MOF Films for Microsensor Coatings
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MOF Films for Microsensor Coatings Alex L. Robinson1, Mark Allendorf2, Vitalie Stavila2, and Steve M. Thornberg1 1 2
Sandia National Laboratories, P.O. Box 5800, Albuquerque, New Mexico 87185, U.S.A. Sandia National Laboratories, PO Box 969, Livermore, California 94551, U.S.A.
ABSTRACT Metal organic framework (MOF) materials are a class of hybrid organic-inorganic crystalline materials whose pore structures and chemical properties can be tailored by the selection of component chemical moieties. Many MOFs have extraordinary intrinsic surface areas, capable of adsorbing large quantities of other chemicals, such as volatile organic compounds or moisture. Upon absorption of guest molecules, many MOFs undergo reversible changes in the dimensions of their unit cells. These properties suggest several routes to chemical sensing in which the transduction mechanisms are: 1) the stress induced at an interface between a flexible MOF layer and a static microcantilever fabricated with a built-in piezoresistive stress sensor; 2) the change in the resonant frequency of an oscillating microcantilever induced by mass adsorption; and 3) the change in the resonant frequency of a acoustic sensor, such as a surface acoustic wave (SAW) sensor through changes in mass loading and film moduli. This paper focuses on humidity sensing by SAWs coated with Cu3(BTC)2 (HKUST-1) over a very broad concentration range. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-AC0494AL85000. INTRODUCTION Metal Organic Framework materials are a class of hybrid inorganic-organic crystalline materials whose pore structure and chemical properties can be synthetically tailored to create a wide degree of flexibility. These properties can be used to preferentially attract and concentrate guest molecules or molecular classes within their pore structure. As some MOFs posses enormous surface areas, significant amounts of guest molecules can be captured. Adsorption is often reversible at room temperature, driven by concentration gradients. Complete regeneration of the pristine MOF can be achieved through heating. Upon absorption of molecules from either the gas phase or solution, many MOFs undergo reversible changes in the dimensions of their unit cells. The properties mentioned above have led to a number of practical applications of MOFs and MOF coatings. Among these are gas sensing [1, 2] storage [3], preconcentration [4], separation [5, 6], and extraction of chemicals from solution [7]. The number of papers and practical implementations are growing rapidly. For gas sensing, a number of transduction mechanisms are possible, including improved Surface Plasmon Resonance Spectroscopy [2],
mass-dampening on QCMs (Quartz Crystal Microbalance) [8, 9, 10], and stress-based detection static microcantilevers [1]. While our present research aims to take advantage of the ve
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