Author Information:

Author: Carlos J. Martinez

Mentor: Steve Semancik

Division: Process Measurements Division

Laboratory: Chemical Science and Technology Laboratory

Room: A 307 Physics Building (221)

Mail Stop: 8362

Telephone: 301-975-4371

Fax: 301-975-2643

Email: cjm@nist.gov

Sigma Xi Member: No

Poster Category: Materials

 

Engineering of Porous, Tin Oxide Nanoparticle Microshells for Sensor Applications

Carlos J. Martinez, Christopher B. Montgomery, Bernard Hockey and Steve Semancik

 

Chemical Science and Technology Laboratory, National Institute of Standards and Technology (NIST), Gaithersburg, MD 20899-8362

 

We have sought to enhance the sensitivity of conductometric gas sensors through the design and fabrication of porous, three-dimensional tin oxide nanoparticle films. These films were fabricated via the self-assembly from solution of nanoparticle-decorated latex microspheres, which serve as sacrificial templates. Through heating, the latex microspheres were removed to reveal a porous 3-dimensional structure composed of interconnected hollow nanoparticle microshells with ultra-thin walls. These structures include macropores (50 nm - 1000 nm) on the inside and between the microshells, and micropores (< 2 nm) and mesopores (2 nm - 50 nm) within the shells. The multiscale porous architecture promotes analyte diffusion and maximizes available active surface area. Sensor measurements were performed by depositing these films onto MEMS microsensor platforms with embedded inter-digitated electrodes and heaters. We report on film conductance changes measured at different temperatures, caused by exposure to test gases (CO, H2O, MeOH) in a dry air background. Special attention was placed on understanding the influence that structural factors (film thickness, packing density) have on the sensitivity, selectivity, stability and response time of these materials. We also compare the performance of these high surface area films to compact microporous nanoparticle films and CVD SnO2 films. The nanoparticle microsphere films exhibited partial selectivity to different gases, good dynamic range at different temperatures and concentrations, as well as good repeatability and stability over long runs. These films also show a two fold and four fold increase in sensitivity to MeOH when compared to SnO2 polycrystalline CVD and microporous nanoparticle films, respectively.