissolves the latent tracks leaving high aspect ratio holes of small diameter (∼10nm) penetrating a film as thick as several microns. These small holes are interesting and useful in their own right and can be made to any desired size by continuing the etching process. Moreover, they serve as molds for electrochemical filling. After this electrodeposition, the mold material can be removed leaving the columns firmly attached to the substrate at the desired orientation. A variety of structures can be envisioned with these techniques. As examples, we have created arrays of Ni and of Pt nanocolumns (∼ 60 nm diameter and ∼ 600 nm long) oriented perpendicular to the substrate. The high aspect ratio and small diameter of the columns enables easy observation of quantum behavior, namely efficient electron field emission and Fowler Nordheim behavior.