Plasmonic transparent conducting metal oxide nanoparticles and films for optical sensing applications
Inventors
Ohodnicki, JR., Paul R. • Wang, Congjun • Andio, Mark A.
Assignees
Publication Number
US-8638440-B1
Publication Date
2014-01-28
Expiration Date
2033-06-26
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Abstract
The disclosure relates to a method of detecting a change in a chemical composition by contacting a doped oxide material with a monitored stream, illuminating the doped oxide material with incident light, collecting exiting light, monitoring an optical signal based on a comparison of the incident light and the exiting light, and detecting a shift in the optical signal. The doped metal oxide has a carrier concentration of at least 1018/cm3, a bandgap of at least 2 eV, and an electronic conductivity of at least 101 S/cm, where parameters are specified at a temperature of 25° C. The optical response of the doped oxide materials results from the high carrier concentration of the doped metal oxide, and the resulting impact of changing gas atmospheres on that relatively high carrier concentration. These changes in effective carrier densities of conducting metal oxide nanoparticles are postulated to be responsible for the change in measured optical absorption associated with free carriers. Exemplary doped metal oxides include but are not limited to Al-doped ZnO, Sn-doped In2O3, Nb-doped TiO2, and F-doped SnO2.
Core Innovation
The invention provides a method to detect changes in the chemical composition of a gas stream by utilizing the optical response of a doped oxide material. This method involves placing a doped metal oxide in a high-temperature gas stream (at least 100° C.), illuminating the doped oxide material with incident light, collecting exiting light (transmitted, reflected, scattered, or a combination), monitoring an optical signal based on comparison of incident and exiting light using optical spectroscopy, and detecting shifts in this optical signal that correspond to changes in chemical composition.
The doped metal oxide has specific physical parameters including a carrier concentration of at least 10^18/cm^3, a bandgap of at least 2 eV, and an electronic conductivity of at least 10^1 S/cm measured at 25° C. The optical response derives from the high carrier concentration of the doped metal oxide and the impact of changing gas atmospheres on this carrier concentration, which alters the free carrier absorption. Exemplary doped metal oxides include Al-doped ZnO, Sn-doped In2O3, Nb-doped TiO2, and F-doped SnO2. The method is applicable at elevated temperatures, typically above 100° C., and the optical signal shifts are monotonic relative to reducing or oxidizing gas concentrations.
The problem addressed is the need for improved sensors capable of operating in harsh environments at elevated temperatures for applications such as fossil-fueled power plants, oxy-fuel combustion, coal gasification, and fuel cells. Existing metal oxide based optical sensors have limitations including poor temperature stability, weak dynamic optical response range, long response times, and reliance on noble metal dopants or complex sensor designs such as fiber Bragg gratings, which are temperature sensitive and costly. The disclosed method offers a way to improve optical sensing without requiring noble metal incorporation or advanced optical fiber designs, maintaining sensor performance at high temperature conditions.
Claims Coverage
The patent includes multiple independent claims outlining inventive features focused on methods for detecting chemical composition changes using doped metal oxide materials with specified physical properties and optical monitoring.
Method of detecting chemical composition change with doped metal oxides
A method comprising placing a doped oxide material with carrier concentration ≥10^18/cm^3, bandgap ≥2 eV, and electronic conductivity ≥10^1 S/cm in a gas stream at ≥100° C., illuminating the material with incident light, collecting transmitted/reflected/scattered exiting light, monitoring an optical signal based on comparison of incident and exiting light by optical spectroscopy, and detecting shifts in the optical signal to detect chemical composition changes in the gas stream.
Use of doped metal oxides with specific crystalline structures and empirical formulas
The doped metal oxide has empirical formula MaOb or AyBxOz with elements occupying special positions within cubic, hexagonal, tetragonal, rhombohedral, orthorhombic, monoclinic, or triclinic crystalline lattices. Exemplars include Zn1-xAlxO, In2-xSnxO3, and Ti1-xNbxO2.
Optical signal shift detection at elevated temperatures linked to reducing gas concentration
Detecting shifts in signal-averaged optical signals of at least 0.1% at monitored stream temperatures ≥200° C., where shifts correspond to increases in reducing gases like H2, CO, or NH3, and the optical signal edge shifts to lower wavelengths.
Incorporation of barrier layers and waveguides
Utilizing barrier layers between the gas stream and doped oxide material to improve selectivity, including diffusion barriers or sieves, and illuminating the doped metal oxide via waveguides such as optical fibers.
Method for determining chemical species concentration
Employing the doped oxide material as a sensing head in an instrument with an interrogator that emits incident light, gathers exiting light, compares optical signals, and communicates a measurand to a meter to evaluate and assign concentration values of chemical species based on observed meter readings relative to references.
Method for detecting reducing gases at elevated temperatures with enhanced doped metal oxides
Detecting concentration changes of reducing gases in gas streams at ≥200° C. using doped metal oxides with carrier concentration ≥10^19/cm^3, bandgap ≥2 eV, and conductivity ≥10^2 S/cm, following elevated temperature reducing treatments.
The independent claims collectively cover methods of detecting changes in chemical compositions or reducing gases in high temperature gas streams using doped metal oxides with defined electronic and optical properties, optical monitoring of incident and exiting light, and apparatus configurations including barrier layers and waveguides to enhance selectivity and detection performance.
Stated Advantages
Provides gas sensing operability in harsh, high temperature environments without reliance on noble metal dopants.
Enables improved optical response signals with measurable shifts correlated to chemical composition changes.
Avoids the complexity and temperature instability issues associated with fiber Bragg gratings or other advanced sensor designs.
Demonstrates reversible, monotonic optical responses to varying concentrations of reducing and oxidizing gases.
Documented Applications
Chemical sensors for high temperature gaseous streams in fossil-fueled power plants, such as oxy-fuel combustion and coal gasification processes.
Monitoring syngas composition in conversion technologies including solid oxide fuel cells and gas turbines.
Harsh environment monitoring in combustion turbines, advanced boiler systems, and domestic manufacturing industries requiring high temperature, reducing or oxidizing gas sensors.
Use in optical fiber-based sensing instruments and waveguide sensors for in situ gas composition monitoring at elevated temperatures.
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