Electronically conducting metal oxide nanoparticles and films for optical sensing applications

• US 8,836,945 B1
• Filed: 12/20/2013
• Issued: 09/16/2014
• Est. Priority Date: 06/27/2012
• Status: Active Grant

• Current Assignee: US Department of Energy (Government of the United States of America)
• Original Assignee: US Department of Energy (Government of the United States of America)
• Inventors: Ohodnicki, Paul R. Jr., Wang, Congjun, Andio, Mark A.
• Primary Examiner(s): NGUYEN, SANG H
• Application Number:
  US14/135,691
• Time in Patent Office: 270 Days
• Field of Search: 356432-448, 356/246, 250/434, 250/548.1, 436/134, 436/167, 436/168, 422/88, 422/91, 422/94, 422/83, 422/68.1
• US Class Current: 356/437
• CPC Class Codes: G01N 21/783 for analysing gases
• CPC Class Codes: G01N 2201/0826 Fibre array at source, distributing

Abstract

The disclosure relates to a method of detecting a change in a chemical composition by contacting a conducting oxide material with a monitored stream, illuminating the conducting 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 conducting metal oxide has a carrier concentration of at least 10¹⁷/cm³, a bandgap of at least 2 eV, and an electronic conductivity of at least 10⁻¹ S/cm, where parameters are specified at the gas stream temperature. The optical response of the conducting oxide materials is proposed to result from the high carrier concentration and electronic conductivity of the conducting metal oxide, and the resulting impact of changing gas atmospheres on that relatively high carrier concentration and electronic conductivity. These changes in effective carrier densities and electronic conductivity of conducting metal oxide films and nanoparticles are postulated to be responsible for the change in measured optical absorption associated with free carriers. Exemplary conducting metal oxides include but are not limited to Al-doped ZnO, Sn-doped In₂O₃, Nb-doped TiO₂, and F-doped SnO₂.

Claims

1. A method of a detecting a change in a chemical composition of a gas stream comprising:

contacting a conducting oxide material with some portion of the gas stream, where the some portion of the gas stream has a gas stream temperature, and where the gas stream temperature is at least 100°

C., and where the conducting oxide material comprises a conducting metal oxide, where the conducting metal oxide has a carrier concentration of at least 10¹⁷/cm³, a bandgap of at least 2 eV, and an electronic conductivity of at least 10<sup>−

1</sup> S/cm at the gas stream temperature;

illuminating the conducting metal oxide with a light source emitting incident light;

collecting exiting light, where the exiting light is light that originates at the light source and is transmitted, reflected, scattered or a combination thereof by the conducting metal oxide;

monitoring an optical signal based on a comparison of the incident light and the exiting light using optical spectroscopy; and

detecting a shift in the optical signal, thereby detecting the change in the chemical composition, and thereby monitoring the chemical composition of the gas stream.

2. The method of claim 1 where the conducting metal oxide has an empirical formula M_aO_b where M comprises one or more elements and where O comprises an oxygen anion and where the conducting 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 at the gas stream temperature.

3. The method of claim 2 where the conducting metal oxide has an empirical formula A_yB_xO_z, where A is a first element and B is a second element.

4. The method of claim 3 where the first element, the second element, and the oxygen anion form a crystalline structure having a crystalline lattice, where the crystalline lattice is cubic, hexagonal, tetragonal, rhombohedral, orthorhombic, monoclinic, or triclinic, and where the first element, the second element, and the oxygen anion occupy special positions within crystalline lattice.

5. The method of claim 4 where the conducting metal oxide comprises Zr_1-xAl_xO₃, In_2-xSn_xO₃, Ti_1-xNb_xO₂ or mixtures thereof.

6. The method of claim 2 where the some portion of the gas stream has a temperature of at least 200°

C.

7. The method of claim 6 where the optical signal is a signal-averaged optical signal, and where the shift in the optical signal is detected when an observed signal-averaged optical signal is at least 0.1% greater or lesser than an initial signal-averaged optical signal.

8. The method of claim 6 where the change in the chemical composition is an increased concentration of a reducing gas, and where the shift in the optical signal is an increase in transmission at a specific wavelength.

9. The method of claim 6 where the exiting light has an optical signal edge between 250 and 550 nanometers, and where the shift in the optical signal comprises a shift in the optical signal edge.

10. The method of claim 6 where the exiting light has an optical signal edge between 1000 and 3750 nanometers, and where the shift in the optical signal comprises a shift in the optical signal edge.

11. The method of claim 6 where the conducting oxide material has an rms surface roughness of at least 15 nanometers.

12. The method of claim 6 where the change in the chemical composition a change in the concentration of a reducing gas, where the reducing gas comprises H₂, CO, NH₃, a hydrocarbon, or mixtures thereof.

