Angle-Resolved Nanosphere Lithography:  Manipulation of Nanoparticle Size, Shape, and Interparticle Spacing

This work presents a novel approach to fine-tuning the size, shape, and interparticle spacing of nanoparticles fabricated by nanosphere lithography (NSL). This approach, termed angle-resolved nanosphere lithography (AR NSL), is a variant of NSL that yields vastly different, and increasingly flexible, nanostructures. This is accomplished by controlling the angle, θ, between the surface normal of the sample assembly and the propagation vector of the material deposition beam. Comparison of experimental results to simulated nanoparticle array geometries generated using an analytical model show excellent qualitative agreement. Using AR NSL, we have demonstrated that it is possible to reduce in-plane nanoparticle dimensions by a factor of 4. This important result shows that it will be possible to achieve fabrication of nanoparticles with precision control of their dimensions in a size regime comparable with the industry standard electron beam lithography. AR NSL provides a massively parallel, rather than serial, nanoparticle fabrication method. One limitation of the AR NSL technique is the inability to pattern an entire substrate with a single nanoparticle geometry without control of the mask domain orientation. While the presence of multiple domains in any given colloidal crystal mask complicates the fabrication of large-area homogeneous nanoparticle arrays, this quality is, in fact, useful in laboratory scale experiments requiring a diverse set of nanostructure features on a single sample. The precision tuning of nanoparticle size, shape, and spacing that can be achieved in a massively parallel, materials/substrate general, and inexpensive fashion using AR NSL is likely to have significant impact on the fields of surface-enhanced spectroscopy, near field optical microscopy, nanoscopic object manipulation, and chemical/biological sensing.