Nanocomposite thin films for optical gas sensing
Inventors
Ohodnicki, Paul R. • Brown, Thomas D.
Assignees
Publication Number
US-8741657-B1
Publication Date
2014-06-03
Expiration Date
2033-02-25
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Abstract
The disclosure relates to a plasmon resonance-based method for gas sensing in a gas stream utilizing a gas sensing material. In an embodiment the gas stream has a temperature greater than about 500° C. The gas sensing material is comprised of gold nanoparticles having an average nanoparticle diameter of less than about 100 nanometers dispersed in an inert matrix having a bandgap greater than or equal to 5 eV, and an oxygen ion conductivity less than approximately 10−7 S/cm at a temperature of 700° C. Exemplary inert matrix materials include SiO2, Al2O3, and Si3N4 as well as modifications to modify the effective refractive indices through combinations and/or doping of such materials. Changes in the chemical composition of the gas stream are detected by changes in the plasmon resonance peak. The method disclosed offers significant advantage over active and reducible matrix materials typically utilized, such as yttria-stabilized zirconia (YSZ) or TiO2.
Core Innovation
The invention provides a method for high temperature gas sensing utilizing shifts in the plasmon resonance peak generated by a gas sensing material comprising gold nanoparticles dispersed in an inert matrix. The gas sensing material exhibits changes to the plasmon resonance peak in response to changes in the chemical composition of a monitored gas stream, including species such as H2, CO, and O2, at temperatures greater than about 500° C.
The gas sensing material consists of gold nanoparticles with average diameters less than about 100 nanometers dispersed in an inert matrix characterized by a bandgap greater than or equal to 5 electron volts and an oxygen ion conductivity less than approximately 10−7 S/cm at 700° C. Exemplary inert matrices include SiO2, Al2O3, and Si3N4, and their derivatives or mixtures. The inert matrix serves primarily to mitigate nanoparticle coarsening at high temperatures and to tailor the effective refractive index for compatibility with optical waveguide based sensors, rather than actively participating in the gas sensing mechanism.
The problem addressed by this invention is the limitation of prior plasmonic gas sensors that generally require catalytically active, reducible, and oxygen conducting matrices such as TiO2 or yttria-stabilized zirconia (YSZ). These prior materials depend on the active role of the matrix phase involving charge transfer or matrix reduction for sensing, which necessitates the presence of oxygen in the gas stream and can suffer from limited thermal and chemical stability. This invention overcomes these limitations by employing an inert matrix that provides enhanced thermal and chemical stability, increased nanoparticle diameter stability, and compatibility with optical waveguide sensors, while enabling plasmon-based gas sensing at temperatures above 500° C.
Claims Coverage
The patent discloses two independent claims directed to methods of detecting changes in chemical composition of gas streams using gold nanoparticles dispersed in an inert matrix.
Gas sensing material composition and properties
The gas sensing material comprises a plurality of gold nanoparticles with average diameters less than about 100 nanometers dispersed in an inert matrix having a bandgap ≥5 eV and oxygen ion conductivity <10−7 S/cm at 700° C., where individual gold nanoparticles consist of elemental gold.
Detection of chemical composition changes via plasmon resonance peak shifts
The method involves illuminating the gas sensing material with incident light, collecting exiting light transmitted or reflected by the material, monitoring shifts in the plasmon resonance peak by absorption spectroscopy, and correlating these shifts to changes in chemical composition of the gas stream.
Operation at high temperatures for gas streams
The method is applicable for gas streams and monitored streams at temperatures greater than or equal to 500° C., enabling high temperature gas sensing.
Use of barrier layers to enhance selectivity and protect sensing material
A barrier layer may be employed between the gas stream and the monitored stream to selectively exclude certain molecular constituents or protect the sensing layer from particulates and corrosive species.
Integration with optical waveguide and evanescent wave illumination
The gas sensing material is configured as a cladding layer in contact with a waveguide core with a higher refractive index, enabling illumination by evanescent waves generated in the waveguide as part of the sensing operation.
The independent claims collectively cover methods for detecting changes in chemical composition of high temperature gas streams by monitoring plasmon resonance peak shifts in a gas sensing material comprising gold nanoparticles dispersed in an inert matrix, optionally employing barrier layers and integration with optical waveguides for enhanced sensing.
Stated Advantages
Enhanced thermal and chemical stability of the gas sensing material under high temperature conditions.
Increased stability and controlled diameter of gold nanoparticles to prevent coarsening at elevated temperatures.
Relative insensitivity of the inert matrix to reducing gases beyond hydrogen, enabling direct interaction of gold nanoparticles with ambient chemical species.
Tunability of the effective refractive index of the gas sensing material for compatibility with optical waveguide based sensors.
Ability to perform gas sensing at temperatures greater than about 500° C. without requiring the presence of oxygen in the sensing environment.
Documented Applications
High temperature gas sensing for gas streams at temperatures greater than about 500° C., including fossil fuel based energy production applications such as coal gasification, solid oxide fuel cells, gas turbines, and advanced combustion systems.
Detection of various chemical species including but not limited to H2, CO, O2, NOx, NH3, hydrocarbons, sulfur-containing compounds, trace metals, fuel gases, halogens, and other gases.
Integration with fiber optic sensor technology using evanescent wave absorption spectroscopy for real-time monitoring of gas composition.
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