嵌入微反应器系统气体传感器的自检程序(10)

Acknowledgments

Part of this work was financed through the EU-funded projects “NANOS4” (FP6-NMP4–CT–2003-001528) and SNOOPY SEC-2012.3.4-4 (2014–2016). Funds for covering the costs to publish in open access were not received by the EU as this paper was published after project termination. 

 

Appendix A
SnO2 nanowires were been synthesized by means of evaporation-condensation method according to the protocol described elsewhere [33,34]. Briefly, alumina substrates (2 mm × 2 mm × 0.25 mm in size) are pre-patterned with Pt acting as catalyst for the growth of nanowires. SnO2 powders are placed in a tubular furnace and heated at a temperature of 1370 °C in a background of 100 mbar of Ar; substrates are lodged downstream in a colder region at around T = 800 °C. Thereafter, Pd nanoparticles are sputtered at room temperature over the nanowire mesh by means of RF magnetron sputtering up to a Pd/Sn ratio of 3(wt %.). Pt electrodes with a comb-like shape and a gap of 200 nm are deposited over the tin oxide layer to provide contacts for two-probe electrical measurements. A Pt meander, acting both as a heater resistance and a temperature sensor is sputtered on the rear side of the substrate. Finally, the device is soldered on a commercial TO38 case. Full details of the sensor layout are provided in [35].

 

Appendix B

The MEMS microheaters were fabricated by a combination of dry and wet etching techniques starting from silicon-on-insulator (SOI) wafers [44,45]. The microstructuring leads to free-standing silicon bridges suspended over a KOH etch groove. Pt electrodes sputtered onto the front side of the silicon bridges served as heater meanders and temperature sensors and as bottom contacts for SnO2 thin films. Thin films of SnO2 were deposited onto pre-processed MEMS microheaters by means of the RGTO (rheotaxial growth and thermal oxidation) technique [43]. The preparation of catalytically enhanced SnO2 starts with the evaporation of a three-layer stack of Sn/Au/Sn onto a pre-fabricated MEMS heater substrate. After evaporation the metallic films are annealed in ambient air at a temperature of 600 °C for several hours to completely convert the tin (Sn) into nano-crystalline SnO2 films [43]. During oxidation nano-crystalline SnO2 films with an average grain size of about 20 nm are formed, alongside with interspersed Au catalyst clusters, which phase-separate from the emerging SnO2 during the tin oxidation process.

 

Author Contributions

Andreas Helwig designed and built the EMRS devices and performed gas sensing tests on these, Angelika Hackner performed the HMDS poisoning experiments on the SnO2 nanowire samples and performed the corresponding gas sensing tests, Gerhard Müller designed and conceived the experiments and performed most of the paper writing, Dario Zappa prepared the SnO2 nanowire samples, Giorgio Sberveglieri developed the RGTO and the evaporation-condensation methods for preparing SnO2 thin films and SnO2 nanowire samples at the University of Brescia. Giorgio Sberveglieri also contributed to the paper writing.

 

Conflicts of Interest

The authors declare no conflict of interest. In particular the founding sponsors had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, and in the decision to publish the results.

 

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