Polycrystalline Diamond MEMS Resonators and Selective Olefin Detection with Gold Nanopartilce Chemiresistors

Nelson Sepulveda-Alancastro,
Graduate Student at Michigan State University,
Michael Rowe,
Graduate Student at University of Michigan
ABSTRACT: (Nelson Sepulveda-Alancastro) Due to material limitations of poly-Si resonators, new materials such as polycrystalline diamond (poly-C) offer an excellent alternate. The goals of this work is to develop a reliable and reproducible poly-C resonator technology for possible applications in resonant sensors and MEMS oscillators, benefiting from carbon based micro and nano technologies developed at Michigan State University, and to study the dissipation mechanisms in poly-C resonators. The poly-C resonators, fabricated at MSU are tested using electrostatic (MSU) and piezoelectric (Sandia National Laboratories) actuation methods.
An earlier study of poly-C resonator technology with minimum feature sizes in the range of 1 – 2 _m led to an excellent quality of released structures. These structures have now been excited using electrostatic actuation.
It has been reported that the optimum diamond grain size can be controlled by adjusting the flow rate of Ar/H2 in the MPCVD reaction chamber. The sidewall smoothness of the fabricated resonator structures using the new films are compared to that of earlier. These results are reported for the first time.

ABSTRACT: (Michael Rowe)The selectivity and enhanced sensitivity toward olefinic organic vapors with chemiresistors having interface layers consisting of thiolate protected gold nanoparticle (MPN) films containing organoplatinum complexes is described. MPNs composed of gold cores (~4.3 nm) encapsulated with 1-octanethiolate ligands were co-dissolved in toluene with Pt(II)Cl2(ethylene)(pyridine) (PtE) and solvent-cast on chemiresistor and QCM sensors. In contrast to the MPN films without PtE, which increased in resistance upon vapor sorption, the PtE-MPN admixture films decreased in resistance for olefinic vapors (ie. 1-octene, ethylene, 1,3-butadiene, and styrene). The resistance of these same PtE-MPN films increased upon exposure to non-olefin vapor analogs (ie. octane and ethylbenzene). The QCM sensor simultaneously recorded a mass increase with exposure of the admixture films to both the olefin and non-olefin vapors, representing uptake of the analyte into the interfacial film. In addition to discriminating between olefin vapors and their non-olefin analogs, these PtE-MPN admixture chemiresistor responses show improved sensitivities and limits of detection. 1,3-Butadiene vapor concentrations of 30 ppm were easily detected by the PtE-MPN admixture chemiresistor, and the limit of detection for styrene was improved by a factor of four compared to a similar MPN film without PtE.