National Science Foundation - Division of Chemical &Transport Systems Particulate & Multiphase Processes Program (1415)
Proposal Number: 0731349 Principal Investigators: Ragan, Regina Affiliation: University of California Irvine Proposal Title: Fabrication and Optimization of Highly Ordered Assemblies of Metallic Nanowire and Nanoparticle Arrays
Metal/rare earth disilicide core-shell nanostructure arrays on silicon substrates that have high density in addition to uniform size and shape will be designed, modeled, and characterized for incorporation into biosensor systems. Although noble metal nanostructures have demonstrated extraordinary capacity for single molecule detection limits in biosensors, one of the most significant challenges to technological developments that capitalize on their unique properties is the fabrication of arrays with monodisperse size, shape and high density using a low cost and high throughput technique. Recently, the principal investigator has developed a unique ultralarge scale compatible fabrication process for dense (~1011 cm-2) ordered arrays of monodisperse Pt and Au coreshell nanostructures on Si substrates. Physical vapor deposition of Pt and Au atoms on self-assembled nanowire templates followed by reactive ion etching produces noble metal/rare earth disilicide core-shell nanostructure arrays with mean particle diameter of less than 10 nm, a narrow size distribution, <1 nm, and inter-particle spacing of ~ 10 nm without lithography. . Fabrication: Preliminary results demonstrate that the proposed synthesis route produced both Pt and Au nanostructures on self-assembled rare earth disilicide nanowires on Si(001) substrates. This successful fabrication technique will thus be applied to fabricate Ag and other metal core-shell structures in order to tune optical responses in different frequency range. . Theory: Theoretical calculations of surface atomic structures of self-assembled templates, their interfaces with the Si(001) surface, and noble metal atom aggregation on nanowire template surfaces will be performed. The goal is to understand assembly mechanisms in order to optimize structure and make our process translatable to other material systems. . Characterization: Atomic level resolution of surface structures and electronic states will be investigated by STM and spectroscopy. Intellectual Merit: Metal nanostructures with diameters much less than the wavelength of light and narrow interparticle spacing have strong near field coupling due to a local enhancement of the electromagnetic field around these particles. We will address fundamental questions in this context: 1) how the arrangement of nanostructures in arrays affects signal enhancements; and 2) how to effectively pattern nanostructures over a large surface. Fabrication of monodisperse metal nanostructures in array format on Si substrates using microelectronic processing methods and combining self- assembly with lithography is unique to this proposal. Through the self-assembly process, the feature size, 8 nm, and inter-particle spacing achievable, ~10 nm, are smaller than that obtained with electron beam lithography and the throughput is much higher; thus unique optical properties can be attained. The synergistic theoretical and experimental studies will allow efficient and rational optimization and eventually massive production of nanostructures for biosensor applications. Broader Impact: Innovative and high-throughput fabrication techniques of nanostructure arrays are significant for many emerging technologies such as nanocatalysis, spintronics, quantum computing and optochemistry. This proposed fundamental study will pave the way for successful fabrication of high density, uniformly dispersed, nanostructure arrays optimized for biosensor applications. Our proposed fabrication technique is apparently translatable for other applications and affords the possibility to scale to large areas for massive production due the compatibility with current semiconductor manufacturing technology. This proposal will also support the continued training of high school, undergraduate and graduate students through research opportunities and outreach activities.
