Fabrication and Characterization of Ultra Thin Resonant Nanocantilevers in Aluminium-Molybdenum Composites
N. Nelson-Fitzpatrick, L.M. Fischer, S. Evoy, C. Ophus, Y. Wang, D. Mitlin, Z-H. Lee, V. Radmilovic and U. Dahmen
University of Alberta, CA
Nanoelectromechanical (NEMS) resonators are of great interest for the assaying of molecular masses and external forces with ultra-high sensitivity. In addition, these devices are amenable to their implementation into large arrays, enabling the realization of multiplexed binding assays that could identify and quantify complex protein mixtures with high throughput. To this date, NEMS research and development have focused on the machining of materials such as silicon, silicon carbide, and silicon nitride. Metallic materials have mostly been overlooked given their limited stiffness and hardness, as well as the challenge associated with the nanomachining of an inherently polycrystalline system. However, the development of NEMS-based devices in such materials would enable new areas of applications for the direct sensing of various chemical compounds without need of intermediate surface derivatization. The development of bimetallic alloys featuring nanometer scale grain structure and enhanced hardness has now opened new opportunities for such development. We here report the fabrication and characterization of nanocantilevers from a novel aluminium-molybdenum nanocomposite. Using a co-sputtering approach, we have realized thin films of Al-Mo alloys of varying composition with amorphous aluminium domains having dimensions on the order of 10nm, as measured by atomic force microscopy (AFM). Mechanical properties of the thin films were also assessed using nanoindentation. The alloys possessed a Young’s modulus as high as 155 GPa, compared to 190 GPa for Si and 70 GPa for pure Al. The alloys also possessed hardness as high as 6 GPa, 2.5 times the value that would be expected from a simple rule of mixtures. Resonant nanocantilevers of width ranging from 200nm to 800nm, thicknesses as small as 20nm, and lengths ranging from 1 to 8um were fabricated in this alloy using a combination of electron beam lithography and lift-off. Resonance frequencies in the 100kHz-1MHz range were measured using a laser interferometric technique. We will present a description on the nucleation and growth of this alloy, report a full analysis of its nanomechanical properties as function of composition and thickness, present preliminary data of the machining and operation of sub-100nm wide resonant devices in this material.
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Nanotech 2006 Conference Program Abstract