XPS AND AFM MEASUREMENTS TO IMPROVE SENSOR PERFORMANCE
David L. Lahr, Kurt D. Benkstein, Jon K.Evju, Chip B. Montgomery, Douglas C. Meier, Reit Artzi-Gerlitz, Steve Semancik
X-ray Photoelectron Spectroscopy (XPS) and Atomic Force Microscopy (AFM) have been used to examine microhotplate (uHP) based chemical sensors, and improve the materials used in establishing their performance capabilities. uHP devices are prepared via a wet chemical etch, and through XPS measurements we have determined that this processing step produces an ultra-thin layer of Pt-silicate on the electrode surfaces of the device; removal of this silicate layer greatly enhances device performance. AFM measurements have revealed that the suspended uHP platforms are concave in shape, presumably the result of epitaxial stress. Thermal annealing of the device does not remove this concavity, but metal electrodes at the surface of the uHP do affect the extent and direction of the concavity.
Sensing materials that are used with uHP sensors have also been investigated. XPS has revealed that “SnO2” thin films are actually composed of a combination of Sn metal, SnO, and SnO2, depending upon the preparation and usage of the device. In addition, it has been determined that a protective fluoro-polymer coating used with the devices can leave behind undesirable amounts of F at the device surface, possibly inhibiting device efficacy.
XPS has also been used to investigate new classes of material for use as sensing materials. It has been determined that similar to “SnO2” thin films, Sn nanowires exhibit a range of chemical states of Sn. Similar results have been observed for SnO2 nanobelts*. The preparation of WO3 nanowires has also been investigated, leading to optimized growth of the nanowires in microporous alumina.
*prepared at the Georgia Institute of Technology by Puxian Gao and Zhang L. Wang
Name: David L. Lahr
Division: Process Measurement Division (836)
Lab: Chemical Science and Technology
location: bldg. 221, room B324
phone: (301) 975 2957
fax: (301) 258 9201
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