| AVS 64th International Symposium & Exhibition | |
| MEMS and NEMS Group | Monday Sessions |
| Session MN+EM+NS-MoA |
| Session: | Nano Optomechanical Systems/Multiscale Nanomanufacturing |
| Presenter: | Anandram Venkatasubramanian, University of Alberta and The National Institute for Nanotechnology, Canada |
| Authors: | A. Venkatasubramanian, University of Alberta and The National Institute for Nanotechnology, Canada V.T.K. Sauer, University of Alberta and The National Institute for Nanotechnology, Canada J.N. Westwood-Bachman, University of Alberta and The National Institute for Nanotechnology, Canada K. Cui, National Institute for Nanotechnology, National Research Council, Canada S.K. Roy, National Institute for Nanotechnology, National Research Council, Canada M. Xia, National Institute for Nanotechnology, National Research Council, Canada D. Wishart, University of Alberta, Canada W.K. Hiebert, University of Alberta and The National Institute for Nanotechnology, Canada |
| Correspondent: | Click to Email |
The Gas chromatography (GC) – Mass spectrometry (MS) system is the industry benchmark in chemical analysis. However the large size of the Mass spectrometry unit makes it unsuitable for portable applications. Hence a portable universal mass sensing device that can be used with portable GCs needs to be developed. In this regard, recent demonstration with nano opto-mechanical system (NOMS) devices in conjunction with a GC system have proven that these kinds of sensors have the breakthrough potential to improve the sensitivity of portable GCs. Those demonstrations using NOMS devices have shown these sensors to match the mass detection limits of nanoelectromechanical systems (NEMS) sensors and can potentially better their performance owing to their superior displacement sensitivity compared to NEMS.
In this regard, a free space interferometry system based nanophotonic sensor was developed and attached to a conventional GC. The nanophotonic sensor consists of a microring racetrack resonator (for concentration sensing) with a nanomechanical beam (for mass sensing) adjacent to it. Common method to improve the sensitivity of a nanomechanical beam is to apply surface coatings. However, the application of surface coatings can potentially affect its universal sensing characteristics. Hence an alternate way to improve the adsorption sensitivity is to increase the surface area of the nanomechanical sensor to aid in increasing the number of gas adsorption sites.
In this paper we increase the surface porosity of nanomechanical beam by stain etching. Care was taken to protect the adjacent microring resonator from stain etching as surface pores can negatively affect the performance of the ring resonator due to increased scattering. The stain etching was conducted using vanadium oxide/Hydrofluoric acid based chemistry to etch ~ 10nm pores of random morphology on the surface. Based on an estimated porosity of <15% by volume, we have noted an increase in mass adsorption of ≥ 50 - 100% when tests were conducted using different volatile organic compounds. In other words, a mass adsorption enhancement factor of 1.5 to 2 has been achieved. Due to this enhanced adsorption, the mass detection threshold has improved by an order of magnitude (~10-19 g). To the best knowledge of the authors, this is the first time NOMS based porous nanomechanical mass sensor has been developed.
Mass Adsorption Enhancement Factor = Adsorption frequency shift for porous beam/Adsorption frequency shift for non porous beam