13. The method of claim 6 where the change in the chemical composition is a change in the concentration of an oxidizing gas, where the oxidizing gas comprises O₂, O₃, NOx, SOx, a halogen, a halogen compound, a sulfuric acid, a nitric acid, a nitrate, or mixtures thereof.

14. The method of claim 2 where the gas stream is comprised of a molecular gas constituent, and further comprising:

utilizing a barrier layer, where the barrier layer material has a first surface and a second surface, where the first surface and the second surface are separated by at least some portion of the barrier layer; and

contacting the first surface of the barrier layer and the gas stream, and withdrawing the some portion of the gas stream from the second surface of the barrier layer, thereby contacting the conducting oxide material with the some portion of the gas stream.

15. The method of claim 2 further comprising:

providing a waveguide comprised of a core material;

placing the conducting oxide material in contact with the core material; and

emitting the incident light from the light source into the core material and illuminating the conducting metal oxide, thereby illuminating the conducting metal oxide with the light source emitting the incident light.

16. The method of claim 1 further comprising monitoring the chemical composition of the gas stream by measuring a resistance of the conducting metal oxide.

17. A method of determining a concentration of a chemical species in the monitored stream using the method of claim 1, further comprising:

placing a sensing head of an instrument in the some portion of the gas stream, where the conducting oxide material comprises the sensing head and where the conducting oxide material is in fluid communication with the some portion of the gas stream, thereby contacting the conducting metal oxide with the some portion of the gas stream;

emitting incident light using an interrogator in optical communication with the conducting oxide material comprising the sensing head and illuminating the conducting oxide material, and gathering exiting light using the interrogator in optical communication with the conducting oxide material, and comparing the optical signal based on a comparison of the incident light and the exiting light with optical spectroscopy using the interrogator, thereby illuminating the gas sensing oxide material with the light source emitting incident light, collecting exiting light, and comparing the incident light and the exiting light using optical spectroscopy;

generating a measurand using the interrogator based on the comparing the incident light and the exiting light, and communicating the measurand to a meter in data communication with the interrogator;

receiving the measurand at the meter and displaying a meter reading on the meter based on the measurand, and observing the meter reading, thereby generating an observed meter reading, and thereby monitoring the optical signal based the comparing the incident light and the exiting light;

evaluating a difference between the observed meter reading and a reference meter reading; and

assigning a value to the concentration of the chemical species in the monitored stream based on the difference between the observed meter reading and the reference meter reading, thereby determining the concentration of the chemical species in the monitored stream.

18. A method of a detecting a change in a concentration of a reducing gas in a gas stream comprising:

generating the gas stream, where the gas stream comprises the reducing gas, and where the gas stream has a temperature of at least 200°

C.;

contacting a conducting oxide material with some portion of the gas stream, where the some portion of the gas stream has a gas stream temperature, where the gas stream temperature is at least 200°

C., and where the conducting oxide material comprises a conducting metal oxide, where the conducting metal oxide has an empirical formula M_aO_b where M comprises one or more elements and where O comprises an oxygen anion, and where the conducting metal oxide has a carrier concentration of at least 10¹⁹/cm³, a bandgap of at least 2 eV, and an electronic conductivity of at least 10² S/cm at the gas stream temperature;

illuminating conducting metal oxide with a light source emitting incident light;

collecting exiting light, where the exiting light is light that originates at the light source and is transmitted, reflected, or a combination thereof by the conducting metal oxide;

monitoring an optical signal based on a comparison of the incident light and the exiting light using optical spectroscopy; and

detecting a shift in the optical signal, thereby detecting the change in the concentration of the reducing gas in the gas stream.

19. The method of claim 18 where the conducting metal oxide has an empirical formula A_yB_xO_z, where A is a first element and B is a second element, where the first element, the second element, and the oxygen anion form a crystalline structure having a crystalline lattice, where the crystalline lattice is cubic, hexagonal, tetragonal, rhombohedral, orthorhombic, monoclinic, or triclinic, and where the first element, the second element, and the oxygen anion occupy special positions within the crystalline lattice.

20. The method of claim 19 where the conducting metal oxide is a non-stoichiometric oxide.

21. The method of claim 19 where the where conducting metal oxide has a carrier concentration of at least 10¹⁹/cm³, a bandgap of at least 2 eV, and an electronic conductivity of at least 10² S/cm at the gas stream temperature following an elevated temperature reducing treatment, where the elevated temperature treatment comprises contacting the conducting metal oxide for a period of at least one hour with a gaseous mixture having a composition of 4 vol. % H₂/balance N₂, where the gaseous mixture is at a temperature of at least 100°

C.