AVS 53rd International Symposium
    Nanometer-scale Science and Technology Tuesday Sessions
       Session NS-TuA

Paper NS-TuA9
Hydrogen Detection NEMS Devices Fabricated from Tunable Microstructure Pd-Ta-X Nanocomposites

Tuesday, November 14, 2006, 4:40 pm, Room 2016

Session: Nanoscale Devices and Detection
Presenter: C. Gilkison, University of Alberta, Canada
Authors: C. Gilkison, University of Alberta, Canada
C. Ophus, University of Alberta, Canada
R. Mohammadi, University of Alberta, Canada
Z. Lee, NCEM, Lawrence Berkeley National Laboratory
V. Radmilovic, NCEM, Lawrence Berkeley National Laboratory
U. Dahmen, NCEM, Lawrence Berkeley National Laboratory
D. Mitlin, University of Alberta, Canada
Correspondent: Click to Email
Macro and micro-scale portable Pd-based resistive hydrogen sensors are considered an established technology. However, because hydrogen needs to both dissociate at the Pd surface and diffuse into the material in a significant quantity, existing portable Pd sensors suffer from relatively slow response times coupled with the requirement of high hydrogen partial pressures for detection. The difficulty in achieving nano-scale sensors, which are intrinsically faster and more sensitive, is related to the difficulty of reproducibly depositing, patterning, etching and releasing very thin Pd lines with high surface to volume ratios. We have developed a family of new thin films based on the Pd-Ta-X (where X is one or more alloy additions) system that have an amorphous-nanocrystalline microstructure. This microstructure is unique and results in materials with exceptional properties including little or no deposition shadowing effects, near atomic level smoothness, very high nanoindentation hardness coupled with ductility, a tunable elastic modulus, metallic conductivity and the ability to still dissociate and absorb hydrogen. These unique features of the Pd-Ta-X nanocomposites have allowed us to fabricate resistive hydrogen sensors with nano-scale width and thickness, but a meter-scale total length, all contained within a micron scale device on a silicon substrate. The combination of a short diffusion length and ultra-high surface to volume ratio has resulted in exquisite detection sensitivity and a very fast response time in these devices. The sensors are strong enough to be partially released from their substrates effectively doubling their surface area to volume ratio, and are easily functionalized to be hydrophobic. We were also able to use these alloys to fabricate the first generation of fully released single-anchored nanometer scale cantilevers, to be used in both static and resonance gas detection mode.