The atomic scale structure and its dependence on Pt concentration of a Pt-doped SnO 2 (Pt/SnO 2 ) thin film produced by a sputter-deposition method was investigated，which showed a high-performance methane gas sensor. Extended X-ray absorption fine structure (EXAFS) and X-ray diffraction (XRD) analyses showed that Pt/SnO 2 has a rutile structure similar to SnO 2 crystals at less than 10 at% Pt where the Pt ion was located at the Sn position in the rutile structure. There was no evidence that Pt metal clusters were formed in the Pt/SnO 2 films. The Pt/SnO 2 structure became amorphous at greater than 11 at% Pt. We found a good correlation between the methane activity and local structure of Pt.

We have directly investigated the chemical state of the Pd species in a real μ-gas sensor device by examining the μ-fluorescence X-ray absorption fine structure. The μ-gas sensor device was heavily damaged by a heating process in which the temperature was ill-controlled, resulting in decrease of methane selectivity. We found that the PdO in the fresh μ-gas sensor was reduced to Pd metal particles as the methane selectivity decreased. Based on the investigation results, we modified the device structure so as to heat up homogeneously. The lifetime of the sensor was then successfully increased by more than 5 years.

We present the design and performance of a high-temperature in situ cell with a large solid angle for fluorescence X-ray absorption fine structure (XAFS) spectra. The cell has a large fluorescence XAFS window (116 mmϕ) near the sample in the cell, realizing a large half-cone angle of 56°. We use a small heater (25 × 35 mm2) to heat the sample locally to 873 K. We measured a Pt–SnO2 thin layer on a Si substrate at reaction conditions having a high activity. In situ measurement enables the analysis of the difference XAFS spectra between before and during the reaction to reveal the structure change during the operation.